text: //===--- ExprConstant.cpp - Expression Constant Evaluator -----------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // This file implements the Expr constant evaluator.
  //
  // Constant expression evaluation produces four main results:
  //
  //  * A success/failure flag indicating whether constant folding was successful.
  //    This is the 'bool' return value used by most of the code in this file. A
  //    'false' return value indicates that constant folding has failed, and any
  //    appropriate diagnostic has already been produced.
  //
  //  * An evaluated result, valid only if constant folding has not failed.
  //
  //  * A flag indicating if evaluation encountered (unevaluated) side-effects.
  //    These arise in cases such as (sideEffect(), 0) and (sideEffect() || 1),
  //    where it is possible to determine the evaluated result regardless.
  //
  //  * A set of notes indicating why the evaluation was not a constant expression
  //    (under the C++11 / C++1y rules only, at the moment), or, if folding failed
  //    too, why the expression could not be folded.
  //
  // If we are checking for a potential constant expression, failure to constant
  // fold a potential constant sub-expression will be indicated by a 'false'
  // return value (the expression could not be folded) and no diagnostic (the
  // expression is not necessarily non-constant).
  //
  //===----------------------------------------------------------------------===//
  
  #include "Interp/Context.h"
  #include "Interp/Frame.h"
  #include "Interp/State.h"
  #include "clang/AST/APValue.h"
  #include "clang/AST/ASTContext.h"
  #include "clang/AST/ASTDiagnostic.h"
  #include "clang/AST/ASTLambda.h"
  #include "clang/AST/Attr.h"
  #include "clang/AST/CXXInheritance.h"
  #include "clang/AST/CharUnits.h"
  #include "clang/AST/CurrentSourceLocExprScope.h"
  #include "clang/AST/Expr.h"
  #include "clang/AST/OSLog.h"
  #include "clang/AST/OptionalDiagnostic.h"
  #include "clang/AST/RecordLayout.h"
  #include "clang/AST/StableHash.h"
  #include "clang/AST/StmtVisitor.h"
  #include "clang/AST/TypeLoc.h"
  #include "clang/Basic/Builtins.h"
  #include "clang/Basic/TargetInfo.h"
  #include "llvm/ADT/APFixedPoint.h"
  #include "llvm/ADT/Optional.h"
  #include "llvm/ADT/SmallBitVector.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/SaveAndRestore.h"
  #include "llvm/Support/raw_ostream.h"
  #include <cstring>
  #include <functional>
  
  #define DEBUG_TYPE "exprconstant"
  
  using namespace clang;
  using llvm::APFixedPoint;
  using llvm::APInt;
  using llvm::APSInt;
  using llvm::APFloat;
  using llvm::FixedPointSemantics;
  using llvm::Optional;
  
  namespace {
    struct LValue;
    class CallStackFrame;
    class EvalInfo;
  
    using SourceLocExprScopeGuard =
        CurrentSourceLocExprScope::SourceLocExprScopeGuard;
  
    static QualType getType(APValue::LValueBase B) {
      return B.getType();
    }
  
    /// Get an LValue path entry, which is known to not be an array index, as a
    /// field declaration.
    static const FieldDecl *getAsField(APValue::LValuePathEntry E) {
      return dyn_cast_or_null<FieldDecl>(E.getAsBaseOrMember().getPointer());
    }
    /// Get an LValue path entry, which is known to not be an array index, as a
    /// base class declaration.
    static const CXXRecordDecl *getAsBaseClass(APValue::LValuePathEntry E) {
      return dyn_cast_or_null<CXXRecordDecl>(E.getAsBaseOrMember().getPointer());
    }
    /// Determine whether this LValue path entry for a base class names a virtual
    /// base class.
    static bool isVirtualBaseClass(APValue::LValuePathEntry E) {
      return E.getAsBaseOrMember().getInt();
    }
  
    /// Given an expression, determine the type used to store the result of
    /// evaluating that expression.
    static QualType getStorageType(const ASTContext &Ctx, const Expr *E) {
      if (E->isRValue())
        return E->getType();
      return Ctx.getLValueReferenceType(E->getType());
    }
  
    /// Given a CallExpr, try to get the alloc_size attribute. May return null.
    static const AllocSizeAttr *getAllocSizeAttr(const CallExpr *CE) {
      const FunctionDecl *Callee = CE->getDirectCallee();
      return Callee ? Callee->getAttr<AllocSizeAttr>() : nullptr;
    }
  
    /// Attempts to unwrap a CallExpr (with an alloc_size attribute) from an Expr.
    /// This will look through a single cast.
    ///
    /// Returns null if we couldn't unwrap a function with alloc_size.
    static const CallExpr *tryUnwrapAllocSizeCall(const Expr *E) {
      if (!E->getType()->isPointerType())
        return nullptr;
  
      E = E->IgnoreParens();
      // If we're doing a variable assignment from e.g. malloc(N), there will
      // probably be a cast of some kind. In exotic cases, we might also see a
      // top-level ExprWithCleanups. Ignore them either way.
      if (const auto *FE = dyn_cast<FullExpr>(E))
        E = FE->getSubExpr()->IgnoreParens();
  
      if (const auto *Cast = dyn_cast<CastExpr>(E))
        E = Cast->getSubExpr()->IgnoreParens();
  
      if (const auto *CE = dyn_cast<CallExpr>(E))
        return getAllocSizeAttr(CE) ? CE : nullptr;
      return nullptr;
    }
  
    /// Determines whether or not the given Base contains a call to a function
    /// with the alloc_size attribute.
    static bool isBaseAnAllocSizeCall(APValue::LValueBase Base) {
      const auto *E = Base.dyn_cast<const Expr *>();
      return E && E->getType()->isPointerType() && tryUnwrapAllocSizeCall(E);
    }
  
    /// Determines whether the given kind of constant expression is only ever
    /// used for name mangling. If so, it's permitted to reference things that we
    /// can't generate code for (in particular, dllimported functions).
    static bool isForManglingOnly(ConstantExprKind Kind) {
      switch (Kind) {
      case ConstantExprKind::Normal:
      case ConstantExprKind::ClassTemplateArgument:
      case ConstantExprKind::ImmediateInvocation:
        // Note that non-type template arguments of class type are emitted as
        // template parameter objects.
        return false;
  
      case ConstantExprKind::NonClassTemplateArgument:
        return true;
      }
      llvm_unreachable("unknown ConstantExprKind");
    }
  
    static bool isTemplateArgument(ConstantExprKind Kind) {
      switch (Kind) {
      case ConstantExprKind::Normal:
      case ConstantExprKind::ImmediateInvocation:
        return false;
  
      case ConstantExprKind::ClassTemplateArgument:
      case ConstantExprKind::NonClassTemplateArgument:
        return true;
      }
      llvm_unreachable("unknown ConstantExprKind");
    }
  
    /// The bound to claim that an array of unknown bound has.
    /// The value in MostDerivedArraySize is undefined in this case. So, set it
    /// to an arbitrary value that's likely to loudly break things if it's used.
    static const uint64_t AssumedSizeForUnsizedArray =
        std::numeric_limits<uint64_t>::max() / 2;
  
    /// Determines if an LValue with the given LValueBase will have an unsized
    /// array in its designator.
    /// Find the path length and type of the most-derived subobject in the given
    /// path, and find the size of the containing array, if any.
    static unsigned
    findMostDerivedSubobject(ASTContext &Ctx, APValue::LValueBase Base,
                             ArrayRef<APValue::LValuePathEntry> Path,
                             uint64_t &ArraySize, QualType &Type, bool &IsArray,
                             bool &FirstEntryIsUnsizedArray) {
      // This only accepts LValueBases from APValues, and APValues don't support
      // arrays that lack size info.
      assert(!isBaseAnAllocSizeCall(Base) &&
             "Unsized arrays shouldn't appear here");
      unsigned MostDerivedLength = 0;
      Type = getType(Base);
  
      for (unsigned I = 0, N = Path.size(); I != N; ++I) {
        if (Type->isArrayType()) {
          const ArrayType *AT = Ctx.getAsArrayType(Type);
          Type = AT->getElementType();
          MostDerivedLength = I + 1;
          IsArray = true;
  
          if (auto *CAT = dyn_cast<ConstantArrayType>(AT)) {
            ArraySize = CAT->getSize().getZExtValue();
          } else {
            assert(I == 0 && "unexpected unsized array designator");
            FirstEntryIsUnsizedArray = true;
            ArraySize = AssumedSizeForUnsizedArray;
          }
        } else if (Type->isAnyComplexType()) {
          const ComplexType *CT = Type->castAs<ComplexType>();
          Type = CT->getElementType();
          ArraySize = 2;
          MostDerivedLength = I + 1;
          IsArray = true;
        } else if (const FieldDecl *FD = getAsField(Path[I])) {
          Type = FD->getType();
          ArraySize = 0;
          MostDerivedLength = I + 1;
          IsArray = false;
        } else {
          // Path[I] describes a base class.
          ArraySize = 0;
          IsArray = false;
        }
      }
      return MostDerivedLength;
    }
  
    /// A path from a glvalue to a subobject of that glvalue.
    struct SubobjectDesignator {
      /// True if the subobject was named in a manner not supported by C++11. Such
      /// lvalues can still be folded, but they are not core constant expressions
      /// and we cannot perform lvalue-to-rvalue conversions on them.
      unsigned Invalid : 1;
  
      /// Is this a pointer one past the end of an object?
      unsigned IsOnePastTheEnd : 1;
  
      /// Indicator of whether the first entry is an unsized array.
      unsigned FirstEntryIsAnUnsizedArray : 1;
  
      /// Indicator of whether the most-derived object is an array element.
      unsigned MostDerivedIsArrayElement : 1;
  
      /// The length of the path to the most-derived object of which this is a
      /// subobject.
      unsigned MostDerivedPathLength : 28;
  
      /// The size of the array of which the most-derived object is an element.
      /// This will always be 0 if the most-derived object is not an array
      /// element. 0 is not an indicator of whether or not the most-derived object
      /// is an array, however, because 0-length arrays are allowed.
      ///
      /// If the current array is an unsized array, the value of this is
      /// undefined.
      uint64_t MostDerivedArraySize;
  
      /// The type of the most derived object referred to by this address.
      QualType MostDerivedType;
  
      typedef APValue::LValuePathEntry PathEntry;
  
      /// The entries on the path from the glvalue to the designated subobject.
      SmallVector<PathEntry, 8> Entries;
  
      SubobjectDesignator() : Invalid(true) {}
  
      explicit SubobjectDesignator(QualType T)
          : Invalid(false), IsOnePastTheEnd(false),
            FirstEntryIsAnUnsizedArray(false), MostDerivedIsArrayElement(false),
            MostDerivedPathLength(0), MostDerivedArraySize(0),
            MostDerivedType(T) {}
  
      SubobjectDesignator(ASTContext &Ctx, const APValue &V)
          : Invalid(!V.isLValue() || !V.hasLValuePath()), IsOnePastTheEnd(false),
            FirstEntryIsAnUnsizedArray(false), MostDerivedIsArrayElement(false),
            MostDerivedPathLength(0), MostDerivedArraySize(0) {
        assert(V.isLValue() && "Non-LValue used to make an LValue designator?");
        if (!Invalid) {
          IsOnePastTheEnd = V.isLValueOnePastTheEnd();
          ArrayRef<PathEntry> VEntries = V.getLValuePath();
          Entries.insert(Entries.end(), VEntries.begin(), VEntries.end());
          if (V.getLValueBase()) {
            bool IsArray = false;
            bool FirstIsUnsizedArray = false;
            MostDerivedPathLength = findMostDerivedSubobject(
                Ctx, V.getLValueBase(), V.getLValuePath(), MostDerivedArraySize,
                MostDerivedType, IsArray, FirstIsUnsizedArray);
            MostDerivedIsArrayElement = IsArray;
            FirstEntryIsAnUnsizedArray = FirstIsUnsizedArray;
          }
        }
      }
  
      void truncate(ASTContext &Ctx, APValue::LValueBase Base,
                    unsigned NewLength) {
        if (Invalid)
          return;
  
        assert(Base && "cannot truncate path for null pointer");
        assert(NewLength <= Entries.size() && "not a truncation");
  
        if (NewLength == Entries.size())
          return;
        Entries.resize(NewLength);
  
        bool IsArray = false;
        bool FirstIsUnsizedArray = false;
        MostDerivedPathLength = findMostDerivedSubobject(
            Ctx, Base, Entries, MostDerivedArraySize, MostDerivedType, IsArray,
            FirstIsUnsizedArray);
        MostDerivedIsArrayElement = IsArray;
        FirstEntryIsAnUnsizedArray = FirstIsUnsizedArray;
      }
  
      void setInvalid() {
        Invalid = true;
        Entries.clear();
      }
  
      /// Determine whether the most derived subobject is an array without a
      /// known bound.
      bool isMostDerivedAnUnsizedArray() const {
        assert(!Invalid && "Calling this makes no sense on invalid designators");
        return Entries.size() == 1 && FirstEntryIsAnUnsizedArray;
      }
  
      /// Determine what the most derived array's size is. Results in an assertion
      /// failure if the most derived array lacks a size.
      uint64_t getMostDerivedArraySize() const {
        assert(!isMostDerivedAnUnsizedArray() && "Unsized array has no size");
        return MostDerivedArraySize;
      }
  
      /// Determine whether this is a one-past-the-end pointer.
      bool isOnePastTheEnd() const {
        assert(!Invalid);
        if (IsOnePastTheEnd)
          return true;
        if (!isMostDerivedAnUnsizedArray() && MostDerivedIsArrayElement &&
            Entries[MostDerivedPathLength - 1].getAsArrayIndex() ==
                MostDerivedArraySize)
          return true;
        return false;
      }
  
      /// Get the range of valid index adjustments in the form
      ///   {maximum value that can be subtracted from this pointer,
      ///    maximum value that can be added to this pointer}
      std::pair<uint64_t, uint64_t> validIndexAdjustments() {
        if (Invalid || isMostDerivedAnUnsizedArray())
          return {0, 0};
  
        // [expr.add]p4: For the purposes of these operators, a pointer to a
        // nonarray object behaves the same as a pointer to the first element of
        // an array of length one with the type of the object as its element type.
        bool IsArray = MostDerivedPathLength == Entries.size() &&
                       MostDerivedIsArrayElement;
        uint64_t ArrayIndex = IsArray ? Entries.back().getAsArrayIndex()
                                      : (uint64_t)IsOnePastTheEnd;
        uint64_t ArraySize =
            IsArray ? getMostDerivedArraySize() : (uint64_t)1;
        return {ArrayIndex, ArraySize - ArrayIndex};
      }
  
      /// Check that this refers to a valid subobject.
      bool isValidSubobject() const {
        if (Invalid)
          return false;
        return !isOnePastTheEnd();
      }
      /// Check that this refers to a valid subobject, and if not, produce a
      /// relevant diagnostic and set the designator as invalid.
      bool checkSubobject(EvalInfo &Info, const Expr *E, CheckSubobjectKind CSK);
  
      /// Get the type of the designated object.
      QualType getType(ASTContext &Ctx) const {
        assert(!Invalid && "invalid designator has no subobject type");
        return MostDerivedPathLength == Entries.size()
                   ? MostDerivedType
                   : Ctx.getRecordType(getAsBaseClass(Entries.back()));
      }
  
      /// Update this designator to refer to the first element within this array.
      void addArrayUnchecked(const ConstantArrayType *CAT) {
        Entries.push_back(PathEntry::ArrayIndex(0));
  
        // This is a most-derived object.
        MostDerivedType = CAT->getElementType();
        MostDerivedIsArrayElement = true;
        MostDerivedArraySize = CAT->getSize().getZExtValue();
        MostDerivedPathLength = Entries.size();
      }
      /// Update this designator to refer to the first element within the array of
      /// elements of type T. This is an array of unknown size.
      void addUnsizedArrayUnchecked(QualType ElemTy) {
        Entries.push_back(PathEntry::ArrayIndex(0));
  
        MostDerivedType = ElemTy;
        MostDerivedIsArrayElement = true;
        // The value in MostDerivedArraySize is undefined in this case. So, set it
        // to an arbitrary value that's likely to loudly break things if it's
        // used.
        MostDerivedArraySize = AssumedSizeForUnsizedArray;
        MostDerivedPathLength = Entries.size();
      }
      /// Update this designator to refer to the given base or member of this
      /// object.
      void addDeclUnchecked(const Decl *D, bool Virtual = false) {
        Entries.push_back(APValue::BaseOrMemberType(D, Virtual));
  
        // If this isn't a base class, it's a new most-derived object.
        if (const FieldDecl *FD = dyn_cast<FieldDecl>(D)) {
          MostDerivedType = FD->getType();
          MostDerivedIsArrayElement = false;
          MostDerivedArraySize = 0;
          MostDerivedPathLength = Entries.size();
        }
      }
      /// Update this designator to refer to the given complex component.
      void addComplexUnchecked(QualType EltTy, bool Imag) {
        Entries.push_back(PathEntry::ArrayIndex(Imag));
  
        // This is technically a most-derived object, though in practice this
        // is unlikely to matter.
        MostDerivedType = EltTy;
        MostDerivedIsArrayElement = true;
        MostDerivedArraySize = 2;
        MostDerivedPathLength = Entries.size();
      }
      void diagnoseUnsizedArrayPointerArithmetic(EvalInfo &Info, const Expr *E);
      void diagnosePointerArithmetic(EvalInfo &Info, const Expr *E,
                                     const APSInt &N);
      /// Add N to the address of this subobject.
      void adjustIndex(EvalInfo &Info, const Expr *E, APSInt N) {
        if (Invalid || !N) return;
        uint64_t TruncatedN = N.extOrTrunc(64).getZExtValue();
        if (isMostDerivedAnUnsizedArray()) {
          diagnoseUnsizedArrayPointerArithmetic(Info, E);
          // Can't verify -- trust that the user is doing the right thing (or if
          // not, trust that the caller will catch the bad behavior).
          // FIXME: Should we reject if this overflows, at least?
          Entries.back() = PathEntry::ArrayIndex(
              Entries.back().getAsArrayIndex() + TruncatedN);
          return;
        }
  
        // [expr.add]p4: For the purposes of these operators, a pointer to a
        // nonarray object behaves the same as a pointer to the first element of
        // an array of length one with the type of the object as its element type.
        bool IsArray = MostDerivedPathLength == Entries.size() &&
                       MostDerivedIsArrayElement;
        uint64_t ArrayIndex = IsArray ? Entries.back().getAsArrayIndex()
                                      : (uint64_t)IsOnePastTheEnd;
        uint64_t ArraySize =
            IsArray ? getMostDerivedArraySize() : (uint64_t)1;
  
        if (N < -(int64_t)ArrayIndex || N > ArraySize - ArrayIndex) {
          // Calculate the actual index in a wide enough type, so we can include
          // it in the note.
          N = N.extend(std::max<unsigned>(N.getBitWidth() + 1, 65));
          (llvm::APInt&)N += ArrayIndex;
          assert(N.ugt(ArraySize) && "bounds check failed for in-bounds index");
          diagnosePointerArithmetic(Info, E, N);
          setInvalid();
          return;
        }
  
        ArrayIndex += TruncatedN;
        assert(ArrayIndex <= ArraySize &&
               "bounds check succeeded for out-of-bounds index");
  
        if (IsArray)
          Entries.back() = PathEntry::ArrayIndex(ArrayIndex);
        else
          IsOnePastTheEnd = (ArrayIndex != 0);
      }
    };
  
    /// A scope at the end of which an object can need to be destroyed.
    enum class ScopeKind {
      Block,
      FullExpression,
      Call
    };
  
    /// A reference to a particular call and its arguments.
    struct CallRef {
      CallRef() : OrigCallee(), CallIndex(0), Version() {}
      CallRef(const FunctionDecl *Callee, unsigned CallIndex, unsigned Version)
          : OrigCallee(Callee), CallIndex(CallIndex), Version(Version) {}
  
      explicit operator bool() const { return OrigCallee; }
  
      /// Get the parameter that the caller initialized, corresponding to the
      /// given parameter in the callee.
      const ParmVarDecl *getOrigParam(const ParmVarDecl *PVD) const {
        return OrigCallee ? OrigCallee->getParamDecl(PVD->getFunctionScopeIndex())
                          : PVD;
      }
  
      /// The callee at the point where the arguments were evaluated. This might
      /// be different from the actual callee (a different redeclaration, or a
      /// virtual override), but this function's parameters are the ones that
      /// appear in the parameter map.
      const FunctionDecl *OrigCallee;
      /// The call index of the frame that holds the argument values.
      unsigned CallIndex;
      /// The version of the parameters corresponding to this call.
      unsigned Version;
    };
  
    /// A stack frame in the constexpr call stack.
    class CallStackFrame : public interp::Frame {
    public:
      EvalInfo &Info;
  
      /// Parent - The caller of this stack frame.
      CallStackFrame *Caller;
  
      /// Callee - The function which was called.
      const FunctionDecl *Callee;
  
      /// This - The binding for the this pointer in this call, if any.
      const LValue *This;
  
      /// Information on how to find the arguments to this call. Our arguments
      /// are stored in our parent's CallStackFrame, using the ParmVarDecl* as a
      /// key and this value as the version.
      CallRef Arguments;
  
      /// Source location information about the default argument or default
      /// initializer expression we're evaluating, if any.
      CurrentSourceLocExprScope CurSourceLocExprScope;
  
      // Note that we intentionally use std::map here so that references to
      // values are stable.
      typedef std::pair<const void *, unsigned> MapKeyTy;
      typedef std::map<MapKeyTy, APValue> MapTy;
      /// Temporaries - Temporary lvalues materialized within this stack frame.
      MapTy Temporaries;
  
      /// CallLoc - The location of the call expression for this call.
      SourceLocation CallLoc;
  
      /// Index - The call index of this call.
      unsigned Index;
  
      /// The stack of integers for tracking version numbers for temporaries.
      SmallVector<unsigned, 2> TempVersionStack = {1};
      unsigned CurTempVersion = TempVersionStack.back();
  
      unsigned getTempVersion() const { return TempVersionStack.back(); }
  
      void pushTempVersion() {
        TempVersionStack.push_back(++CurTempVersion);
      }
  
      void popTempVersion() {
        TempVersionStack.pop_back();
      }
  
      CallRef createCall(const FunctionDecl *Callee) {
        return {Callee, Index, ++CurTempVersion};
      }
  
      // FIXME: Adding this to every 'CallStackFrame' may have a nontrivial impact
      // on the overall stack usage of deeply-recursing constexpr evaluations.
      // (We should cache this map rather than recomputing it repeatedly.)
      // But let's try this and see how it goes; we can look into caching the map
      // as a later change.
  
      /// LambdaCaptureFields - Mapping from captured variables/this to
      /// corresponding data members in the closure class.
      llvm::DenseMap<const VarDecl *, FieldDecl *> LambdaCaptureFields;
      FieldDecl *LambdaThisCaptureField;
  
      CallStackFrame(EvalInfo &Info, SourceLocation CallLoc,
                     const FunctionDecl *Callee, const LValue *This,
                     CallRef Arguments);
      ~CallStackFrame();
  
      // Return the temporary for Key whose version number is Version.
      APValue *getTemporary(const void *Key, unsigned Version) {
        MapKeyTy KV(Key, Version);
        auto LB = Temporaries.lower_bound(KV);
        if (LB != Temporaries.end() && LB->first == KV)
          return &LB->second;
        // Pair (Key,Version) wasn't found in the map. Check that no elements
        // in the map have 'Key' as their key.
        assert((LB == Temporaries.end() || LB->first.first != Key) &&
               (LB == Temporaries.begin() || std::prev(LB)->first.first != Key) &&
               "Element with key 'Key' found in map");
        return nullptr;
      }
  
      // Return the current temporary for Key in the map.
      APValue *getCurrentTemporary(const void *Key) {
        auto UB = Temporaries.upper_bound(MapKeyTy(Key, UINT_MAX));
        if (UB != Temporaries.begin() && std::prev(UB)->first.first == Key)
          return &std::prev(UB)->second;
        return nullptr;
      }
  
      // Return the version number of the current temporary for Key.
      unsigned getCurrentTemporaryVersion(const void *Key) const {
        auto UB = Temporaries.upper_bound(MapKeyTy(Key, UINT_MAX));
        if (UB != Temporaries.begin() && std::prev(UB)->first.first == Key)
          return std::prev(UB)->first.second;
        return 0;
      }
  
      /// Allocate storage for an object of type T in this stack frame.
      /// Populates LV with a handle to the created object. Key identifies
      /// the temporary within the stack frame, and must not be reused without
      /// bumping the temporary version number.
      template<typename KeyT>
      APValue &createTemporary(const KeyT *Key, QualType T,
                               ScopeKind Scope, LValue &LV);
  
      /// Allocate storage for a parameter of a function call made in this frame.
      APValue &createParam(CallRef Args, const ParmVarDecl *PVD, LValue &LV);
  
      void describe(llvm::raw_ostream &OS) override;
  
      Frame *getCaller() const override { return Caller; }
      SourceLocation getCallLocation() const override { return CallLoc; }
      const FunctionDecl *getCallee() const override { return Callee; }
  
      bool isStdFunction() const {
        for (const DeclContext *DC = Callee; DC; DC = DC->getParent())
          if (DC->isStdNamespace())
            return true;
        return false;
      }
  
    private:
      APValue &createLocal(APValue::LValueBase Base, const void *Key, QualType T,
                           ScopeKind Scope);
    };
  
    /// Temporarily override 'this'.
    class ThisOverrideRAII {
    public:
      ThisOverrideRAII(CallStackFrame &Frame, const LValue *NewThis, bool Enable)
          : Frame(Frame), OldThis(Frame.This) {
        if (Enable)
          Frame.This = NewThis;
      }
      ~ThisOverrideRAII() {
        Frame.This = OldThis;
      }
    private:
      CallStackFrame &Frame;
      const LValue *OldThis;
    };
  }
  
  static bool HandleDestruction(EvalInfo &Info, const Expr *E,
                                const LValue &This, QualType ThisType);
  static bool HandleDestruction(EvalInfo &Info, SourceLocation Loc,
                                APValue::LValueBase LVBase, APValue &Value,
                                QualType T);
  
  namespace {
    /// A cleanup, and a flag indicating whether it is lifetime-extended.
    class Cleanup {
      llvm::PointerIntPair<APValue*, 2, ScopeKind> Value;
      APValue::LValueBase Base;
      QualType T;
  
    public:
      Cleanup(APValue *Val, APValue::LValueBase Base, QualType T,
              ScopeKind Scope)
          : Value(Val, Scope), Base(Base), T(T) {}
  
      /// Determine whether this cleanup should be performed at the end of the
      /// given kind of scope.
      bool isDestroyedAtEndOf(ScopeKind K) const {
        return (int)Value.getInt() >= (int)K;
      }
      bool endLifetime(EvalInfo &Info, bool RunDestructors) {
        if (RunDestructors) {
          SourceLocation Loc;
          if (const ValueDecl *VD = Base.dyn_cast<const ValueDecl*>())
            Loc = VD->getLocation();
          else if (const Expr *E = Base.dyn_cast<const Expr*>())
            Loc = E->getExprLoc();
          return HandleDestruction(Info, Loc, Base, *Value.getPointer(), T);
        }
        *Value.getPointer() = APValue();
        return true;
      }
  
      bool hasSideEffect() {
        return T.isDestructedType();
      }
    };
  
    /// A reference to an object whose construction we are currently evaluating.
    struct ObjectUnderConstruction {
      APValue::LValueBase Base;
      ArrayRef<APValue::LValuePathEntry> Path;
      friend bool operator==(const ObjectUnderConstruction &LHS,
                             const ObjectUnderConstruction &RHS) {
        return LHS.Base == RHS.Base && LHS.Path == RHS.Path;
      }
      friend llvm::hash_code hash_value(const ObjectUnderConstruction &Obj) {
        return llvm::hash_combine(Obj.Base, Obj.Path);
      }
    };
    enum class ConstructionPhase {
      None,
      Bases,
      AfterBases,
      AfterFields,
      Destroying,
      DestroyingBases
    };
  }
  
  namespace llvm {
  template<> struct DenseMapInfo<ObjectUnderConstruction> {
    using Base = DenseMapInfo<APValue::LValueBase>;
    static ObjectUnderConstruction getEmptyKey() {
      return {Base::getEmptyKey(), {}}; }
    static ObjectUnderConstruction getTombstoneKey() {
      return {Base::getTombstoneKey(), {}};
    }
    static unsigned getHashValue(const ObjectUnderConstruction &Object) {
      return hash_value(Object);
    }
    static bool isEqual(const ObjectUnderConstruction &LHS,
                        const ObjectUnderConstruction &RHS) {
      return LHS == RHS;
    }
  };
  }
  
  namespace {
    /// A dynamically-allocated heap object.
    struct DynAlloc {
      /// The value of this heap-allocated object.
      APValue Value;
      /// The allocating expression; used for diagnostics. Either a CXXNewExpr
      /// or a CallExpr (the latter is for direct calls to operator new inside
      /// std::allocator<T>::allocate).
      const Expr *AllocExpr = nullptr;
  
      enum Kind {
        New,
        ArrayNew,
        StdAllocator
      };
  
      /// Get the kind of the allocation. This must match between allocation
      /// and deallocation.
      Kind getKind() const {
        if (auto *NE = dyn_cast<CXXNewExpr>(AllocExpr))
          return NE->isArray() ? ArrayNew : New;
        assert(isa<CallExpr>(AllocExpr));
        return StdAllocator;
      }
    };
  
    struct DynAllocOrder {
      bool operator()(DynamicAllocLValue L, DynamicAllocLValue R) const {
        return L.getIndex() < R.getIndex();
      }
    };
  
    /// EvalInfo - This is a private struct used by the evaluator to capture
    /// information about a subexpression as it is folded.  It retains information
    /// about the AST context, but also maintains information about the folded
    /// expression.
    ///
    /// If an expression could be evaluated, it is still possible it is not a C
    /// "integer constant expression" or constant expression.  If not, this struct
    /// captures information about how and why not.
    ///
    /// One bit of information passed *into* the request for constant folding
    /// indicates whether the subexpression is "evaluated" or not according to C
    /// rules.  For example, the RHS of (0 && foo()) is not evaluated.  We can
    /// evaluate the expression regardless of what the RHS is, but C only allows
    /// certain things in certain situations.
    class EvalInfo : public interp::State {
    public:
      ASTContext &Ctx;
  
      /// EvalStatus - Contains information about the evaluation.
      Expr::EvalStatus &EvalStatus;
  
      /// CurrentCall - The top of the constexpr call stack.
      CallStackFrame *CurrentCall;
  
      /// CallStackDepth - The number of calls in the call stack right now.
      unsigned CallStackDepth;
  
      /// NextCallIndex - The next call index to assign.
      unsigned NextCallIndex;
  
      /// StepsLeft - The remaining number of evaluation steps we're permitted
      /// to perform. This is essentially a limit for the number of statements
      /// we will evaluate.
      unsigned StepsLeft;
  
      /// Enable the experimental new constant interpreter. If an expression is
      /// not supported by the interpreter, an error is triggered.
      bool EnableNewConstInterp;
  
      /// BottomFrame - The frame in which evaluation started. This must be
      /// initialized after CurrentCall and CallStackDepth.
      CallStackFrame BottomFrame;
  
      /// A stack of values whose lifetimes end at the end of some surrounding
      /// evaluation frame.
      llvm::SmallVector<Cleanup, 16> CleanupStack;
  
      /// EvaluatingDecl - This is the declaration whose initializer is being
      /// evaluated, if any.
      APValue::LValueBase EvaluatingDecl;
  
      enum class EvaluatingDeclKind {
        None,
        /// We're evaluating the construction of EvaluatingDecl.
        Ctor,
        /// We're evaluating the destruction of EvaluatingDecl.
        Dtor,
      };
      EvaluatingDeclKind IsEvaluatingDecl = EvaluatingDeclKind::None;
  
      /// EvaluatingDeclValue - This is the value being constructed for the
      /// declaration whose initializer is being evaluated, if any.
      APValue *EvaluatingDeclValue;
  
      /// Set of objects that are currently being constructed.
      llvm::DenseMap<ObjectUnderConstruction, ConstructionPhase>
          ObjectsUnderConstruction;
  
      /// Current heap allocations, along with the location where each was
      /// allocated. We use std::map here because we need stable addresses
      /// for the stored APValues.
      std::map<DynamicAllocLValue, DynAlloc, DynAllocOrder> HeapAllocs;
  
      /// The number of heap allocations performed so far in this evaluation.
      unsigned NumHeapAllocs = 0;
  
      struct EvaluatingConstructorRAII {
        EvalInfo &EI;
        ObjectUnderConstruction Object;
        bool DidInsert;
        EvaluatingConstructorRAII(EvalInfo &EI, ObjectUnderConstruction Object,
                                  bool HasBases)
            : EI(EI), Object(Object) {
          DidInsert =
              EI.ObjectsUnderConstruction
                  .insert({Object, HasBases ? ConstructionPhase::Bases
                                            : ConstructionPhase::AfterBases})
                  .second;
        }
        void finishedConstructingBases() {
          EI.ObjectsUnderConstruction[Object] = ConstructionPhase::AfterBases;
        }
        void finishedConstructingFields() {
          EI.ObjectsUnderConstruction[Object] = ConstructionPhase::AfterFields;
        }
        ~EvaluatingConstructorRAII() {
          if (DidInsert) EI.ObjectsUnderConstruction.erase(Object);
        }
      };
  
      struct EvaluatingDestructorRAII {
        EvalInfo &EI;
        ObjectUnderConstruction Object;
        bool DidInsert;
        EvaluatingDestructorRAII(EvalInfo &EI, ObjectUnderConstruction Object)
            : EI(EI), Object(Object) {
          DidInsert = EI.ObjectsUnderConstruction
                          .insert({Object, ConstructionPhase::Destroying})
                          .second;
        }
        void startedDestroyingBases() {
          EI.ObjectsUnderConstruction[Object] =
              ConstructionPhase::DestroyingBases;
        }
        ~EvaluatingDestructorRAII() {
          if (DidInsert)
            EI.ObjectsUnderConstruction.erase(Object);
        }
      };
  
      ConstructionPhase
      isEvaluatingCtorDtor(APValue::LValueBase Base,
                           ArrayRef<APValue::LValuePathEntry> Path) {
        return ObjectsUnderConstruction.lookup({Base, Path});
      }
  
      /// If we're currently speculatively evaluating, the outermost call stack
      /// depth at which we can mutate state, otherwise 0.
      unsigned SpeculativeEvaluationDepth = 0;
  
      /// The current array initialization index, if we're performing array
      /// initialization.
      uint64_t ArrayInitIndex = -1;
  
      /// HasActiveDiagnostic - Was the previous diagnostic stored? If so, further
      /// notes attached to it will also be stored, otherwise they will not be.
      bool HasActiveDiagnostic;
  
      /// Have we emitted a diagnostic explaining why we couldn't constant
      /// fold (not just why it's not strictly a constant expression)?
      bool HasFoldFailureDiagnostic;
  
      /// Whether or not we're in a context where the front end requires a
      /// constant value.
      bool InConstantContext;
  
      /// Whether we're checking that an expression is a potential constant
      /// expression. If so, do not fail on constructs that could become constant
      /// later on (such as a use of an undefined global).
      bool CheckingPotentialConstantExpression = false;
  
      /// Whether we're checking for an expression that has undefined behavior.
      /// If so, we will produce warnings if we encounter an operation that is
      /// always undefined.
      ///
      /// Note that we still need to evaluate the expression normally when this
      /// is set; this is used when evaluating ICEs in C.
      bool CheckingForUndefinedBehavior = false;
  
      enum EvaluationMode {
        /// Evaluate as a constant expression. Stop if we find that the expression
        /// is not a constant expression.
        EM_ConstantExpression,
  
        /// Evaluate as a constant expression. Stop if we find that the expression
        /// is not a constant expression. Some expressions can be retried in the
        /// optimizer if we don't constant fold them here, but in an unevaluated
        /// context we try to fold them immediately since the optimizer never
        /// gets a chance to look at it.
        EM_ConstantExpressionUnevaluated,
  
        /// Fold the expression to a constant. Stop if we hit a side-effect that
        /// we can't model.
        EM_ConstantFold,
  
        /// Evaluate in any way we know how. Don't worry about side-effects that
        /// can't be modeled.
        EM_IgnoreSideEffects,
      } EvalMode;
  
      /// Are we checking whether the expression is a potential constant
      /// expression?
      bool checkingPotentialConstantExpression() const override  {
        return CheckingPotentialConstantExpression;
      }
  
      /// Are we checking an expression for overflow?
      // FIXME: We should check for any kind of undefined or suspicious behavior
      // in such constructs, not just overflow.
      bool checkingForUndefinedBehavior() const override {
        return CheckingForUndefinedBehavior;
      }
  
      EvalInfo(const ASTContext &C, Expr::EvalStatus &S, EvaluationMode Mode)
          : Ctx(const_cast<ASTContext &>(C)), EvalStatus(S), CurrentCall(nullptr),
            CallStackDepth(0), NextCallIndex(1),
            StepsLeft(C.getLangOpts().ConstexprStepLimit),
            EnableNewConstInterp(C.getLangOpts().EnableNewConstInterp),
            BottomFrame(*this, SourceLocation(), nullptr, nullptr, CallRef()),
            EvaluatingDecl((const ValueDecl *)nullptr),
            EvaluatingDeclValue(nullptr), HasActiveDiagnostic(false),
            HasFoldFailureDiagnostic(false), InConstantContext(false),
            EvalMode(Mode) {}
  
      ~EvalInfo() {
        discardCleanups();
      }
  
      void setEvaluatingDecl(APValue::LValueBase Base, APValue &Value,
                             EvaluatingDeclKind EDK = EvaluatingDeclKind::Ctor) {
        EvaluatingDecl = Base;
        IsEvaluatingDecl = EDK;
        EvaluatingDeclValue = &Value;
      }
  
      bool CheckCallLimit(SourceLocation Loc) {
        // Don't perform any constexpr calls (other than the call we're checking)
        // when checking a potential constant expression.
        if (checkingPotentialConstantExpression() && CallStackDepth > 1)
          return false;
        if (NextCallIndex == 0) {
          // NextCallIndex has wrapped around.
          FFDiag(Loc, diag::note_constexpr_call_limit_exceeded);
          return false;
        }
        if (CallStackDepth <= getLangOpts().ConstexprCallDepth)
          return true;
        FFDiag(Loc, diag::note_constexpr_depth_limit_exceeded)
          << getLangOpts().ConstexprCallDepth;
        return false;
      }
  
      std::pair<CallStackFrame *, unsigned>
      getCallFrameAndDepth(unsigned CallIndex) {
        assert(CallIndex && "no call index in getCallFrameAndDepth");
        // We will eventually hit BottomFrame, which has Index 1, so Frame can't
        // be null in this loop.
        unsigned Depth = CallStackDepth;
        CallStackFrame *Frame = CurrentCall;
        while (Frame->Index > CallIndex) {
          Frame = Frame->Caller;
          --Depth;
        }
        if (Frame->Index == CallIndex)
          return {Frame, Depth};
        return {nullptr, 0};
      }
  
      bool nextStep(const Stmt *S) {
        if (!StepsLeft) {
          FFDiag(S->getBeginLoc(), diag::note_constexpr_step_limit_exceeded);
          return false;
        }
        --StepsLeft;
        return true;
      }
  
      APValue *createHeapAlloc(const Expr *E, QualType T, LValue &LV);
  
      Optional<DynAlloc*> lookupDynamicAlloc(DynamicAllocLValue DA) {
        Optional<DynAlloc*> Result;
        auto It = HeapAllocs.find(DA);
        if (It != HeapAllocs.end())
          Result = &It->second;
        return Result;
      }
  
      /// Get the allocated storage for the given parameter of the given call.
      APValue *getParamSlot(CallRef Call, const ParmVarDecl *PVD) {
        CallStackFrame *Frame = getCallFrameAndDepth(Call.CallIndex).first;
        return Frame ? Frame->getTemporary(Call.getOrigParam(PVD), Call.Version)
                     : nullptr;
      }
  
      /// Information about a stack frame for std::allocator<T>::[de]allocate.
      struct StdAllocatorCaller {
        unsigned FrameIndex;
        QualType ElemType;
        explicit operator bool() const { return FrameIndex != 0; };
      };
  
      StdAllocatorCaller getStdAllocatorCaller(StringRef FnName) const {
        for (const CallStackFrame *Call = CurrentCall; Call != &BottomFrame;
             Call = Call->Caller) {
          const auto *MD = dyn_cast_or_null<CXXMethodDecl>(Call->Callee);
          if (!MD)
            continue;
          const IdentifierInfo *FnII = MD->getIdentifier();
          if (!FnII || !FnII->isStr(FnName))
            continue;
  
          const auto *CTSD =
              dyn_cast<ClassTemplateSpecializationDecl>(MD->getParent());
          if (!CTSD)
            continue;
  
          const IdentifierInfo *ClassII = CTSD->getIdentifier();
          const TemplateArgumentList &TAL = CTSD->getTemplateArgs();
          if (CTSD->isInStdNamespace() && ClassII &&
              ClassII->isStr("allocator") && TAL.size() >= 1 &&
              TAL[0].getKind() == TemplateArgument::Type)
            return {Call->Index, TAL[0].getAsType()};
        }
  
        return {};
      }
  
      void performLifetimeExtension() {
        // Disable the cleanups for lifetime-extended temporaries.
        CleanupStack.erase(std::remove_if(CleanupStack.begin(),
                                          CleanupStack.end(),
                                          [](Cleanup &C) {
                                            return !C.isDestroyedAtEndOf(
                                                ScopeKind::FullExpression);
                                          }),
                           CleanupStack.end());
       }
  
      /// Throw away any remaining cleanups at the end of evaluation. If any
      /// cleanups would have had a side-effect, note that as an unmodeled
      /// side-effect and return false. Otherwise, return true.
      bool discardCleanups() {
        for (Cleanup &C : CleanupStack) {
          if (C.hasSideEffect() && !noteSideEffect()) {
            CleanupStack.clear();
            return false;
          }
        }
        CleanupStack.clear();
        return true;
      }
  
    private:
      interp::Frame *getCurrentFrame() override { return CurrentCall; }
      const interp::Frame *getBottomFrame() const override { return &BottomFrame; }
  
      bool hasActiveDiagnostic() override { return HasActiveDiagnostic; }
      void setActiveDiagnostic(bool Flag) override { HasActiveDiagnostic = Flag; }
  
      void setFoldFailureDiagnostic(bool Flag) override {
        HasFoldFailureDiagnostic = Flag;
      }
  
      Expr::EvalStatus &getEvalStatus() const override { return EvalStatus; }
  
      ASTContext &getCtx() const override { return Ctx; }
  
      // If we have a prior diagnostic, it will be noting that the expression
      // isn't a constant expression. This diagnostic is more important,
      // unless we require this evaluation to produce a constant expression.
      //
      // FIXME: We might want to show both diagnostics to the user in
      // EM_ConstantFold mode.
      bool hasPriorDiagnostic() override {
        if (!EvalStatus.Diag->empty()) {
          switch (EvalMode) {
          case EM_ConstantFold:
          case EM_IgnoreSideEffects:
            if (!HasFoldFailureDiagnostic)
              break;
            // We've already failed to fold something. Keep that diagnostic.
            LLVM_FALLTHROUGH;
          case EM_ConstantExpression:
          case EM_ConstantExpressionUnevaluated:
            setActiveDiagnostic(false);
            return true;
          }
        }
        return false;
      }
  
      unsigned getCallStackDepth() override { return CallStackDepth; }
  
    public:
      /// Should we continue evaluation after encountering a side-effect that we
      /// couldn't model?
      bool keepEvaluatingAfterSideEffect() {
        switch (EvalMode) {
        case EM_IgnoreSideEffects:
          return true;
  
        case EM_ConstantExpression:
        case EM_ConstantExpressionUnevaluated:
        case EM_ConstantFold:
          // By default, assume any side effect might be valid in some other
          // evaluation of this expression from a different context.
          return checkingPotentialConstantExpression() ||
                 checkingForUndefinedBehavior();
        }
        llvm_unreachable("Missed EvalMode case");
      }
  
      /// Note that we have had a side-effect, and determine whether we should
      /// keep evaluating.
      bool noteSideEffect() {
        EvalStatus.HasSideEffects = true;
        return keepEvaluatingAfterSideEffect();
      }
  
      /// Should we continue evaluation after encountering undefined behavior?
      bool keepEvaluatingAfterUndefinedBehavior() {
        switch (EvalMode) {
        case EM_IgnoreSideEffects:
        case EM_ConstantFold:
          return true;
  
        case EM_ConstantExpression:
        case EM_ConstantExpressionUnevaluated:
          return checkingForUndefinedBehavior();
        }
        llvm_unreachable("Missed EvalMode case");
      }
  
      /// Note that we hit something that was technically undefined behavior, but
      /// that we can evaluate past it (such as signed overflow or floating-point
      /// division by zero.)
      bool noteUndefinedBehavior() override {
        EvalStatus.HasUndefinedBehavior = true;
        return keepEvaluatingAfterUndefinedBehavior();
      }
  
      /// Should we continue evaluation as much as possible after encountering a
      /// construct which can't be reduced to a value?
      bool keepEvaluatingAfterFailure() const override {
        if (!StepsLeft)
          return false;
  
        switch (EvalMode) {
        case EM_ConstantExpression:
        case EM_ConstantExpressionUnevaluated:
        case EM_ConstantFold:
        case EM_IgnoreSideEffects:
          return checkingPotentialConstantExpression() ||
                 checkingForUndefinedBehavior();
        }
        llvm_unreachable("Missed EvalMode case");
      }
  
      /// Notes that we failed to evaluate an expression that other expressions
      /// directly depend on, and determine if we should keep evaluating. This
      /// should only be called if we actually intend to keep evaluating.
      ///
      /// Call noteSideEffect() instead if we may be able to ignore the value that
      /// we failed to evaluate, e.g. if we failed to evaluate Foo() in:
      ///
      /// (Foo(), 1)      // use noteSideEffect
      /// (Foo() || true) // use noteSideEffect
      /// Foo() + 1       // use noteFailure
      LLVM_NODISCARD bool noteFailure() {
        // Failure when evaluating some expression often means there is some
        // subexpression whose evaluation was skipped. Therefore, (because we
        // don't track whether we skipped an expression when unwinding after an
        // evaluation failure) every evaluation failure that bubbles up from a
        // subexpression implies that a side-effect has potentially happened. We
        // skip setting the HasSideEffects flag to true until we decide to
        // continue evaluating after that point, which happens here.
        bool KeepGoing = keepEvaluatingAfterFailure();
        EvalStatus.HasSideEffects |= KeepGoing;
        return KeepGoing;
      }
  
      class ArrayInitLoopIndex {
        EvalInfo &Info;
        uint64_t OuterIndex;
  
      public:
        ArrayInitLoopIndex(EvalInfo &Info)
            : Info(Info), OuterIndex(Info.ArrayInitIndex) {
          Info.ArrayInitIndex = 0;
        }
        ~ArrayInitLoopIndex() { Info.ArrayInitIndex = OuterIndex; }
  
        operator uint64_t&() { return Info.ArrayInitIndex; }
      };
    };
  
    /// Object used to treat all foldable expressions as constant expressions.
    struct FoldConstant {
      EvalInfo &Info;
      bool Enabled;
      bool HadNoPriorDiags;
      EvalInfo::EvaluationMode OldMode;
  
      explicit FoldConstant(EvalInfo &Info, bool Enabled)
        : Info(Info),
          Enabled(Enabled),
          HadNoPriorDiags(Info.EvalStatus.Diag &&
                          Info.EvalStatus.Diag->empty() &&
                          !Info.EvalStatus.HasSideEffects),
          OldMode(Info.EvalMode) {
        if (Enabled)
          Info.EvalMode = EvalInfo::EM_ConstantFold;
      }
      void keepDiagnostics() { Enabled = false; }
      ~FoldConstant() {
        if (Enabled && HadNoPriorDiags && !Info.EvalStatus.Diag->empty() &&
            !Info.EvalStatus.HasSideEffects)
          Info.EvalStatus.Diag->clear();
        Info.EvalMode = OldMode;
      }
    };
  
    /// RAII object used to set the current evaluation mode to ignore
    /// side-effects.
    struct IgnoreSideEffectsRAII {
      EvalInfo &Info;
      EvalInfo::EvaluationMode OldMode;
      explicit IgnoreSideEffectsRAII(EvalInfo &Info)
          : Info(Info), OldMode(Info.EvalMode) {
        Info.EvalMode = EvalInfo::EM_IgnoreSideEffects;
      }
  
      ~IgnoreSideEffectsRAII() { Info.EvalMode = OldMode; }
    };
  
    /// RAII object used to optionally suppress diagnostics and side-effects from
    /// a speculative evaluation.
    class SpeculativeEvaluationRAII {
      EvalInfo *Info = nullptr;
      Expr::EvalStatus OldStatus;
      unsigned OldSpeculativeEvaluationDepth;
  
      void moveFromAndCancel(SpeculativeEvaluationRAII &&Other) {
        Info = Other.Info;
        OldStatus = Other.OldStatus;
        OldSpeculativeEvaluationDepth = Other.OldSpeculativeEvaluationDepth;
        Other.Info = nullptr;
      }
  
      void maybeRestoreState() {
        if (!Info)
          return;
  
        Info->EvalStatus = OldStatus;
        Info->SpeculativeEvaluationDepth = OldSpeculativeEvaluationDepth;
      }
  
    public:
      SpeculativeEvaluationRAII() = default;
  
      SpeculativeEvaluationRAII(
          EvalInfo &Info, SmallVectorImpl<PartialDiagnosticAt> *NewDiag = nullptr)
          : Info(&Info), OldStatus(Info.EvalStatus),
            OldSpeculativeEvaluationDepth(Info.SpeculativeEvaluationDepth) {
        Info.EvalStatus.Diag = NewDiag;
        Info.SpeculativeEvaluationDepth = Info.CallStackDepth + 1;
      }
  
      SpeculativeEvaluationRAII(const SpeculativeEvaluationRAII &Other) = delete;
      SpeculativeEvaluationRAII(SpeculativeEvaluationRAII &&Other) {
        moveFromAndCancel(std::move(Other));
      }
  
      SpeculativeEvaluationRAII &operator=(SpeculativeEvaluationRAII &&Other) {
        maybeRestoreState();
        moveFromAndCancel(std::move(Other));
        return *this;
      }
  
      ~SpeculativeEvaluationRAII() { maybeRestoreState(); }
    };
  
    /// RAII object wrapping a full-expression or block scope, and handling
    /// the ending of the lifetime of temporaries created within it.
    template<ScopeKind Kind>
    class ScopeRAII {
      EvalInfo &Info;
      unsigned OldStackSize;
    public:
      ScopeRAII(EvalInfo &Info)
          : Info(Info), OldStackSize(Info.CleanupStack.size()) {
        // Push a new temporary version. This is needed to distinguish between
        // temporaries created in different iterations of a loop.
        Info.CurrentCall->pushTempVersion();
      }
      bool destroy(bool RunDestructors = true) {
        bool OK = cleanup(Info, RunDestructors, OldStackSize);
        OldStackSize = -1U;
        return OK;
      }
      ~ScopeRAII() {
        if (OldStackSize != -1U)
          destroy(false);
        // Body moved to a static method to encourage the compiler to inline away
        // instances of this class.
        Info.CurrentCall->popTempVersion();
      }
    private:
      static bool cleanup(EvalInfo &Info, bool RunDestructors,
                          unsigned OldStackSize) {
        assert(OldStackSize <= Info.CleanupStack.size() &&
               "running cleanups out of order?");
  
        // Run all cleanups for a block scope, and non-lifetime-extended cleanups
        // for a full-expression scope.
        bool Success = true;
        for (unsigned I = Info.CleanupStack.size(); I > OldStackSize; --I) {
          if (Info.CleanupStack[I - 1].isDestroyedAtEndOf(Kind)) {
            if (!Info.CleanupStack[I - 1].endLifetime(Info, RunDestructors)) {
              Success = false;
              break;
            }
          }
        }
  
        // Compact any retained cleanups.
        auto NewEnd = Info.CleanupStack.begin() + OldStackSize;
        if (Kind != ScopeKind::Block)
          NewEnd =
              std::remove_if(NewEnd, Info.CleanupStack.end(), [](Cleanup &C) {
                return C.isDestroyedAtEndOf(Kind);
              });
        Info.CleanupStack.erase(NewEnd, Info.CleanupStack.end());
        return Success;
      }
    };
    typedef ScopeRAII<ScopeKind::Block> BlockScopeRAII;
    typedef ScopeRAII<ScopeKind::FullExpression> FullExpressionRAII;
    typedef ScopeRAII<ScopeKind::Call> CallScopeRAII;
  }
  
  bool SubobjectDesignator::checkSubobject(EvalInfo &Info, const Expr *E,
                                           CheckSubobjectKind CSK) {
    if (Invalid)
      return false;
    if (isOnePastTheEnd()) {
      Info.CCEDiag(E, diag::note_constexpr_past_end_subobject)
        << CSK;
      setInvalid();
      return false;
    }
    // Note, we do not diagnose if isMostDerivedAnUnsizedArray(), because there
    // must actually be at least one array element; even a VLA cannot have a
    // bound of zero. And if our index is nonzero, we already had a CCEDiag.
    return true;
  }
  
  void SubobjectDesignator::diagnoseUnsizedArrayPointerArithmetic(EvalInfo &Info,
                                                                  const Expr *E) {
    Info.CCEDiag(E, diag::note_constexpr_unsized_array_indexed);
    // Do not set the designator as invalid: we can represent this situation,
    // and correct handling of __builtin_object_size requires us to do so.
  }
  
  void SubobjectDesignator::diagnosePointerArithmetic(EvalInfo &Info,
                                                      const Expr *E,
                                                      const APSInt &N) {
    // If we're complaining, we must be able to statically determine the size of
    // the most derived array.
    if (MostDerivedPathLength == Entries.size() && MostDerivedIsArrayElement)
      Info.CCEDiag(E, diag::note_constexpr_array_index)
        << N << /*array*/ 0
        << static_cast<unsigned>(getMostDerivedArraySize());
    else
      Info.CCEDiag(E, diag::note_constexpr_array_index)
        << N << /*non-array*/ 1;
    setInvalid();
  }
  
  CallStackFrame::CallStackFrame(EvalInfo &Info, SourceLocation CallLoc,
                                 const FunctionDecl *Callee, const LValue *This,
                                 CallRef Call)
      : Info(Info), Caller(Info.CurrentCall), Callee(Callee), This(This),
        Arguments(Call), CallLoc(CallLoc), Index(Info.NextCallIndex++) {
    Info.CurrentCall = this;
    ++Info.CallStackDepth;
  }
  
  CallStackFrame::~CallStackFrame() {
    assert(Info.CurrentCall == this && "calls retired out of order");
    --Info.CallStackDepth;
    Info.CurrentCall = Caller;
  }
  
  static bool isRead(AccessKinds AK) {
    return AK == AK_Read || AK == AK_ReadObjectRepresentation;
  }
  
  static bool isModification(AccessKinds AK) {
    switch (AK) {
    case AK_Read:
    case AK_ReadObjectRepresentation:
    case AK_MemberCall:
    case AK_DynamicCast:
    case AK_TypeId:
      return false;
    case AK_Assign:
    case AK_Increment:
    case AK_Decrement:
    case AK_Construct:
    case AK_Destroy:
      return true;
    }
    llvm_unreachable("unknown access kind");
  }
  
  static bool isAnyAccess(AccessKinds AK) {
    return isRead(AK) || isModification(AK);
  }
  
  /// Is this an access per the C++ definition?
  static bool isFormalAccess(AccessKinds AK) {
    return isAnyAccess(AK) && AK != AK_Construct && AK != AK_Destroy;
  }
  
  /// Is this kind of axcess valid on an indeterminate object value?
  static bool isValidIndeterminateAccess(AccessKinds AK) {
    switch (AK) {
    case AK_Read:
    case AK_Increment:
    case AK_Decrement:
      // These need the object's value.
      return false;
  
    case AK_ReadObjectRepresentation:
    case AK_Assign:
    case AK_Construct:
    case AK_Destroy:
      // Construction and destruction don't need the value.
      return true;
  
    case AK_MemberCall:
    case AK_DynamicCast:
    case AK_TypeId:
      // These aren't really meaningful on scalars.
      return true;
    }
    llvm_unreachable("unknown access kind");
  }
  
  namespace {
    struct ComplexValue {
    private:
      bool IsInt;
  
    public:
      APSInt IntReal, IntImag;
      APFloat FloatReal, FloatImag;
  
      ComplexValue() : FloatReal(APFloat::Bogus()), FloatImag(APFloat::Bogus()) {}
  
      void makeComplexFloat() { IsInt = false; }
      bool isComplexFloat() const { return !IsInt; }
      APFloat &getComplexFloatReal() { return FloatReal; }
      APFloat &getComplexFloatImag() { return FloatImag; }
  
      void makeComplexInt() { IsInt = true; }
      bool isComplexInt() const { return IsInt; }
      APSInt &getComplexIntReal() { return IntReal; }
      APSInt &getComplexIntImag() { return IntImag; }
  
      void moveInto(APValue &v) const {
        if (isComplexFloat())
          v = APValue(FloatReal, FloatImag);
        else
          v = APValue(IntReal, IntImag);
      }
      void setFrom(const APValue &v) {
        assert(v.isComplexFloat() || v.isComplexInt());
        if (v.isComplexFloat()) {
          makeComplexFloat();
          FloatReal = v.getComplexFloatReal();
          FloatImag = v.getComplexFloatImag();
        } else {
          makeComplexInt();
          IntReal = v.getComplexIntReal();
          IntImag = v.getComplexIntImag();
        }
      }
    };
  
    struct LValue {
      APValue::LValueBase Base;
      CharUnits Offset;
      SubobjectDesignator Designator;
      bool IsNullPtr : 1;
      bool InvalidBase : 1;
  
      const APValue::LValueBase getLValueBase() const { return Base; }
      CharUnits &getLValueOffset() { return Offset; }
      const CharUnits &getLValueOffset() const { return Offset; }
      SubobjectDesignator &getLValueDesignator() { return Designator; }
      const SubobjectDesignator &getLValueDesignator() const { return Designator;}
      bool isNullPointer() const { return IsNullPtr;}
  
      unsigned getLValueCallIndex() const { return Base.getCallIndex(); }
      unsigned getLValueVersion() const { return Base.getVersion(); }
  
      void moveInto(APValue &V) const {
        if (Designator.Invalid)
          V = APValue(Base, Offset, APValue::NoLValuePath(), IsNullPtr);
        else {
          assert(!InvalidBase && "APValues can't handle invalid LValue bases");
          V = APValue(Base, Offset, Designator.Entries,
                      Designator.IsOnePastTheEnd, IsNullPtr);
        }
      }
      void setFrom(ASTContext &Ctx, const APValue &V) {
        assert(V.isLValue() && "Setting LValue from a non-LValue?");
        Base = V.getLValueBase();
        Offset = V.getLValueOffset();
        InvalidBase = false;
        Designator = SubobjectDesignator(Ctx, V);
        IsNullPtr = V.isNullPointer();
      }
  
      void set(APValue::LValueBase B, bool BInvalid = false) {
  #ifndef NDEBUG
        // We only allow a few types of invalid bases. Enforce that here.
        if (BInvalid) {
          const auto *E = B.get<const Expr *>();
          assert((isa<MemberExpr>(E) || tryUnwrapAllocSizeCall(E)) &&
                 "Unexpected type of invalid base");
        }
  #endif
  
        Base = B;
        Offset = CharUnits::fromQuantity(0);
        InvalidBase = BInvalid;
        Designator = SubobjectDesignator(getType(B));
        IsNullPtr = false;
      }
  
      void setNull(ASTContext &Ctx, QualType PointerTy) {
        Base = (const ValueDecl *)nullptr;
        Offset =
            CharUnits::fromQuantity(Ctx.getTargetNullPointerValue(PointerTy));
        InvalidBase = false;
        Designator = SubobjectDesignator(PointerTy->getPointeeType());
        IsNullPtr = true;
      }
  
      void setInvalid(APValue::LValueBase B, unsigned I = 0) {
        set(B, true);
      }
  
      std::string toString(ASTContext &Ctx, QualType T) const {
        APValue Printable;
        moveInto(Printable);
        return Printable.getAsString(Ctx, T);
      }
  
    private:
      // Check that this LValue is not based on a null pointer. If it is, produce
      // a diagnostic and mark the designator as invalid.
      template <typename GenDiagType>
      bool checkNullPointerDiagnosingWith(const GenDiagType &GenDiag) {
        if (Designator.Invalid)
          return false;
        if (IsNullPtr) {
          GenDiag();
          Designator.setInvalid();
          return false;
        }
        return true;
      }
  
    public:
      bool checkNullPointer(EvalInfo &Info, const Expr *E,
                            CheckSubobjectKind CSK) {
        return checkNullPointerDiagnosingWith([&Info, E, CSK] {
          Info.CCEDiag(E, diag::note_constexpr_null_subobject) << CSK;
        });
      }
  
      bool checkNullPointerForFoldAccess(EvalInfo &Info, const Expr *E,
                                         AccessKinds AK) {
        return checkNullPointerDiagnosingWith([&Info, E, AK] {
          Info.FFDiag(E, diag::note_constexpr_access_null) << AK;
        });
      }
  
      // Check this LValue refers to an object. If not, set the designator to be
      // invalid and emit a diagnostic.
      bool checkSubobject(EvalInfo &Info, const Expr *E, CheckSubobjectKind CSK) {
        return (CSK == CSK_ArrayToPointer || checkNullPointer(Info, E, CSK)) &&
               Designator.checkSubobject(Info, E, CSK);
      }
  
      void addDecl(EvalInfo &Info, const Expr *E,
                   const Decl *D, bool Virtual = false) {
        if (checkSubobject(Info, E, isa<FieldDecl>(D) ? CSK_Field : CSK_Base))
          Designator.addDeclUnchecked(D, Virtual);
      }
      void addUnsizedArray(EvalInfo &Info, const Expr *E, QualType ElemTy) {
        if (!Designator.Entries.empty()) {
          Info.CCEDiag(E, diag::note_constexpr_unsupported_unsized_array);
          Designator.setInvalid();
          return;
        }
        if (checkSubobject(Info, E, CSK_ArrayToPointer)) {
          assert(getType(Base)->isPointerType() || getType(Base)->isArrayType());
          Designator.FirstEntryIsAnUnsizedArray = true;
          Designator.addUnsizedArrayUnchecked(ElemTy);
        }
      }
      void addArray(EvalInfo &Info, const Expr *E, const ConstantArrayType *CAT) {
        if (checkSubobject(Info, E, CSK_ArrayToPointer))
          Designator.addArrayUnchecked(CAT);
      }
      void addComplex(EvalInfo &Info, const Expr *E, QualType EltTy, bool Imag) {
        if (checkSubobject(Info, E, Imag ? CSK_Imag : CSK_Real))
          Designator.addComplexUnchecked(EltTy, Imag);
      }
      void clearIsNullPointer() {
        IsNullPtr = false;
      }
      void adjustOffsetAndIndex(EvalInfo &Info, const Expr *E,
                                const APSInt &Index, CharUnits ElementSize) {
        // An index of 0 has no effect. (In C, adding 0 to a null pointer is UB,
        // but we're not required to diagnose it and it's valid in C++.)
        if (!Index)
          return;
  
        // Compute the new offset in the appropriate width, wrapping at 64 bits.
        // FIXME: When compiling for a 32-bit target, we should use 32-bit
        // offsets.
        uint64_t Offset64 = Offset.getQuantity();
        uint64_t ElemSize64 = ElementSize.getQuantity();
        uint64_t Index64 = Index.extOrTrunc(64).getZExtValue();
        Offset = CharUnits::fromQuantity(Offset64 + ElemSize64 * Index64);
  
        if (checkNullPointer(Info, E, CSK_ArrayIndex))
          Designator.adjustIndex(Info, E, Index);
        clearIsNullPointer();
      }
      void adjustOffset(CharUnits N) {
        Offset += N;
        if (N.getQuantity())
          clearIsNullPointer();
      }
    };
  
    struct MemberPtr {
      MemberPtr() {}
      explicit MemberPtr(const ValueDecl *Decl) :
        DeclAndIsDerivedMember(Decl, false), Path() {}
  
      /// The member or (direct or indirect) field referred to by this member
      /// pointer, or 0 if this is a null member pointer.
      const ValueDecl *getDecl() const {
        return DeclAndIsDerivedMember.getPointer();
      }
      /// Is this actually a member of some type derived from the relevant class?
      bool isDerivedMember() const {
        return DeclAndIsDerivedMember.getInt();
      }
      /// Get the class which the declaration actually lives in.
      const CXXRecordDecl *getContainingRecord() const {
        return cast<CXXRecordDecl>(
            DeclAndIsDerivedMember.getPointer()->getDeclContext());
      }
  
      void moveInto(APValue &V) const {
        V = APValue(getDecl(), isDerivedMember(), Path);
      }
      void setFrom(const APValue &V) {
        assert(V.isMemberPointer());
        DeclAndIsDerivedMember.setPointer(V.getMemberPointerDecl());
        DeclAndIsDerivedMember.setInt(V.isMemberPointerToDerivedMember());
        Path.clear();
        ArrayRef<const CXXRecordDecl*> P = V.getMemberPointerPath();
        Path.insert(Path.end(), P.begin(), P.end());
      }
  
      /// DeclAndIsDerivedMember - The member declaration, and a flag indicating
      /// whether the member is a member of some class derived from the class type
      /// of the member pointer.
      llvm::PointerIntPair<const ValueDecl*, 1, bool> DeclAndIsDerivedMember;
      /// Path - The path of base/derived classes from the member declaration's
      /// class (exclusive) to the class type of the member pointer (inclusive).
      SmallVector<const CXXRecordDecl*, 4> Path;
  
      /// Perform a cast towards the class of the Decl (either up or down the
      /// hierarchy).
      bool castBack(const CXXRecordDecl *Class) {
        assert(!Path.empty());
        const CXXRecordDecl *Expected;
        if (Path.size() >= 2)
          Expected = Path[Path.size() - 2];
        else
          Expected = getContainingRecord();
        if (Expected->getCanonicalDecl() != Class->getCanonicalDecl()) {
          // C++11 [expr.static.cast]p12: In a conversion from (D::*) to (B::*),
          // if B does not contain the original member and is not a base or
          // derived class of the class containing the original member, the result
          // of the cast is undefined.
          // C++11 [conv.mem]p2 does not cover this case for a cast from (B::*) to
          // (D::*). We consider that to be a language defect.
          return false;
        }
        Path.pop_back();
        return true;
      }
      /// Perform a base-to-derived member pointer cast.
      bool castToDerived(const CXXRecordDecl *Derived) {
        if (!getDecl())
          return true;
        if (!isDerivedMember()) {
          Path.push_back(Derived);
          return true;
        }
        if (!castBack(Derived))
          return false;
        if (Path.empty())
          DeclAndIsDerivedMember.setInt(false);
        return true;
      }
      /// Perform a derived-to-base member pointer cast.
      bool castToBase(const CXXRecordDecl *Base) {
        if (!getDecl())
          return true;
        if (Path.empty())
          DeclAndIsDerivedMember.setInt(true);
        if (isDerivedMember()) {
          Path.push_back(Base);
          return true;
        }
        return castBack(Base);
      }
    };
  
    /// Compare two member pointers, which are assumed to be of the same type.
    static bool operator==(const MemberPtr &LHS, const MemberPtr &RHS) {
      if (!LHS.getDecl() || !RHS.getDecl())
        return !LHS.getDecl() && !RHS.getDecl();
      if (LHS.getDecl()->getCanonicalDecl() != RHS.getDecl()->getCanonicalDecl())
        return false;
      return LHS.Path == RHS.Path;
    }
  }
  
  static bool Evaluate(APValue &Result, EvalInfo &Info, const Expr *E);
  static bool EvaluateInPlace(APValue &Result, EvalInfo &Info,
                              const LValue &This, const Expr *E,
                              bool AllowNonLiteralTypes = false);
  static bool EvaluateLValue(const Expr *E, LValue &Result, EvalInfo &Info,
                             bool InvalidBaseOK = false);
  static bool EvaluatePointer(const Expr *E, LValue &Result, EvalInfo &Info,
                              bool InvalidBaseOK = false);
  static bool EvaluateMemberPointer(const Expr *E, MemberPtr &Result,
                                    EvalInfo &Info);
  static bool EvaluateTemporary(const Expr *E, LValue &Result, EvalInfo &Info);
  static bool EvaluateInteger(const Expr *E, APSInt &Result, EvalInfo &Info);
  static bool EvaluateIntegerOrLValue(const Expr *E, APValue &Result,
                                      EvalInfo &Info);
  static bool EvaluateFloat(const Expr *E, APFloat &Result, EvalInfo &Info);
  static bool EvaluateComplex(const Expr *E, ComplexValue &Res, EvalInfo &Info);
  static bool EvaluateAtomic(const Expr *E, const LValue *This, APValue &Result,
                             EvalInfo &Info);
  static bool EvaluateAsRValue(EvalInfo &Info, const Expr *E, APValue &Result);
  
  /// Evaluate an integer or fixed point expression into an APResult.
  static bool EvaluateFixedPointOrInteger(const Expr *E, APFixedPoint &Result,
                                          EvalInfo &Info);
  
  /// Evaluate only a fixed point expression into an APResult.
  static bool EvaluateFixedPoint(const Expr *E, APFixedPoint &Result,
                                 EvalInfo &Info);
  
  //===----------------------------------------------------------------------===//
  // Misc utilities
  //===----------------------------------------------------------------------===//
  
  /// Negate an APSInt in place, converting it to a signed form if necessary, and
  /// preserving its value (by extending by up to one bit as needed).
  static void negateAsSigned(APSInt &Int) {
    if (Int.isUnsigned() || Int.isMinSignedValue()) {
      Int = Int.extend(Int.getBitWidth() + 1);
      Int.setIsSigned(true);
    }
    Int = -Int;
  }
  
  template<typename KeyT>
  APValue &CallStackFrame::createTemporary(const KeyT *Key, QualType T,
                                           ScopeKind Scope, LValue &LV) {
    unsigned Version = getTempVersion();
    APValue::LValueBase Base(Key, Index, Version);
    LV.set(Base);
    return createLocal(Base, Key, T, Scope);
  }
  
  /// Allocate storage for a parameter of a function call made in this frame.
  APValue &CallStackFrame::createParam(CallRef Args, const ParmVarDecl *PVD,
                                       LValue &LV) {
    assert(Args.CallIndex == Index && "creating parameter in wrong frame");
    APValue::LValueBase Base(PVD, Index, Args.Version);
    LV.set(Base);
    // We always destroy parameters at the end of the call, even if we'd allow
    // them to live to the end of the full-expression at runtime, in order to
    // give portable results and match other compilers.
    return createLocal(Base, PVD, PVD->getType(), ScopeKind::Call);
  }
  
  APValue &CallStackFrame::createLocal(APValue::LValueBase Base, const void *Key,
                                       QualType T, ScopeKind Scope) {
    assert(Base.getCallIndex() == Index && "lvalue for wrong frame");
    unsigned Version = Base.getVersion();
    APValue &Result = Temporaries[MapKeyTy(Key, Version)];
    assert(Result.isAbsent() && "local created multiple times");
  
    // If we're creating a local immediately in the operand of a speculative
    // evaluation, don't register a cleanup to be run outside the speculative
    // evaluation context, since we won't actually be able to initialize this
    // object.
    if (Index <= Info.SpeculativeEvaluationDepth) {
      if (T.isDestructedType())
        Info.noteSideEffect();
    } else {
      Info.CleanupStack.push_back(Cleanup(&Result, Base, T, Scope));
    }
    return Result;
  }
  
  APValue *EvalInfo::createHeapAlloc(const Expr *E, QualType T, LValue &LV) {
    if (NumHeapAllocs > DynamicAllocLValue::getMaxIndex()) {
      FFDiag(E, diag::note_constexpr_heap_alloc_limit_exceeded);
      return nullptr;
    }
  
    DynamicAllocLValue DA(NumHeapAllocs++);
    LV.set(APValue::LValueBase::getDynamicAlloc(DA, T));
    auto Result = HeapAllocs.emplace(std::piecewise_construct,
                                     std::forward_as_tuple(DA), std::tuple<>());
    assert(Result.second && "reused a heap alloc index?");
    Result.first->second.AllocExpr = E;
    return &Result.first->second.Value;
  }
  
  /// Produce a string describing the given constexpr call.
  void CallStackFrame::describe(raw_ostream &Out) {
    unsigned ArgIndex = 0;
    bool IsMemberCall = isa<CXXMethodDecl>(Callee) &&
                        !isa<CXXConstructorDecl>(Callee) &&
                        cast<CXXMethodDecl>(Callee)->isInstance();
  
    if (!IsMemberCall)
      Out << *Callee << '(';
  
    if (This && IsMemberCall) {
      APValue Val;
      This->moveInto(Val);
      Val.printPretty(Out, Info.Ctx,
                      This->Designator.MostDerivedType);
      // FIXME: Add parens around Val if needed.
      Out << "->" << *Callee << '(';
      IsMemberCall = false;
    }
  
    for (FunctionDecl::param_const_iterator I = Callee->param_begin(),
         E = Callee->param_end(); I != E; ++I, ++ArgIndex) {
      if (ArgIndex > (unsigned)IsMemberCall)
        Out << ", ";
  
      const ParmVarDecl *Param = *I;
      APValue *V = Info.getParamSlot(Arguments, Param);
      if (V)
        V->printPretty(Out, Info.Ctx, Param->getType());
      else
        Out << "<...>";
  
      if (ArgIndex == 0 && IsMemberCall)
        Out << "->" << *Callee << '(';
    }
  
    Out << ')';
  }
  
  /// Evaluate an expression to see if it had side-effects, and discard its
  /// result.
  /// \return \c true if the caller should keep evaluating.
  static bool EvaluateIgnoredValue(EvalInfo &Info, const Expr *E) {
    assert(!E->isValueDependent());
    APValue Scratch;
    if (!Evaluate(Scratch, Info, E))
      // We don't need the value, but we might have skipped a side effect here.
      return Info.noteSideEffect();
    return true;
  }
  
  /// Should this call expression be treated as a string literal?
  static bool IsStringLiteralCall(const CallExpr *E) {
    unsigned Builtin = E->getBuiltinCallee();
    return (Builtin == Builtin::BI__builtin___CFStringMakeConstantString ||
            Builtin == Builtin::BI__builtin___NSStringMakeConstantString);
  }
  
  static bool isGlobalCallLValue(const CallExpr *E) {
    if (IsStringLiteralCall(E))
      return true;
  
    switch (E->getBuiltinCallee()) {
    case Builtin::BI__builtin_ptrauth_sign_constant:
      return true;
  
    default:
      return false;
    }
  }
  
  static bool IsGlobalLValue(APValue::LValueBase B) {
    // C++11 [expr.const]p3 An address constant expression is a prvalue core
    // constant expression of pointer type that evaluates to...
  
