text: //===- ExprClassification.cpp - Expression AST Node Implementation --------===//
  //
  // 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 Expr::classify.
  //
  //===----------------------------------------------------------------------===//
  
  #include "clang/AST/Expr.h"
  #include "clang/AST/ASTContext.h"
  #include "clang/AST/DeclCXX.h"
  #include "clang/AST/DeclObjC.h"
  #include "clang/AST/DeclTemplate.h"
  #include "clang/AST/ExprCXX.h"
  #include "clang/AST/ExprObjC.h"
  #include "llvm/Support/ErrorHandling.h"
  
  using namespace clang;
  
  using Cl = Expr::Classification;
  
  static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E);
  static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D);
  static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T);
  static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E);
  static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E);
  static Cl::Kinds ClassifyConditional(ASTContext &Ctx,
                                       const Expr *trueExpr,
                                       const Expr *falseExpr);
  static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
                                         Cl::Kinds Kind, SourceLocation &Loc);
  
  Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const {
    assert(!TR->isReferenceType() && "Expressions can't have reference type.");
  
    Cl::Kinds kind = ClassifyInternal(Ctx, this);
    // C99 6.3.2.1: An lvalue is an expression with an object type or an
    //   incomplete type other than void.
    if (!Ctx.getLangOpts().CPlusPlus) {
      // Thus, no functions.
      if (TR->isFunctionType() || TR == Ctx.OverloadTy)
        kind = Cl::CL_Function;
      // No void either, but qualified void is OK because it is "other than void".
      // Void "lvalues" are classified as addressable void values, which are void
      // expressions whose address can be taken.
      else if (TR->isVoidType() && !TR.hasQualifiers())
        kind = (kind == Cl::CL_LValue ? Cl::CL_AddressableVoid : Cl::CL_Void);
    }
  
    // Enable this assertion for testing.
    switch (kind) {
    case Cl::CL_LValue: assert(getValueKind() == VK_LValue); break;
    case Cl::CL_XValue: assert(getValueKind() == VK_XValue); break;
    case Cl::CL_Function:
    case Cl::CL_Void:
    case Cl::CL_AddressableVoid:
    case Cl::CL_DuplicateVectorComponents:
    case Cl::CL_MemberFunction:
    case Cl::CL_SubObjCPropertySetting:
    case Cl::CL_ClassTemporary:
    case Cl::CL_ArrayTemporary:
    case Cl::CL_ObjCMessageRValue:
    case Cl::CL_PRValue: assert(getValueKind() == VK_RValue); break;
    }
  
    Cl::ModifiableType modifiable = Cl::CM_Untested;
    if (Loc)
      modifiable = IsModifiable(Ctx, this, kind, *Loc);
    return Classification(kind, modifiable);
  }
  
  /// Classify an expression which creates a temporary, based on its type.
  static Cl::Kinds ClassifyTemporary(QualType T) {
    if (T->isRecordType())
      return Cl::CL_ClassTemporary;
    if (T->isArrayType())
      return Cl::CL_ArrayTemporary;
  
    // No special classification: these don't behave differently from normal
    // prvalues.
    return Cl::CL_PRValue;
  }
  
  static Cl::Kinds ClassifyExprValueKind(const LangOptions &Lang,
                                         const Expr *E,
                                         ExprValueKind Kind) {
    switch (Kind) {
    case VK_RValue:
      return Lang.CPlusPlus ? ClassifyTemporary(E->getType()) : Cl::CL_PRValue;
    case VK_LValue:
      return Cl::CL_LValue;
    case VK_XValue:
      return Cl::CL_XValue;
    }
    llvm_unreachable("Invalid value category of implicit cast.");
  }
  
  static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
    // This function takes the first stab at classifying expressions.
    const LangOptions &Lang = Ctx.getLangOpts();
  
    switch (E->getStmtClass()) {
    case Stmt::NoStmtClass:
  #define ABSTRACT_STMT(Kind)
  #define STMT(Kind, Base) case Expr::Kind##Class:
  #define EXPR(Kind, Base)
  #include "clang/AST/StmtNodes.inc"
      llvm_unreachable("cannot classify a statement");
  
      // First come the expressions that are always lvalues, unconditionally.
    case Expr::ObjCIsaExprClass:
      // C++ [expr.prim.general]p1: A string literal is an lvalue.
    case Expr::StringLiteralClass:
      // @encode is equivalent to its string
    case Expr::ObjCEncodeExprClass:
      // __func__ and friends are too.
    case Expr::PredefinedExprClass:
      // Property references are lvalues
    case Expr::ObjCSubscriptRefExprClass:
    case Expr::ObjCPropertyRefExprClass:
      // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of...
    case Expr::CXXTypeidExprClass:
    case Expr::CXXUuidofExprClass:
      // Unresolved lookups and uncorrected typos get classified as lvalues.
      // FIXME: Is this wise? Should they get their own kind?
    case Expr::UnresolvedLookupExprClass:
    case Expr::UnresolvedMemberExprClass:
    case Expr::TypoExprClass:
    case Expr::RecoveryExprClass:
    case Expr::DependentCoawaitExprClass:
    case Expr::CXXDependentScopeMemberExprClass:
    case Expr::DependentScopeDeclRefExprClass:
      // ObjC instance variables are lvalues
      // FIXME: ObjC++0x might have different rules
    case Expr::ObjCIvarRefExprClass:
    case Expr::FunctionParmPackExprClass:
    case Expr::MSPropertyRefExprClass:
    case Expr::MSPropertySubscriptExprClass:
    case Expr::OMPArraySectionExprClass:
    case Expr::OMPArrayShapingExprClass:
    case Expr::OMPIteratorExprClass:
      return Cl::CL_LValue;
  
      // C99 6.5.2.5p5 says that compound literals are lvalues.
      // In C++, they're prvalue temporaries, except for file-scope arrays.
    case Expr::CompoundLiteralExprClass:
      return !E->isLValue() ? ClassifyTemporary(E->getType()) : Cl::CL_LValue;
  
      // Expressions that are prvalues.
    case Expr::CXXBoolLiteralExprClass:
    case Expr::CXXPseudoDestructorExprClass:
    case Expr::UnaryExprOrTypeTraitExprClass:
    case Expr::CXXNewExprClass:
    case Expr::CXXThisExprClass:
    case Expr::CXXNullPtrLiteralExprClass:
    case Expr::ImaginaryLiteralClass:
    case Expr::GNUNullExprClass:
    case Expr::OffsetOfExprClass:
    case Expr::CXXThrowExprClass:
    case Expr::ShuffleVectorExprClass:
    case Expr::ConvertVectorExprClass:
    case Expr::IntegerLiteralClass:
    case Expr::FixedPointLiteralClass:
    case Expr::CharacterLiteralClass:
    case Expr::AddrLabelExprClass:
    case Expr::CXXDeleteExprClass:
    case Expr::ImplicitValueInitExprClass:
    case Expr::BlockExprClass:
    case Expr::FloatingLiteralClass:
    case Expr::CXXNoexceptExprClass:
    case Expr::CXXScalarValueInitExprClass:
    case Expr::TypeTraitExprClass:
    case Expr::ArrayTypeTraitExprClass:
    case Expr::ExpressionTraitExprClass:
    case Expr::ObjCSelectorExprClass:
    case Expr::ObjCProtocolExprClass:
    case Expr::ObjCStringLiteralClass:
    case Expr::ObjCBoxedExprClass:
    case Expr::ObjCArrayLiteralClass:
    case Expr::ObjCDictionaryLiteralClass:
    case Expr::ObjCBoolLiteralExprClass:
    case Expr::ObjCAvailabilityCheckExprClass:
    case Expr::ParenListExprClass:
    case Expr::SizeOfPackExprClass:
    case Expr::SubstNonTypeTemplateParmPackExprClass:
    case Expr::AsTypeExprClass:
    case Expr::ObjCIndirectCopyRestoreExprClass:
    case Expr::AtomicExprClass:
    case Expr::CXXFoldExprClass:
    case Expr::ArrayInitLoopExprClass:
    case Expr::ArrayInitIndexExprClass:
    case Expr::NoInitExprClass:
    case Expr::DesignatedInitUpdateExprClass:
    case Expr::SourceLocExprClass:
    case Expr::ConceptSpecializationExprClass:
    case Expr::RequiresExprClass:
      return Cl::CL_PRValue;
  
    case Expr::ConstantExprClass:
      return ClassifyInternal(Ctx, cast<ConstantExpr>(E)->getSubExpr());
  