    // ... a null pointer value, or a prvalue core constant expression of type
    // std::nullptr_t.
    if (!B) return true;
  
    if (const ValueDecl *D = B.dyn_cast<const ValueDecl*>()) {
      // ... the address of an object with static storage duration,
      if (const VarDecl *VD = dyn_cast<VarDecl>(D))
        return VD->hasGlobalStorage();
      if (isa<TemplateParamObjectDecl>(D))
        return true;
      // ... the address of a function,
      // ... the address of a GUID [MS extension],
      return isa<FunctionDecl>(D) || isa<MSGuidDecl>(D);
    }
  
    if (B.is<TypeInfoLValue>() || B.is<DynamicAllocLValue>())
      return true;
  
    const Expr *E = B.get<const Expr*>();
    switch (E->getStmtClass()) {
    default:
      return false;
    case Expr::CompoundLiteralExprClass: {
      const CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
      return CLE->isFileScope() && CLE->isLValue();
    }
    case Expr::MaterializeTemporaryExprClass:
      // A materialized temporary might have been lifetime-extended to static
      // storage duration.
      return cast<MaterializeTemporaryExpr>(E)->getStorageDuration() == SD_Static;
    // A string literal has static storage duration.
    case Expr::StringLiteralClass:
    case Expr::PredefinedExprClass:
    case Expr::ObjCStringLiteralClass:
    case Expr::ObjCEncodeExprClass:
      return true;
    case Expr::ObjCBoxedExprClass:
      return cast<ObjCBoxedExpr>(E)->isExpressibleAsConstantInitializer();
    case Expr::CallExprClass:
      return isGlobalCallLValue(cast<CallExpr>(E));
    // For GCC compatibility, &&label has static storage duration.
    case Expr::AddrLabelExprClass:
      return true;
    // A Block literal expression may be used as the initialization value for
    // Block variables at global or local static scope.
    case Expr::BlockExprClass:
      return !cast<BlockExpr>(E)->getBlockDecl()->hasCaptures();
    case Expr::ImplicitValueInitExprClass:
      // FIXME:
      // We can never form an lvalue with an implicit value initialization as its
      // base through expression evaluation, so these only appear in one case: the
      // implicit variable declaration we invent when checking whether a constexpr
      // constructor can produce a constant expression. We must assume that such
      // an expression might be a global lvalue.
      return true;
    }
  }
  
  static const ValueDecl *GetLValueBaseDecl(const LValue &LVal) {
    return LVal.Base.dyn_cast<const ValueDecl*>();
  }
  
  static bool IsLiteralLValue(const LValue &Value) {
    if (Value.getLValueCallIndex())
      return false;
    const Expr *E = Value.Base.dyn_cast<const Expr*>();
    return E && !isa<MaterializeTemporaryExpr>(E);
  }
  
  static bool IsWeakLValue(const LValue &Value) {
    const ValueDecl *Decl = GetLValueBaseDecl(Value);
    return Decl && Decl->isWeak();
  }
  
  static bool isZeroSized(const LValue &Value) {
    const ValueDecl *Decl = GetLValueBaseDecl(Value);
    if (Decl && isa<VarDecl>(Decl)) {
      QualType Ty = Decl->getType();
      if (Ty->isArrayType())
        return Ty->isIncompleteType() ||
               Decl->getASTContext().getTypeSize(Ty) == 0;
    }
    return false;
  }
  
  static bool HasSameBase(const LValue &A, const LValue &B) {
    if (!A.getLValueBase())
      return !B.getLValueBase();
    if (!B.getLValueBase())
      return false;
  
    if (A.getLValueBase().getOpaqueValue() !=
        B.getLValueBase().getOpaqueValue())
      return false;
  
    return A.getLValueCallIndex() == B.getLValueCallIndex() &&
           A.getLValueVersion() == B.getLValueVersion();
  }
  
  static void NoteLValueLocation(EvalInfo &Info, APValue::LValueBase Base) {
    assert(Base && "no location for a null lvalue");
    const ValueDecl *VD = Base.dyn_cast<const ValueDecl*>();
  
    // For a parameter, find the corresponding call stack frame (if it still
    // exists), and point at the parameter of the function definition we actually
    // invoked.
    if (auto *PVD = dyn_cast_or_null<ParmVarDecl>(VD)) {
      unsigned Idx = PVD->getFunctionScopeIndex();
      for (CallStackFrame *F = Info.CurrentCall; F; F = F->Caller) {
        if (F->Arguments.CallIndex == Base.getCallIndex() &&
            F->Arguments.Version == Base.getVersion() && F->Callee &&
            Idx < F->Callee->getNumParams()) {
          VD = F->Callee->getParamDecl(Idx);
          break;
        }
      }
    }
  
    if (VD)
      Info.Note(VD->getLocation(), diag::note_declared_at);
    else if (const Expr *E = Base.dyn_cast<const Expr*>())
      Info.Note(E->getExprLoc(), diag::note_constexpr_temporary_here);
    else if (DynamicAllocLValue DA = Base.dyn_cast<DynamicAllocLValue>()) {
      // FIXME: Produce a note for dangling pointers too.
      if (Optional<DynAlloc*> Alloc = Info.lookupDynamicAlloc(DA))
        Info.Note((*Alloc)->AllocExpr->getExprLoc(),
                  diag::note_constexpr_dynamic_alloc_here);
    }
    // We have no information to show for a typeid(T) object.
  }
  
  enum class CheckEvaluationResultKind {
    ConstantExpression,
    FullyInitialized,
  };
  
  /// Materialized temporaries that we've already checked to determine if they're
  /// initializsed by a constant expression.
  using CheckedTemporaries =
      llvm::SmallPtrSet<const MaterializeTemporaryExpr *, 8>;
  
  static bool CheckEvaluationResult(CheckEvaluationResultKind CERK,
                                    EvalInfo &Info, SourceLocation DiagLoc,
                                    QualType Type, const APValue &Value,
                                    ConstantExprKind Kind,
                                    SourceLocation SubobjectLoc,
                                    CheckedTemporaries &CheckedTemps);
  
  /// Check that this reference or pointer core constant expression is a valid
  /// value for an address or reference constant expression. Return true if we
  /// can fold this expression, whether or not it's a constant expression.
  static bool CheckLValueConstantExpression(EvalInfo &Info, SourceLocation Loc,
                                            QualType Type, const LValue &LVal,
                                            ConstantExprKind Kind,
                                            CheckedTemporaries &CheckedTemps) {
    bool IsReferenceType = Type->isReferenceType();
  
    APValue::LValueBase Base = LVal.getLValueBase();
    const SubobjectDesignator &Designator = LVal.getLValueDesignator();
  
    const Expr *BaseE = Base.dyn_cast<const Expr *>();
    const ValueDecl *BaseVD = Base.dyn_cast<const ValueDecl*>();
  
    // Additional restrictions apply in a template argument. We only enforce the
    // C++20 restrictions here; additional syntactic and semantic restrictions
    // are applied elsewhere.
    if (isTemplateArgument(Kind)) {
      int InvalidBaseKind = -1;
      StringRef Ident;
      if (Base.is<TypeInfoLValue>())
        InvalidBaseKind = 0;
      else if (isa_and_nonnull<StringLiteral>(BaseE))
        InvalidBaseKind = 1;
      else if (isa_and_nonnull<MaterializeTemporaryExpr>(BaseE) ||
               isa_and_nonnull<LifetimeExtendedTemporaryDecl>(BaseVD))
        InvalidBaseKind = 2;
      else if (auto *PE = dyn_cast_or_null<PredefinedExpr>(BaseE)) {
        InvalidBaseKind = 3;
        Ident = PE->getIdentKindName();
      }
  
      if (InvalidBaseKind != -1) {
        Info.FFDiag(Loc, diag::note_constexpr_invalid_template_arg)
            << IsReferenceType << !Designator.Entries.empty() << InvalidBaseKind
            << Ident;
        return false;
      }
    }
  
    if (auto *FD = dyn_cast_or_null<FunctionDecl>(BaseVD)) {
      if (FD->isConsteval()) {
        Info.FFDiag(Loc, diag::note_consteval_address_accessible)
            << !Type->isAnyPointerType();
        Info.Note(FD->getLocation(), diag::note_declared_at);
        return false;
      }
    }
  
    // Check that the object is a global. Note that the fake 'this' object we
    // manufacture when checking potential constant expressions is conservatively
    // assumed to be global here.
    if (!IsGlobalLValue(Base)) {
      if (Info.getLangOpts().CPlusPlus11) {
        const ValueDecl *VD = Base.dyn_cast<const ValueDecl*>();
        Info.FFDiag(Loc, diag::note_constexpr_non_global, 1)
          << IsReferenceType << !Designator.Entries.empty()
          << !!VD << VD;
  
        auto *VarD = dyn_cast_or_null<VarDecl>(VD);
        if (VarD && VarD->isConstexpr()) {
          // Non-static local constexpr variables have unintuitive semantics:
          //   constexpr int a = 1;
          //   constexpr const int *p = &a;
          // ... is invalid because the address of 'a' is not constant. Suggest
          // adding a 'static' in this case.
          Info.Note(VarD->getLocation(), diag::note_constexpr_not_static)
              << VarD
              << FixItHint::CreateInsertion(VarD->getBeginLoc(), "static ");
        } else {
          NoteLValueLocation(Info, Base);
        }
      } else {
        Info.FFDiag(Loc);
      }
      // Don't allow references to temporaries to escape.
      return false;
    }
    assert((Info.checkingPotentialConstantExpression() ||
            LVal.getLValueCallIndex() == 0) &&
           "have call index for global lvalue");
  
    if (Base.is<DynamicAllocLValue>()) {
      Info.FFDiag(Loc, diag::note_constexpr_dynamic_alloc)
          << IsReferenceType << !Designator.Entries.empty();
      NoteLValueLocation(Info, Base);
      return false;
    }
  
    if (BaseVD) {
      if (const VarDecl *Var = dyn_cast<const VarDecl>(BaseVD)) {
        // Check if this is a thread-local variable.
        if (Var->getTLSKind())
          // FIXME: Diagnostic!
          return false;
  
        // A dllimport variable never acts like a constant, unless we're
        // evaluating a value for use only in name mangling.
        if (!isForManglingOnly(Kind) && Var->hasAttr<DLLImportAttr>())
          // FIXME: Diagnostic!
          return false;
      }
      if (const auto *FD = dyn_cast<const FunctionDecl>(BaseVD)) {
        // __declspec(dllimport) must be handled very carefully:
        // We must never initialize an expression with the thunk in C++.
        // Doing otherwise would allow the same id-expression to yield
        // different addresses for the same function in different translation
        // units.  However, this means that we must dynamically initialize the
        // expression with the contents of the import address table at runtime.
        //
        // The C language has no notion of ODR; furthermore, it has no notion of
        // dynamic initialization.  This means that we are permitted to
        // perform initialization with the address of the thunk.
        if (Info.getLangOpts().CPlusPlus && !isForManglingOnly(Kind) &&
            FD->hasAttr<DLLImportAttr>())
          // FIXME: Diagnostic!
          return false;
      }
    } else if (const auto *MTE =
                   dyn_cast_or_null<MaterializeTemporaryExpr>(BaseE)) {
      if (CheckedTemps.insert(MTE).second) {
        QualType TempType = getType(Base);
        if (TempType.isDestructedType()) {
          Info.FFDiag(MTE->getExprLoc(),
                      diag::note_constexpr_unsupported_temporary_nontrivial_dtor)
              << TempType;
          return false;
        }
  
        APValue *V = MTE->getOrCreateValue(false);
        assert(V && "evasluation result refers to uninitialised temporary");
        if (!CheckEvaluationResult(CheckEvaluationResultKind::ConstantExpression,
                                   Info, MTE->getExprLoc(), TempType, *V,
                                   Kind, SourceLocation(), CheckedTemps))
          return false;
      }
    }
  
    // Allow address constant expressions to be past-the-end pointers. This is
    // an extension: the standard requires them to point to an object.
    if (!IsReferenceType)
      return true;
  
    // A reference constant expression must refer to an object.
    if (!Base) {
      // FIXME: diagnostic
      Info.CCEDiag(Loc);
      return true;
    }
  
    // Does this refer one past the end of some object?
    if (!Designator.Invalid && Designator.isOnePastTheEnd()) {
      Info.FFDiag(Loc, diag::note_constexpr_past_end, 1)
        << !Designator.Entries.empty() << !!BaseVD << BaseVD;
      NoteLValueLocation(Info, Base);
    }
  
    return true;
  }
  
  /// Member pointers are constant expressions unless they point to a
  /// non-virtual dllimport member function.
  static bool CheckMemberPointerConstantExpression(EvalInfo &Info,
                                                   SourceLocation Loc,
                                                   QualType Type,
                                                   const APValue &Value,
                                                   ConstantExprKind Kind) {
    const ValueDecl *Member = Value.getMemberPointerDecl();
    const auto *FD = dyn_cast_or_null<CXXMethodDecl>(Member);
    if (!FD)
      return true;
    if (FD->isConsteval()) {
      Info.FFDiag(Loc, diag::note_consteval_address_accessible) << /*pointer*/ 0;
      Info.Note(FD->getLocation(), diag::note_declared_at);
      return false;
    }
    return isForManglingOnly(Kind) || FD->isVirtual() ||
           !FD->hasAttr<DLLImportAttr>();
  }
  
  /// Check that this core constant expression is of literal type, and if not,
  /// produce an appropriate diagnostic.
  static bool CheckLiteralType(EvalInfo &Info, const Expr *E,
                               const LValue *This = nullptr) {
    if (!E->isRValue() || E->getType()->isLiteralType(Info.Ctx))
      return true;
  
    // C++1y: A constant initializer for an object o [...] may also invoke
    // constexpr constructors for o and its subobjects even if those objects
    // are of non-literal class types.
    //
    // C++11 missed this detail for aggregates, so classes like this:
    //   struct foo_t { union { int i; volatile int j; } u; };
    // are not (obviously) initializable like so:
    //   __attribute__((__require_constant_initialization__))
    //   static const foo_t x = {{0}};
    // because "i" is a subobject with non-literal initialization (due to the
    // volatile member of the union). See:
    //   http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1677
    // Therefore, we use the C++1y behavior.
    if (This && Info.EvaluatingDecl == This->getLValueBase())
      return true;
  
    // Prvalue constant expressions must be of literal types.
    if (Info.getLangOpts().CPlusPlus11)
      Info.FFDiag(E, diag::note_constexpr_nonliteral)
        << E->getType();
    else
      Info.FFDiag(E, diag::note_invalid_subexpr_in_const_expr);
    return false;
  }
  
  static bool CheckEvaluationResult(CheckEvaluationResultKind CERK,
                                    EvalInfo &Info, SourceLocation DiagLoc,
                                    QualType Type, const APValue &Value,
                                    ConstantExprKind Kind,
                                    SourceLocation SubobjectLoc,
                                    CheckedTemporaries &CheckedTemps) {
    if (!Value.hasValue()) {
      Info.FFDiag(DiagLoc, diag::note_constexpr_uninitialized)
        << true << Type;
      if (SubobjectLoc.isValid())
        Info.Note(SubobjectLoc, diag::note_constexpr_subobject_declared_here);
      return false;
    }
  
    // We allow _Atomic(T) to be initialized from anything that T can be
    // initialized from.
    if (const AtomicType *AT = Type->getAs<AtomicType>())
      Type = AT->getValueType();
  
    // Core issue 1454: For a literal constant expression of array or class type,
    // each subobject of its value shall have been initialized by a constant
    // expression.
    if (Value.isArray()) {
      QualType EltTy = Type->castAsArrayTypeUnsafe()->getElementType();
      for (unsigned I = 0, N = Value.getArrayInitializedElts(); I != N; ++I) {
        if (!CheckEvaluationResult(CERK, Info, DiagLoc, EltTy,
                                   Value.getArrayInitializedElt(I), Kind,
                                   SubobjectLoc, CheckedTemps))
          return false;
      }
      if (!Value.hasArrayFiller())
        return true;
      return CheckEvaluationResult(CERK, Info, DiagLoc, EltTy,
                                   Value.getArrayFiller(), Kind, SubobjectLoc,
                                   CheckedTemps);
    }
    if (Value.isUnion() && Value.getUnionField()) {
      return CheckEvaluationResult(
          CERK, Info, DiagLoc, Value.getUnionField()->getType(),
          Value.getUnionValue(), Kind, Value.getUnionField()->getLocation(),
          CheckedTemps);
    }
    if (Value.isStruct()) {
      RecordDecl *RD = Type->castAs<RecordType>()->getDecl();
      if (const CXXRecordDecl *CD = dyn_cast<CXXRecordDecl>(RD)) {
        unsigned BaseIndex = 0;
        for (const CXXBaseSpecifier &BS : CD->bases()) {
          if (!CheckEvaluationResult(CERK, Info, DiagLoc, BS.getType(),
                                     Value.getStructBase(BaseIndex), Kind,
                                     BS.getBeginLoc(), CheckedTemps))
            return false;
          ++BaseIndex;
        }
      }
      for (const auto *I : RD->fields()) {
        if (I->isUnnamedBitfield())
          continue;
  
        if (!CheckEvaluationResult(CERK, Info, DiagLoc, I->getType(),
                                   Value.getStructField(I->getFieldIndex()),
                                   Kind, I->getLocation(), CheckedTemps))
          return false;
      }
    }
  
    if (Value.isLValue() &&
        CERK == CheckEvaluationResultKind::ConstantExpression) {
      LValue LVal;
      LVal.setFrom(Info.Ctx, Value);
      return CheckLValueConstantExpression(Info, DiagLoc, Type, LVal, Kind,
                                           CheckedTemps);
    }
  
    if (Value.isMemberPointer() &&
        CERK == CheckEvaluationResultKind::ConstantExpression)
      return CheckMemberPointerConstantExpression(Info, DiagLoc, Type, Value, Kind);
  
    // Everything else is fine.
    return true;
  }
  
  /// Check that this core constant expression value is a valid value for a
  /// constant expression. If not, report an appropriate diagnostic. Does not
  /// check that the expression is of literal type.
  static bool CheckConstantExpression(EvalInfo &Info, SourceLocation DiagLoc,
                                      QualType Type, const APValue &Value,
                                      ConstantExprKind Kind) {
    // Nothing to check for a constant expression of type 'cv void'.
    if (Type->isVoidType())
      return true;
  
    CheckedTemporaries CheckedTemps;
    return CheckEvaluationResult(CheckEvaluationResultKind::ConstantExpression,
                                 Info, DiagLoc, Type, Value, Kind,
                                 SourceLocation(), CheckedTemps);
  }
  
  /// Check that this evaluated value is fully-initialized and can be loaded by
  /// an lvalue-to-rvalue conversion.
  static bool CheckFullyInitialized(EvalInfo &Info, SourceLocation DiagLoc,
                                    QualType Type, const APValue &Value) {
    CheckedTemporaries CheckedTemps;
    return CheckEvaluationResult(
        CheckEvaluationResultKind::FullyInitialized, Info, DiagLoc, Type, Value,
        ConstantExprKind::Normal, SourceLocation(), CheckedTemps);
  }
  
  /// Enforce C++2a [expr.const]/4.17, which disallows new-expressions unless
  /// "the allocated storage is deallocated within the evaluation".
  static bool CheckMemoryLeaks(EvalInfo &Info) {
    if (!Info.HeapAllocs.empty()) {
      // We can still fold to a constant despite a compile-time memory leak,
      // so long as the heap allocation isn't referenced in the result (we check
      // that in CheckConstantExpression).
      Info.CCEDiag(Info.HeapAllocs.begin()->second.AllocExpr,
                   diag::note_constexpr_memory_leak)
          << unsigned(Info.HeapAllocs.size() - 1);
    }
    return true;
  }
  
  static bool EvalPointerValueAsBool(const APValue &Value, bool &Result) {
    // A null base expression indicates a null pointer.  These are always
    // evaluatable, and they are false unless the offset is zero.
    if (!Value.getLValueBase()) {
      Result = !Value.getLValueOffset().isZero();
      return true;
    }
  
    // We have a non-null base.  These are generally known to be true, but if it's
    // a weak declaration it can be null at runtime.
    Result = true;
    const ValueDecl *Decl = Value.getLValueBase().dyn_cast<const ValueDecl*>();
    return !Decl || !Decl->isWeak();
  }
  
  static bool HandleConversionToBool(const APValue &Val, bool &Result) {
    switch (Val.getKind()) {
    case APValue::None:
    case APValue::Indeterminate:
      return false;
    case APValue::Int:
      Result = Val.getInt().getBoolValue();
      return true;
    case APValue::FixedPoint:
      Result = Val.getFixedPoint().getBoolValue();
      return true;
    case APValue::Float:
      Result = !Val.getFloat().isZero();
      return true;
    case APValue::ComplexInt:
      Result = Val.getComplexIntReal().getBoolValue() ||
               Val.getComplexIntImag().getBoolValue();
      return true;
    case APValue::ComplexFloat:
      Result = !Val.getComplexFloatReal().isZero() ||
               !Val.getComplexFloatImag().isZero();
      return true;
    case APValue::LValue:
      return EvalPointerValueAsBool(Val, Result);
    case APValue::MemberPointer:
      Result = Val.getMemberPointerDecl();
      return true;
    case APValue::Vector:
    case APValue::Array:
    case APValue::Struct:
    case APValue::Union:
    case APValue::AddrLabelDiff:
      return false;
    }
  
    llvm_unreachable("unknown APValue kind");
  }
  
  static bool EvaluateAsBooleanCondition(const Expr *E, bool &Result,
                                         EvalInfo &Info) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && "missing lvalue-to-rvalue conv in bool condition");
    APValue Val;
    if (!Evaluate(Val, Info, E))
      return false;
    return HandleConversionToBool(Val, Result);
  }
  
  template<typename T>
  static bool HandleOverflow(EvalInfo &Info, const Expr *E,
                             const T &SrcValue, QualType DestType) {
    Info.CCEDiag(E, diag::note_constexpr_overflow)
      << SrcValue << DestType;
    return Info.noteUndefinedBehavior();
  }
  
  static bool HandleFloatToIntCast(EvalInfo &Info, const Expr *E,
                                   QualType SrcType, const APFloat &Value,
                                   QualType DestType, APSInt &Result) {
    unsigned DestWidth = Info.Ctx.getIntWidth(DestType);
    // Determine whether we are converting to unsigned or signed.
    bool DestSigned = DestType->isSignedIntegerOrEnumerationType();
  
    Result = APSInt(DestWidth, !DestSigned);
    bool ignored;
    if (Value.convertToInteger(Result, llvm::APFloat::rmTowardZero, &ignored)
        & APFloat::opInvalidOp)
      return HandleOverflow(Info, E, Value, DestType);
    return true;
  }
  
  /// Get rounding mode used for evaluation of the specified expression.
  /// \param[out] DynamicRM Is set to true is the requested rounding mode is
  ///                       dynamic.
  /// If rounding mode is unknown at compile time, still try to evaluate the
  /// expression. If the result is exact, it does not depend on rounding mode.
  /// So return "tonearest" mode instead of "dynamic".
  static llvm::RoundingMode getActiveRoundingMode(EvalInfo &Info, const Expr *E,
                                                  bool &DynamicRM) {
    llvm::RoundingMode RM =
        E->getFPFeaturesInEffect(Info.Ctx.getLangOpts()).getRoundingMode();
    DynamicRM = (RM == llvm::RoundingMode::Dynamic);
    if (DynamicRM)
      RM = llvm::RoundingMode::NearestTiesToEven;
    return RM;
  }
  
  /// Check if the given evaluation result is allowed for constant evaluation.
  static bool checkFloatingPointResult(EvalInfo &Info, const Expr *E,
                                       APFloat::opStatus St) {
    // In a constant context, assume that any dynamic rounding mode or FP
    // exception state matches the default floating-point environment.
    if (Info.InConstantContext)
      return true;
  
    FPOptions FPO = E->getFPFeaturesInEffect(Info.Ctx.getLangOpts());
    if ((St & APFloat::opInexact) &&
        FPO.getRoundingMode() == llvm::RoundingMode::Dynamic) {
      // Inexact result means that it depends on rounding mode. If the requested
      // mode is dynamic, the evaluation cannot be made in compile time.
      Info.FFDiag(E, diag::note_constexpr_dynamic_rounding);
      return false;
    }
  
    if ((St != APFloat::opOK) &&
        (FPO.getRoundingMode() == llvm::RoundingMode::Dynamic ||
         FPO.getFPExceptionMode() != LangOptions::FPE_Ignore ||
         FPO.getAllowFEnvAccess())) {
      Info.FFDiag(E, diag::note_constexpr_float_arithmetic_strict);
      return false;
    }
  
    if ((St & APFloat::opStatus::opInvalidOp) &&
        FPO.getFPExceptionMode() != LangOptions::FPE_Ignore) {
      // There is no usefully definable result.
      Info.FFDiag(E);
      return false;
    }
  
    // FIXME: if:
    // - evaluation triggered other FP exception, and
    // - exception mode is not "ignore", and
    // - the expression being evaluated is not a part of global variable
    //   initializer,
    // the evaluation probably need to be rejected.
    return true;
  }
  
  static bool HandleFloatToFloatCast(EvalInfo &Info, const Expr *E,
                                     QualType SrcType, QualType DestType,
                                     APFloat &Result) {
    assert(isa<CastExpr>(E) || isa<CompoundAssignOperator>(E));
    bool DynamicRM;
    llvm::RoundingMode RM = getActiveRoundingMode(Info, E, DynamicRM);
    APFloat::opStatus St;
    APFloat Value = Result;
    bool ignored;
    St = Result.convert(Info.Ctx.getFloatTypeSemantics(DestType), RM, &ignored);
    return checkFloatingPointResult(Info, E, St);
  }
  
  static APSInt HandleIntToIntCast(EvalInfo &Info, const Expr *E,
                                   QualType DestType, QualType SrcType,
                                   const APSInt &Value) {
    unsigned DestWidth = Info.Ctx.getIntWidth(DestType);
    // Figure out if this is a truncate, extend or noop cast.
    // If the input is signed, do a sign extend, noop, or truncate.
    APSInt Result = Value.extOrTrunc(DestWidth);
    Result.setIsUnsigned(DestType->isUnsignedIntegerOrEnumerationType());
    if (DestType->isBooleanType())
      Result = Value.getBoolValue();
    return Result;
  }
  
  static bool HandleIntToFloatCast(EvalInfo &Info, const Expr *E,
                                   const FPOptions FPO,
                                   QualType SrcType, const APSInt &Value,
                                   QualType DestType, APFloat &Result) {
    Result = APFloat(Info.Ctx.getFloatTypeSemantics(DestType), 1);
    APFloat::opStatus St = Result.convertFromAPInt(Value, Value.isSigned(),
         APFloat::rmNearestTiesToEven);
    if (!Info.InConstantContext && St != llvm::APFloatBase::opOK &&
        FPO.isFPConstrained()) {
      Info.FFDiag(E, diag::note_constexpr_float_arithmetic_strict);
      return false;
    }
    return true;
  }
  
  static bool truncateBitfieldValue(EvalInfo &Info, const Expr *E,
                                    APValue &Value, const FieldDecl *FD) {
    assert(FD->isBitField() && "truncateBitfieldValue on non-bitfield");
  
    if (!Value.isInt()) {
      // Trying to store a pointer-cast-to-integer into a bitfield.
      // FIXME: In this case, we should provide the diagnostic for casting
      // a pointer to an integer.
      assert(Value.isLValue() && "integral value neither int nor lvalue?");
      Info.FFDiag(E);
      return false;
    }
  
    APSInt &Int = Value.getInt();
    unsigned OldBitWidth = Int.getBitWidth();
    unsigned NewBitWidth = FD->getBitWidthValue(Info.Ctx);
    if (NewBitWidth < OldBitWidth)
      Int = Int.trunc(NewBitWidth).extend(OldBitWidth);
    return true;
  }
  
  static bool EvalAndBitcastToAPInt(EvalInfo &Info, const Expr *E,
                                    llvm::APInt &Res) {
    APValue SVal;
    if (!Evaluate(SVal, Info, E))
      return false;
    if (SVal.isInt()) {
      Res = SVal.getInt();
      return true;
    }
    if (SVal.isFloat()) {
      Res = SVal.getFloat().bitcastToAPInt();
      return true;
    }
    if (SVal.isVector()) {
      QualType VecTy = E->getType();
      unsigned VecSize = Info.Ctx.getTypeSize(VecTy);
      QualType EltTy = VecTy->castAs<VectorType>()->getElementType();
      unsigned EltSize = Info.Ctx.getTypeSize(EltTy);
      bool BigEndian = Info.Ctx.getTargetInfo().isBigEndian();
      Res = llvm::APInt::getNullValue(VecSize);
      for (unsigned i = 0; i < SVal.getVectorLength(); i++) {
        APValue &Elt = SVal.getVectorElt(i);
        llvm::APInt EltAsInt;
        if (Elt.isInt()) {
          EltAsInt = Elt.getInt();
        } else if (Elt.isFloat()) {
          EltAsInt = Elt.getFloat().bitcastToAPInt();
        } else {
          // Don't try to handle vectors of anything other than int or float
          // (not sure if it's possible to hit this case).
          Info.FFDiag(E, diag::note_invalid_subexpr_in_const_expr);
          return false;
        }
        unsigned BaseEltSize = EltAsInt.getBitWidth();
        if (BigEndian)
          Res |= EltAsInt.zextOrTrunc(VecSize).rotr(i*EltSize+BaseEltSize);
        else
          Res |= EltAsInt.zextOrTrunc(VecSize).rotl(i*EltSize);
      }
      return true;
    }
    // Give up if the input isn't an int, float, or vector.  For example, we
    // reject "(v4i16)(intptr_t)&a".
    Info.FFDiag(E, diag::note_invalid_subexpr_in_const_expr);
    return false;
  }
  
  /// Perform the given integer operation, which is known to need at most BitWidth
  /// bits, and check for overflow in the original type (if that type was not an
  /// unsigned type).
  template<typename Operation>
  static bool CheckedIntArithmetic(EvalInfo &Info, const Expr *E,
                                   const APSInt &LHS, const APSInt &RHS,
                                   unsigned BitWidth, Operation Op,
                                   APSInt &Result) {
    if (LHS.isUnsigned()) {
      Result = Op(LHS, RHS);
      return true;
    }
  
    APSInt Value(Op(LHS.extend(BitWidth), RHS.extend(BitWidth)), false);
    Result = Value.trunc(LHS.getBitWidth());
    if (Result.extend(BitWidth) != Value) {
      if (Info.checkingForUndefinedBehavior())
        Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
                                         diag::warn_integer_constant_overflow)
            << Result.toString(10) << E->getType();
      return HandleOverflow(Info, E, Value, E->getType());
    }
    return true;
  }
  
  /// Perform the given binary integer operation.
  static bool handleIntIntBinOp(EvalInfo &Info, const Expr *E, const APSInt &LHS,
                                BinaryOperatorKind Opcode, APSInt RHS,
                                APSInt &Result) {
    switch (Opcode) {
    default:
      Info.FFDiag(E);
      return false;
    case BO_Mul:
      return CheckedIntArithmetic(Info, E, LHS, RHS, LHS.getBitWidth() * 2,
                                  std::multiplies<APSInt>(), Result);
    case BO_Add:
      return CheckedIntArithmetic(Info, E, LHS, RHS, LHS.getBitWidth() + 1,
                                  std::plus<APSInt>(), Result);
    case BO_Sub:
      return CheckedIntArithmetic(Info, E, LHS, RHS, LHS.getBitWidth() + 1,
                                  std::minus<APSInt>(), Result);
    case BO_And: Result = LHS & RHS; return true;
    case BO_Xor: Result = LHS ^ RHS; return true;
    case BO_Or:  Result = LHS | RHS; return true;
    case BO_Div:
    case BO_Rem:
      if (RHS == 0) {
        Info.FFDiag(E, diag::note_expr_divide_by_zero);
        return false;
      }
      Result = (Opcode == BO_Rem ? LHS % RHS : LHS / RHS);
      // Check for overflow case: INT_MIN / -1 or INT_MIN % -1. APSInt supports
      // this operation and gives the two's complement result.
      if (RHS.isNegative() && RHS.isAllOnesValue() &&
          LHS.isSigned() && LHS.isMinSignedValue())
        return HandleOverflow(Info, E, -LHS.extend(LHS.getBitWidth() + 1),
                              E->getType());
      return true;
    case BO_Shl: {
      if (Info.getLangOpts().OpenCL)
        // OpenCL 6.3j: shift values are effectively % word size of LHS.
        RHS &= APSInt(llvm::APInt(RHS.getBitWidth(),
                      static_cast<uint64_t>(LHS.getBitWidth() - 1)),
                      RHS.isUnsigned());
      else if (RHS.isSigned() && RHS.isNegative()) {
        // During constant-folding, a negative shift is an opposite shift. Such
        // a shift is not a constant expression.
        Info.CCEDiag(E, diag::note_constexpr_negative_shift) << RHS;
        RHS = -RHS;
        goto shift_right;
      }
    shift_left:
      // C++11 [expr.shift]p1: Shift width must be less than the bit width of
      // the shifted type.
      unsigned SA = (unsigned) RHS.getLimitedValue(LHS.getBitWidth()-1);
      if (SA != RHS) {
        Info.CCEDiag(E, diag::note_constexpr_large_shift)
          << RHS << E->getType() << LHS.getBitWidth();
      } else if (LHS.isSigned() && !Info.getLangOpts().CPlusPlus20) {
        // C++11 [expr.shift]p2: A signed left shift must have a non-negative
        // operand, and must not overflow the corresponding unsigned type.
        // C++2a [expr.shift]p2: E1 << E2 is the unique value congruent to
        // E1 x 2^E2 module 2^N.
        if (LHS.isNegative())
          Info.CCEDiag(E, diag::note_constexpr_lshift_of_negative) << LHS;
        else if (LHS.countLeadingZeros() < SA)
          Info.CCEDiag(E, diag::note_constexpr_lshift_discards);
      }
      Result = LHS << SA;
      return true;
    }
    case BO_Shr: {
      if (Info.getLangOpts().OpenCL)
        // OpenCL 6.3j: shift values are effectively % word size of LHS.
        RHS &= APSInt(llvm::APInt(RHS.getBitWidth(),
                      static_cast<uint64_t>(LHS.getBitWidth() - 1)),
                      RHS.isUnsigned());
      else if (RHS.isSigned() && RHS.isNegative()) {
        // During constant-folding, a negative shift is an opposite shift. Such a
        // shift is not a constant expression.
        Info.CCEDiag(E, diag::note_constexpr_negative_shift) << RHS;
        RHS = -RHS;
        goto shift_left;
      }
    shift_right:
      // C++11 [expr.shift]p1: Shift width must be less than the bit width of the
      // shifted type.
      unsigned SA = (unsigned) RHS.getLimitedValue(LHS.getBitWidth()-1);
      if (SA != RHS)
        Info.CCEDiag(E, diag::note_constexpr_large_shift)
          << RHS << E->getType() << LHS.getBitWidth();
      Result = LHS >> SA;
      return true;
    }
  
    case BO_LT: Result = LHS < RHS; return true;
    case BO_GT: Result = LHS > RHS; return true;
    case BO_LE: Result = LHS <= RHS; return true;
    case BO_GE: Result = LHS >= RHS; return true;
    case BO_EQ: Result = LHS == RHS; return true;
    case BO_NE: Result = LHS != RHS; return true;
    case BO_Cmp:
      llvm_unreachable("BO_Cmp should be handled elsewhere");
    }
  }
  
  /// Perform the given binary floating-point operation, in-place, on LHS.
  static bool handleFloatFloatBinOp(EvalInfo &Info, const BinaryOperator *E,
                                    APFloat &LHS, BinaryOperatorKind Opcode,
                                    const APFloat &RHS) {
    bool DynamicRM;
    llvm::RoundingMode RM = getActiveRoundingMode(Info, E, DynamicRM);
    APFloat::opStatus St;
    switch (Opcode) {
    default:
      Info.FFDiag(E);
      return false;
    case BO_Mul:
      St = LHS.multiply(RHS, RM);
      break;
    case BO_Add:
      St = LHS.add(RHS, RM);
      break;
    case BO_Sub:
      St = LHS.subtract(RHS, RM);
      break;
    case BO_Div:
      // [expr.mul]p4:
      //   If the second operand of / or % is zero the behavior is undefined.
      if (RHS.isZero())
        Info.CCEDiag(E, diag::note_expr_divide_by_zero);
      St = LHS.divide(RHS, RM);
      break;
    }
  
    // [expr.pre]p4:
    //   If during the evaluation of an expression, the result is not
    //   mathematically defined [...], the behavior is undefined.
    // FIXME: C++ rules require us to not conform to IEEE 754 here.
    if (LHS.isNaN()) {
      Info.CCEDiag(E, diag::note_constexpr_float_arithmetic) << LHS.isNaN();
      return Info.noteUndefinedBehavior();
    }
  
    return checkFloatingPointResult(Info, E, St);
  }
  
  static bool handleLogicalOpForVector(const APInt &LHSValue,
                                       BinaryOperatorKind Opcode,
                                       const APInt &RHSValue, APInt &Result) {
    bool LHS = (LHSValue != 0);
    bool RHS = (RHSValue != 0);
  
    if (Opcode == BO_LAnd)
      Result = LHS && RHS;
    else
      Result = LHS || RHS;
    return true;
  }
  static bool handleLogicalOpForVector(const APFloat &LHSValue,
                                       BinaryOperatorKind Opcode,
                                       const APFloat &RHSValue, APInt &Result) {
    bool LHS = !LHSValue.isZero();
    bool RHS = !RHSValue.isZero();
  
    if (Opcode == BO_LAnd)
      Result = LHS && RHS;
    else
      Result = LHS || RHS;
    return true;
  }
  
  static bool handleLogicalOpForVector(const APValue &LHSValue,
                                       BinaryOperatorKind Opcode,
                                       const APValue &RHSValue, APInt &Result) {
    // The result is always an int type, however operands match the first.
    if (LHSValue.getKind() == APValue::Int)
      return handleLogicalOpForVector(LHSValue.getInt(), Opcode,
                                      RHSValue.getInt(), Result);
    assert(LHSValue.getKind() == APValue::Float && "Should be no other options");
    return handleLogicalOpForVector(LHSValue.getFloat(), Opcode,
                                    RHSValue.getFloat(), Result);
  }
  
  template <typename APTy>
  static bool
  handleCompareOpForVectorHelper(const APTy &LHSValue, BinaryOperatorKind Opcode,
                                 const APTy &RHSValue, APInt &Result) {
    switch (Opcode) {
    default:
      llvm_unreachable("unsupported binary operator");
    case BO_EQ:
      Result = (LHSValue == RHSValue);
      break;
    case BO_NE:
      Result = (LHSValue != RHSValue);
      break;
    case BO_LT:
      Result = (LHSValue < RHSValue);
      break;
    case BO_GT:
      Result = (LHSValue > RHSValue);
      break;
    case BO_LE:
      Result = (LHSValue <= RHSValue);
      break;
    case BO_GE:
      Result = (LHSValue >= RHSValue);
      break;
    }
  
    return true;
  }
  
  static bool handleCompareOpForVector(const APValue &LHSValue,
                                       BinaryOperatorKind Opcode,
                                       const APValue &RHSValue, APInt &Result) {
    // The result is always an int type, however operands match the first.
    if (LHSValue.getKind() == APValue::Int)
      return handleCompareOpForVectorHelper(LHSValue.getInt(), Opcode,
                                            RHSValue.getInt(), Result);
    assert(LHSValue.getKind() == APValue::Float && "Should be no other options");
    return handleCompareOpForVectorHelper(LHSValue.getFloat(), Opcode,
                                          RHSValue.getFloat(), Result);
  }
  
  // Perform binary operations for vector types, in place on the LHS.
  static bool handleVectorVectorBinOp(EvalInfo &Info, const BinaryOperator *E,
                                      BinaryOperatorKind Opcode,
                                      APValue &LHSValue,
                                      const APValue &RHSValue) {
    assert(Opcode != BO_PtrMemD && Opcode != BO_PtrMemI &&
           "Operation not supported on vector types");
  
    const auto *VT = E->getType()->castAs<VectorType>();
    unsigned NumElements = VT->getNumElements();
    QualType EltTy = VT->getElementType();
  
    // In the cases (typically C as I've observed) where we aren't evaluating
    // constexpr but are checking for cases where the LHS isn't yet evaluatable,
    // just give up.
    if (!LHSValue.isVector()) {
      assert(LHSValue.isLValue() &&
             "A vector result that isn't a vector OR uncalculated LValue");
      Info.FFDiag(E);
      return false;
    }
  
    assert(LHSValue.getVectorLength() == NumElements &&
           RHSValue.getVectorLength() == NumElements && "Different vector sizes");
  
    SmallVector<APValue, 4> ResultElements;
  
    for (unsigned EltNum = 0; EltNum < NumElements; ++EltNum) {
      APValue LHSElt = LHSValue.getVectorElt(EltNum);
      APValue RHSElt = RHSValue.getVectorElt(EltNum);
  
      if (EltTy->isIntegerType()) {
        APSInt EltResult{Info.Ctx.getIntWidth(EltTy),
                         EltTy->isUnsignedIntegerType()};
        bool Success = true;
  
        if (BinaryOperator::isLogicalOp(Opcode))
          Success = handleLogicalOpForVector(LHSElt, Opcode, RHSElt, EltResult);
        else if (BinaryOperator::isComparisonOp(Opcode))
          Success = handleCompareOpForVector(LHSElt, Opcode, RHSElt, EltResult);
        else
          Success = handleIntIntBinOp(Info, E, LHSElt.getInt(), Opcode,
                                      RHSElt.getInt(), EltResult);
  
        if (!Success) {
          Info.FFDiag(E);
          return false;
        }
        ResultElements.emplace_back(EltResult);
  
      } else if (EltTy->isFloatingType()) {
        assert(LHSElt.getKind() == APValue::Float &&
               RHSElt.getKind() == APValue::Float &&
               "Mismatched LHS/RHS/Result Type");
        APFloat LHSFloat = LHSElt.getFloat();
  
        if (!handleFloatFloatBinOp(Info, E, LHSFloat, Opcode,
                                   RHSElt.getFloat())) {
          Info.FFDiag(E);
          return false;
        }
  
        ResultElements.emplace_back(LHSFloat);
      }
    }
  
    LHSValue = APValue(ResultElements.data(), ResultElements.size());
    return true;
  }
  
  /// Cast an lvalue referring to a base subobject to a derived class, by
  /// truncating the lvalue's path to the given length.
  static bool CastToDerivedClass(EvalInfo &Info, const Expr *E, LValue &Result,
                                 const RecordDecl *TruncatedType,
                                 unsigned TruncatedElements) {
    SubobjectDesignator &D = Result.Designator;
  
    // Check we actually point to a derived class object.
    if (TruncatedElements == D.Entries.size())
      return true;
    assert(TruncatedElements >= D.MostDerivedPathLength &&
           "not casting to a derived class");
    if (!Result.checkSubobject(Info, E, CSK_Derived))
      return false;
  
    // Truncate the path to the subobject, and remove any derived-to-base offsets.
    const RecordDecl *RD = TruncatedType;
    for (unsigned I = TruncatedElements, N = D.Entries.size(); I != N; ++I) {
      if (RD->isInvalidDecl()) return false;
      const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);
      const CXXRecordDecl *Base = getAsBaseClass(D.Entries[I]);
      if (isVirtualBaseClass(D.Entries[I]))
        Result.Offset -= Layout.getVBaseClassOffset(Base);
      else
        Result.Offset -= Layout.getBaseClassOffset(Base);
      RD = Base;
    }
    D.Entries.resize(TruncatedElements);
    return true;
  }
  
  static bool HandleLValueDirectBase(EvalInfo &Info, const Expr *E, LValue &Obj,
                                     const CXXRecordDecl *Derived,
                                     const CXXRecordDecl *Base,
                                     const ASTRecordLayout *RL = nullptr) {
    if (!RL) {
      if (Derived->isInvalidDecl()) return false;
      RL = &Info.Ctx.getASTRecordLayout(Derived);
    }
  
    Obj.getLValueOffset() += RL->getBaseClassOffset(Base);
    Obj.addDecl(Info, E, Base, /*Virtual*/ false);
    return true;
  }
  
  static bool HandleLValueBase(EvalInfo &Info, const Expr *E, LValue &Obj,
                               const CXXRecordDecl *DerivedDecl,
                               const CXXBaseSpecifier *Base) {
    const CXXRecordDecl *BaseDecl = Base->getType()->getAsCXXRecordDecl();
  
    if (!Base->isVirtual())
      return HandleLValueDirectBase(Info, E, Obj, DerivedDecl, BaseDecl);
  
    SubobjectDesignator &D = Obj.Designator;
    if (D.Invalid)
      return false;
  
    // Extract most-derived object and corresponding type.
    DerivedDecl = D.MostDerivedType->getAsCXXRecordDecl();
    if (!CastToDerivedClass(Info, E, Obj, DerivedDecl, D.MostDerivedPathLength))
      return false;
  
    // Find the virtual base class.
    if (DerivedDecl->isInvalidDecl()) return false;
    const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(DerivedDecl);
    Obj.getLValueOffset() += Layout.getVBaseClassOffset(BaseDecl);
    Obj.addDecl(Info, E, BaseDecl, /*Virtual*/ true);
    return true;
  }
  
  static bool HandleLValueBasePath(EvalInfo &Info, const CastExpr *E,
                                   QualType Type, LValue &Result) {
    for (CastExpr::path_const_iterator PathI = E->path_begin(),
                                       PathE = E->path_end();
         PathI != PathE; ++PathI) {
      if (!HandleLValueBase(Info, E, Result, Type->getAsCXXRecordDecl(),
                            *PathI))
        return false;
      Type = (*PathI)->getType();
    }
    return true;
  }
  
  /// Cast an lvalue referring to a derived class to a known base subobject.
  static bool CastToBaseClass(EvalInfo &Info, const Expr *E, LValue &Result,
                              const CXXRecordDecl *DerivedRD,
                              const CXXRecordDecl *BaseRD) {
    CXXBasePaths Paths(/*FindAmbiguities=*/false,
                       /*RecordPaths=*/true, /*DetectVirtual=*/false);
    if (!DerivedRD->isDerivedFrom(BaseRD, Paths))
      llvm_unreachable("Class must be derived from the passed in base class!");
  
    for (CXXBasePathElement &Elem : Paths.front())
      if (!HandleLValueBase(Info, E, Result, Elem.Class, Elem.Base))
        return false;
    return true;
  }
  
  /// Update LVal to refer to the given field, which must be a member of the type
  /// currently described by LVal.
  static bool HandleLValueMember(EvalInfo &Info, const Expr *E, LValue &LVal,
                                 const FieldDecl *FD,
                                 const ASTRecordLayout *RL = nullptr) {
    if (!RL) {
      if (FD->getParent()->isInvalidDecl()) return false;
      RL = &Info.Ctx.getASTRecordLayout(FD->getParent());
    }
  
    unsigned I = FD->getFieldIndex();
    LVal.adjustOffset(Info.Ctx.toCharUnitsFromBits(RL->getFieldOffset(I)));
    LVal.addDecl(Info, E, FD);
    return true;
  }
  
  /// Update LVal to refer to the given indirect field.
  static bool HandleLValueIndirectMember(EvalInfo &Info, const Expr *E,
                                         LValue &LVal,
                                         const IndirectFieldDecl *IFD) {
    for (const auto *C : IFD->chain())
      if (!HandleLValueMember(Info, E, LVal, cast<FieldDecl>(C)))
        return false;
    return true;
  }
  
  /// Get the size of the given type in char units.
  static bool HandleSizeof(EvalInfo &Info, SourceLocation Loc,
                           QualType Type, CharUnits &Size) {
    // sizeof(void), __alignof__(void), sizeof(function) = 1 as a gcc
    // extension.
    if (Type->isVoidType() || Type->isFunctionType()) {
      Size = CharUnits::One();
      return true;
    }
  
    if (Type->isDependentType()) {
      Info.FFDiag(Loc);
      return false;
    }
  
    if (!Type->isConstantSizeType()) {
      // sizeof(vla) is not a constantexpr: C99 6.5.3.4p2.
      // FIXME: Better diagnostic.
      Info.FFDiag(Loc);
      return false;
    }
  
    Size = Info.Ctx.getTypeSizeInChars(Type);
    return true;
  }
  
  /// Update a pointer value to model pointer arithmetic.
  /// \param Info - Information about the ongoing evaluation.
  /// \param E - The expression being evaluated, for diagnostic purposes.
  /// \param LVal - The pointer value to be updated.
  /// \param EltTy - The pointee type represented by LVal.
  /// \param Adjustment - The adjustment, in objects of type EltTy, to add.
  static bool HandleLValueArrayAdjustment(EvalInfo &Info, const Expr *E,
                                          LValue &LVal, QualType EltTy,
                                          APSInt Adjustment) {
    CharUnits SizeOfPointee;
    if (!HandleSizeof(Info, E->getExprLoc(), EltTy, SizeOfPointee))
      return false;
  
    LVal.adjustOffsetAndIndex(Info, E, Adjustment, SizeOfPointee);
    return true;
  }
  
  static bool HandleLValueArrayAdjustment(EvalInfo &Info, const Expr *E,
                                          LValue &LVal, QualType EltTy,
                                          int64_t Adjustment) {
    return HandleLValueArrayAdjustment(Info, E, LVal, EltTy,
                                       APSInt::get(Adjustment));
  }
  
  /// Update an lvalue to refer to a component of a complex number.
  /// \param Info - Information about the ongoing evaluation.
  /// \param LVal - The lvalue to be updated.
  /// \param EltTy - The complex number's component type.
  /// \param Imag - False for the real component, true for the imaginary.
  static bool HandleLValueComplexElement(EvalInfo &Info, const Expr *E,
                                         LValue &LVal, QualType EltTy,
                                         bool Imag) {
    if (Imag) {
      CharUnits SizeOfComponent;
      if (!HandleSizeof(Info, E->getExprLoc(), EltTy, SizeOfComponent))
        return false;
      LVal.Offset += SizeOfComponent;
    }
    LVal.addComplex(Info, E, EltTy, Imag);
    return true;
  }
  
  /// Try to evaluate the initializer for a variable declaration.
  ///
  /// \param Info   Information about the ongoing evaluation.
  /// \param E      An expression to be used when printing diagnostics.
  /// \param VD     The variable whose initializer should be obtained.
  /// \param Version The version of the variable within the frame.
  /// \param Frame  The frame in which the variable was created. Must be null
  ///               if this variable is not local to the evaluation.
  /// \param Result Filled in with a pointer to the value of the variable.
  static bool evaluateVarDeclInit(EvalInfo &Info, const Expr *E,
                                  const VarDecl *VD, CallStackFrame *Frame,
                                  unsigned Version, APValue *&Result) {
    APValue::LValueBase Base(VD, Frame ? Frame->Index : 0, Version);
  
    // If this is a local variable, dig out its value.
    if (Frame) {
      Result = Frame->getTemporary(VD, Version);
      if (Result)
        return true;
  
      if (!isa<ParmVarDecl>(VD)) {
        // Assume variables referenced within a lambda's call operator that were
        // not declared within the call operator are captures and during checking
        // of a potential constant expression, assume they are unknown constant
        // expressions.
        assert(isLambdaCallOperator(Frame->Callee) &&
               (VD->getDeclContext() != Frame->Callee || VD->isInitCapture()) &&
               "missing value for local variable");
        if (Info.checkingPotentialConstantExpression())
          return false;
        // FIXME: This diagnostic is bogus; we do support captures. Is this code
        // still reachable at all?
        Info.FFDiag(E->getBeginLoc(),
                    diag::note_unimplemented_constexpr_lambda_feature_ast)
            << "captures not currently allowed";
        return false;
      }
    }
  
    // If we're currently evaluating the initializer of this declaration, use that
    // in-flight value.
    if (Info.EvaluatingDecl == Base) {
      Result = Info.EvaluatingDeclValue;
      return true;
    }
  
    if (isa<ParmVarDecl>(VD)) {
      // Assume parameters of a potential constant expression are usable in
      // constant expressions.
      if (!Info.checkingPotentialConstantExpression() ||
          !Info.CurrentCall->Callee ||
          !Info.CurrentCall->Callee->Equals(VD->getDeclContext())) {
        if (Info.getLangOpts().CPlusPlus11) {
          Info.FFDiag(E, diag::note_constexpr_function_param_value_unknown)
              << VD;
          NoteLValueLocation(Info, Base);
        } else {
          Info.FFDiag(E);
        }
      }
      return false;
    }
  
    // Dig out the initializer, and use the declaration which it's attached to.
    // FIXME: We should eventually check whether the variable has a reachable
    // initializing declaration.
    const Expr *Init = VD->getAnyInitializer(VD);
    if (!Init) {
      // Don't diagnose during potential constant expression checking; an
      // initializer might be added later.
      if (!Info.checkingPotentialConstantExpression()) {
        Info.FFDiag(E, diag::note_constexpr_var_init_unknown, 1)
          << VD;
        NoteLValueLocation(Info, Base);
      }
      return false;
    }
  
    if (Init->isValueDependent()) {
      // The DeclRefExpr is not value-dependent, but the variable it refers to
      // has a value-dependent initializer. This should only happen in
      // constant-folding cases, where the variable is not actually of a suitable
      // type for use in a constant expression (otherwise the DeclRefExpr would
      // have been value-dependent too), so diagnose that.
      assert(!VD->mightBeUsableInConstantExpressions(Info.Ctx));
      if (!Info.checkingPotentialConstantExpression()) {
        Info.FFDiag(E, Info.getLangOpts().CPlusPlus11
                           ? diag::note_constexpr_ltor_non_constexpr
                           : diag::note_constexpr_ltor_non_integral, 1)
            << VD << VD->getType();
        NoteLValueLocation(Info, Base);
      }
      return false;
    }
  
    // Check that we can fold the initializer. In C++, we will have already done
    // this in the cases where it matters for conformance.
    if (!VD->evaluateValue()) {
      Info.FFDiag(E, diag::note_constexpr_var_init_non_constant, 1) << VD;
      NoteLValueLocation(Info, Base);
      return false;
    }
  
    // Check that the variable is actually usable in constant expressions. For a
    // const integral variable or a reference, we might have a non-constant
    // initializer that we can nonetheless evaluate the initializer for. Such
    // variables are not usable in constant expressions. In C++98, the
    // initializer also syntactically needs to be an ICE.
    //
    // FIXME: We don't diagnose cases that aren't potentially usable in constant
    // expressions here; doing so would regress diagnostics for things like
    // reading from a volatile constexpr variable.
    if ((Info.getLangOpts().CPlusPlus && !VD->hasConstantInitialization() &&
         VD->mightBeUsableInConstantExpressions(Info.Ctx)) ||
        ((Info.getLangOpts().CPlusPlus || Info.getLangOpts().OpenCL) &&
         !Info.getLangOpts().CPlusPlus11 && !VD->hasICEInitializer(Info.Ctx))) {
      Info.CCEDiag(E, diag::note_constexpr_var_init_non_constant, 1) << VD;
      NoteLValueLocation(Info, Base);
    }
  
    // Never use the initializer of a weak variable, not even for constant
    // folding. We can't be sure that this is the definition that will be used.
    if (VD->isWeak()) {
      Info.FFDiag(E, diag::note_constexpr_var_init_weak) << VD;
      NoteLValueLocation(Info, Base);
      return false;
    }
  
    Result = VD->getEvaluatedValue();
    return true;
  }
  
  /// Get the base index of the given base class within an APValue representing
  /// the given derived class.
  static unsigned getBaseIndex(const CXXRecordDecl *Derived,
                               const CXXRecordDecl *Base) {
    Base = Base->getCanonicalDecl();
    unsigned Index = 0;
    for (CXXRecordDecl::base_class_const_iterator I = Derived->bases_begin(),
           E = Derived->bases_end(); I != E; ++I, ++Index) {
      if (I->getType()->getAsCXXRecordDecl()->getCanonicalDecl() == Base)
        return Index;
    }
  
    llvm_unreachable("base class missing from derived class's bases list");
  }
  
  /// Extract the value of a character from a string literal.
  static APSInt extractStringLiteralCharacter(EvalInfo &Info, const Expr *Lit,
                                              uint64_t Index) {
    assert(!isa<SourceLocExpr>(Lit) &&
           "SourceLocExpr should have already been converted to a StringLiteral");
  
    // FIXME: Support MakeStringConstant
    if (const auto *ObjCEnc = dyn_cast<ObjCEncodeExpr>(Lit)) {
      std::string Str;
      Info.Ctx.getObjCEncodingForType(ObjCEnc->getEncodedType(), Str);
      assert(Index <= Str.size() && "Index too large");
      return APSInt::getUnsigned(Str.c_str()[Index]);
    }
  
    if (auto PE = dyn_cast<PredefinedExpr>(Lit))
      Lit = PE->getFunctionName();
    const StringLiteral *S = cast<StringLiteral>(Lit);
    const ConstantArrayType *CAT =
        Info.Ctx.getAsConstantArrayType(S->getType());
    assert(CAT && "string literal isn't an array");
    QualType CharType = CAT->getElementType();
    assert(CharType->isIntegerType() && "unexpected character type");
  
    APSInt Value(S->getCharByteWidth() * Info.Ctx.getCharWidth(),
                 CharType->isUnsignedIntegerType());
    if (Index < S->getLength())
      Value = S->getCodeUnit(Index);
    return Value;
  }
  
  // Expand a string literal into an array of characters.
  //
  // FIXME: This is inefficient; we should probably introduce something similar
  // to the LLVM ConstantDataArray to make this cheaper.
  static void expandStringLiteral(EvalInfo &Info, const StringLiteral *S,
                                  APValue &Result,
                                  QualType AllocType = QualType()) {
    const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(
        AllocType.isNull() ? S->getType() : AllocType);
    assert(CAT && "string literal isn't an array");
    QualType CharType = CAT->getElementType();
    assert(CharType->isIntegerType() && "unexpected character type");
  
    unsigned Elts = CAT->getSize().getZExtValue();
    Result = APValue(APValue::UninitArray(),
                     std::min(S->getLength(), Elts), Elts);
    APSInt Value(S->getCharByteWidth() * Info.Ctx.getCharWidth(),
                 CharType->isUnsignedIntegerType());
    if (Result.hasArrayFiller())
      Result.getArrayFiller() = APValue(Value);
    for (unsigned I = 0, N = Result.getArrayInitializedElts(); I != N; ++I) {
      Value = S->getCodeUnit(I);
      Result.getArrayInitializedElt(I) = APValue(Value);
    }
  }
  
  // Expand an array so that it has more than Index filled elements.
  static void expandArray(APValue &Array, unsigned Index) {
    unsigned Size = Array.getArraySize();
    assert(Index < Size);
  
    // Always at least double the number of elements for which we store a value.
    unsigned OldElts = Array.getArrayInitializedElts();
    unsigned NewElts = std::max(Index+1, OldElts * 2);
    NewElts = std::min(Size, std::max(NewElts, 8u));
  
    // Copy the data across.
    APValue NewValue(APValue::UninitArray(), NewElts, Size);
    for (unsigned I = 0; I != OldElts; ++I)
      NewValue.getArrayInitializedElt(I).swap(Array.getArrayInitializedElt(I));
    for (unsigned I = OldElts; I != NewElts; ++I)
      NewValue.getArrayInitializedElt(I) = Array.getArrayFiller();
    if (NewValue.hasArrayFiller())
      NewValue.getArrayFiller() = Array.getArrayFiller();
    Array.swap(NewValue);
  }
  
  /// Determine whether a type would actually be read by an lvalue-to-rvalue
  /// conversion. If it's of class type, we may assume that the copy operation
  /// is trivial. Note that this is never true for a union type with fields
  /// (because the copy always "reads" the active member) and always true for
  /// a non-class type.
  static bool isReadByLvalueToRvalueConversion(const CXXRecordDecl *RD);
  static bool isReadByLvalueToRvalueConversion(QualType T) {
    CXXRecordDecl *RD = T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
    return !RD || isReadByLvalueToRvalueConversion(RD);
  }
  static bool isReadByLvalueToRvalueConversion(const CXXRecordDecl *RD) {
    // FIXME: A trivial copy of a union copies the object representation, even if
    // the union is empty.
    if (RD->isUnion())
      return !RD->field_empty();
    if (RD->isEmpty())
      return false;
  
    for (auto *Field : RD->fields())
      if (!Field->isUnnamedBitfield() &&
          isReadByLvalueToRvalueConversion(Field->getType()))
        return true;
  
    for (auto &BaseSpec : RD->bases())
      if (isReadByLvalueToRvalueConversion(BaseSpec.getType()))
        return true;
  
    return false;
  }
  
  /// Diagnose an attempt to read from any unreadable field within the specified
  /// type, which might be a class type.
  static bool diagnoseMutableFields(EvalInfo &Info, const Expr *E, AccessKinds AK,
                                    QualType T) {
    CXXRecordDecl *RD = T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
    if (!RD)
      return false;
  
    if (!RD->hasMutableFields())
      return false;
  
    for (auto *Field : RD->fields()) {
      // If we're actually going to read this field in some way, then it can't
      // be mutable. If we're in a union, then assigning to a mutable field
      // (even an empty one) can change the active member, so that's not OK.
      // FIXME: Add core issue number for the union case.
      if (Field->isMutable() &&
          (RD->isUnion() || isReadByLvalueToRvalueConversion(Field->getType()))) {
        Info.FFDiag(E, diag::note_constexpr_access_mutable, 1) << AK << Field;
        Info.Note(Field->getLocation(), diag::note_declared_at);
        return true;
      }
  
      if (diagnoseMutableFields(Info, E, AK, Field->getType()))
        return true;
    }
  
    for (auto &BaseSpec : RD->bases())
      if (diagnoseMutableFields(Info, E, AK, BaseSpec.getType()))
        return true;
  
    // All mutable fields were empty, and thus not actually read.
    return false;
  }
  
  static bool lifetimeStartedInEvaluation(EvalInfo &Info,
                                          APValue::LValueBase Base,
                                          bool MutableSubobject = false) {
    // A temporary or transient heap allocation we created.
    if (Base.getCallIndex() || Base.is<DynamicAllocLValue>())
      return true;
  
    switch (Info.IsEvaluatingDecl) {
    case EvalInfo::EvaluatingDeclKind::None:
      return false;
  
    case EvalInfo::EvaluatingDeclKind::Ctor:
      // The variable whose initializer we're evaluating.
      if (Info.EvaluatingDecl == Base)
        return true;
  
      // A temporary lifetime-extended by the variable whose initializer we're
      // evaluating.
      if (auto *BaseE = Base.dyn_cast<const Expr *>())
        if (auto *BaseMTE = dyn_cast<MaterializeTemporaryExpr>(BaseE))
          return Info.EvaluatingDecl == BaseMTE->getExtendingDecl();
      return false;
  
    case EvalInfo::EvaluatingDeclKind::Dtor:
      // C++2a [expr.const]p6:
      //   [during constant destruction] the lifetime of a and its non-mutable
      //   subobjects (but not its mutable subobjects) [are] considered to start
      //   within e.
      if (MutableSubobject || Base != Info.EvaluatingDecl)
        return false;
      // FIXME: We can meaningfully extend this to cover non-const objects, but
      // we will need special handling: we should be able to access only
      // subobjects of such objects that are themselves declared const.
      QualType T = getType(Base);
      return T.isConstQualified() || T->isReferenceType();
    }
  
    llvm_unreachable("unknown evaluating decl kind");
  }
  
  namespace {
  /// A handle to a complete object (an object that is not a subobject of
  /// another object).
  struct CompleteObject {
    /// The identity of the object.
    APValue::LValueBase Base;
    /// The value of the complete object.
    APValue *Value;
    /// The type of the complete object.
    QualType Type;
  
    CompleteObject() : Value(nullptr) {}
    CompleteObject(APValue::LValueBase Base, APValue *Value, QualType Type)
        : Base(Base), Value(Value), Type(Type) {}
  
    bool mayAccessMutableMembers(EvalInfo &Info, AccessKinds AK) const {
      // If this isn't a "real" access (eg, if it's just accessing the type
      // info), allow it. We assume the type doesn't change dynamically for
      // subobjects of constexpr objects (even though we'd hit UB here if it
      // did). FIXME: Is this right?
      if (!isAnyAccess(AK))
        return true;
  
      // In C++14 onwards, it is permitted to read a mutable member whose
      // lifetime began within the evaluation.
      // FIXME: Should we also allow this in C++11?
      if (!Info.getLangOpts().CPlusPlus14)
        return false;
      return lifetimeStartedInEvaluation(Info, Base, /*MutableSubobject*/true);
    }
  
    explicit operator bool() const { return !Type.isNull(); }
  };
  } // end anonymous namespace
  
  static QualType getSubobjectType(QualType ObjType, QualType SubobjType,
                                   bool IsMutable = false) {
    // C++ [basic.type.qualifier]p1:
    // - A const object is an object of type const T or a non-mutable subobject
    //   of a const object.
    if (ObjType.isConstQualified() && !IsMutable)
      SubobjType.addConst();
    // - A volatile object is an object of type const T or a subobject of a
    //   volatile object.
    if (ObjType.isVolatileQualified())
      SubobjType.addVolatile();
    return SubobjType;
  }
  
  /// Find the designated sub-object of an rvalue.
  template<typename SubobjectHandler>
  typename SubobjectHandler::result_type
  findSubobject(EvalInfo &Info, const Expr *E, const CompleteObject &Obj,
                const SubobjectDesignator &Sub, SubobjectHandler &handler) {
    if (Sub.Invalid)
      // A diagnostic will have already been produced.
      return handler.failed();
    if (Sub.isOnePastTheEnd() || Sub.isMostDerivedAnUnsizedArray()) {
      if (Info.getLangOpts().CPlusPlus11)
        Info.FFDiag(E, Sub.isOnePastTheEnd()
                           ? diag::note_constexpr_access_past_end
                           : diag::note_constexpr_access_unsized_array)
            << handler.AccessKind;
      else
        Info.FFDiag(E);
      return handler.failed();
    }
  
    APValue *O = Obj.Value;
    QualType ObjType = Obj.Type;
    const FieldDecl *LastField = nullptr;
    const FieldDecl *VolatileField = nullptr;
  
    // Walk the designator's path to find the subobject.
    for (unsigned I = 0, N = Sub.Entries.size(); /**/; ++I) {
      // Reading an indeterminate value is undefined, but assigning over one is OK.
      if ((O->isAbsent() && !(handler.AccessKind == AK_Construct && I == N)) ||
          (O->isIndeterminate() &&
           !isValidIndeterminateAccess(handler.AccessKind))) {
        if (!Info.checkingPotentialConstantExpression())
          Info.FFDiag(E, diag::note_constexpr_access_uninit)
              << handler.AccessKind << O->isIndeterminate();
        return handler.failed();
      }
  
      // C++ [class.ctor]p5, C++ [class.dtor]p5:
      //    const and volatile semantics are not applied on an object under
      //    {con,de}struction.
      if ((ObjType.isConstQualified() || ObjType.isVolatileQualified()) &&
          ObjType->isRecordType() &&
          Info.isEvaluatingCtorDtor(
              Obj.Base, llvm::makeArrayRef(Sub.Entries.begin(),
                                           Sub.Entries.begin() + I)) !=
                            ConstructionPhase::None) {
        ObjType = Info.Ctx.getCanonicalType(ObjType);
        ObjType.removeLocalConst();
        ObjType.removeLocalVolatile();
      }
  
      // If this is our last pass, check that the final object type is OK.
      if (I == N || (I == N - 1 && ObjType->isAnyComplexType())) {
        // Accesses to volatile objects are prohibited.
        if (ObjType.isVolatileQualified() && isFormalAccess(handler.AccessKind)) {
          if (Info.getLangOpts().CPlusPlus) {
            int DiagKind;
            SourceLocation Loc;
            const NamedDecl *Decl = nullptr;
            if (VolatileField) {
              DiagKind = 2;
              Loc = VolatileField->getLocation();
              Decl = VolatileField;
            } else if (auto *VD = Obj.Base.dyn_cast<const ValueDecl*>()) {
              DiagKind = 1;
              Loc = VD->getLocation();
              Decl = VD;
            } else {
              DiagKind = 0;
              if (auto *E = Obj.Base.dyn_cast<const Expr *>())
                Loc = E->getExprLoc();
            }
            Info.FFDiag(E, diag::note_constexpr_access_volatile_obj, 1)
                << handler.AccessKind << DiagKind << Decl;
            Info.Note(Loc, diag::note_constexpr_volatile_here) << DiagKind;
          } else {
            Info.FFDiag(E, diag::note_invalid_subexpr_in_const_expr);
          }
          return handler.failed();
        }
  
        // If we are reading an object of class type, there may still be more
        // things we need to check: if there are any mutable subobjects, we
        // cannot perform this read. (This only happens when performing a trivial
        // copy or assignment.)
        if (ObjType->isRecordType() &&
            !Obj.mayAccessMutableMembers(Info, handler.AccessKind) &&
            diagnoseMutableFields(Info, E, handler.AccessKind, ObjType))
          return handler.failed();
      }
  
      if (I == N) {
        if (!handler.found(*O, ObjType))
          return false;
  
        // If we modified a bit-field, truncate it to the right width.
        if (isModification(handler.AccessKind) &&
            LastField && LastField->isBitField() &&
            !truncateBitfieldValue(Info, E, *O, LastField))
          return false;
  
        return true;
      }
  
      LastField = nullptr;
      if (ObjType->isArrayType()) {
        // Next subobject is an array element.
        const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(ObjType);
        assert(CAT && "vla in literal type?");
        uint64_t Index = Sub.Entries[I].getAsArrayIndex();
        if (CAT->getSize().ule(Index)) {
          // Note, it should not be possible to form a pointer with a valid
          // designator which points more than one past the end of the array.
          if (Info.getLangOpts().CPlusPlus11)
            Info.FFDiag(E, diag::note_constexpr_access_past_end)
              << handler.AccessKind;
          else
            Info.FFDiag(E);
          return handler.failed();
        }
  
        ObjType = CAT->getElementType();
  
        if (O->getArrayInitializedElts() > Index)
          O = &O->getArrayInitializedElt(Index);
        else if (!isRead(handler.AccessKind)) {
          expandArray(*O, Index);
          O = &O->getArrayInitializedElt(Index);
        } else
          O = &O->getArrayFiller();
      } else if (ObjType->isAnyComplexType()) {
        // Next subobject is a complex number.
        uint64_t Index = Sub.Entries[I].getAsArrayIndex();
        if (Index > 1) {
          if (Info.getLangOpts().CPlusPlus11)
            Info.FFDiag(E, diag::note_constexpr_access_past_end)
              << handler.AccessKind;
          else
            Info.FFDiag(E);
          return handler.failed();
        }
  
        ObjType = getSubobjectType(
            ObjType, ObjType->castAs<ComplexType>()->getElementType());
  
        assert(I == N - 1 && "extracting subobject of scalar?");
        if (O->isComplexInt()) {
          return handler.found(Index ? O->getComplexIntImag()
                                     : O->getComplexIntReal(), ObjType);
        } else {
          assert(O->isComplexFloat());
          return handler.found(Index ? O->getComplexFloatImag()
                                     : O->getComplexFloatReal(), ObjType);
        }
      } else if (const FieldDecl *Field = getAsField(Sub.Entries[I])) {
        if (Field->isMutable() &&
            !Obj.mayAccessMutableMembers(Info, handler.AccessKind)) {
          Info.FFDiag(E, diag::note_constexpr_access_mutable, 1)
            << handler.AccessKind << Field;
          Info.Note(Field->getLocation(), diag::note_declared_at);
          return handler.failed();
        }
  
        // Next subobject is a class, struct or union field.
        RecordDecl *RD = ObjType->castAs<RecordType>()->getDecl();
        if (RD->isUnion()) {
          const FieldDecl *UnionField = O->getUnionField();
          if (!UnionField ||
              UnionField->getCanonicalDecl() != Field->getCanonicalDecl()) {
            if (I == N - 1 && handler.AccessKind == AK_Construct) {
              // Placement new onto an inactive union member makes it active.
              O->setUnion(Field, APValue());
            } else {
              // FIXME: If O->getUnionValue() is absent, report that there's no
              // active union member rather than reporting the prior active union
              // member. We'll need to fix nullptr_t to not use APValue() as its
              // representation first.
              Info.FFDiag(E, diag::note_constexpr_access_inactive_union_member)
                  << handler.AccessKind << Field << !UnionField << UnionField;
              return handler.failed();
            }
          }
          O = &O->getUnionValue();
        } else
          O = &O->getStructField(Field->getFieldIndex());
  
        ObjType = getSubobjectType(ObjType, Field->getType(), Field->isMutable());
        LastField = Field;
        if (Field->getType().isVolatileQualified())
          VolatileField = Field;
      } else {
        // Next subobject is a base class.
        const CXXRecordDecl *Derived = ObjType->getAsCXXRecordDecl();
        const CXXRecordDecl *Base = getAsBaseClass(Sub.Entries[I]);
        O = &O->getStructBase(getBaseIndex(Derived, Base));
  
        ObjType = getSubobjectType(ObjType, Info.Ctx.getRecordType(Base));
      }
    }
  }
  
  namespace {
  struct ExtractSubobjectHandler {
    EvalInfo &Info;
    const Expr *E;
    APValue &Result;
    const AccessKinds AccessKind;
  
    typedef bool result_type;
    bool failed() { return false; }
    bool found(APValue &Subobj, QualType SubobjType) {
      Result = Subobj;
      if (AccessKind == AK_ReadObjectRepresentation)
        return true;
      return CheckFullyInitialized(Info, E->getExprLoc(), SubobjType, Result);
    }
    bool found(APSInt &Value, QualType SubobjType) {
      Result = APValue(Value);
      return true;
    }
    bool found(APFloat &Value, QualType SubobjType) {
      Result = APValue(Value);
      return true;
    }
  };
  } // end anonymous namespace
  
  /// Extract the designated sub-object of an rvalue.
  static bool extractSubobject(EvalInfo &Info, const Expr *E,
                               const CompleteObject &Obj,
                               const SubobjectDesignator &Sub, APValue &Result,
                               AccessKinds AK = AK_Read) {
    assert(AK == AK_Read || AK == AK_ReadObjectRepresentation);
    ExtractSubobjectHandler Handler = {Info, E, Result, AK};
    return findSubobject(Info, E, Obj, Sub, Handler);
  }
  
  namespace {
  struct ModifySubobjectHandler {
    EvalInfo &Info;
    APValue &NewVal;
    const Expr *E;
  
    typedef bool result_type;
    static const AccessKinds AccessKind = AK_Assign;
  
    bool checkConst(QualType QT) {
      // Assigning to a const object has undefined behavior.
      if (QT.isConstQualified()) {
        Info.FFDiag(E, diag::note_constexpr_modify_const_type) << QT;
        return false;
      }
      return true;
    }
  
    bool failed() { return false; }
    bool found(APValue &Subobj, QualType SubobjType) {
      if (!checkConst(SubobjType))
        return false;
      // We've been given ownership of NewVal, so just swap it in.
      Subobj.swap(NewVal);
      return true;
    }
    bool found(APSInt &Value, QualType SubobjType) {
      if (!checkConst(SubobjType))
        return false;
      if (!NewVal.isInt()) {
        // Maybe trying to write a cast pointer value into a complex?
        Info.FFDiag(E);
        return false;
      }
      Value = NewVal.getInt();
      return true;
    }
    bool found(APFloat &Value, QualType SubobjType) {
      if (!checkConst(SubobjType))
        return false;
      Value = NewVal.getFloat();
      return true;
    }
  };
  } // end anonymous namespace
  
  const AccessKinds ModifySubobjectHandler::AccessKind;
  
  /// Update the designated sub-object of an rvalue to the given value.
  static bool modifySubobject(EvalInfo &Info, const Expr *E,
                              const CompleteObject &Obj,
                              const SubobjectDesignator &Sub,
                              APValue &NewVal) {
    ModifySubobjectHandler Handler = { Info, NewVal, E };
    return findSubobject(Info, E, Obj, Sub, Handler);
  }
  
  /// Find the position where two subobject designators diverge, or equivalently
  /// the length of the common initial subsequence.
  static unsigned FindDesignatorMismatch(QualType ObjType,
                                         const SubobjectDesignator &A,
                                         const SubobjectDesignator &B,
                                         bool &WasArrayIndex) {
    unsigned I = 0, N = std::min(A.Entries.size(), B.Entries.size());
    for (/**/; I != N; ++I) {
      if (!ObjType.isNull() &&
          (ObjType->isArrayType() || ObjType->isAnyComplexType())) {
        // Next subobject is an array element.
        if (A.Entries[I].getAsArrayIndex() != B.Entries[I].getAsArrayIndex()) {
          WasArrayIndex = true;
          return I;
        }
        if (ObjType->isAnyComplexType())
          ObjType = ObjType->castAs<ComplexType>()->getElementType();
        else
          ObjType = ObjType->castAsArrayTypeUnsafe()->getElementType();
      } else {
        if (A.Entries[I].getAsBaseOrMember() !=
            B.Entries[I].getAsBaseOrMember()) {
          WasArrayIndex = false;
          return I;
        }
        if (const FieldDecl *FD = getAsField(A.Entries[I]))
          // Next subobject is a field.
          ObjType = FD->getType();
        else
          // Next subobject is a base class.
          ObjType = QualType();
      }
    }
    WasArrayIndex = false;
    return I;
  }
  
  /// Determine whether the given subobject designators refer to elements of the
  /// same array object.
  static bool AreElementsOfSameArray(QualType ObjType,
                                     const SubobjectDesignator &A,
                                     const SubobjectDesignator &B) {
    if (A.Entries.size() != B.Entries.size())
      return false;
  
    bool IsArray = A.MostDerivedIsArrayElement;
    if (IsArray && A.MostDerivedPathLength != A.Entries.size())
      // A is a subobject of the array element.
      return false;
  
    // If A (and B) designates an array element, the last entry will be the array
    // index. That doesn't have to match. Otherwise, we're in the 'implicit array
    // of length 1' case, and the entire path must match.
    bool WasArrayIndex;
    unsigned CommonLength = FindDesignatorMismatch(ObjType, A, B, WasArrayIndex);
    return CommonLength >= A.Entries.size() - IsArray;
  }
  
  /// Find the complete object to which an LValue refers.
  static CompleteObject findCompleteObject(EvalInfo &Info, const Expr *E,
                                           AccessKinds AK, const LValue &LVal,
                                           QualType LValType) {
    if (LVal.InvalidBase) {
      Info.FFDiag(E);
      return CompleteObject();
    }
  
    if (!LVal.Base) {
      Info.FFDiag(E, diag::note_constexpr_access_null) << AK;
      return CompleteObject();
    }
  