      // Next come the complicated cases.
    case Expr::SubstNonTypeTemplateParmExprClass:
      return ClassifyInternal(Ctx,
                   cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
  
      // C, C++98 [expr.sub]p1: The result is an lvalue of type "T".
      // C++11 (DR1213): in the case of an array operand, the result is an lvalue
      //                 if that operand is an lvalue and an xvalue otherwise.
      // Subscripting vector types is more like member access.
    case Expr::ArraySubscriptExprClass:
      if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
        return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
      if (Lang.CPlusPlus11) {
        // Step over the array-to-pointer decay if present, but not over the
        // temporary materialization.
        auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts();
        if (Base->getType()->isArrayType())
          return ClassifyInternal(Ctx, Base);
      }
      return Cl::CL_LValue;
  
      // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
      //   function or variable and a prvalue otherwise.
    case Expr::DeclRefExprClass:
      if (E->getType() == Ctx.UnknownAnyTy)
        return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
                 ? Cl::CL_PRValue : Cl::CL_LValue;
      return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
  
      // Member access is complex.
    case Expr::MemberExprClass:
      return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
  
    case Expr::UnaryOperatorClass:
      switch (cast<UnaryOperator>(E)->getOpcode()) {
        // C++ [expr.unary.op]p1: The unary * operator performs indirection:
        //   [...] the result is an lvalue referring to the object or function
        //   to which the expression points.
      case UO_Deref:
        return Cl::CL_LValue;
  
        // GNU extensions, simply look through them.
      case UO_Extension:
        return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
  
      // Treat _Real and _Imag basically as if they were member
      // expressions:  l-value only if the operand is a true l-value.
      case UO_Real:
      case UO_Imag: {
        const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
        Cl::Kinds K = ClassifyInternal(Ctx, Op);
        if (K != Cl::CL_LValue) return K;
  
        if (isa<ObjCPropertyRefExpr>(Op))
          return Cl::CL_SubObjCPropertySetting;
        return Cl::CL_LValue;
      }
  
        // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
        //   lvalue, [...]
        // Not so in C.
      case UO_PreInc:
      case UO_PreDec:
        return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
  
      default:
        return Cl::CL_PRValue;
      }
  
    case Expr::OpaqueValueExprClass:
      return ClassifyExprValueKind(Lang, E, E->getValueKind());
  
      // Pseudo-object expressions can produce l-values with reference magic.
    case Expr::PseudoObjectExprClass:
      return ClassifyExprValueKind(Lang, E,
                                   cast<PseudoObjectExpr>(E)->getValueKind());
  
      // Implicit casts are lvalues if they're lvalue casts. Other than that, we
      // only specifically record class temporaries.
    case Expr::ImplicitCastExprClass:
      return ClassifyExprValueKind(Lang, E, E->getValueKind());
  
      // C++ [expr.prim.general]p4: The presence of parentheses does not affect
      //   whether the expression is an lvalue.
    case Expr::ParenExprClass:
      return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
  
      // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
      // or a void expression if its result expression is, respectively, an
      // lvalue, a function designator, or a void expression.
    case Expr::GenericSelectionExprClass:
      if (cast<GenericSelectionExpr>(E)->isResultDependent())
        return Cl::CL_PRValue;
      return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
  
    case Expr::BinaryOperatorClass:
    case Expr::CompoundAssignOperatorClass:
      // C doesn't have any binary expressions that are lvalues.
      if (Lang.CPlusPlus)
        return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
      return Cl::CL_PRValue;
  
    case Expr::CallExprClass:
    case Expr::CXXOperatorCallExprClass:
    case Expr::CXXMemberCallExprClass:
    case Expr::UserDefinedLiteralClass:
    case Expr::CUDAKernelCallExprClass:
      return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));
  
    case Expr::CXXRewrittenBinaryOperatorClass:
      return ClassifyInternal(
          Ctx, cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm());
  
      // __builtin_choose_expr is equivalent to the chosen expression.
    case Expr::ChooseExprClass:
      return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
  
      // Extended vector element access is an lvalue unless there are duplicates
      // in the shuffle expression.
    case Expr::ExtVectorElementExprClass:
      if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
        return Cl::CL_DuplicateVectorComponents;
      if (cast<ExtVectorElementExpr>(E)->isArrow())
        return Cl::CL_LValue;
      return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
  