    CallStackFrame *Frame = nullptr;
    unsigned Depth = 0;
    if (LVal.getLValueCallIndex()) {
      std::tie(Frame, Depth) =
          Info.getCallFrameAndDepth(LVal.getLValueCallIndex());
      if (!Frame) {
        Info.FFDiag(E, diag::note_constexpr_lifetime_ended, 1)
          << AK << LVal.Base.is<const ValueDecl*>();
        NoteLValueLocation(Info, LVal.Base);
        return CompleteObject();
      }
    }
  
    bool IsAccess = isAnyAccess(AK);
  
    // C++11 DR1311: An lvalue-to-rvalue conversion on a volatile-qualified type
    // is not a constant expression (even if the object is non-volatile). We also
    // apply this rule to C++98, in order to conform to the expected 'volatile'
    // semantics.
    if (isFormalAccess(AK) && LValType.isVolatileQualified()) {
      if (Info.getLangOpts().CPlusPlus)
        Info.FFDiag(E, diag::note_constexpr_access_volatile_type)
          << AK << LValType;
      else
        Info.FFDiag(E);
      return CompleteObject();
    }
  
    // Compute value storage location and type of base object.
    APValue *BaseVal = nullptr;
    QualType BaseType = getType(LVal.Base);
  
    if (Info.getLangOpts().CPlusPlus14 && LVal.Base == Info.EvaluatingDecl &&
        lifetimeStartedInEvaluation(Info, LVal.Base)) {
      // This is the object whose initializer we're evaluating, so its lifetime
      // started in the current evaluation.
      BaseVal = Info.EvaluatingDeclValue;
    } else if (const ValueDecl *D = LVal.Base.dyn_cast<const ValueDecl *>()) {
      // Allow reading from a GUID declaration.
      if (auto *GD = dyn_cast<MSGuidDecl>(D)) {
        if (isModification(AK)) {
          // All the remaining cases do not permit modification of the object.
          Info.FFDiag(E, diag::note_constexpr_modify_global);
          return CompleteObject();
        }
        APValue &V = GD->getAsAPValue();
        if (V.isAbsent()) {
          Info.FFDiag(E, diag::note_constexpr_unsupported_layout)
              << GD->getType();
          return CompleteObject();
        }
        return CompleteObject(LVal.Base, &V, GD->getType());
      }
  
      // Allow reading from template parameter objects.
      if (auto *TPO = dyn_cast<TemplateParamObjectDecl>(D)) {
        if (isModification(AK)) {
          Info.FFDiag(E, diag::note_constexpr_modify_global);
          return CompleteObject();
        }
        return CompleteObject(LVal.Base, const_cast<APValue *>(&TPO->getValue()),
                              TPO->getType());
      }
  
      // In C++98, const, non-volatile integers initialized with ICEs are ICEs.
      // In C++11, constexpr, non-volatile variables initialized with constant
      // expressions are constant expressions too. Inside constexpr functions,
      // parameters are constant expressions even if they're non-const.
      // In C++1y, objects local to a constant expression (those with a Frame) are
      // both readable and writable inside constant expressions.
      // In C, such things can also be folded, although they are not ICEs.
      const VarDecl *VD = dyn_cast<VarDecl>(D);
      if (VD) {
        if (const VarDecl *VDef = VD->getDefinition(Info.Ctx))
          VD = VDef;
      }
      if (!VD || VD->isInvalidDecl()) {
        Info.FFDiag(E);
        return CompleteObject();
      }
  
      bool IsConstant = BaseType.isConstant(Info.Ctx);
  
      // Unless we're looking at a local variable or argument in a constexpr call,
      // the variable we're reading must be const.
      if (!Frame) {
        if (IsAccess && isa<ParmVarDecl>(VD)) {
          // Access of a parameter that's not associated with a frame isn't going
          // to work out, but we can leave it to evaluateVarDeclInit to provide a
          // suitable diagnostic.
        } else if (Info.getLangOpts().CPlusPlus14 &&
                   lifetimeStartedInEvaluation(Info, LVal.Base)) {
          // OK, we can read and modify an object if we're in the process of
          // evaluating its initializer, because its lifetime began in this
          // evaluation.
        } else if (isModification(AK)) {
          // All the remaining cases do not permit modification of the object.
          Info.FFDiag(E, diag::note_constexpr_modify_global);
          return CompleteObject();
        } else if (VD->isConstexpr()) {
          // OK, we can read this variable.
        } else if (BaseType->isIntegralOrEnumerationType()) {
          if (!IsConstant) {
            if (!IsAccess)
              return CompleteObject(LVal.getLValueBase(), nullptr, BaseType);
            if (Info.getLangOpts().CPlusPlus) {
              Info.FFDiag(E, diag::note_constexpr_ltor_non_const_int, 1) << VD;
              Info.Note(VD->getLocation(), diag::note_declared_at);
            } else {
              Info.FFDiag(E);
            }
            return CompleteObject();
          }
        } else if (!IsAccess) {
          return CompleteObject(LVal.getLValueBase(), nullptr, BaseType);
        } else if (IsConstant && Info.checkingPotentialConstantExpression() &&
                   BaseType->isLiteralType(Info.Ctx) && !VD->hasDefinition()) {
          // This variable might end up being constexpr. Don't diagnose it yet.
        } else if (IsConstant) {
          // Keep evaluating to see what we can do. In particular, we support
          // folding of const floating-point types, in order to make static const
          // data members of such types (supported as an extension) more useful.
          if (Info.getLangOpts().CPlusPlus) {
            Info.CCEDiag(E, Info.getLangOpts().CPlusPlus11
                                ? diag::note_constexpr_ltor_non_constexpr
                                : diag::note_constexpr_ltor_non_integral, 1)
                << VD << BaseType;
            Info.Note(VD->getLocation(), diag::note_declared_at);
          } else {
            Info.CCEDiag(E);
          }
        } else {
          // Never allow reading a non-const value.
          if (Info.getLangOpts().CPlusPlus) {
            Info.FFDiag(E, Info.getLangOpts().CPlusPlus11
                               ? diag::note_constexpr_ltor_non_constexpr
                               : diag::note_constexpr_ltor_non_integral, 1)
                << VD << BaseType;
            Info.Note(VD->getLocation(), diag::note_declared_at);
          } else {
            Info.FFDiag(E);
          }
          return CompleteObject();
        }
      }
  
      if (!evaluateVarDeclInit(Info, E, VD, Frame, LVal.getLValueVersion(), BaseVal))
        return CompleteObject();
    } else if (DynamicAllocLValue DA = LVal.Base.dyn_cast<DynamicAllocLValue>()) {
      Optional<DynAlloc*> Alloc = Info.lookupDynamicAlloc(DA);
      if (!Alloc) {
        Info.FFDiag(E, diag::note_constexpr_access_deleted_object) << AK;
        return CompleteObject();
      }
      return CompleteObject(LVal.Base, &(*Alloc)->Value,
                            LVal.Base.getDynamicAllocType());
    } else {
      const Expr *Base = LVal.Base.dyn_cast<const Expr*>();
  
      if (!Frame) {
        if (const MaterializeTemporaryExpr *MTE =
                dyn_cast_or_null<MaterializeTemporaryExpr>(Base)) {
          assert(MTE->getStorageDuration() == SD_Static &&
                 "should have a frame for a non-global materialized temporary");
  
          // C++20 [expr.const]p4: [DR2126]
          //   An object or reference is usable in constant expressions if it is
          //   - a temporary object of non-volatile const-qualified literal type
          //     whose lifetime is extended to that of a variable that is usable
          //     in constant expressions
          //
          // C++20 [expr.const]p5:
          //  an lvalue-to-rvalue conversion [is not allowed unless it applies to]
          //   - a non-volatile glvalue that refers to an object that is usable
          //     in constant expressions, or
          //   - a non-volatile glvalue of literal type that refers to a
          //     non-volatile object whose lifetime began within the evaluation
          //     of E;
          //
          // C++11 misses the 'began within the evaluation of e' check and
          // instead allows all temporaries, including things like:
          //   int &&r = 1;
          //   int x = ++r;
          //   constexpr int k = r;
          // Therefore we use the C++14-onwards rules in C++11 too.
          //
          // Note that temporaries whose lifetimes began while evaluating a
          // variable's constructor are not usable while evaluating the
          // corresponding destructor, not even if they're of const-qualified
          // types.
          if (!MTE->isUsableInConstantExpressions(Info.Ctx) &&
              !lifetimeStartedInEvaluation(Info, LVal.Base)) {
            if (!IsAccess)
              return CompleteObject(LVal.getLValueBase(), nullptr, BaseType);
            Info.FFDiag(E, diag::note_constexpr_access_static_temporary, 1) << AK;
            Info.Note(MTE->getExprLoc(), diag::note_constexpr_temporary_here);
            return CompleteObject();
          }
  
          BaseVal = MTE->getOrCreateValue(false);
          assert(BaseVal && "got reference to unevaluated temporary");
        } else {
          if (!IsAccess)
            return CompleteObject(LVal.getLValueBase(), nullptr, BaseType);
          APValue Val;
          LVal.moveInto(Val);
          Info.FFDiag(E, diag::note_constexpr_access_unreadable_object)
              << AK
              << Val.getAsString(Info.Ctx,
                                 Info.Ctx.getLValueReferenceType(LValType));
          NoteLValueLocation(Info, LVal.Base);
          return CompleteObject();
        }
      } else {
        BaseVal = Frame->getTemporary(Base, LVal.Base.getVersion());
        assert(BaseVal && "missing value for temporary");
      }
    }
  
    // In C++14, we can't safely access any mutable state when we might be
    // evaluating after an unmodeled side effect. Parameters are modeled as state
    // in the caller, but aren't visible once the call returns, so they can be
    // modified in a speculatively-evaluated call.
    //
    // FIXME: Not all local state is mutable. Allow local constant subobjects
    // to be read here (but take care with 'mutable' fields).
    unsigned VisibleDepth = Depth;
    if (llvm::isa_and_nonnull<ParmVarDecl>(
            LVal.Base.dyn_cast<const ValueDecl *>()))
      ++VisibleDepth;
    if ((Frame && Info.getLangOpts().CPlusPlus14 &&
         Info.EvalStatus.HasSideEffects) ||
        (isModification(AK) && VisibleDepth < Info.SpeculativeEvaluationDepth))
      return CompleteObject();
  
    return CompleteObject(LVal.getLValueBase(), BaseVal, BaseType);
  }
  
  /// Perform an lvalue-to-rvalue conversion on the given glvalue. This
  /// can also be used for 'lvalue-to-lvalue' conversions for looking up the
  /// glvalue referred to by an entity of reference type.
  ///
  /// \param Info - Information about the ongoing evaluation.
  /// \param Conv - The expression for which we are performing the conversion.
  ///               Used for diagnostics.
  /// \param Type - The type of the glvalue (before stripping cv-qualifiers in the
  ///               case of a non-class type).
  /// \param LVal - The glvalue on which we are attempting to perform this action.
  /// \param RVal - The produced value will be placed here.
  /// \param WantObjectRepresentation - If true, we're looking for the object
  ///               representation rather than the value, and in particular,
  ///               there is no requirement that the result be fully initialized.
  static bool
  handleLValueToRValueConversion(EvalInfo &Info, const Expr *Conv, QualType Type,
                                 const LValue &LVal, APValue &RVal,
                                 bool WantObjectRepresentation = false) {
    if (LVal.Designator.Invalid)
      return false;
  
    // Check for special cases where there is no existing APValue to look at.
    const Expr *Base = LVal.Base.dyn_cast<const Expr*>();
  
    AccessKinds AK =
        WantObjectRepresentation ? AK_ReadObjectRepresentation : AK_Read;
  
    if (Base && !LVal.getLValueCallIndex() && !Type.isVolatileQualified()) {
      if (const CompoundLiteralExpr *CLE = dyn_cast<CompoundLiteralExpr>(Base)) {
        // In C99, a CompoundLiteralExpr is an lvalue, and we defer evaluating the
        // initializer until now for such expressions. Such an expression can't be
        // an ICE in C, so this only matters for fold.
        if (Type.isVolatileQualified()) {
          Info.FFDiag(Conv);
          return false;
        }
        APValue Lit;
        if (!Evaluate(Lit, Info, CLE->getInitializer()))
          return false;
        CompleteObject LitObj(LVal.Base, &Lit, Base->getType());
        return extractSubobject(Info, Conv, LitObj, LVal.Designator, RVal, AK);
      } else if (isa<StringLiteral>(Base) || isa<PredefinedExpr>(Base)) {
        // Special-case character extraction so we don't have to construct an
        // APValue for the whole string.
        assert(LVal.Designator.Entries.size() <= 1 &&
               "Can only read characters from string literals");
        if (LVal.Designator.Entries.empty()) {
          // Fail for now for LValue to RValue conversion of an array.
          // (This shouldn't show up in C/C++, but it could be triggered by a
          // weird EvaluateAsRValue call from a tool.)
          Info.FFDiag(Conv);
          return false;
        }
        if (LVal.Designator.isOnePastTheEnd()) {
          if (Info.getLangOpts().CPlusPlus11)
            Info.FFDiag(Conv, diag::note_constexpr_access_past_end) << AK;
          else
            Info.FFDiag(Conv);
          return false;
        }
        uint64_t CharIndex = LVal.Designator.Entries[0].getAsArrayIndex();
        RVal = APValue(extractStringLiteralCharacter(Info, Base, CharIndex));
        return true;
      }
    }
  
    CompleteObject Obj = findCompleteObject(Info, Conv, AK, LVal, Type);
    return Obj && extractSubobject(Info, Conv, Obj, LVal.Designator, RVal, AK);
  }
  
  /// Perform an assignment of Val to LVal. Takes ownership of Val.
  static bool handleAssignment(EvalInfo &Info, const Expr *E, const LValue &LVal,
                               QualType LValType, APValue &Val) {
    if (LVal.Designator.Invalid)
      return false;
  
    if (!Info.getLangOpts().CPlusPlus14) {
      Info.FFDiag(E);
      return false;
    }
  
    CompleteObject Obj = findCompleteObject(Info, E, AK_Assign, LVal, LValType);
    return Obj && modifySubobject(Info, E, Obj, LVal.Designator, Val);
  }
  
  namespace {
  struct CompoundAssignSubobjectHandler {
    EvalInfo &Info;
    const CompoundAssignOperator *E;
    QualType PromotedLHSType;
    BinaryOperatorKind Opcode;
    const APValue &RHS;
  
    static const AccessKinds AccessKind = AK_Assign;
  
    typedef bool result_type;
  
    bool checkConst(QualType QT) {
      // Assigning to a const object has undefined behavior.
      if (QT.isConstQualified()) {
        Info.FFDiag(E, diag::note_constexpr_modify_const_type) << QT;
        return false;
      }
      return true;
    }
  
    bool failed() { return false; }
    bool found(APValue &Subobj, QualType SubobjType) {
      switch (Subobj.getKind()) {
      case APValue::Int:
        return found(Subobj.getInt(), SubobjType);
      case APValue::Float:
        return found(Subobj.getFloat(), SubobjType);
      case APValue::ComplexInt:
      case APValue::ComplexFloat:
        // FIXME: Implement complex compound assignment.
        Info.FFDiag(E);
        return false;
      case APValue::LValue:
        return foundPointer(Subobj, SubobjType);
      case APValue::Vector:
        return foundVector(Subobj, SubobjType);
      default:
        // FIXME: can this happen?
        Info.FFDiag(E);
        return false;
      }
    }
  
    bool foundVector(APValue &Value, QualType SubobjType) {
      if (!checkConst(SubobjType))
        return false;
  
      if (!SubobjType->isVectorType()) {
        Info.FFDiag(E);
        return false;
      }
      return handleVectorVectorBinOp(Info, E, Opcode, Value, RHS);
    }
  
    bool found(APSInt &Value, QualType SubobjType) {
      if (!checkConst(SubobjType))
        return false;
  
      if (!SubobjType->isIntegerType()) {
        // We don't support compound assignment on integer-cast-to-pointer
        // values.
        Info.FFDiag(E);
        return false;
      }
  
      if (RHS.isInt()) {
        APSInt LHS =
            HandleIntToIntCast(Info, E, PromotedLHSType, SubobjType, Value);
        if (!handleIntIntBinOp(Info, E, LHS, Opcode, RHS.getInt(), LHS))
          return false;
        Value = HandleIntToIntCast(Info, E, SubobjType, PromotedLHSType, LHS);
        return true;
      } else if (RHS.isFloat()) {
        const FPOptions FPO = E->getFPFeaturesInEffect(
                                      Info.Ctx.getLangOpts());
        APFloat FValue(0.0);
        return HandleIntToFloatCast(Info, E, FPO, SubobjType, Value,
                                    PromotedLHSType, FValue) &&
               handleFloatFloatBinOp(Info, E, FValue, Opcode, RHS.getFloat()) &&
               HandleFloatToIntCast(Info, E, PromotedLHSType, FValue, SubobjType,
                                    Value);
      }
  
      Info.FFDiag(E);
      return false;
    }
    bool found(APFloat &Value, QualType SubobjType) {
      return checkConst(SubobjType) &&
             HandleFloatToFloatCast(Info, E, SubobjType, PromotedLHSType,
                                    Value) &&
             handleFloatFloatBinOp(Info, E, Value, Opcode, RHS.getFloat()) &&
             HandleFloatToFloatCast(Info, E, PromotedLHSType, SubobjType, Value);
    }
    bool foundPointer(APValue &Subobj, QualType SubobjType) {
      if (!checkConst(SubobjType))
        return false;
  
      QualType PointeeType;
      if (const PointerType *PT = SubobjType->getAs<PointerType>())
        PointeeType = PT->getPointeeType();
  
      if (PointeeType.isNull() || !RHS.isInt() ||
          (Opcode != BO_Add && Opcode != BO_Sub)) {
        Info.FFDiag(E);
        return false;
      }
  
      APSInt Offset = RHS.getInt();
      if (Opcode == BO_Sub)
        negateAsSigned(Offset);
  
      LValue LVal;
      LVal.setFrom(Info.Ctx, Subobj);
      if (!HandleLValueArrayAdjustment(Info, E, LVal, PointeeType, Offset))
        return false;
      LVal.moveInto(Subobj);
      return true;
    }
  };
  } // end anonymous namespace
  
  const AccessKinds CompoundAssignSubobjectHandler::AccessKind;
  
  /// Perform a compound assignment of LVal <op>= RVal.
  static bool handleCompoundAssignment(EvalInfo &Info,
                                       const CompoundAssignOperator *E,
                                       const LValue &LVal, QualType LValType,
                                       QualType PromotedLValType,
                                       BinaryOperatorKind Opcode,
                                       const APValue &RVal) {
    if (LVal.Designator.Invalid)
      return false;
  
    if (!Info.getLangOpts().CPlusPlus14) {
      Info.FFDiag(E);
      return false;
    }
  
    CompleteObject Obj = findCompleteObject(Info, E, AK_Assign, LVal, LValType);
    CompoundAssignSubobjectHandler Handler = { Info, E, PromotedLValType, Opcode,
                                               RVal };
    return Obj && findSubobject(Info, E, Obj, LVal.Designator, Handler);
  }
  
  namespace {
  struct IncDecSubobjectHandler {
    EvalInfo &Info;
    const UnaryOperator *E;
    AccessKinds AccessKind;
    APValue *Old;
  
    typedef bool result_type;
  
    bool checkConst(QualType QT) {
      // Assigning to a const object has undefined behavior.
      if (QT.isConstQualified()) {
        Info.FFDiag(E, diag::note_constexpr_modify_const_type) << QT;
        return false;
      }
      return true;
    }
  
    bool failed() { return false; }
    bool found(APValue &Subobj, QualType SubobjType) {
      // Stash the old value. Also clear Old, so we don't clobber it later
      // if we're post-incrementing a complex.
      if (Old) {
        *Old = Subobj;
        Old = nullptr;
      }
  
      switch (Subobj.getKind()) {
      case APValue::Int:
        return found(Subobj.getInt(), SubobjType);
      case APValue::Float:
        return found(Subobj.getFloat(), SubobjType);
      case APValue::ComplexInt:
        return found(Subobj.getComplexIntReal(),
                     SubobjType->castAs<ComplexType>()->getElementType()
                       .withCVRQualifiers(SubobjType.getCVRQualifiers()));
      case APValue::ComplexFloat:
        return found(Subobj.getComplexFloatReal(),
                     SubobjType->castAs<ComplexType>()->getElementType()
                       .withCVRQualifiers(SubobjType.getCVRQualifiers()));
      case APValue::LValue:
        return foundPointer(Subobj, SubobjType);
      default:
        // FIXME: can this happen?
        Info.FFDiag(E);
        return false;
      }
    }
    bool found(APSInt &Value, QualType SubobjType) {
      if (!checkConst(SubobjType))
        return false;
  
      if (!SubobjType->isIntegerType()) {
        // We don't support increment / decrement on integer-cast-to-pointer
        // values.
        Info.FFDiag(E);
        return false;
      }
  
      if (Old) *Old = APValue(Value);
  
      // bool arithmetic promotes to int, and the conversion back to bool
      // doesn't reduce mod 2^n, so special-case it.
      if (SubobjType->isBooleanType()) {
        if (AccessKind == AK_Increment)
          Value = 1;
        else
          Value = !Value;
        return true;
      }
  
      bool WasNegative = Value.isNegative();
      if (AccessKind == AK_Increment) {
        ++Value;
  
        if (!WasNegative && Value.isNegative() && E->canOverflow()) {
          APSInt ActualValue(Value, /*IsUnsigned*/true);
          return HandleOverflow(Info, E, ActualValue, SubobjType);
        }
      } else {
        --Value;
  
        if (WasNegative && !Value.isNegative() && E->canOverflow()) {
          unsigned BitWidth = Value.getBitWidth();
          APSInt ActualValue(Value.sext(BitWidth + 1), /*IsUnsigned*/false);
          ActualValue.setBit(BitWidth);
          return HandleOverflow(Info, E, ActualValue, SubobjType);
        }
      }
      return true;
    }
    bool found(APFloat &Value, QualType SubobjType) {
      if (!checkConst(SubobjType))
        return false;
  
      if (Old) *Old = APValue(Value);
  
      APFloat One(Value.getSemantics(), 1);
      if (AccessKind == AK_Increment)
        Value.add(One, APFloat::rmNearestTiesToEven);
      else
        Value.subtract(One, APFloat::rmNearestTiesToEven);
      return true;
    }
    bool foundPointer(APValue &Subobj, QualType SubobjType) {
      if (!checkConst(SubobjType))
        return false;
  
      QualType PointeeType;
      if (const PointerType *PT = SubobjType->getAs<PointerType>())
        PointeeType = PT->getPointeeType();
      else {
        Info.FFDiag(E);
        return false;
      }
  
      LValue LVal;
      LVal.setFrom(Info.Ctx, Subobj);
      if (!HandleLValueArrayAdjustment(Info, E, LVal, PointeeType,
                                       AccessKind == AK_Increment ? 1 : -1))
        return false;
      LVal.moveInto(Subobj);
      return true;
    }
  };
  } // end anonymous namespace
  
  /// Perform an increment or decrement on LVal.
  static bool handleIncDec(EvalInfo &Info, const Expr *E, const LValue &LVal,
                           QualType LValType, bool IsIncrement, APValue *Old) {
    if (LVal.Designator.Invalid)
      return false;
  
    if (!Info.getLangOpts().CPlusPlus14) {
      Info.FFDiag(E);
      return false;
    }
  
    AccessKinds AK = IsIncrement ? AK_Increment : AK_Decrement;
    CompleteObject Obj = findCompleteObject(Info, E, AK, LVal, LValType);
    IncDecSubobjectHandler Handler = {Info, cast<UnaryOperator>(E), AK, Old};
    return Obj && findSubobject(Info, E, Obj, LVal.Designator, Handler);
  }
  
  /// Build an lvalue for the object argument of a member function call.
  static bool EvaluateObjectArgument(EvalInfo &Info, const Expr *Object,
                                     LValue &This) {
    if (Object->getType()->isPointerType() && Object->isRValue())
      return EvaluatePointer(Object, This, Info);
  
    if (Object->isGLValue())
      return EvaluateLValue(Object, This, Info);
  
    if (Object->getType()->isLiteralType(Info.Ctx))
      return EvaluateTemporary(Object, This, Info);
  
    Info.FFDiag(Object, diag::note_constexpr_nonliteral) << Object->getType();
    return false;
  }
  
  /// HandleMemberPointerAccess - Evaluate a member access operation and build an
  /// lvalue referring to the result.
  ///
  /// \param Info - Information about the ongoing evaluation.
  /// \param LV - An lvalue referring to the base of the member pointer.
  /// \param RHS - The member pointer expression.
  /// \param IncludeMember - Specifies whether the member itself is included in
  ///        the resulting LValue subobject designator. This is not possible when
  ///        creating a bound member function.
  /// \return The field or method declaration to which the member pointer refers,
  ///         or 0 if evaluation fails.
  static const ValueDecl *HandleMemberPointerAccess(EvalInfo &Info,
                                                    QualType LVType,
                                                    LValue &LV,
                                                    const Expr *RHS,
                                                    bool IncludeMember = true) {
    MemberPtr MemPtr;
    if (!EvaluateMemberPointer(RHS, MemPtr, Info))
      return nullptr;
  
    // C++11 [expr.mptr.oper]p6: If the second operand is the null pointer to
    // member value, the behavior is undefined.
    if (!MemPtr.getDecl()) {
      // FIXME: Specific diagnostic.
      Info.FFDiag(RHS);
      return nullptr;
    }
  
    if (MemPtr.isDerivedMember()) {
      // This is a member of some derived class. Truncate LV appropriately.
      // The end of the derived-to-base path for the base object must match the
      // derived-to-base path for the member pointer.
      if (LV.Designator.MostDerivedPathLength + MemPtr.Path.size() >
          LV.Designator.Entries.size()) {
        Info.FFDiag(RHS);
        return nullptr;
      }
      unsigned PathLengthToMember =
          LV.Designator.Entries.size() - MemPtr.Path.size();
      for (unsigned I = 0, N = MemPtr.Path.size(); I != N; ++I) {
        const CXXRecordDecl *LVDecl = getAsBaseClass(
            LV.Designator.Entries[PathLengthToMember + I]);
        const CXXRecordDecl *MPDecl = MemPtr.Path[I];
        if (LVDecl->getCanonicalDecl() != MPDecl->getCanonicalDecl()) {
          Info.FFDiag(RHS);
          return nullptr;
        }
      }
  
      // Truncate the lvalue to the appropriate derived class.
      if (!CastToDerivedClass(Info, RHS, LV, MemPtr.getContainingRecord(),
                              PathLengthToMember))
        return nullptr;
    } else if (!MemPtr.Path.empty()) {
      // Extend the LValue path with the member pointer's path.
      LV.Designator.Entries.reserve(LV.Designator.Entries.size() +
                                    MemPtr.Path.size() + IncludeMember);
  
      // Walk down to the appropriate base class.
      if (const PointerType *PT = LVType->getAs<PointerType>())
        LVType = PT->getPointeeType();
      const CXXRecordDecl *RD = LVType->getAsCXXRecordDecl();
      assert(RD && "member pointer access on non-class-type expression");
      // The first class in the path is that of the lvalue.
      for (unsigned I = 1, N = MemPtr.Path.size(); I != N; ++I) {
        const CXXRecordDecl *Base = MemPtr.Path[N - I - 1];
        if (!HandleLValueDirectBase(Info, RHS, LV, RD, Base))
          return nullptr;
        RD = Base;
      }
      // Finally cast to the class containing the member.
      if (!HandleLValueDirectBase(Info, RHS, LV, RD,
                                  MemPtr.getContainingRecord()))
        return nullptr;
    }
  
    // Add the member. Note that we cannot build bound member functions here.
    if (IncludeMember) {
      if (const FieldDecl *FD = dyn_cast<FieldDecl>(MemPtr.getDecl())) {
        if (!HandleLValueMember(Info, RHS, LV, FD))
          return nullptr;
      } else if (const IndirectFieldDecl *IFD =
                   dyn_cast<IndirectFieldDecl>(MemPtr.getDecl())) {
        if (!HandleLValueIndirectMember(Info, RHS, LV, IFD))
          return nullptr;
      } else {
        llvm_unreachable("can't construct reference to bound member function");
      }
    }
  
    return MemPtr.getDecl();
  }
  
  static const ValueDecl *HandleMemberPointerAccess(EvalInfo &Info,
                                                    const BinaryOperator *BO,
                                                    LValue &LV,
                                                    bool IncludeMember = true) {
    assert(BO->getOpcode() == BO_PtrMemD || BO->getOpcode() == BO_PtrMemI);
  
    if (!EvaluateObjectArgument(Info, BO->getLHS(), LV)) {
      if (Info.noteFailure()) {
        MemberPtr MemPtr;
        EvaluateMemberPointer(BO->getRHS(), MemPtr, Info);
      }
      return nullptr;
    }
  
    return HandleMemberPointerAccess(Info, BO->getLHS()->getType(), LV,
                                     BO->getRHS(), IncludeMember);
  }
  
  /// HandleBaseToDerivedCast - Apply the given base-to-derived cast operation on
  /// the provided lvalue, which currently refers to the base object.
  static bool HandleBaseToDerivedCast(EvalInfo &Info, const CastExpr *E,
                                      LValue &Result) {
    SubobjectDesignator &D = Result.Designator;
    if (D.Invalid || !Result.checkNullPointer(Info, E, CSK_Derived))
      return false;
  
    QualType TargetQT = E->getType();
    if (const PointerType *PT = TargetQT->getAs<PointerType>())
      TargetQT = PT->getPointeeType();
  
    // Check this cast lands within the final derived-to-base subobject path.
    if (D.MostDerivedPathLength + E->path_size() > D.Entries.size()) {
      Info.CCEDiag(E, diag::note_constexpr_invalid_downcast)
        << D.MostDerivedType << TargetQT;
      return false;
    }
  
    // Check the type of the final cast. We don't need to check the path,
    // since a cast can only be formed if the path is unique.
    unsigned NewEntriesSize = D.Entries.size() - E->path_size();
    const CXXRecordDecl *TargetType = TargetQT->getAsCXXRecordDecl();
    const CXXRecordDecl *FinalType;
    if (NewEntriesSize == D.MostDerivedPathLength)
      FinalType = D.MostDerivedType->getAsCXXRecordDecl();
    else
      FinalType = getAsBaseClass(D.Entries[NewEntriesSize - 1]);
    if (FinalType->getCanonicalDecl() != TargetType->getCanonicalDecl()) {
      Info.CCEDiag(E, diag::note_constexpr_invalid_downcast)
        << D.MostDerivedType << TargetQT;
      return false;
    }
  
    // Truncate the lvalue to the appropriate derived class.
    return CastToDerivedClass(Info, E, Result, TargetType, NewEntriesSize);
  }
  
  /// Get the value to use for a default-initialized object of type T.
  /// Return false if it encounters something invalid.
  static bool getDefaultInitValue(QualType T, APValue &Result) {
    bool Success = true;
    if (auto *RD = T->getAsCXXRecordDecl()) {
      if (RD->isInvalidDecl()) {
        Result = APValue();
        return false;
      }
      if (RD->isUnion()) {
        Result = APValue((const FieldDecl *)nullptr);
        return true;
      }
      Result = APValue(APValue::UninitStruct(), RD->getNumBases(),
                       std::distance(RD->field_begin(), RD->field_end()));
  
      unsigned Index = 0;
      for (CXXRecordDecl::base_class_const_iterator I = RD->bases_begin(),
                                                    End = RD->bases_end();
           I != End; ++I, ++Index)
        Success &= getDefaultInitValue(I->getType(), Result.getStructBase(Index));
  
      for (const auto *I : RD->fields()) {
        if (I->isUnnamedBitfield())
          continue;
        Success &= getDefaultInitValue(I->getType(),
                                       Result.getStructField(I->getFieldIndex()));
      }
      return Success;
    }
  
    if (auto *AT =
            dyn_cast_or_null<ConstantArrayType>(T->getAsArrayTypeUnsafe())) {
      Result = APValue(APValue::UninitArray(), 0, AT->getSize().getZExtValue());
      if (Result.hasArrayFiller())
        Success &=
            getDefaultInitValue(AT->getElementType(), Result.getArrayFiller());
  
      return Success;
    }
  
    Result = APValue::IndeterminateValue();
    return true;
  }
  
  namespace {
  enum EvalStmtResult {
    /// Evaluation failed.
    ESR_Failed,
    /// Hit a 'return' statement.
    ESR_Returned,
    /// Evaluation succeeded.
    ESR_Succeeded,
    /// Hit a 'continue' statement.
    ESR_Continue,
    /// Hit a 'break' statement.
    ESR_Break,
    /// Still scanning for 'case' or 'default' statement.
    ESR_CaseNotFound
  };
  }
  
  static bool EvaluateVarDecl(EvalInfo &Info, const VarDecl *VD) {
    // We don't need to evaluate the initializer for a static local.
    if (!VD->hasLocalStorage())
      return true;
  
    LValue Result;
    APValue &Val = Info.CurrentCall->createTemporary(VD, VD->getType(),
                                                     ScopeKind::Block, Result);
  
    const Expr *InitE = VD->getInit();
    if (!InitE) {
      if (VD->getType()->isDependentType())
        return Info.noteSideEffect();
      return getDefaultInitValue(VD->getType(), Val);
    }
    if (InitE->isValueDependent())
      return false;
  
    if (!EvaluateInPlace(Val, Info, Result, InitE)) {
      // Wipe out any partially-computed value, to allow tracking that this
      // evaluation failed.
      Val = APValue();
      return false;
    }
  
    return true;
  }
  
  static bool EvaluateDecl(EvalInfo &Info, const Decl *D) {
    bool OK = true;
  
    if (const VarDecl *VD = dyn_cast<VarDecl>(D))
      OK &= EvaluateVarDecl(Info, VD);
  
    if (const DecompositionDecl *DD = dyn_cast<DecompositionDecl>(D))
      for (auto *BD : DD->bindings())
        if (auto *VD = BD->getHoldingVar())
          OK &= EvaluateDecl(Info, VD);
  
    return OK;
  }
  
  static bool EvaluateDependentExpr(const Expr *E, EvalInfo &Info) {
    assert(E->isValueDependent());
    if (Info.noteSideEffect())
      return true;
    assert(E->containsErrors() && "valid value-dependent expression should never "
                                  "reach invalid code path.");
    return false;
  }
  
  /// Evaluate a condition (either a variable declaration or an expression).
  static bool EvaluateCond(EvalInfo &Info, const VarDecl *CondDecl,
                           const Expr *Cond, bool &Result) {
    if (Cond->isValueDependent())
      return false;
    FullExpressionRAII Scope(Info);
    if (CondDecl && !EvaluateDecl(Info, CondDecl))
      return false;
    if (!EvaluateAsBooleanCondition(Cond, Result, Info))
      return false;
    return Scope.destroy();
  }
  
  namespace {
  /// A location where the result (returned value) of evaluating a
  /// statement should be stored.
  struct StmtResult {
    /// The APValue that should be filled in with the returned value.
    APValue &Value;
    /// The location containing the result, if any (used to support RVO).
    const LValue *Slot;
  };
  
  struct TempVersionRAII {
    CallStackFrame &Frame;
  
    TempVersionRAII(CallStackFrame &Frame) : Frame(Frame) {
      Frame.pushTempVersion();
    }
  
    ~TempVersionRAII() {
      Frame.popTempVersion();
    }
  };
  
  }
  
  static EvalStmtResult EvaluateStmt(StmtResult &Result, EvalInfo &Info,
                                     const Stmt *S,
                                     const SwitchCase *SC = nullptr);
  
  /// Evaluate the body of a loop, and translate the result as appropriate.
  static EvalStmtResult EvaluateLoopBody(StmtResult &Result, EvalInfo &Info,
                                         const Stmt *Body,
                                         const SwitchCase *Case = nullptr) {
    BlockScopeRAII Scope(Info);
  
    EvalStmtResult ESR = EvaluateStmt(Result, Info, Body, Case);
    if (ESR != ESR_Failed && ESR != ESR_CaseNotFound && !Scope.destroy())
      ESR = ESR_Failed;
  
    switch (ESR) {
    case ESR_Break:
      return ESR_Succeeded;
    case ESR_Succeeded:
    case ESR_Continue:
      return ESR_Continue;
    case ESR_Failed:
    case ESR_Returned:
    case ESR_CaseNotFound:
      return ESR;
    }
    llvm_unreachable("Invalid EvalStmtResult!");
  }
  
  /// Evaluate a switch statement.
  static EvalStmtResult EvaluateSwitch(StmtResult &Result, EvalInfo &Info,
                                       const SwitchStmt *SS) {
    BlockScopeRAII Scope(Info);
  
    // Evaluate the switch condition.
    APSInt Value;
    {
      if (const Stmt *Init = SS->getInit()) {
        EvalStmtResult ESR = EvaluateStmt(Result, Info, Init);
        if (ESR != ESR_Succeeded) {
          if (ESR != ESR_Failed && !Scope.destroy())
            ESR = ESR_Failed;
          return ESR;
        }
      }
  
      FullExpressionRAII CondScope(Info);
      if (SS->getConditionVariable() &&
          !EvaluateDecl(Info, SS->getConditionVariable()))
        return ESR_Failed;
      if (!EvaluateInteger(SS->getCond(), Value, Info))
        return ESR_Failed;
      if (!CondScope.destroy())
        return ESR_Failed;
    }
  
    // Find the switch case corresponding to the value of the condition.
    // FIXME: Cache this lookup.
    const SwitchCase *Found = nullptr;
    for (const SwitchCase *SC = SS->getSwitchCaseList(); SC;
         SC = SC->getNextSwitchCase()) {
      if (isa<DefaultStmt>(SC)) {
        Found = SC;
        continue;
      }
  
      const CaseStmt *CS = cast<CaseStmt>(SC);
      APSInt LHS = CS->getLHS()->EvaluateKnownConstInt(Info.Ctx);
      APSInt RHS = CS->getRHS() ? CS->getRHS()->EvaluateKnownConstInt(Info.Ctx)
                                : LHS;
      if (LHS <= Value && Value <= RHS) {
        Found = SC;
        break;
      }
    }
  
    if (!Found)
      return Scope.destroy() ? ESR_Succeeded : ESR_Failed;
  
    // Search the switch body for the switch case and evaluate it from there.
    EvalStmtResult ESR = EvaluateStmt(Result, Info, SS->getBody(), Found);
    if (ESR != ESR_Failed && ESR != ESR_CaseNotFound && !Scope.destroy())
      return ESR_Failed;
  
    switch (ESR) {
    case ESR_Break:
      return ESR_Succeeded;
    case ESR_Succeeded:
    case ESR_Continue:
    case ESR_Failed:
    case ESR_Returned:
      return ESR;
    case ESR_CaseNotFound:
      // This can only happen if the switch case is nested within a statement
      // expression. We have no intention of supporting that.
      Info.FFDiag(Found->getBeginLoc(),
                  diag::note_constexpr_stmt_expr_unsupported);
      return ESR_Failed;
    }
    llvm_unreachable("Invalid EvalStmtResult!");
  }
  
  // Evaluate a statement.
  static EvalStmtResult EvaluateStmt(StmtResult &Result, EvalInfo &Info,
                                     const Stmt *S, const SwitchCase *Case) {
    if (!Info.nextStep(S))
      return ESR_Failed;
  
    // If we're hunting down a 'case' or 'default' label, recurse through
    // substatements until we hit the label.
    if (Case) {
      switch (S->getStmtClass()) {
      case Stmt::CompoundStmtClass:
        // FIXME: Precompute which substatement of a compound statement we
        // would jump to, and go straight there rather than performing a
        // linear scan each time.
      case Stmt::LabelStmtClass:
      case Stmt::AttributedStmtClass:
      case Stmt::DoStmtClass:
        break;
  
      case Stmt::CaseStmtClass:
      case Stmt::DefaultStmtClass:
        if (Case == S)
          Case = nullptr;
        break;
  
      case Stmt::IfStmtClass: {
        // FIXME: Precompute which side of an 'if' we would jump to, and go
        // straight there rather than scanning both sides.
        const IfStmt *IS = cast<IfStmt>(S);
  
        // Wrap the evaluation in a block scope, in case it's a DeclStmt
        // preceded by our switch label.
        BlockScopeRAII Scope(Info);
  
        // Step into the init statement in case it brings an (uninitialized)
        // variable into scope.
        if (const Stmt *Init = IS->getInit()) {
          EvalStmtResult ESR = EvaluateStmt(Result, Info, Init, Case);
          if (ESR != ESR_CaseNotFound) {
            assert(ESR != ESR_Succeeded);
            return ESR;
          }
        }
  
        // Condition variable must be initialized if it exists.
        // FIXME: We can skip evaluating the body if there's a condition
        // variable, as there can't be any case labels within it.
        // (The same is true for 'for' statements.)
  
        EvalStmtResult ESR = EvaluateStmt(Result, Info, IS->getThen(), Case);
        if (ESR == ESR_Failed)
          return ESR;
        if (ESR != ESR_CaseNotFound)
          return Scope.destroy() ? ESR : ESR_Failed;
        if (!IS->getElse())
          return ESR_CaseNotFound;
  
        ESR = EvaluateStmt(Result, Info, IS->getElse(), Case);
        if (ESR == ESR_Failed)
          return ESR;
        if (ESR != ESR_CaseNotFound)
          return Scope.destroy() ? ESR : ESR_Failed;
        return ESR_CaseNotFound;
      }
  
      case Stmt::WhileStmtClass: {
        EvalStmtResult ESR =
            EvaluateLoopBody(Result, Info, cast<WhileStmt>(S)->getBody(), Case);
        if (ESR != ESR_Continue)
          return ESR;
        break;
      }
  
      case Stmt::ForStmtClass: {
        const ForStmt *FS = cast<ForStmt>(S);
        BlockScopeRAII Scope(Info);
  
        // Step into the init statement in case it brings an (uninitialized)
        // variable into scope.
        if (const Stmt *Init = FS->getInit()) {
          EvalStmtResult ESR = EvaluateStmt(Result, Info, Init, Case);
          if (ESR != ESR_CaseNotFound) {
            assert(ESR != ESR_Succeeded);
            return ESR;
          }
        }
  
        EvalStmtResult ESR =
            EvaluateLoopBody(Result, Info, FS->getBody(), Case);
        if (ESR != ESR_Continue)
          return ESR;
        if (const auto *Inc = FS->getInc()) {
          if (Inc->isValueDependent()) {
            if (!EvaluateDependentExpr(Inc, Info))
              return ESR_Failed;
          } else {
            FullExpressionRAII IncScope(Info);
            if (!EvaluateIgnoredValue(Info, Inc) || !IncScope.destroy())
              return ESR_Failed;
          }
        }
        break;
      }
  
      case Stmt::DeclStmtClass: {
        // Start the lifetime of any uninitialized variables we encounter. They
        // might be used by the selected branch of the switch.
        const DeclStmt *DS = cast<DeclStmt>(S);
        for (const auto *D : DS->decls()) {
          if (const auto *VD = dyn_cast<VarDecl>(D)) {
            if (VD->hasLocalStorage() && !VD->getInit())
              if (!EvaluateVarDecl(Info, VD))
                return ESR_Failed;
            // FIXME: If the variable has initialization that can't be jumped
            // over, bail out of any immediately-surrounding compound-statement
            // too. There can't be any case labels here.
          }
        }
        return ESR_CaseNotFound;
      }
  
      default:
        return ESR_CaseNotFound;
      }
    }
  
    switch (S->getStmtClass()) {
    default:
      if (const Expr *E = dyn_cast<Expr>(S)) {
        if (E->isValueDependent()) {
          if (!EvaluateDependentExpr(E, Info))
            return ESR_Failed;
        } else {
          // Don't bother evaluating beyond an expression-statement which couldn't
          // be evaluated.
          // FIXME: Do we need the FullExpressionRAII object here?
          // VisitExprWithCleanups should create one when necessary.
          FullExpressionRAII Scope(Info);
          if (!EvaluateIgnoredValue(Info, E) || !Scope.destroy())
            return ESR_Failed;
        }
        return ESR_Succeeded;
      }
  
      Info.FFDiag(S->getBeginLoc());
      return ESR_Failed;
  
    case Stmt::NullStmtClass:
      return ESR_Succeeded;
  
    case Stmt::DeclStmtClass: {
      const DeclStmt *DS = cast<DeclStmt>(S);
      for (const auto *D : DS->decls()) {
        // Each declaration initialization is its own full-expression.
        FullExpressionRAII Scope(Info);
        if (!EvaluateDecl(Info, D) && !Info.noteFailure())
          return ESR_Failed;
        if (!Scope.destroy())
          return ESR_Failed;
      }
      return ESR_Succeeded;
    }
  
    case Stmt::ReturnStmtClass: {
      const Expr *RetExpr = cast<ReturnStmt>(S)->getRetValue();
      FullExpressionRAII Scope(Info);
      if (RetExpr && RetExpr->isValueDependent()) {
        EvaluateDependentExpr(RetExpr, Info);
        // We know we returned, but we don't know what the value is.
        return ESR_Failed;
      }
      if (RetExpr &&
          !(Result.Slot
                ? EvaluateInPlace(Result.Value, Info, *Result.Slot, RetExpr)
                : Evaluate(Result.Value, Info, RetExpr)))
        return ESR_Failed;
      return Scope.destroy() ? ESR_Returned : ESR_Failed;
    }
  
    case Stmt::CompoundStmtClass: {
      BlockScopeRAII Scope(Info);
  
      const CompoundStmt *CS = cast<CompoundStmt>(S);
      for (const auto *BI : CS->body()) {
        EvalStmtResult ESR = EvaluateStmt(Result, Info, BI, Case);
        if (ESR == ESR_Succeeded)
          Case = nullptr;
        else if (ESR != ESR_CaseNotFound) {
          if (ESR != ESR_Failed && !Scope.destroy())
            return ESR_Failed;
          return ESR;
        }
      }
      if (Case)
        return ESR_CaseNotFound;
      return Scope.destroy() ? ESR_Succeeded : ESR_Failed;
    }
  
    case Stmt::IfStmtClass: {
      const IfStmt *IS = cast<IfStmt>(S);
  
      // Evaluate the condition, as either a var decl or as an expression.
      BlockScopeRAII Scope(Info);
      if (const Stmt *Init = IS->getInit()) {
        EvalStmtResult ESR = EvaluateStmt(Result, Info, Init);
        if (ESR != ESR_Succeeded) {
          if (ESR != ESR_Failed && !Scope.destroy())
            return ESR_Failed;
          return ESR;
        }
      }
      bool Cond;
      if (!EvaluateCond(Info, IS->getConditionVariable(), IS->getCond(), Cond))
        return ESR_Failed;
  
      if (const Stmt *SubStmt = Cond ? IS->getThen() : IS->getElse()) {
        EvalStmtResult ESR = EvaluateStmt(Result, Info, SubStmt);
        if (ESR != ESR_Succeeded) {
          if (ESR != ESR_Failed && !Scope.destroy())
            return ESR_Failed;
          return ESR;
        }
      }
      return Scope.destroy() ? ESR_Succeeded : ESR_Failed;
    }
  
    case Stmt::WhileStmtClass: {
      const WhileStmt *WS = cast<WhileStmt>(S);
      while (true) {
        BlockScopeRAII Scope(Info);
        bool Continue;
        if (!EvaluateCond(Info, WS->getConditionVariable(), WS->getCond(),
                          Continue))
          return ESR_Failed;
        if (!Continue)
          break;
  
        EvalStmtResult ESR = EvaluateLoopBody(Result, Info, WS->getBody());
        if (ESR != ESR_Continue) {
          if (ESR != ESR_Failed && !Scope.destroy())
            return ESR_Failed;
          return ESR;
        }
        if (!Scope.destroy())
          return ESR_Failed;
      }
      return ESR_Succeeded;
    }
  
    case Stmt::DoStmtClass: {
      const DoStmt *DS = cast<DoStmt>(S);
      bool Continue;
      do {
        EvalStmtResult ESR = EvaluateLoopBody(Result, Info, DS->getBody(), Case);
        if (ESR != ESR_Continue)
          return ESR;
        Case = nullptr;
  
        if (DS->getCond()->isValueDependent()) {
          EvaluateDependentExpr(DS->getCond(), Info);
          // Bailout as we don't know whether to keep going or terminate the loop.
          return ESR_Failed;
        }
        FullExpressionRAII CondScope(Info);
        if (!EvaluateAsBooleanCondition(DS->getCond(), Continue, Info) ||
            !CondScope.destroy())
          return ESR_Failed;
      } while (Continue);
      return ESR_Succeeded;
    }
  
    case Stmt::ForStmtClass: {
      const ForStmt *FS = cast<ForStmt>(S);
      BlockScopeRAII ForScope(Info);
      if (FS->getInit()) {
        EvalStmtResult ESR = EvaluateStmt(Result, Info, FS->getInit());
        if (ESR != ESR_Succeeded) {
          if (ESR != ESR_Failed && !ForScope.destroy())
            return ESR_Failed;
          return ESR;
        }
      }
      while (true) {
        BlockScopeRAII IterScope(Info);
        bool Continue = true;
        if (FS->getCond() && !EvaluateCond(Info, FS->getConditionVariable(),
                                           FS->getCond(), Continue))
          return ESR_Failed;
        if (!Continue)
          break;
  
        EvalStmtResult ESR = EvaluateLoopBody(Result, Info, FS->getBody());
        if (ESR != ESR_Continue) {
          if (ESR != ESR_Failed && (!IterScope.destroy() || !ForScope.destroy()))
            return ESR_Failed;
          return ESR;
        }
  
        if (const auto *Inc = FS->getInc()) {
          if (Inc->isValueDependent()) {
            if (!EvaluateDependentExpr(Inc, Info))
              return ESR_Failed;
          } else {
            FullExpressionRAII IncScope(Info);
            if (!EvaluateIgnoredValue(Info, Inc) || !IncScope.destroy())
              return ESR_Failed;
          }
        }
  
        if (!IterScope.destroy())
          return ESR_Failed;
      }
      return ForScope.destroy() ? ESR_Succeeded : ESR_Failed;
    }
  
    case Stmt::CXXForRangeStmtClass: {
      const CXXForRangeStmt *FS = cast<CXXForRangeStmt>(S);
      BlockScopeRAII Scope(Info);
  
      // Evaluate the init-statement if present.
      if (FS->getInit()) {
        EvalStmtResult ESR = EvaluateStmt(Result, Info, FS->getInit());
        if (ESR != ESR_Succeeded) {
          if (ESR != ESR_Failed && !Scope.destroy())
            return ESR_Failed;
          return ESR;
        }
      }
  
      // Initialize the __range variable.
      EvalStmtResult ESR = EvaluateStmt(Result, Info, FS->getRangeStmt());
      if (ESR != ESR_Succeeded) {
        if (ESR != ESR_Failed && !Scope.destroy())
          return ESR_Failed;
        return ESR;
      }
  
      // Create the __begin and __end iterators.
      ESR = EvaluateStmt(Result, Info, FS->getBeginStmt());
      if (ESR != ESR_Succeeded) {
        if (ESR != ESR_Failed && !Scope.destroy())
          return ESR_Failed;
        return ESR;
      }
      ESR = EvaluateStmt(Result, Info, FS->getEndStmt());
      if (ESR != ESR_Succeeded) {
        if (ESR != ESR_Failed && !Scope.destroy())
          return ESR_Failed;
        return ESR;
      }
  
      while (true) {
        // Condition: __begin != __end.
        {
          if (FS->getCond()->isValueDependent()) {
            EvaluateDependentExpr(FS->getCond(), Info);
            // We don't know whether to keep going or terminate the loop.
            return ESR_Failed;
          }
          bool Continue = true;
          FullExpressionRAII CondExpr(Info);
          if (!EvaluateAsBooleanCondition(FS->getCond(), Continue, Info))
            return ESR_Failed;
          if (!Continue)
            break;
        }
  
        // User's variable declaration, initialized by *__begin.
        BlockScopeRAII InnerScope(Info);
        ESR = EvaluateStmt(Result, Info, FS->getLoopVarStmt());
        if (ESR != ESR_Succeeded) {
          if (ESR != ESR_Failed && (!InnerScope.destroy() || !Scope.destroy()))
            return ESR_Failed;
          return ESR;
        }
  
        // Loop body.
        ESR = EvaluateLoopBody(Result, Info, FS->getBody());
        if (ESR != ESR_Continue) {
          if (ESR != ESR_Failed && (!InnerScope.destroy() || !Scope.destroy()))
            return ESR_Failed;
          return ESR;
        }
        if (FS->getInc()->isValueDependent()) {
          if (!EvaluateDependentExpr(FS->getInc(), Info))
            return ESR_Failed;
        } else {
          // Increment: ++__begin
          if (!EvaluateIgnoredValue(Info, FS->getInc()))
            return ESR_Failed;
        }
  
        if (!InnerScope.destroy())
          return ESR_Failed;
      }
  
      return Scope.destroy() ? ESR_Succeeded : ESR_Failed;
    }
  
    case Stmt::SwitchStmtClass:
      return EvaluateSwitch(Result, Info, cast<SwitchStmt>(S));
  
    case Stmt::ContinueStmtClass:
      return ESR_Continue;
  
    case Stmt::BreakStmtClass:
      return ESR_Break;
  
    case Stmt::LabelStmtClass:
      return EvaluateStmt(Result, Info, cast<LabelStmt>(S)->getSubStmt(), Case);
  
    case Stmt::AttributedStmtClass:
      // As a general principle, C++11 attributes can be ignored without
      // any semantic impact.
      return EvaluateStmt(Result, Info, cast<AttributedStmt>(S)->getSubStmt(),
                          Case);
  
    case Stmt::CaseStmtClass:
    case Stmt::DefaultStmtClass:
      return EvaluateStmt(Result, Info, cast<SwitchCase>(S)->getSubStmt(), Case);
    case Stmt::CXXTryStmtClass:
      // Evaluate try blocks by evaluating all sub statements.
      return EvaluateStmt(Result, Info, cast<CXXTryStmt>(S)->getTryBlock(), Case);
    }
  }
  
  /// CheckTrivialDefaultConstructor - Check whether a constructor is a trivial
  /// default constructor. If so, we'll fold it whether or not it's marked as
  /// constexpr. If it is marked as constexpr, we will never implicitly define it,
  /// so we need special handling.
  static bool CheckTrivialDefaultConstructor(EvalInfo &Info, SourceLocation Loc,
                                             const CXXConstructorDecl *CD,
                                             bool IsValueInitialization) {
    if (!CD->isTrivial() || !CD->isDefaultConstructor())
      return false;
  
    // Value-initialization does not call a trivial default constructor, so such a
    // call is a core constant expression whether or not the constructor is
    // constexpr.
    if (!CD->isConstexpr() && !IsValueInitialization) {
      if (Info.getLangOpts().CPlusPlus11) {
        // FIXME: If DiagDecl is an implicitly-declared special member function,
        // we should be much more explicit about why it's not constexpr.
        Info.CCEDiag(Loc, diag::note_constexpr_invalid_function, 1)
          << /*IsConstexpr*/0 << /*IsConstructor*/1 << CD;
        Info.Note(CD->getLocation(), diag::note_declared_at);
      } else {
        Info.CCEDiag(Loc, diag::note_invalid_subexpr_in_const_expr);
      }
    }
    return true;
  }
  
  /// CheckConstexprFunction - Check that a function can be called in a constant
  /// expression.
  static bool CheckConstexprFunction(EvalInfo &Info, SourceLocation CallLoc,
                                     const FunctionDecl *Declaration,
                                     const FunctionDecl *Definition,
                                     const Stmt *Body) {
    // Potential constant expressions can contain calls to declared, but not yet
    // defined, constexpr functions.
    if (Info.checkingPotentialConstantExpression() && !Definition &&
        Declaration->isConstexpr())
      return false;
  
    // Bail out if the function declaration itself is invalid.  We will
    // have produced a relevant diagnostic while parsing it, so just
    // note the problematic sub-expression.
    if (Declaration->isInvalidDecl()) {
      Info.FFDiag(CallLoc, diag::note_invalid_subexpr_in_const_expr);
      return false;
    }
  
    // DR1872: An instantiated virtual constexpr function can't be called in a
    // constant expression (prior to C++20). We can still constant-fold such a
    // call.
    if (!Info.Ctx.getLangOpts().CPlusPlus20 && isa<CXXMethodDecl>(Declaration) &&
        cast<CXXMethodDecl>(Declaration)->isVirtual())
      Info.CCEDiag(CallLoc, diag::note_constexpr_virtual_call);
  
    if (Definition && Definition->isInvalidDecl()) {
      Info.FFDiag(CallLoc, diag::note_invalid_subexpr_in_const_expr);
      return false;
    }
  
    // Can we evaluate this function call?
    if (Definition && Definition->isConstexpr() && Body)
      return true;
  
    if (Info.getLangOpts().CPlusPlus11) {
      const FunctionDecl *DiagDecl = Definition ? Definition : Declaration;
  
      // If this function is not constexpr because it is an inherited
      // non-constexpr constructor, diagnose that directly.
      auto *CD = dyn_cast<CXXConstructorDecl>(DiagDecl);
      if (CD && CD->isInheritingConstructor()) {
        auto *Inherited = CD->getInheritedConstructor().getConstructor();
        if (!Inherited->isConstexpr())
          DiagDecl = CD = Inherited;
      }
  
      // FIXME: If DiagDecl is an implicitly-declared special member function
      // or an inheriting constructor, we should be much more explicit about why
      // it's not constexpr.
      if (CD && CD->isInheritingConstructor())
        Info.FFDiag(CallLoc, diag::note_constexpr_invalid_inhctor, 1)
          << CD->getInheritedConstructor().getConstructor()->getParent();
      else
        Info.FFDiag(CallLoc, diag::note_constexpr_invalid_function, 1)
          << DiagDecl->isConstexpr() << (bool)CD << DiagDecl;
      Info.Note(DiagDecl->getLocation(), diag::note_declared_at);
    } else {
      Info.FFDiag(CallLoc, diag::note_invalid_subexpr_in_const_expr);
    }
    return false;
  }
  
  namespace {
  struct CheckDynamicTypeHandler {
    AccessKinds AccessKind;
    typedef bool result_type;
    bool failed() { return false; }
    bool found(APValue &Subobj, QualType SubobjType) { return true; }
    bool found(APSInt &Value, QualType SubobjType) { return true; }
    bool found(APFloat &Value, QualType SubobjType) { return true; }
  };
  } // end anonymous namespace
  
  /// Check that we can access the notional vptr of an object / determine its
  /// dynamic type.
  static bool checkDynamicType(EvalInfo &Info, const Expr *E, const LValue &This,
                               AccessKinds AK, bool Polymorphic) {
    if (This.Designator.Invalid)
      return false;
  
    CompleteObject Obj = findCompleteObject(Info, E, AK, This, QualType());
  
    if (!Obj)
      return false;
  
    if (!Obj.Value) {
      // The object is not usable in constant expressions, so we can't inspect
      // its value to see if it's in-lifetime or what the active union members
      // are. We can still check for a one-past-the-end lvalue.
      if (This.Designator.isOnePastTheEnd() ||
          This.Designator.isMostDerivedAnUnsizedArray()) {
        Info.FFDiag(E, This.Designator.isOnePastTheEnd()
                           ? diag::note_constexpr_access_past_end
                           : diag::note_constexpr_access_unsized_array)
            << AK;
        return false;
      } else if (Polymorphic) {
        // Conservatively refuse to perform a polymorphic operation if we would
        // not be able to read a notional 'vptr' value.
        APValue Val;
        This.moveInto(Val);
        QualType StarThisType =
            Info.Ctx.getLValueReferenceType(This.Designator.getType(Info.Ctx));
        Info.FFDiag(E, diag::note_constexpr_polymorphic_unknown_dynamic_type)
            << AK << Val.getAsString(Info.Ctx, StarThisType);
        return false;
      }
      return true;
    }
  
    CheckDynamicTypeHandler Handler{AK};
    return Obj && findSubobject(Info, E, Obj, This.Designator, Handler);
  }
  
  /// Check that the pointee of the 'this' pointer in a member function call is
  /// either within its lifetime or in its period of construction or destruction.
  static bool
  checkNonVirtualMemberCallThisPointer(EvalInfo &Info, const Expr *E,
                                       const LValue &This,
                                       const CXXMethodDecl *NamedMember) {
    return checkDynamicType(
        Info, E, This,
        isa<CXXDestructorDecl>(NamedMember) ? AK_Destroy : AK_MemberCall, false);
  }
  
  struct DynamicType {
    /// The dynamic class type of the object.
    const CXXRecordDecl *Type;
    /// The corresponding path length in the lvalue.
    unsigned PathLength;
  };
  
  static const CXXRecordDecl *getBaseClassType(SubobjectDesignator &Designator,
                                               unsigned PathLength) {
    assert(PathLength >= Designator.MostDerivedPathLength && PathLength <=
        Designator.Entries.size() && "invalid path length");
    return (PathLength == Designator.MostDerivedPathLength)
               ? Designator.MostDerivedType->getAsCXXRecordDecl()
               : getAsBaseClass(Designator.Entries[PathLength - 1]);
  }
  
  /// Determine the dynamic type of an object.
  static Optional<DynamicType> ComputeDynamicType(EvalInfo &Info, const Expr *E,
                                                  LValue &This, AccessKinds AK) {
    // If we don't have an lvalue denoting an object of class type, there is no
    // meaningful dynamic type. (We consider objects of non-class type to have no
    // dynamic type.)
    if (!checkDynamicType(Info, E, This, AK, true))
      return None;
  
    // Refuse to compute a dynamic type in the presence of virtual bases. This
    // shouldn't happen other than in constant-folding situations, since literal
    // types can't have virtual bases.
    //
    // Note that consumers of DynamicType assume that the type has no virtual
    // bases, and will need modifications if this restriction is relaxed.
    const CXXRecordDecl *Class =
        This.Designator.MostDerivedType->getAsCXXRecordDecl();
    if (!Class || Class->getNumVBases()) {
      Info.FFDiag(E);
      return None;
    }
  
    // FIXME: For very deep class hierarchies, it might be beneficial to use a
    // binary search here instead. But the overwhelmingly common case is that
    // we're not in the middle of a constructor, so it probably doesn't matter
    // in practice.
    ArrayRef<APValue::LValuePathEntry> Path = This.Designator.Entries;
    for (unsigned PathLength = This.Designator.MostDerivedPathLength;
         PathLength <= Path.size(); ++PathLength) {
      switch (Info.isEvaluatingCtorDtor(This.getLValueBase(),
                                        Path.slice(0, PathLength))) {
      case ConstructionPhase::Bases:
      case ConstructionPhase::DestroyingBases:
        // We're constructing or destroying a base class. This is not the dynamic
        // type.
        break;
  
      case ConstructionPhase::None:
      case ConstructionPhase::AfterBases:
      case ConstructionPhase::AfterFields:
      case ConstructionPhase::Destroying:
        // We've finished constructing the base classes and not yet started
        // destroying them again, so this is the dynamic type.
        return DynamicType{getBaseClassType(This.Designator, PathLength),
                           PathLength};
      }
    }
  
    // CWG issue 1517: we're constructing a base class of the object described by
    // 'This', so that object has not yet begun its period of construction and
    // any polymorphic operation on it results in undefined behavior.
    Info.FFDiag(E);
    return None;
  }
  
  /// Perform virtual dispatch.
  static const CXXMethodDecl *HandleVirtualDispatch(
      EvalInfo &Info, const Expr *E, LValue &This, const CXXMethodDecl *Found,
      llvm::SmallVectorImpl<QualType> &CovariantAdjustmentPath) {
    Optional<DynamicType> DynType = ComputeDynamicType(
        Info, E, This,
        isa<CXXDestructorDecl>(Found) ? AK_Destroy : AK_MemberCall);
    if (!DynType)
      return nullptr;
  
    // Find the final overrider. It must be declared in one of the classes on the
    // path from the dynamic type to the static type.
    // FIXME: If we ever allow literal types to have virtual base classes, that
    // won't be true.
    const CXXMethodDecl *Callee = Found;
    unsigned PathLength = DynType->PathLength;
    for (/**/; PathLength <= This.Designator.Entries.size(); ++PathLength) {
      const CXXRecordDecl *Class = getBaseClassType(This.Designator, PathLength);
      const CXXMethodDecl *Overrider =
          Found->getCorrespondingMethodDeclaredInClass(Class, false);
      if (Overrider) {
        Callee = Overrider;
        break;
      }
    }
  
    // C++2a [class.abstract]p6:
    //   the effect of making a virtual call to a pure virtual function [...] is
    //   undefined
    if (Callee->isPure()) {
      Info.FFDiag(E, diag::note_constexpr_pure_virtual_call, 1) << Callee;
      Info.Note(Callee->getLocation(), diag::note_declared_at);
      return nullptr;
    }
  
    // If necessary, walk the rest of the path to determine the sequence of
    // covariant adjustment steps to apply.
    if (!Info.Ctx.hasSameUnqualifiedType(Callee->getReturnType(),
                                         Found->getReturnType())) {
      CovariantAdjustmentPath.push_back(Callee->getReturnType());
      for (unsigned CovariantPathLength = PathLength + 1;
           CovariantPathLength != This.Designator.Entries.size();
           ++CovariantPathLength) {
        const CXXRecordDecl *NextClass =
            getBaseClassType(This.Designator, CovariantPathLength);
        const CXXMethodDecl *Next =
            Found->getCorrespondingMethodDeclaredInClass(NextClass, false);
        if (Next && !Info.Ctx.hasSameUnqualifiedType(
                        Next->getReturnType(), CovariantAdjustmentPath.back()))
          CovariantAdjustmentPath.push_back(Next->getReturnType());
      }
      if (!Info.Ctx.hasSameUnqualifiedType(Found->getReturnType(),
                                           CovariantAdjustmentPath.back()))
        CovariantAdjustmentPath.push_back(Found->getReturnType());
    }
  
    // Perform 'this' adjustment.
    if (!CastToDerivedClass(Info, E, This, Callee->getParent(), PathLength))
      return nullptr;
  
    return Callee;
  }
  
  /// Perform the adjustment from a value returned by a virtual function to
  /// a value of the statically expected type, which may be a pointer or
  /// reference to a base class of the returned type.
  static bool HandleCovariantReturnAdjustment(EvalInfo &Info, const Expr *E,
                                              APValue &Result,
                                              ArrayRef<QualType> Path) {
    assert(Result.isLValue() &&
           "unexpected kind of APValue for covariant return");
    if (Result.isNullPointer())
      return true;
  
    LValue LVal;
    LVal.setFrom(Info.Ctx, Result);
  
    const CXXRecordDecl *OldClass = Path[0]->getPointeeCXXRecordDecl();
    for (unsigned I = 1; I != Path.size(); ++I) {
      const CXXRecordDecl *NewClass = Path[I]->getPointeeCXXRecordDecl();
      assert(OldClass && NewClass && "unexpected kind of covariant return");
      if (OldClass != NewClass &&
          !CastToBaseClass(Info, E, LVal, OldClass, NewClass))
        return false;
      OldClass = NewClass;
    }
  
    LVal.moveInto(Result);
    return true;
  }
  
  /// Determine whether \p Base, which is known to be a direct base class of
  /// \p Derived, is a public base class.
  static bool isBaseClassPublic(const CXXRecordDecl *Derived,
                                const CXXRecordDecl *Base) {
    for (const CXXBaseSpecifier &BaseSpec : Derived->bases()) {
      auto *BaseClass = BaseSpec.getType()->getAsCXXRecordDecl();
      if (BaseClass && declaresSameEntity(BaseClass, Base))
        return BaseSpec.getAccessSpecifier() == AS_public;
    }
    llvm_unreachable("Base is not a direct base of Derived");
  }
  
  /// Apply the given dynamic cast operation on the provided lvalue.
  ///
  /// This implements the hard case of dynamic_cast, requiring a "runtime check"
  /// to find a suitable target subobject.
  static bool HandleDynamicCast(EvalInfo &Info, const ExplicitCastExpr *E,
                                LValue &Ptr) {
    // We can't do anything with a non-symbolic pointer value.
    SubobjectDesignator &D = Ptr.Designator;
    if (D.Invalid)
      return false;
  
    // C++ [expr.dynamic.cast]p6:
    //   If v is a null pointer value, the result is a null pointer value.
    if (Ptr.isNullPointer() && !E->isGLValue())
      return true;
  
    // For all the other cases, we need the pointer to point to an object within
    // its lifetime / period of construction / destruction, and we need to know
    // its dynamic type.
    Optional<DynamicType> DynType =
        ComputeDynamicType(Info, E, Ptr, AK_DynamicCast);
    if (!DynType)
      return false;
  
    // C++ [expr.dynamic.cast]p7:
    //   If T is "pointer to cv void", then the result is a pointer to the most
    //   derived object
    if (E->getType()->isVoidPointerType())
      return CastToDerivedClass(Info, E, Ptr, DynType->Type, DynType->PathLength);
  
    const CXXRecordDecl *C = E->getTypeAsWritten()->getPointeeCXXRecordDecl();
    assert(C && "dynamic_cast target is not void pointer nor class");
    CanQualType CQT = Info.Ctx.getCanonicalType(Info.Ctx.getRecordType(C));
  
    auto RuntimeCheckFailed = [&] (CXXBasePaths *Paths) {
      // C++ [expr.dynamic.cast]p9:
      if (!E->isGLValue()) {
        //   The value of a failed cast to pointer type is the null pointer value
        //   of the required result type.
        Ptr.setNull(Info.Ctx, E->getType());
        return true;
      }
  
      //   A failed cast to reference type throws [...] std::bad_cast.
      unsigned DiagKind;
      if (!Paths && (declaresSameEntity(DynType->Type, C) ||
                     DynType->Type->isDerivedFrom(C)))
        DiagKind = 0;
      else if (!Paths || Paths->begin() == Paths->end())
        DiagKind = 1;
      else if (Paths->isAmbiguous(CQT))
        DiagKind = 2;
      else {
        assert(Paths->front().Access != AS_public && "why did the cast fail?");
        DiagKind = 3;
      }
      Info.FFDiag(E, diag::note_constexpr_dynamic_cast_to_reference_failed)
          << DiagKind << Ptr.Designator.getType(Info.Ctx)
          << Info.Ctx.getRecordType(DynType->Type)
          << E->getType().getUnqualifiedType();
      return false;
    };
  
    // Runtime check, phase 1:
    //   Walk from the base subobject towards the derived object looking for the
    //   target type.
    for (int PathLength = Ptr.Designator.Entries.size();
         PathLength >= (int)DynType->PathLength; --PathLength) {
      const CXXRecordDecl *Class = getBaseClassType(Ptr.Designator, PathLength);
      if (declaresSameEntity(Class, C))
        return CastToDerivedClass(Info, E, Ptr, Class, PathLength);
      // We can only walk across public inheritance edges.
      if (PathLength > (int)DynType->PathLength &&
          !isBaseClassPublic(getBaseClassType(Ptr.Designator, PathLength - 1),
                             Class))
        return RuntimeCheckFailed(nullptr);
    }
  
    // Runtime check, phase 2:
    //   Search the dynamic type for an unambiguous public base of type C.
    CXXBasePaths Paths(/*FindAmbiguities=*/true,
                       /*RecordPaths=*/true, /*DetectVirtual=*/false);
    if (DynType->Type->isDerivedFrom(C, Paths) && !Paths.isAmbiguous(CQT) &&
        Paths.front().Access == AS_public) {
      // Downcast to the dynamic type...
      if (!CastToDerivedClass(Info, E, Ptr, DynType->Type, DynType->PathLength))
        return false;
      // ... then upcast to the chosen base class subobject.
      for (CXXBasePathElement &Elem : Paths.front())
        if (!HandleLValueBase(Info, E, Ptr, Elem.Class, Elem.Base))
          return false;
      return true;
    }
  
    // Otherwise, the runtime check fails.
    return RuntimeCheckFailed(&Paths);
  }
  
  namespace {
  struct StartLifetimeOfUnionMemberHandler {
    EvalInfo &Info;
    const Expr *LHSExpr;
    const FieldDecl *Field;
    bool DuringInit;
    bool Failed = false;
    static const AccessKinds AccessKind = AK_Assign;
  
    typedef bool result_type;
    bool failed() { return Failed; }
    bool found(APValue &Subobj, QualType SubobjType) {
      // We are supposed to perform no initialization but begin the lifetime of
      // the object. We interpret that as meaning to do what default
      // initialization of the object would do if all constructors involved were
      // trivial:
      //  * All base, non-variant member, and array element subobjects' lifetimes
      //    begin
      //  * No variant members' lifetimes begin
      //  * All scalar subobjects whose lifetimes begin have indeterminate values
      assert(SubobjType->isUnionType());
      if (declaresSameEntity(Subobj.getUnionField(), Field)) {
        // This union member is already active. If it's also in-lifetime, there's
        // nothing to do.
        if (Subobj.getUnionValue().hasValue())
          return true;
      } else if (DuringInit) {
        // We're currently in the process of initializing a different union
        // member.  If we carried on, that initialization would attempt to
        // store to an inactive union member, resulting in undefined behavior.
        Info.FFDiag(LHSExpr,
                    diag::note_constexpr_union_member_change_during_init);
        return false;
      }
      APValue Result;
      Failed = !getDefaultInitValue(Field->getType(), Result);
      Subobj.setUnion(Field, Result);
      return true;
    }
    bool found(APSInt &Value, QualType SubobjType) {
      llvm_unreachable("wrong value kind for union object");
    }
    bool found(APFloat &Value, QualType SubobjType) {
      llvm_unreachable("wrong value kind for union object");
    }
  };
  } // end anonymous namespace
  
  const AccessKinds StartLifetimeOfUnionMemberHandler::AccessKind;
  
  /// Handle a builtin simple-assignment or a call to a trivial assignment
  /// operator whose left-hand side might involve a union member access. If it
  /// does, implicitly start the lifetime of any accessed union elements per
  /// C++20 [class.union]5.
  static bool HandleUnionActiveMemberChange(EvalInfo &Info, const Expr *LHSExpr,
                                            const LValue &LHS) {
    if (LHS.InvalidBase || LHS.Designator.Invalid)
      return false;
  
    llvm::SmallVector<std::pair<unsigned, const FieldDecl*>, 4> UnionPathLengths;
    // C++ [class.union]p5:
    //   define the set S(E) of subexpressions of E as follows:
    unsigned PathLength = LHS.Designator.Entries.size();
    for (const Expr *E = LHSExpr; E != nullptr;) {
      //   -- If E is of the form A.B, S(E) contains the elements of S(A)...
      if (auto *ME = dyn_cast<MemberExpr>(E)) {
        auto *FD = dyn_cast<FieldDecl>(ME->getMemberDecl());
        // Note that we can't implicitly start the lifetime of a reference,
        // so we don't need to proceed any further if we reach one.
        if (!FD || FD->getType()->isReferenceType())
          break;
  
        //    ... and also contains A.B if B names a union member ...
        if (FD->getParent()->isUnion()) {
          //    ... of a non-class, non-array type, or of a class type with a
          //    trivial default constructor that is not deleted, or an array of
          //    such types.
          auto *RD =
              FD->getType()->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
          if (!RD || RD->hasTrivialDefaultConstructor())
            UnionPathLengths.push_back({PathLength - 1, FD});
        }
  
        E = ME->getBase();
        --PathLength;
        assert(declaresSameEntity(FD,
                                  LHS.Designator.Entries[PathLength]
                                      .getAsBaseOrMember().getPointer()));
  
        //   -- If E is of the form A[B] and is interpreted as a built-in array
        //      subscripting operator, S(E) is [S(the array operand, if any)].
      } else if (auto *ASE = dyn_cast<ArraySubscriptExpr>(E)) {
        // Step over an ArrayToPointerDecay implicit cast.
        auto *Base = ASE->getBase()->IgnoreImplicit();
        if (!Base->getType()->isArrayType())
          break;
  
        E = Base;
        --PathLength;
  
      } else if (auto *ICE = dyn_cast<ImplicitCastExpr>(E)) {
        // Step over a derived-to-base conversion.
        E = ICE->getSubExpr();
        if (ICE->getCastKind() == CK_NoOp)
          continue;
        if (ICE->getCastKind() != CK_DerivedToBase &&
            ICE->getCastKind() != CK_UncheckedDerivedToBase)
          break;
        // Walk path backwards as we walk up from the base to the derived class.
        for (const CXXBaseSpecifier *Elt : llvm::reverse(ICE->path())) {
          --PathLength;
          (void)Elt;
          assert(declaresSameEntity(Elt->getType()->getAsCXXRecordDecl(),
                                    LHS.Designator.Entries[PathLength]
                                        .getAsBaseOrMember().getPointer()));
        }
  
      //   -- Otherwise, S(E) is empty.
      } else {
        break;
      }
    }
  
    // Common case: no unions' lifetimes are started.
    if (UnionPathLengths.empty())
      return true;
  
    //   if modification of X [would access an inactive union member], an object
    //   of the type of X is implicitly created
    CompleteObject Obj =
        findCompleteObject(Info, LHSExpr, AK_Assign, LHS, LHSExpr->getType());
    if (!Obj)
      return false;
    for (std::pair<unsigned, const FieldDecl *> LengthAndField :
             llvm::reverse(UnionPathLengths)) {
      // Form a designator for the union object.
      SubobjectDesignator D = LHS.Designator;
      D.truncate(Info.Ctx, LHS.Base, LengthAndField.first);
  
      bool DuringInit = Info.isEvaluatingCtorDtor(LHS.Base, D.Entries) ==
                        ConstructionPhase::AfterBases;
      StartLifetimeOfUnionMemberHandler StartLifetime{
          Info, LHSExpr, LengthAndField.second, DuringInit};
      if (!findSubobject(Info, LHSExpr, Obj, D, StartLifetime))
        return false;
    }
  
    return true;
  }
  
  static bool EvaluateCallArg(const ParmVarDecl *PVD, const Expr *Arg,
                              CallRef Call, EvalInfo &Info,
                              bool NonNull = false) {
    LValue LV;
    // Create the parameter slot and register its destruction. For a vararg
    // argument, create a temporary.
    // FIXME: For calling conventions that destroy parameters in the callee,
    // should we consider performing destruction when the function returns
    // instead?
    APValue &V = PVD ? Info.CurrentCall->createParam(Call, PVD, LV)
                     : Info.CurrentCall->createTemporary(Arg, Arg->getType(),
                                                         ScopeKind::Call, LV);
    if (!EvaluateInPlace(V, Info, LV, Arg))
      return false;
  
    // Passing a null pointer to an __attribute__((nonnull)) parameter results in
    // undefined behavior, so is non-constant.
    if (NonNull && V.isLValue() && V.isNullPointer()) {
      Info.CCEDiag(Arg, diag::note_non_null_attribute_failed);
      return false;
    }
  
    return true;
  }
  
  /// Evaluate the arguments to a function call.
  static bool EvaluateArgs(ArrayRef<const Expr *> Args, CallRef Call,
                           EvalInfo &Info, const FunctionDecl *Callee,
                           bool RightToLeft = false) {
    bool Success = true;
    llvm::SmallBitVector ForbiddenNullArgs;
    if (Callee->hasAttr<NonNullAttr>()) {
      ForbiddenNullArgs.resize(Args.size());
      for (const auto *Attr : Callee->specific_attrs<NonNullAttr>()) {
        if (!Attr->args_size()) {
          ForbiddenNullArgs.set();
          break;
        } else
          for (auto Idx : Attr->args()) {
            unsigned ASTIdx = Idx.getASTIndex();
            if (ASTIdx >= Args.size())
              continue;
            ForbiddenNullArgs[ASTIdx] = 1;
          }
      }
    }
    for (unsigned I = 0; I < Args.size(); I++) {
      unsigned Idx = RightToLeft ? Args.size() - I - 1 : I;
      const ParmVarDecl *PVD =
          Idx < Callee->getNumParams() ? Callee->getParamDecl(Idx) : nullptr;
      bool NonNull = !ForbiddenNullArgs.empty() && ForbiddenNullArgs[Idx];
      if (!EvaluateCallArg(PVD, Args[Idx], Call, Info, NonNull)) {
        // If we're checking for a potential constant expression, evaluate all
        // initializers even if some of them fail.
        if (!Info.noteFailure())
          return false;
        Success = false;
      }
    }
    return Success;
  }
  
  /// Perform a trivial copy from Param, which is the parameter of a copy or move
  /// constructor or assignment operator.
  static bool handleTrivialCopy(EvalInfo &Info, const ParmVarDecl *Param,
                                const Expr *E, APValue &Result,
                                bool CopyObjectRepresentation) {
    // Find the reference argument.
    CallStackFrame *Frame = Info.CurrentCall;
    APValue *RefValue = Info.getParamSlot(Frame->Arguments, Param);
    if (!RefValue) {
      Info.FFDiag(E);
      return false;
    }
  
    // Copy out the contents of the RHS object.
    LValue RefLValue;
    RefLValue.setFrom(Info.Ctx, *RefValue);
    return handleLValueToRValueConversion(
        Info, E, Param->getType().getNonReferenceType(), RefLValue, Result,
        CopyObjectRepresentation);
  }
  
  /// Evaluate a function call.
  static bool HandleFunctionCall(SourceLocation CallLoc,
                                 const FunctionDecl *Callee, const LValue *This,
                                 ArrayRef<const Expr *> Args, CallRef Call,
                                 const Stmt *Body, EvalInfo &Info,
                                 APValue &Result, const LValue *ResultSlot) {
    if (!Info.CheckCallLimit(CallLoc))
      return false;
  
    CallStackFrame Frame(Info, CallLoc, Callee, This, Call);
  
    // For a trivial copy or move assignment, perform an APValue copy. This is
    // essential for unions, where the operations performed by the assignment
    // operator cannot be represented as statements.
    //
    // Skip this for non-union classes with no fields; in that case, the defaulted
    // copy/move does not actually read the object.
    const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Callee);
    if (MD && MD->isDefaulted() &&
        (MD->getParent()->isUnion() ||
         (MD->isTrivial() &&
          isReadByLvalueToRvalueConversion(MD->getParent())))) {
      assert(This &&
             (MD->isCopyAssignmentOperator() || MD->isMoveAssignmentOperator()));
      APValue RHSValue;
      if (!handleTrivialCopy(Info, MD->getParamDecl(0), Args[0], RHSValue,
                             MD->getParent()->isUnion()))
        return false;
      if (Info.getLangOpts().CPlusPlus20 && MD->isTrivial() &&
          !HandleUnionActiveMemberChange(Info, Args[0], *This))
        return false;
      if (!handleAssignment(Info, Args[0], *This, MD->getThisType(),
                            RHSValue))
        return false;
      This->moveInto(Result);
      return true;
    } else if (MD && isLambdaCallOperator(MD)) {
      // We're in a lambda; determine the lambda capture field maps unless we're
      // just constexpr checking a lambda's call operator. constexpr checking is
      // done before the captures have been added to the closure object (unless
      // we're inferring constexpr-ness), so we don't have access to them in this
      // case. But since we don't need the captures to constexpr check, we can
      // just ignore them.
      if (!Info.checkingPotentialConstantExpression())
        MD->getParent()->getCaptureFields(Frame.LambdaCaptureFields,
                                          Frame.LambdaThisCaptureField);
    }
  
    StmtResult Ret = {Result, ResultSlot};
    EvalStmtResult ESR = EvaluateStmt(Ret, Info, Body);
    if (ESR == ESR_Succeeded) {
      if (Callee->getReturnType()->isVoidType())
        return true;
      Info.FFDiag(Callee->getEndLoc(), diag::note_constexpr_no_return);
    }
    return ESR == ESR_Returned;
  }
  
  /// Evaluate a constructor call.
  static bool HandleConstructorCall(const Expr *E, const LValue &This,
                                    CallRef Call,
                                    const CXXConstructorDecl *Definition,
                                    EvalInfo &Info, APValue &Result) {
    SourceLocation CallLoc = E->getExprLoc();
    if (!Info.CheckCallLimit(CallLoc))
      return false;
  
    const CXXRecordDecl *RD = Definition->getParent();
    if (RD->getNumVBases()) {
      Info.FFDiag(CallLoc, diag::note_constexpr_virtual_base) << RD;
      return false;
    }
  
    EvalInfo::EvaluatingConstructorRAII EvalObj(
        Info,
        ObjectUnderConstruction{This.getLValueBase(), This.Designator.Entries},
        RD->getNumBases());
    CallStackFrame Frame(Info, CallLoc, Definition, &This, Call);
  
    // FIXME: Creating an APValue just to hold a nonexistent return value is
    // wasteful.
    APValue RetVal;
    StmtResult Ret = {RetVal, nullptr};
  
    // If it's a delegating constructor, delegate.
    if (Definition->isDelegatingConstructor()) {
      CXXConstructorDecl::init_const_iterator I = Definition->init_begin();
      if ((*I)->getInit()->isValueDependent()) {
        if (!EvaluateDependentExpr((*I)->getInit(), Info))
          return false;
      } else {
        FullExpressionRAII InitScope(Info);
        if (!EvaluateInPlace(Result, Info, This, (*I)->getInit()) ||
            !InitScope.destroy())
          return false;
      }
      return EvaluateStmt(Ret, Info, Definition->getBody()) != ESR_Failed;
    }
  
    // For a trivial copy or move constructor, perform an APValue copy. This is
    // essential for unions (or classes with anonymous union members), where the
    // operations performed by the constructor cannot be represented by
    // ctor-initializers.
    //
    // Skip this for empty non-union classes; we should not perform an
    // lvalue-to-rvalue conversion on them because their copy constructor does not
    // actually read them.
    if (Definition->isDefaulted() && Definition->isCopyOrMoveConstructor() &&
        (Definition->getParent()->isUnion() ||
         (Definition->isTrivial() &&
          isReadByLvalueToRvalueConversion(Definition->getParent())))) {
      return handleTrivialCopy(Info, Definition->getParamDecl(0), E, Result,
                               Definition->getParent()->isUnion());
    }
  
    // Reserve space for the struct members.
    if (!Result.hasValue()) {
      if (!RD->isUnion())
        Result = APValue(APValue::UninitStruct(), RD->getNumBases(),
                         std::distance(RD->field_begin(), RD->field_end()));
      else
        // A union starts with no active member.
        Result = APValue((const FieldDecl*)nullptr);
    }
  
    if (RD->isInvalidDecl()) return false;
    const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);
  
    // A scope for temporaries lifetime-extended by reference members.
    BlockScopeRAII LifetimeExtendedScope(Info);
  
    bool Success = true;
    unsigned BasesSeen = 0;
  #ifndef NDEBUG
    CXXRecordDecl::base_class_const_iterator BaseIt = RD->bases_begin();
  #endif
    CXXRecordDecl::field_iterator FieldIt = RD->field_begin();
    auto SkipToField = [&](FieldDecl *FD, bool Indirect) {
      // We might be initializing the same field again if this is an indirect
      // field initialization.
      if (FieldIt == RD->field_end() ||
          FieldIt->getFieldIndex() > FD->getFieldIndex()) {
        assert(Indirect && "fields out of order?");
        return;
      }
  
      // Default-initialize any fields with no explicit initializer.
      for (; !declaresSameEntity(*FieldIt, FD); ++FieldIt) {
        assert(FieldIt != RD->field_end() && "missing field?");
        if (!FieldIt->isUnnamedBitfield())
          Success &= getDefaultInitValue(
              FieldIt->getType(),
              Result.getStructField(FieldIt->getFieldIndex()));
      }
      ++FieldIt;
    };
    for (const auto *I : Definition->inits()) {
      LValue Subobject = This;
      LValue SubobjectParent = This;
      APValue *Value = &Result;
  
      // Determine the subobject to initialize.
      FieldDecl *FD = nullptr;
      if (I->isBaseInitializer()) {
        QualType BaseType(I->getBaseClass(), 0);
  #ifndef NDEBUG
        // Non-virtual base classes are initialized in the order in the class
        // definition. We have already checked for virtual base classes.
        assert(!BaseIt->isVirtual() && "virtual base for literal type");
        assert(Info.Ctx.hasSameType(BaseIt->getType(), BaseType) &&
               "base class initializers not in expected order");
        ++BaseIt;
  #endif
        if (!HandleLValueDirectBase(Info, I->getInit(), Subobject, RD,
                                    BaseType->getAsCXXRecordDecl(), &Layout))
          return false;
        Value = &Result.getStructBase(BasesSeen++);
      } else if ((FD = I->getMember())) {
        if (!HandleLValueMember(Info, I->getInit(), Subobject, FD, &Layout))
          return false;
        if (RD->isUnion()) {
          Result = APValue(FD);
          Value = &Result.getUnionValue();
        } else {
          SkipToField(FD, false);
          Value = &Result.getStructField(FD->getFieldIndex());
        }
      } else if (IndirectFieldDecl *IFD = I->getIndirectMember()) {
        // Walk the indirect field decl's chain to find the object to initialize,
        // and make sure we've initialized every step along it.
        auto IndirectFieldChain = IFD->chain();
        for (auto *C : IndirectFieldChain) {
          FD = cast<FieldDecl>(C);
          CXXRecordDecl *CD = cast<CXXRecordDecl>(FD->getParent());
          // Switch the union field if it differs. This happens if we had
          // preceding zero-initialization, and we're now initializing a union
          // subobject other than the first.
          // FIXME: In this case, the values of the other subobjects are
          // specified, since zero-initialization sets all padding bits to zero.
          if (!Value->hasValue() ||
              (Value->isUnion() && Value->getUnionField() != FD)) {
            if (CD->isUnion())
              *Value = APValue(FD);
            else
              // FIXME: This immediately starts the lifetime of all members of
              // an anonymous struct. It would be preferable to strictly start
              // member lifetime in initialization order.
              Success &= getDefaultInitValue(Info.Ctx.getRecordType(CD), *Value);
          }
          // Store Subobject as its parent before updating it for the last element
          // in the chain.
          if (C == IndirectFieldChain.back())
            SubobjectParent = Subobject;
          if (!HandleLValueMember(Info, I->getInit(), Subobject, FD))
            return false;
          if (CD->isUnion())
            Value = &Value->getUnionValue();
          else {
            if (C == IndirectFieldChain.front() && !RD->isUnion())
              SkipToField(FD, true);
            Value = &Value->getStructField(FD->getFieldIndex());
          }
        }
      } else {
        llvm_unreachable("unknown base initializer kind");
      }
  
      // Need to override This for implicit field initializers as in this case
      // This refers to innermost anonymous struct/union containing initializer,
      // not to currently constructed class.
      const Expr *Init = I->getInit();
      if (Init->isValueDependent()) {
        if (!EvaluateDependentExpr(Init, Info))
          return false;
      } else {
        ThisOverrideRAII ThisOverride(*Info.CurrentCall, &SubobjectParent,
                                      isa<CXXDefaultInitExpr>(Init));
        FullExpressionRAII InitScope(Info);
        if (!EvaluateInPlace(*Value, Info, Subobject, Init) ||
            (FD && FD->isBitField() &&
             !truncateBitfieldValue(Info, Init, *Value, FD))) {
          // If we're checking for a potential constant expression, evaluate all
          // initializers even if some of them fail.
          if (!Info.noteFailure())
            return false;
          Success = false;
        }
      }
  
      // This is the point at which the dynamic type of the object becomes this
      // class type.
      if (I->isBaseInitializer() && BasesSeen == RD->getNumBases())
        EvalObj.finishedConstructingBases();
    }
  
    // Default-initialize any remaining fields.
    if (!RD->isUnion()) {
      for (; FieldIt != RD->field_end(); ++FieldIt) {
        if (!FieldIt->isUnnamedBitfield())
          Success &= getDefaultInitValue(
              FieldIt->getType(),
              Result.getStructField(FieldIt->getFieldIndex()));
      }
    }
  
    EvalObj.finishedConstructingFields();
  
    return Success &&
           EvaluateStmt(Ret, Info, Definition->getBody()) != ESR_Failed &&
           LifetimeExtendedScope.destroy();
  }
  
  static bool HandleConstructorCall(const Expr *E, const LValue &This,
                                    ArrayRef<const Expr*> Args,
                                    const CXXConstructorDecl *Definition,
                                    EvalInfo &Info, APValue &Result) {
    CallScopeRAII CallScope(Info);
    CallRef Call = Info.CurrentCall->createCall(Definition);
    if (!EvaluateArgs(Args, Call, Info, Definition))
      return false;
  
    return HandleConstructorCall(E, This, Call, Definition, Info, Result) &&
           CallScope.destroy();
  }
  
  static bool HandleDestructionImpl(EvalInfo &Info, SourceLocation CallLoc,
                                    const LValue &This, APValue &Value,
                                    QualType T) {
    // Objects can only be destroyed while they're within their lifetimes.
    // FIXME: We have no representation for whether an object of type nullptr_t
    // is in its lifetime; it usually doesn't matter. Perhaps we should model it
    // as indeterminate instead?
    if (Value.isAbsent() && !T->isNullPtrType()) {
      APValue Printable;
      This.moveInto(Printable);
      Info.FFDiag(CallLoc, diag::note_constexpr_destroy_out_of_lifetime)
        << Printable.getAsString(Info.Ctx, Info.Ctx.getLValueReferenceType(T));
      return false;
    }
  
    // Invent an expression for location purposes.
    // FIXME: We shouldn't need to do this.
    OpaqueValueExpr LocE(CallLoc, Info.Ctx.IntTy, VK_RValue);
  
    // For arrays, destroy elements right-to-left.
    if (const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(T)) {
      uint64_t Size = CAT->getSize().getZExtValue();
      QualType ElemT = CAT->getElementType();
  
      LValue ElemLV = This;
      ElemLV.addArray(Info, &LocE, CAT);
      if (!HandleLValueArrayAdjustment(Info, &LocE, ElemLV, ElemT, Size))
        return false;
  
      // Ensure that we have actual array elements available to destroy; the
      // destructors might mutate the value, so we can't run them on the array
      // filler.
      if (Size && Size > Value.getArrayInitializedElts())
        expandArray(Value, Value.getArraySize() - 1);
  
      for (; Size != 0; --Size) {
        APValue &Elem = Value.getArrayInitializedElt(Size - 1);
        if (!HandleLValueArrayAdjustment(Info, &LocE, ElemLV, ElemT, -1) ||
            !HandleDestructionImpl(Info, CallLoc, ElemLV, Elem, ElemT))
          return false;
      }
  
      // End the lifetime of this array now.
      Value = APValue();
      return true;
    }
  
    const CXXRecordDecl *RD = T->getAsCXXRecordDecl();
    if (!RD) {
      if (T.isDestructedType()) {
        Info.FFDiag(CallLoc, diag::note_constexpr_unsupported_destruction) << T;
        return false;
      }
  
      Value = APValue();
      return true;
    }
  
    if (RD->getNumVBases()) {
      Info.FFDiag(CallLoc, diag::note_constexpr_virtual_base) << RD;
      return false;
    }
  
    const CXXDestructorDecl *DD = RD->getDestructor();
    if (!DD && !RD->hasTrivialDestructor()) {
      Info.FFDiag(CallLoc);
      return false;
    }
  
    if (!DD || DD->isTrivial() ||
        (RD->isAnonymousStructOrUnion() && RD->isUnion())) {
      // A trivial destructor just ends the lifetime of the object. Check for
      // this case before checking for a body, because we might not bother
      // building a body for a trivial destructor. Note that it doesn't matter
      // whether the destructor is constexpr in this case; all trivial
      // destructors are constexpr.
      //
      // If an anonymous union would be destroyed, some enclosing destructor must
      // have been explicitly defined, and the anonymous union destruction should
      // have no effect.
      Value = APValue();
      return true;
    }
  
    if (!Info.CheckCallLimit(CallLoc))
      return false;
  
    const FunctionDecl *Definition = nullptr;
    const Stmt *Body = DD->getBody(Definition);
  
    if (!CheckConstexprFunction(Info, CallLoc, DD, Definition, Body))
      return false;
  
    CallStackFrame Frame(Info, CallLoc, Definition, &This, CallRef());
  
    // We're now in the period of destruction of this object.
    unsigned BasesLeft = RD->getNumBases();
    EvalInfo::EvaluatingDestructorRAII EvalObj(
        Info,
        ObjectUnderConstruction{This.getLValueBase(), This.Designator.Entries});
    if (!EvalObj.DidInsert) {
      // C++2a [class.dtor]p19:
      //   the behavior is undefined if the destructor is invoked for an object
      //   whose lifetime has ended
      // (Note that formally the lifetime ends when the period of destruction
      // begins, even though certain uses of the object remain valid until the
      // period of destruction ends.)
      Info.FFDiag(CallLoc, diag::note_constexpr_double_destroy);
      return false;
    }
  
    // FIXME: Creating an APValue just to hold a nonexistent return value is
    // wasteful.
    APValue RetVal;
    StmtResult Ret = {RetVal, nullptr};
    if (EvaluateStmt(Ret, Info, Definition->getBody()) == ESR_Failed)
      return false;
  
    // A union destructor does not implicitly destroy its members.
    if (RD->isUnion())
      return true;
  
    const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);
  
    // We don't have a good way to iterate fields in reverse, so collect all the
    // fields first and then walk them backwards.
    SmallVector<FieldDecl*, 16> Fields(RD->field_begin(), RD->field_end());
    for (const FieldDecl *FD : llvm::reverse(Fields)) {
      if (FD->isUnnamedBitfield())
        continue;
  
      LValue Subobject = This;
      if (!HandleLValueMember(Info, &LocE, Subobject, FD, &Layout))
        return false;
  
      APValue *SubobjectValue = &Value.getStructField(FD->getFieldIndex());
      if (!HandleDestructionImpl(Info, CallLoc, Subobject, *SubobjectValue,
                                 FD->getType()))
        return false;
    }
  
    if (BasesLeft != 0)
      EvalObj.startedDestroyingBases();
  
    // Destroy base classes in reverse order.
    for (const CXXBaseSpecifier &Base : llvm::reverse(RD->bases())) {
      --BasesLeft;
  
      QualType BaseType = Base.getType();
      LValue Subobject = This;
      if (!HandleLValueDirectBase(Info, &LocE, Subobject, RD,
                                  BaseType->getAsCXXRecordDecl(), &Layout))
        return false;
  
      APValue *SubobjectValue = &Value.getStructBase(BasesLeft);
      if (!HandleDestructionImpl(Info, CallLoc, Subobject, *SubobjectValue,
                                 BaseType))
        return false;
    }
    assert(BasesLeft == 0 && "NumBases was wrong?");
  
    // The period of destruction ends now. The object is gone.
    Value = APValue();
    return true;
  }
  
  namespace {
  struct DestroyObjectHandler {
    EvalInfo &Info;
    const Expr *E;
    const LValue &This;
    const AccessKinds AccessKind;
  
    typedef bool result_type;
    bool failed() { return false; }
    bool found(APValue &Subobj, QualType SubobjType) {
      return HandleDestructionImpl(Info, E->getExprLoc(), This, Subobj,
                                   SubobjType);
    }
    bool found(APSInt &Value, QualType SubobjType) {
      Info.FFDiag(E, diag::note_constexpr_destroy_complex_elem);
      return false;
    }
    bool found(APFloat &Value, QualType SubobjType) {
      Info.FFDiag(E, diag::note_constexpr_destroy_complex_elem);
      return false;
    }
  };
  }
  
  /// Perform a destructor or pseudo-destructor call on the given object, which
  /// might in general not be a complete object.
  static bool HandleDestruction(EvalInfo &Info, const Expr *E,
                                const LValue &This, QualType ThisType) {
    CompleteObject Obj = findCompleteObject(Info, E, AK_Destroy, This, ThisType);
    DestroyObjectHandler Handler = {Info, E, This, AK_Destroy};
    return Obj && findSubobject(Info, E, Obj, This.Designator, Handler);
  }
  
  /// Destroy and end the lifetime of the given complete object.
  static bool HandleDestruction(EvalInfo &Info, SourceLocation Loc,
                                APValue::LValueBase LVBase, APValue &Value,
                                QualType T) {
    // If we've had an unmodeled side-effect, we can't rely on mutable state
    // (such as the object we're about to destroy) being correct.
    if (Info.EvalStatus.HasSideEffects)
      return false;
  
    LValue LV;
    LV.set({LVBase});
    return HandleDestructionImpl(Info, Loc, LV, Value, T);
  }
  
  /// Perform a call to 'perator new' or to `__builtin_operator_new'.
  static bool HandleOperatorNewCall(EvalInfo &Info, const CallExpr *E,
                                    LValue &Result) {
    if (Info.checkingPotentialConstantExpression() ||
        Info.SpeculativeEvaluationDepth)
      return false;
  
    // This is permitted only within a call to std::allocator<T>::allocate.
    auto Caller = Info.getStdAllocatorCaller("allocate");
    if (!Caller) {
      Info.FFDiag(E->getExprLoc(), Info.getLangOpts().CPlusPlus20
                                       ? diag::note_constexpr_new_untyped
                                       : diag::note_constexpr_new);
      return false;
    }
  
    QualType ElemType = Caller.ElemType;
    if (ElemType->isIncompleteType() || ElemType->isFunctionType()) {
      Info.FFDiag(E->getExprLoc(),
                  diag::note_constexpr_new_not_complete_object_type)
          << (ElemType->isIncompleteType() ? 0 : 1) << ElemType;
      return false;
    }
  
    APSInt ByteSize;
    if (!EvaluateInteger(E->getArg(0), ByteSize, Info))
      return false;
    bool IsNothrow = false;
    for (unsigned I = 1, N = E->getNumArgs(); I != N; ++I) {
      EvaluateIgnoredValue(Info, E->getArg(I));
      IsNothrow |= E->getType()->isNothrowT();
    }
  
    CharUnits ElemSize;
    if (!HandleSizeof(Info, E->getExprLoc(), ElemType, ElemSize))
      return false;
    APInt Size, Remainder;
    APInt ElemSizeAP(ByteSize.getBitWidth(), ElemSize.getQuantity());
    APInt::udivrem(ByteSize, ElemSizeAP, Size, Remainder);
    if (Remainder != 0) {
      // This likely indicates a bug in the implementation of 'std::allocator'.
      Info.FFDiag(E->getExprLoc(), diag::note_constexpr_operator_new_bad_size)
          << ByteSize << APSInt(ElemSizeAP, true) << ElemType;
      return false;
    }
  
    if (ByteSize.getActiveBits() > ConstantArrayType::getMaxSizeBits(Info.Ctx)) {
      if (IsNothrow) {
        Result.setNull(Info.Ctx, E->getType());
        return true;
      }
  
      Info.FFDiag(E, diag::note_constexpr_new_too_large) << APSInt(Size, true);
      return false;
    }
  
    QualType AllocType = Info.Ctx.getConstantArrayType(ElemType, Size, nullptr,
                                                       ArrayType::Normal, 0);
    APValue *Val = Info.createHeapAlloc(E, AllocType, Result);
    *Val = APValue(APValue::UninitArray(), 0, Size.getZExtValue());
    Result.addArray(Info, E, cast<ConstantArrayType>(AllocType));
    return true;
  }
  
  static bool hasVirtualDestructor(QualType T) {
    if (CXXRecordDecl *RD = T->getAsCXXRecordDecl())
      if (CXXDestructorDecl *DD = RD->getDestructor())
        return DD->isVirtual();
    return false;
  }
  
  static const FunctionDecl *getVirtualOperatorDelete(QualType T) {
    if (CXXRecordDecl *RD = T->getAsCXXRecordDecl())
      if (CXXDestructorDecl *DD = RD->getDestructor())
        return DD->isVirtual() ? DD->getOperatorDelete() : nullptr;
    return nullptr;
  }
  
  /// Check that the given object is a suitable pointer to a heap allocation that
  /// still exists and is of the right kind for the purpose of a deletion.
  ///
  /// On success, returns the heap allocation to deallocate. On failure, produces
  /// a diagnostic and returns None.
  static Optional<DynAlloc *> CheckDeleteKind(EvalInfo &Info, const Expr *E,
                                              const LValue &Pointer,
                                              DynAlloc::Kind DeallocKind) {
    auto PointerAsString = [&] {
      return Pointer.toString(Info.Ctx, Info.Ctx.VoidPtrTy);
    };
  
    DynamicAllocLValue DA = Pointer.Base.dyn_cast<DynamicAllocLValue>();
    if (!DA) {
      Info.FFDiag(E, diag::note_constexpr_delete_not_heap_alloc)
          << PointerAsString();
      if (Pointer.Base)
        NoteLValueLocation(Info, Pointer.Base);
      return None;
    }
  
    Optional<DynAlloc *> Alloc = Info.lookupDynamicAlloc(DA);
    if (!Alloc) {
      Info.FFDiag(E, diag::note_constexpr_double_delete);
      return None;
    }
  
    QualType AllocType = Pointer.Base.getDynamicAllocType();
    if (DeallocKind != (*Alloc)->getKind()) {
      Info.FFDiag(E, diag::note_constexpr_new_delete_mismatch)
          << DeallocKind << (*Alloc)->getKind() << AllocType;
      NoteLValueLocation(Info, Pointer.Base);
      return None;
    }
  
    bool Subobject = false;
    if (DeallocKind == DynAlloc::New) {
      Subobject = Pointer.Designator.MostDerivedPathLength != 0 ||
                  Pointer.Designator.isOnePastTheEnd();
    } else {
      Subobject = Pointer.Designator.Entries.size() != 1 ||
                  Pointer.Designator.Entries[0].getAsArrayIndex() != 0;
    }
    if (Subobject) {
      Info.FFDiag(E, diag::note_constexpr_delete_subobject)
          << PointerAsString() << Pointer.Designator.isOnePastTheEnd();
      return None;
    }
  
    return Alloc;
  }
  
  // Perform a call to 'operator delete' or '__builtin_operator_delete'.
  bool HandleOperatorDeleteCall(EvalInfo &Info, const CallExpr *E) {
    if (Info.checkingPotentialConstantExpression() ||
        Info.SpeculativeEvaluationDepth)
      return false;
  
    // This is permitted only within a call to std::allocator<T>::deallocate.
    if (!Info.getStdAllocatorCaller("deallocate")) {
      Info.FFDiag(E->getExprLoc());
      return true;
    }
  
    LValue Pointer;
    if (!EvaluatePointer(E->getArg(0), Pointer, Info))
      return false;
    for (unsigned I = 1, N = E->getNumArgs(); I != N; ++I)
      EvaluateIgnoredValue(Info, E->getArg(I));
  
    if (Pointer.Designator.Invalid)
      return false;
  
    // Deleting a null pointer has no effect.
    if (Pointer.isNullPointer())
      return true;
  
    if (!CheckDeleteKind(Info, E, Pointer, DynAlloc::StdAllocator))
      return false;
  
    Info.HeapAllocs.erase(Pointer.Base.get<DynamicAllocLValue>());
    return true;
  }
  
  //===----------------------------------------------------------------------===//
  // Generic Evaluation
  //===----------------------------------------------------------------------===//
  namespace {
  
  class BitCastBuffer {
    // FIXME: We're going to need bit-level granularity when we support
    // bit-fields.
    // FIXME: Its possible under the C++ standard for 'char' to not be 8 bits, but
    // we don't support a host or target where that is the case. Still, we should
    // use a more generic type in case we ever do.
    SmallVector<Optional<unsigned char>, 32> Bytes;
  
    static_assert(std::numeric_limits<unsigned char>::digits >= 8,
                  "Need at least 8 bit unsigned char");
  
    bool TargetIsLittleEndian;
  
  public:
    BitCastBuffer(CharUnits Width, bool TargetIsLittleEndian)
        : Bytes(Width.getQuantity()),
          TargetIsLittleEndian(TargetIsLittleEndian) {}
  
    LLVM_NODISCARD
    bool readObject(CharUnits Offset, CharUnits Width,
                    SmallVectorImpl<unsigned char> &Output) const {
      for (CharUnits I = Offset, E = Offset + Width; I != E; ++I) {
        // If a byte of an integer is uninitialized, then the whole integer is
        // uninitalized.
        if (!Bytes[I.getQuantity()])
          return false;
        Output.push_back(*Bytes[I.getQuantity()]);
      }
      if (llvm::sys::IsLittleEndianHost != TargetIsLittleEndian)
        std::reverse(Output.begin(), Output.end());
      return true;
    }
  
    void writeObject(CharUnits Offset, SmallVectorImpl<unsigned char> &Input) {
      if (llvm::sys::IsLittleEndianHost != TargetIsLittleEndian)
        std::reverse(Input.begin(), Input.end());
  
      size_t Index = 0;
      for (unsigned char Byte : Input) {
        assert(!Bytes[Offset.getQuantity() + Index] && "overwriting a byte?");
        Bytes[Offset.getQuantity() + Index] = Byte;
        ++Index;
      }
    }
  
    size_t size() { return Bytes.size(); }
  };
  
  /// Traverse an APValue to produce an BitCastBuffer, emulating how the current
  /// target would represent the value at runtime.
  class APValueToBufferConverter {
    EvalInfo &Info;
    BitCastBuffer Buffer;
    const CastExpr *BCE;
  
    APValueToBufferConverter(EvalInfo &Info, CharUnits ObjectWidth,
                             const CastExpr *BCE)
        : Info(Info),
          Buffer(ObjectWidth, Info.Ctx.getTargetInfo().isLittleEndian()),
          BCE(BCE) {}
  
    bool visit(const APValue &Val, QualType Ty) {
      return visit(Val, Ty, CharUnits::fromQuantity(0));
    }
  
    // Write out Val with type Ty into Buffer starting at Offset.
    bool visit(const APValue &Val, QualType Ty, CharUnits Offset) {
      assert((size_t)Offset.getQuantity() <= Buffer.size());
  
      // As a special case, nullptr_t has an indeterminate value.
      if (Ty->isNullPtrType())
        return true;
  
      // Dig through Src to find the byte at SrcOffset.
      switch (Val.getKind()) {
      case APValue::Indeterminate:
      case APValue::None:
        return true;
  
      case APValue::Int:
        return visitInt(Val.getInt(), Ty, Offset);
      case APValue::Float:
        return visitFloat(Val.getFloat(), Ty, Offset);
      case APValue::Array:
        return visitArray(Val, Ty, Offset);
      case APValue::Struct:
        return visitRecord(Val, Ty, Offset);
  
      case APValue::ComplexInt:
      case APValue::ComplexFloat:
      case APValue::Vector:
      case APValue::FixedPoint:
        // FIXME: We should support these.
  
      case APValue::Union:
      case APValue::MemberPointer:
      case APValue::AddrLabelDiff: {
        Info.FFDiag(BCE->getBeginLoc(),
                    diag::note_constexpr_bit_cast_unsupported_type)
            << Ty;
        return false;
      }
  
      case APValue::LValue:
        llvm_unreachable("LValue subobject in bit_cast?");
      }
      llvm_unreachable("Unhandled APValue::ValueKind");
    }
  
    bool visitRecord(const APValue &Val, QualType Ty, CharUnits Offset) {
      const RecordDecl *RD = Ty->getAsRecordDecl();
      const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);
  
      // Visit the base classes.
      if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
        for (size_t I = 0, E = CXXRD->getNumBases(); I != E; ++I) {
          const CXXBaseSpecifier &BS = CXXRD->bases_begin()[I];
          CXXRecordDecl *BaseDecl = BS.getType()->getAsCXXRecordDecl();
  
          if (!visitRecord(Val.getStructBase(I), BS.getType(),
                           Layout.getBaseClassOffset(BaseDecl) + Offset))
            return false;
        }
      }
  
      // Visit the fields.
      unsigned FieldIdx = 0;
      for (FieldDecl *FD : RD->fields()) {
        if (FD->isBitField()) {
          Info.FFDiag(BCE->getBeginLoc(),
                      diag::note_constexpr_bit_cast_unsupported_bitfield);
          return false;
        }
  
        uint64_t FieldOffsetBits = Layout.getFieldOffset(FieldIdx);
  
        assert(FieldOffsetBits % Info.Ctx.getCharWidth() == 0 &&
               "only bit-fields can have sub-char alignment");
        CharUnits FieldOffset =
            Info.Ctx.toCharUnitsFromBits(FieldOffsetBits) + Offset;
        QualType FieldTy = FD->getType();
        if (!visit(Val.getStructField(FieldIdx), FieldTy, FieldOffset))
          return false;
        ++FieldIdx;
      }
  
      return true;
    }
  
    bool visitArray(const APValue &Val, QualType Ty, CharUnits Offset) {
      const auto *CAT =
          dyn_cast_or_null<ConstantArrayType>(Ty->getAsArrayTypeUnsafe());
      if (!CAT)
        return false;
  
      CharUnits ElemWidth = Info.Ctx.getTypeSizeInChars(CAT->getElementType());
      unsigned NumInitializedElts = Val.getArrayInitializedElts();
      unsigned ArraySize = Val.getArraySize();
      // First, initialize the initialized elements.
      for (unsigned I = 0; I != NumInitializedElts; ++I) {
        const APValue &SubObj = Val.getArrayInitializedElt(I);
        if (!visit(SubObj, CAT->getElementType(), Offset + I * ElemWidth))
          return false;
      }
  
      // Next, initialize the rest of the array using the filler.
      if (Val.hasArrayFiller()) {
        const APValue &Filler = Val.getArrayFiller();
        for (unsigned I = NumInitializedElts; I != ArraySize; ++I) {
          if (!visit(Filler, CAT->getElementType(), Offset + I * ElemWidth))
            return false;
        }
      }
  
      return true;
    }
  
    bool visitInt(const APSInt &Val, QualType Ty, CharUnits Offset) {
      APSInt AdjustedVal = Val;
      unsigned Width = AdjustedVal.getBitWidth();
      if (Ty->isBooleanType()) {
        Width = Info.Ctx.getTypeSize(Ty);
        AdjustedVal = AdjustedVal.extend(Width);
      }
  
      SmallVector<unsigned char, 8> Bytes(Width / 8);
      llvm::StoreIntToMemory(AdjustedVal, &*Bytes.begin(), Width / 8);
      Buffer.writeObject(Offset, Bytes);
      return true;
    }
  
    bool visitFloat(const APFloat &Val, QualType Ty, CharUnits Offset) {
      APSInt AsInt(Val.bitcastToAPInt());
      return visitInt(AsInt, Ty, Offset);
    }
  
  public:
    static Optional<BitCastBuffer> convert(EvalInfo &Info, const APValue &Src,
                                           const CastExpr *BCE) {
      CharUnits DstSize = Info.Ctx.getTypeSizeInChars(BCE->getType());
      APValueToBufferConverter Converter(Info, DstSize, BCE);
      if (!Converter.visit(Src, BCE->getSubExpr()->getType()))
        return None;
      return Converter.Buffer;
    }
  };
  
  /// Write an BitCastBuffer into an APValue.
  class BufferToAPValueConverter {
    EvalInfo &Info;
    const BitCastBuffer &Buffer;
    const CastExpr *BCE;
  
    BufferToAPValueConverter(EvalInfo &Info, const BitCastBuffer &Buffer,
                             const CastExpr *BCE)
        : Info(Info), Buffer(Buffer), BCE(BCE) {}
  
    // Emit an unsupported bit_cast type error. Sema refuses to build a bit_cast
    // with an invalid type, so anything left is a deficiency on our part (FIXME).
    // Ideally this will be unreachable.
    llvm::NoneType unsupportedType(QualType Ty) {
      Info.FFDiag(BCE->getBeginLoc(),
                  diag::note_constexpr_bit_cast_unsupported_type)
          << Ty;
      return None;
    }
  
    llvm::NoneType unrepresentableValue(QualType Ty, const APSInt &Val) {
      Info.FFDiag(BCE->getBeginLoc(),
                  diag::note_constexpr_bit_cast_unrepresentable_value)
          << Ty << Val.toString(/*Radix=*/10);
      return None;
    }
  
    Optional<APValue> visit(const BuiltinType *T, CharUnits Offset,
                            const EnumType *EnumSugar = nullptr) {
      if (T->isNullPtrType()) {
        uint64_t NullValue = Info.Ctx.getTargetNullPointerValue(QualType(T, 0));
        return APValue((Expr *)nullptr,
                       /*Offset=*/CharUnits::fromQuantity(NullValue),
                       APValue::NoLValuePath{}, /*IsNullPtr=*/true);
      }
  
      CharUnits SizeOf = Info.Ctx.getTypeSizeInChars(T);
  
      // Work around floating point types that contain unused padding bytes. This
      // is really just `long double` on x86, which is the only fundamental type
      // with padding bytes.
      if (T->isRealFloatingType()) {
        const llvm::fltSemantics &Semantics =
            Info.Ctx.getFloatTypeSemantics(QualType(T, 0));
        unsigned NumBits = llvm::APFloatBase::getSizeInBits(Semantics);
        assert(NumBits % 8 == 0);
        CharUnits NumBytes = CharUnits::fromQuantity(NumBits / 8);
        if (NumBytes != SizeOf)
          SizeOf = NumBytes;
      }
  
      SmallVector<uint8_t, 8> Bytes;
      if (!Buffer.readObject(Offset, SizeOf, Bytes)) {
        // If this is std::byte or unsigned char, then its okay to store an
        // indeterminate value.
        bool IsStdByte = EnumSugar && EnumSugar->isStdByteType();
        bool IsUChar =
            !EnumSugar && (T->isSpecificBuiltinType(BuiltinType::UChar) ||
                           T->isSpecificBuiltinType(BuiltinType::Char_U));
        if (!IsStdByte && !IsUChar) {
          QualType DisplayType(EnumSugar ? (const Type *)EnumSugar : T, 0);
          Info.FFDiag(BCE->getExprLoc(),
                      diag::note_constexpr_bit_cast_indet_dest)
              << DisplayType << Info.Ctx.getLangOpts().CharIsSigned;
          return None;
        }
  
        return APValue::IndeterminateValue();
      }
  
      APSInt Val(SizeOf.getQuantity() * Info.Ctx.getCharWidth(), true);
      llvm::LoadIntFromMemory(Val, &*Bytes.begin(), Bytes.size());
  
      if (T->isIntegralOrEnumerationType()) {
        Val.setIsSigned(T->isSignedIntegerOrEnumerationType());
  
        unsigned IntWidth = Info.Ctx.getIntWidth(QualType(T, 0));
        if (IntWidth != Val.getBitWidth()) {
          APSInt Truncated = Val.trunc(IntWidth);
          if (Truncated.extend(Val.getBitWidth()) != Val)
            return unrepresentableValue(QualType(T, 0), Val);
          Val = Truncated;
        }
  
        return APValue(Val);
      }
  
      if (T->isRealFloatingType()) {
        const llvm::fltSemantics &Semantics =
            Info.Ctx.getFloatTypeSemantics(QualType(T, 0));
        return APValue(APFloat(Semantics, Val));
      }
  
      return unsupportedType(QualType(T, 0));
    }
  
    Optional<APValue> visit(const RecordType *RTy, CharUnits Offset) {
      const RecordDecl *RD = RTy->getAsRecordDecl();
      const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);
  
      unsigned NumBases = 0;
      if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RD))
        NumBases = CXXRD->getNumBases();
  
      APValue ResultVal(APValue::UninitStruct(), NumBases,
                        std::distance(RD->field_begin(), RD->field_end()));
  
      // Visit the base classes.
      if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
        for (size_t I = 0, E = CXXRD->getNumBases(); I != E; ++I) {
          const CXXBaseSpecifier &BS = CXXRD->bases_begin()[I];
          CXXRecordDecl *BaseDecl = BS.getType()->getAsCXXRecordDecl();
          if (BaseDecl->isEmpty() ||
              Info.Ctx.getASTRecordLayout(BaseDecl).getNonVirtualSize().isZero())
            continue;
  
          Optional<APValue> SubObj = visitType(
              BS.getType(), Layout.getBaseClassOffset(BaseDecl) + Offset);
          if (!SubObj)
            return None;
          ResultVal.getStructBase(I) = *SubObj;
        }
      }
  
      // Visit the fields.
      unsigned FieldIdx = 0;
      for (FieldDecl *FD : RD->fields()) {
        // FIXME: We don't currently support bit-fields. A lot of the logic for
        // this is in CodeGen, so we need to factor it around.
        if (FD->isBitField()) {
          Info.FFDiag(BCE->getBeginLoc(),
                      diag::note_constexpr_bit_cast_unsupported_bitfield);
          return None;
        }
  
        uint64_t FieldOffsetBits = Layout.getFieldOffset(FieldIdx);
        assert(FieldOffsetBits % Info.Ctx.getCharWidth() == 0);
  
        CharUnits FieldOffset =
            CharUnits::fromQuantity(FieldOffsetBits / Info.Ctx.getCharWidth()) +
            Offset;
        QualType FieldTy = FD->getType();
        Optional<APValue> SubObj = visitType(FieldTy, FieldOffset);
        if (!SubObj)
          return None;
        ResultVal.getStructField(FieldIdx) = *SubObj;
        ++FieldIdx;
      }
  
      return ResultVal;
    }
  
    Optional<APValue> visit(const EnumType *Ty, CharUnits Offset) {
      QualType RepresentationType = Ty->getDecl()->getIntegerType();
      assert(!RepresentationType.isNull() &&
             "enum forward decl should be caught by Sema");
      const auto *AsBuiltin =
          RepresentationType.getCanonicalType()->castAs<BuiltinType>();
      // Recurse into the underlying type. Treat std::byte transparently as
      // unsigned char.
      return visit(AsBuiltin, Offset, /*EnumTy=*/Ty);
    }
  
    Optional<APValue> visit(const ConstantArrayType *Ty, CharUnits Offset) {
      size_t Size = Ty->getSize().getLimitedValue();
      CharUnits ElementWidth = Info.Ctx.getTypeSizeInChars(Ty->getElementType());
  
      APValue ArrayValue(APValue::UninitArray(), Size, Size);
      for (size_t I = 0; I != Size; ++I) {
        Optional<APValue> ElementValue =
            visitType(Ty->getElementType(), Offset + I * ElementWidth);
        if (!ElementValue)
          return None;
        ArrayValue.getArrayInitializedElt(I) = std::move(*ElementValue);
      }
  
      return ArrayValue;
    }
  
    Optional<APValue> visit(const Type *Ty, CharUnits Offset) {
      return unsupportedType(QualType(Ty, 0));
    }
  
    Optional<APValue> visitType(QualType Ty, CharUnits Offset) {
      QualType Can = Ty.getCanonicalType();
  
      switch (Can->getTypeClass()) {
  #define TYPE(Class, Base)                                                      \
    case Type::Class:                                                            \
      return visit(cast<Class##Type>(Can.getTypePtr()), Offset);
  #define ABSTRACT_TYPE(Class, Base)
  #define NON_CANONICAL_TYPE(Class, Base)                                        \
    case Type::Class:                                                            \
      llvm_unreachable("non-canonical type should be impossible!");
  #define DEPENDENT_TYPE(Class, Base)                                            \
    case Type::Class:                                                            \
      llvm_unreachable(                                                          \
          "dependent types aren't supported in the constant evaluator!");
  #define NON_CANONICAL_UNLESS_DEPENDENT(Class, Base)                            \
    case Type::Class:                                                            \
      llvm_unreachable("either dependent or not canonical!");
  #include "clang/AST/TypeNodes.inc"
      }
      llvm_unreachable("Unhandled Type::TypeClass");
    }
  
  public:
    // Pull out a full value of type DstType.
    static Optional<APValue> convert(EvalInfo &Info, BitCastBuffer &Buffer,
                                     const CastExpr *BCE) {
      BufferToAPValueConverter Converter(Info, Buffer, BCE);
      return Converter.visitType(BCE->getType(), CharUnits::fromQuantity(0));
    }
  };
  
  static bool checkBitCastConstexprEligibilityType(SourceLocation Loc,
                                                   QualType Ty, EvalInfo *Info,
                                                   const ASTContext &Ctx,
                                                   bool CheckingDest) {
    Ty = Ty.getCanonicalType();
  
    auto diag = [&](int Reason) {
      if (Info)
        Info->FFDiag(Loc, diag::note_constexpr_bit_cast_invalid_type)
            << CheckingDest << (Reason == 4) << Reason;
      return false;
    };
    auto note = [&](int Construct, QualType NoteTy, SourceLocation NoteLoc) {
      if (Info)
        Info->Note(NoteLoc, diag::note_constexpr_bit_cast_invalid_subtype)
            << NoteTy << Construct << Ty;
      return false;
    };
  
    if (Ty->isUnionType())
      return diag(0);
    if (Ty->isPointerType())
      return diag(1);
    if (Ty->isMemberPointerType())
      return diag(2);
    if (Ty.isVolatileQualified())
      return diag(3);
  
    if (RecordDecl *Record = Ty->getAsRecordDecl()) {
      if (auto *CXXRD = dyn_cast<CXXRecordDecl>(Record)) {
        for (CXXBaseSpecifier &BS : CXXRD->bases())
          if (!checkBitCastConstexprEligibilityType(Loc, BS.getType(), Info, Ctx,
                                                    CheckingDest))
            return note(1, BS.getType(), BS.getBeginLoc());
      }
      for (FieldDecl *FD : Record->fields()) {
        if (FD->getType()->isReferenceType())
          return diag(4);
        if (!checkBitCastConstexprEligibilityType(Loc, FD->getType(), Info, Ctx,
                                                  CheckingDest))
          return note(0, FD->getType(), FD->getBeginLoc());
      }
    }
  
    if (Ty->isArrayType() &&
        !checkBitCastConstexprEligibilityType(Loc, Ctx.getBaseElementType(Ty),
                                              Info, Ctx, CheckingDest))
      return false;
  
    return true;
  }
  
  static bool checkBitCastConstexprEligibility(EvalInfo *Info,
                                               const ASTContext &Ctx,
                                               const CastExpr *BCE) {
    bool DestOK = checkBitCastConstexprEligibilityType(
        BCE->getBeginLoc(), BCE->getType(), Info, Ctx, true);
    bool SourceOK = DestOK && checkBitCastConstexprEligibilityType(
                                  BCE->getBeginLoc(),
                                  BCE->getSubExpr()->getType(), Info, Ctx, false);
    return SourceOK;
  }
  
  static bool handleLValueToRValueBitCast(EvalInfo &Info, APValue &DestValue,
                                          APValue &SourceValue,
                                          const CastExpr *BCE) {
    assert(CHAR_BIT == 8 && Info.Ctx.getTargetInfo().getCharWidth() == 8 &&
           "no host or target supports non 8-bit chars");
    assert(SourceValue.isLValue() &&
           "LValueToRValueBitcast requires an lvalue operand!");
  
    if (!checkBitCastConstexprEligibility(&Info, Info.Ctx, BCE))
      return false;
  
    LValue SourceLValue;
    APValue SourceRValue;
    SourceLValue.setFrom(Info.Ctx, SourceValue);
    if (!handleLValueToRValueConversion(
            Info, BCE, BCE->getSubExpr()->getType().withConst(), SourceLValue,
            SourceRValue, /*WantObjectRepresentation=*/true))
      return false;
  
    // Read out SourceValue into a char buffer.
    Optional<BitCastBuffer> Buffer =
        APValueToBufferConverter::convert(Info, SourceRValue, BCE);
    if (!Buffer)
      return false;
  
    // Write out the buffer into a new APValue.
    Optional<APValue> MaybeDestValue =
        BufferToAPValueConverter::convert(Info, *Buffer, BCE);
    if (!MaybeDestValue)
      return false;
  
    DestValue = std::move(*MaybeDestValue);
    return true;
  }
  
  template <class Derived>
  class ExprEvaluatorBase
    : public ConstStmtVisitor<Derived, bool> {
  private:
    Derived &getDerived() { return static_cast<Derived&>(*this); }
    bool DerivedSuccess(const APValue &V, const Expr *E) {
      return getDerived().Success(V, E);
    }
    bool DerivedZeroInitialization(const Expr *E) {
      return getDerived().ZeroInitialization(E);
    }
  
    // Check whether a conditional operator with a non-constant condition is a
    // potential constant expression. If neither arm is a potential constant
    // expression, then the conditional operator is not either.
    template<typename ConditionalOperator>
    void CheckPotentialConstantConditional(const ConditionalOperator *E) {
      assert(Info.checkingPotentialConstantExpression());
  
      // Speculatively evaluate both arms.
      SmallVector<PartialDiagnosticAt, 8> Diag;
      {
        SpeculativeEvaluationRAII Speculate(Info, &Diag);
        StmtVisitorTy::Visit(E->getFalseExpr());
        if (Diag.empty())
          return;
      }
  
      {
        SpeculativeEvaluationRAII Speculate(Info, &Diag);
        Diag.clear();
        StmtVisitorTy::Visit(E->getTrueExpr());
        if (Diag.empty())
          return;
      }
  
      Error(E, diag::note_constexpr_conditional_never_const);
    }
  
  
    template<typename ConditionalOperator>
    bool HandleConditionalOperator(const ConditionalOperator *E) {
      bool BoolResult;
      if (!EvaluateAsBooleanCondition(E->getCond(), BoolResult, Info)) {
        if (Info.checkingPotentialConstantExpression() && Info.noteFailure()) {
          CheckPotentialConstantConditional(E);
          return false;
        }
        if (Info.noteFailure()) {
          StmtVisitorTy::Visit(E->getTrueExpr());
          StmtVisitorTy::Visit(E->getFalseExpr());
        }
        return false;
      }
  
      Expr *EvalExpr = BoolResult ? E->getTrueExpr() : E->getFalseExpr();
      return StmtVisitorTy::Visit(EvalExpr);
    }
  
  protected:
    EvalInfo &Info;
    typedef ConstStmtVisitor<Derived, bool> StmtVisitorTy;
    typedef ExprEvaluatorBase ExprEvaluatorBaseTy;
  
    OptionalDiagnostic CCEDiag(const Expr *E, diag::kind D) {
      return Info.CCEDiag(E, D);
    }
  
    bool ZeroInitialization(const Expr *E) { return Error(E); }
  
  public:
    ExprEvaluatorBase(EvalInfo &Info) : Info(Info) {}
  
    EvalInfo &getEvalInfo() { return Info; }
  
    /// Report an evaluation error. This should only be called when an error is
    /// first discovered. When propagating an error, just return false.
    bool Error(const Expr *E, diag::kind D) {
      Info.FFDiag(E, D);
      return false;
    }
    bool Error(const Expr *E) {
      return Error(E, diag::note_invalid_subexpr_in_const_expr);
    }
  
    bool VisitStmt(const Stmt *) {
      llvm_unreachable("Expression evaluator should not be called on stmts");
    }
    bool VisitExpr(const Expr *E) {
      return Error(E);
    }
  
    bool VisitConstantExpr(const ConstantExpr *E) {
      if (E->hasAPValueResult())
        return DerivedSuccess(E->getAPValueResult(), E);
  
      return StmtVisitorTy::Visit(E->getSubExpr());
    }
  
    bool VisitParenExpr(const ParenExpr *E)
      { return StmtVisitorTy::Visit(E->getSubExpr()); }
    bool VisitUnaryExtension(const UnaryOperator *E)
      { return StmtVisitorTy::Visit(E->getSubExpr()); }
    bool VisitUnaryPlus(const UnaryOperator *E)
      { return StmtVisitorTy::Visit(E->getSubExpr()); }
    bool VisitChooseExpr(const ChooseExpr *E)
      { return StmtVisitorTy::Visit(E->getChosenSubExpr()); }
    bool VisitGenericSelectionExpr(const GenericSelectionExpr *E)
      { return StmtVisitorTy::Visit(E->getResultExpr()); }
    bool VisitSubstNonTypeTemplateParmExpr(const SubstNonTypeTemplateParmExpr *E)
      { return StmtVisitorTy::Visit(E->getReplacement()); }
    bool VisitCXXDefaultArgExpr(const CXXDefaultArgExpr *E) {
      TempVersionRAII RAII(*Info.CurrentCall);
      SourceLocExprScopeGuard Guard(E, Info.CurrentCall->CurSourceLocExprScope);
      return StmtVisitorTy::Visit(E->getExpr());
    }
    bool VisitCXXDefaultInitExpr(const CXXDefaultInitExpr *E) {
      TempVersionRAII RAII(*Info.CurrentCall);
      // The initializer may not have been parsed yet, or might be erroneous.
      if (!E->getExpr())
        return Error(E);
      SourceLocExprScopeGuard Guard(E, Info.CurrentCall->CurSourceLocExprScope);
      return StmtVisitorTy::Visit(E->getExpr());
    }
  
    bool VisitExprWithCleanups(const ExprWithCleanups *E) {
      FullExpressionRAII Scope(Info);
      return StmtVisitorTy::Visit(E->getSubExpr()) && Scope.destroy();
    }
  
    // Temporaries are registered when created, so we don't care about
    // CXXBindTemporaryExpr.
    bool VisitCXXBindTemporaryExpr(const CXXBindTemporaryExpr *E) {
      return StmtVisitorTy::Visit(E->getSubExpr());
    }
  
    bool VisitCXXReinterpretCastExpr(const CXXReinterpretCastExpr *E) {
      CCEDiag(E, diag::note_constexpr_invalid_cast) << 0;
      return static_cast<Derived*>(this)->VisitCastExpr(E);
    }
    bool VisitCXXDynamicCastExpr(const CXXDynamicCastExpr *E) {
      if (!Info.Ctx.getLangOpts().CPlusPlus20)
        CCEDiag(E, diag::note_constexpr_invalid_cast) << 1;
      return static_cast<Derived*>(this)->VisitCastExpr(E);
    }
    bool VisitBuiltinBitCastExpr(const BuiltinBitCastExpr *E) {
      return static_cast<Derived*>(this)->VisitCastExpr(E);
    }
  
    bool VisitBinaryOperator(const BinaryOperator *E) {
      switch (E->getOpcode()) {
      default:
        return Error(E);
  
      case BO_Comma:
        VisitIgnoredValue(E->getLHS());
        return StmtVisitorTy::Visit(E->getRHS());
  
      case BO_PtrMemD:
      case BO_PtrMemI: {
        LValue Obj;
        if (!HandleMemberPointerAccess(Info, E, Obj))
          return false;
        APValue Result;
        if (!handleLValueToRValueConversion(Info, E, E->getType(), Obj, Result))
          return false;
        return DerivedSuccess(Result, E);
      }
      }
    }
  
    bool VisitCXXRewrittenBinaryOperator(const CXXRewrittenBinaryOperator *E) {
      return StmtVisitorTy::Visit(E->getSemanticForm());
    }
  
    bool VisitBinaryConditionalOperator(const BinaryConditionalOperator *E) {
      // Evaluate and cache the common expression. We treat it as a temporary,
      // even though it's not quite the same thing.
      LValue CommonLV;
      if (!Evaluate(Info.CurrentCall->createTemporary(
                        E->getOpaqueValue(),
                        getStorageType(Info.Ctx, E->getOpaqueValue()),
                        ScopeKind::FullExpression, CommonLV),
                    Info, E->getCommon()))
        return false;
  
      return HandleConditionalOperator(E);
    }
  
    bool VisitConditionalOperator(const ConditionalOperator *E) {
      bool IsBcpCall = false;
      // If the condition (ignoring parens) is a __builtin_constant_p call,
      // the result is a constant expression if it can be folded without
      // side-effects. This is an important GNU extension. See GCC PR38377
      // for discussion.
      if (const CallExpr *CallCE =
            dyn_cast<CallExpr>(E->getCond()->IgnoreParenCasts()))
        if (CallCE->getBuiltinCallee() == Builtin::BI__builtin_constant_p)
          IsBcpCall = true;
  
      // Always assume __builtin_constant_p(...) ? ... : ... is a potential
      // constant expression; we can't check whether it's potentially foldable.
      // FIXME: We should instead treat __builtin_constant_p as non-constant if
      // it would return 'false' in this mode.
      if (Info.checkingPotentialConstantExpression() && IsBcpCall)
        return false;
  
      FoldConstant Fold(Info, IsBcpCall);
      if (!HandleConditionalOperator(E)) {
        Fold.keepDiagnostics();
        return false;
      }
  
      return true;
    }
  
    bool VisitOpaqueValueExpr(const OpaqueValueExpr *E) {
      if (APValue *Value = Info.CurrentCall->getCurrentTemporary(E))
        return DerivedSuccess(*Value, E);
  
      const Expr *Source = E->getSourceExpr();
      if (!Source)
        return Error(E);
      if (Source == E) { // sanity checking.
        assert(0 && "OpaqueValueExpr recursively refers to itself");
        return Error(E);
      }
      return StmtVisitorTy::Visit(Source);
    }
  
    bool VisitPseudoObjectExpr(const PseudoObjectExpr *E) {
      for (const Expr *SemE : E->semantics()) {
        if (auto *OVE = dyn_cast<OpaqueValueExpr>(SemE)) {
          // FIXME: We can't handle the case where an OpaqueValueExpr is also the
          // result expression: there could be two different LValues that would
          // refer to the same object in that case, and we can't model that.
          if (SemE == E->getResultExpr())
            return Error(E);
  
          // Unique OVEs get evaluated if and when we encounter them when
          // emitting the rest of the semantic form, rather than eagerly.
          if (OVE->isUnique())
            continue;
  
          LValue LV;
          if (!Evaluate(Info.CurrentCall->createTemporary(
                            OVE, getStorageType(Info.Ctx, OVE),
                            ScopeKind::FullExpression, LV),
                        Info, OVE->getSourceExpr()))
            return false;
        } else if (SemE == E->getResultExpr()) {
          if (!StmtVisitorTy::Visit(SemE))
            return false;
        } else {
          if (!EvaluateIgnoredValue(Info, SemE))
            return false;
        }
      }
      return true;
    }
  
    bool VisitCallExpr(const CallExpr *E) {
      APValue Result;
      if (!handleCallExpr(E, Result, nullptr))
        return false;
      return DerivedSuccess(Result, E);
    }
  
    bool handleCallExpr(const CallExpr *E, APValue &Result,
                       const LValue *ResultSlot) {
      CallScopeRAII CallScope(Info);
  
      const Expr *Callee = E->getCallee()->IgnoreParens();
      QualType CalleeType = Callee->getType();
  
      const FunctionDecl *FD = nullptr;
      LValue *This = nullptr, ThisVal;
      auto Args = llvm::makeArrayRef(E->getArgs(), E->getNumArgs());
      bool HasQualifier = false;
  
      CallRef Call;
  
      // Extract function decl and 'this' pointer from the callee.
      if (CalleeType->isSpecificBuiltinType(BuiltinType::BoundMember)) {
        const CXXMethodDecl *Member = nullptr;
        if (const MemberExpr *ME = dyn_cast<MemberExpr>(Callee)) {
          // Explicit bound member calls, such as x.f() or p->g();
          if (!EvaluateObjectArgument(Info, ME->getBase(), ThisVal))
            return false;
          Member = dyn_cast<CXXMethodDecl>(ME->getMemberDecl());
          if (!Member)
            return Error(Callee);
          This = &ThisVal;
          HasQualifier = ME->hasQualifier();
        } else if (const BinaryOperator *BE = dyn_cast<BinaryOperator>(Callee)) {
          // Indirect bound member calls ('.*' or '->*').
          const ValueDecl *D =
              HandleMemberPointerAccess(Info, BE, ThisVal, false);
          if (!D)
            return false;
          Member = dyn_cast<CXXMethodDecl>(D);
          if (!Member)
            return Error(Callee);
          This = &ThisVal;
        } else if (const auto *PDE = dyn_cast<CXXPseudoDestructorExpr>(Callee)) {
          if (!Info.getLangOpts().CPlusPlus20)
            Info.CCEDiag(PDE, diag::note_constexpr_pseudo_destructor);
          return EvaluateObjectArgument(Info, PDE->getBase(), ThisVal) &&
                 HandleDestruction(Info, PDE, ThisVal, PDE->getDestroyedType());
        } else
          return Error(Callee);
        FD = Member;
      } else if (CalleeType->isFunctionPointerType()) {
        LValue CalleeLV;
        if (!EvaluatePointer(Callee, CalleeLV, Info))
          return false;
  
        if (!CalleeLV.getLValueOffset().isZero())
          return Error(Callee);
        FD = dyn_cast_or_null<FunctionDecl>(
            CalleeLV.getLValueBase().dyn_cast<const ValueDecl *>());
        if (!FD)
          return Error(Callee);
        // Don't call function pointers which have been cast to some other type.
        // Per DR (no number yet), the caller and callee can differ in noexcept.
        if (!Info.Ctx.hasSameFunctionTypeIgnoringExceptionSpec(
          CalleeType->getPointeeType(), FD->getType())) {
          return Error(E);
        }
  
        // For an (overloaded) assignment expression, evaluate the RHS before the
        // LHS.
        auto *OCE = dyn_cast<CXXOperatorCallExpr>(E);
        if (OCE && OCE->isAssignmentOp()) {
          assert(Args.size() == 2 && "wrong number of arguments in assignment");
          Call = Info.CurrentCall->createCall(FD);
          if (!EvaluateArgs(isa<CXXMethodDecl>(FD) ? Args.slice(1) : Args, Call,
                            Info, FD, /*RightToLeft=*/true))
            return false;
        }
  
        // Overloaded operator calls to member functions are represented as normal
        // calls with '*this' as the first argument.
        const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD);
        if (MD && !MD->isStatic()) {
          // FIXME: When selecting an implicit conversion for an overloaded
          // operator delete, we sometimes try to evaluate calls to conversion
          // operators without a 'this' parameter!
          if (Args.empty())
            return Error(E);
  
          if (!EvaluateObjectArgument(Info, Args[0], ThisVal))
            return false;
          This = &ThisVal;
          Args = Args.slice(1);
        } else if (MD && MD->isLambdaStaticInvoker()) {
          // Map the static invoker for the lambda back to the call operator.
          // Conveniently, we don't have to slice out the 'this' argument (as is
          // being done for the non-static case), since a static member function
          // doesn't have an implicit argument passed in.
          const CXXRecordDecl *ClosureClass = MD->getParent();
          assert(
              ClosureClass->captures_begin() == ClosureClass->captures_end() &&
              "Number of captures must be zero for conversion to function-ptr");
  
          const CXXMethodDecl *LambdaCallOp =
              ClosureClass->getLambdaCallOperator();
  
          // Set 'FD', the function that will be called below, to the call
          // operator.  If the closure object represents a generic lambda, find
          // the corresponding specialization of the call operator.
  
          if (ClosureClass->isGenericLambda()) {
            assert(MD->isFunctionTemplateSpecialization() &&
                   "A generic lambda's static-invoker function must be a "
                   "template specialization");
            const TemplateArgumentList *TAL = MD->getTemplateSpecializationArgs();
            FunctionTemplateDecl *CallOpTemplate =
                LambdaCallOp->getDescribedFunctionTemplate();
            void *InsertPos = nullptr;
            FunctionDecl *CorrespondingCallOpSpecialization =
                CallOpTemplate->findSpecialization(TAL->asArray(), InsertPos);
            assert(CorrespondingCallOpSpecialization &&
                   "We must always have a function call operator specialization "
                   "that corresponds to our static invoker specialization");
            FD = cast<CXXMethodDecl>(CorrespondingCallOpSpecialization);
          } else
            FD = LambdaCallOp;
        } else if (FD->isReplaceableGlobalAllocationFunction()) {
          if (FD->getDeclName().getCXXOverloadedOperator() == OO_New ||
              FD->getDeclName().getCXXOverloadedOperator() == OO_Array_New) {
            LValue Ptr;
            if (!HandleOperatorNewCall(Info, E, Ptr))
              return false;
            Ptr.moveInto(Result);
            return CallScope.destroy();
          } else {
            return HandleOperatorDeleteCall(Info, E) && CallScope.destroy();
          }
        }
      } else
        return Error(E);
  
      // Evaluate the arguments now if we've not already done so.
      if (!Call) {
        Call = Info.CurrentCall->createCall(FD);
        if (!EvaluateArgs(Args, Call, Info, FD))
          return false;
      }
  
      SmallVector<QualType, 4> CovariantAdjustmentPath;
      if (This) {
        auto *NamedMember = dyn_cast<CXXMethodDecl>(FD);
        if (NamedMember && NamedMember->isVirtual() && !HasQualifier) {
          // Perform virtual dispatch, if necessary.
          FD = HandleVirtualDispatch(Info, E, *This, NamedMember,
                                     CovariantAdjustmentPath);
          if (!FD)
            return false;
        } else {
          // Check that the 'this' pointer points to an object of the right type.
          // FIXME: If this is an assignment operator call, we may need to change
          // the active union member before we check this.
          if (!checkNonVirtualMemberCallThisPointer(Info, E, *This, NamedMember))
            return false;
        }
      }
  
      // Destructor calls are different enough that they have their own codepath.
      if (auto *DD = dyn_cast<CXXDestructorDecl>(FD)) {
        assert(This && "no 'this' pointer for destructor call");
        return HandleDestruction(Info, E, *This,
                                 Info.Ctx.getRecordType(DD->getParent())) &&
               CallScope.destroy();
      }
  
      const FunctionDecl *Definition = nullptr;
      Stmt *Body = FD->getBody(Definition);
  
      if (!CheckConstexprFunction(Info, E->getExprLoc(), FD, Definition, Body) ||
          !HandleFunctionCall(E->getExprLoc(), Definition, This, Args, Call,
                              Body, Info, Result, ResultSlot))
        return false;
  
      if (!CovariantAdjustmentPath.empty() &&
          !HandleCovariantReturnAdjustment(Info, E, Result,
                                           CovariantAdjustmentPath))
        return false;
  
      return CallScope.destroy();
    }
  
    bool VisitCompoundLiteralExpr(const CompoundLiteralExpr *E) {
      return StmtVisitorTy::Visit(E->getInitializer());
    }
    bool VisitInitListExpr(const InitListExpr *E) {
      if (E->getNumInits() == 0)
        return DerivedZeroInitialization(E);
      if (E->getNumInits() == 1)
        return StmtVisitorTy::Visit(E->getInit(0));
      return Error(E);
    }
    bool VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E) {
      return DerivedZeroInitialization(E);
    }
    bool VisitCXXScalarValueInitExpr(const CXXScalarValueInitExpr *E) {
      return DerivedZeroInitialization(E);
    }
    bool VisitCXXNullPtrLiteralExpr(const CXXNullPtrLiteralExpr *E) {
      return DerivedZeroInitialization(E);
    }
  
    /// A member expression where the object is a prvalue is itself a prvalue.
    bool VisitMemberExpr(const MemberExpr *E) {
      assert(!Info.Ctx.getLangOpts().CPlusPlus11 &&
             "missing temporary materialization conversion");
      assert(!E->isArrow() && "missing call to bound member function?");
  
      APValue Val;
      if (!Evaluate(Val, Info, E->getBase()))
        return false;
  
      QualType BaseTy = E->getBase()->getType();
  
      const FieldDecl *FD = dyn_cast<FieldDecl>(E->getMemberDecl());
      if (!FD) return Error(E);
      assert(!FD->getType()->isReferenceType() && "prvalue reference?");
      assert(BaseTy->castAs<RecordType>()->getDecl()->getCanonicalDecl() ==
             FD->getParent()->getCanonicalDecl() && "record / field mismatch");
  
      // Note: there is no lvalue base here. But this case should only ever
      // happen in C or in C++98, where we cannot be evaluating a constexpr
      // constructor, which is the only case the base matters.
      CompleteObject Obj(APValue::LValueBase(), &Val, BaseTy);
      SubobjectDesignator Designator(BaseTy);
      Designator.addDeclUnchecked(FD);
  
      APValue Result;
      return extractSubobject(Info, E, Obj, Designator, Result) &&
             DerivedSuccess(Result, E);
    }
  
    bool VisitExtVectorElementExpr(const ExtVectorElementExpr *E) {
      APValue Val;
      if (!Evaluate(Val, Info, E->getBase()))
        return false;
  
      if (Val.isVector()) {
        SmallVector<uint32_t, 4> Indices;
        E->getEncodedElementAccess(Indices);
        if (Indices.size() == 1) {
          // Return scalar.
          return DerivedSuccess(Val.getVectorElt(Indices[0]), E);
        } else {
          // Construct new APValue vector.
          SmallVector<APValue, 4> Elts;
          for (unsigned I = 0; I < Indices.size(); ++I) {
            Elts.push_back(Val.getVectorElt(Indices[I]));
          }
          APValue VecResult(Elts.data(), Indices.size());
          return DerivedSuccess(VecResult, E);
        }
      }
  
      return false;
    }
  
    bool VisitCastExpr(const CastExpr *E) {
      switch (E->getCastKind()) {
      default:
        break;
  
      case CK_AtomicToNonAtomic: {
        APValue AtomicVal;
        // This does not need to be done in place even for class/array types:
        // atomic-to-non-atomic conversion implies copying the object
        // representation.
        if (!Evaluate(AtomicVal, Info, E->getSubExpr()))
          return false;
        return DerivedSuccess(AtomicVal, E);
      }
  
      case CK_NoOp:
      case CK_UserDefinedConversion:
        return StmtVisitorTy::Visit(E->getSubExpr());
  
      case CK_LValueToRValue: {
        LValue LVal;
        if (!EvaluateLValue(E->getSubExpr(), LVal, Info))
          return false;
        APValue RVal;
        // Note, we use the subexpression's type in order to retain cv-qualifiers.
        if (!handleLValueToRValueConversion(Info, E, E->getSubExpr()->getType(),
                                            LVal, RVal))
          return false;
        return DerivedSuccess(RVal, E);
      }
      case CK_LValueToRValueBitCast: {
        APValue DestValue, SourceValue;
        if (!Evaluate(SourceValue, Info, E->getSubExpr()))
          return false;
        if (!handleLValueToRValueBitCast(Info, DestValue, SourceValue, E))
          return false;
        return DerivedSuccess(DestValue, E);
      }
  
      case CK_AddressSpaceConversion: {
        APValue Value;
        if (!Evaluate(Value, Info, E->getSubExpr()))
          return false;
        return DerivedSuccess(Value, E);
      }
      }
  
      return Error(E);
    }
  
    bool VisitUnaryPostInc(const UnaryOperator *UO) {
      return VisitUnaryPostIncDec(UO);
    }
    bool VisitUnaryPostDec(const UnaryOperator *UO) {
      return VisitUnaryPostIncDec(UO);
    }
    bool VisitUnaryPostIncDec(const UnaryOperator *UO) {
      if (!Info.getLangOpts().CPlusPlus14 && !Info.keepEvaluatingAfterFailure())
        return Error(UO);
  
      LValue LVal;
      if (!EvaluateLValue(UO->getSubExpr(), LVal, Info))
        return false;
      APValue RVal;
      if (!handleIncDec(this->Info, UO, LVal, UO->getSubExpr()->getType(),
                        UO->isIncrementOp(), &RVal))
        return false;
      return DerivedSuccess(RVal, UO);
    }
  
    bool VisitStmtExpr(const StmtExpr *E) {
      // We will have checked the full-expressions inside the statement expression
      // when they were completed, and don't need to check them again now.
      llvm::SaveAndRestore<bool> NotCheckingForUB(
          Info.CheckingForUndefinedBehavior, false);
  
      const CompoundStmt *CS = E->getSubStmt();
      if (CS->body_empty())
        return true;
  
      BlockScopeRAII Scope(Info);
      for (CompoundStmt::const_body_iterator BI = CS->body_begin(),
                                             BE = CS->body_end();
           /**/; ++BI) {
        if (BI + 1 == BE) {
          const Expr *FinalExpr = dyn_cast<Expr>(*BI);
          if (!FinalExpr) {
            Info.FFDiag((*BI)->getBeginLoc(),
                        diag::note_constexpr_stmt_expr_unsupported);
            return false;
          }
          return this->Visit(FinalExpr) && Scope.destroy();
        }
  
        APValue ReturnValue;
        StmtResult Result = { ReturnValue, nullptr };
        EvalStmtResult ESR = EvaluateStmt(Result, Info, *BI);
        if (ESR != ESR_Succeeded) {
          // FIXME: If the statement-expression terminated due to 'return',
          // 'break', or 'continue', it would be nice to propagate that to
          // the outer statement evaluation rather than bailing out.
          if (ESR != ESR_Failed)
            Info.FFDiag((*BI)->getBeginLoc(),
                        diag::note_constexpr_stmt_expr_unsupported);
          return false;
        }
      }
  
      llvm_unreachable("Return from function from the loop above.");
    }
  
    /// Visit a value which is evaluated, but whose value is ignored.
    void VisitIgnoredValue(const Expr *E) {
      EvaluateIgnoredValue(Info, E);
    }
  
    /// Potentially visit a MemberExpr's base expression.
    void VisitIgnoredBaseExpression(const Expr *E) {
      // While MSVC doesn't evaluate the base expression, it does diagnose the
      // presence of side-effecting behavior.
      if (Info.getLangOpts().MSVCCompat && !E->HasSideEffects(Info.Ctx))
        return;
      VisitIgnoredValue(E);
    }
  };
  
  } // namespace
  
  //===----------------------------------------------------------------------===//
  // Common base class for lvalue and temporary evaluation.
  //===----------------------------------------------------------------------===//
  namespace {
  template<class Derived>
  class LValueExprEvaluatorBase
    : public ExprEvaluatorBase<Derived> {
  protected:
    LValue &Result;
    bool InvalidBaseOK;
    typedef LValueExprEvaluatorBase LValueExprEvaluatorBaseTy;
    typedef ExprEvaluatorBase<Derived> ExprEvaluatorBaseTy;
  
    bool Success(APValue::LValueBase B) {
      Result.set(B);
      return true;
    }
  
    bool evaluatePointer(const Expr *E, LValue &Result) {
      return EvaluatePointer(E, Result, this->Info, InvalidBaseOK);
    }
  
  public:
    LValueExprEvaluatorBase(EvalInfo &Info, LValue &Result, bool InvalidBaseOK)
        : ExprEvaluatorBaseTy(Info), Result(Result),
          InvalidBaseOK(InvalidBaseOK) {}
  
    bool Success(const APValue &V, const Expr *E) {
      Result.setFrom(this->Info.Ctx, V);
      return true;
    }
  
    bool VisitMemberExpr(const MemberExpr *E) {
      // Handle non-static data members.
      QualType BaseTy;
      bool EvalOK;
      if (E->isArrow()) {
        EvalOK = evaluatePointer(E->getBase(), Result);
        BaseTy = E->getBase()->getType()->castAs<PointerType>()->getPointeeType();
      } else if (E->getBase()->isRValue()) {
        assert(E->getBase()->getType()->isRecordType());
        EvalOK = EvaluateTemporary(E->getBase(), Result, this->Info);
        BaseTy = E->getBase()->getType();
      } else {
        EvalOK = this->Visit(E->getBase());
        BaseTy = E->getBase()->getType();
      }
      if (!EvalOK) {
        if (!InvalidBaseOK)
          return false;
        Result.setInvalid(E);
        return true;
      }
  
      const ValueDecl *MD = E->getMemberDecl();
      if (const FieldDecl *FD = dyn_cast<FieldDecl>(E->getMemberDecl())) {
        assert(BaseTy->castAs<RecordType>()->getDecl()->getCanonicalDecl() ==
               FD->getParent()->getCanonicalDecl() && "record / field mismatch");
        (void)BaseTy;
        if (!HandleLValueMember(this->Info, E, Result, FD))
          return false;
      } else if (const IndirectFieldDecl *IFD = dyn_cast<IndirectFieldDecl>(MD)) {
        if (!HandleLValueIndirectMember(this->Info, E, Result, IFD))
          return false;
      } else
        return this->Error(E);
  
      if (MD->getType()->isReferenceType()) {
        APValue RefValue;
        if (!handleLValueToRValueConversion(this->Info, E, MD->getType(), Result,
                                            RefValue))
          return false;
        return Success(RefValue, E);
      }
      return true;
    }
  
    bool VisitBinaryOperator(const BinaryOperator *E) {
      switch (E->getOpcode()) {
      default:
        return ExprEvaluatorBaseTy::VisitBinaryOperator(E);
  
      case BO_PtrMemD:
      case BO_PtrMemI:
        return HandleMemberPointerAccess(this->Info, E, Result);
      }
    }
  
    bool VisitCastExpr(const CastExpr *E) {
      switch (E->getCastKind()) {
      default:
        return ExprEvaluatorBaseTy::VisitCastExpr(E);
  
      case CK_DerivedToBase:
      case CK_UncheckedDerivedToBase:
        if (!this->Visit(E->getSubExpr()))
          return false;
  
        // Now figure out the necessary offset to add to the base LV to get from
        // the derived class to the base class.
        return HandleLValueBasePath(this->Info, E, E->getSubExpr()->getType(),
                                    Result);
      }
    }
  };
  }
  
  //===----------------------------------------------------------------------===//
  // LValue Evaluation
  //
  // This is used for evaluating lvalues (in C and C++), xvalues (in C++11),
  // function designators (in C), decl references to void objects (in C), and
  // temporaries (if building with -Wno-address-of-temporary).
  //
  // LValue evaluation produces values comprising a base expression of one of the
  // following types:
  // - Declarations
  //  * VarDecl
  //  * FunctionDecl
  // - Literals
  //  * CompoundLiteralExpr in C (and in global scope in C++)
  //  * StringLiteral
  //  * PredefinedExpr
  //  * ObjCStringLiteralExpr
  //  * ObjCEncodeExpr
  //  * AddrLabelExpr
  //  * BlockExpr
  //  * CallExpr for a MakeStringConstant builtin
  // - typeid(T) expressions, as TypeInfoLValues
  // - Locals and temporaries
  //  * MaterializeTemporaryExpr
  //  * Any Expr, with a CallIndex indicating the function in which the temporary
  //    was evaluated, for cases where the MaterializeTemporaryExpr is missing
  //    from the AST (FIXME).
  //  * A MaterializeTemporaryExpr that has static storage duration, with no
  //    CallIndex, for a lifetime-extended temporary.
  //  * The ConstantExpr that is currently being evaluated during evaluation of an
  //    immediate invocation.
  // plus an offset in bytes.
  //===----------------------------------------------------------------------===//
  namespace {
  class LValueExprEvaluator
    : public LValueExprEvaluatorBase<LValueExprEvaluator> {
  public:
    LValueExprEvaluator(EvalInfo &Info, LValue &Result, bool InvalidBaseOK) :
      LValueExprEvaluatorBaseTy(Info, Result, InvalidBaseOK) {}
  
    bool VisitVarDecl(const Expr *E, const VarDecl *VD);
    bool VisitUnaryPreIncDec(const UnaryOperator *UO);
  
    bool VisitDeclRefExpr(const DeclRefExpr *E);
    bool VisitPredefinedExpr(const PredefinedExpr *E) { return Success(E); }
    bool VisitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *E);
    bool VisitCompoundLiteralExpr(const CompoundLiteralExpr *E);
    bool VisitMemberExpr(const MemberExpr *E);
    bool VisitStringLiteral(const StringLiteral *E) { return Success(E); }
    bool VisitObjCEncodeExpr(const ObjCEncodeExpr *E) { return Success(E); }
    bool VisitCXXTypeidExpr(const CXXTypeidExpr *E);
    bool VisitCXXUuidofExpr(const CXXUuidofExpr *E);
    bool VisitArraySubscriptExpr(const ArraySubscriptExpr *E);
    bool VisitUnaryDeref(const UnaryOperator *E);
    bool VisitUnaryReal(const UnaryOperator *E);
    bool VisitUnaryImag(const UnaryOperator *E);
    bool VisitUnaryPreInc(const UnaryOperator *UO) {
      return VisitUnaryPreIncDec(UO);
    }
    bool VisitUnaryPreDec(const UnaryOperator *UO) {
      return VisitUnaryPreIncDec(UO);
    }
    bool VisitBinAssign(const BinaryOperator *BO);
    bool VisitCompoundAssignOperator(const CompoundAssignOperator *CAO);
  
    bool VisitCastExpr(const CastExpr *E) {
      switch (E->getCastKind()) {
      default:
        return LValueExprEvaluatorBaseTy::VisitCastExpr(E);
  
      case CK_LValueBitCast:
        this->CCEDiag(E, diag::note_constexpr_invalid_cast) << 2;
        if (!Visit(E->getSubExpr()))
          return false;
        Result.Designator.setInvalid();
        return true;
  
      case CK_BaseToDerived:
        if (!Visit(E->getSubExpr()))
          return false;
        return HandleBaseToDerivedCast(Info, E, Result);
  
      case CK_Dynamic:
        if (!Visit(E->getSubExpr()))
          return false;
        return HandleDynamicCast(Info, cast<ExplicitCastExpr>(E), Result);
      }
    }
  };
  } // end anonymous namespace
  
  /// Evaluate an expression as an lvalue. This can be legitimately called on
  /// expressions which are not glvalues, in three cases:
  ///  * function designators in C, and
  ///  * "extern void" objects
  ///  * @selector() expressions in Objective-C
  static bool EvaluateLValue(const Expr *E, LValue &Result, EvalInfo &Info,
                             bool InvalidBaseOK) {
    assert(!E->isValueDependent());
    assert(E->isGLValue() || E->getType()->isFunctionType() ||
           E->getType()->isVoidType() || isa<ObjCSelectorExpr>(E));
    return LValueExprEvaluator(Info, Result, InvalidBaseOK).Visit(E);
  }
  
  bool LValueExprEvaluator::VisitDeclRefExpr(const DeclRefExpr *E) {
    const NamedDecl *D = E->getDecl();
    if (isa<FunctionDecl, MSGuidDecl, TemplateParamObjectDecl>(D))
      return Success(cast<ValueDecl>(D));
    if (const VarDecl *VD = dyn_cast<VarDecl>(D))
      return VisitVarDecl(E, VD);
    if (const BindingDecl *BD = dyn_cast<BindingDecl>(D))
      return Visit(BD->getBinding());
    return Error(E);
  }
  
  
  bool LValueExprEvaluator::VisitVarDecl(const Expr *E, const VarDecl *VD) {
  
    // If we are within a lambda's call operator, check whether the 'VD' referred
    // to within 'E' actually represents a lambda-capture that maps to a
    // data-member/field within the closure object, and if so, evaluate to the
    // field or what the field refers to.
    if (Info.CurrentCall && isLambdaCallOperator(Info.CurrentCall->Callee) &&
        isa<DeclRefExpr>(E) &&
        cast<DeclRefExpr>(E)->refersToEnclosingVariableOrCapture()) {
      // We don't always have a complete capture-map when checking or inferring if
      // the function call operator meets the requirements of a constexpr function
      // - but we don't need to evaluate the captures to determine constexprness
      // (dcl.constexpr C++17).
      if (Info.checkingPotentialConstantExpression())
        return false;
  
      if (auto *FD = Info.CurrentCall->LambdaCaptureFields.lookup(VD)) {
        // Start with 'Result' referring to the complete closure object...
        Result = *Info.CurrentCall->This;
        // ... then update it to refer to the field of the closure object
        // that represents the capture.
        if (!HandleLValueMember(Info, E, Result, FD))
          return false;
        // And if the field is of reference type, update 'Result' to refer to what
        // the field refers to.
        if (FD->getType()->isReferenceType()) {
          APValue RVal;
          if (!handleLValueToRValueConversion(Info, E, FD->getType(), Result,
                                              RVal))
            return false;
          Result.setFrom(Info.Ctx, RVal);
        }
        return true;
      }
    }
  
    CallStackFrame *Frame = nullptr;
    unsigned Version = 0;
    if (VD->hasLocalStorage()) {
      // Only if a local variable was declared in the function currently being
      // evaluated, do we expect to be able to find its value in the current
      // frame. (Otherwise it was likely declared in an enclosing context and
      // could either have a valid evaluatable value (for e.g. a constexpr
      // variable) or be ill-formed (and trigger an appropriate evaluation
      // diagnostic)).
      CallStackFrame *CurrFrame = Info.CurrentCall;
      if (CurrFrame->Callee && CurrFrame->Callee->Equals(VD->getDeclContext())) {
        // Function parameters are stored in some caller's frame. (Usually the
        // immediate caller, but for an inherited constructor they may be more
        // distant.)
        if (auto *PVD = dyn_cast<ParmVarDecl>(VD)) {
          if (CurrFrame->Arguments) {
            VD = CurrFrame->Arguments.getOrigParam(PVD);
            Frame =
                Info.getCallFrameAndDepth(CurrFrame->Arguments.CallIndex).first;
            Version = CurrFrame->Arguments.Version;
          }
        } else {
          Frame = CurrFrame;
          Version = CurrFrame->getCurrentTemporaryVersion(VD);
        }
      }
    }
  
    if (!VD->getType()->isReferenceType()) {
      if (Frame) {
        Result.set({VD, Frame->Index, Version});
        return true;
      }
      return Success(VD);
    }
  
    if (!Info.getLangOpts().CPlusPlus11) {
      Info.CCEDiag(E, diag::note_constexpr_ltor_non_integral, 1)
          << VD << VD->getType();
      Info.Note(VD->getLocation(), diag::note_declared_at);
    }
  
    APValue *V;
    if (!evaluateVarDeclInit(Info, E, VD, Frame, Version, V))
      return false;
    if (!V->hasValue()) {
      // FIXME: Is it possible for V to be indeterminate here? If so, we should
      // adjust the diagnostic to say that.
      if (!Info.checkingPotentialConstantExpression())
        Info.FFDiag(E, diag::note_constexpr_use_uninit_reference);
      return false;
    }
    return Success(*V, E);
  }
  
  bool LValueExprEvaluator::VisitMaterializeTemporaryExpr(
      const MaterializeTemporaryExpr *E) {
    // Walk through the expression to find the materialized temporary itself.
    SmallVector<const Expr *, 2> CommaLHSs;
    SmallVector<SubobjectAdjustment, 2> Adjustments;
    const Expr *Inner =
        E->getSubExpr()->skipRValueSubobjectAdjustments(CommaLHSs, Adjustments);
  
    // If we passed any comma operators, evaluate their LHSs.
    for (unsigned I = 0, N = CommaLHSs.size(); I != N; ++I)
      if (!EvaluateIgnoredValue(Info, CommaLHSs[I]))
        return false;
  
    // A materialized temporary with static storage duration can appear within the
    // result of a constant expression evaluation, so we need to preserve its
    // value for use outside this evaluation.
    APValue *Value;
    if (E->getStorageDuration() == SD_Static) {
      // FIXME: What about SD_Thread?
      Value = E->getOrCreateValue(true);
      *Value = APValue();
      Result.set(E);
    } else {
      Value = &Info.CurrentCall->createTemporary(
          E, E->getType(),
          E->getStorageDuration() == SD_FullExpression ? ScopeKind::FullExpression
                                                       : ScopeKind::Block,
          Result);
    }
  
    QualType Type = Inner->getType();
  
    // Materialize the temporary itself.
    if (!EvaluateInPlace(*Value, Info, Result, Inner)) {
      *Value = APValue();
      return false;
    }
  
    // Adjust our lvalue to refer to the desired subobject.
    for (unsigned I = Adjustments.size(); I != 0; /**/) {
      --I;
      switch (Adjustments[I].Kind) {
      case SubobjectAdjustment::DerivedToBaseAdjustment:
        if (!HandleLValueBasePath(Info, Adjustments[I].DerivedToBase.BasePath,
                                  Type, Result))
          return false;
        Type = Adjustments[I].DerivedToBase.BasePath->getType();
        break;
  
      case SubobjectAdjustment::FieldAdjustment:
        if (!HandleLValueMember(Info, E, Result, Adjustments[I].Field))
          return false;
        Type = Adjustments[I].Field->getType();
        break;
  
      case SubobjectAdjustment::MemberPointerAdjustment:
        if (!HandleMemberPointerAccess(this->Info, Type, Result,
                                       Adjustments[I].Ptr.RHS))
          return false;
        Type = Adjustments[I].Ptr.MPT->getPointeeType();
        break;
      }
    }
  
    return true;
  }
  
  bool
  LValueExprEvaluator::VisitCompoundLiteralExpr(const CompoundLiteralExpr *E) {
    assert((!Info.getLangOpts().CPlusPlus || E->isFileScope()) &&
           "lvalue compound literal in c++?");
    // Defer visiting the literal until the lvalue-to-rvalue conversion. We can
    // only see this when folding in C, so there's no standard to follow here.
    return Success(E);
  }
  
  bool LValueExprEvaluator::VisitCXXTypeidExpr(const CXXTypeidExpr *E) {
    TypeInfoLValue TypeInfo;
  
    if (!E->isPotentiallyEvaluated()) {
      if (E->isTypeOperand())
        TypeInfo = TypeInfoLValue(E->getTypeOperand(Info.Ctx).getTypePtr());
      else
        TypeInfo = TypeInfoLValue(E->getExprOperand()->getType().getTypePtr());
    } else {
      if (!Info.Ctx.getLangOpts().CPlusPlus20) {
        Info.CCEDiag(E, diag::note_constexpr_typeid_polymorphic)
          << E->getExprOperand()->getType()
          << E->getExprOperand()->getSourceRange();
      }
  
      if (!Visit(E->getExprOperand()))
        return false;
  
      Optional<DynamicType> DynType =
          ComputeDynamicType(Info, E, Result, AK_TypeId);
      if (!DynType)
        return false;
  
      TypeInfo =
          TypeInfoLValue(Info.Ctx.getRecordType(DynType->Type).getTypePtr());
    }
  
    return Success(APValue::LValueBase::getTypeInfo(TypeInfo, E->getType()));
  }
  
  bool LValueExprEvaluator::VisitCXXUuidofExpr(const CXXUuidofExpr *E) {
    return Success(E->getGuidDecl());
  }
  
  bool LValueExprEvaluator::VisitMemberExpr(const MemberExpr *E) {
    // Handle static data members.
    if (const VarDecl *VD = dyn_cast<VarDecl>(E->getMemberDecl())) {
      VisitIgnoredBaseExpression(E->getBase());
      return VisitVarDecl(E, VD);
    }
  
    // Handle static member functions.
    if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(E->getMemberDecl())) {
      if (MD->isStatic()) {
        VisitIgnoredBaseExpression(E->getBase());
        return Success(MD);
      }
    }
  
    // Handle non-static data members.
    return LValueExprEvaluatorBaseTy::VisitMemberExpr(E);
  }
  
  bool LValueExprEvaluator::VisitArraySubscriptExpr(const ArraySubscriptExpr *E) {
    // FIXME: Deal with vectors as array subscript bases.
    if (E->getBase()->getType()->isVectorType())
      return Error(E);
  
    APSInt Index;
    bool Success = true;
  
    // C++17's rules require us to evaluate the LHS first, regardless of which
    // side is the base.
    for (const Expr *SubExpr : {E->getLHS(), E->getRHS()}) {
      if (SubExpr == E->getBase() ? !evaluatePointer(SubExpr, Result)
                                  : !EvaluateInteger(SubExpr, Index, Info)) {
        if (!Info.noteFailure())
          return false;
        Success = false;
      }
    }
  
    return Success &&
           HandleLValueArrayAdjustment(Info, E, Result, E->getType(), Index);
  }
  
  bool LValueExprEvaluator::VisitUnaryDeref(const UnaryOperator *E) {
    return evaluatePointer(E->getSubExpr(), Result);
  }
  
  bool LValueExprEvaluator::VisitUnaryReal(const UnaryOperator *E) {
    if (!Visit(E->getSubExpr()))
      return false;
    // __real is a no-op on scalar lvalues.
    if (E->getSubExpr()->getType()->isAnyComplexType())
      HandleLValueComplexElement(Info, E, Result, E->getType(), false);
    return true;
  }
  
  bool LValueExprEvaluator::VisitUnaryImag(const UnaryOperator *E) {
    assert(E->getSubExpr()->getType()->isAnyComplexType() &&
           "lvalue __imag__ on scalar?");
    if (!Visit(E->getSubExpr()))
      return false;
    HandleLValueComplexElement(Info, E, Result, E->getType(), true);
    return true;
  }
  
  bool LValueExprEvaluator::VisitUnaryPreIncDec(const UnaryOperator *UO) {
    if (!Info.getLangOpts().CPlusPlus14 && !Info.keepEvaluatingAfterFailure())
      return Error(UO);
  
    if (!this->Visit(UO->getSubExpr()))
      return false;
  
    return handleIncDec(
        this->Info, UO, Result, UO->getSubExpr()->getType(),
        UO->isIncrementOp(), nullptr);
  }
  
  bool LValueExprEvaluator::VisitCompoundAssignOperator(
      const CompoundAssignOperator *CAO) {
    if (!Info.getLangOpts().CPlusPlus14 && !Info.keepEvaluatingAfterFailure())
      return Error(CAO);
  
    bool Success = true;
  
    // C++17 onwards require that we evaluate the RHS first.
    APValue RHS;
    if (!Evaluate(RHS, this->Info, CAO->getRHS())) {
      if (!Info.noteFailure())
        return false;
      Success = false;
    }
  
    // The overall lvalue result is the result of evaluating the LHS.
    if (!this->Visit(CAO->getLHS()) || !Success)
      return false;
  
    return handleCompoundAssignment(
        this->Info, CAO,
        Result, CAO->getLHS()->getType(), CAO->getComputationLHSType(),
        CAO->getOpForCompoundAssignment(CAO->getOpcode()), RHS);
  }
  
  bool LValueExprEvaluator::VisitBinAssign(const BinaryOperator *E) {
    if (!Info.getLangOpts().CPlusPlus14 && !Info.keepEvaluatingAfterFailure())
      return Error(E);
  
    bool Success = true;
  
    // C++17 onwards require that we evaluate the RHS first.
    APValue NewVal;
    if (!Evaluate(NewVal, this->Info, E->getRHS())) {
      if (!Info.noteFailure())
        return false;
      Success = false;
    }
  
    if (!this->Visit(E->getLHS()) || !Success)
      return false;
  
    if (Info.getLangOpts().CPlusPlus20 &&
        !HandleUnionActiveMemberChange(Info, E->getLHS(), Result))
      return false;
  
    return handleAssignment(this->Info, E, Result, E->getLHS()->getType(),
                            NewVal);
  }
  
  //===----------------------------------------------------------------------===//
  // Pointer Evaluation
  //===----------------------------------------------------------------------===//
  
  /// Attempts to compute the number of bytes available at the pointer
  /// returned by a function with the alloc_size attribute. Returns true if we
  /// were successful. Places an unsigned number into `Result`.
  ///
  /// This expects the given CallExpr to be a call to a function with an
  /// alloc_size attribute.
  static bool getBytesReturnedByAllocSizeCall(const ASTContext &Ctx,
                                              const CallExpr *Call,
                                              llvm::APInt &Result) {
    const AllocSizeAttr *AllocSize = getAllocSizeAttr(Call);
  
    assert(AllocSize && AllocSize->getElemSizeParam().isValid());
    unsigned SizeArgNo = AllocSize->getElemSizeParam().getASTIndex();
    unsigned BitsInSizeT = Ctx.getTypeSize(Ctx.getSizeType());
    if (Call->getNumArgs() <= SizeArgNo)
      return false;
  
    auto EvaluateAsSizeT = [&](const Expr *E, APSInt &Into) {
      Expr::EvalResult ExprResult;
      if (!E->EvaluateAsInt(ExprResult, Ctx, Expr::SE_AllowSideEffects))
        return false;
      Into = ExprResult.Val.getInt();
      if (Into.isNegative() || !Into.isIntN(BitsInSizeT))
        return false;
      Into = Into.zextOrSelf(BitsInSizeT);
      return true;
    };
  
    APSInt SizeOfElem;
    if (!EvaluateAsSizeT(Call->getArg(SizeArgNo), SizeOfElem))
      return false;
  
    if (!AllocSize->getNumElemsParam().isValid()) {
      Result = std::move(SizeOfElem);
      return true;
    }
  
    APSInt NumberOfElems;
    unsigned NumArgNo = AllocSize->getNumElemsParam().getASTIndex();
    if (!EvaluateAsSizeT(Call->getArg(NumArgNo), NumberOfElems))
      return false;
  
    bool Overflow;
    llvm::APInt BytesAvailable = SizeOfElem.umul_ov(NumberOfElems, Overflow);
    if (Overflow)
      return false;
  
    Result = std::move(BytesAvailable);
    return true;
  }
  
  /// Convenience function. LVal's base must be a call to an alloc_size
  /// function.
  static bool getBytesReturnedByAllocSizeCall(const ASTContext &Ctx,
                                              const LValue &LVal,
                                              llvm::APInt &Result) {
    assert(isBaseAnAllocSizeCall(LVal.getLValueBase()) &&
           "Can't get the size of a non alloc_size function");
    const auto *Base = LVal.getLValueBase().get<const Expr *>();
    const CallExpr *CE = tryUnwrapAllocSizeCall(Base);
    return getBytesReturnedByAllocSizeCall(Ctx, CE, Result);
  }
  
  /// Attempts to evaluate the given LValueBase as the result of a call to
  /// a function with the alloc_size attribute. If it was possible to do so, this
  /// function will return true, make Result's Base point to said function call,
  /// and mark Result's Base as invalid.
  static bool evaluateLValueAsAllocSize(EvalInfo &Info, APValue::LValueBase Base,
                                        LValue &Result) {
    if (Base.isNull())
      return false;
  
    // Because we do no form of static analysis, we only support const variables.
    //
    // Additionally, we can't support parameters, nor can we support static
    // variables (in the latter case, use-before-assign isn't UB; in the former,
    // we have no clue what they'll be assigned to).
    const auto *VD =
        dyn_cast_or_null<VarDecl>(Base.dyn_cast<const ValueDecl *>());
    if (!VD || !VD->isLocalVarDecl() || !VD->getType().isConstQualified())
      return false;
  
    const Expr *Init = VD->getAnyInitializer();
    if (!Init)
      return false;
  
    const Expr *E = Init->IgnoreParens();
    if (!tryUnwrapAllocSizeCall(E))
      return false;
  
    // Store E instead of E unwrapped so that the type of the LValue's base is
    // what the user wanted.
    Result.setInvalid(E);
  
    QualType Pointee = E->getType()->castAs<PointerType>()->getPointeeType();
    Result.addUnsizedArray(Info, E, Pointee);
    return true;
  }
  
  namespace {
  class PointerExprEvaluator
    : public ExprEvaluatorBase<PointerExprEvaluator> {
    LValue &Result;
    bool InvalidBaseOK;
  
    bool Success(const Expr *E) {
      Result.set(E);
      return true;
    }
  
    bool evaluateLValue(const Expr *E, LValue &Result) {
      return EvaluateLValue(E, Result, Info, InvalidBaseOK);
    }
  
    bool evaluatePointer(const Expr *E, LValue &Result) {
      return EvaluatePointer(E, Result, Info, InvalidBaseOK);
    }
  
    bool visitNonBuiltinCallExpr(const CallExpr *E);
  public:
  
    PointerExprEvaluator(EvalInfo &info, LValue &Result, bool InvalidBaseOK)
        : ExprEvaluatorBaseTy(info), Result(Result),
          InvalidBaseOK(InvalidBaseOK) {}
  
    bool Success(const APValue &V, const Expr *E) {
      Result.setFrom(Info.Ctx, V);
      return true;
    }
    bool ZeroInitialization(const Expr *E) {
      Result.setNull(Info.Ctx, E->getType());
      return true;
    }
  
    bool VisitBinaryOperator(const BinaryOperator *E);
    bool VisitCastExpr(const CastExpr* E);
    bool VisitUnaryAddrOf(const UnaryOperator *E);
    bool VisitObjCStringLiteral(const ObjCStringLiteral *E)
        { return Success(E); }
    bool VisitObjCBoxedExpr(const ObjCBoxedExpr *E) {
      if (E->isExpressibleAsConstantInitializer())
        return Success(E);
      if (Info.noteFailure())
        EvaluateIgnoredValue(Info, E->getSubExpr());
      return Error(E);
    }
    bool VisitAddrLabelExpr(const AddrLabelExpr *E)
        { return Success(E); }
    bool VisitCallExpr(const CallExpr *E);
    bool VisitBuiltinCallExpr(const CallExpr *E, unsigned BuiltinOp);
    bool VisitBlockExpr(const BlockExpr *E) {
      if (!E->getBlockDecl()->hasCaptures())
        return Success(E);
      return Error(E);
    }
    bool VisitCXXThisExpr(const CXXThisExpr *E) {
      // Can't look at 'this' when checking a potential constant expression.
      if (Info.checkingPotentialConstantExpression())
        return false;
      if (!Info.CurrentCall->This) {
        if (Info.getLangOpts().CPlusPlus11)
          Info.FFDiag(E, diag::note_constexpr_this) << E->isImplicit();
        else
          Info.FFDiag(E);
        return false;
      }
      Result = *Info.CurrentCall->This;
      // If we are inside a lambda's call operator, the 'this' expression refers
      // to the enclosing '*this' object (either by value or reference) which is
      // either copied into the closure object's field that represents the '*this'
      // or refers to '*this'.
      if (isLambdaCallOperator(Info.CurrentCall->Callee)) {
        // Ensure we actually have captured 'this'. (an error will have
        // been previously reported if not).
        if (!Info.CurrentCall->LambdaThisCaptureField)
          return false;
  
        // Update 'Result' to refer to the data member/field of the closure object
        // that represents the '*this' capture.
        if (!HandleLValueMember(Info, E, Result,
                               Info.CurrentCall->LambdaThisCaptureField))
          return false;
        // If we captured '*this' by reference, replace the field with its referent.
        if (Info.CurrentCall->LambdaThisCaptureField->getType()
                ->isPointerType()) {
          APValue RVal;
          if (!handleLValueToRValueConversion(Info, E, E->getType(), Result,
                                              RVal))
            return false;
  
          Result.setFrom(Info.Ctx, RVal);
        }
      }
      return true;
    }
  
    bool VisitCXXNewExpr(const CXXNewExpr *E);
  
    bool VisitSourceLocExpr(const SourceLocExpr *E) {
      assert(E->isStringType() && "SourceLocExpr isn't a pointer type?");
      APValue LValResult = E->EvaluateInContext(
          Info.Ctx, Info.CurrentCall->CurSourceLocExprScope.getDefaultExpr());
      Result.setFrom(Info.Ctx, LValResult);
      return true;
    }
  
    // FIXME: Missing: @protocol, @selector
  };
  } // end anonymous namespace
  
  static bool EvaluatePointer(const Expr* E, LValue& Result, EvalInfo &Info,
                              bool InvalidBaseOK) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && E->getType()->hasPointerRepresentation());
    return PointerExprEvaluator(Info, Result, InvalidBaseOK).Visit(E);
  }
  
  bool PointerExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
    if (E->getOpcode() != BO_Add &&
        E->getOpcode() != BO_Sub)
      return ExprEvaluatorBaseTy::VisitBinaryOperator(E);
  
    const Expr *PExp = E->getLHS();
    const Expr *IExp = E->getRHS();
    if (IExp->getType()->isPointerType())
      std::swap(PExp, IExp);
  
    bool EvalPtrOK = evaluatePointer(PExp, Result);
    if (!EvalPtrOK && !Info.noteFailure())
      return false;
  
    llvm::APSInt Offset;
    if (!EvaluateInteger(IExp, Offset, Info) || !EvalPtrOK)
      return false;
  
    if (E->getOpcode() == BO_Sub)
      negateAsSigned(Offset);
  
    QualType Pointee = PExp->getType()->castAs<PointerType>()->getPointeeType();
    return HandleLValueArrayAdjustment(Info, E, Result, Pointee, Offset);
  }
  
  bool PointerExprEvaluator::VisitUnaryAddrOf(const UnaryOperator *E) {
    return evaluateLValue(E->getSubExpr(), Result);
  }
  
  bool PointerExprEvaluator::VisitCastExpr(const CastExpr *E) {
    const Expr *SubExpr = E->getSubExpr();
  
    switch (E->getCastKind()) {
    default:
      break;
    case CK_BitCast:
    case CK_CPointerToObjCPointerCast:
    case CK_BlockPointerToObjCPointerCast:
    case CK_AnyPointerToBlockPointerCast:
    case CK_AddressSpaceConversion:
      if (!Visit(SubExpr))
        return false;
      // Bitcasts to cv void* are static_casts, not reinterpret_casts, so are
      // permitted in constant expressions in C++11. Bitcasts from cv void* are
      // also static_casts, but we disallow them as a resolution to DR1312.
      if (!E->getType()->isVoidPointerType()) {
        if (!Result.InvalidBase && !Result.Designator.Invalid &&
            !Result.IsNullPtr &&
            Info.Ctx.hasSameUnqualifiedType(Result.Designator.getType(Info.Ctx),
                                            E->getType()->getPointeeType()) &&
            Info.getStdAllocatorCaller("allocate")) {
          // Inside a call to std::allocator::allocate and friends, we permit
          // casting from void* back to cv1 T* for a pointer that points to a
          // cv2 T.
        } else {
          Result.Designator.setInvalid();
          if (SubExpr->getType()->isVoidPointerType())
            CCEDiag(E, diag::note_constexpr_invalid_cast)
              << 3 << SubExpr->getType();
          else
            CCEDiag(E, diag::note_constexpr_invalid_cast) << 2;
        }
      }
      if (E->getCastKind() == CK_AddressSpaceConversion && Result.IsNullPtr)
        ZeroInitialization(E);
      return true;
  
    case CK_DerivedToBase:
    case CK_UncheckedDerivedToBase:
      if (!evaluatePointer(E->getSubExpr(), Result))
        return false;
      if (!Result.Base && Result.Offset.isZero())
        return true;
  
      // Now figure out the necessary offset to add to the base LV to get from
      // the derived class to the base class.
      return HandleLValueBasePath(Info, E, E->getSubExpr()->getType()->
                                    castAs<PointerType>()->getPointeeType(),
                                  Result);
  
    case CK_BaseToDerived:
      if (!Visit(E->getSubExpr()))
        return false;
      if (!Result.Base && Result.Offset.isZero())
        return true;
      return HandleBaseToDerivedCast(Info, E, Result);
  
    case CK_Dynamic:
      if (!Visit(E->getSubExpr()))
        return false;
      return HandleDynamicCast(Info, cast<ExplicitCastExpr>(E), Result);
  
    case CK_NullToPointer:
      VisitIgnoredValue(E->getSubExpr());
      return ZeroInitialization(E);
  
    case CK_IntegralToPointer: {
      CCEDiag(E, diag::note_constexpr_invalid_cast) << 2;
  
      APValue Value;
      if (!EvaluateIntegerOrLValue(SubExpr, Value, Info))
        break;
  
      if (Value.isInt()) {
        unsigned Size = Info.Ctx.getTypeSize(E->getType());
        uint64_t N = Value.getInt().extOrTrunc(Size).getZExtValue();
        Result.Base = (Expr*)nullptr;
        Result.InvalidBase = false;
        Result.Offset = CharUnits::fromQuantity(N);
        Result.Designator.setInvalid();
        Result.IsNullPtr = false;
        return true;
      } else {
        // Cast is of an lvalue, no need to change value.
        Result.setFrom(Info.Ctx, Value);
        return true;
      }
    }
  
    case CK_ArrayToPointerDecay: {
      if (SubExpr->isGLValue()) {
        if (!evaluateLValue(SubExpr, Result))
          return false;
      } else {
        APValue &Value = Info.CurrentCall->createTemporary(
            SubExpr, SubExpr->getType(), ScopeKind::FullExpression, Result);
        if (!EvaluateInPlace(Value, Info, Result, SubExpr))
          return false;
      }
      // The result is a pointer to the first element of the array.
      auto *AT = Info.Ctx.getAsArrayType(SubExpr->getType());
      if (auto *CAT = dyn_cast<ConstantArrayType>(AT))
        Result.addArray(Info, E, CAT);
      else
        Result.addUnsizedArray(Info, E, AT->getElementType());
      return true;
    }
  
    case CK_FunctionToPointerDecay:
      return evaluateLValue(SubExpr, Result);
  
    case CK_LValueToRValue: {
      LValue LVal;
      if (!evaluateLValue(E->getSubExpr(), LVal))
        return false;
  
      APValue RVal;
      // Note, we use the subexpression's type in order to retain cv-qualifiers.
      if (!handleLValueToRValueConversion(Info, E, E->getSubExpr()->getType(),
                                          LVal, RVal))
        return InvalidBaseOK &&
               evaluateLValueAsAllocSize(Info, LVal.Base, Result);
      return Success(RVal, E);
    }
    }
  
    return ExprEvaluatorBaseTy::VisitCastExpr(E);
  }
  
  static CharUnits GetAlignOfType(EvalInfo &Info, QualType T,
                                  UnaryExprOrTypeTrait ExprKind) {
    // C++ [expr.alignof]p3:
    //     When alignof is applied to a reference type, the result is the
    //     alignment of the referenced type.
    if (const ReferenceType *Ref = T->getAs<ReferenceType>())
      T = Ref->getPointeeType();
  
    if (T.getQualifiers().hasUnaligned())
      return CharUnits::One();
  
    const bool AlignOfReturnsPreferred =
        Info.Ctx.getLangOpts().getClangABICompat() <= LangOptions::ClangABI::Ver7;
  
    // __alignof is defined to return the preferred alignment.
    // Before 8, clang returned the preferred alignment for alignof and _Alignof
    // as well.
    if (ExprKind == UETT_PreferredAlignOf || AlignOfReturnsPreferred)
      return Info.Ctx.toCharUnitsFromBits(
        Info.Ctx.getPreferredTypeAlign(T.getTypePtr()));
    // alignof and _Alignof are defined to return the ABI alignment.
    else if (ExprKind == UETT_AlignOf)
      return Info.Ctx.getTypeAlignInChars(T.getTypePtr());
    else
      llvm_unreachable("GetAlignOfType on a non-alignment ExprKind");
  }
  
  static CharUnits GetAlignOfExpr(EvalInfo &Info, const Expr *E,
                                  UnaryExprOrTypeTrait ExprKind) {
    E = E->IgnoreParens();
  
    // The kinds of expressions that we have special-case logic here for
    // should be kept up to date with the special checks for those
    // expressions in Sema.
  
    // alignof decl is always accepted, even if it doesn't make sense: we default
    // to 1 in those cases.
    if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
      return Info.Ctx.getDeclAlign(DRE->getDecl(),
                                   /*RefAsPointee*/true);
  
    if (const MemberExpr *ME = dyn_cast<MemberExpr>(E))
      return Info.Ctx.getDeclAlign(ME->getMemberDecl(),
                                   /*RefAsPointee*/true);
  
    return GetAlignOfType(Info, E->getType(), ExprKind);
  }
  
  static CharUnits getBaseAlignment(EvalInfo &Info, const LValue &Value) {
    if (const auto *VD = Value.Base.dyn_cast<const ValueDecl *>())
      return Info.Ctx.getDeclAlign(VD);
    if (const auto *E = Value.Base.dyn_cast<const Expr *>())
      return GetAlignOfExpr(Info, E, UETT_AlignOf);
    return GetAlignOfType(Info, Value.Base.getTypeInfoType(), UETT_AlignOf);
  }
  
  /// Evaluate the value of the alignment argument to __builtin_align_{up,down},
  /// __builtin_is_aligned and __builtin_assume_aligned.
  static bool getAlignmentArgument(const Expr *E, QualType ForType,
                                   EvalInfo &Info, APSInt &Alignment) {
    if (!EvaluateInteger(E, Alignment, Info))
      return false;
    if (Alignment < 0 || !Alignment.isPowerOf2()) {
      Info.FFDiag(E, diag::note_constexpr_invalid_alignment) << Alignment;
      return false;
    }
    unsigned SrcWidth = Info.Ctx.getIntWidth(ForType);
    APSInt MaxValue(APInt::getOneBitSet(SrcWidth, SrcWidth - 1));
    if (APSInt::compareValues(Alignment, MaxValue) > 0) {
      Info.FFDiag(E, diag::note_constexpr_alignment_too_big)
          << MaxValue << ForType << Alignment;
      return false;
    }
    // Ensure both alignment and source value have the same bit width so that we
    // don't assert when computing the resulting value.
    APSInt ExtAlignment =
        APSInt(Alignment.zextOrTrunc(SrcWidth), /*isUnsigned=*/true);
    assert(APSInt::compareValues(Alignment, ExtAlignment) == 0 &&
           "Alignment should not be changed by ext/trunc");
    Alignment = ExtAlignment;
    assert(Alignment.getBitWidth() == SrcWidth);
    return true;
  }
  
  // To be clear: this happily visits unsupported builtins. Better name welcomed.
  bool PointerExprEvaluator::visitNonBuiltinCallExpr(const CallExpr *E) {
    if (ExprEvaluatorBaseTy::VisitCallExpr(E))
      return true;
  
    if (!(InvalidBaseOK && getAllocSizeAttr(E)))
      return false;
  
    Result.setInvalid(E);
    QualType PointeeTy = E->getType()->castAs<PointerType>()->getPointeeType();
    Result.addUnsizedArray(Info, E, PointeeTy);
    return true;
  }
  
  bool PointerExprEvaluator::VisitCallExpr(const CallExpr *E) {
    if (IsStringLiteralCall(E))
      return Success(E);
  
    if (unsigned BuiltinOp = E->getBuiltinCallee())
      return VisitBuiltinCallExpr(E, BuiltinOp);
  
    return visitNonBuiltinCallExpr(E);
  }
  
  // Determine if T is a character type for which we guarantee that
  // sizeof(T) == 1.
  static bool isOneByteCharacterType(QualType T) {
    return T->isCharType() || T->isChar8Type();
  }
  
  bool PointerExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
                                                  unsigned BuiltinOp) {
    switch (BuiltinOp) {
    case Builtin::BI__builtin_addressof:
      return evaluateLValue(E->getArg(0), Result);
    case Builtin::BI__builtin_assume_aligned: {
      // We need to be very careful here because: if the pointer does not have the
      // asserted alignment, then the behavior is undefined, and undefined
      // behavior is non-constant.
      if (!evaluatePointer(E->getArg(0), Result))
        return false;
  
      LValue OffsetResult(Result);
      APSInt Alignment;
      if (!getAlignmentArgument(E->getArg(1), E->getArg(0)->getType(), Info,
                                Alignment))
        return false;
      CharUnits Align = CharUnits::fromQuantity(Alignment.getZExtValue());
  
      if (E->getNumArgs() > 2) {
        APSInt Offset;
        if (!EvaluateInteger(E->getArg(2), Offset, Info))
          return false;
  
        int64_t AdditionalOffset = -Offset.getZExtValue();
        OffsetResult.Offset += CharUnits::fromQuantity(AdditionalOffset);
      }
  
      // If there is a base object, then it must have the correct alignment.
      if (OffsetResult.Base) {
        CharUnits BaseAlignment = getBaseAlignment(Info, OffsetResult);
  
        if (BaseAlignment < Align) {
          Result.Designator.setInvalid();
          // FIXME: Add support to Diagnostic for long / long long.
          CCEDiag(E->getArg(0),
                  diag::note_constexpr_baa_insufficient_alignment) << 0
            << (unsigned)BaseAlignment.getQuantity()
            << (unsigned)Align.getQuantity();
          return false;
        }
      }
  
      // The offset must also have the correct alignment.
      if (OffsetResult.Offset.alignTo(Align) != OffsetResult.Offset) {
        Result.Designator.setInvalid();
  
        (OffsetResult.Base
             ? CCEDiag(E->getArg(0),
                       diag::note_constexpr_baa_insufficient_alignment) << 1
             : CCEDiag(E->getArg(0),
                       diag::note_constexpr_baa_value_insufficient_alignment))
          << (int)OffsetResult.Offset.getQuantity()
          << (unsigned)Align.getQuantity();
        return false;
      }
  
      return true;
    }
    case Builtin::BI__builtin_align_up:
    case Builtin::BI__builtin_align_down: {
      if (!evaluatePointer(E->getArg(0), Result))
        return false;
      APSInt Alignment;
      if (!getAlignmentArgument(E->getArg(1), E->getArg(0)->getType(), Info,
                                Alignment))
        return false;
      CharUnits BaseAlignment = getBaseAlignment(Info, Result);
      CharUnits PtrAlign = BaseAlignment.alignmentAtOffset(Result.Offset);
      // For align_up/align_down, we can return the same value if the alignment
      // is known to be greater or equal to the requested value.
      if (PtrAlign.getQuantity() >= Alignment)
        return true;
  
      // The alignment could be greater than the minimum at run-time, so we cannot
      // infer much about the resulting pointer value. One case is possible:
      // For `_Alignas(32) char buf[N]; __builtin_align_down(&buf[idx], 32)` we
      // can infer the correct index if the requested alignment is smaller than
      // the base alignment so we can perform the computation on the offset.
      if (BaseAlignment.getQuantity() >= Alignment) {
        assert(Alignment.getBitWidth() <= 64 &&
               "Cannot handle > 64-bit address-space");
        uint64_t Alignment64 = Alignment.getZExtValue();
        CharUnits NewOffset = CharUnits::fromQuantity(
            BuiltinOp == Builtin::BI__builtin_align_down
                ? llvm::alignDown(Result.Offset.getQuantity(), Alignment64)
                : llvm::alignTo(Result.Offset.getQuantity(), Alignment64));
        Result.adjustOffset(NewOffset - Result.Offset);
        // TODO: diagnose out-of-bounds values/only allow for arrays?
        return true;
      }
      // Otherwise, we cannot constant-evaluate the result.
      Info.FFDiag(E->getArg(0), diag::note_constexpr_alignment_adjust)
          << Alignment;
      return false;
    }
    case Builtin::BI__builtin_operator_new:
      return HandleOperatorNewCall(Info, E, Result);
    case Builtin::BI__builtin_ptrauth_sign_constant:
      return Success(E);
    case Builtin::BI__builtin_launder:
      return evaluatePointer(E->getArg(0), Result);
    case Builtin::BIstrchr:
    case Builtin::BIwcschr:
    case Builtin::BImemchr:
    case Builtin::BIwmemchr:
      if (Info.getLangOpts().CPlusPlus11)
        Info.CCEDiag(E, diag::note_constexpr_invalid_function)
          << /*isConstexpr*/0 << /*isConstructor*/0
          << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) + "'");
      else
        Info.CCEDiag(E, diag::note_invalid_subexpr_in_const_expr);
      LLVM_FALLTHROUGH;
    case Builtin::BI__builtin_strchr:
    case Builtin::BI__builtin_wcschr:
    case Builtin::BI__builtin_memchr:
    case Builtin::BI__builtin_char_memchr:
    case Builtin::BI__builtin_wmemchr: {
      if (!Visit(E->getArg(0)))
        return false;
      APSInt Desired;
      if (!EvaluateInteger(E->getArg(1), Desired, Info))
        return false;
      uint64_t MaxLength = uint64_t(-1);
      if (BuiltinOp != Builtin::BIstrchr &&
          BuiltinOp != Builtin::BIwcschr &&
          BuiltinOp != Builtin::BI__builtin_strchr &&
          BuiltinOp != Builtin::BI__builtin_wcschr) {
        APSInt N;
        if (!EvaluateInteger(E->getArg(2), N, Info))
          return false;
        MaxLength = N.getExtValue();
      }
      // We cannot find the value if there are no candidates to match against.
      if (MaxLength == 0u)
        return ZeroInitialization(E);
      if (!Result.checkNullPointerForFoldAccess(Info, E, AK_Read) ||
          Result.Designator.Invalid)
        return false;
      QualType CharTy = Result.Designator.getType(Info.Ctx);
      bool IsRawByte = BuiltinOp == Builtin::BImemchr ||
                       BuiltinOp == Builtin::BI__builtin_memchr;
      assert(IsRawByte ||
             Info.Ctx.hasSameUnqualifiedType(
                 CharTy, E->getArg(0)->getType()->getPointeeType()));
      // Pointers to const void may point to objects of incomplete type.
      if (IsRawByte && CharTy->isIncompleteType()) {
        Info.FFDiag(E, diag::note_constexpr_ltor_incomplete_type) << CharTy;
        return false;
      }
      // Give up on byte-oriented matching against multibyte elements.
      // FIXME: We can compare the bytes in the correct order.
      if (IsRawByte && !isOneByteCharacterType(CharTy)) {
        Info.FFDiag(E, diag::note_constexpr_memchr_unsupported)
            << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) + "'")
            << CharTy;
        return false;
      }
      // Figure out what value we're actually looking for (after converting to
      // the corresponding unsigned type if necessary).
      uint64_t DesiredVal;
      bool StopAtNull = false;
      switch (BuiltinOp) {
      case Builtin::BIstrchr:
      case Builtin::BI__builtin_strchr:
        // strchr compares directly to the passed integer, and therefore
        // always fails if given an int that is not a char.
        if (!APSInt::isSameValue(HandleIntToIntCast(Info, E, CharTy,
                                                    E->getArg(1)->getType(),
                                                    Desired),
                                 Desired))
          return ZeroInitialization(E);
        StopAtNull = true;
        LLVM_FALLTHROUGH;
      case Builtin::BImemchr:
      case Builtin::BI__builtin_memchr:
      case Builtin::BI__builtin_char_memchr:
        // memchr compares by converting both sides to unsigned char. That's also
        // correct for strchr if we get this far (to cope with plain char being
        // unsigned in the strchr case).
        DesiredVal = Desired.trunc(Info.Ctx.getCharWidth()).getZExtValue();
        break;
  
      case Builtin::BIwcschr:
      case Builtin::BI__builtin_wcschr:
        StopAtNull = true;
        LLVM_FALLTHROUGH;
      case Builtin::BIwmemchr:
      case Builtin::BI__builtin_wmemchr:
        // wcschr and wmemchr are given a wchar_t to look for. Just use it.
        DesiredVal = Desired.getZExtValue();
        break;
      }
  
      for (; MaxLength; --MaxLength) {
        APValue Char;
        if (!handleLValueToRValueConversion(Info, E, CharTy, Result, Char) ||
            !Char.isInt())
          return false;
        if (Char.getInt().getZExtValue() == DesiredVal)
          return true;
        if (StopAtNull && !Char.getInt())
          break;
        if (!HandleLValueArrayAdjustment(Info, E, Result, CharTy, 1))
          return false;
      }
      // Not found: return nullptr.
      return ZeroInitialization(E);
    }
  
    case Builtin::BImemcpy:
    case Builtin::BImemmove:
    case Builtin::BIwmemcpy:
    case Builtin::BIwmemmove:
      if (Info.getLangOpts().CPlusPlus11)
        Info.CCEDiag(E, diag::note_constexpr_invalid_function)
          << /*isConstexpr*/0 << /*isConstructor*/0
          << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) + "'");
      else
        Info.CCEDiag(E, diag::note_invalid_subexpr_in_const_expr);
      LLVM_FALLTHROUGH;
    case Builtin::BI__builtin_memcpy:
    case Builtin::BI__builtin_memmove:
    case Builtin::BI__builtin_wmemcpy:
    case Builtin::BI__builtin_wmemmove: {
      bool WChar = BuiltinOp == Builtin::BIwmemcpy ||
                   BuiltinOp == Builtin::BIwmemmove ||
                   BuiltinOp == Builtin::BI__builtin_wmemcpy ||
                   BuiltinOp == Builtin::BI__builtin_wmemmove;
      bool Move = BuiltinOp == Builtin::BImemmove ||
                  BuiltinOp == Builtin::BIwmemmove ||
                  BuiltinOp == Builtin::BI__builtin_memmove ||
                  BuiltinOp == Builtin::BI__builtin_wmemmove;
  
      // The result of mem* is the first argument.
      if (!Visit(E->getArg(0)))
        return false;
      LValue Dest = Result;
  
      LValue Src;
      if (!EvaluatePointer(E->getArg(1), Src, Info))
        return false;
  
      APSInt N;
      if (!EvaluateInteger(E->getArg(2), N, Info))
        return false;
      assert(!N.isSigned() && "memcpy and friends take an unsigned size");
  
      // If the size is zero, we treat this as always being a valid no-op.
      // (Even if one of the src and dest pointers is null.)
      if (!N)
        return true;
  
      // Otherwise, if either of the operands is null, we can't proceed. Don't
      // try to determine the type of the copied objects, because there aren't
      // any.
      if (!Src.Base || !Dest.Base) {
        APValue Val;
        (!Src.Base ? Src : Dest).moveInto(Val);
        Info.FFDiag(E, diag::note_constexpr_memcpy_null)
            << Move << WChar << !!Src.Base
            << Val.getAsString(Info.Ctx, E->getArg(0)->getType());
        return false;
      }
      if (Src.Designator.Invalid || Dest.Designator.Invalid)
        return false;
  
      // We require that Src and Dest are both pointers to arrays of
      // trivially-copyable type. (For the wide version, the designator will be
      // invalid if the designated object is not a wchar_t.)
      QualType T = Dest.Designator.getType(Info.Ctx);
      QualType SrcT = Src.Designator.getType(Info.Ctx);
      if (!Info.Ctx.hasSameUnqualifiedType(T, SrcT)) {
        // FIXME: Consider using our bit_cast implementation to support this.
        Info.FFDiag(E, diag::note_constexpr_memcpy_type_pun) << Move << SrcT << T;
        return false;
      }
      if (T->isIncompleteType()) {
        Info.FFDiag(E, diag::note_constexpr_memcpy_incomplete_type) << Move << T;
        return false;
      }
      if (!T.isTriviallyCopyableType(Info.Ctx)) {
        Info.FFDiag(E, diag::note_constexpr_memcpy_nontrivial) << Move << T;
        return false;
      }
  
      // Figure out how many T's we're copying.
      uint64_t TSize = Info.Ctx.getTypeSizeInChars(T).getQuantity();
      if (!WChar) {
        uint64_t Remainder;
        llvm::APInt OrigN = N;
        llvm::APInt::udivrem(OrigN, TSize, N, Remainder);
        if (Remainder) {
          Info.FFDiag(E, diag::note_constexpr_memcpy_unsupported)
              << Move << WChar << 0 << T << OrigN.toString(10, /*Signed*/false)
              << (unsigned)TSize;
          return false;
        }
      }
  
      // Check that the copying will remain within the arrays, just so that we
      // can give a more meaningful diagnostic. This implicitly also checks that
      // N fits into 64 bits.
      uint64_t RemainingSrcSize = Src.Designator.validIndexAdjustments().second;
      uint64_t RemainingDestSize = Dest.Designator.validIndexAdjustments().second;
      if (N.ugt(RemainingSrcSize) || N.ugt(RemainingDestSize)) {
        Info.FFDiag(E, diag::note_constexpr_memcpy_unsupported)
            << Move << WChar << (N.ugt(RemainingSrcSize) ? 1 : 2) << T
            << N.toString(10, /*Signed*/false);
        return false;
      }
      uint64_t NElems = N.getZExtValue();
      uint64_t NBytes = NElems * TSize;
  
      // Check for overlap.
      int Direction = 1;
      if (HasSameBase(Src, Dest)) {
        uint64_t SrcOffset = Src.getLValueOffset().getQuantity();
        uint64_t DestOffset = Dest.getLValueOffset().getQuantity();
        if (DestOffset >= SrcOffset && DestOffset - SrcOffset < NBytes) {
          // Dest is inside the source region.
          if (!Move) {
            Info.FFDiag(E, diag::note_constexpr_memcpy_overlap) << WChar;
            return false;
          }
          // For memmove and friends, copy backwards.
          if (!HandleLValueArrayAdjustment(Info, E, Src, T, NElems - 1) ||
              !HandleLValueArrayAdjustment(Info, E, Dest, T, NElems - 1))
            return false;
          Direction = -1;
        } else if (!Move && SrcOffset >= DestOffset &&
                   SrcOffset - DestOffset < NBytes) {
          // Src is inside the destination region for memcpy: invalid.
          Info.FFDiag(E, diag::note_constexpr_memcpy_overlap) << WChar;
          return false;
        }
      }
  
      while (true) {
        APValue Val;
        // FIXME: Set WantObjectRepresentation to true if we're copying a
        // char-like type?
        if (!handleLValueToRValueConversion(Info, E, T, Src, Val) ||
            !handleAssignment(Info, E, Dest, T, Val))
          return false;
        // Do not iterate past the last element; if we're copying backwards, that
        // might take us off the start of the array.
        if (--NElems == 0)
          return true;
        if (!HandleLValueArrayAdjustment(Info, E, Src, T, Direction) ||
            !HandleLValueArrayAdjustment(Info, E, Dest, T, Direction))
          return false;
      }
    }
  
    default:
      break;
    }
  
    return visitNonBuiltinCallExpr(E);
  }
  
  static bool EvaluateArrayNewInitList(EvalInfo &Info, LValue &This,
                                       APValue &Result, const InitListExpr *ILE,
                                       QualType AllocType);
  static bool EvaluateArrayNewConstructExpr(EvalInfo &Info, LValue &This,
                                            APValue &Result,
                                            const CXXConstructExpr *CCE,
                                            QualType AllocType);
  
  bool PointerExprEvaluator::VisitCXXNewExpr(const CXXNewExpr *E) {
    if (!Info.getLangOpts().CPlusPlus20)
      Info.CCEDiag(E, diag::note_constexpr_new);
  
    // We cannot speculatively evaluate a delete expression.
    if (Info.SpeculativeEvaluationDepth)
      return false;
  
    FunctionDecl *OperatorNew = E->getOperatorNew();
  
    bool IsNothrow = false;
    bool IsPlacement = false;
    if (OperatorNew->isReservedGlobalPlacementOperator() &&
        Info.CurrentCall->isStdFunction() && !E->isArray()) {
      // FIXME Support array placement new.
      assert(E->getNumPlacementArgs() == 1);
      if (!EvaluatePointer(E->getPlacementArg(0), Result, Info))
        return false;
      if (Result.Designator.Invalid)
        return false;
      IsPlacement = true;
    } else if (!OperatorNew->isReplaceableGlobalAllocationFunction()) {
      Info.FFDiag(E, diag::note_constexpr_new_non_replaceable)
          << isa<CXXMethodDecl>(OperatorNew) << OperatorNew;
      return false;
    } else if (E->getNumPlacementArgs()) {
      // The only new-placement list we support is of the form (std::nothrow).
      //
      // FIXME: There is no restriction on this, but it's not clear that any
      // other form makes any sense. We get here for cases such as:
      //
      //   new (std::align_val_t{N}) X(int)
      //
      // (which should presumably be valid only if N is a multiple of
      // alignof(int), and in any case can't be deallocated unless N is
      // alignof(X) and X has new-extended alignment).
      if (E->getNumPlacementArgs() != 1 ||
          !E->getPlacementArg(0)->getType()->isNothrowT())
        return Error(E, diag::note_constexpr_new_placement);
  
      LValue Nothrow;
      if (!EvaluateLValue(E->getPlacementArg(0), Nothrow, Info))
        return false;
      IsNothrow = true;
    }
  
    const Expr *Init = E->getInitializer();
    const InitListExpr *ResizedArrayILE = nullptr;
    const CXXConstructExpr *ResizedArrayCCE = nullptr;
    bool ValueInit = false;
  
    QualType AllocType = E->getAllocatedType();
    if (Optional<const Expr*> ArraySize = E->getArraySize()) {
      const Expr *Stripped = *ArraySize;
      for (; auto *ICE = dyn_cast<ImplicitCastExpr>(Stripped);
           Stripped = ICE->getSubExpr())
        if (ICE->getCastKind() != CK_NoOp &&
            ICE->getCastKind() != CK_IntegralCast)
          break;
  
      llvm::APSInt ArrayBound;
      if (!EvaluateInteger(Stripped, ArrayBound, Info))
        return false;
  
      // C++ [expr.new]p9:
      //   The expression is erroneous if:
      //   -- [...] its value before converting to size_t [or] applying the
      //      second standard conversion sequence is less than zero
      if (ArrayBound.isSigned() && ArrayBound.isNegative()) {
        if (IsNothrow)
          return ZeroInitialization(E);
  
        Info.FFDiag(*ArraySize, diag::note_constexpr_new_negative)
            << ArrayBound << (*ArraySize)->getSourceRange();
        return false;
      }
  
      //   -- its value is such that the size of the allocated object would
      //      exceed the implementation-defined limit
      if (ConstantArrayType::getNumAddressingBits(Info.Ctx, AllocType,
                                                  ArrayBound) >
          ConstantArrayType::getMaxSizeBits(Info.Ctx)) {
        if (IsNothrow)
          return ZeroInitialization(E);
  
        Info.FFDiag(*ArraySize, diag::note_constexpr_new_too_large)
          << ArrayBound << (*ArraySize)->getSourceRange();
        return false;
      }
  
      //   -- the new-initializer is a braced-init-list and the number of
      //      array elements for which initializers are provided [...]
      //      exceeds the number of elements to initialize
      if (!Init) {
        // No initialization is performed.
      } else if (isa<CXXScalarValueInitExpr>(Init) ||
                 isa<ImplicitValueInitExpr>(Init)) {
        ValueInit = true;
      } else if (auto *CCE = dyn_cast<CXXConstructExpr>(Init)) {
        ResizedArrayCCE = CCE;
      } else {
        auto *CAT = Info.Ctx.getAsConstantArrayType(Init->getType());
        assert(CAT && "unexpected type for array initializer");
  
        unsigned Bits =
            std::max(CAT->getSize().getBitWidth(), ArrayBound.getBitWidth());
        llvm::APInt InitBound = CAT->getSize().zextOrSelf(Bits);
        llvm::APInt AllocBound = ArrayBound.zextOrSelf(Bits);
        if (InitBound.ugt(AllocBound)) {
          if (IsNothrow)
            return ZeroInitialization(E);
  
          Info.FFDiag(*ArraySize, diag::note_constexpr_new_too_small)
              << AllocBound.toString(10, /*Signed=*/false)
              << InitBound.toString(10, /*Signed=*/false)
              << (*ArraySize)->getSourceRange();
          return false;
        }
  
        // If the sizes differ, we must have an initializer list, and we need
        // special handling for this case when we initialize.
        if (InitBound != AllocBound)
          ResizedArrayILE = cast<InitListExpr>(Init);
      }
  
      AllocType = Info.Ctx.getConstantArrayType(AllocType, ArrayBound, nullptr,
                                                ArrayType::Normal, 0);
    } else {
      assert(!AllocType->isArrayType() &&
             "array allocation with non-array new");
    }
  
    APValue *Val;
    if (IsPlacement) {
      AccessKinds AK = AK_Construct;
      struct FindObjectHandler {
        EvalInfo &Info;
        const Expr *E;
        QualType AllocType;
        const AccessKinds AccessKind;
        APValue *Value;
  
        typedef bool result_type;
        bool failed() { return false; }
        bool found(APValue &Subobj, QualType SubobjType) {
          // FIXME: Reject the cases where [basic.life]p8 would not permit the
          // old name of the object to be used to name the new object.
          if (!Info.Ctx.hasSameUnqualifiedType(SubobjType, AllocType)) {
            Info.FFDiag(E, diag::note_constexpr_placement_new_wrong_type) <<
              SubobjType << AllocType;
            return false;
          }
          Value = &Subobj;
          return true;
        }
        bool found(APSInt &Value, QualType SubobjType) {
          Info.FFDiag(E, diag::note_constexpr_construct_complex_elem);
          return false;
        }
        bool found(APFloat &Value, QualType SubobjType) {
          Info.FFDiag(E, diag::note_constexpr_construct_complex_elem);
          return false;
        }
      } Handler = {Info, E, AllocType, AK, nullptr};
  
      CompleteObject Obj = findCompleteObject(Info, E, AK, Result, AllocType);
      if (!Obj || !findSubobject(Info, E, Obj, Result.Designator, Handler))
        return false;
  
      Val = Handler.Value;
  
      // [basic.life]p1:
      //   The lifetime of an object o of type T ends when [...] the storage
      //   which the object occupies is [...] reused by an object that is not
      //   nested within o (6.6.2).
      *Val = APValue();
    } else {
      // Perform the allocation and obtain a pointer to the resulting object.
      Val = Info.createHeapAlloc(E, AllocType, Result);
      if (!Val)
        return false;
    }
  
    if (ValueInit) {
      ImplicitValueInitExpr VIE(AllocType);
      if (!EvaluateInPlace(*Val, Info, Result, &VIE))
        return false;
    } else if (ResizedArrayILE) {
      if (!EvaluateArrayNewInitList(Info, Result, *Val, ResizedArrayILE,
                                    AllocType))
        return false;
    } else if (ResizedArrayCCE) {
      if (!EvaluateArrayNewConstructExpr(Info, Result, *Val, ResizedArrayCCE,
                                         AllocType))
        return false;
    } else if (Init) {
      if (!EvaluateInPlace(*Val, Info, Result, Init))
        return false;
    } else if (!getDefaultInitValue(AllocType, *Val)) {
      return false;
    }
  
    // Array new returns a pointer to the first element, not a pointer to the
    // array.
    if (auto *AT = AllocType->getAsArrayTypeUnsafe())
      Result.addArray(Info, E, cast<ConstantArrayType>(AT));
  
    return true;
  }
  //===----------------------------------------------------------------------===//
  // Member Pointer Evaluation
  //===----------------------------------------------------------------------===//
  
  namespace {
  class MemberPointerExprEvaluator
    : public ExprEvaluatorBase<MemberPointerExprEvaluator> {
    MemberPtr &Result;
  
    bool Success(const ValueDecl *D) {
      Result = MemberPtr(D);
      return true;
    }
  public:
  
    MemberPointerExprEvaluator(EvalInfo &Info, MemberPtr &Result)
      : ExprEvaluatorBaseTy(Info), Result(Result) {}
  
    bool Success(const APValue &V, const Expr *E) {
      Result.setFrom(V);
      return true;
    }
    bool ZeroInitialization(const Expr *E) {
      return Success((const ValueDecl*)nullptr);
    }
  
    bool VisitCastExpr(const CastExpr *E);
    bool VisitUnaryAddrOf(const UnaryOperator *E);
  };
  } // end anonymous namespace
  
  static bool EvaluateMemberPointer(const Expr *E, MemberPtr &Result,
                                    EvalInfo &Info) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && E->getType()->isMemberPointerType());
    return MemberPointerExprEvaluator(Info, Result).Visit(E);
  }
  
  bool MemberPointerExprEvaluator::VisitCastExpr(const CastExpr *E) {
    switch (E->getCastKind()) {
    default:
      return ExprEvaluatorBaseTy::VisitCastExpr(E);
  
    case CK_NullToMemberPointer:
      VisitIgnoredValue(E->getSubExpr());
      return ZeroInitialization(E);
  
    case CK_BaseToDerivedMemberPointer: {
      if (!Visit(E->getSubExpr()))
        return false;
      if (E->path_empty())
        return true;
      // Base-to-derived member pointer casts store the path in derived-to-base
      // order, so iterate backwards. The CXXBaseSpecifier also provides us with
      // the wrong end of the derived->base arc, so stagger the path by one class.
      typedef std::reverse_iterator<CastExpr::path_const_iterator> ReverseIter;
      for (ReverseIter PathI(E->path_end() - 1), PathE(E->path_begin());
           PathI != PathE; ++PathI) {
        assert(!(*PathI)->isVirtual() && "memptr cast through vbase");
        const CXXRecordDecl *Derived = (*PathI)->getType()->getAsCXXRecordDecl();
        if (!Result.castToDerived(Derived))
          return Error(E);
      }
      const Type *FinalTy = E->getType()->castAs<MemberPointerType>()->getClass();
      if (!Result.castToDerived(FinalTy->getAsCXXRecordDecl()))
        return Error(E);
      return true;
    }
  
    case CK_DerivedToBaseMemberPointer:
      if (!Visit(E->getSubExpr()))
        return false;
      for (CastExpr::path_const_iterator PathI = E->path_begin(),
           PathE = E->path_end(); PathI != PathE; ++PathI) {
        assert(!(*PathI)->isVirtual() && "memptr cast through vbase");
        const CXXRecordDecl *Base = (*PathI)->getType()->getAsCXXRecordDecl();
        if (!Result.castToBase(Base))
          return Error(E);
      }
      return true;
    }
  }
  
  bool MemberPointerExprEvaluator::VisitUnaryAddrOf(const UnaryOperator *E) {
    // C++11 [expr.unary.op]p3 has very strict rules on how the address of a
    // member can be formed.
    return Success(cast<DeclRefExpr>(E->getSubExpr())->getDecl());
  }
  
  //===----------------------------------------------------------------------===//
  // Record Evaluation
  //===----------------------------------------------------------------------===//
  
  namespace {
    class RecordExprEvaluator
    : public ExprEvaluatorBase<RecordExprEvaluator> {
      const LValue &This;
      APValue &Result;
    public:
  
      RecordExprEvaluator(EvalInfo &info, const LValue &This, APValue &Result)
        : ExprEvaluatorBaseTy(info), This(This), Result(Result) {}
  
      bool Success(const APValue &V, const Expr *E) {
        Result = V;
        return true;
      }
      bool ZeroInitialization(const Expr *E) {
        return ZeroInitialization(E, E->getType());
      }
      bool ZeroInitialization(const Expr *E, QualType T);
  
      bool VisitCallExpr(const CallExpr *E) {
        return handleCallExpr(E, Result, &This);
      }
      bool VisitCastExpr(const CastExpr *E);
      bool VisitInitListExpr(const InitListExpr *E);
      bool VisitCXXConstructExpr(const CXXConstructExpr *E) {
        return VisitCXXConstructExpr(E, E->getType());
      }
      bool VisitLambdaExpr(const LambdaExpr *E);
      bool VisitCXXInheritedCtorInitExpr(const CXXInheritedCtorInitExpr *E);
      bool VisitCXXConstructExpr(const CXXConstructExpr *E, QualType T);
      bool VisitCXXStdInitializerListExpr(const CXXStdInitializerListExpr *E);
      bool VisitBinCmp(const BinaryOperator *E);
    };
  }
  
  /// Perform zero-initialization on an object of non-union class type.
  /// C++11 [dcl.init]p5:
  ///  To zero-initialize an object or reference of type T means:
  ///    [...]
  ///    -- if T is a (possibly cv-qualified) non-union class type,
  ///       each non-static data member and each base-class subobject is
  ///       zero-initialized
  static bool HandleClassZeroInitialization(EvalInfo &Info, const Expr *E,
                                            const RecordDecl *RD,
                                            const LValue &This, APValue &Result) {
    assert(!RD->isUnion() && "Expected non-union class type");
    const CXXRecordDecl *CD = dyn_cast<CXXRecordDecl>(RD);
    Result = APValue(APValue::UninitStruct(), CD ? CD->getNumBases() : 0,
                     std::distance(RD->field_begin(), RD->field_end()));
  
    if (RD->isInvalidDecl()) return false;
    const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);
  
    if (CD) {
      unsigned Index = 0;
      for (CXXRecordDecl::base_class_const_iterator I = CD->bases_begin(),
             End = CD->bases_end(); I != End; ++I, ++Index) {
        const CXXRecordDecl *Base = I->getType()->getAsCXXRecordDecl();
        LValue Subobject = This;
        if (!HandleLValueDirectBase(Info, E, Subobject, CD, Base, &Layout))
          return false;
        if (!HandleClassZeroInitialization(Info, E, Base, Subobject,
                                           Result.getStructBase(Index)))
          return false;
      }
    }
  
    for (const auto *I : RD->fields()) {
      // -- if T is a reference type, no initialization is performed.
      if (I->isUnnamedBitfield() || I->getType()->isReferenceType())
        continue;
  
      LValue Subobject = This;
      if (!HandleLValueMember(Info, E, Subobject, I, &Layout))
        return false;
  
      ImplicitValueInitExpr VIE(I->getType());
      if (!EvaluateInPlace(
            Result.getStructField(I->getFieldIndex()), Info, Subobject, &VIE))
        return false;
    }
  
    return true;
  }
  
  bool RecordExprEvaluator::ZeroInitialization(const Expr *E, QualType T) {
    const RecordDecl *RD = T->castAs<RecordType>()->getDecl();
    if (RD->isInvalidDecl()) return false;
    if (RD->isUnion()) {
      // C++11 [dcl.init]p5: If T is a (possibly cv-qualified) union type, the
      // object's first non-static named data member is zero-initialized
      RecordDecl::field_iterator I = RD->field_begin();
      while (I != RD->field_end() && (*I)->isUnnamedBitfield())
        ++I;
      if (I == RD->field_end()) {
        Result = APValue((const FieldDecl*)nullptr);
        return true;
      }
  
      LValue Subobject = This;
      if (!HandleLValueMember(Info, E, Subobject, *I))
        return false;
      Result = APValue(*I);
      ImplicitValueInitExpr VIE(I->getType());
      return EvaluateInPlace(Result.getUnionValue(), Info, Subobject, &VIE);
    }
  
    if (isa<CXXRecordDecl>(RD) && cast<CXXRecordDecl>(RD)->getNumVBases()) {
      Info.FFDiag(E, diag::note_constexpr_virtual_base) << RD;
      return false;
    }
  
    return HandleClassZeroInitialization(Info, E, RD, This, Result);
  }
  
  bool RecordExprEvaluator::VisitCastExpr(const CastExpr *E) {
    switch (E->getCastKind()) {
    default:
      return ExprEvaluatorBaseTy::VisitCastExpr(E);
  
    case CK_ConstructorConversion:
      return Visit(E->getSubExpr());
  
    case CK_DerivedToBase:
    case CK_UncheckedDerivedToBase: {
      APValue DerivedObject;
      if (!Evaluate(DerivedObject, Info, E->getSubExpr()))
        return false;
      if (!DerivedObject.isStruct())
        return Error(E->getSubExpr());
  
      // Derived-to-base rvalue conversion: just slice off the derived part.
      APValue *Value = &DerivedObject;
      const CXXRecordDecl *RD = E->getSubExpr()->getType()->getAsCXXRecordDecl();
      for (CastExpr::path_const_iterator PathI = E->path_begin(),
           PathE = E->path_end(); PathI != PathE; ++PathI) {
        assert(!(*PathI)->isVirtual() && "record rvalue with virtual base");
        const CXXRecordDecl *Base = (*PathI)->getType()->getAsCXXRecordDecl();
        Value = &Value->getStructBase(getBaseIndex(RD, Base));
        RD = Base;
      }
      Result = *Value;
      return true;
    }
    }
  }
  
  bool RecordExprEvaluator::VisitInitListExpr(const InitListExpr *E) {
    if (E->isTransparent())
      return Visit(E->getInit(0));
  
    const RecordDecl *RD = E->getType()->castAs<RecordType>()->getDecl();
    if (RD->isInvalidDecl()) return false;
    const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);
    auto *CXXRD = dyn_cast<CXXRecordDecl>(RD);
  
    EvalInfo::EvaluatingConstructorRAII EvalObj(
        Info,
        ObjectUnderConstruction{This.getLValueBase(), This.Designator.Entries},
        CXXRD && CXXRD->getNumBases());
  
    if (RD->isUnion()) {
      const FieldDecl *Field = E->getInitializedFieldInUnion();
      Result = APValue(Field);
      if (!Field)
        return true;
  
      // If the initializer list for a union does not contain any elements, the
      // first element of the union is value-initialized.
      // FIXME: The element should be initialized from an initializer list.
      //        Is this difference ever observable for initializer lists which
      //        we don't build?
      ImplicitValueInitExpr VIE(Field->getType());
      const Expr *InitExpr = E->getNumInits() ? E->getInit(0) : &VIE;
  
      LValue Subobject = This;
      if (!HandleLValueMember(Info, InitExpr, Subobject, Field, &Layout))
        return false;
  
      // Temporarily override This, in case there's a CXXDefaultInitExpr in here.
      ThisOverrideRAII ThisOverride(*Info.CurrentCall, &This,
                                    isa<CXXDefaultInitExpr>(InitExpr));
  
      if (EvaluateInPlace(Result.getUnionValue(), Info, Subobject, InitExpr)) {
        if (Field->isBitField())
          return truncateBitfieldValue(Info, InitExpr, Result.getUnionValue(),
                                       Field);
        return true;
      }
  
      return false;
    }
  
    if (!Result.hasValue())
      Result = APValue(APValue::UninitStruct(), CXXRD ? CXXRD->getNumBases() : 0,
                       std::distance(RD->field_begin(), RD->field_end()));
    unsigned ElementNo = 0;
    bool Success = true;
  
    // Initialize base classes.
    if (CXXRD && CXXRD->getNumBases()) {
      for (const auto &Base : CXXRD->bases()) {
        assert(ElementNo < E->getNumInits() && "missing init for base class");
        const Expr *Init = E->getInit(ElementNo);
  
        LValue Subobject = This;
        if (!HandleLValueBase(Info, Init, Subobject, CXXRD, &Base))
          return false;
  
        APValue &FieldVal = Result.getStructBase(ElementNo);
        if (!EvaluateInPlace(FieldVal, Info, Subobject, Init)) {
          if (!Info.noteFailure())
            return false;
          Success = false;
        }
        ++ElementNo;
      }
  
      EvalObj.finishedConstructingBases();
    }
  
    // Initialize members.
    for (const auto *Field : RD->fields()) {
      // Anonymous bit-fields are not considered members of the class for
      // purposes of aggregate initialization.
      if (Field->isUnnamedBitfield())
        continue;
  
      LValue Subobject = This;
  
      bool HaveInit = ElementNo < E->getNumInits();
  
      // FIXME: Diagnostics here should point to the end of the initializer
      // list, not the start.
      if (!HandleLValueMember(Info, HaveInit ? E->getInit(ElementNo) : E,
                              Subobject, Field, &Layout))
        return false;
  
      // Perform an implicit value-initialization for members beyond the end of
      // the initializer list.
      ImplicitValueInitExpr VIE(HaveInit ? Info.Ctx.IntTy : Field->getType());
      const Expr *Init = HaveInit ? E->getInit(ElementNo++) : &VIE;
  
      // Temporarily override This, in case there's a CXXDefaultInitExpr in here.
      ThisOverrideRAII ThisOverride(*Info.CurrentCall, &This,
                                    isa<CXXDefaultInitExpr>(Init));
  
      APValue &FieldVal = Result.getStructField(Field->getFieldIndex());
      if (!EvaluateInPlace(FieldVal, Info, Subobject, Init) ||
          (Field->isBitField() && !truncateBitfieldValue(Info, Init,
                                                         FieldVal, Field))) {
        if (!Info.noteFailure())
          return false;
        Success = false;
      }
    }
  
    EvalObj.finishedConstructingFields();
  
    return Success;
  }
  
  bool RecordExprEvaluator::VisitCXXConstructExpr(const CXXConstructExpr *E,
                                                  QualType T) {
    // Note that E's type is not necessarily the type of our class here; we might
    // be initializing an array element instead.
    const CXXConstructorDecl *FD = E->getConstructor();
    if (FD->isInvalidDecl() || FD->getParent()->isInvalidDecl()) return false;
  
    bool ZeroInit = E->requiresZeroInitialization();
    if (CheckTrivialDefaultConstructor(Info, E->getExprLoc(), FD, ZeroInit)) {
      // If we've already performed zero-initialization, we're already done.
      if (Result.hasValue())
        return true;
  
      if (ZeroInit)
        return ZeroInitialization(E, T);
  
      return getDefaultInitValue(T, Result);
    }
  
    const FunctionDecl *Definition = nullptr;
    auto Body = FD->getBody(Definition);
  
    if (!CheckConstexprFunction(Info, E->getExprLoc(), FD, Definition, Body))
      return false;
  
    // Avoid materializing a temporary for an elidable copy/move constructor.
    if (E->isElidable() && !ZeroInit)
      if (const MaterializeTemporaryExpr *ME
            = dyn_cast<MaterializeTemporaryExpr>(E->getArg(0)))
        return Visit(ME->getSubExpr());
  
    if (ZeroInit && !ZeroInitialization(E, T))
      return false;
  
    auto Args = llvm::makeArrayRef(E->getArgs(), E->getNumArgs());
    return HandleConstructorCall(E, This, Args,
                                 cast<CXXConstructorDecl>(Definition), Info,
                                 Result);
  }
  
  bool RecordExprEvaluator::VisitCXXInheritedCtorInitExpr(
      const CXXInheritedCtorInitExpr *E) {
    if (!Info.CurrentCall) {
      assert(Info.checkingPotentialConstantExpression());
      return false;
    }
  
    const CXXConstructorDecl *FD = E->getConstructor();
    if (FD->isInvalidDecl() || FD->getParent()->isInvalidDecl())
      return false;
  
    const FunctionDecl *Definition = nullptr;
    auto Body = FD->getBody(Definition);
  
    if (!CheckConstexprFunction(Info, E->getExprLoc(), FD, Definition, Body))
      return false;
  
    return HandleConstructorCall(E, This, Info.CurrentCall->Arguments,
                                 cast<CXXConstructorDecl>(Definition), Info,
                                 Result);
  }
  
  bool RecordExprEvaluator::VisitCXXStdInitializerListExpr(
      const CXXStdInitializerListExpr *E) {
    const ConstantArrayType *ArrayType =
        Info.Ctx.getAsConstantArrayType(E->getSubExpr()->getType());
  
    LValue Array;
    if (!EvaluateLValue(E->getSubExpr(), Array, Info))
      return false;
  
    // Get a pointer to the first element of the array.
    Array.addArray(Info, E, ArrayType);
  
    auto InvalidType = [&] {
      Info.FFDiag(E, diag::note_constexpr_unsupported_layout)
        << E->getType();
      return false;
    };
  
    // FIXME: Perform the checks on the field types in SemaInit.
    RecordDecl *Record = E->getType()->castAs<RecordType>()->getDecl();
    RecordDecl::field_iterator Field = Record->field_begin();
    if (Field == Record->field_end())
      return InvalidType();
  
    // Start pointer.
    if (!Field->getType()->isPointerType() ||
        !Info.Ctx.hasSameType(Field->getType()->getPointeeType(),
                              ArrayType->getElementType()))
      return InvalidType();
  
    // FIXME: What if the initializer_list type has base classes, etc?
    Result = APValue(APValue::UninitStruct(), 0, 2);
    Array.moveInto(Result.getStructField(0));
  
    if (++Field == Record->field_end())
      return InvalidType();
  
    if (Field->getType()->isPointerType() &&
        Info.Ctx.hasSameType(Field->getType()->getPointeeType(),
                             ArrayType->getElementType())) {
      // End pointer.
      if (!HandleLValueArrayAdjustment(Info, E, Array,
                                       ArrayType->getElementType(),
                                       ArrayType->getSize().getZExtValue()))
        return false;
      Array.moveInto(Result.getStructField(1));
    } else if (Info.Ctx.hasSameType(Field->getType(), Info.Ctx.getSizeType()))
      // Length.
      Result.getStructField(1) = APValue(APSInt(ArrayType->getSize()));
    else
      return InvalidType();
  
    if (++Field != Record->field_end())
      return InvalidType();
  
    return true;
  }
  
  bool RecordExprEvaluator::VisitLambdaExpr(const LambdaExpr *E) {
    const CXXRecordDecl *ClosureClass = E->getLambdaClass();
    if (ClosureClass->isInvalidDecl())
      return false;
  
    const size_t NumFields =
        std::distance(ClosureClass->field_begin(), ClosureClass->field_end());
  
    assert(NumFields == (size_t)std::distance(E->capture_init_begin(),
                                              E->capture_init_end()) &&
           "The number of lambda capture initializers should equal the number of "
           "fields within the closure type");
  
    Result = APValue(APValue::UninitStruct(), /*NumBases*/0, NumFields);
    // Iterate through all the lambda's closure object's fields and initialize
    // them.
    auto *CaptureInitIt = E->capture_init_begin();
    const LambdaCapture *CaptureIt = ClosureClass->captures_begin();
    bool Success = true;
    const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(ClosureClass);
    for (const auto *Field : ClosureClass->fields()) {
      assert(CaptureInitIt != E->capture_init_end());
      // Get the initializer for this field
      Expr *const CurFieldInit = *CaptureInitIt++;
  
      // If there is no initializer, either this is a VLA or an error has
      // occurred.
      if (!CurFieldInit)
        return Error(E);
  
      LValue Subobject = This;
  
      if (!HandleLValueMember(Info, E, Subobject, Field, &Layout))
        return false;
  
      APValue &FieldVal = Result.getStructField(Field->getFieldIndex());
      if (!EvaluateInPlace(FieldVal, Info, Subobject, CurFieldInit)) {
        if (!Info.keepEvaluatingAfterFailure())
          return false;
        Success = false;
      }
      ++CaptureIt;
    }
    return Success;
  }
  
  static bool EvaluateRecord(const Expr *E, const LValue &This,
                             APValue &Result, EvalInfo &Info) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && E->getType()->isRecordType() &&
           "can't evaluate expression as a record rvalue");
    return RecordExprEvaluator(Info, This, Result).Visit(E);
  }
  
  //===----------------------------------------------------------------------===//
  // Temporary Evaluation
  //
  // Temporaries are represented in the AST as rvalues, but generally behave like
  // lvalues. The full-object of which the temporary is a subobject is implicitly
  // materialized so that a reference can bind to it.
  //===----------------------------------------------------------------------===//
  namespace {
  class TemporaryExprEvaluator
    : public LValueExprEvaluatorBase<TemporaryExprEvaluator> {
  public:
    TemporaryExprEvaluator(EvalInfo &Info, LValue &Result) :
      LValueExprEvaluatorBaseTy(Info, Result, false) {}
  
    /// Visit an expression which constructs the value of this temporary.
    bool VisitConstructExpr(const Expr *E) {
      APValue &Value = Info.CurrentCall->createTemporary(
          E, E->getType(), ScopeKind::FullExpression, Result);
      return EvaluateInPlace(Value, Info, Result, E);
    }
  
    bool VisitCastExpr(const CastExpr *E) {
      switch (E->getCastKind()) {
      default:
        return LValueExprEvaluatorBaseTy::VisitCastExpr(E);
  
      case CK_ConstructorConversion:
        return VisitConstructExpr(E->getSubExpr());
      }
    }
    bool VisitInitListExpr(const InitListExpr *E) {
      return VisitConstructExpr(E);
    }
    bool VisitCXXConstructExpr(const CXXConstructExpr *E) {
      return VisitConstructExpr(E);
    }
    bool VisitCallExpr(const CallExpr *E) {
      return VisitConstructExpr(E);
    }
    bool VisitCXXStdInitializerListExpr(const CXXStdInitializerListExpr *E) {
      return VisitConstructExpr(E);
    }
    bool VisitLambdaExpr(const LambdaExpr *E) {
      return VisitConstructExpr(E);
    }
  };
  } // end anonymous namespace
  
  /// Evaluate an expression of record type as a temporary.
  static bool EvaluateTemporary(const Expr *E, LValue &Result, EvalInfo &Info) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && E->getType()->isRecordType());
    return TemporaryExprEvaluator(Info, Result).Visit(E);
  }
  
  //===----------------------------------------------------------------------===//
  // Vector Evaluation
  //===----------------------------------------------------------------------===//
  
  namespace {
    class VectorExprEvaluator
    : public ExprEvaluatorBase<VectorExprEvaluator> {
      APValue &Result;
    public:
  
      VectorExprEvaluator(EvalInfo &info, APValue &Result)
        : ExprEvaluatorBaseTy(info), Result(Result) {}
  
      bool Success(ArrayRef<APValue> V, const Expr *E) {
        assert(V.size() == E->getType()->castAs<VectorType>()->getNumElements());
        // FIXME: remove this APValue copy.
        Result = APValue(V.data(), V.size());
        return true;
      }
      bool Success(const APValue &V, const Expr *E) {
        assert(V.isVector());
        Result = V;
        return true;
      }
      bool ZeroInitialization(const Expr *E);
  
      bool VisitUnaryReal(const UnaryOperator *E)
        { return Visit(E->getSubExpr()); }
      bool VisitCastExpr(const CastExpr* E);
      bool VisitInitListExpr(const InitListExpr *E);
      bool VisitUnaryImag(const UnaryOperator *E);
      bool VisitBinaryOperator(const BinaryOperator *E);
      // FIXME: Missing: unary -, unary ~, conditional operator (for GNU
      //                 conditional select), shufflevector, ExtVectorElementExpr
    };
  } // end anonymous namespace
  
  static bool EvaluateVector(const Expr* E, APValue& Result, EvalInfo &Info) {
    assert(E->isRValue() && E->getType()->isVectorType() &&"not a vector rvalue");
    return VectorExprEvaluator(Info, Result).Visit(E);
  }
  
  bool VectorExprEvaluator::VisitCastExpr(const CastExpr *E) {
    const VectorType *VTy = E->getType()->castAs<VectorType>();
    unsigned NElts = VTy->getNumElements();
  
    const Expr *SE = E->getSubExpr();
    QualType SETy = SE->getType();
  
    switch (E->getCastKind()) {
    case CK_VectorSplat: {
      APValue Val = APValue();
      if (SETy->isIntegerType()) {
        APSInt IntResult;
        if (!EvaluateInteger(SE, IntResult, Info))
          return false;
        Val = APValue(std::move(IntResult));
      } else if (SETy->isRealFloatingType()) {
        APFloat FloatResult(0.0);
        if (!EvaluateFloat(SE, FloatResult, Info))
          return false;
        Val = APValue(std::move(FloatResult));
      } else {
        return Error(E);
      }
  
      // Splat and create vector APValue.
      SmallVector<APValue, 4> Elts(NElts, Val);
      return Success(Elts, E);
    }
    case CK_BitCast: {
      // Evaluate the operand into an APInt we can extract from.
      llvm::APInt SValInt;
      if (!EvalAndBitcastToAPInt(Info, SE, SValInt))
        return false;
      // Extract the elements
      QualType EltTy = VTy->getElementType();
      unsigned EltSize = Info.Ctx.getTypeSize(EltTy);
      bool BigEndian = Info.Ctx.getTargetInfo().isBigEndian();
      SmallVector<APValue, 4> Elts;
      if (EltTy->isRealFloatingType()) {
        const llvm::fltSemantics &Sem = Info.Ctx.getFloatTypeSemantics(EltTy);
        unsigned FloatEltSize = EltSize;
        if (&Sem == &APFloat::x87DoubleExtended())
          FloatEltSize = 80;
        for (unsigned i = 0; i < NElts; i++) {
          llvm::APInt Elt;
          if (BigEndian)
            Elt = SValInt.rotl(i*EltSize+FloatEltSize).trunc(FloatEltSize);
          else
            Elt = SValInt.rotr(i*EltSize).trunc(FloatEltSize);
          Elts.push_back(APValue(APFloat(Sem, Elt)));
        }
      } else if (EltTy->isIntegerType()) {
        for (unsigned i = 0; i < NElts; i++) {
          llvm::APInt Elt;
          if (BigEndian)
            Elt = SValInt.rotl(i*EltSize+EltSize).zextOrTrunc(EltSize);
          else
            Elt = SValInt.rotr(i*EltSize).zextOrTrunc(EltSize);
          Elts.push_back(APValue(APSInt(Elt, !EltTy->isSignedIntegerType())));
        }
      } else {
        return Error(E);
      }
      return Success(Elts, E);
    }
    default:
      return ExprEvaluatorBaseTy::VisitCastExpr(E);
    }
  }
  
  bool
  VectorExprEvaluator::VisitInitListExpr(const InitListExpr *E) {
    const VectorType *VT = E->getType()->castAs<VectorType>();
    unsigned NumInits = E->getNumInits();
    unsigned NumElements = VT->getNumElements();
  
    QualType EltTy = VT->getElementType();
    SmallVector<APValue, 4> Elements;
  
    // The number of initializers can be less than the number of
    // vector elements. For OpenCL, this can be due to nested vector
    // initialization. For GCC compatibility, missing trailing elements
    // should be initialized with zeroes.
    unsigned CountInits = 0, CountElts = 0;
    while (CountElts < NumElements) {
      // Handle nested vector initialization.
      if (CountInits < NumInits
          && E->getInit(CountInits)->getType()->isVectorType()) {
        APValue v;
        if (!EvaluateVector(E->getInit(CountInits), v, Info))
          return Error(E);
        unsigned vlen = v.getVectorLength();
        for (unsigned j = 0; j < vlen; j++)
          Elements.push_back(v.getVectorElt(j));
        CountElts += vlen;
      } else if (EltTy->isIntegerType()) {
        llvm::APSInt sInt(32);
        if (CountInits < NumInits) {
          if (!EvaluateInteger(E->getInit(CountInits), sInt, Info))
            return false;
        } else // trailing integer zero.
          sInt = Info.Ctx.MakeIntValue(0, EltTy);
        Elements.push_back(APValue(sInt));
        CountElts++;
      } else {
        llvm::APFloat f(0.0);
        if (CountInits < NumInits) {
          if (!EvaluateFloat(E->getInit(CountInits), f, Info))
            return false;
        } else // trailing float zero.
          f = APFloat::getZero(Info.Ctx.getFloatTypeSemantics(EltTy));
        Elements.push_back(APValue(f));
        CountElts++;
      }
      CountInits++;
    }
    return Success(Elements, E);
  }
  
  bool
  VectorExprEvaluator::ZeroInitialization(const Expr *E) {
    const auto *VT = E->getType()->castAs<VectorType>();
    QualType EltTy = VT->getElementType();
    APValue ZeroElement;
    if (EltTy->isIntegerType())
      ZeroElement = APValue(Info.Ctx.MakeIntValue(0, EltTy));
    else
      ZeroElement =
          APValue(APFloat::getZero(Info.Ctx.getFloatTypeSemantics(EltTy)));
  
    SmallVector<APValue, 4> Elements(VT->getNumElements(), ZeroElement);
    return Success(Elements, E);
  }
  
  bool VectorExprEvaluator::VisitUnaryImag(const UnaryOperator *E) {
    VisitIgnoredValue(E->getSubExpr());
    return ZeroInitialization(E);
  }
  
  bool VectorExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
    BinaryOperatorKind Op = E->getOpcode();
    assert(Op != BO_PtrMemD && Op != BO_PtrMemI && Op != BO_Cmp &&
           "Operation not supported on vector types");
  
    if (Op == BO_Comma)
      return ExprEvaluatorBaseTy::VisitBinaryOperator(E);
  
    Expr *LHS = E->getLHS();
    Expr *RHS = E->getRHS();
  
    assert(LHS->getType()->isVectorType() && RHS->getType()->isVectorType() &&
           "Must both be vector types");
    // Checking JUST the types are the same would be fine, except shifts don't
    // need to have their types be the same (since you always shift by an int).
    assert(LHS->getType()->getAs<VectorType>()->getNumElements() ==
               E->getType()->getAs<VectorType>()->getNumElements() &&
           RHS->getType()->getAs<VectorType>()->getNumElements() ==
               E->getType()->getAs<VectorType>()->getNumElements() &&
           "All operands must be the same size.");
  
    APValue LHSValue;
    APValue RHSValue;
    bool LHSOK = Evaluate(LHSValue, Info, LHS);
    if (!LHSOK && !Info.noteFailure())
      return false;
    if (!Evaluate(RHSValue, Info, RHS) || !LHSOK)
      return false;
  
    if (!handleVectorVectorBinOp(Info, E, Op, LHSValue, RHSValue))
      return false;
  
    return Success(LHSValue, E);
  }
  
  //===----------------------------------------------------------------------===//
  // Array Evaluation
  //===----------------------------------------------------------------------===//
  
  namespace {
    class ArrayExprEvaluator
    : public ExprEvaluatorBase<ArrayExprEvaluator> {
      const LValue &This;
      APValue &Result;
    public:
  
      ArrayExprEvaluator(EvalInfo &Info, const LValue &This, APValue &Result)
        : ExprEvaluatorBaseTy(Info), This(This), Result(Result) {}
  
      bool Success(const APValue &V, const Expr *E) {
        assert(V.isArray() && "expected array");
        Result = V;
        return true;
      }
  
      bool ZeroInitialization(const Expr *E) {
        const ConstantArrayType *CAT =
            Info.Ctx.getAsConstantArrayType(E->getType());
        if (!CAT) {
          if (E->getType()->isIncompleteArrayType()) {
            // We can be asked to zero-initialize a flexible array member; this
            // is represented as an ImplicitValueInitExpr of incomplete array
            // type. In this case, the array has zero elements.
            Result = APValue(APValue::UninitArray(), 0, 0);
            return true;
          }
          // FIXME: We could handle VLAs here.
          return Error(E);
        }
  
        Result = APValue(APValue::UninitArray(), 0,
                         CAT->getSize().getZExtValue());
        if (!Result.hasArrayFiller()) return true;
  
        // Zero-initialize all elements.
        LValue Subobject = This;
        Subobject.addArray(Info, E, CAT);
        ImplicitValueInitExpr VIE(CAT->getElementType());
        return EvaluateInPlace(Result.getArrayFiller(), Info, Subobject, &VIE);
      }
  
      bool VisitCallExpr(const CallExpr *E) {
        return handleCallExpr(E, Result, &This);
      }
      bool VisitInitListExpr(const InitListExpr *E,
                             QualType AllocType = QualType());
      bool VisitArrayInitLoopExpr(const ArrayInitLoopExpr *E);
      bool VisitCXXConstructExpr(const CXXConstructExpr *E);
      bool VisitCXXConstructExpr(const CXXConstructExpr *E,
                                 const LValue &Subobject,
                                 APValue *Value, QualType Type);
      bool VisitStringLiteral(const StringLiteral *E,
                              QualType AllocType = QualType()) {
        expandStringLiteral(Info, E, Result, AllocType);
        return true;
      }
    };
  } // end anonymous namespace
  
  static bool EvaluateArray(const Expr *E, const LValue &This,
                            APValue &Result, EvalInfo &Info) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && E->getType()->isArrayType() && "not an array rvalue");
    return ArrayExprEvaluator(Info, This, Result).Visit(E);
  }
  
  static bool EvaluateArrayNewInitList(EvalInfo &Info, LValue &This,
                                       APValue &Result, const InitListExpr *ILE,
                                       QualType AllocType) {
    assert(!ILE->isValueDependent());
    assert(ILE->isRValue() && ILE->getType()->isArrayType() &&
           "not an array rvalue");
    return ArrayExprEvaluator(Info, This, Result)
        .VisitInitListExpr(ILE, AllocType);
  }
  
  static bool EvaluateArrayNewConstructExpr(EvalInfo &Info, LValue &This,
                                            APValue &Result,
                                            const CXXConstructExpr *CCE,
                                            QualType AllocType) {
    assert(!CCE->isValueDependent());
    assert(CCE->isRValue() && CCE->getType()->isArrayType() &&
           "not an array rvalue");
    return ArrayExprEvaluator(Info, This, Result)
        .VisitCXXConstructExpr(CCE, This, &Result, AllocType);
  }
  
  // Return true iff the given array filler may depend on the element index.
  static bool MaybeElementDependentArrayFiller(const Expr *FillerExpr) {
    // For now, just allow non-class value-initialization and initialization
    // lists comprised of them.
    if (isa<ImplicitValueInitExpr>(FillerExpr))
      return false;
    if (const InitListExpr *ILE = dyn_cast<InitListExpr>(FillerExpr)) {
      for (unsigned I = 0, E = ILE->getNumInits(); I != E; ++I) {
        if (MaybeElementDependentArrayFiller(ILE->getInit(I)))
          return true;
      }
      return false;
    }
    return true;
  }
  
  bool ArrayExprEvaluator::VisitInitListExpr(const InitListExpr *E,
                                             QualType AllocType) {
    const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(
        AllocType.isNull() ? E->getType() : AllocType);
    if (!CAT)
      return Error(E);
  
    // C++11 [dcl.init.string]p1: A char array [...] can be initialized by [...]
    // an appropriately-typed string literal enclosed in braces.
    if (E->isStringLiteralInit()) {
      auto *SL = dyn_cast<StringLiteral>(E->getInit(0)->IgnoreParens());
      // FIXME: Support ObjCEncodeExpr here once we support it in
      // ArrayExprEvaluator generally.
      if (!SL)
        return Error(E);
      return VisitStringLiteral(SL, AllocType);
    }
  
    bool Success = true;
  
    assert((!Result.isArray() || Result.getArrayInitializedElts() == 0) &&
           "zero-initialized array shouldn't have any initialized elts");
    APValue Filler;
    if (Result.isArray() && Result.hasArrayFiller())
      Filler = Result.getArrayFiller();
  
    unsigned NumEltsToInit = E->getNumInits();
    unsigned NumElts = CAT->getSize().getZExtValue();
    const Expr *FillerExpr = E->hasArrayFiller() ? E->getArrayFiller() : nullptr;
  
    // If the initializer might depend on the array index, run it for each
    // array element.
    if (NumEltsToInit != NumElts && MaybeElementDependentArrayFiller(FillerExpr))
      NumEltsToInit = NumElts;
  
    LLVM_DEBUG(llvm::dbgs() << "The number of elements to initialize: "
                            << NumEltsToInit << ".\n");
  
    Result = APValue(APValue::UninitArray(), NumEltsToInit, NumElts);
  
    // If the array was previously zero-initialized, preserve the
    // zero-initialized values.
    if (Filler.hasValue()) {
      for (unsigned I = 0, E = Result.getArrayInitializedElts(); I != E; ++I)
        Result.getArrayInitializedElt(I) = Filler;
      if (Result.hasArrayFiller())
        Result.getArrayFiller() = Filler;
    }
  
    LValue Subobject = This;
    Subobject.addArray(Info, E, CAT);
    for (unsigned Index = 0; Index != NumEltsToInit; ++Index) {
      const Expr *Init =
          Index < E->getNumInits() ? E->getInit(Index) : FillerExpr;
      if (!EvaluateInPlace(Result.getArrayInitializedElt(Index),
                           Info, Subobject, Init) ||
          !HandleLValueArrayAdjustment(Info, Init, Subobject,
                                       CAT->getElementType(), 1)) {
        if (!Info.noteFailure())
          return false;
        Success = false;
      }
    }
  
    if (!Result.hasArrayFiller())
      return Success;
  
    // If we get here, we have a trivial filler, which we can just evaluate
    // once and splat over the rest of the array elements.
    assert(FillerExpr && "no array filler for incomplete init list");
    return EvaluateInPlace(Result.getArrayFiller(), Info, Subobject,
                           FillerExpr) && Success;
  }
  
  bool ArrayExprEvaluator::VisitArrayInitLoopExpr(const ArrayInitLoopExpr *E) {
    LValue CommonLV;
    if (E->getCommonExpr() &&
        !Evaluate(Info.CurrentCall->createTemporary(
                      E->getCommonExpr(),
                      getStorageType(Info.Ctx, E->getCommonExpr()),
                      ScopeKind::FullExpression, CommonLV),
                  Info, E->getCommonExpr()->getSourceExpr()))
      return false;
  
    auto *CAT = cast<ConstantArrayType>(E->getType()->castAsArrayTypeUnsafe());
  
    uint64_t Elements = CAT->getSize().getZExtValue();
    Result = APValue(APValue::UninitArray(), Elements, Elements);
  
    LValue Subobject = This;
    Subobject.addArray(Info, E, CAT);
  
    bool Success = true;
    for (EvalInfo::ArrayInitLoopIndex Index(Info); Index != Elements; ++Index) {
      if (!EvaluateInPlace(Result.getArrayInitializedElt(Index),
                           Info, Subobject, E->getSubExpr()) ||
          !HandleLValueArrayAdjustment(Info, E, Subobject,
                                       CAT->getElementType(), 1)) {
        if (!Info.noteFailure())
          return false;
        Success = false;
      }
    }
  
    return Success;
  }
  
  bool ArrayExprEvaluator::VisitCXXConstructExpr(const CXXConstructExpr *E) {
    return VisitCXXConstructExpr(E, This, &Result, E->getType());
  }
  
  bool ArrayExprEvaluator::VisitCXXConstructExpr(const CXXConstructExpr *E,
                                                 const LValue &Subobject,
                                                 APValue *Value,
                                                 QualType Type) {
    bool HadZeroInit = Value->hasValue();
  
    if (const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(Type)) {
      unsigned N = CAT->getSize().getZExtValue();
  
      // Preserve the array filler if we had prior zero-initialization.
      APValue Filler =
        HadZeroInit && Value->hasArrayFiller() ? Value->getArrayFiller()
                                               : APValue();
  
      *Value = APValue(APValue::UninitArray(), N, N);
  
      if (HadZeroInit)
        for (unsigned I = 0; I != N; ++I)
          Value->getArrayInitializedElt(I) = Filler;
  
      // Initialize the elements.
      LValue ArrayElt = Subobject;
      ArrayElt.addArray(Info, E, CAT);
      for (unsigned I = 0; I != N; ++I)
        if (!VisitCXXConstructExpr(E, ArrayElt, &Value->getArrayInitializedElt(I),
                                   CAT->getElementType()) ||
            !HandleLValueArrayAdjustment(Info, E, ArrayElt,
                                         CAT->getElementType(), 1))
          return false;
  
      return true;
    }
  
    if (!Type->isRecordType())
      return Error(E);
  
    return RecordExprEvaluator(Info, Subobject, *Value)
               .VisitCXXConstructExpr(E, Type);
  }
  
  //===----------------------------------------------------------------------===//
  // Integer Evaluation
  //
  // As a GNU extension, we support casting pointers to sufficiently-wide integer
  // types and back in constant folding. Integer values are thus represented
  // either as an integer-valued APValue, or as an lvalue-valued APValue.
  //===----------------------------------------------------------------------===//
  
  namespace {
  class IntExprEvaluator
          : public ExprEvaluatorBase<IntExprEvaluator> {
    APValue &Result;
  public:
    IntExprEvaluator(EvalInfo &info, APValue &result)
        : ExprEvaluatorBaseTy(info), Result(result) {}
  
    bool Success(const llvm::APSInt &SI, const Expr *E, APValue &Result) {
      assert(E->getType()->isIntegralOrEnumerationType() &&
             "Invalid evaluation result.");
      assert(SI.isSigned() == E->getType()->isSignedIntegerOrEnumerationType() &&
             "Invalid evaluation result.");
      assert(SI.getBitWidth() == Info.Ctx.getIntWidth(E->getType()) &&
             "Invalid evaluation result.");
      Result = APValue(SI);
      return true;
    }
    bool Success(const llvm::APSInt &SI, const Expr *E) {
      return Success(SI, E, Result);
    }
  
    bool Success(const llvm::APInt &I, const Expr *E, APValue &Result) {
      assert(E->getType()->isIntegralOrEnumerationType() &&
             "Invalid evaluation result.");
      assert(I.getBitWidth() == Info.Ctx.getIntWidth(E->getType()) &&
             "Invalid evaluation result.");
      Result = APValue(APSInt(I));
      Result.getInt().setIsUnsigned(
                              E->getType()->isUnsignedIntegerOrEnumerationType());
      return true;
    }
    bool Success(const llvm::APInt &I, const Expr *E) {
      return Success(I, E, Result);
    }
  
    bool Success(uint64_t Value, const Expr *E, APValue &Result) {
      assert(E->getType()->isIntegralOrEnumerationType() &&
             "Invalid evaluation result.");
      Result = APValue(Info.Ctx.MakeIntValue(Value, E->getType()));
      return true;
    }
    bool Success(uint64_t Value, const Expr *E) {
      return Success(Value, E, Result);
    }
  
    bool Success(CharUnits Size, const Expr *E) {
      return Success(Size.getQuantity(), E);
    }
  
    bool Success(const APValue &V, const Expr *E) {
      if (V.isLValue() || V.isAddrLabelDiff() || V.isIndeterminate()) {
        Result = V;
        return true;
      }
      return Success(V.getInt(), E);
    }
  
    bool ZeroInitialization(const Expr *E) { return Success(0, E); }
  
    //===--------------------------------------------------------------------===//
    //                            Visitor Methods
    //===--------------------------------------------------------------------===//
  
    bool VisitIntegerLiteral(const IntegerLiteral *E) {
      return Success(E->getValue(), E);
    }
    bool VisitCharacterLiteral(const CharacterLiteral *E) {
      return Success(E->getValue(), E);
    }
  
    bool CheckReferencedDecl(const Expr *E, const Decl *D);
    bool VisitDeclRefExpr(const DeclRefExpr *E) {
      if (CheckReferencedDecl(E, E->getDecl()))
        return true;
  
      return ExprEvaluatorBaseTy::VisitDeclRefExpr(E);
    }
    bool VisitMemberExpr(const MemberExpr *E) {
      if (CheckReferencedDecl(E, E->getMemberDecl())) {
        VisitIgnoredBaseExpression(E->getBase());
        return true;
      }
  
      return ExprEvaluatorBaseTy::VisitMemberExpr(E);
    }
  
    bool VisitCallExpr(const CallExpr *E);
    bool VisitBuiltinCallExpr(const CallExpr *E, unsigned BuiltinOp);
    bool VisitBinaryOperator(const BinaryOperator *E);
    bool VisitOffsetOfExpr(const OffsetOfExpr *E);
    bool VisitUnaryOperator(const UnaryOperator *E);
  
    bool VisitCastExpr(const CastExpr* E);
    bool VisitUnaryExprOrTypeTraitExpr(const UnaryExprOrTypeTraitExpr *E);
  
    bool VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E) {
      return Success(E->getValue(), E);
    }
  
    bool VisitObjCBoolLiteralExpr(const ObjCBoolLiteralExpr *E) {
      return Success(E->getValue(), E);
    }
  
    bool VisitArrayInitIndexExpr(const ArrayInitIndexExpr *E) {
      if (Info.ArrayInitIndex == uint64_t(-1)) {
        // We were asked to evaluate this subexpression independent of the
        // enclosing ArrayInitLoopExpr. We can't do that.
        Info.FFDiag(E);
        return false;
      }
      return Success(Info.ArrayInitIndex, E);
    }
  
    // Note, GNU defines __null as an integer, not a pointer.
    bool VisitGNUNullExpr(const GNUNullExpr *E) {
      return ZeroInitialization(E);
    }
  
    bool VisitTypeTraitExpr(const TypeTraitExpr *E) {
      return Success(E->getValue(), E);
    }
  
    bool VisitArrayTypeTraitExpr(const ArrayTypeTraitExpr *E) {
      return Success(E->getValue(), E);
    }
  
    bool VisitExpressionTraitExpr(const ExpressionTraitExpr *E) {
      return Success(E->getValue(), E);
    }
  
    bool VisitUnaryReal(const UnaryOperator *E);
    bool VisitUnaryImag(const UnaryOperator *E);
  
    bool VisitCXXNoexceptExpr(const CXXNoexceptExpr *E);
    bool VisitSizeOfPackExpr(const SizeOfPackExpr *E);
    bool VisitSourceLocExpr(const SourceLocExpr *E);
    bool VisitConceptSpecializationExpr(const ConceptSpecializationExpr *E);
    bool VisitRequiresExpr(const RequiresExpr *E);
    // FIXME: Missing: array subscript of vector, member of vector
  };
  
  class FixedPointExprEvaluator
      : public ExprEvaluatorBase<FixedPointExprEvaluator> {
    APValue &Result;
  
   public:
    FixedPointExprEvaluator(EvalInfo &info, APValue &result)
        : ExprEvaluatorBaseTy(info), Result(result) {}
  
    bool Success(const llvm::APInt &I, const Expr *E) {
      return Success(
          APFixedPoint(I, Info.Ctx.getFixedPointSemantics(E->getType())), E);
    }
  
    bool Success(uint64_t Value, const Expr *E) {
      return Success(
          APFixedPoint(Value, Info.Ctx.getFixedPointSemantics(E->getType())), E);
    }
  
    bool Success(const APValue &V, const Expr *E) {
      return Success(V.getFixedPoint(), E);
    }
  
    bool Success(const APFixedPoint &V, const Expr *E) {
      assert(E->getType()->isFixedPointType() && "Invalid evaluation result.");
      assert(V.getWidth() == Info.Ctx.getIntWidth(E->getType()) &&
             "Invalid evaluation result.");
      Result = APValue(V);
      return true;
    }
  
    //===--------------------------------------------------------------------===//
    //                            Visitor Methods
    //===--------------------------------------------------------------------===//
  
    bool VisitFixedPointLiteral(const FixedPointLiteral *E) {
      return Success(E->getValue(), E);
    }
  
    bool VisitCastExpr(const CastExpr *E);
    bool VisitUnaryOperator(const UnaryOperator *E);
    bool VisitBinaryOperator(const BinaryOperator *E);
  };
  } // end anonymous namespace
  
  /// EvaluateIntegerOrLValue - Evaluate an rvalue integral-typed expression, and
  /// produce either the integer value or a pointer.
  ///
  /// GCC has a heinous extension which folds casts between pointer types and
  /// pointer-sized integral types. We support this by allowing the evaluation of
  /// an integer rvalue to produce a pointer (represented as an lvalue) instead.
  /// Some simple arithmetic on such values is supported (they are treated much
  /// like char*).
  static bool EvaluateIntegerOrLValue(const Expr *E, APValue &Result,
                                      EvalInfo &Info) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && E->getType()->isIntegralOrEnumerationType());
    return IntExprEvaluator(Info, Result).Visit(E);
  }
  
  static bool EvaluateInteger(const Expr *E, APSInt &Result, EvalInfo &Info) {
    assert(!E->isValueDependent());
    APValue Val;
    if (!EvaluateIntegerOrLValue(E, Val, Info))
      return false;
    if (!Val.isInt()) {
      // FIXME: It would be better to produce the diagnostic for casting
      //        a pointer to an integer.
      Info.FFDiag(E, diag::note_invalid_subexpr_in_const_expr);
      return false;
    }
    Result = Val.getInt();
    return true;
  }
  
  bool IntExprEvaluator::VisitSourceLocExpr(const SourceLocExpr *E) {
    APValue Evaluated = E->EvaluateInContext(
        Info.Ctx, Info.CurrentCall->CurSourceLocExprScope.getDefaultExpr());
    return Success(Evaluated, E);
  }
  
  static bool EvaluateFixedPoint(const Expr *E, APFixedPoint &Result,
                                 EvalInfo &Info) {
    assert(!E->isValueDependent());
    if (E->getType()->isFixedPointType()) {
      APValue Val;
      if (!FixedPointExprEvaluator(Info, Val).Visit(E))
        return false;
      if (!Val.isFixedPoint())
        return false;
  
      Result = Val.getFixedPoint();
      return true;
    }
    return false;
  }
  
  static bool EvaluateFixedPointOrInteger(const Expr *E, APFixedPoint &Result,
                                          EvalInfo &Info) {
    assert(!E->isValueDependent());
    if (E->getType()->isIntegerType()) {
      auto FXSema = Info.Ctx.getFixedPointSemantics(E->getType());
      APSInt Val;
      if (!EvaluateInteger(E, Val, Info))
        return false;
      Result = APFixedPoint(Val, FXSema);
      return true;
    } else if (E->getType()->isFixedPointType()) {
      return EvaluateFixedPoint(E, Result, Info);
    }
    return false;
  }
  
  /// Check whether the given declaration can be directly converted to an integral
  /// rvalue. If not, no diagnostic is produced; there are other things we can
  /// try.
  bool IntExprEvaluator::CheckReferencedDecl(const Expr* E, const Decl* D) {
    // Enums are integer constant exprs.
    if (const EnumConstantDecl *ECD = dyn_cast<EnumConstantDecl>(D)) {
      // Check for signedness/width mismatches between E type and ECD value.
      bool SameSign = (ECD->getInitVal().isSigned()
                       == E->getType()->isSignedIntegerOrEnumerationType());
      bool SameWidth = (ECD->getInitVal().getBitWidth()
                        == Info.Ctx.getIntWidth(E->getType()));
      if (SameSign && SameWidth)
        return Success(ECD->getInitVal(), E);
      else {
        // Get rid of mismatch (otherwise Success assertions will fail)
        // by computing a new value matching the type of E.
        llvm::APSInt Val = ECD->getInitVal();
        if (!SameSign)
          Val.setIsSigned(!ECD->getInitVal().isSigned());
        if (!SameWidth)
          Val = Val.extOrTrunc(Info.Ctx.getIntWidth(E->getType()));
        return Success(Val, E);
      }
    }
    return false;
  }
  
  /// Values returned by __builtin_classify_type, chosen to match the values
  /// produced by GCC's builtin.
  enum class GCCTypeClass {
    None = -1,
    Void = 0,
    Integer = 1,
    // GCC reserves 2 for character types, but instead classifies them as
    // integers.
    Enum = 3,
    Bool = 4,
    Pointer = 5,
    // GCC reserves 6 for references, but appears to never use it (because
    // expressions never have reference type, presumably).
    PointerToDataMember = 7,
    RealFloat = 8,
    Complex = 9,
    // GCC reserves 10 for functions, but does not use it since GCC version 6 due
    // to decay to pointer. (Prior to version 6 it was only used in C++ mode).
    // GCC claims to reserve 11 for pointers to member functions, but *actually*
    // uses 12 for that purpose, same as for a class or struct. Maybe it
    // internally implements a pointer to member as a struct?  Who knows.
    PointerToMemberFunction = 12, // Not a bug, see above.
    ClassOrStruct = 12,
    Union = 13,
    // GCC reserves 14 for arrays, but does not use it since GCC version 6 due to
    // decay to pointer. (Prior to version 6 it was only used in C++ mode).
    // GCC reserves 15 for strings, but actually uses 5 (pointer) for string
    // literals.
  };
  
  /// EvaluateBuiltinClassifyType - Evaluate __builtin_classify_type the same way
  /// as GCC.
  static GCCTypeClass
  EvaluateBuiltinClassifyType(QualType T, const LangOptions &LangOpts) {
    assert(!T->isDependentType() && "unexpected dependent type");
  
    QualType CanTy = T.getCanonicalType();
    const BuiltinType *BT = dyn_cast<BuiltinType>(CanTy);
  
    switch (CanTy->getTypeClass()) {
  #define TYPE(ID, BASE)
  #define DEPENDENT_TYPE(ID, BASE) case Type::ID:
  #define NON_CANONICAL_TYPE(ID, BASE) case Type::ID:
  #define NON_CANONICAL_UNLESS_DEPENDENT_TYPE(ID, BASE) case Type::ID:
  #include "clang/AST/TypeNodes.inc"
    case Type::Auto:
    case Type::DeducedTemplateSpecialization:
        llvm_unreachable("unexpected non-canonical or dependent type");
  
    case Type::Builtin:
      switch (BT->getKind()) {
  #define BUILTIN_TYPE(ID, SINGLETON_ID)
  #define SIGNED_TYPE(ID, SINGLETON_ID) \
      case BuiltinType::ID: return GCCTypeClass::Integer;
  #define FLOATING_TYPE(ID, SINGLETON_ID) \
      case BuiltinType::ID: return GCCTypeClass::RealFloat;
  #define PLACEHOLDER_TYPE(ID, SINGLETON_ID) \
      case BuiltinType::ID: break;
  #include "clang/AST/BuiltinTypes.def"
      case BuiltinType::Void:
        return GCCTypeClass::Void;
  
      case BuiltinType::Bool:
        return GCCTypeClass::Bool;
  
      case BuiltinType::Char_U:
      case BuiltinType::UChar:
      case BuiltinType::WChar_U:
      case BuiltinType::Char8:
      case BuiltinType::Char16:
      case BuiltinType::Char32:
      case BuiltinType::UShort:
      case BuiltinType::UInt:
      case BuiltinType::ULong:
      case BuiltinType::ULongLong:
      case BuiltinType::UInt128:
        return GCCTypeClass::Integer;
  
      case BuiltinType::UShortAccum:
      case BuiltinType::UAccum:
      case BuiltinType::ULongAccum:
      case BuiltinType::UShortFract:
      case BuiltinType::UFract:
      case BuiltinType::ULongFract:
      case BuiltinType::SatUShortAccum:
      case BuiltinType::SatUAccum:
      case BuiltinType::SatULongAccum:
      case BuiltinType::SatUShortFract:
      case BuiltinType::SatUFract:
      case BuiltinType::SatULongFract:
        return GCCTypeClass::None;
  
      case BuiltinType::NullPtr:
  
      case BuiltinType::ObjCId:
      case BuiltinType::ObjCClass:
      case BuiltinType::ObjCSel:
  #define IMAGE_TYPE(ImgType, Id, SingletonId, Access, Suffix) \
      case BuiltinType::Id:
  #include "clang/Basic/OpenCLImageTypes.def"
  #define EXT_OPAQUE_TYPE(ExtType, Id, Ext) \
      case BuiltinType::Id:
  #include "clang/Basic/OpenCLExtensionTypes.def"
      case BuiltinType::OCLSampler:
      case BuiltinType::OCLEvent:
      case BuiltinType::OCLClkEvent:
      case BuiltinType::OCLQueue:
      case BuiltinType::OCLReserveID:
  #define SVE_TYPE(Name, Id, SingletonId) \
      case BuiltinType::Id:
  #include "clang/Basic/AArch64SVEACLETypes.def"
  #define PPC_VECTOR_TYPE(Name, Id, Size) \
      case BuiltinType::Id:
  #include "clang/Basic/PPCTypes.def"
  #define RVV_TYPE(Name, Id, SingletonId) case BuiltinType::Id:
  #include "clang/Basic/RISCVVTypes.def"
        return GCCTypeClass::None;
  
      case BuiltinType::Dependent:
        llvm_unreachable("unexpected dependent type");
      };
      llvm_unreachable("unexpected placeholder type");
  
    case Type::Enum:
      return LangOpts.CPlusPlus ? GCCTypeClass::Enum : GCCTypeClass::Integer;
  
    case Type::Pointer:
    case Type::ConstantArray:
    case Type::VariableArray:
    case Type::IncompleteArray:
    case Type::FunctionNoProto:
    case Type::FunctionProto:
      return GCCTypeClass::Pointer;
  
    case Type::MemberPointer:
      return CanTy->isMemberDataPointerType()
                 ? GCCTypeClass::PointerToDataMember
                 : GCCTypeClass::PointerToMemberFunction;
  
    case Type::Complex:
      return GCCTypeClass::Complex;
  
    case Type::Record:
      return CanTy->isUnionType() ? GCCTypeClass::Union
                                  : GCCTypeClass::ClassOrStruct;
  
    case Type::Atomic:
      // GCC classifies _Atomic T the same as T.
      return EvaluateBuiltinClassifyType(
          CanTy->castAs<AtomicType>()->getValueType(), LangOpts);
  
    case Type::BlockPointer:
    case Type::Vector:
    case Type::ExtVector:
    case Type::ConstantMatrix:
    case Type::ObjCObject:
    case Type::ObjCInterface:
    case Type::ObjCObjectPointer:
    case Type::Pipe:
    case Type::ExtInt:
      // GCC classifies vectors as None. We follow its lead and classify all
      // other types that don't fit into the regular classification the same way.
      return GCCTypeClass::None;
  
    case Type::LValueReference:
    case Type::RValueReference:
      llvm_unreachable("invalid type for expression");
    }
  
    llvm_unreachable("unexpected type class");
  }
  
  /// EvaluateBuiltinClassifyType - Evaluate __builtin_classify_type the same way
  /// as GCC.
  static GCCTypeClass
  EvaluateBuiltinClassifyType(const CallExpr *E, const LangOptions &LangOpts) {
    // If no argument was supplied, default to None. This isn't
    // ideal, however it is what gcc does.
    if (E->getNumArgs() == 0)
      return GCCTypeClass::None;
  
    // FIXME: Bizarrely, GCC treats a call with more than one argument as not
    // being an ICE, but still folds it to a constant using the type of the first
    // argument.
    return EvaluateBuiltinClassifyType(E->getArg(0)->getType(), LangOpts);
  }
  
  /// EvaluateBuiltinConstantPForLValue - Determine the result of
  /// __builtin_constant_p when applied to the given pointer.
  ///
  /// A pointer is only "constant" if it is null (or a pointer cast to integer)
  /// or it points to the first character of a string literal.
  static bool EvaluateBuiltinConstantPForLValue(const APValue &LV) {
    APValue::LValueBase Base = LV.getLValueBase();
    if (Base.isNull()) {
      // A null base is acceptable.
      return true;
    } else if (const Expr *E = Base.dyn_cast<const Expr *>()) {
      if (!isa<StringLiteral>(E))
        return false;
      return LV.getLValueOffset().isZero();
    } else if (Base.is<TypeInfoLValue>()) {
      // Surprisingly, GCC considers __builtin_constant_p(&typeid(int)) to
      // evaluate to true.
      return true;
    } else {
      // Any other base is not constant enough for GCC.
      return false;
    }
  }
  
  /// EvaluateBuiltinConstantP - Evaluate __builtin_constant_p as similarly to
  /// GCC as we can manage.
  static bool EvaluateBuiltinConstantP(EvalInfo &Info, const Expr *Arg) {
    // This evaluation is not permitted to have side-effects, so evaluate it in
    // a speculative evaluation context.
    SpeculativeEvaluationRAII SpeculativeEval(Info);
  
    // Constant-folding is always enabled for the operand of __builtin_constant_p
    // (even when the enclosing evaluation context otherwise requires a strict
    // language-specific constant expression).
    FoldConstant Fold(Info, true);
  
    QualType ArgType = Arg->getType();
  
    // __builtin_constant_p always has one operand. The rules which gcc follows
    // are not precisely documented, but are as follows:
    //
    //  - If the operand is of integral, floating, complex or enumeration type,
    //    and can be folded to a known value of that type, it returns 1.
    //  - If the operand can be folded to a pointer to the first character
    //    of a string literal (or such a pointer cast to an integral type)
    //    or to a null pointer or an integer cast to a pointer, it returns 1.
    //
    // Otherwise, it returns 0.
    //
    // FIXME: GCC also intends to return 1 for literals of aggregate types, but
    // its support for this did not work prior to GCC 9 and is not yet well
    // understood.
    if (ArgType->isIntegralOrEnumerationType() || ArgType->isFloatingType() ||
        ArgType->isAnyComplexType() || ArgType->isPointerType() ||
        ArgType->isNullPtrType()) {
      APValue V;
      if (!::EvaluateAsRValue(Info, Arg, V) || Info.EvalStatus.HasSideEffects) {
        Fold.keepDiagnostics();
        return false;
      }
  
      // For a pointer (possibly cast to integer), there are special rules.
      if (V.getKind() == APValue::LValue)
        return EvaluateBuiltinConstantPForLValue(V);
  
      // Otherwise, any constant value is good enough.
      return V.hasValue();
    }
  
    // Anything else isn't considered to be sufficiently constant.
    return false;
  }
  
  /// Retrieves the "underlying object type" of the given expression,
  /// as used by __builtin_object_size.
  static QualType getObjectType(APValue::LValueBase B) {
    if (const ValueDecl *D = B.dyn_cast<const ValueDecl*>()) {
      if (const VarDecl *VD = dyn_cast<VarDecl>(D))
        return VD->getType();
    } else if (const Expr *E = B.dyn_cast<const Expr*>()) {
      if (isa<CompoundLiteralExpr>(E))
        return E->getType();
    } else if (B.is<TypeInfoLValue>()) {
      return B.getTypeInfoType();
    } else if (B.is<DynamicAllocLValue>()) {
      return B.getDynamicAllocType();
    }
  
    return QualType();
  }
  
  /// A more selective version of E->IgnoreParenCasts for
  /// tryEvaluateBuiltinObjectSize. This ignores some casts/parens that serve only
  /// to change the type of E.
  /// Ex. For E = `(short*)((char*)(&foo))`, returns `&foo`
  ///
  /// Always returns an RValue with a pointer representation.
  static const Expr *ignorePointerCastsAndParens(const Expr *E) {
    assert(E->isRValue() && E->getType()->hasPointerRepresentation());
  
    auto *NoParens = E->IgnoreParens();
    auto *Cast = dyn_cast<CastExpr>(NoParens);
    if (Cast == nullptr)
      return NoParens;
  
    // We only conservatively allow a few kinds of casts, because this code is
    // inherently a simple solution that seeks to support the common case.
    auto CastKind = Cast->getCastKind();
    if (CastKind != CK_NoOp && CastKind != CK_BitCast &&
        CastKind != CK_AddressSpaceConversion)
      return NoParens;
  
    auto *SubExpr = Cast->getSubExpr();
    if (!SubExpr->getType()->hasPointerRepresentation() || !SubExpr->isRValue())
      return NoParens;
    return ignorePointerCastsAndParens(SubExpr);
  }
  
  /// Checks to see if the given LValue's Designator is at the end of the LValue's
  /// record layout. e.g.
  ///   struct { struct { int a, b; } fst, snd; } obj;
  ///   obj.fst   // no
  ///   obj.snd   // yes
  ///   obj.fst.a // no
  ///   obj.fst.b // no
  ///   obj.snd.a // no
  ///   obj.snd.b // yes
  ///
  /// Please note: this function is specialized for how __builtin_object_size
  /// views "objects".
  ///
  /// If this encounters an invalid RecordDecl or otherwise cannot determine the
  /// correct result, it will always return true.
  static bool isDesignatorAtObjectEnd(const ASTContext &Ctx, const LValue &LVal) {
    assert(!LVal.Designator.Invalid);
  
    auto IsLastOrInvalidFieldDecl = [&Ctx](const FieldDecl *FD, bool &Invalid) {
      const RecordDecl *Parent = FD->getParent();
      Invalid = Parent->isInvalidDecl();
      if (Invalid || Parent->isUnion())
        return true;
      const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(Parent);
      return FD->getFieldIndex() + 1 == Layout.getFieldCount();
    };
  
    auto &Base = LVal.getLValueBase();
    if (auto *ME = dyn_cast_or_null<MemberExpr>(Base.dyn_cast<const Expr *>())) {
      if (auto *FD = dyn_cast<FieldDecl>(ME->getMemberDecl())) {
        bool Invalid;
        if (!IsLastOrInvalidFieldDecl(FD, Invalid))
          return Invalid;
      } else if (auto *IFD = dyn_cast<IndirectFieldDecl>(ME->getMemberDecl())) {
        for (auto *FD : IFD->chain()) {
          bool Invalid;
          if (!IsLastOrInvalidFieldDecl(cast<FieldDecl>(FD), Invalid))
            return Invalid;
        }
      }
    }
  
    unsigned I = 0;
    QualType BaseType = getType(Base);
    if (LVal.Designator.FirstEntryIsAnUnsizedArray) {
      // If we don't know the array bound, conservatively assume we're looking at
      // the final array element.
      ++I;
      if (BaseType->isIncompleteArrayType())
        BaseType = Ctx.getAsArrayType(BaseType)->getElementType();
      else
        BaseType = BaseType->castAs<PointerType>()->getPointeeType();
    }
  
    for (unsigned E = LVal.Designator.Entries.size(); I != E; ++I) {
      const auto &Entry = LVal.Designator.Entries[I];
      if (BaseType->isArrayType()) {
        // Because __builtin_object_size treats arrays as objects, we can ignore
        // the index iff this is the last array in the Designator.
        if (I + 1 == E)
          return true;
        const auto *CAT = cast<ConstantArrayType>(Ctx.getAsArrayType(BaseType));
        uint64_t Index = Entry.getAsArrayIndex();
        if (Index + 1 != CAT->getSize())
          return false;
        BaseType = CAT->getElementType();
      } else if (BaseType->isAnyComplexType()) {
        const auto *CT = BaseType->castAs<ComplexType>();
        uint64_t Index = Entry.getAsArrayIndex();
        if (Index != 1)
          return false;
        BaseType = CT->getElementType();
      } else if (auto *FD = getAsField(Entry)) {
        bool Invalid;
        if (!IsLastOrInvalidFieldDecl(FD, Invalid))
          return Invalid;
        BaseType = FD->getType();
      } else {
        assert(getAsBaseClass(Entry) && "Expecting cast to a base class");
        return false;
      }
    }
    return true;
  }
  
  /// Tests to see if the LValue has a user-specified designator (that isn't
  /// necessarily valid). Note that this always returns 'true' if the LValue has
  /// an unsized array as its first designator entry, because there's currently no
  /// way to tell if the user typed *foo or foo[0].
  static bool refersToCompleteObject(const LValue &LVal) {
    if (LVal.Designator.Invalid)
      return false;
  
    if (!LVal.Designator.Entries.empty())
      return LVal.Designator.isMostDerivedAnUnsizedArray();
  
    if (!LVal.InvalidBase)
      return true;
  
    // If `E` is a MemberExpr, then the first part of the designator is hiding in
    // the LValueBase.
    const auto *E = LVal.Base.dyn_cast<const Expr *>();
    return !E || !isa<MemberExpr>(E);
  }
  
  /// Attempts to detect a user writing into a piece of memory that's impossible
  /// to figure out the size of by just using types.
  static bool isUserWritingOffTheEnd(const ASTContext &Ctx, const LValue &LVal) {
    const SubobjectDesignator &Designator = LVal.Designator;
    // Notes:
    // - Users can only write off of the end when we have an invalid base. Invalid
    //   bases imply we don't know where the memory came from.
    // - We used to be a bit more aggressive here; we'd only be conservative if
    //   the array at the end was flexible, or if it had 0 or 1 elements. This
    //   broke some common standard library extensions (PR30346), but was
    //   otherwise seemingly fine. It may be useful to reintroduce this behavior
    //   with some sort of list. OTOH, it seems that GCC is always
    //   conservative with the last element in structs (if it's an array), so our
    //   current behavior is more compatible than an explicit list approach would
    //   be.
    return LVal.InvalidBase &&
           Designator.Entries.size() == Designator.MostDerivedPathLength &&
           Designator.MostDerivedIsArrayElement &&
           isDesignatorAtObjectEnd(Ctx, LVal);
  }
  
  /// Converts the given APInt to CharUnits, assuming the APInt is unsigned.
  /// Fails if the conversion would cause loss of precision.
  static bool convertUnsignedAPIntToCharUnits(const llvm::APInt &Int,
                                              CharUnits &Result) {
    auto CharUnitsMax = std::numeric_limits<CharUnits::QuantityType>::max();
    if (Int.ugt(CharUnitsMax))
      return false;
    Result = CharUnits::fromQuantity(Int.getZExtValue());
    return true;
  }
  
  /// Helper for tryEvaluateBuiltinObjectSize -- Given an LValue, this will
  /// determine how many bytes exist from the beginning of the object to either
  /// the end of the current subobject, or the end of the object itself, depending
  /// on what the LValue looks like + the value of Type.
  ///
  /// If this returns false, the value of Result is undefined.
  static bool determineEndOffset(EvalInfo &Info, SourceLocation ExprLoc,
                                 unsigned Type, const LValue &LVal,
                                 CharUnits &EndOffset) {
    bool DetermineForCompleteObject = refersToCompleteObject(LVal);
  
    auto CheckedHandleSizeof = [&](QualType Ty, CharUnits &Result) {
      if (Ty.isNull() || Ty->isIncompleteType() || Ty->isFunctionType())
        return false;
      return HandleSizeof(Info, ExprLoc, Ty, Result);
    };
  
    // We want to evaluate the size of the entire object. This is a valid fallback
    // for when Type=1 and the designator is invalid, because we're asked for an
    // upper-bound.
    if (!(Type & 1) || LVal.Designator.Invalid || DetermineForCompleteObject) {
      // Type=3 wants a lower bound, so we can't fall back to this.
      if (Type == 3 && !DetermineForCompleteObject)
        return false;
  
      llvm::APInt APEndOffset;
      if (isBaseAnAllocSizeCall(LVal.getLValueBase()) &&
          getBytesReturnedByAllocSizeCall(Info.Ctx, LVal, APEndOffset))
        return convertUnsignedAPIntToCharUnits(APEndOffset, EndOffset);
  
      if (LVal.InvalidBase)
        return false;
  
      QualType BaseTy = getObjectType(LVal.getLValueBase());
      return CheckedHandleSizeof(BaseTy, EndOffset);
    }
  
    // We want to evaluate the size of a subobject.
    const SubobjectDesignator &Designator = LVal.Designator;
  
    // The following is a moderately common idiom in C:
    //
    // struct Foo { int a; char c[1]; };
    // struct Foo *F = (struct Foo *)malloc(sizeof(struct Foo) + strlen(Bar));
    // strcpy(&F->c[0], Bar);
    //
    // In order to not break too much legacy code, we need to support it.
    if (isUserWritingOffTheEnd(Info.Ctx, LVal)) {
      // If we can resolve this to an alloc_size call, we can hand that back,
      // because we know for certain how many bytes there are to write to.
      llvm::APInt APEndOffset;
      if (isBaseAnAllocSizeCall(LVal.getLValueBase()) &&
          getBytesReturnedByAllocSizeCall(Info.Ctx, LVal, APEndOffset))
        return convertUnsignedAPIntToCharUnits(APEndOffset, EndOffset);
  
      // If we cannot determine the size of the initial allocation, then we can't
      // given an accurate upper-bound. However, we are still able to give
      // conservative lower-bounds for Type=3.
      if (Type == 1)
        return false;
    }
  
    CharUnits BytesPerElem;
    if (!CheckedHandleSizeof(Designator.MostDerivedType, BytesPerElem))
      return false;
  
    // According to the GCC documentation, we want the size of the subobject
    // denoted by the pointer. But that's not quite right -- what we actually
    // want is the size of the immediately-enclosing array, if there is one.
    int64_t ElemsRemaining;
    if (Designator.MostDerivedIsArrayElement &&
        Designator.Entries.size() == Designator.MostDerivedPathLength) {
      uint64_t ArraySize = Designator.getMostDerivedArraySize();
      uint64_t ArrayIndex = Designator.Entries.back().getAsArrayIndex();
      ElemsRemaining = ArraySize <= ArrayIndex ? 0 : ArraySize - ArrayIndex;
    } else {
      ElemsRemaining = Designator.isOnePastTheEnd() ? 0 : 1;
    }
  
    EndOffset = LVal.getLValueOffset() + BytesPerElem * ElemsRemaining;
    return true;
  }
  
  /// Tries to evaluate the __builtin_object_size for @p E. If successful,
  /// returns true and stores the result in @p Size.
  ///
  /// If @p WasError is non-null, this will report whether the failure to evaluate
  /// is to be treated as an Error in IntExprEvaluator.
  static bool tryEvaluateBuiltinObjectSize(const Expr *E, unsigned Type,
                                           EvalInfo &Info, uint64_t &Size) {
    // Determine the denoted object.
    LValue LVal;
    {
      // The operand of __builtin_object_size is never evaluated for side-effects.
      // If there are any, but we can determine the pointed-to object anyway, then
      // ignore the side-effects.
      SpeculativeEvaluationRAII SpeculativeEval(Info);
      IgnoreSideEffectsRAII Fold(Info);
  
      if (E->isGLValue()) {
        // It's possible for us to be given GLValues if we're called via
        // Expr::tryEvaluateObjectSize.
        APValue RVal;
        if (!EvaluateAsRValue(Info, E, RVal))
          return false;
        LVal.setFrom(Info.Ctx, RVal);
      } else if (!EvaluatePointer(ignorePointerCastsAndParens(E), LVal, Info,
                                  /*InvalidBaseOK=*/true))
        return false;
    }
  
    // If we point to before the start of the object, there are no accessible
    // bytes.
    if (LVal.getLValueOffset().isNegative()) {
      Size = 0;
      return true;
    }
  
    CharUnits EndOffset;
    if (!determineEndOffset(Info, E->getExprLoc(), Type, LVal, EndOffset))
      return false;
  
    // If we've fallen outside of the end offset, just pretend there's nothing to
    // write to/read from.
    if (EndOffset <= LVal.getLValueOffset())
      Size = 0;
    else
      Size = (EndOffset - LVal.getLValueOffset()).getQuantity();
    return true;
  }
  
  bool IntExprEvaluator::VisitCallExpr(const CallExpr *E) {
    if (unsigned BuiltinOp = E->getBuiltinCallee())
      return VisitBuiltinCallExpr(E, BuiltinOp);
  
    return ExprEvaluatorBaseTy::VisitCallExpr(E);
  }
  
  static bool getBuiltinAlignArguments(const CallExpr *E, EvalInfo &Info,
                                       APValue &Val, APSInt &Alignment) {
    QualType SrcTy = E->getArg(0)->getType();
    if (!getAlignmentArgument(E->getArg(1), SrcTy, Info, Alignment))
      return false;
    // Even though we are evaluating integer expressions we could get a pointer
    // argument for the __builtin_is_aligned() case.
    if (SrcTy->isPointerType()) {
      LValue Ptr;
      if (!EvaluatePointer(E->getArg(0), Ptr, Info))
        return false;
      Ptr.moveInto(Val);
    } else if (!SrcTy->isIntegralOrEnumerationType()) {
      Info.FFDiag(E->getArg(0));
      return false;
    } else {
      APSInt SrcInt;
      if (!EvaluateInteger(E->getArg(0), SrcInt, Info))
        return false;
      assert(SrcInt.getBitWidth() >= Alignment.getBitWidth() &&
             "Bit widths must be the same");
      Val = APValue(SrcInt);
    }
    assert(Val.hasValue());
    return true;
  }
  
  bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
                                              unsigned BuiltinOp) {
    switch (BuiltinOp) {
    default:
      return ExprEvaluatorBaseTy::VisitCallExpr(E);
  
    case Builtin::BI__builtin_dynamic_object_size:
    case Builtin::BI__builtin_object_size: {
      // The type was checked when we built the expression.
      unsigned Type =
          E->getArg(1)->EvaluateKnownConstInt(Info.Ctx).getZExtValue();
      assert(Type <= 3 && "unexpected type");
  
      uint64_t Size;
      if (tryEvaluateBuiltinObjectSize(E->getArg(0), Type, Info, Size))
        return Success(Size, E);
  
      if (E->getArg(0)->HasSideEffects(Info.Ctx))
        return Success((Type & 2) ? 0 : -1, E);
  
      // Expression had no side effects, but we couldn't statically determine the
      // size of the referenced object.
      switch (Info.EvalMode) {
      case EvalInfo::EM_ConstantExpression:
      case EvalInfo::EM_ConstantFold:
      case EvalInfo::EM_IgnoreSideEffects:
        // Leave it to IR generation.
        return Error(E);
      case EvalInfo::EM_ConstantExpressionUnevaluated:
        // Reduce it to a constant now.
        return Success((Type & 2) ? 0 : -1, E);
      }
  
      llvm_unreachable("unexpected EvalMode");
    }
  
    case Builtin::BI__builtin_os_log_format_buffer_size: {
      analyze_os_log::OSLogBufferLayout Layout;
      analyze_os_log::computeOSLogBufferLayout(Info.Ctx, E, Layout);
      return Success(Layout.size().getQuantity(), E);
    }
  
    case Builtin::BI__builtin_is_aligned: {
      APValue Src;
      APSInt Alignment;
      if (!getBuiltinAlignArguments(E, Info, Src, Alignment))
        return false;
      if (Src.isLValue()) {
        // If we evaluated a pointer, check the minimum known alignment.
        LValue Ptr;
        Ptr.setFrom(Info.Ctx, Src);
        CharUnits BaseAlignment = getBaseAlignment(Info, Ptr);
        CharUnits PtrAlign = BaseAlignment.alignmentAtOffset(Ptr.Offset);
        // We can return true if the known alignment at the computed offset is
        // greater than the requested alignment.
        assert(PtrAlign.isPowerOfTwo());
        assert(Alignment.isPowerOf2());
        if (PtrAlign.getQuantity() >= Alignment)
          return Success(1, E);
        // If the alignment is not known to be sufficient, some cases could still
        // be aligned at run time. However, if the requested alignment is less or
        // equal to the base alignment and the offset is not aligned, we know that
        // the run-time value can never be aligned.
        if (BaseAlignment.getQuantity() >= Alignment &&
            PtrAlign.getQuantity() < Alignment)
          return Success(0, E);
        // Otherwise we can't infer whether the value is sufficiently aligned.
        // TODO: __builtin_is_aligned(__builtin_align_{down,up{(expr, N), N)
        //  in cases where we can't fully evaluate the pointer.
        Info.FFDiag(E->getArg(0), diag::note_constexpr_alignment_compute)
            << Alignment;
        return false;
      }
      assert(Src.isInt());
      return Success((Src.getInt() & (Alignment - 1)) == 0 ? 1 : 0, E);
    }
    case Builtin::BI__builtin_align_up: {
      APValue Src;
      APSInt Alignment;
      if (!getBuiltinAlignArguments(E, Info, Src, Alignment))
        return false;
      if (!Src.isInt())
        return Error(E);
      APSInt AlignedVal =
          APSInt((Src.getInt() + (Alignment - 1)) & ~(Alignment - 1),
                 Src.getInt().isUnsigned());
      assert(AlignedVal.getBitWidth() == Src.getInt().getBitWidth());
      return Success(AlignedVal, E);
    }
    case Builtin::BI__builtin_align_down: {
      APValue Src;
      APSInt Alignment;
      if (!getBuiltinAlignArguments(E, Info, Src, Alignment))
        return false;
      if (!Src.isInt())
        return Error(E);
      APSInt AlignedVal =
          APSInt(Src.getInt() & ~(Alignment - 1), Src.getInt().isUnsigned());
      assert(AlignedVal.getBitWidth() == Src.getInt().getBitWidth());
      return Success(AlignedVal, E);
    }
  
    case Builtin::BI__builtin_bitreverse8:
    case Builtin::BI__builtin_bitreverse16:
    case Builtin::BI__builtin_bitreverse32:
    case Builtin::BI__builtin_bitreverse64: {
      APSInt Val;
      if (!EvaluateInteger(E->getArg(0), Val, Info))
        return false;
  
      return Success(Val.reverseBits(), E);
    }
  
    case Builtin::BI__builtin_bswap16:
    case Builtin::BI__builtin_bswap32:
    case Builtin::BI__builtin_bswap64: {
      APSInt Val;
      if (!EvaluateInteger(E->getArg(0), Val, Info))
        return false;
  
      return Success(Val.byteSwap(), E);
    }
  
    case Builtin::BI__builtin_classify_type:
      return Success((int)EvaluateBuiltinClassifyType(E, Info.getLangOpts()), E);
  
    case Builtin::BI__builtin_clrsb:
    case Builtin::BI__builtin_clrsbl:
    case Builtin::BI__builtin_clrsbll: {
      APSInt Val;
      if (!EvaluateInteger(E->getArg(0), Val, Info))
        return false;
  
      return Success(Val.getBitWidth() - Val.getMinSignedBits(), E);
    }
  
    case Builtin::BI__builtin_clz:
    case Builtin::BI__builtin_clzl:
    case Builtin::BI__builtin_clzll:
    case Builtin::BI__builtin_clzs: {
      APSInt Val;
      if (!EvaluateInteger(E->getArg(0), Val, Info))
        return false;
      if (!Val)
        return Error(E);
  
      return Success(Val.countLeadingZeros(), E);
    }
  
    case Builtin::BI__builtin_constant_p: {
      const Expr *Arg = E->getArg(0);
      if (EvaluateBuiltinConstantP(Info, Arg))
        return Success(true, E);
      if (Info.InConstantContext || Arg->HasSideEffects(Info.Ctx)) {
        // Outside a constant context, eagerly evaluate to false in the presence
        // of side-effects in order to avoid -Wunsequenced false-positives in
        // a branch on __builtin_constant_p(expr).
        return Success(false, E);
      }
      Info.FFDiag(E, diag::note_invalid_subexpr_in_const_expr);
      return false;
    }
  
    case Builtin::BI__builtin_is_constant_evaluated: {
      const auto *Callee = Info.CurrentCall->getCallee();
      if (Info.InConstantContext && !Info.CheckingPotentialConstantExpression &&
          (Info.CallStackDepth == 1 ||
           (Info.CallStackDepth == 2 && Callee->isInStdNamespace() &&
            Callee->getIdentifier() &&
            Callee->getIdentifier()->isStr("is_constant_evaluated")))) {
        // FIXME: Find a better way to avoid duplicated diagnostics.
        if (Info.EvalStatus.Diag)
          Info.report((Info.CallStackDepth == 1) ? E->getExprLoc()
                                                 : Info.CurrentCall->CallLoc,
                      diag::warn_is_constant_evaluated_always_true_constexpr)
              << (Info.CallStackDepth == 1 ? "__builtin_is_constant_evaluated"
                                           : "std::is_constant_evaluated");
      }
  
      return Success(Info.InConstantContext, E);
    }
  
    case Builtin::BI__builtin_ctz:
    case Builtin::BI__builtin_ctzl:
    case Builtin::BI__builtin_ctzll:
    case Builtin::BI__builtin_ctzs: {
      APSInt Val;
      if (!EvaluateInteger(E->getArg(0), Val, Info))
        return false;
      if (!Val)
        return Error(E);
  
      return Success(Val.countTrailingZeros(), E);
    }
  
    case Builtin::BI__builtin_eh_return_data_regno: {
      int Operand = E->getArg(0)->EvaluateKnownConstInt(Info.Ctx).getZExtValue();
      Operand = Info.Ctx.getTargetInfo().getEHDataRegisterNumber(Operand);
      return Success(Operand, E);
    }
  
    case Builtin::BI__builtin_expect:
    case Builtin::BI__builtin_expect_with_probability:
      return Visit(E->getArg(0));
  
    case Builtin::BI__builtin_ptrauth_string_discriminator: {
      auto literal = cast<StringLiteral>(E->getArg(0)->IgnoreParenImpCasts());
      auto result = getPointerAuthStringDiscriminator(Info.Ctx,
                                                      literal->getString());
      return Success(result, E);
    }
  
    case Builtin::BI__builtin_ffs:
    case Builtin::BI__builtin_ffsl:
    case Builtin::BI__builtin_ffsll: {
      APSInt Val;
      if (!EvaluateInteger(E->getArg(0), Val, Info))
        return false;
  
      unsigned N = Val.countTrailingZeros();
      return Success(N == Val.getBitWidth() ? 0 : N + 1, E);
    }
  
    case Builtin::BI__builtin_fpclassify: {
      APFloat Val(0.0);
      if (!EvaluateFloat(E->getArg(5), Val, Info))
        return false;
      unsigned Arg;
      switch (Val.getCategory()) {
      case APFloat::fcNaN: Arg = 0; break;
      case APFloat::fcInfinity: Arg = 1; break;
      case APFloat::fcNormal: Arg = Val.isDenormal() ? 3 : 2; break;
      case APFloat::fcZero: Arg = 4; break;
      }
      return Visit(E->getArg(Arg));
    }
  
    case Builtin::BI__builtin_isinf_sign: {
      APFloat Val(0.0);
      return EvaluateFloat(E->getArg(0), Val, Info) &&
             Success(Val.isInfinity() ? (Val.isNegative() ? -1 : 1) : 0, E);
    }
  
    case Builtin::BI__builtin_isinf: {
      APFloat Val(0.0);
      return EvaluateFloat(E->getArg(0), Val, Info) &&
             Success(Val.isInfinity() ? 1 : 0, E);
    }
  
    case Builtin::BI__builtin_isfinite: {
      APFloat Val(0.0);
      return EvaluateFloat(E->getArg(0), Val, Info) &&
             Success(Val.isFinite() ? 1 : 0, E);
    }
  
    case Builtin::BI__builtin_isnan: {
      APFloat Val(0.0);
      return EvaluateFloat(E->getArg(0), Val, Info) &&
             Success(Val.isNaN() ? 1 : 0, E);
    }
  
    case Builtin::BI__builtin_isnormal: {
      APFloat Val(0.0);
      return EvaluateFloat(E->getArg(0), Val, Info) &&
             Success(Val.isNormal() ? 1 : 0, E);
    }
  
    case Builtin::BI__builtin_parity:
    case Builtin::BI__builtin_parityl:
    case Builtin::BI__builtin_parityll: {
      APSInt Val;
      if (!EvaluateInteger(E->getArg(0), Val, Info))
        return false;
  
      return Success(Val.countPopulation() % 2, E);
    }
  
    case Builtin::BI__builtin_popcount:
    case Builtin::BI__builtin_popcountl:
    case Builtin::BI__builtin_popcountll: {
      APSInt Val;
      if (!EvaluateInteger(E->getArg(0), Val, Info))
        return false;
  
      return Success(Val.countPopulation(), E);
    }
  
    case Builtin::BI__builtin_rotateleft8:
    case Builtin::BI__builtin_rotateleft16:
    case Builtin::BI__builtin_rotateleft32:
    case Builtin::BI__builtin_rotateleft64:
    case Builtin::BI_rotl8: // Microsoft variants of rotate right
    case Builtin::BI_rotl16:
    case Builtin::BI_rotl:
    case Builtin::BI_lrotl:
    case Builtin::BI_rotl64: {
      APSInt Val, Amt;
      if (!EvaluateInteger(E->getArg(0), Val, Info) ||
          !EvaluateInteger(E->getArg(1), Amt, Info))
        return false;
  
      return Success(Val.rotl(Amt.urem(Val.getBitWidth())), E);
    }
  
    case Builtin::BI__builtin_rotateright8:
    case Builtin::BI__builtin_rotateright16:
    case Builtin::BI__builtin_rotateright32:
    case Builtin::BI__builtin_rotateright64:
    case Builtin::BI_rotr8: // Microsoft variants of rotate right
    case Builtin::BI_rotr16:
    case Builtin::BI_rotr:
    case Builtin::BI_lrotr:
    case Builtin::BI_rotr64: {
      APSInt Val, Amt;
      if (!EvaluateInteger(E->getArg(0), Val, Info) ||
          !EvaluateInteger(E->getArg(1), Amt, Info))
        return false;
  
      return Success(Val.rotr(Amt.urem(Val.getBitWidth())), E);
    }
  
    case Builtin::BIstrlen:
    case Builtin::BIwcslen:
      // A call to strlen is not a constant expression.
      if (Info.getLangOpts().CPlusPlus11)
        Info.CCEDiag(E, diag::note_constexpr_invalid_function)
          << /*isConstexpr*/0 << /*isConstructor*/0
          << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) + "'");
      else
        Info.CCEDiag(E, diag::note_invalid_subexpr_in_const_expr);
      LLVM_FALLTHROUGH;
    case Builtin::BI__builtin_strlen:
    case Builtin::BI__builtin_wcslen: {
      // As an extension, we support __builtin_strlen() as a constant expression,
      // and support folding strlen() to a constant.
      LValue String;
      if (!EvaluatePointer(E->getArg(0), String, Info))
        return false;
  
      QualType CharTy = E->getArg(0)->getType()->getPointeeType();
  
      // Fast path: if it's a string literal, search the string value.
      if (const StringLiteral *S = dyn_cast_or_null<StringLiteral>(
              String.getLValueBase().dyn_cast<const Expr *>())) {
        // The string literal may have embedded null characters. Find the first
        // one and truncate there.
        StringRef Str = S->getBytes();
        int64_t Off = String.Offset.getQuantity();
        if (Off >= 0 && (uint64_t)Off <= (uint64_t)Str.size() &&
            S->getCharByteWidth() == 1 &&
            // FIXME: Add fast-path for wchar_t too.
            Info.Ctx.hasSameUnqualifiedType(CharTy, Info.Ctx.CharTy)) {
          Str = Str.substr(Off);
  
          StringRef::size_type Pos = Str.find(0);
          if (Pos != StringRef::npos)
            Str = Str.substr(0, Pos);
  
          return Success(Str.size(), E);
        }
  
        // Fall through to slow path to issue appropriate diagnostic.
      }
  
      // Slow path: scan the bytes of the string looking for the terminating 0.
      for (uint64_t Strlen = 0; /**/; ++Strlen) {
        APValue Char;
        if (!handleLValueToRValueConversion(Info, E, CharTy, String, Char) ||
            !Char.isInt())
          return false;
        if (!Char.getInt())
          return Success(Strlen, E);
        if (!HandleLValueArrayAdjustment(Info, E, String, CharTy, 1))
          return false;
      }
    }
  
    case Builtin::BIstrcmp:
    case Builtin::BIwcscmp:
    case Builtin::BIstrncmp:
    case Builtin::BIwcsncmp:
    case Builtin::BImemcmp:
    case Builtin::BIbcmp:
    case Builtin::BIwmemcmp:
      // A call to strlen is not a constant expression.
      if (Info.getLangOpts().CPlusPlus11)
        Info.CCEDiag(E, diag::note_constexpr_invalid_function)
          << /*isConstexpr*/0 << /*isConstructor*/0
          << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) + "'");
      else
        Info.CCEDiag(E, diag::note_invalid_subexpr_in_const_expr);
      LLVM_FALLTHROUGH;
    case Builtin::BI__builtin_strcmp:
    case Builtin::BI__builtin_wcscmp:
    case Builtin::BI__builtin_strncmp:
    case Builtin::BI__builtin_wcsncmp:
    case Builtin::BI__builtin_memcmp:
    case Builtin::BI__builtin_bcmp:
    case Builtin::BI__builtin_wmemcmp: {
      LValue String1, String2;
      if (!EvaluatePointer(E->getArg(0), String1, Info) ||
          !EvaluatePointer(E->getArg(1), String2, Info))
        return false;
  
      uint64_t MaxLength = uint64_t(-1);
      if (BuiltinOp != Builtin::BIstrcmp &&
          BuiltinOp != Builtin::BIwcscmp &&
          BuiltinOp != Builtin::BI__builtin_strcmp &&
          BuiltinOp != Builtin::BI__builtin_wcscmp) {
        APSInt N;
        if (!EvaluateInteger(E->getArg(2), N, Info))
          return false;
        MaxLength = N.getExtValue();
      }
  
      // Empty substrings compare equal by definition.
      if (MaxLength == 0u)
        return Success(0, E);
  
      if (!String1.checkNullPointerForFoldAccess(Info, E, AK_Read) ||
          !String2.checkNullPointerForFoldAccess(Info, E, AK_Read) ||
          String1.Designator.Invalid || String2.Designator.Invalid)
        return false;
  
      QualType CharTy1 = String1.Designator.getType(Info.Ctx);
      QualType CharTy2 = String2.Designator.getType(Info.Ctx);
  
      bool IsRawByte = BuiltinOp == Builtin::BImemcmp ||
                       BuiltinOp == Builtin::BIbcmp ||
                       BuiltinOp == Builtin::BI__builtin_memcmp ||
                       BuiltinOp == Builtin::BI__builtin_bcmp;
  
      assert(IsRawByte ||
             (Info.Ctx.hasSameUnqualifiedType(
                  CharTy1, E->getArg(0)->getType()->getPointeeType()) &&
              Info.Ctx.hasSameUnqualifiedType(CharTy1, CharTy2)));
  
      // For memcmp, allow comparing any arrays of '[[un]signed] char' or
      // 'char8_t', but no other types.
      if (IsRawByte &&
          !(isOneByteCharacterType(CharTy1) && isOneByteCharacterType(CharTy2))) {
        // FIXME: Consider using our bit_cast implementation to support this.
        Info.FFDiag(E, diag::note_constexpr_memcmp_unsupported)
            << (std::string("'") + Info.Ctx.BuiltinInfo.getName(BuiltinOp) + "'")
            << CharTy1 << CharTy2;
        return false;
      }
  
      const auto &ReadCurElems = [&](APValue &Char1, APValue &Char2) {
        return handleLValueToRValueConversion(Info, E, CharTy1, String1, Char1) &&
               handleLValueToRValueConversion(Info, E, CharTy2, String2, Char2) &&
               Char1.isInt() && Char2.isInt();
      };
      const auto &AdvanceElems = [&] {
        return HandleLValueArrayAdjustment(Info, E, String1, CharTy1, 1) &&
               HandleLValueArrayAdjustment(Info, E, String2, CharTy2, 1);
      };
  
      bool StopAtNull =
          (BuiltinOp != Builtin::BImemcmp && BuiltinOp != Builtin::BIbcmp &&
           BuiltinOp != Builtin::BIwmemcmp &&
           BuiltinOp != Builtin::BI__builtin_memcmp &&
           BuiltinOp != Builtin::BI__builtin_bcmp &&
           BuiltinOp != Builtin::BI__builtin_wmemcmp);
      bool IsWide = BuiltinOp == Builtin::BIwcscmp ||
                    BuiltinOp == Builtin::BIwcsncmp ||
                    BuiltinOp == Builtin::BIwmemcmp ||
                    BuiltinOp == Builtin::BI__builtin_wcscmp ||
                    BuiltinOp == Builtin::BI__builtin_wcsncmp ||
                    BuiltinOp == Builtin::BI__builtin_wmemcmp;
  
      for (; MaxLength; --MaxLength) {
        APValue Char1, Char2;
        if (!ReadCurElems(Char1, Char2))
          return false;
        if (Char1.getInt().ne(Char2.getInt())) {
          if (IsWide) // wmemcmp compares with wchar_t signedness.
            return Success(Char1.getInt() < Char2.getInt() ? -1 : 1, E);
          // memcmp always compares unsigned chars.
          return Success(Char1.getInt().ult(Char2.getInt()) ? -1 : 1, E);
        }
        if (StopAtNull && !Char1.getInt())
          return Success(0, E);
        assert(!(StopAtNull && !Char2.getInt()));
        if (!AdvanceElems())
          return false;
      }
      // We hit the strncmp / memcmp limit.
      return Success(0, E);
    }
  
    case Builtin::BI__atomic_always_lock_free:
    case Builtin::BI__atomic_is_lock_free:
    case Builtin::BI__c11_atomic_is_lock_free: {
      APSInt SizeVal;
      if (!EvaluateInteger(E->getArg(0), SizeVal, Info))
        return false;
  
      // For __atomic_is_lock_free(sizeof(_Atomic(T))), if the size is a power
      // of two less than or equal to the maximum inline atomic width, we know it
      // is lock-free.  If the size isn't a power of two, or greater than the
      // maximum alignment where we promote atomics, we know it is not lock-free
      // (at least not in the sense of atomic_is_lock_free).  Otherwise,
      // the answer can only be determined at runtime; for example, 16-byte
      // atomics have lock-free implementations on some, but not all,
      // x86-64 processors.
  
      // Check power-of-two.
      CharUnits Size = CharUnits::fromQuantity(SizeVal.getZExtValue());
      if (Size.isPowerOfTwo()) {
        // Check against inlining width.
        unsigned InlineWidthBits =
            Info.Ctx.getTargetInfo().getMaxAtomicInlineWidth();
        if (Size <= Info.Ctx.toCharUnitsFromBits(InlineWidthBits)) {
          if (BuiltinOp == Builtin::BI__c11_atomic_is_lock_free ||
              Size == CharUnits::One() ||
              E->getArg(1)->isNullPointerConstant(Info.Ctx,
                                                  Expr::NPC_NeverValueDependent))
            // OK, we will inline appropriately-aligned operations of this size,
            // and _Atomic(T) is appropriately-aligned.
            return Success(1, E);
  
          QualType PointeeType = E->getArg(1)->IgnoreImpCasts()->getType()->
            castAs<PointerType>()->getPointeeType();
          if (!PointeeType->isIncompleteType() &&
              Info.Ctx.getTypeAlignInChars(PointeeType) >= Size) {
            // OK, we will inline operations on this object.
            return Success(1, E);
          }
        }
      }
  
      return BuiltinOp == Builtin::BI__atomic_always_lock_free ?
          Success(0, E) : Error(E);
    }
    case Builtin::BIomp_is_initial_device:
      // We can decide statically which value the runtime would return if called.
      return Success(Info.getLangOpts().OpenMPIsDevice ? 0 : 1, E);
    case Builtin::BI__builtin_add_overflow:
    case Builtin::BI__builtin_sub_overflow:
    case Builtin::BI__builtin_mul_overflow:
    case Builtin::BI__builtin_sadd_overflow:
    case Builtin::BI__builtin_uadd_overflow:
    case Builtin::BI__builtin_uaddl_overflow:
    case Builtin::BI__builtin_uaddll_overflow:
    case Builtin::BI__builtin_usub_overflow:
    case Builtin::BI__builtin_usubl_overflow:
    case Builtin::BI__builtin_usubll_overflow:
    case Builtin::BI__builtin_umul_overflow:
    case Builtin::BI__builtin_umull_overflow:
    case Builtin::BI__builtin_umulll_overflow:
    case Builtin::BI__builtin_saddl_overflow:
    case Builtin::BI__builtin_saddll_overflow:
    case Builtin::BI__builtin_ssub_overflow:
    case Builtin::BI__builtin_ssubl_overflow:
    case Builtin::BI__builtin_ssubll_overflow:
    case Builtin::BI__builtin_smul_overflow:
    case Builtin::BI__builtin_smull_overflow:
    case Builtin::BI__builtin_smulll_overflow: {
      LValue ResultLValue;
      APSInt LHS, RHS;
  
      QualType ResultType = E->getArg(2)->getType()->getPointeeType();
      if (!EvaluateInteger(E->getArg(0), LHS, Info) ||
          !EvaluateInteger(E->getArg(1), RHS, Info) ||
          !EvaluatePointer(E->getArg(2), ResultLValue, Info))
        return false;
  
      APSInt Result;
      bool DidOverflow = false;
  
      // If the types don't have to match, enlarge all 3 to the largest of them.
      if (BuiltinOp == Builtin::BI__builtin_add_overflow ||
          BuiltinOp == Builtin::BI__builtin_sub_overflow ||
          BuiltinOp == Builtin::BI__builtin_mul_overflow) {
        bool IsSigned = LHS.isSigned() || RHS.isSigned() ||
                        ResultType->isSignedIntegerOrEnumerationType();
        bool AllSigned = LHS.isSigned() && RHS.isSigned() &&
                        ResultType->isSignedIntegerOrEnumerationType();
        uint64_t LHSSize = LHS.getBitWidth();
        uint64_t RHSSize = RHS.getBitWidth();
        uint64_t ResultSize = Info.Ctx.getTypeSize(ResultType);
        uint64_t MaxBits = std::max(std::max(LHSSize, RHSSize), ResultSize);
  
        // Add an additional bit if the signedness isn't uniformly agreed to. We
        // could do this ONLY if there is a signed and an unsigned that both have
        // MaxBits, but the code to check that is pretty nasty.  The issue will be
        // caught in the shrink-to-result later anyway.
        if (IsSigned && !AllSigned)
          ++MaxBits;
  
        LHS = APSInt(LHS.extOrTrunc(MaxBits), !IsSigned);
        RHS = APSInt(RHS.extOrTrunc(MaxBits), !IsSigned);
        Result = APSInt(MaxBits, !IsSigned);
      }
  
      // Find largest int.
      switch (BuiltinOp) {
      default:
        llvm_unreachable("Invalid value for BuiltinOp");
      case Builtin::BI__builtin_add_overflow:
      case Builtin::BI__builtin_sadd_overflow:
      case Builtin::BI__builtin_saddl_overflow:
      case Builtin::BI__builtin_saddll_overflow:
      case Builtin::BI__builtin_uadd_overflow:
      case Builtin::BI__builtin_uaddl_overflow:
      case Builtin::BI__builtin_uaddll_overflow:
        Result = LHS.isSigned() ? LHS.sadd_ov(RHS, DidOverflow)
                                : LHS.uadd_ov(RHS, DidOverflow);
        break;
      case Builtin::BI__builtin_sub_overflow:
      case Builtin::BI__builtin_ssub_overflow:
      case Builtin::BI__builtin_ssubl_overflow:
      case Builtin::BI__builtin_ssubll_overflow:
      case Builtin::BI__builtin_usub_overflow:
      case Builtin::BI__builtin_usubl_overflow:
      case Builtin::BI__builtin_usubll_overflow:
        Result = LHS.isSigned() ? LHS.ssub_ov(RHS, DidOverflow)
                                : LHS.usub_ov(RHS, DidOverflow);
        break;
      case Builtin::BI__builtin_mul_overflow:
      case Builtin::BI__builtin_smul_overflow:
      case Builtin::BI__builtin_smull_overflow:
      case Builtin::BI__builtin_smulll_overflow:
      case Builtin::BI__builtin_umul_overflow:
      case Builtin::BI__builtin_umull_overflow:
      case Builtin::BI__builtin_umulll_overflow:
        Result = LHS.isSigned() ? LHS.smul_ov(RHS, DidOverflow)
                                : LHS.umul_ov(RHS, DidOverflow);
        break;
      }
  
      // In the case where multiple sizes are allowed, truncate and see if
      // the values are the same.
      if (BuiltinOp == Builtin::BI__builtin_add_overflow ||
          BuiltinOp == Builtin::BI__builtin_sub_overflow ||
          BuiltinOp == Builtin::BI__builtin_mul_overflow) {
        // APSInt doesn't have a TruncOrSelf, so we use extOrTrunc instead,
        // since it will give us the behavior of a TruncOrSelf in the case where
        // its parameter <= its size.  We previously set Result to be at least the
        // type-size of the result, so getTypeSize(ResultType) <= Result.BitWidth
        // will work exactly like TruncOrSelf.
        APSInt Temp = Result.extOrTrunc(Info.Ctx.getTypeSize(ResultType));
        Temp.setIsSigned(ResultType->isSignedIntegerOrEnumerationType());
  
        if (!APSInt::isSameValue(Temp, Result))
          DidOverflow = true;
        Result = Temp;
      }
  
      APValue APV{Result};
      if (!handleAssignment(Info, E, ResultLValue, ResultType, APV))
        return false;
      return Success(DidOverflow, E);
    }
    }
  }
  
  /// Determine whether this is a pointer past the end of the complete
  /// object referred to by the lvalue.
  static bool isOnePastTheEndOfCompleteObject(const ASTContext &Ctx,
                                              const LValue &LV) {
    // A null pointer can be viewed as being "past the end" but we don't
    // choose to look at it that way here.
    if (!LV.getLValueBase())
      return false;
  
    // If the designator is valid and refers to a subobject, we're not pointing
    // past the end.
    if (!LV.getLValueDesignator().Invalid &&
        !LV.getLValueDesignator().isOnePastTheEnd())
      return false;
  
    // A pointer to an incomplete type might be past-the-end if the type's size is
    // zero.  We cannot tell because the type is incomplete.
    QualType Ty = getType(LV.getLValueBase());
    if (Ty->isIncompleteType())
      return true;
  
    // We're a past-the-end pointer if we point to the byte after the object,
    // no matter what our type or path is.
    auto Size = Ctx.getTypeSizeInChars(Ty);
    return LV.getLValueOffset() == Size;
  }
  
  namespace {
  
  /// Data recursive integer evaluator of certain binary operators.
  ///
  /// We use a data recursive algorithm for binary operators so that we are able
  /// to handle extreme cases of chained binary operators without causing stack
  /// overflow.
  class DataRecursiveIntBinOpEvaluator {
    struct EvalResult {
      APValue Val;
      bool Failed;
  
      EvalResult() : Failed(false) { }
  
      void swap(EvalResult &RHS) {
        Val.swap(RHS.Val);
        Failed = RHS.Failed;
        RHS.Failed = false;
      }
    };
  
    struct Job {
      const Expr *E;
      EvalResult LHSResult; // meaningful only for binary operator expression.
      enum { AnyExprKind, BinOpKind, BinOpVisitedLHSKind } Kind;
  
      Job() = default;
      Job(Job &&) = default;
  
      void startSpeculativeEval(EvalInfo &Info) {
        SpecEvalRAII = SpeculativeEvaluationRAII(Info);
      }
  
    private:
      SpeculativeEvaluationRAII SpecEvalRAII;
    };
  
    SmallVector<Job, 16> Queue;
  
    IntExprEvaluator &IntEval;
    EvalInfo &Info;
    APValue &FinalResult;
  
  public:
    DataRecursiveIntBinOpEvaluator(IntExprEvaluator &IntEval, APValue &Result)
      : IntEval(IntEval), Info(IntEval.getEvalInfo()), FinalResult(Result) { }
  
    /// True if \param E is a binary operator that we are going to handle
    /// data recursively.
    /// We handle binary operators that are comma, logical, or that have operands
    /// with integral or enumeration type.
    static bool shouldEnqueue(const BinaryOperator *E) {
      return E->getOpcode() == BO_Comma || E->isLogicalOp() ||
             (E->isRValue() && E->getType()->isIntegralOrEnumerationType() &&
              E->getLHS()->getType()->isIntegralOrEnumerationType() &&
              E->getRHS()->getType()->isIntegralOrEnumerationType());
    }
  
    bool Traverse(const BinaryOperator *E) {
      enqueue(E);
      EvalResult PrevResult;
      while (!Queue.empty())
        process(PrevResult);
  
      if (PrevResult.Failed) return false;
  
      FinalResult.swap(PrevResult.Val);
      return true;
    }
  
  private:
    bool Success(uint64_t Value, const Expr *E, APValue &Result) {
      return IntEval.Success(Value, E, Result);
    }
    bool Success(const APSInt &Value, const Expr *E, APValue &Result) {
      return IntEval.Success(Value, E, Result);
    }
    bool Error(const Expr *E) {
      return IntEval.Error(E);
    }
    bool Error(const Expr *E, diag::kind D) {
      return IntEval.Error(E, D);
    }
  
    OptionalDiagnostic CCEDiag(const Expr *E, diag::kind D) {
      return Info.CCEDiag(E, D);
    }
  
    // Returns true if visiting the RHS is necessary, false otherwise.
    bool VisitBinOpLHSOnly(EvalResult &LHSResult, const BinaryOperator *E,
                           bool &SuppressRHSDiags);
  
    bool VisitBinOp(const EvalResult &LHSResult, const EvalResult &RHSResult,
                    const BinaryOperator *E, APValue &Result);
  
    void EvaluateExpr(const Expr *E, EvalResult &Result) {
      Result.Failed = !Evaluate(Result.Val, Info, E);
      if (Result.Failed)
        Result.Val = APValue();
    }
  
    void process(EvalResult &Result);
  
    void enqueue(const Expr *E) {
      E = E->IgnoreParens();
      Queue.resize(Queue.size()+1);
      Queue.back().E = E;
      Queue.back().Kind = Job::AnyExprKind;
    }
  };
  
  }
  
  bool DataRecursiveIntBinOpEvaluator::
         VisitBinOpLHSOnly(EvalResult &LHSResult, const BinaryOperator *E,
                           bool &SuppressRHSDiags) {
    if (E->getOpcode() == BO_Comma) {
      // Ignore LHS but note if we could not evaluate it.
      if (LHSResult.Failed)
        return Info.noteSideEffect();
      return true;
    }
  
    if (E->isLogicalOp()) {
      bool LHSAsBool;
      if (!LHSResult.Failed && HandleConversionToBool(LHSResult.Val, LHSAsBool)) {
        // We were able to evaluate the LHS, see if we can get away with not
        // evaluating the RHS: 0 && X -> 0, 1 || X -> 1
        if (LHSAsBool == (E->getOpcode() == BO_LOr)) {
          Success(LHSAsBool, E, LHSResult.Val);
          return false; // Ignore RHS
        }
      } else {
        LHSResult.Failed = true;
  
        // Since we weren't able to evaluate the left hand side, it
        // might have had side effects.
        if (!Info.noteSideEffect())
          return false;
  
        // We can't evaluate the LHS; however, sometimes the result
        // is determined by the RHS: X && 0 -> 0, X || 1 -> 1.
        // Don't ignore RHS and suppress diagnostics from this arm.
        SuppressRHSDiags = true;
      }
  
      return true;
    }
  
    assert(E->getLHS()->getType()->isIntegralOrEnumerationType() &&
           E->getRHS()->getType()->isIntegralOrEnumerationType());
  
    if (LHSResult.Failed && !Info.noteFailure())
      return false; // Ignore RHS;
  
    return true;
  }
  
  static void addOrSubLValueAsInteger(APValue &LVal, const APSInt &Index,
                                      bool IsSub) {
    // Compute the new offset in the appropriate width, wrapping at 64 bits.
    // FIXME: When compiling for a 32-bit target, we should use 32-bit
    // offsets.
    assert(!LVal.hasLValuePath() && "have designator for integer lvalue");
    CharUnits &Offset = LVal.getLValueOffset();
    uint64_t Offset64 = Offset.getQuantity();
    uint64_t Index64 = Index.extOrTrunc(64).getZExtValue();
    Offset = CharUnits::fromQuantity(IsSub ? Offset64 - Index64
                                           : Offset64 + Index64);
  }
  
  bool DataRecursiveIntBinOpEvaluator::
         VisitBinOp(const EvalResult &LHSResult, const EvalResult &RHSResult,
                    const BinaryOperator *E, APValue &Result) {
    if (E->getOpcode() == BO_Comma) {
      if (RHSResult.Failed)
        return false;
      Result = RHSResult.Val;
      return true;
    }
  
    if (E->isLogicalOp()) {
      bool lhsResult, rhsResult;
      bool LHSIsOK = HandleConversionToBool(LHSResult.Val, lhsResult);
      bool RHSIsOK = HandleConversionToBool(RHSResult.Val, rhsResult);
  
      if (LHSIsOK) {
        if (RHSIsOK) {
          if (E->getOpcode() == BO_LOr)
            return Success(lhsResult || rhsResult, E, Result);
          else
            return Success(lhsResult && rhsResult, E, Result);
        }
      } else {
        if (RHSIsOK) {
          // We can't evaluate the LHS; however, sometimes the result
          // is determined by the RHS: X && 0 -> 0, X || 1 -> 1.
          if (rhsResult == (E->getOpcode() == BO_LOr))
            return Success(rhsResult, E, Result);
        }
      }
  
      return false;
    }
  
    assert(E->getLHS()->getType()->isIntegralOrEnumerationType() &&
           E->getRHS()->getType()->isIntegralOrEnumerationType());
  
    if (LHSResult.Failed || RHSResult.Failed)
      return false;
  
    const APValue &LHSVal = LHSResult.Val;
    const APValue &RHSVal = RHSResult.Val;
  
    // Handle cases like (unsigned long)&a + 4.
    if (E->isAdditiveOp() && LHSVal.isLValue() && RHSVal.isInt()) {
      Result = LHSVal;
      addOrSubLValueAsInteger(Result, RHSVal.getInt(), E->getOpcode() == BO_Sub);
      return true;
    }
  
    // Handle cases like 4 + (unsigned long)&a
    if (E->getOpcode() == BO_Add &&
        RHSVal.isLValue() && LHSVal.isInt()) {
      Result = RHSVal;
      addOrSubLValueAsInteger(Result, LHSVal.getInt(), /*IsSub*/false);
      return true;
    }
  
    if (E->getOpcode() == BO_Sub && LHSVal.isLValue() && RHSVal.isLValue()) {
      // Handle (intptr_t)&&A - (intptr_t)&&B.
      if (!LHSVal.getLValueOffset().isZero() ||
          !RHSVal.getLValueOffset().isZero())
        return false;
      const Expr *LHSExpr = LHSVal.getLValueBase().dyn_cast<const Expr*>();
      const Expr *RHSExpr = RHSVal.getLValueBase().dyn_cast<const Expr*>();
      if (!LHSExpr || !RHSExpr)
        return false;
      const AddrLabelExpr *LHSAddrExpr = dyn_cast<AddrLabelExpr>(LHSExpr);
      const AddrLabelExpr *RHSAddrExpr = dyn_cast<AddrLabelExpr>(RHSExpr);
      if (!LHSAddrExpr || !RHSAddrExpr)
        return false;
      // Make sure both labels come from the same function.
      if (LHSAddrExpr->getLabel()->getDeclContext() !=
          RHSAddrExpr->getLabel()->getDeclContext())
        return false;
      Result = APValue(LHSAddrExpr, RHSAddrExpr);
      return true;
    }
  
    // All the remaining cases expect both operands to be an integer
    if (!LHSVal.isInt() || !RHSVal.isInt())
      return Error(E);
  
    // Set up the width and signedness manually, in case it can't be deduced
    // from the operation we're performing.
    // FIXME: Don't do this in the cases where we can deduce it.
    APSInt Value(Info.Ctx.getIntWidth(E->getType()),
                 E->getType()->isUnsignedIntegerOrEnumerationType());
    if (!handleIntIntBinOp(Info, E, LHSVal.getInt(), E->getOpcode(),
                           RHSVal.getInt(), Value))
      return false;
    return Success(Value, E, Result);
  }
  
  void DataRecursiveIntBinOpEvaluator::process(EvalResult &Result) {
    Job &job = Queue.back();
  
    switch (job.Kind) {
      case Job::AnyExprKind: {
        if (const BinaryOperator *Bop = dyn_cast<BinaryOperator>(job.E)) {
          if (shouldEnqueue(Bop)) {
            job.Kind = Job::BinOpKind;
            enqueue(Bop->getLHS());
            return;
          }
        }
  
        EvaluateExpr(job.E, Result);
        Queue.pop_back();
        return;
      }
  
      case Job::BinOpKind: {
        const BinaryOperator *Bop = cast<BinaryOperator>(job.E);
        bool SuppressRHSDiags = false;
        if (!VisitBinOpLHSOnly(Result, Bop, SuppressRHSDiags)) {
          Queue.pop_back();
          return;
        }
        if (SuppressRHSDiags)
          job.startSpeculativeEval(Info);
        job.LHSResult.swap(Result);
        job.Kind = Job::BinOpVisitedLHSKind;
        enqueue(Bop->getRHS());
        return;
      }
  
      case Job::BinOpVisitedLHSKind: {
        const BinaryOperator *Bop = cast<BinaryOperator>(job.E);
        EvalResult RHS;
        RHS.swap(Result);
        Result.Failed = !VisitBinOp(job.LHSResult, RHS, Bop, Result.Val);
        Queue.pop_back();
        return;
      }
    }
  
    llvm_unreachable("Invalid Job::Kind!");
  }
  
  namespace {
  /// Used when we determine that we should fail, but can keep evaluating prior to
  /// noting that we had a failure.
  class DelayedNoteFailureRAII {
    EvalInfo &Info;
    bool NoteFailure;
  
  public:
    DelayedNoteFailureRAII(EvalInfo &Info, bool NoteFailure = true)
        : Info(Info), NoteFailure(NoteFailure) {}
    ~DelayedNoteFailureRAII() {
      if (NoteFailure) {
        bool ContinueAfterFailure = Info.noteFailure();
        (void)ContinueAfterFailure;
        assert(ContinueAfterFailure &&
               "Shouldn't have kept evaluating on failure.");
      }
    }
  };
  
  enum class CmpResult {
    Unequal,
    Less,
    Equal,
    Greater,
    Unordered,
  };
  }
  
  template <class SuccessCB, class AfterCB>
  static bool
  EvaluateComparisonBinaryOperator(EvalInfo &Info, const BinaryOperator *E,
                                   SuccessCB &&Success, AfterCB &&DoAfter) {
    assert(!E->isValueDependent());
    assert(E->isComparisonOp() && "expected comparison operator");
    assert((E->getOpcode() == BO_Cmp ||
            E->getType()->isIntegralOrEnumerationType()) &&
           "unsupported binary expression evaluation");
    auto Error = [&](const Expr *E) {
      Info.FFDiag(E, diag::note_invalid_subexpr_in_const_expr);
      return false;
    };
  
    bool IsRelational = E->isRelationalOp() || E->getOpcode() == BO_Cmp;
    bool IsEquality = E->isEqualityOp();
  
    QualType LHSTy = E->getLHS()->getType();
    QualType RHSTy = E->getRHS()->getType();
  
    if (LHSTy->isIntegralOrEnumerationType() &&
        RHSTy->isIntegralOrEnumerationType()) {
      APSInt LHS, RHS;
      bool LHSOK = EvaluateInteger(E->getLHS(), LHS, Info);
      if (!LHSOK && !Info.noteFailure())
        return false;
      if (!EvaluateInteger(E->getRHS(), RHS, Info) || !LHSOK)
        return false;
      if (LHS < RHS)
        return Success(CmpResult::Less, E);
      if (LHS > RHS)
        return Success(CmpResult::Greater, E);
      return Success(CmpResult::Equal, E);
    }
  
    if (LHSTy->isFixedPointType() || RHSTy->isFixedPointType()) {
      APFixedPoint LHSFX(Info.Ctx.getFixedPointSemantics(LHSTy));
      APFixedPoint RHSFX(Info.Ctx.getFixedPointSemantics(RHSTy));
  
      bool LHSOK = EvaluateFixedPointOrInteger(E->getLHS(), LHSFX, Info);
      if (!LHSOK && !Info.noteFailure())
        return false;
      if (!EvaluateFixedPointOrInteger(E->getRHS(), RHSFX, Info) || !LHSOK)
        return false;
      if (LHSFX < RHSFX)
        return Success(CmpResult::Less, E);
      if (LHSFX > RHSFX)
        return Success(CmpResult::Greater, E);
      return Success(CmpResult::Equal, E);
    }
  
    if (LHSTy->isAnyComplexType() || RHSTy->isAnyComplexType()) {
      ComplexValue LHS, RHS;
      bool LHSOK;
      if (E->isAssignmentOp()) {
        LValue LV;
        EvaluateLValue(E->getLHS(), LV, Info);
        LHSOK = false;
      } else if (LHSTy->isRealFloatingType()) {
        LHSOK = EvaluateFloat(E->getLHS(), LHS.FloatReal, Info);
        if (LHSOK) {
          LHS.makeComplexFloat();
          LHS.FloatImag = APFloat(LHS.FloatReal.getSemantics());
        }
      } else {
        LHSOK = EvaluateComplex(E->getLHS(), LHS, Info);
      }
      if (!LHSOK && !Info.noteFailure())
        return false;
  
      if (E->getRHS()->getType()->isRealFloatingType()) {
        if (!EvaluateFloat(E->getRHS(), RHS.FloatReal, Info) || !LHSOK)
          return false;
        RHS.makeComplexFloat();
        RHS.FloatImag = APFloat(RHS.FloatReal.getSemantics());
      } else if (!EvaluateComplex(E->getRHS(), RHS, Info) || !LHSOK)
        return false;
  
      if (LHS.isComplexFloat()) {
        APFloat::cmpResult CR_r =
          LHS.getComplexFloatReal().compare(RHS.getComplexFloatReal());
        APFloat::cmpResult CR_i =
          LHS.getComplexFloatImag().compare(RHS.getComplexFloatImag());
        bool IsEqual = CR_r == APFloat::cmpEqual && CR_i == APFloat::cmpEqual;
        return Success(IsEqual ? CmpResult::Equal : CmpResult::Unequal, E);
      } else {
        assert(IsEquality && "invalid complex comparison");
        bool IsEqual = LHS.getComplexIntReal() == RHS.getComplexIntReal() &&
                       LHS.getComplexIntImag() == RHS.getComplexIntImag();
        return Success(IsEqual ? CmpResult::Equal : CmpResult::Unequal, E);
      }
    }
  
    if (LHSTy->isRealFloatingType() &&
        RHSTy->isRealFloatingType()) {
      APFloat RHS(0.0), LHS(0.0);
  
      bool LHSOK = EvaluateFloat(E->getRHS(), RHS, Info);
      if (!LHSOK && !Info.noteFailure())
        return false;
  
      if (!EvaluateFloat(E->getLHS(), LHS, Info) || !LHSOK)
        return false;
  
      assert(E->isComparisonOp() && "Invalid binary operator!");
      llvm::APFloatBase::cmpResult APFloatCmpResult = LHS.compare(RHS);
      if (!Info.InConstantContext &&
          APFloatCmpResult == APFloat::cmpUnordered &&
          E->getFPFeaturesInEffect(Info.Ctx.getLangOpts()).isFPConstrained()) {
        // Note: Compares may raise invalid in some cases involving NaN or sNaN.
        Info.FFDiag(E, diag::note_constexpr_float_arithmetic_strict);
        return false;
      }
      auto GetCmpRes = [&]() {
        switch (APFloatCmpResult) {
        case APFloat::cmpEqual:
          return CmpResult::Equal;
        case APFloat::cmpLessThan:
          return CmpResult::Less;
        case APFloat::cmpGreaterThan:
          return CmpResult::Greater;
        case APFloat::cmpUnordered:
          return CmpResult::Unordered;
        }
        llvm_unreachable("Unrecognised APFloat::cmpResult enum");
      };
      return Success(GetCmpRes(), E);
    }
  
    if (LHSTy->isPointerType() && RHSTy->isPointerType()) {
      LValue LHSValue, RHSValue;
  
      bool LHSOK = EvaluatePointer(E->getLHS(), LHSValue, Info);
      if (!LHSOK && !Info.noteFailure())
        return false;
  
      if (!EvaluatePointer(E->getRHS(), RHSValue, Info) || !LHSOK)
        return false;
  
      // Reject differing bases from the normal codepath; we special-case
      // comparisons to null.
      if (!HasSameBase(LHSValue, RHSValue)) {
        // Inequalities and subtractions between unrelated pointers have
        // unspecified or undefined behavior.
        if (!IsEquality) {
          Info.FFDiag(E, diag::note_constexpr_pointer_comparison_unspecified);
          return false;
        }
        // A constant address may compare equal to the address of a symbol.
        // The one exception is that address of an object cannot compare equal
        // to a null pointer constant.
        if ((!LHSValue.Base && !LHSValue.Offset.isZero()) ||
            (!RHSValue.Base && !RHSValue.Offset.isZero()))
          return Error(E);
        // It's implementation-defined whether distinct literals will have
        // distinct addresses. In clang, the result of such a comparison is
        // unspecified, so it is not a constant expression. However, we do know
        // that the address of a literal will be non-null.
        if ((IsLiteralLValue(LHSValue) || IsLiteralLValue(RHSValue)) &&
            LHSValue.Base && RHSValue.Base)
          return Error(E);
        // We can't tell whether weak symbols will end up pointing to the same
        // object.
        if (IsWeakLValue(LHSValue) || IsWeakLValue(RHSValue))
          return Error(E);
        // We can't compare the address of the start of one object with the
        // past-the-end address of another object, per C++ DR1652.
        if ((LHSValue.Base && LHSValue.Offset.isZero() &&
             isOnePastTheEndOfCompleteObject(Info.Ctx, RHSValue)) ||
            (RHSValue.Base && RHSValue.Offset.isZero() &&
             isOnePastTheEndOfCompleteObject(Info.Ctx, LHSValue)))
          return Error(E);
        // We can't tell whether an object is at the same address as another
        // zero sized object.
        if ((RHSValue.Base && isZeroSized(LHSValue)) ||
            (LHSValue.Base && isZeroSized(RHSValue)))
          return Error(E);
        return Success(CmpResult::Unequal, E);
      }
  
      const CharUnits &LHSOffset = LHSValue.getLValueOffset();
      const CharUnits &RHSOffset = RHSValue.getLValueOffset();
  
      SubobjectDesignator &LHSDesignator = LHSValue.getLValueDesignator();
      SubobjectDesignator &RHSDesignator = RHSValue.getLValueDesignator();
  
      // C++11 [expr.rel]p3:
      //   Pointers to void (after pointer conversions) can be compared, with a
      //   result defined as follows: If both pointers represent the same
      //   address or are both the null pointer value, the result is true if the
      //   operator is <= or >= and false otherwise; otherwise the result is
      //   unspecified.
      // We interpret this as applying to pointers to *cv* void.
      if (LHSTy->isVoidPointerType() && LHSOffset != RHSOffset && IsRelational)
        Info.CCEDiag(E, diag::note_constexpr_void_comparison);
  
      // C++11 [expr.rel]p2:
      // - If two pointers point to non-static data members of the same object,
      //   or to subobjects or array elements fo such members, recursively, the
      //   pointer to the later declared member compares greater provided the
      //   two members have the same access control and provided their class is
      //   not a union.
      //   [...]
      // - Otherwise pointer comparisons are unspecified.
      if (!LHSDesignator.Invalid && !RHSDesignator.Invalid && IsRelational) {
        bool WasArrayIndex;
        unsigned Mismatch = FindDesignatorMismatch(
            getType(LHSValue.Base), LHSDesignator, RHSDesignator, WasArrayIndex);
        // At the point where the designators diverge, the comparison has a
        // specified value if:
        //  - we are comparing array indices
        //  - we are comparing fields of a union, or fields with the same access
        // Otherwise, the result is unspecified and thus the comparison is not a
        // constant expression.
        if (!WasArrayIndex && Mismatch < LHSDesignator.Entries.size() &&
            Mismatch < RHSDesignator.Entries.size()) {
          const FieldDecl *LF = getAsField(LHSDesignator.Entries[Mismatch]);
          const FieldDecl *RF = getAsField(RHSDesignator.Entries[Mismatch]);
          if (!LF && !RF)
            Info.CCEDiag(E, diag::note_constexpr_pointer_comparison_base_classes);
          else if (!LF)
            Info.CCEDiag(E, diag::note_constexpr_pointer_comparison_base_field)
                << getAsBaseClass(LHSDesignator.Entries[Mismatch])
                << RF->getParent() << RF;
          else if (!RF)
            Info.CCEDiag(E, diag::note_constexpr_pointer_comparison_base_field)
                << getAsBaseClass(RHSDesignator.Entries[Mismatch])
                << LF->getParent() << LF;
          else if (!LF->getParent()->isUnion() &&
                   LF->getAccess() != RF->getAccess())
            Info.CCEDiag(E,
                         diag::note_constexpr_pointer_comparison_differing_access)
                << LF << LF->getAccess() << RF << RF->getAccess()
                << LF->getParent();
        }
      }
  
      // The comparison here must be unsigned, and performed with the same
      // width as the pointer.
      unsigned PtrSize = Info.Ctx.getTypeSize(LHSTy);
      uint64_t CompareLHS = LHSOffset.getQuantity();
      uint64_t CompareRHS = RHSOffset.getQuantity();
      assert(PtrSize <= 64 && "Unexpected pointer width");
      uint64_t Mask = ~0ULL >> (64 - PtrSize);
      CompareLHS &= Mask;
      CompareRHS &= Mask;
  
      // If there is a base and this is a relational operator, we can only
      // compare pointers within the object in question; otherwise, the result
      // depends on where the object is located in memory.
      if (!LHSValue.Base.isNull() && IsRelational) {
        QualType BaseTy = getType(LHSValue.Base);
        if (BaseTy->isIncompleteType())
          return Error(E);
        CharUnits Size = Info.Ctx.getTypeSizeInChars(BaseTy);
        uint64_t OffsetLimit = Size.getQuantity();
        if (CompareLHS > OffsetLimit || CompareRHS > OffsetLimit)
          return Error(E);
      }
  
      if (CompareLHS < CompareRHS)
        return Success(CmpResult::Less, E);
      if (CompareLHS > CompareRHS)
        return Success(CmpResult::Greater, E);
      return Success(CmpResult::Equal, E);
    }
  
    if (LHSTy->isMemberPointerType()) {
      assert(IsEquality && "unexpected member pointer operation");
      assert(RHSTy->isMemberPointerType() && "invalid comparison");
  
      MemberPtr LHSValue, RHSValue;
  
      bool LHSOK = EvaluateMemberPointer(E->getLHS(), LHSValue, Info);
      if (!LHSOK && !Info.noteFailure())
        return false;
  
      if (!EvaluateMemberPointer(E->getRHS(), RHSValue, Info) || !LHSOK)
        return false;
  
      // C++11 [expr.eq]p2:
      //   If both operands are null, they compare equal. Otherwise if only one is
      //   null, they compare unequal.
      if (!LHSValue.getDecl() || !RHSValue.getDecl()) {
        bool Equal = !LHSValue.getDecl() && !RHSValue.getDecl();
        return Success(Equal ? CmpResult::Equal : CmpResult::Unequal, E);
      }
  
      //   Otherwise if either is a pointer to a virtual member function, the
      //   result is unspecified.
      if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(LHSValue.getDecl()))
        if (MD->isVirtual())
          Info.CCEDiag(E, diag::note_constexpr_compare_virtual_mem_ptr) << MD;
      if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(RHSValue.getDecl()))
        if (MD->isVirtual())
          Info.CCEDiag(E, diag::note_constexpr_compare_virtual_mem_ptr) << MD;
  
      //   Otherwise they compare equal if and only if they would refer to the
      //   same member of the same most derived object or the same subobject if
      //   they were dereferenced with a hypothetical object of the associated
      //   class type.
      bool Equal = LHSValue == RHSValue;
      return Success(Equal ? CmpResult::Equal : CmpResult::Unequal, E);
    }
  
    if (LHSTy->isNullPtrType()) {
      assert(E->isComparisonOp() && "unexpected nullptr operation");
      assert(RHSTy->isNullPtrType() && "missing pointer conversion");
      // C++11 [expr.rel]p4, [expr.eq]p3: If two operands of type std::nullptr_t
      // are compared, the result is true of the operator is <=, >= or ==, and
      // false otherwise.
      return Success(CmpResult::Equal, E);
    }
  
    return DoAfter();
  }
  
  bool RecordExprEvaluator::VisitBinCmp(const BinaryOperator *E) {
    if (!CheckLiteralType(Info, E))
      return false;
  
    auto OnSuccess = [&](CmpResult CR, const BinaryOperator *E) {
      ComparisonCategoryResult CCR;
      switch (CR) {
      case CmpResult::Unequal:
        llvm_unreachable("should never produce Unequal for three-way comparison");
      case CmpResult::Less:
        CCR = ComparisonCategoryResult::Less;
        break;
      case CmpResult::Equal:
        CCR = ComparisonCategoryResult::Equal;
        break;
      case CmpResult::Greater:
        CCR = ComparisonCategoryResult::Greater;
        break;
      case CmpResult::Unordered:
        CCR = ComparisonCategoryResult::Unordered;
        break;
      }
      // Evaluation succeeded. Lookup the information for the comparison category
      // type and fetch the VarDecl for the result.
      const ComparisonCategoryInfo &CmpInfo =
          Info.Ctx.CompCategories.getInfoForType(E->getType());
      const VarDecl *VD = CmpInfo.getValueInfo(CmpInfo.makeWeakResult(CCR))->VD;
      // Check and evaluate the result as a constant expression.
      LValue LV;
      LV.set(VD);
      if (!handleLValueToRValueConversion(Info, E, E->getType(), LV, Result))
        return false;
      return CheckConstantExpression(Info, E->getExprLoc(), E->getType(), Result,
                                     ConstantExprKind::Normal);
    };
    return EvaluateComparisonBinaryOperator(Info, E, OnSuccess, [&]() {
      return ExprEvaluatorBaseTy::VisitBinCmp(E);
    });
  }
  
  bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
    // We don't call noteFailure immediately because the assignment happens after
    // we evaluate LHS and RHS.
    if (!Info.keepEvaluatingAfterFailure() && E->isAssignmentOp())
      return Error(E);
  
    DelayedNoteFailureRAII MaybeNoteFailureLater(Info, E->isAssignmentOp());
    if (DataRecursiveIntBinOpEvaluator::shouldEnqueue(E))
      return DataRecursiveIntBinOpEvaluator(*this, Result).Traverse(E);
  
    assert((!E->getLHS()->getType()->isIntegralOrEnumerationType() ||
            !E->getRHS()->getType()->isIntegralOrEnumerationType()) &&
           "DataRecursiveIntBinOpEvaluator should have handled integral types");
  
    if (E->isComparisonOp()) {
      // Evaluate builtin binary comparisons by evaluating them as three-way
      // comparisons and then translating the result.
      auto OnSuccess = [&](CmpResult CR, const BinaryOperator *E) {
        assert((CR != CmpResult::Unequal || E->isEqualityOp()) &&
               "should only produce Unequal for equality comparisons");
        bool IsEqual   = CR == CmpResult::Equal,
             IsLess    = CR == CmpResult::Less,
             IsGreater = CR == CmpResult::Greater;
        auto Op = E->getOpcode();
        switch (Op) {
        default:
          llvm_unreachable("unsupported binary operator");
        case BO_EQ:
        case BO_NE:
          return Success(IsEqual == (Op == BO_EQ), E);
        case BO_LT:
          return Success(IsLess, E);
        case BO_GT:
          return Success(IsGreater, E);
        case BO_LE:
          return Success(IsEqual || IsLess, E);
        case BO_GE:
          return Success(IsEqual || IsGreater, E);
        }
      };
      return EvaluateComparisonBinaryOperator(Info, E, OnSuccess, [&]() {
        return ExprEvaluatorBaseTy::VisitBinaryOperator(E);
      });
    }
  
    QualType LHSTy = E->getLHS()->getType();
    QualType RHSTy = E->getRHS()->getType();
  
    if (LHSTy->isPointerType() && RHSTy->isPointerType() &&
        E->getOpcode() == BO_Sub) {
      LValue LHSValue, RHSValue;
  
      bool LHSOK = EvaluatePointer(E->getLHS(), LHSValue, Info);
      if (!LHSOK && !Info.noteFailure())
        return false;
  
      if (!EvaluatePointer(E->getRHS(), RHSValue, Info) || !LHSOK)
        return false;
  
      // Reject differing bases from the normal codepath; we special-case
      // comparisons to null.
      if (!HasSameBase(LHSValue, RHSValue)) {
        // Handle &&A - &&B.
        if (!LHSValue.Offset.isZero() || !RHSValue.Offset.isZero())
          return Error(E);
        const Expr *LHSExpr = LHSValue.Base.dyn_cast<const Expr *>();
        const Expr *RHSExpr = RHSValue.Base.dyn_cast<const Expr *>();
        if (!LHSExpr || !RHSExpr)
          return Error(E);
        const AddrLabelExpr *LHSAddrExpr = dyn_cast<AddrLabelExpr>(LHSExpr);
        const AddrLabelExpr *RHSAddrExpr = dyn_cast<AddrLabelExpr>(RHSExpr);
        if (!LHSAddrExpr || !RHSAddrExpr)
          return Error(E);
        // Make sure both labels come from the same function.
        if (LHSAddrExpr->getLabel()->getDeclContext() !=
            RHSAddrExpr->getLabel()->getDeclContext())
          return Error(E);
        return Success(APValue(LHSAddrExpr, RHSAddrExpr), E);
      }
      const CharUnits &LHSOffset = LHSValue.getLValueOffset();
      const CharUnits &RHSOffset = RHSValue.getLValueOffset();
  
      SubobjectDesignator &LHSDesignator = LHSValue.getLValueDesignator();
      SubobjectDesignator &RHSDesignator = RHSValue.getLValueDesignator();
  
      // C++11 [expr.add]p6:
      //   Unless both pointers point to elements of the same array object, or
      //   one past the last element of the array object, the behavior is
      //   undefined.
      if (!LHSDesignator.Invalid && !RHSDesignator.Invalid &&
          !AreElementsOfSameArray(getType(LHSValue.Base), LHSDesignator,
                                  RHSDesignator))
        Info.CCEDiag(E, diag::note_constexpr_pointer_subtraction_not_same_array);
  
      QualType Type = E->getLHS()->getType();
      QualType ElementType = Type->castAs<PointerType>()->getPointeeType();
  
      CharUnits ElementSize;
      if (!HandleSizeof(Info, E->getExprLoc(), ElementType, ElementSize))
        return false;
  
      // As an extension, a type may have zero size (empty struct or union in
      // C, array of zero length). Pointer subtraction in such cases has
      // undefined behavior, so is not constant.
      if (ElementSize.isZero()) {
        Info.FFDiag(E, diag::note_constexpr_pointer_subtraction_zero_size)
            << ElementType;
        return false;
      }
  
      // FIXME: LLVM and GCC both compute LHSOffset - RHSOffset at runtime,
      // and produce incorrect results when it overflows. Such behavior
      // appears to be non-conforming, but is common, so perhaps we should
      // assume the standard intended for such cases to be undefined behavior
      // and check for them.
  
      // Compute (LHSOffset - RHSOffset) / Size carefully, checking for
      // overflow in the final conversion to ptrdiff_t.
      APSInt LHS(llvm::APInt(65, (int64_t)LHSOffset.getQuantity(), true), false);
      APSInt RHS(llvm::APInt(65, (int64_t)RHSOffset.getQuantity(), true), false);
      APSInt ElemSize(llvm::APInt(65, (int64_t)ElementSize.getQuantity(), true),
                      false);
      APSInt TrueResult = (LHS - RHS) / ElemSize;
      APSInt Result = TrueResult.trunc(Info.Ctx.getIntWidth(E->getType()));
  
      if (Result.extend(65) != TrueResult &&
          !HandleOverflow(Info, E, TrueResult, E->getType()))
        return false;
      return Success(Result, E);
    }
  
    return ExprEvaluatorBaseTy::VisitBinaryOperator(E);
  }
  
  /// VisitUnaryExprOrTypeTraitExpr - Evaluate a sizeof, alignof or vec_step with
  /// a result as the expression's type.
  bool IntExprEvaluator::VisitUnaryExprOrTypeTraitExpr(
                                      const UnaryExprOrTypeTraitExpr *E) {
    switch(E->getKind()) {
    case UETT_PreferredAlignOf:
    case UETT_AlignOf: {
      if (E->isArgumentType())
        return Success(GetAlignOfType(Info, E->getArgumentType(), E->getKind()),
                       E);
      else
        return Success(GetAlignOfExpr(Info, E->getArgumentExpr(), E->getKind()),
                       E);
    }
  
    case UETT_PtrAuthTypeDiscriminator: {
      if (E->getArgumentType()->isDependentType())
        return false;
      return Success(
          Info.Ctx.getPointerAuthTypeDiscriminator(E->getArgumentType()), E);
    }
    case UETT_VecStep: {
      QualType Ty = E->getTypeOfArgument();
  
      if (Ty->isVectorType()) {
        unsigned n = Ty->castAs<VectorType>()->getNumElements();
  
        // The vec_step built-in functions that take a 3-component
        // vector return 4. (OpenCL 1.1 spec 6.11.12)
        if (n == 3)
          n = 4;
  
        return Success(n, E);
      } else
        return Success(1, E);
    }
  
    case UETT_SizeOf: {
      QualType SrcTy = E->getTypeOfArgument();
      // C++ [expr.sizeof]p2: "When applied to a reference or a reference type,
      //   the result is the size of the referenced type."
      if (const ReferenceType *Ref = SrcTy->getAs<ReferenceType>())
        SrcTy = Ref->getPointeeType();
  
      CharUnits Sizeof;
      if (!HandleSizeof(Info, E->getExprLoc(), SrcTy, Sizeof))
        return false;
      return Success(Sizeof, E);
    }
    case UETT_OpenMPRequiredSimdAlign:
      assert(E->isArgumentType());
      return Success(
          Info.Ctx.toCharUnitsFromBits(
                      Info.Ctx.getOpenMPDefaultSimdAlign(E->getArgumentType()))
              .getQuantity(),
          E);
    }
  
    llvm_unreachable("unknown expr/type trait");
  }
  
  bool IntExprEvaluator::VisitOffsetOfExpr(const OffsetOfExpr *OOE) {
    CharUnits Result;
    unsigned n = OOE->getNumComponents();
    if (n == 0)
      return Error(OOE);
    QualType CurrentType = OOE->getTypeSourceInfo()->getType();
    for (unsigned i = 0; i != n; ++i) {
      OffsetOfNode ON = OOE->getComponent(i);
      switch (ON.getKind()) {
      case OffsetOfNode::Array: {
        const Expr *Idx = OOE->getIndexExpr(ON.getArrayExprIndex());
        APSInt IdxResult;
        if (!EvaluateInteger(Idx, IdxResult, Info))
          return false;
        const ArrayType *AT = Info.Ctx.getAsArrayType(CurrentType);
        if (!AT)
          return Error(OOE);
        CurrentType = AT->getElementType();
        CharUnits ElementSize = Info.Ctx.getTypeSizeInChars(CurrentType);
        Result += IdxResult.getSExtValue() * ElementSize;
        break;
      }
  
      case OffsetOfNode::Field: {
        FieldDecl *MemberDecl = ON.getField();
        const RecordType *RT = CurrentType->getAs<RecordType>();
        if (!RT)
          return Error(OOE);
        RecordDecl *RD = RT->getDecl();
        if (RD->isInvalidDecl()) return false;
        const ASTRecordLayout &RL = Info.Ctx.getASTRecordLayout(RD);
        unsigned i = MemberDecl->getFieldIndex();
        assert(i < RL.getFieldCount() && "offsetof field in wrong type");
        Result += Info.Ctx.toCharUnitsFromBits(RL.getFieldOffset(i));
        CurrentType = MemberDecl->getType().getNonReferenceType();
        break;
      }
  
      case OffsetOfNode::Identifier:
        llvm_unreachable("dependent __builtin_offsetof");
  
      case OffsetOfNode::Base: {
        CXXBaseSpecifier *BaseSpec = ON.getBase();
        if (BaseSpec->isVirtual())
          return Error(OOE);
  
        // Find the layout of the class whose base we are looking into.
        const RecordType *RT = CurrentType->getAs<RecordType>();
        if (!RT)
          return Error(OOE);
        RecordDecl *RD = RT->getDecl();
        if (RD->isInvalidDecl()) return false;
        const ASTRecordLayout &RL = Info.Ctx.getASTRecordLayout(RD);
  
        // Find the base class itself.
        CurrentType = BaseSpec->getType();
        const RecordType *BaseRT = CurrentType->getAs<RecordType>();
        if (!BaseRT)
          return Error(OOE);
  
        // Add the offset to the base.
        Result += RL.getBaseClassOffset(cast<CXXRecordDecl>(BaseRT->getDecl()));
        break;
      }
      }
    }
    return Success(Result, OOE);
  }
  
  bool IntExprEvaluator::VisitUnaryOperator(const UnaryOperator *E) {
    switch (E->getOpcode()) {
    default:
      // Address, indirect, pre/post inc/dec, etc are not valid constant exprs.
      // See C99 6.6p3.
      return Error(E);
    case UO_Extension:
      // FIXME: Should extension allow i-c-e extension expressions in its scope?
      // If so, we could clear the diagnostic ID.
      return Visit(E->getSubExpr());
    case UO_Plus:
      // The result is just the value.
      return Visit(E->getSubExpr());
    case UO_Minus: {
      if (!Visit(E->getSubExpr()))
        return false;
      if (!Result.isInt()) return Error(E);
      const APSInt &Value = Result.getInt();
      if (Value.isSigned() && Value.isMinSignedValue() && E->canOverflow() &&
          !HandleOverflow(Info, E, -Value.extend(Value.getBitWidth() + 1),
                          E->getType()))
        return false;
      return Success(-Value, E);
    }
    case UO_Not: {
      if (!Visit(E->getSubExpr()))
        return false;
      if (!Result.isInt()) return Error(E);
      return Success(~Result.getInt(), E);
    }
    case UO_LNot: {
      bool bres;
      if (!EvaluateAsBooleanCondition(E->getSubExpr(), bres, Info))
        return false;
      return Success(!bres, E);
    }
    }
  }
  
  /// HandleCast - This is used to evaluate implicit or explicit casts where the
  /// result type is integer.
  bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
    const Expr *SubExpr = E->getSubExpr();
    QualType DestType = E->getType();
    QualType SrcType = SubExpr->getType();
  
    switch (E->getCastKind()) {
    case CK_BaseToDerived:
    case CK_DerivedToBase:
    case CK_UncheckedDerivedToBase:
    case CK_Dynamic:
    case CK_ToUnion:
    case CK_ArrayToPointerDecay:
    case CK_FunctionToPointerDecay:
    case CK_NullToPointer:
    case CK_NullToMemberPointer:
    case CK_BaseToDerivedMemberPointer:
    case CK_DerivedToBaseMemberPointer:
    case CK_ReinterpretMemberPointer:
    case CK_ConstructorConversion:
    case CK_IntegralToPointer:
    case CK_ToVoid:
    case CK_VectorSplat:
    case CK_IntegralToFloating:
    case CK_FloatingCast:
    case CK_CPointerToObjCPointerCast:
    case CK_BlockPointerToObjCPointerCast:
    case CK_AnyPointerToBlockPointerCast:
    case CK_ObjCObjectLValueCast:
    case CK_FloatingRealToComplex:
    case CK_FloatingComplexToReal:
    case CK_FloatingComplexCast:
    case CK_FloatingComplexToIntegralComplex:
    case CK_IntegralRealToComplex:
    case CK_IntegralComplexCast:
    case CK_IntegralComplexToFloatingComplex:
    case CK_BuiltinFnToFnPtr:
    case CK_ZeroToOCLOpaqueType:
    case CK_NonAtomicToAtomic:
    case CK_AddressSpaceConversion:
    case CK_IntToOCLSampler:
    case CK_FloatingToFixedPoint:
    case CK_FixedPointToFloating:
    case CK_FixedPointCast:
    case CK_IntegralToFixedPoint:
      llvm_unreachable("invalid cast kind for integral value");
  
    case CK_BitCast:
    case CK_Dependent:
    case CK_LValueBitCast:
    case CK_ARCProduceObject:
    case CK_ARCConsumeObject:
    case CK_ARCReclaimReturnedObject:
    case CK_ARCExtendBlockObject:
    case CK_CopyAndAutoreleaseBlockObject:
      return Error(E);
  
    case CK_UserDefinedConversion:
    case CK_LValueToRValue:
    case CK_AtomicToNonAtomic:
    case CK_NoOp:
    case CK_LValueToRValueBitCast:
      return ExprEvaluatorBaseTy::VisitCastExpr(E);
  
    case CK_MemberPointerToBoolean:
    case CK_PointerToBoolean:
    case CK_IntegralToBoolean:
    case CK_FloatingToBoolean:
    case CK_BooleanToSignedIntegral:
    case CK_FloatingComplexToBoolean:
    case CK_IntegralComplexToBoolean: {
      bool BoolResult;
      if (!EvaluateAsBooleanCondition(SubExpr, BoolResult, Info))
        return false;
      uint64_t IntResult = BoolResult;
      if (BoolResult && E->getCastKind() == CK_BooleanToSignedIntegral)
        IntResult = (uint64_t)-1;
      return Success(IntResult, E);
    }
  
    case CK_FixedPointToIntegral: {
      APFixedPoint Src(Info.Ctx.getFixedPointSemantics(SrcType));
      if (!EvaluateFixedPoint(SubExpr, Src, Info))
        return false;
      bool Overflowed;
      llvm::APSInt Result = Src.convertToInt(
          Info.Ctx.getIntWidth(DestType),
          DestType->isSignedIntegerOrEnumerationType(), &Overflowed);
      if (Overflowed && !HandleOverflow(Info, E, Result, DestType))
        return false;
      return Success(Result, E);
    }
  
    case CK_FixedPointToBoolean: {
      // Unsigned padding does not affect this.
      APValue Val;
      if (!Evaluate(Val, Info, SubExpr))
        return false;
      return Success(Val.getFixedPoint().getBoolValue(), E);
    }
  
    case CK_IntegralCast: {
      if (!Visit(SubExpr))
        return false;
  
      if (!Result.isInt()) {
        // Allow casts of address-of-label differences if they are no-ops
        // or narrowing.  (The narrowing case isn't actually guaranteed to
        // be constant-evaluatable except in some narrow cases which are hard
        // to detect here.  We let it through on the assumption the user knows
        // what they are doing.)
        if (Result.isAddrLabelDiff())
          return Info.Ctx.getTypeSize(DestType) <= Info.Ctx.getTypeSize(SrcType);
        // Only allow casts of lvalues if they are lossless.
        return Info.Ctx.getTypeSize(DestType) == Info.Ctx.getTypeSize(SrcType);
      }
  
      return Success(HandleIntToIntCast(Info, E, DestType, SrcType,
                                        Result.getInt()), E);
    }
  
    case CK_PointerToIntegral: {
      CCEDiag(E, diag::note_constexpr_invalid_cast) << 2;
  
      LValue LV;
      if (!EvaluatePointer(SubExpr, LV, Info))
        return false;
  
      if (LV.getLValueBase()) {
        // Only allow based lvalue casts if they are lossless.
        // FIXME: Allow a larger integer size than the pointer size, and allow
        // narrowing back down to pointer width in subsequent integral casts.
        // FIXME: Check integer type's active bits, not its type size.
        if (Info.Ctx.getTypeSize(DestType) != Info.Ctx.getTypeSize(SrcType))
          return Error(E);
  
        LV.Designator.setInvalid();
        LV.moveInto(Result);
        return true;
      }
  
      APSInt AsInt;
      APValue V;
      LV.moveInto(V);
      if (!V.toIntegralConstant(AsInt, SrcType, Info.Ctx))
        llvm_unreachable("Can't cast this!");
  
      return Success(HandleIntToIntCast(Info, E, DestType, SrcType, AsInt), E);
    }
  
    case CK_IntegralComplexToReal: {
      ComplexValue C;
      if (!EvaluateComplex(SubExpr, C, Info))
        return false;
      return Success(C.getComplexIntReal(), E);
    }
  
    case CK_FloatingToIntegral: {
      APFloat F(0.0);
      if (!EvaluateFloat(SubExpr, F, Info))
        return false;
  
      APSInt Value;
      if (!HandleFloatToIntCast(Info, E, SrcType, F, DestType, Value))
        return false;
      return Success(Value, E);
    }
    }
  
    llvm_unreachable("unknown cast resulting in integral value");
  }
  
  bool IntExprEvaluator::VisitUnaryReal(const UnaryOperator *E) {
    if (E->getSubExpr()->getType()->isAnyComplexType()) {
      ComplexValue LV;
      if (!EvaluateComplex(E->getSubExpr(), LV, Info))
        return false;
      if (!LV.isComplexInt())
        return Error(E);
      return Success(LV.getComplexIntReal(), E);
    }
  
    return Visit(E->getSubExpr());
  }
  
  bool IntExprEvaluator::VisitUnaryImag(const UnaryOperator *E) {
    if (E->getSubExpr()->getType()->isComplexIntegerType()) {
      ComplexValue LV;
      if (!EvaluateComplex(E->getSubExpr(), LV, Info))
        return false;
      if (!LV.isComplexInt())
        return Error(E);
      return Success(LV.getComplexIntImag(), E);
    }
  
    VisitIgnoredValue(E->getSubExpr());
    return Success(0, E);
  }
  
  bool IntExprEvaluator::VisitSizeOfPackExpr(const SizeOfPackExpr *E) {
    return Success(E->getPackLength(), E);
  }
  
  bool IntExprEvaluator::VisitCXXNoexceptExpr(const CXXNoexceptExpr *E) {
    return Success(E->getValue(), E);
  }
  
  bool IntExprEvaluator::VisitConceptSpecializationExpr(
         const ConceptSpecializationExpr *E) {
    return Success(E->isSatisfied(), E);
  }
  
  bool IntExprEvaluator::VisitRequiresExpr(const RequiresExpr *E) {
    return Success(E->isSatisfied(), E);
  }
  
  bool FixedPointExprEvaluator::VisitUnaryOperator(const UnaryOperator *E) {
    switch (E->getOpcode()) {
      default:
        // Invalid unary operators
        return Error(E);
      case UO_Plus:
        // The result is just the value.
        return Visit(E->getSubExpr());
      case UO_Minus: {
        if (!Visit(E->getSubExpr())) return false;
        if (!Result.isFixedPoint())
          return Error(E);
        bool Overflowed;
        APFixedPoint Negated = Result.getFixedPoint().negate(&Overflowed);
        if (Overflowed && !HandleOverflow(Info, E, Negated, E->getType()))
          return false;
        return Success(Negated, E);
      }
      case UO_LNot: {
        bool bres;
        if (!EvaluateAsBooleanCondition(E->getSubExpr(), bres, Info))
          return false;
        return Success(!bres, E);
      }
    }
  }
  
  bool FixedPointExprEvaluator::VisitCastExpr(const CastExpr *E) {
    const Expr *SubExpr = E->getSubExpr();
    QualType DestType = E->getType();
    assert(DestType->isFixedPointType() &&
           "Expected destination type to be a fixed point type");
    auto DestFXSema = Info.Ctx.getFixedPointSemantics(DestType);
  
    switch (E->getCastKind()) {
    case CK_FixedPointCast: {
      APFixedPoint Src(Info.Ctx.getFixedPointSemantics(SubExpr->getType()));
      if (!EvaluateFixedPoint(SubExpr, Src, Info))
        return false;
      bool Overflowed;
      APFixedPoint Result = Src.convert(DestFXSema, &Overflowed);
      if (Overflowed) {
        if (Info.checkingForUndefinedBehavior())
          Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
                                           diag::warn_fixedpoint_constant_overflow)
            << Result.toString() << E->getType();
        if (!HandleOverflow(Info, E, Result, E->getType()))
          return false;
      }
      return Success(Result, E);
    }
    case CK_IntegralToFixedPoint: {
      APSInt Src;
      if (!EvaluateInteger(SubExpr, Src, Info))
        return false;
  
      bool Overflowed;
      APFixedPoint IntResult = APFixedPoint::getFromIntValue(
          Src, Info.Ctx.getFixedPointSemantics(DestType), &Overflowed);
  
      if (Overflowed) {
        if (Info.checkingForUndefinedBehavior())
          Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
                                           diag::warn_fixedpoint_constant_overflow)
            << IntResult.toString() << E->getType();
        if (!HandleOverflow(Info, E, IntResult, E->getType()))
          return false;
      }
  
      return Success(IntResult, E);
    }
    case CK_FloatingToFixedPoint: {
      APFloat Src(0.0);
      if (!EvaluateFloat(SubExpr, Src, Info))
        return false;
  
      bool Overflowed;
      APFixedPoint Result = APFixedPoint::getFromFloatValue(
          Src, Info.Ctx.getFixedPointSemantics(DestType), &Overflowed);
  
      if (Overflowed) {
        if (Info.checkingForUndefinedBehavior())
          Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
                                           diag::warn_fixedpoint_constant_overflow)
            << Result.toString() << E->getType();
        if (!HandleOverflow(Info, E, Result, E->getType()))
          return false;
      }
  
      return Success(Result, E);
    }
    case CK_NoOp:
    case CK_LValueToRValue:
      return ExprEvaluatorBaseTy::VisitCastExpr(E);
    default:
      return Error(E);
    }
  }
  
  bool FixedPointExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
    if (E->isPtrMemOp() || E->isAssignmentOp() || E->getOpcode() == BO_Comma)
      return ExprEvaluatorBaseTy::VisitBinaryOperator(E);
  
    const Expr *LHS = E->getLHS();
    const Expr *RHS = E->getRHS();
    FixedPointSemantics ResultFXSema =
        Info.Ctx.getFixedPointSemantics(E->getType());
  
    APFixedPoint LHSFX(Info.Ctx.getFixedPointSemantics(LHS->getType()));
    if (!EvaluateFixedPointOrInteger(LHS, LHSFX, Info))
      return false;
    APFixedPoint RHSFX(Info.Ctx.getFixedPointSemantics(RHS->getType()));
    if (!EvaluateFixedPointOrInteger(RHS, RHSFX, Info))
      return false;
  
    bool OpOverflow = false, ConversionOverflow = false;
    APFixedPoint Result(LHSFX.getSemantics());
    switch (E->getOpcode()) {
    case BO_Add: {
      Result = LHSFX.add(RHSFX, &OpOverflow)
                    .convert(ResultFXSema, &ConversionOverflow);
      break;
    }
    case BO_Sub: {
      Result = LHSFX.sub(RHSFX, &OpOverflow)
                    .convert(ResultFXSema, &ConversionOverflow);
      break;
    }
    case BO_Mul: {
      Result = LHSFX.mul(RHSFX, &OpOverflow)
                    .convert(ResultFXSema, &ConversionOverflow);
      break;
    }
    case BO_Div: {
      if (RHSFX.getValue() == 0) {
        Info.FFDiag(E, diag::note_expr_divide_by_zero);
        return false;
      }
      Result = LHSFX.div(RHSFX, &OpOverflow)
                    .convert(ResultFXSema, &ConversionOverflow);
      break;
    }
    case BO_Shl:
    case BO_Shr: {
      FixedPointSemantics LHSSema = LHSFX.getSemantics();
      llvm::APSInt RHSVal = RHSFX.getValue();
  
      unsigned ShiftBW =
          LHSSema.getWidth() - (unsigned)LHSSema.hasUnsignedPadding();
      unsigned Amt = RHSVal.getLimitedValue(ShiftBW - 1);
      // Embedded-C 4.1.6.2.2:
      //   The right operand must be nonnegative and less than the total number
      //   of (nonpadding) bits of the fixed-point operand ...
      if (RHSVal.isNegative())
        Info.CCEDiag(E, diag::note_constexpr_negative_shift) << RHSVal;
      else if (Amt != RHSVal)
        Info.CCEDiag(E, diag::note_constexpr_large_shift)
            << RHSVal << E->getType() << ShiftBW;
  
      if (E->getOpcode() == BO_Shl)
        Result = LHSFX.shl(Amt, &OpOverflow);
      else
        Result = LHSFX.shr(Amt, &OpOverflow);
      break;
    }
    default:
      return false;
    }
    if (OpOverflow || ConversionOverflow) {
      if (Info.checkingForUndefinedBehavior())
        Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
                                         diag::warn_fixedpoint_constant_overflow)
          << Result.toString() << E->getType();
      if (!HandleOverflow(Info, E, Result, E->getType()))
        return false;
    }
    return Success(Result, E);
  }
  
  //===----------------------------------------------------------------------===//
  // Float Evaluation
  //===----------------------------------------------------------------------===//
  
  namespace {
  class FloatExprEvaluator
    : public ExprEvaluatorBase<FloatExprEvaluator> {
    APFloat &Result;
  public:
    FloatExprEvaluator(EvalInfo &info, APFloat &result)
      : ExprEvaluatorBaseTy(info), Result(result) {}
  
    bool Success(const APValue &V, const Expr *e) {
      Result = V.getFloat();
      return true;
    }
  
    bool ZeroInitialization(const Expr *E) {
      Result = APFloat::getZero(Info.Ctx.getFloatTypeSemantics(E->getType()));
      return true;
    }
  
    bool VisitCallExpr(const CallExpr *E);
  
    bool VisitUnaryOperator(const UnaryOperator *E);
    bool VisitBinaryOperator(const BinaryOperator *E);
    bool VisitFloatingLiteral(const FloatingLiteral *E);
    bool VisitCastExpr(const CastExpr *E);
  
    bool VisitUnaryReal(const UnaryOperator *E);
    bool VisitUnaryImag(const UnaryOperator *E);
  
    // FIXME: Missing: array subscript of vector, member of vector
  };
  } // end anonymous namespace
  
  static bool EvaluateFloat(const Expr* E, APFloat& Result, EvalInfo &Info) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && E->getType()->isRealFloatingType());
    return FloatExprEvaluator(Info, Result).Visit(E);
  }
  
  static bool TryEvaluateBuiltinNaN(const ASTContext &Context,
                                    QualType ResultTy,
                                    const Expr *Arg,
                                    bool SNaN,
                                    llvm::APFloat &Result) {
    const StringLiteral *S = dyn_cast<StringLiteral>(Arg->IgnoreParenCasts());
    if (!S) return false;
  
    const llvm::fltSemantics &Sem = Context.getFloatTypeSemantics(ResultTy);
  
    llvm::APInt fill;
  
    // Treat empty strings as if they were zero.
    if (S->getString().empty())
      fill = llvm::APInt(32, 0);
    else if (S->getString().getAsInteger(0, fill))
      return false;
  
    if (Context.getTargetInfo().isNan2008()) {
      if (SNaN)
        Result = llvm::APFloat::getSNaN(Sem, false, &fill);
      else
        Result = llvm::APFloat::getQNaN(Sem, false, &fill);
    } else {
      // Prior to IEEE 754-2008, architectures were allowed to choose whether
      // the first bit of their significand was set for qNaN or sNaN. MIPS chose
      // a different encoding to what became a standard in 2008, and for pre-
      // 2008 revisions, MIPS interpreted sNaN-2008 as qNan and qNaN-2008 as
      // sNaN. This is now known as "legacy NaN" encoding.
      if (SNaN)
        Result = llvm::APFloat::getQNaN(Sem, false, &fill);
      else
        Result = llvm::APFloat::getSNaN(Sem, false, &fill);
    }
  
    return true;
  }
  
  bool FloatExprEvaluator::VisitCallExpr(const CallExpr *E) {
    switch (E->getBuiltinCallee()) {
    default:
      return ExprEvaluatorBaseTy::VisitCallExpr(E);
  
    case Builtin::BI__builtin_huge_val:
    case Builtin::BI__builtin_huge_valf:
    case Builtin::BI__builtin_huge_vall:
    case Builtin::BI__builtin_huge_valf128:
    case Builtin::BI__builtin_inf:
    case Builtin::BI__builtin_inff:
    case Builtin::BI__builtin_infl:
    case Builtin::BI__builtin_inff128: {
      const llvm::fltSemantics &Sem =
        Info.Ctx.getFloatTypeSemantics(E->getType());
      Result = llvm::APFloat::getInf(Sem);
      return true;
    }
  
    case Builtin::BI__builtin_nans:
    case Builtin::BI__builtin_nansf:
    case Builtin::BI__builtin_nansl:
    case Builtin::BI__builtin_nansf128:
      if (!TryEvaluateBuiltinNaN(Info.Ctx, E->getType(), E->getArg(0),
                                 true, Result))
        return Error(E);
      return true;
  
    case Builtin::BI__builtin_nan:
    case Builtin::BI__builtin_nanf:
    case Builtin::BI__builtin_nanl:
    case Builtin::BI__builtin_nanf128:
      // If this is __builtin_nan() turn this into a nan, otherwise we
      // can't constant fold it.
      if (!TryEvaluateBuiltinNaN(Info.Ctx, E->getType(), E->getArg(0),
                                 false, Result))
        return Error(E);
      return true;
  
    case Builtin::BI__builtin_fabs:
    case Builtin::BI__builtin_fabsf:
    case Builtin::BI__builtin_fabsl:
    case Builtin::BI__builtin_fabsf128:
      // The C standard says "fabs raises no floating-point exceptions,
      // even if x is a signaling NaN. The returned value is independent of
      // the current rounding direction mode."  Therefore constant folding can
      // proceed without regard to the floating point settings.
      // Reference, WG14 N2478 F.10.4.3
      if (!EvaluateFloat(E->getArg(0), Result, Info))
        return false;
  
      if (Result.isNegative())
        Result.changeSign();
      return true;
  
    // FIXME: Builtin::BI__builtin_powi
    // FIXME: Builtin::BI__builtin_powif
    // FIXME: Builtin::BI__builtin_powil
  
    case Builtin::BI__builtin_copysign:
    case Builtin::BI__builtin_copysignf:
    case Builtin::BI__builtin_copysignl:
    case Builtin::BI__builtin_copysignf128: {
      APFloat RHS(0.);
      if (!EvaluateFloat(E->getArg(0), Result, Info) ||
          !EvaluateFloat(E->getArg(1), RHS, Info))
        return false;
      Result.copySign(RHS);
      return true;
    }
    }
  }
  
  bool FloatExprEvaluator::VisitUnaryReal(const UnaryOperator *E) {
    if (E->getSubExpr()->getType()->isAnyComplexType()) {
      ComplexValue CV;
      if (!EvaluateComplex(E->getSubExpr(), CV, Info))
        return false;
      Result = CV.FloatReal;
      return true;
    }
  
    return Visit(E->getSubExpr());
  }
  
  bool FloatExprEvaluator::VisitUnaryImag(const UnaryOperator *E) {
    if (E->getSubExpr()->getType()->isAnyComplexType()) {
      ComplexValue CV;
      if (!EvaluateComplex(E->getSubExpr(), CV, Info))
        return false;
      Result = CV.FloatImag;
      return true;
    }
  
    VisitIgnoredValue(E->getSubExpr());
    const llvm::fltSemantics &Sem = Info.Ctx.getFloatTypeSemantics(E->getType());
    Result = llvm::APFloat::getZero(Sem);
    return true;
  }
  
  bool FloatExprEvaluator::VisitUnaryOperator(const UnaryOperator *E) {
    switch (E->getOpcode()) {
    default: return Error(E);
    case UO_Plus:
      return EvaluateFloat(E->getSubExpr(), Result, Info);
    case UO_Minus:
      // In C standard, WG14 N2478 F.3 p4
      // "the unary - raises no floating point exceptions,
      // even if the operand is signalling."
      if (!EvaluateFloat(E->getSubExpr(), Result, Info))
        return false;
      Result.changeSign();
      return true;
    }
  }
  
  bool FloatExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
    if (E->isPtrMemOp() || E->isAssignmentOp() || E->getOpcode() == BO_Comma)
      return ExprEvaluatorBaseTy::VisitBinaryOperator(E);
  
    APFloat RHS(0.0);
    bool LHSOK = EvaluateFloat(E->getLHS(), Result, Info);
    if (!LHSOK && !Info.noteFailure())
      return false;
    return EvaluateFloat(E->getRHS(), RHS, Info) && LHSOK &&
           handleFloatFloatBinOp(Info, E, Result, E->getOpcode(), RHS);
  }
  
  bool FloatExprEvaluator::VisitFloatingLiteral(const FloatingLiteral *E) {
    Result = E->getValue();
    return true;
  }
  
  bool FloatExprEvaluator::VisitCastExpr(const CastExpr *E) {
    const Expr* SubExpr = E->getSubExpr();
  
    switch (E->getCastKind()) {
    default:
      return ExprEvaluatorBaseTy::VisitCastExpr(E);
  
    case CK_IntegralToFloating: {
      APSInt IntResult;
      const FPOptions FPO = E->getFPFeaturesInEffect(
                                    Info.Ctx.getLangOpts());
      return EvaluateInteger(SubExpr, IntResult, Info) &&
             HandleIntToFloatCast(Info, E, FPO, SubExpr->getType(),
                                  IntResult, E->getType(), Result);
    }
  
    case CK_FixedPointToFloating: {
      APFixedPoint FixResult(Info.Ctx.getFixedPointSemantics(SubExpr->getType()));
      if (!EvaluateFixedPoint(SubExpr, FixResult, Info))
        return false;
      Result =
          FixResult.convertToFloat(Info.Ctx.getFloatTypeSemantics(E->getType()));
      return true;
    }
  
    case CK_FloatingCast: {
      if (!Visit(SubExpr))
        return false;
      return HandleFloatToFloatCast(Info, E, SubExpr->getType(), E->getType(),
                                    Result);
    }
  
    case CK_FloatingComplexToReal: {
      ComplexValue V;
      if (!EvaluateComplex(SubExpr, V, Info))
        return false;
      Result = V.getComplexFloatReal();
      return true;
    }
    }
  }
  
  //===----------------------------------------------------------------------===//
  // Complex Evaluation (for float and integer)
  //===----------------------------------------------------------------------===//
  
  namespace {
  class ComplexExprEvaluator
    : public ExprEvaluatorBase<ComplexExprEvaluator> {
    ComplexValue &Result;
  
  public:
    ComplexExprEvaluator(EvalInfo &info, ComplexValue &Result)
      : ExprEvaluatorBaseTy(info), Result(Result) {}
  
    bool Success(const APValue &V, const Expr *e) {
      Result.setFrom(V);
      return true;
    }
  
    bool ZeroInitialization(const Expr *E);
  
    //===--------------------------------------------------------------------===//
    //                            Visitor Methods
    //===--------------------------------------------------------------------===//
  
    bool VisitImaginaryLiteral(const ImaginaryLiteral *E);
    bool VisitCastExpr(const CastExpr *E);
    bool VisitBinaryOperator(const BinaryOperator *E);
    bool VisitUnaryOperator(const UnaryOperator *E);
    bool VisitInitListExpr(const InitListExpr *E);
    bool VisitCallExpr(const CallExpr *E);
  };
  } // end anonymous namespace
  
  static bool EvaluateComplex(const Expr *E, ComplexValue &Result,
                              EvalInfo &Info) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && E->getType()->isAnyComplexType());
    return ComplexExprEvaluator(Info, Result).Visit(E);
  }
  
  bool ComplexExprEvaluator::ZeroInitialization(const Expr *E) {
    QualType ElemTy = E->getType()->castAs<ComplexType>()->getElementType();
    if (ElemTy->isRealFloatingType()) {
      Result.makeComplexFloat();
      APFloat Zero = APFloat::getZero(Info.Ctx.getFloatTypeSemantics(ElemTy));
      Result.FloatReal = Zero;
      Result.FloatImag = Zero;
    } else {
      Result.makeComplexInt();
      APSInt Zero = Info.Ctx.MakeIntValue(0, ElemTy);
      Result.IntReal = Zero;
      Result.IntImag = Zero;
    }
    return true;
  }
  
  bool ComplexExprEvaluator::VisitImaginaryLiteral(const ImaginaryLiteral *E) {
    const Expr* SubExpr = E->getSubExpr();
  
    if (SubExpr->getType()->isRealFloatingType()) {
      Result.makeComplexFloat();
      APFloat &Imag = Result.FloatImag;
      if (!EvaluateFloat(SubExpr, Imag, Info))
        return false;
  
      Result.FloatReal = APFloat(Imag.getSemantics());
      return true;
    } else {
      assert(SubExpr->getType()->isIntegerType() &&
             "Unexpected imaginary literal.");
  
      Result.makeComplexInt();
      APSInt &Imag = Result.IntImag;
      if (!EvaluateInteger(SubExpr, Imag, Info))
        return false;
  
      Result.IntReal = APSInt(Imag.getBitWidth(), !Imag.isSigned());
      return true;
    }
  }
  
  bool ComplexExprEvaluator::VisitCastExpr(const CastExpr *E) {
  
    switch (E->getCastKind()) {
    case CK_BitCast:
    case CK_BaseToDerived:
    case CK_DerivedToBase:
    case CK_UncheckedDerivedToBase:
    case CK_Dynamic:
    case CK_ToUnion:
    case CK_ArrayToPointerDecay:
    case CK_FunctionToPointerDecay:
    case CK_NullToPointer:
    case CK_NullToMemberPointer:
    case CK_BaseToDerivedMemberPointer:
    case CK_DerivedToBaseMemberPointer:
    case CK_MemberPointerToBoolean:
    case CK_ReinterpretMemberPointer:
    case CK_ConstructorConversion:
    case CK_IntegralToPointer:
    case CK_PointerToIntegral:
    case CK_PointerToBoolean:
    case CK_ToVoid:
    case CK_VectorSplat:
    case CK_IntegralCast:
    case CK_BooleanToSignedIntegral:
    case CK_IntegralToBoolean:
    case CK_IntegralToFloating:
    case CK_FloatingToIntegral:
    case CK_FloatingToBoolean:
    case CK_FloatingCast:
    case CK_CPointerToObjCPointerCast:
    case CK_BlockPointerToObjCPointerCast:
    case CK_AnyPointerToBlockPointerCast:
    case CK_ObjCObjectLValueCast:
    case CK_FloatingComplexToReal:
    case CK_FloatingComplexToBoolean:
    case CK_IntegralComplexToReal:
    case CK_IntegralComplexToBoolean:
    case CK_ARCProduceObject:
    case CK_ARCConsumeObject:
    case CK_ARCReclaimReturnedObject:
    case CK_ARCExtendBlockObject:
    case CK_CopyAndAutoreleaseBlockObject:
    case CK_BuiltinFnToFnPtr:
    case CK_ZeroToOCLOpaqueType:
    case CK_NonAtomicToAtomic:
    case CK_AddressSpaceConversion:
    case CK_IntToOCLSampler:
    case CK_FloatingToFixedPoint:
    case CK_FixedPointToFloating:
    case CK_FixedPointCast:
    case CK_FixedPointToBoolean:
    case CK_FixedPointToIntegral:
    case CK_IntegralToFixedPoint:
      llvm_unreachable("invalid cast kind for complex value");
  
    case CK_LValueToRValue:
    case CK_AtomicToNonAtomic:
    case CK_NoOp:
    case CK_LValueToRValueBitCast:
      return ExprEvaluatorBaseTy::VisitCastExpr(E);
  
    case CK_Dependent:
    case CK_LValueBitCast:
    case CK_UserDefinedConversion:
      return Error(E);
  
    case CK_FloatingRealToComplex: {
      APFloat &Real = Result.FloatReal;
      if (!EvaluateFloat(E->getSubExpr(), Real, Info))
        return false;
  
      Result.makeComplexFloat();
      Result.FloatImag = APFloat(Real.getSemantics());
      return true;
    }
  
    case CK_FloatingComplexCast: {
      if (!Visit(E->getSubExpr()))
        return false;
  
      QualType To = E->getType()->castAs<ComplexType>()->getElementType();
      QualType From
        = E->getSubExpr()->getType()->castAs<ComplexType>()->getElementType();
  
      return HandleFloatToFloatCast(Info, E, From, To, Result.FloatReal) &&
             HandleFloatToFloatCast(Info, E, From, To, Result.FloatImag);
    }
  
    case CK_FloatingComplexToIntegralComplex: {
      if (!Visit(E->getSubExpr()))
        return false;
  
      QualType To = E->getType()->castAs<ComplexType>()->getElementType();
      QualType From
        = E->getSubExpr()->getType()->castAs<ComplexType>()->getElementType();
      Result.makeComplexInt();
      return HandleFloatToIntCast(Info, E, From, Result.FloatReal,
                                  To, Result.IntReal) &&
             HandleFloatToIntCast(Info, E, From, Result.FloatImag,
                                  To, Result.IntImag);
    }
  
    case CK_IntegralRealToComplex: {
      APSInt &Real = Result.IntReal;
      if (!EvaluateInteger(E->getSubExpr(), Real, Info))
        return false;
  
      Result.makeComplexInt();
      Result.IntImag = APSInt(Real.getBitWidth(), !Real.isSigned());
      return true;
    }
  
    case CK_IntegralComplexCast: {
      if (!Visit(E->getSubExpr()))
        return false;
  
      QualType To = E->getType()->castAs<ComplexType>()->getElementType();
      QualType From
        = E->getSubExpr()->getType()->castAs<ComplexType>()->getElementType();
  
      Result.IntReal = HandleIntToIntCast(Info, E, To, From, Result.IntReal);
      Result.IntImag = HandleIntToIntCast(Info, E, To, From, Result.IntImag);
      return true;
    }
  
    case CK_IntegralComplexToFloatingComplex: {
      if (!Visit(E->getSubExpr()))
        return false;
  
      const FPOptions FPO = E->getFPFeaturesInEffect(
                                    Info.Ctx.getLangOpts());
      QualType To = E->getType()->castAs<ComplexType>()->getElementType();
      QualType From
        = E->getSubExpr()->getType()->castAs<ComplexType>()->getElementType();
      Result.makeComplexFloat();
      return HandleIntToFloatCast(Info, E, FPO, From, Result.IntReal,
                                  To, Result.FloatReal) &&
             HandleIntToFloatCast(Info, E, FPO, From, Result.IntImag,
                                  To, Result.FloatImag);
    }
    }
  
    llvm_unreachable("unknown cast resulting in complex value");
  }
  
  bool ComplexExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
    if (E->isPtrMemOp() || E->isAssignmentOp() || E->getOpcode() == BO_Comma)
      return ExprEvaluatorBaseTy::VisitBinaryOperator(E);
  
    // Track whether the LHS or RHS is real at the type system level. When this is
    // the case we can simplify our evaluation strategy.
    bool LHSReal = false, RHSReal = false;
  
    bool LHSOK;
    if (E->getLHS()->getType()->isRealFloatingType()) {
      LHSReal = true;
      APFloat &Real = Result.FloatReal;
      LHSOK = EvaluateFloat(E->getLHS(), Real, Info);
      if (LHSOK) {
        Result.makeComplexFloat();
        Result.FloatImag = APFloat(Real.getSemantics());
      }
    } else {
      LHSOK = Visit(E->getLHS());
    }
    if (!LHSOK && !Info.noteFailure())
      return false;
  
    ComplexValue RHS;
    if (E->getRHS()->getType()->isRealFloatingType()) {
      RHSReal = true;
      APFloat &Real = RHS.FloatReal;
      if (!EvaluateFloat(E->getRHS(), Real, Info) || !LHSOK)
        return false;
      RHS.makeComplexFloat();
      RHS.FloatImag = APFloat(Real.getSemantics());
    } else if (!EvaluateComplex(E->getRHS(), RHS, Info) || !LHSOK)
      return false;
  
    assert(!(LHSReal && RHSReal) &&
           "Cannot have both operands of a complex operation be real.");
    switch (E->getOpcode()) {
    default: return Error(E);
    case BO_Add:
      if (Result.isComplexFloat()) {
        Result.getComplexFloatReal().add(RHS.getComplexFloatReal(),
                                         APFloat::rmNearestTiesToEven);
        if (LHSReal)
          Result.getComplexFloatImag() = RHS.getComplexFloatImag();
        else if (!RHSReal)
          Result.getComplexFloatImag().add(RHS.getComplexFloatImag(),
                                           APFloat::rmNearestTiesToEven);
      } else {
        Result.getComplexIntReal() += RHS.getComplexIntReal();
        Result.getComplexIntImag() += RHS.getComplexIntImag();
      }
      break;
    case BO_Sub:
      if (Result.isComplexFloat()) {
        Result.getComplexFloatReal().subtract(RHS.getComplexFloatReal(),
                                              APFloat::rmNearestTiesToEven);
        if (LHSReal) {
          Result.getComplexFloatImag() = RHS.getComplexFloatImag();
          Result.getComplexFloatImag().changeSign();
        } else if (!RHSReal) {
          Result.getComplexFloatImag().subtract(RHS.getComplexFloatImag(),
                                                APFloat::rmNearestTiesToEven);
        }
      } else {
        Result.getComplexIntReal() -= RHS.getComplexIntReal();
        Result.getComplexIntImag() -= RHS.getComplexIntImag();
      }
      break;
    case BO_Mul:
      if (Result.isComplexFloat()) {
        // This is an implementation of complex multiplication according to the
        // constraints laid out in C11 Annex G. The implementation uses the
        // following naming scheme:
        //   (a + ib) * (c + id)
        ComplexValue LHS = Result;
        APFloat &A = LHS.getComplexFloatReal();
        APFloat &B = LHS.getComplexFloatImag();
        APFloat &C = RHS.getComplexFloatReal();
        APFloat &D = RHS.getComplexFloatImag();
        APFloat &ResR = Result.getComplexFloatReal();
        APFloat &ResI = Result.getComplexFloatImag();
        if (LHSReal) {
          assert(!RHSReal && "Cannot have two real operands for a complex op!");
          ResR = A * C;
          ResI = A * D;
        } else if (RHSReal) {
          ResR = C * A;
          ResI = C * B;
        } else {
          // In the fully general case, we need to handle NaNs and infinities
          // robustly.
          APFloat AC = A * C;
          APFloat BD = B * D;
          APFloat AD = A * D;
          APFloat BC = B * C;
          ResR = AC - BD;
          ResI = AD + BC;
          if (ResR.isNaN() && ResI.isNaN()) {
            bool Recalc = false;
            if (A.isInfinity() || B.isInfinity()) {
              A = APFloat::copySign(
                  APFloat(A.getSemantics(), A.isInfinity() ? 1 : 0), A);
              B = APFloat::copySign(
                  APFloat(B.getSemantics(), B.isInfinity() ? 1 : 0), B);
              if (C.isNaN())
                C = APFloat::copySign(APFloat(C.getSemantics()), C);
              if (D.isNaN())
                D = APFloat::copySign(APFloat(D.getSemantics()), D);
              Recalc = true;
            }
            if (C.isInfinity() || D.isInfinity()) {
              C = APFloat::copySign(
                  APFloat(C.getSemantics(), C.isInfinity() ? 1 : 0), C);
              D = APFloat::copySign(
                  APFloat(D.getSemantics(), D.isInfinity() ? 1 : 0), D);
              if (A.isNaN())
                A = APFloat::copySign(APFloat(A.getSemantics()), A);
              if (B.isNaN())
                B = APFloat::copySign(APFloat(B.getSemantics()), B);
              Recalc = true;
            }
            if (!Recalc && (AC.isInfinity() || BD.isInfinity() ||
                            AD.isInfinity() || BC.isInfinity())) {
              if (A.isNaN())
                A = APFloat::copySign(APFloat(A.getSemantics()), A);
              if (B.isNaN())
                B = APFloat::copySign(APFloat(B.getSemantics()), B);
              if (C.isNaN())
                C = APFloat::copySign(APFloat(C.getSemantics()), C);
              if (D.isNaN())
                D = APFloat::copySign(APFloat(D.getSemantics()), D);
              Recalc = true;
            }
            if (Recalc) {
              ResR = APFloat::getInf(A.getSemantics()) * (A * C - B * D);
              ResI = APFloat::getInf(A.getSemantics()) * (A * D + B * C);
            }
          }
        }
      } else {
        ComplexValue LHS = Result;
        Result.getComplexIntReal() =
          (LHS.getComplexIntReal() * RHS.getComplexIntReal() -
           LHS.getComplexIntImag() * RHS.getComplexIntImag());
        Result.getComplexIntImag() =
          (LHS.getComplexIntReal() * RHS.getComplexIntImag() +
           LHS.getComplexIntImag() * RHS.getComplexIntReal());
      }
      break;
    case BO_Div:
      if (Result.isComplexFloat()) {
        // This is an implementation of complex division according to the
        // constraints laid out in C11 Annex G. The implementation uses the
        // following naming scheme:
        //   (a + ib) / (c + id)
        ComplexValue LHS = Result;
        APFloat &A = LHS.getComplexFloatReal();
        APFloat &B = LHS.getComplexFloatImag();
        APFloat &C = RHS.getComplexFloatReal();
        APFloat &D = RHS.getComplexFloatImag();
        APFloat &ResR = Result.getComplexFloatReal();
        APFloat &ResI = Result.getComplexFloatImag();
        if (RHSReal) {
          ResR = A / C;
          ResI = B / C;
        } else {
          if (LHSReal) {
            // No real optimizations we can do here, stub out with zero.
            B = APFloat::getZero(A.getSemantics());
          }
          int DenomLogB = 0;
          APFloat MaxCD = maxnum(abs(C), abs(D));
          if (MaxCD.isFinite()) {
            DenomLogB = ilogb(MaxCD);
            C = scalbn(C, -DenomLogB, APFloat::rmNearestTiesToEven);
            D = scalbn(D, -DenomLogB, APFloat::rmNearestTiesToEven);
          }
          APFloat Denom = C * C + D * D;
          ResR = scalbn((A * C + B * D) / Denom, -DenomLogB,
                        APFloat::rmNearestTiesToEven);
          ResI = scalbn((B * C - A * D) / Denom, -DenomLogB,
                        APFloat::rmNearestTiesToEven);
          if (ResR.isNaN() && ResI.isNaN()) {
            if (Denom.isPosZero() && (!A.isNaN() || !B.isNaN())) {
              ResR = APFloat::getInf(ResR.getSemantics(), C.isNegative()) * A;
              ResI = APFloat::getInf(ResR.getSemantics(), C.isNegative()) * B;
            } else if ((A.isInfinity() || B.isInfinity()) && C.isFinite() &&
                       D.isFinite()) {
              A = APFloat::copySign(
                  APFloat(A.getSemantics(), A.isInfinity() ? 1 : 0), A);
              B = APFloat::copySign(
                  APFloat(B.getSemantics(), B.isInfinity() ? 1 : 0), B);
              ResR = APFloat::getInf(ResR.getSemantics()) * (A * C + B * D);
              ResI = APFloat::getInf(ResI.getSemantics()) * (B * C - A * D);
            } else if (MaxCD.isInfinity() && A.isFinite() && B.isFinite()) {
              C = APFloat::copySign(
                  APFloat(C.getSemantics(), C.isInfinity() ? 1 : 0), C);
              D = APFloat::copySign(
                  APFloat(D.getSemantics(), D.isInfinity() ? 1 : 0), D);
              ResR = APFloat::getZero(ResR.getSemantics()) * (A * C + B * D);
              ResI = APFloat::getZero(ResI.getSemantics()) * (B * C - A * D);
            }
          }
        }
      } else {
        if (RHS.getComplexIntReal() == 0 && RHS.getComplexIntImag() == 0)
          return Error(E, diag::note_expr_divide_by_zero);
  
        ComplexValue LHS = Result;
        APSInt Den = RHS.getComplexIntReal() * RHS.getComplexIntReal() +
          RHS.getComplexIntImag() * RHS.getComplexIntImag();
        Result.getComplexIntReal() =
          (LHS.getComplexIntReal() * RHS.getComplexIntReal() +
           LHS.getComplexIntImag() * RHS.getComplexIntImag()) / Den;
        Result.getComplexIntImag() =
          (LHS.getComplexIntImag() * RHS.getComplexIntReal() -
           LHS.getComplexIntReal() * RHS.getComplexIntImag()) / Den;
      }
      break;
    }
  
    return true;
  }
  
  bool ComplexExprEvaluator::VisitUnaryOperator(const UnaryOperator *E) {
    // Get the operand value into 'Result'.
    if (!Visit(E->getSubExpr()))
      return false;
  
    switch (E->getOpcode()) {
    default:
      return Error(E);
    case UO_Extension:
      return true;
    case UO_Plus:
      // The result is always just the subexpr.
      return true;
    case UO_Minus:
      if (Result.isComplexFloat()) {
        Result.getComplexFloatReal().changeSign();
        Result.getComplexFloatImag().changeSign();
      }
      else {
        Result.getComplexIntReal() = -Result.getComplexIntReal();
        Result.getComplexIntImag() = -Result.getComplexIntImag();
      }
      return true;
    case UO_Not:
      if (Result.isComplexFloat())
        Result.getComplexFloatImag().changeSign();
      else
        Result.getComplexIntImag() = -Result.getComplexIntImag();
      return true;
    }
  }
  
  bool ComplexExprEvaluator::VisitInitListExpr(const InitListExpr *E) {
    if (E->getNumInits() == 2) {
      if (E->getType()->isComplexType()) {
        Result.makeComplexFloat();
        if (!EvaluateFloat(E->getInit(0), Result.FloatReal, Info))
          return false;
        if (!EvaluateFloat(E->getInit(1), Result.FloatImag, Info))
          return false;
      } else {
        Result.makeComplexInt();
        if (!EvaluateInteger(E->getInit(0), Result.IntReal, Info))
          return false;
        if (!EvaluateInteger(E->getInit(1), Result.IntImag, Info))
          return false;
      }
      return true;
    }
    return ExprEvaluatorBaseTy::VisitInitListExpr(E);
  }
  
  bool ComplexExprEvaluator::VisitCallExpr(const CallExpr *E) {
    switch (E->getBuiltinCallee()) {
    case Builtin::BI__builtin_complex:
      Result.makeComplexFloat();
      if (!EvaluateFloat(E->getArg(0), Result.FloatReal, Info))
        return false;
      if (!EvaluateFloat(E->getArg(1), Result.FloatImag, Info))
        return false;
      return true;
  
    default:
      break;
    }
  
    return ExprEvaluatorBaseTy::VisitCallExpr(E);
  }
  
  //===----------------------------------------------------------------------===//
  // Atomic expression evaluation, essentially just handling the NonAtomicToAtomic
  // implicit conversion.
  //===----------------------------------------------------------------------===//
  
  namespace {
  class AtomicExprEvaluator :
      public ExprEvaluatorBase<AtomicExprEvaluator> {
    const LValue *This;
    APValue &Result;
  public:
    AtomicExprEvaluator(EvalInfo &Info, const LValue *This, APValue &Result)
        : ExprEvaluatorBaseTy(Info), This(This), Result(Result) {}
  
    bool Success(const APValue &V, const Expr *E) {
      Result = V;
      return true;
    }
  
    bool ZeroInitialization(const Expr *E) {
      ImplicitValueInitExpr VIE(
          E->getType()->castAs<AtomicType>()->getValueType());
      // For atomic-qualified class (and array) types in C++, initialize the
      // _Atomic-wrapped subobject directly, in-place.
      return This ? EvaluateInPlace(Result, Info, *This, &VIE)
                  : Evaluate(Result, Info, &VIE);
    }
  
    bool VisitCastExpr(const CastExpr *E) {
      switch (E->getCastKind()) {
      default:
        return ExprEvaluatorBaseTy::VisitCastExpr(E);
      case CK_NonAtomicToAtomic:
        return This ? EvaluateInPlace(Result, Info, *This, E->getSubExpr())
                    : Evaluate(Result, Info, E->getSubExpr());
      }
    }
  };
  } // end anonymous namespace
  
  static bool EvaluateAtomic(const Expr *E, const LValue *This, APValue &Result,
                             EvalInfo &Info) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && E->getType()->isAtomicType());
    return AtomicExprEvaluator(Info, This, Result).Visit(E);
  }
  
  //===----------------------------------------------------------------------===//
  // Void expression evaluation, primarily for a cast to void on the LHS of a
  // comma operator
  //===----------------------------------------------------------------------===//
  
  namespace {
  class VoidExprEvaluator
    : public ExprEvaluatorBase<VoidExprEvaluator> {
  public:
    VoidExprEvaluator(EvalInfo &Info) : ExprEvaluatorBaseTy(Info) {}
  
    bool Success(const APValue &V, const Expr *e) { return true; }
  
    bool ZeroInitialization(const Expr *E) { return true; }
  
    bool VisitCastExpr(const CastExpr *E) {
      switch (E->getCastKind()) {
      default:
        return ExprEvaluatorBaseTy::VisitCastExpr(E);
      case CK_ToVoid:
        VisitIgnoredValue(E->getSubExpr());
        return true;
      }
    }
  
    bool VisitCallExpr(const CallExpr *E) {
      switch (E->getBuiltinCallee()) {
      case Builtin::BI__assume:
      case Builtin::BI__builtin_assume:
        // The argument is not evaluated!
        return true;
  
      case Builtin::BI__builtin_operator_delete:
        return HandleOperatorDeleteCall(Info, E);
  
      default:
        break;
      }
  
      return ExprEvaluatorBaseTy::VisitCallExpr(E);
    }
  
    bool VisitCXXDeleteExpr(const CXXDeleteExpr *E);
  };
  } // end anonymous namespace
  
  bool VoidExprEvaluator::VisitCXXDeleteExpr(const CXXDeleteExpr *E) {
    // We cannot speculatively evaluate a delete expression.
    if (Info.SpeculativeEvaluationDepth)
      return false;
  
    FunctionDecl *OperatorDelete = E->getOperatorDelete();
    if (!OperatorDelete->isReplaceableGlobalAllocationFunction()) {
      Info.FFDiag(E, diag::note_constexpr_new_non_replaceable)
          << isa<CXXMethodDecl>(OperatorDelete) << OperatorDelete;
      return false;
    }
  
    const Expr *Arg = E->getArgument();
  
    LValue Pointer;
    if (!EvaluatePointer(Arg, Pointer, Info))
      return false;
    if (Pointer.Designator.Invalid)
      return false;
  
    // Deleting a null pointer has no effect.
    if (Pointer.isNullPointer()) {
      // This is the only case where we need to produce an extension warning:
      // the only other way we can succeed is if we find a dynamic allocation,
      // and we will have warned when we allocated it in that case.
      if (!Info.getLangOpts().CPlusPlus20)
        Info.CCEDiag(E, diag::note_constexpr_new);
      return true;
    }
  
    Optional<DynAlloc *> Alloc = CheckDeleteKind(
        Info, E, Pointer, E->isArrayForm() ? DynAlloc::ArrayNew : DynAlloc::New);
    if (!Alloc)
      return false;
    QualType AllocType = Pointer.Base.getDynamicAllocType();
  
    // For the non-array case, the designator must be empty if the static type
    // does not have a virtual destructor.
    if (!E->isArrayForm() && Pointer.Designator.Entries.size() != 0 &&
        !hasVirtualDestructor(Arg->getType()->getPointeeType())) {
      Info.FFDiag(E, diag::note_constexpr_delete_base_nonvirt_dtor)
          << Arg->getType()->getPointeeType() << AllocType;
      return false;
    }
  
    // For a class type with a virtual destructor, the selected operator delete
    // is the one looked up when building the destructor.
    if (!E->isArrayForm() && !E->isGlobalDelete()) {
      const FunctionDecl *VirtualDelete = getVirtualOperatorDelete(AllocType);
      if (VirtualDelete &&
          !VirtualDelete->isReplaceableGlobalAllocationFunction()) {
        Info.FFDiag(E, diag::note_constexpr_new_non_replaceable)
            << isa<CXXMethodDecl>(VirtualDelete) << VirtualDelete;
        return false;
      }
    }
  
    if (!HandleDestruction(Info, E->getExprLoc(), Pointer.getLValueBase(),
                           (*Alloc)->Value, AllocType))
      return false;
  
    if (!Info.HeapAllocs.erase(Pointer.Base.dyn_cast<DynamicAllocLValue>())) {
      // The element was already erased. This means the destructor call also
      // deleted the object.
      // FIXME: This probably results in undefined behavior before we get this
      // far, and should be diagnosed elsewhere first.
      Info.FFDiag(E, diag::note_constexpr_double_delete);
      return false;
    }
  
    return true;
  }
  
  static bool EvaluateVoid(const Expr *E, EvalInfo &Info) {
    assert(!E->isValueDependent());
    assert(E->isRValue() && E->getType()->isVoidType());
    return VoidExprEvaluator(Info).Visit(E);
  }
  
  //===----------------------------------------------------------------------===//
  // Top level Expr::EvaluateAsRValue method.
  //===----------------------------------------------------------------------===//
  
  static bool Evaluate(APValue &Result, EvalInfo &Info, const Expr *E) {
    assert(!E->isValueDependent());
    // In C, function designators are not lvalues, but we evaluate them as if they
    // are.
    QualType T = E->getType();
    if (E->isGLValue() || T->isFunctionType()) {
      LValue LV;
      if (!EvaluateLValue(E, LV, Info))
        return false;
      LV.moveInto(Result);
    } else if (T->isVectorType()) {
      if (!EvaluateVector(E, Result, Info))
        return false;
    } else if (T->isIntegralOrEnumerationType()) {
      if (!IntExprEvaluator(Info, Result).Visit(E))
        return false;
    } else if (T->hasPointerRepresentation()) {
      LValue LV;
      if (!EvaluatePointer(E, LV, Info))
        return false;
      LV.moveInto(Result);
    } else if (T->isRealFloatingType()) {
      llvm::APFloat F(0.0);
      if (!EvaluateFloat(E, F, Info))
        return false;
      Result = APValue(F);
    } else if (T->isAnyComplexType()) {
      ComplexValue C;
      if (!EvaluateComplex(E, C, Info))
        return false;
      C.moveInto(Result);
    } else if (T->isFixedPointType()) {
      if (!FixedPointExprEvaluator(Info, Result).Visit(E)) return false;
    } else if (T->isMemberPointerType()) {
      MemberPtr P;
      if (!EvaluateMemberPointer(E, P, Info))
        return false;
      P.moveInto(Result);
      return true;
    } else if (T->isArrayType()) {
      LValue LV;
      APValue &Value =
          Info.CurrentCall->createTemporary(E, T, ScopeKind::FullExpression, LV);
      if (!EvaluateArray(E, LV, Value, Info))
        return false;
      Result = Value;
    } else if (T->isRecordType()) {
      LValue LV;
      APValue &Value =
          Info.CurrentCall->createTemporary(E, T, ScopeKind::FullExpression, LV);
      if (!EvaluateRecord(E, LV, Value, Info))
        return false;
      Result = Value;
    } else if (T->isVoidType()) {
      if (!Info.getLangOpts().CPlusPlus11)
        Info.CCEDiag(E, diag::note_constexpr_nonliteral)
          << E->getType();
      if (!EvaluateVoid(E, Info))
        return false;
    } else if (T->isAtomicType()) {
      QualType Unqual = T.getAtomicUnqualifiedType();
      if (Unqual->isArrayType() || Unqual->isRecordType()) {
        LValue LV;
        APValue &Value = Info.CurrentCall->createTemporary(
            E, Unqual, ScopeKind::FullExpression, LV);
        if (!EvaluateAtomic(E, &LV, Value, Info))
          return false;
      } else {
        if (!EvaluateAtomic(E, nullptr, Result, Info))
          return false;
      }
    } else if (Info.getLangOpts().CPlusPlus11) {
      Info.FFDiag(E, diag::note_constexpr_nonliteral) << E->getType();
      return false;
    } else {
      Info.FFDiag(E, diag::note_invalid_subexpr_in_const_expr);
      return false;
    }
  
    return true;
  }
  
  /// EvaluateInPlace - Evaluate an expression in-place in an APValue. In some
  /// cases, the in-place evaluation is essential, since later initializers for
  /// an object can indirectly refer to subobjects which were initialized earlier.
  static bool EvaluateInPlace(APValue &Result, EvalInfo &Info, const LValue &This,
                              const Expr *E, bool AllowNonLiteralTypes) {
    assert(!E->isValueDependent());
  
    if (!AllowNonLiteralTypes && !CheckLiteralType(Info, E, &This))
      return false;
  
    if (E->isRValue()) {
      // Evaluate arrays and record types in-place, so that later initializers can
      // refer to earlier-initialized members of the object.
      QualType T = E->getType();
      if (T->isArrayType())
        return EvaluateArray(E, This, Result, Info);
      else if (T->isRecordType())
        return EvaluateRecord(E, This, Result, Info);
      else if (T->isAtomicType()) {
        QualType Unqual = T.getAtomicUnqualifiedType();
        if (Unqual->isArrayType() || Unqual->isRecordType())
          return EvaluateAtomic(E, &This, Result, Info);
      }
    }
  
    // For any other type, in-place evaluation is unimportant.
    return Evaluate(Result, Info, E);
  }
  
  /// EvaluateAsRValue - Try to evaluate this expression, performing an implicit
  /// lvalue-to-rvalue cast if it is an lvalue.
  static bool EvaluateAsRValue(EvalInfo &Info, const Expr *E, APValue &Result) {
    assert(!E->isValueDependent());
    if (Info.EnableNewConstInterp) {
      if (!Info.Ctx.getInterpContext().evaluateAsRValue(Info, E, Result))
        return false;
    } else {
      if (E->getType().isNull())
        return false;
  
      if (!CheckLiteralType(Info, E))
        return false;
  
      if (!::Evaluate(Result, Info, E))
        return false;
  
      if (E->isGLValue()) {
        LValue LV;
        LV.setFrom(Info.Ctx, Result);
        if (!handleLValueToRValueConversion(Info, E, E->getType(), LV, Result))
          return false;
      }
    }
  
    // Check this core constant expression is a constant expression.
    return CheckConstantExpression(Info, E->getExprLoc(), E->getType(), Result,
                                   ConstantExprKind::Normal) &&
           CheckMemoryLeaks(Info);
  }
  
  static bool FastEvaluateAsRValue(const Expr *Exp, Expr::EvalResult &Result,
                                   const ASTContext &Ctx, bool &IsConst) {
    // Fast-path evaluations of integer literals, since we sometimes see files
    // containing vast quantities of these.
    if (const IntegerLiteral *L = dyn_cast<IntegerLiteral>(Exp)) {
      Result.Val = APValue(APSInt(L->getValue(),
                                  L->getType()->isUnsignedIntegerType()));
      IsConst = true;
      return true;
    }
  
    // This case should be rare, but we need to check it before we check on
    // the type below.
    if (Exp->getType().isNull()) {
      IsConst = false;
      return true;
    }
  
    // FIXME: Evaluating values of large array and record types can cause
    // performance problems. Only do so in C++11 for now.
    if (Exp->isRValue() && (Exp->getType()->isArrayType() ||
                            Exp->getType()->isRecordType()) &&
        !Ctx.getLangOpts().CPlusPlus11) {
      IsConst = false;
      return true;
    }
    return false;
  }
  
  static bool hasUnacceptableSideEffect(Expr::EvalStatus &Result,
                                        Expr::SideEffectsKind SEK) {
    return (SEK < Expr::SE_AllowSideEffects && Result.HasSideEffects) ||
           (SEK < Expr::SE_AllowUndefinedBehavior && Result.HasUndefinedBehavior);
  }
  
  static bool EvaluateAsRValue(const Expr *E, Expr::EvalResult &Result,
                               const ASTContext &Ctx, EvalInfo &Info) {
    assert(!E->isValueDependent());
    bool IsConst;
    if (FastEvaluateAsRValue(E, Result, Ctx, IsConst))
      return IsConst;
  
    return EvaluateAsRValue(Info, E, Result.Val);
  }
  
  static bool EvaluateAsInt(const Expr *E, Expr::EvalResult &ExprResult,
                            const ASTContext &Ctx,
                            Expr::SideEffectsKind AllowSideEffects,
                            EvalInfo &Info) {
    assert(!E->isValueDependent());
    if (!E->getType()->isIntegralOrEnumerationType())
      return false;
  
    if (!::EvaluateAsRValue(E, ExprResult, Ctx, Info) ||
        !ExprResult.Val.isInt() ||
        hasUnacceptableSideEffect(ExprResult, AllowSideEffects))
      return false;
  
    return true;
  }
  
  static bool EvaluateAsFixedPoint(const Expr *E, Expr::EvalResult &ExprResult,
                                   const ASTContext &Ctx,
                                   Expr::SideEffectsKind AllowSideEffects,
                                   EvalInfo &Info) {
    assert(!E->isValueDependent());
    if (!E->getType()->isFixedPointType())
      return false;
  
    if (!::EvaluateAsRValue(E, ExprResult, Ctx, Info))
      return false;
  
    if (!ExprResult.Val.isFixedPoint() ||
        hasUnacceptableSideEffect(ExprResult, AllowSideEffects))
      return false;
  
    return true;
  }
  
  /// EvaluateAsRValue - Return true if this is a constant which we can fold using
  /// any crazy technique (that has nothing to do with language standards) that
  /// we want to.  If this function returns true, it returns the folded constant
  /// in Result. If this expression is a glvalue, an lvalue-to-rvalue conversion
  /// will be applied to the result.
  bool Expr::EvaluateAsRValue(EvalResult &Result, const ASTContext &Ctx,
                              bool InConstantContext) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
    EvalInfo Info(Ctx, Result, EvalInfo::EM_IgnoreSideEffects);
    Info.InConstantContext = InConstantContext;
    return ::EvaluateAsRValue(this, Result, Ctx, Info);
  }
  
  bool Expr::EvaluateAsBooleanCondition(bool &Result, const ASTContext &Ctx,
                                        bool InConstantContext) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
    EvalResult Scratch;
    return EvaluateAsRValue(Scratch, Ctx, InConstantContext) &&
           HandleConversionToBool(Scratch.Val, Result);
  }
  
  bool Expr::EvaluateAsInt(EvalResult &Result, const ASTContext &Ctx,
                           SideEffectsKind AllowSideEffects,
                           bool InConstantContext) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
    EvalInfo Info(Ctx, Result, EvalInfo::EM_IgnoreSideEffects);
    Info.InConstantContext = InConstantContext;
    return ::EvaluateAsInt(this, Result, Ctx, AllowSideEffects, Info);
  }
  
  bool Expr::EvaluateAsFixedPoint(EvalResult &Result, const ASTContext &Ctx,
                                  SideEffectsKind AllowSideEffects,
                                  bool InConstantContext) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
    EvalInfo Info(Ctx, Result, EvalInfo::EM_IgnoreSideEffects);
    Info.InConstantContext = InConstantContext;
    return ::EvaluateAsFixedPoint(this, Result, Ctx, AllowSideEffects, Info);
  }
  
  bool Expr::EvaluateAsFloat(APFloat &Result, const ASTContext &Ctx,
                             SideEffectsKind AllowSideEffects,
                             bool InConstantContext) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    if (!getType()->isRealFloatingType())
      return false;
  
    EvalResult ExprResult;
    if (!EvaluateAsRValue(ExprResult, Ctx, InConstantContext) ||
        !ExprResult.Val.isFloat() ||
        hasUnacceptableSideEffect(ExprResult, AllowSideEffects))
      return false;
  
    Result = ExprResult.Val.getFloat();
    return true;
  }
  
  bool Expr::EvaluateAsLValue(EvalResult &Result, const ASTContext &Ctx,
                              bool InConstantContext) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    EvalInfo Info(Ctx, Result, EvalInfo::EM_ConstantFold);
    Info.InConstantContext = InConstantContext;
    LValue LV;
    CheckedTemporaries CheckedTemps;
    if (!EvaluateLValue(this, LV, Info) || !Info.discardCleanups() ||
        Result.HasSideEffects ||
        !CheckLValueConstantExpression(Info, getExprLoc(),
                                       Ctx.getLValueReferenceType(getType()), LV,
                                       ConstantExprKind::Normal, CheckedTemps))
      return false;
  
    LV.moveInto(Result.Val);
    return true;
  }
  
  static bool EvaluateDestruction(const ASTContext &Ctx, APValue::LValueBase Base,
                                  APValue DestroyedValue, QualType Type,
                                  SourceLocation Loc, Expr::EvalStatus &EStatus,
                                  bool IsConstantDestruction) {
    EvalInfo Info(Ctx, EStatus,
                  IsConstantDestruction ? EvalInfo::EM_ConstantExpression
                                        : EvalInfo::EM_ConstantFold);
    Info.setEvaluatingDecl(Base, DestroyedValue,
                           EvalInfo::EvaluatingDeclKind::Dtor);
    Info.InConstantContext = IsConstantDestruction;
  
    LValue LVal;
    LVal.set(Base);
  
    if (!HandleDestruction(Info, Loc, Base, DestroyedValue, Type) ||
        EStatus.HasSideEffects)
      return false;
  
    if (!Info.discardCleanups())
      llvm_unreachable("Unhandled cleanup; missing full expression marker?");
  
    return true;
  }
  
  bool Expr::EvaluateAsConstantExpr(EvalResult &Result, const ASTContext &Ctx,
                                    ConstantExprKind Kind) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    EvalInfo::EvaluationMode EM = EvalInfo::EM_ConstantExpression;
    EvalInfo Info(Ctx, Result, EM);
    Info.InConstantContext = true;
  
    // The type of the object we're initializing is 'const T' for a class NTTP.
    QualType T = getType();
    if (Kind == ConstantExprKind::ClassTemplateArgument)
      T.addConst();
  
    // If we're evaluating a prvalue, fake up a MaterializeTemporaryExpr to
    // represent the result of the evaluation. CheckConstantExpression ensures
    // this doesn't escape.
    MaterializeTemporaryExpr BaseMTE(T, const_cast<Expr*>(this), true);
    APValue::LValueBase Base(&BaseMTE);
  
    Info.setEvaluatingDecl(Base, Result.Val);
    LValue LVal;
    LVal.set(Base);
  
    if (!::EvaluateInPlace(Result.Val, Info, LVal, this) || Result.HasSideEffects)
      return false;
  
    if (!Info.discardCleanups())
      llvm_unreachable("Unhandled cleanup; missing full expression marker?");
  
    if (!CheckConstantExpression(Info, getExprLoc(), getStorageType(Ctx, this),
                                 Result.Val, Kind))
      return false;
    if (!CheckMemoryLeaks(Info))
      return false;
  
    // If this is a class template argument, it's required to have constant
    // destruction too.
    if (Kind == ConstantExprKind::ClassTemplateArgument &&
        (!EvaluateDestruction(Ctx, Base, Result.Val, T, getBeginLoc(), Result,
                              true) ||
         Result.HasSideEffects)) {
      // FIXME: Prefix a note to indicate that the problem is lack of constant
      // destruction.
      return false;
    }
  
    return true;
  }
  
  bool Expr::EvaluateAsInitializer(APValue &Value, const ASTContext &Ctx,
                                   const VarDecl *VD,
                                   SmallVectorImpl<PartialDiagnosticAt> &Notes,
                                   bool IsConstantInitialization) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    // FIXME: Evaluating initializers for large array and record types can cause
    // performance problems. Only do so in C++11 for now.
    if (isRValue() && (getType()->isArrayType() || getType()->isRecordType()) &&
        !Ctx.getLangOpts().CPlusPlus11)
      return false;
  
    Expr::EvalStatus EStatus;
    EStatus.Diag = &Notes;
  
    EvalInfo Info(Ctx, EStatus,
                  (IsConstantInitialization && Ctx.getLangOpts().CPlusPlus11)
                      ? EvalInfo::EM_ConstantExpression
                      : EvalInfo::EM_ConstantFold);
    Info.setEvaluatingDecl(VD, Value);
    Info.InConstantContext = IsConstantInitialization;
  
    SourceLocation DeclLoc = VD->getLocation();
    QualType DeclTy = VD->getType();
  
    if (Info.EnableNewConstInterp) {
      auto &InterpCtx = const_cast<ASTContext &>(Ctx).getInterpContext();
      if (!InterpCtx.evaluateAsInitializer(Info, VD, Value))
        return false;
    } else {
      LValue LVal;
      LVal.set(VD);
  
      if (!EvaluateInPlace(Value, Info, LVal, this,
                           /*AllowNonLiteralTypes=*/true) ||
          EStatus.HasSideEffects)
        return false;
  
      // At this point, any lifetime-extended temporaries are completely
      // initialized.
      Info.performLifetimeExtension();
  
      if (!Info.discardCleanups())
        llvm_unreachable("Unhandled cleanup; missing full expression marker?");
    }
    return CheckConstantExpression(Info, DeclLoc, DeclTy, Value,
                                   ConstantExprKind::Normal) &&
           CheckMemoryLeaks(Info);
  }
  
  bool VarDecl::evaluateDestruction(
      SmallVectorImpl<PartialDiagnosticAt> &Notes) const {
    Expr::EvalStatus EStatus;
    EStatus.Diag = &Notes;
  
    // Only treat the destruction as constant destruction if we formally have
    // constant initialization (or are usable in a constant expression).
    bool IsConstantDestruction = hasConstantInitialization();
  
    // Make a copy of the value for the destructor to mutate, if we know it.
    // Otherwise, treat the value as default-initialized; if the destructor works
    // anyway, then the destruction is constant (and must be essentially empty).
    APValue DestroyedValue;
    if (getEvaluatedValue() && !getEvaluatedValue()->isAbsent())
      DestroyedValue = *getEvaluatedValue();
    else if (!getDefaultInitValue(getType(), DestroyedValue))
      return false;
  
    if (!EvaluateDestruction(getASTContext(), this, std::move(DestroyedValue),
                             getType(), getLocation(), EStatus,
                             IsConstantDestruction) ||
        EStatus.HasSideEffects)
      return false;
  
    ensureEvaluatedStmt()->HasConstantDestruction = true;
    return true;
  }
  
  /// isEvaluatable - Call EvaluateAsRValue to see if this expression can be
  /// constant folded, but discard the result.
  bool Expr::isEvaluatable(const ASTContext &Ctx, SideEffectsKind SEK) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    EvalResult Result;
    return EvaluateAsRValue(Result, Ctx, /* in constant context */ true) &&
           !hasUnacceptableSideEffect(Result, SEK);
  }
  
  APSInt Expr::EvaluateKnownConstInt(const ASTContext &Ctx,
                      SmallVectorImpl<PartialDiagnosticAt> *Diag) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    EvalResult EVResult;
    EVResult.Diag = Diag;
    EvalInfo Info(Ctx, EVResult, EvalInfo::EM_IgnoreSideEffects);
    Info.InConstantContext = true;
  
    bool Result = ::EvaluateAsRValue(this, EVResult, Ctx, Info);
    (void)Result;
    assert(Result && "Could not evaluate expression");
    assert(EVResult.Val.isInt() && "Expression did not evaluate to integer");
  
    return EVResult.Val.getInt();
  }
  
  APSInt Expr::EvaluateKnownConstIntCheckOverflow(
      const ASTContext &Ctx, SmallVectorImpl<PartialDiagnosticAt> *Diag) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    EvalResult EVResult;
    EVResult.Diag = Diag;
    EvalInfo Info(Ctx, EVResult, EvalInfo::EM_IgnoreSideEffects);
    Info.InConstantContext = true;
    Info.CheckingForUndefinedBehavior = true;
  
    bool Result = ::EvaluateAsRValue(Info, this, EVResult.Val);
    (void)Result;
    assert(Result && "Could not evaluate expression");
    assert(EVResult.Val.isInt() && "Expression did not evaluate to integer");
  
    return EVResult.Val.getInt();
  }
  
  void Expr::EvaluateForOverflow(const ASTContext &Ctx) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    bool IsConst;
    EvalResult EVResult;
    if (!FastEvaluateAsRValue(this, EVResult, Ctx, IsConst)) {
      EvalInfo Info(Ctx, EVResult, EvalInfo::EM_IgnoreSideEffects);
      Info.CheckingForUndefinedBehavior = true;
      (void)::EvaluateAsRValue(Info, this, EVResult.Val);
    }
  }
  
  bool Expr::EvalResult::isGlobalLValue() const {
    assert(Val.isLValue());
    return IsGlobalLValue(Val.getLValueBase());
  }
  
  /// isIntegerConstantExpr - this recursive routine will test if an expression is
  /// an integer constant expression.
  
  /// FIXME: Pass up a reason why! Invalid operation in i-c-e, division by zero,
  /// comma, etc
  
  // CheckICE - This function does the fundamental ICE checking: the returned
  // ICEDiag contains an ICEKind indicating whether the expression is an ICE,
  // and a (possibly null) SourceLocation indicating the location of the problem.
  //
  // Note that to reduce code duplication, this helper does no evaluation
  // itself; the caller checks whether the expression is evaluatable, and
  // in the rare cases where CheckICE actually cares about the evaluated
  // value, it calls into Evaluate.
  
  namespace {
  
  enum ICEKind {
    /// This expression is an ICE.
    IK_ICE,
    /// This expression is not an ICE, but if it isn't evaluated, it's
    /// a legal subexpression for an ICE. This return value is used to handle
    /// the comma operator in C99 mode, and non-constant subexpressions.
    IK_ICEIfUnevaluated,
    /// This expression is not an ICE, and is not a legal subexpression for one.
    IK_NotICE
  };
  
  struct ICEDiag {
    ICEKind Kind;
    SourceLocation Loc;
  
    ICEDiag(ICEKind IK, SourceLocation l) : Kind(IK), Loc(l) {}
  };
  
  }
  
  static ICEDiag NoDiag() { return ICEDiag(IK_ICE, SourceLocation()); }
  
  static ICEDiag Worst(ICEDiag A, ICEDiag B) { return A.Kind >= B.Kind ? A : B; }
  
  static ICEDiag CheckEvalInICE(const Expr* E, const ASTContext &Ctx) {
    Expr::EvalResult EVResult;
    Expr::EvalStatus Status;
    EvalInfo Info(Ctx, Status, EvalInfo::EM_ConstantExpression);
  
    Info.InConstantContext = true;
    if (!::EvaluateAsRValue(E, EVResult, Ctx, Info) || EVResult.HasSideEffects ||
        !EVResult.Val.isInt())
      return ICEDiag(IK_NotICE, E->getBeginLoc());
  
    return NoDiag();
  }
  
  static ICEDiag CheckICE(const Expr* E, const ASTContext &Ctx) {
    assert(!E->isValueDependent() && "Should not see value dependent exprs!");
    if (!E->getType()->isIntegralOrEnumerationType())
      return ICEDiag(IK_NotICE, E->getBeginLoc());
  
    switch (E->getStmtClass()) {
  #define ABSTRACT_STMT(Node)
  #define STMT(Node, Base) case Expr::Node##Class:
  #define EXPR(Node, Base)
  #include "clang/AST/StmtNodes.inc"
    case Expr::PredefinedExprClass:
    case Expr::FloatingLiteralClass:
    case Expr::ImaginaryLiteralClass:
    case Expr::StringLiteralClass:
    case Expr::ArraySubscriptExprClass:
    case Expr::MatrixSubscriptExprClass:
    case Expr::OMPArraySectionExprClass:
    case Expr::OMPArrayShapingExprClass:
    case Expr::OMPIteratorExprClass:
    case Expr::MemberExprClass:
    case Expr::CompoundAssignOperatorClass:
    case Expr::CompoundLiteralExprClass:
    case Expr::ExtVectorElementExprClass:
    case Expr::DesignatedInitExprClass:
    case Expr::ArrayInitLoopExprClass:
    case Expr::ArrayInitIndexExprClass:
    case Expr::NoInitExprClass:
    case Expr::DesignatedInitUpdateExprClass:
    case Expr::ImplicitValueInitExprClass:
    case Expr::ParenListExprClass:
    case Expr::VAArgExprClass:
    case Expr::AddrLabelExprClass:
    case Expr::StmtExprClass:
    case Expr::CXXMemberCallExprClass:
    case Expr::CUDAKernelCallExprClass:
    case Expr::CXXAddrspaceCastExprClass:
    case Expr::CXXDynamicCastExprClass:
    case Expr::CXXTypeidExprClass:
    case Expr::CXXUuidofExprClass:
    case Expr::MSPropertyRefExprClass:
    case Expr::MSPropertySubscriptExprClass:
    case Expr::CXXNullPtrLiteralExprClass:
    case Expr::UserDefinedLiteralClass:
    case Expr::CXXThisExprClass:
    case Expr::CXXThrowExprClass:
    case Expr::CXXNewExprClass:
    case Expr::CXXDeleteExprClass:
    case Expr::CXXPseudoDestructorExprClass:
    case Expr::UnresolvedLookupExprClass:
    case Expr::TypoExprClass:
    case Expr::RecoveryExprClass:
    case Expr::DependentScopeDeclRefExprClass:
    case Expr::CXXConstructExprClass:
    case Expr::CXXInheritedCtorInitExprClass:
    case Expr::CXXStdInitializerListExprClass:
    case Expr::CXXBindTemporaryExprClass:
    case Expr::ExprWithCleanupsClass:
    case Expr::CXXTemporaryObjectExprClass:
    case Expr::CXXUnresolvedConstructExprClass:
    case Expr::CXXDependentScopeMemberExprClass:
    case Expr::UnresolvedMemberExprClass:
    case Expr::ObjCStringLiteralClass:
    case Expr::ObjCBoxedExprClass:
    case Expr::ObjCArrayLiteralClass:
    case Expr::ObjCDictionaryLiteralClass:
    case Expr::ObjCEncodeExprClass:
    case Expr::ObjCMessageExprClass:
    case Expr::ObjCSelectorExprClass:
    case Expr::ObjCProtocolExprClass:
    case Expr::ObjCIvarRefExprClass:
    case Expr::ObjCPropertyRefExprClass:
    case Expr::ObjCSubscriptRefExprClass:
    case Expr::ObjCIsaExprClass:
    case Expr::ObjCAvailabilityCheckExprClass:
    case Expr::ShuffleVectorExprClass:
    case Expr::ConvertVectorExprClass:
    case Expr::BlockExprClass:
    case Expr::NoStmtClass:
    case Expr::OpaqueValueExprClass:
    case Expr::PackExpansionExprClass:
    case Expr::SubstNonTypeTemplateParmPackExprClass:
    case Expr::FunctionParmPackExprClass:
    case Expr::AsTypeExprClass:
    case Expr::ObjCIndirectCopyRestoreExprClass:
    case Expr::MaterializeTemporaryExprClass:
    case Expr::PseudoObjectExprClass:
    case Expr::AtomicExprClass:
    case Expr::LambdaExprClass:
    case Expr::CXXFoldExprClass:
    case Expr::CoawaitExprClass:
    case Expr::DependentCoawaitExprClass:
    case Expr::CoyieldExprClass:
      return ICEDiag(IK_NotICE, E->getBeginLoc());
  
    case Expr::InitListExprClass: {
      // C++03 [dcl.init]p13: If T is a scalar type, then a declaration of the
      // form "T x = { a };" is equivalent to "T x = a;".
      // Unless we're initializing a reference, T is a scalar as it is known to be
      // of integral or enumeration type.
      if (E->isRValue())
        if (cast<InitListExpr>(E)->getNumInits() == 1)
          return CheckICE(cast<InitListExpr>(E)->getInit(0), Ctx);
      return ICEDiag(IK_NotICE, E->getBeginLoc());
    }
  
    case Expr::SizeOfPackExprClass:
    case Expr::GNUNullExprClass:
    case Expr::SourceLocExprClass:
      return NoDiag();
  
    case Expr::SubstNonTypeTemplateParmExprClass:
      return
        CheckICE(cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement(), Ctx);
  
    case Expr::ConstantExprClass:
      return CheckICE(cast<ConstantExpr>(E)->getSubExpr(), Ctx);
  
    case Expr::ParenExprClass:
      return CheckICE(cast<ParenExpr>(E)->getSubExpr(), Ctx);
    case Expr::GenericSelectionExprClass:
      return CheckICE(cast<GenericSelectionExpr>(E)->getResultExpr(), Ctx);
    case Expr::IntegerLiteralClass:
    case Expr::FixedPointLiteralClass:
    case Expr::CharacterLiteralClass:
    case Expr::ObjCBoolLiteralExprClass:
    case Expr::CXXBoolLiteralExprClass:
    case Expr::CXXScalarValueInitExprClass:
    case Expr::TypeTraitExprClass:
    case Expr::ConceptSpecializationExprClass:
    case Expr::RequiresExprClass:
    case Expr::ArrayTypeTraitExprClass:
    case Expr::ExpressionTraitExprClass:
    case Expr::CXXNoexceptExprClass:
      return NoDiag();
    case Expr::CallExprClass:
    case Expr::CXXOperatorCallExprClass: {
      // C99 6.6/3 allows function calls within unevaluated subexpressions of
      // constant expressions, but they can never be ICEs because an ICE cannot
      // contain an operand of (pointer to) function type.
      const CallExpr *CE = cast<CallExpr>(E);
      if (CE->getBuiltinCallee())
        return CheckEvalInICE(E, Ctx);
      return ICEDiag(IK_NotICE, E->getBeginLoc());
    }
    case Expr::CXXRewrittenBinaryOperatorClass:
      return CheckICE(cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm(),
                      Ctx);
    case Expr::DeclRefExprClass: {
      const NamedDecl *D = cast<DeclRefExpr>(E)->getDecl();
      if (isa<EnumConstantDecl>(D))
        return NoDiag();
  
      // C++ and OpenCL (FIXME: spec reference?) allow reading const-qualified
      // integer variables in constant expressions:
      //
      // C++ 7.1.5.1p2
      //   A variable of non-volatile const-qualified integral or enumeration
      //   type initialized by an ICE can be used in ICEs.
      //
      // We sometimes use CheckICE to check the C++98 rules in C++11 mode. In
      // that mode, use of reference variables should not be allowed.
      const VarDecl *VD = dyn_cast<VarDecl>(D);
      if (VD && VD->isUsableInConstantExpressions(Ctx) &&
          !VD->getType()->isReferenceType())
        return NoDiag();
  
      return ICEDiag(IK_NotICE, E->getBeginLoc());
    }
    case Expr::UnaryOperatorClass: {
      const UnaryOperator *Exp = cast<UnaryOperator>(E);
      switch (Exp->getOpcode()) {
      case UO_PostInc:
      case UO_PostDec:
      case UO_PreInc:
      case UO_PreDec:
      case UO_AddrOf:
      case UO_Deref:
      case UO_Coawait:
        // C99 6.6/3 allows increment and decrement within unevaluated
        // subexpressions of constant expressions, but they can never be ICEs
        // because an ICE cannot contain an lvalue operand.
        return ICEDiag(IK_NotICE, E->getBeginLoc());
      case UO_Extension:
      case UO_LNot:
      case UO_Plus:
      case UO_Minus:
      case UO_Not:
      case UO_Real:
      case UO_Imag:
        return CheckICE(Exp->getSubExpr(), Ctx);
      }
      llvm_unreachable("invalid unary operator class");
    }
    case Expr::OffsetOfExprClass: {
      // Note that per C99, offsetof must be an ICE. And AFAIK, using
      // EvaluateAsRValue matches the proposed gcc behavior for cases like
      // "offsetof(struct s{int x[4];}, x[1.0])".  This doesn't affect
      // compliance: we should warn earlier for offsetof expressions with
      // array subscripts that aren't ICEs, and if the array subscripts
      // are ICEs, the value of the offsetof must be an integer constant.
      return CheckEvalInICE(E, Ctx);
    }
    case Expr::UnaryExprOrTypeTraitExprClass: {
      const UnaryExprOrTypeTraitExpr *Exp = cast<UnaryExprOrTypeTraitExpr>(E);
      if ((Exp->getKind() ==  UETT_SizeOf) &&
          Exp->getTypeOfArgument()->isVariableArrayType())
        return ICEDiag(IK_NotICE, E->getBeginLoc());
      return NoDiag();
    }
    case Expr::BinaryOperatorClass: {
      const BinaryOperator *Exp = cast<BinaryOperator>(E);
      switch (Exp->getOpcode()) {
      case BO_PtrMemD:
      case BO_PtrMemI:
      case BO_Assign:
      case BO_MulAssign:
      case BO_DivAssign:
      case BO_RemAssign:
      case BO_AddAssign:
      case BO_SubAssign:
      case BO_ShlAssign:
      case BO_ShrAssign:
      case BO_AndAssign:
      case BO_XorAssign:
      case BO_OrAssign:
        // C99 6.6/3 allows assignments within unevaluated subexpressions of
        // constant expressions, but they can never be ICEs because an ICE cannot
        // contain an lvalue operand.
        return ICEDiag(IK_NotICE, E->getBeginLoc());
  
      case BO_Mul:
      case BO_Div:
      case BO_Rem:
      case BO_Add:
      case BO_Sub:
      case BO_Shl:
      case BO_Shr:
      case BO_LT:
      case BO_GT:
      case BO_LE:
      case BO_GE:
      case BO_EQ:
      case BO_NE:
      case BO_And:
      case BO_Xor:
      case BO_Or:
      case BO_Comma:
      case BO_Cmp: {
        ICEDiag LHSResult = CheckICE(Exp->getLHS(), Ctx);
        ICEDiag RHSResult = CheckICE(Exp->getRHS(), Ctx);
        if (Exp->getOpcode() == BO_Div ||
            Exp->getOpcode() == BO_Rem) {
          // EvaluateAsRValue gives an error for undefined Div/Rem, so make sure
          // we don't evaluate one.
          if (LHSResult.Kind == IK_ICE && RHSResult.Kind == IK_ICE) {
            llvm::APSInt REval = Exp->getRHS()->EvaluateKnownConstInt(Ctx);
            if (REval == 0)
              return ICEDiag(IK_ICEIfUnevaluated, E->getBeginLoc());
            if (REval.isSigned() && REval.isAllOnesValue()) {
              llvm::APSInt LEval = Exp->getLHS()->EvaluateKnownConstInt(Ctx);
              if (LEval.isMinSignedValue())
                return ICEDiag(IK_ICEIfUnevaluated, E->getBeginLoc());
            }
          }
        }
        if (Exp->getOpcode() == BO_Comma) {
          if (Ctx.getLangOpts().C99) {
            // C99 6.6p3 introduces a strange edge case: comma can be in an ICE
            // if it isn't evaluated.
            if (LHSResult.Kind == IK_ICE && RHSResult.Kind == IK_ICE)
              return ICEDiag(IK_ICEIfUnevaluated, E->getBeginLoc());
          } else {
            // In both C89 and C++, commas in ICEs are illegal.
            return ICEDiag(IK_NotICE, E->getBeginLoc());
          }
        }
        return Worst(LHSResult, RHSResult);
      }
      case BO_LAnd:
      case BO_LOr: {
        ICEDiag LHSResult = CheckICE(Exp->getLHS(), Ctx);
        ICEDiag RHSResult = CheckICE(Exp->getRHS(), Ctx);
        if (LHSResult.Kind == IK_ICE && RHSResult.Kind == IK_ICEIfUnevaluated) {
          // Rare case where the RHS has a comma "side-effect"; we need
          // to actually check the condition to see whether the side
          // with the comma is evaluated.
          if ((Exp->getOpcode() == BO_LAnd) !=
              (Exp->getLHS()->EvaluateKnownConstInt(Ctx) == 0))
            return RHSResult;
          return NoDiag();
        }
  
        return Worst(LHSResult, RHSResult);
      }
      }
      llvm_unreachable("invalid binary operator kind");
    }
    case Expr::ImplicitCastExprClass:
    case Expr::CStyleCastExprClass:
    case Expr::CXXFunctionalCastExprClass:
    case Expr::CXXStaticCastExprClass:
    case Expr::CXXReinterpretCastExprClass:
    case Expr::CXXConstCastExprClass:
    case Expr::ObjCBridgedCastExprClass: {
      const Expr *SubExpr = cast<CastExpr>(E)->getSubExpr();
      if (isa<ExplicitCastExpr>(E)) {
        if (const FloatingLiteral *FL
              = dyn_cast<FloatingLiteral>(SubExpr->IgnoreParenImpCasts())) {
          unsigned DestWidth = Ctx.getIntWidth(E->getType());
          bool DestSigned = E->getType()->isSignedIntegerOrEnumerationType();
          APSInt IgnoredVal(DestWidth, !DestSigned);
          bool Ignored;
          // If the value does not fit in the destination type, the behavior is
          // undefined, so we are not required to treat it as a constant
          // expression.
          if (FL->getValue().convertToInteger(IgnoredVal,
                                              llvm::APFloat::rmTowardZero,
                                              &Ignored) & APFloat::opInvalidOp)
            return ICEDiag(IK_NotICE, E->getBeginLoc());
          return NoDiag();
        }
      }
      switch (cast<CastExpr>(E)->getCastKind()) {
      case CK_LValueToRValue:
      case CK_AtomicToNonAtomic:
      case CK_NonAtomicToAtomic:
      case CK_NoOp:
      case CK_IntegralToBoolean:
      case CK_IntegralCast:
        return CheckICE(SubExpr, Ctx);
      default:
        return ICEDiag(IK_NotICE, E->getBeginLoc());
      }
    }
    case Expr::BinaryConditionalOperatorClass: {
      const BinaryConditionalOperator *Exp = cast<BinaryConditionalOperator>(E);
      ICEDiag CommonResult = CheckICE(Exp->getCommon(), Ctx);
      if (CommonResult.Kind == IK_NotICE) return CommonResult;
      ICEDiag FalseResult = CheckICE(Exp->getFalseExpr(), Ctx);
      if (FalseResult.Kind == IK_NotICE) return FalseResult;
      if (CommonResult.Kind == IK_ICEIfUnevaluated) return CommonResult;
      if (FalseResult.Kind == IK_ICEIfUnevaluated &&
          Exp->getCommon()->EvaluateKnownConstInt(Ctx) != 0) return NoDiag();
      return FalseResult;
    }
    case Expr::ConditionalOperatorClass: {
      const ConditionalOperator *Exp = cast<ConditionalOperator>(E);
      // If the condition (ignoring parens) is a __builtin_constant_p call,
      // then only the true side is actually considered in an integer constant
      // expression, and it is fully evaluated.  This is an important GNU
      // extension.  See GCC PR38377 for discussion.
      if (const CallExpr *CallCE
          = dyn_cast<CallExpr>(Exp->getCond()->IgnoreParenCasts()))
        if (CallCE->getBuiltinCallee() == Builtin::BI__builtin_constant_p)
          return CheckEvalInICE(E, Ctx);
      ICEDiag CondResult = CheckICE(Exp->getCond(), Ctx);
      if (CondResult.Kind == IK_NotICE)
        return CondResult;
  
      ICEDiag TrueResult = CheckICE(Exp->getTrueExpr(), Ctx);
      ICEDiag FalseResult = CheckICE(Exp->getFalseExpr(), Ctx);
  
      if (TrueResult.Kind == IK_NotICE)
        return TrueResult;
      if (FalseResult.Kind == IK_NotICE)
        return FalseResult;
      if (CondResult.Kind == IK_ICEIfUnevaluated)
        return CondResult;
      if (TrueResult.Kind == IK_ICE && FalseResult.Kind == IK_ICE)
        return NoDiag();
      // Rare case where the diagnostics depend on which side is evaluated
      // Note that if we get here, CondResult is 0, and at least one of
      // TrueResult and FalseResult is non-zero.
      if (Exp->getCond()->EvaluateKnownConstInt(Ctx) == 0)
        return FalseResult;
      return TrueResult;
    }
    case Expr::CXXDefaultArgExprClass:
      return CheckICE(cast<CXXDefaultArgExpr>(E)->getExpr(), Ctx);
    case Expr::CXXDefaultInitExprClass:
      return CheckICE(cast<CXXDefaultInitExpr>(E)->getExpr(), Ctx);
    case Expr::ChooseExprClass: {
      return CheckICE(cast<ChooseExpr>(E)->getChosenSubExpr(), Ctx);
    }
    case Expr::BuiltinBitCastExprClass: {
      if (!checkBitCastConstexprEligibility(nullptr, Ctx, cast<CastExpr>(E)))
        return ICEDiag(IK_NotICE, E->getBeginLoc());
      return CheckICE(cast<CastExpr>(E)->getSubExpr(), Ctx);
    }
    }
  
    llvm_unreachable("Invalid StmtClass!");
  }
  
  /// Evaluate an expression as a C++11 integral constant expression.
  static bool EvaluateCPlusPlus11IntegralConstantExpr(const ASTContext &Ctx,
                                                      const Expr *E,
                                                      llvm::APSInt *Value,
                                                      SourceLocation *Loc) {
    if (!E->getType()->isIntegralOrUnscopedEnumerationType()) {
      if (Loc) *Loc = E->getExprLoc();
      return false;
    }
  
    APValue Result;
    if (!E->isCXX11ConstantExpr(Ctx, &Result, Loc))
      return false;
  
    if (!Result.isInt()) {
      if (Loc) *Loc = E->getExprLoc();
      return false;
    }
  
    if (Value) *Value = Result.getInt();
    return true;
  }
  
  bool Expr::isIntegerConstantExpr(const ASTContext &Ctx,
                                   SourceLocation *Loc) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    if (Ctx.getLangOpts().CPlusPlus11)
      return EvaluateCPlusPlus11IntegralConstantExpr(Ctx, this, nullptr, Loc);
  
    ICEDiag D = CheckICE(this, Ctx);
    if (D.Kind != IK_ICE) {
      if (Loc) *Loc = D.Loc;
      return false;
    }
    return true;
  }
  
  Optional<llvm::APSInt> Expr::getIntegerConstantExpr(const ASTContext &Ctx,
                                                      SourceLocation *Loc,
                                                      bool isEvaluated) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    APSInt Value;
  
    if (Ctx.getLangOpts().CPlusPlus11) {
      if (EvaluateCPlusPlus11IntegralConstantExpr(Ctx, this, &Value, Loc))
        return Value;
      return None;
    }
  
    if (!isIntegerConstantExpr(Ctx, Loc))
      return None;
  
    // The only possible side-effects here are due to UB discovered in the
    // evaluation (for instance, INT_MAX + 1). In such a case, we are still
    // required to treat the expression as an ICE, so we produce the folded
    // value.
    EvalResult ExprResult;
    Expr::EvalStatus Status;
    EvalInfo Info(Ctx, Status, EvalInfo::EM_IgnoreSideEffects);
    Info.InConstantContext = true;
  
    if (!::EvaluateAsInt(this, ExprResult, Ctx, SE_AllowSideEffects, Info))
      llvm_unreachable("ICE cannot be evaluated!");
  
    return ExprResult.Val.getInt();
  }
  
  bool Expr::isCXX98IntegralConstantExpr(const ASTContext &Ctx) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    return CheckICE(this, Ctx).Kind == IK_ICE;
  }
  
  bool Expr::isCXX11ConstantExpr(const ASTContext &Ctx, APValue *Result,
                                 SourceLocation *Loc) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    // We support this checking in C++98 mode in order to diagnose compatibility
    // issues.
    assert(Ctx.getLangOpts().CPlusPlus);
  
    // Build evaluation settings.
    Expr::EvalStatus Status;
    SmallVector<PartialDiagnosticAt, 8> Diags;
    Status.Diag = &Diags;
    EvalInfo Info(Ctx, Status, EvalInfo::EM_ConstantExpression);
  
    APValue Scratch;
    bool IsConstExpr =
        ::EvaluateAsRValue(Info, this, Result ? *Result : Scratch) &&
        // FIXME: We don't produce a diagnostic for this, but the callers that
        // call us on arbitrary full-expressions should generally not care.
        Info.discardCleanups() && !Status.HasSideEffects;
  
    if (!Diags.empty()) {
      IsConstExpr = false;
      if (Loc) *Loc = Diags[0].first;
    } else if (!IsConstExpr) {
      // FIXME: This shouldn't happen.
      if (Loc) *Loc = getExprLoc();
    }
  
    return IsConstExpr;
  }
  
  bool Expr::EvaluateWithSubstitution(APValue &Value, ASTContext &Ctx,
                                      const FunctionDecl *Callee,
                                      ArrayRef<const Expr*> Args,
                                      const Expr *This) const {
    assert(!isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    Expr::EvalStatus Status;
    EvalInfo Info(Ctx, Status, EvalInfo::EM_ConstantExpressionUnevaluated);
    Info.InConstantContext = true;
  
    LValue ThisVal;
    const LValue *ThisPtr = nullptr;
    if (This) {
  #ifndef NDEBUG
      auto *MD = dyn_cast<CXXMethodDecl>(Callee);
      assert(MD && "Don't provide `this` for non-methods.");
      assert(!MD->isStatic() && "Don't provide `this` for static methods.");
  #endif
      if (!This->isValueDependent() &&
          EvaluateObjectArgument(Info, This, ThisVal) &&
          !Info.EvalStatus.HasSideEffects)
        ThisPtr = &ThisVal;
  
      // Ignore any side-effects from a failed evaluation. This is safe because
      // they can't interfere with any other argument evaluation.
      Info.EvalStatus.HasSideEffects = false;
    }
  
    CallRef Call = Info.CurrentCall->createCall(Callee);
    for (ArrayRef<const Expr*>::iterator I = Args.begin(), E = Args.end();
         I != E; ++I) {
      unsigned Idx = I - Args.begin();
      if (Idx >= Callee->getNumParams())
        break;
      const ParmVarDecl *PVD = Callee->getParamDecl(Idx);
      if ((*I)->isValueDependent() ||
          !EvaluateCallArg(PVD, *I, Call, Info) ||
          Info.EvalStatus.HasSideEffects) {
        // If evaluation fails, throw away the argument entirely.
        if (APValue *Slot = Info.getParamSlot(Call, PVD))
          *Slot = APValue();
      }
  
      // Ignore any side-effects from a failed evaluation. This is safe because
      // they can't interfere with any other argument evaluation.
      Info.EvalStatus.HasSideEffects = false;
    }
  
    // Parameter cleanups happen in the caller and are not part of this
    // evaluation.
    Info.discardCleanups();
    Info.EvalStatus.HasSideEffects = false;
  
    // Build fake call to Callee.
    CallStackFrame Frame(Info, Callee->getLocation(), Callee, ThisPtr, Call);
    // FIXME: Missing ExprWithCleanups in enable_if conditions?
    FullExpressionRAII Scope(Info);
    return Evaluate(Value, Info, this) && Scope.destroy() &&
           !Info.EvalStatus.HasSideEffects;
  }
  
  bool Expr::isPotentialConstantExpr(const FunctionDecl *FD,
                                     SmallVectorImpl<
                                       PartialDiagnosticAt> &Diags) {
    // FIXME: It would be useful to check constexpr function templates, but at the
    // moment the constant expression evaluator cannot cope with the non-rigorous
    // ASTs which we build for dependent expressions.
    if (FD->isDependentContext())
      return true;
  
    Expr::EvalStatus Status;
    Status.Diag = &Diags;
  
    EvalInfo Info(FD->getASTContext(), Status, EvalInfo::EM_ConstantExpression);
    Info.InConstantContext = true;
    Info.CheckingPotentialConstantExpression = true;
  
    // The constexpr VM attempts to compile all methods to bytecode here.
    if (Info.EnableNewConstInterp) {
      Info.Ctx.getInterpContext().isPotentialConstantExpr(Info, FD);
      return Diags.empty();
    }
  
    const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD);
    const CXXRecordDecl *RD = MD ? MD->getParent()->getCanonicalDecl() : nullptr;
  
    // Fabricate an arbitrary expression on the stack and pretend that it
    // is a temporary being used as the 'this' pointer.
    LValue This;
    ImplicitValueInitExpr VIE(RD ? Info.Ctx.getRecordType(RD) : Info.Ctx.IntTy);
    This.set({&VIE, Info.CurrentCall->Index});
  
    ArrayRef<const Expr*> Args;
  
    APValue Scratch;
    if (const CXXConstructorDecl *CD = dyn_cast<CXXConstructorDecl>(FD)) {
      // Evaluate the call as a constant initializer, to allow the construction
      // of objects of non-literal types.
      Info.setEvaluatingDecl(This.getLValueBase(), Scratch);
      HandleConstructorCall(&VIE, This, Args, CD, Info, Scratch);
    } else {
      SourceLocation Loc = FD->getLocation();
      HandleFunctionCall(Loc, FD, (MD && MD->isInstance()) ? &This : nullptr,
                         Args, CallRef(), FD->getBody(), Info, Scratch, nullptr);
    }
  
    return Diags.empty();
  }
  
  bool Expr::isPotentialConstantExprUnevaluated(Expr *E,
                                                const FunctionDecl *FD,
                                                SmallVectorImpl<
                                                  PartialDiagnosticAt> &Diags) {
    assert(!E->isValueDependent() &&
           "Expression evaluator can't be called on a dependent expression.");
  
    Expr::EvalStatus Status;
    Status.Diag = &Diags;
  
    EvalInfo Info(FD->getASTContext(), Status,
                  EvalInfo::EM_ConstantExpressionUnevaluated);
    Info.InConstantContext = true;
    Info.CheckingPotentialConstantExpression = true;
  
    // Fabricate a call stack frame to give the arguments a plausible cover story.
    CallStackFrame Frame(Info, SourceLocation(), FD, /*This*/ nullptr, CallRef());
  
    APValue ResultScratch;
    Evaluate(ResultScratch, Info, E);
    return Diags.empty();
  }
  
  bool Expr::tryEvaluateObjectSize(uint64_t &Result, ASTContext &Ctx,
                                   unsigned Type) const {
    if (!getType()->isPointerType())
      return false;
  
    Expr::EvalStatus Status;
    EvalInfo Info(Ctx, Status, EvalInfo::EM_ConstantFold);
    return tryEvaluateBuiltinObjectSize(this, Type, Info, Result);
  }
  