      // Simply look at the actual default argument.
    case Expr::CXXDefaultArgExprClass:
      return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
  
      // Same idea for default initializers.
    case Expr::CXXDefaultInitExprClass:
      return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
  
      // Same idea for temporary binding.
    case Expr::CXXBindTemporaryExprClass:
      return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
  
      // And the cleanups guard.
    case Expr::ExprWithCleanupsClass:
      return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
  
      // Casts depend completely on the target type. All casts work the same.
    case Expr::CStyleCastExprClass:
    case Expr::CXXFunctionalCastExprClass:
    case Expr::CXXStaticCastExprClass:
    case Expr::CXXDynamicCastExprClass:
    case Expr::CXXReinterpretCastExprClass:
    case Expr::CXXConstCastExprClass:
    case Expr::ObjCBridgedCastExprClass:
    case Expr::BuiltinBitCastExprClass:
      // Only in C++ can casts be interesting at all.
      if (!Lang.CPlusPlus) return Cl::CL_PRValue;
      return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
  
    case Expr::CXXUnresolvedConstructExprClass:
      return ClassifyUnnamed(Ctx,
                        cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
  
    case Expr::BinaryConditionalOperatorClass: {
      if (!Lang.CPlusPlus) return Cl::CL_PRValue;
      const auto *co = cast<BinaryConditionalOperator>(E);
      return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
    }
  
    case Expr::ConditionalOperatorClass: {
      // Once again, only C++ is interesting.
      if (!Lang.CPlusPlus) return Cl::CL_PRValue;
      const auto *co = cast<ConditionalOperator>(E);
      return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
    }
  
      // ObjC message sends are effectively function calls, if the target function
      // is known.
    case Expr::ObjCMessageExprClass:
      if (const ObjCMethodDecl *Method =
            cast<ObjCMessageExpr>(E)->getMethodDecl()) {
        Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType());
        return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
      }
      return Cl::CL_PRValue;
  
      // Some C++ expressions are always class temporaries.
    case Expr::CXXConstructExprClass:
    case Expr::CXXInheritedCtorInitExprClass:
    case Expr::CXXTemporaryObjectExprClass:
    case Expr::LambdaExprClass:
    case Expr::CXXStdInitializerListExprClass:
      return Cl::CL_ClassTemporary;
  
    case Expr::VAArgExprClass:
      return ClassifyUnnamed(Ctx, E->getType());
  
    case Expr::DesignatedInitExprClass:
      return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
  
    case Expr::StmtExprClass: {
      const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
      if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
        return ClassifyUnnamed(Ctx, LastExpr->getType());
      return Cl::CL_PRValue;
    }
  
    case Expr::PackExpansionExprClass:
      return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
  
    case Expr::MaterializeTemporaryExprClass:
      return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
                ? Cl::CL_LValue
                : Cl::CL_XValue;
  
    case Expr::InitListExprClass:
      // An init list can be an lvalue if it is bound to a reference and
      // contains only one element. In that case, we look at that element
      // for an exact classification. Init list creation takes care of the
      // value kind for us, so we only need to fine-tune.
      if (E->isRValue())
        return ClassifyExprValueKind(Lang, E, E->getValueKind());
      assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
             "Only 1-element init lists can be glvalues.");
      return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
  
    case Expr::CoawaitExprClass:
    case Expr::CoyieldExprClass:
      return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr());
    }
  
    llvm_unreachable("unhandled expression kind in classification");
  }
  
  /// ClassifyDecl - Return the classification of an expression referencing the
  /// given declaration.
  static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
    // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
    //   function, variable, or data member and a prvalue otherwise.
    // In C, functions are not lvalues.
    // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
    // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
    // special-case this.
  
    if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
      return Cl::CL_MemberFunction;
  
    bool islvalue;
    if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D))
      islvalue = NTTParm->getType()->isReferenceType();
    else
      islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
                 isa<IndirectFieldDecl>(D) ||
                 isa<BindingDecl>(D) ||
                 isa<MSGuidDecl>(D) ||
                 (Ctx.getLangOpts().CPlusPlus &&
                  (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) ||
                   isa<FunctionTemplateDecl>(D)));
  
    return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
  }
  
  /// ClassifyUnnamed - Return the classification of an expression yielding an
  /// unnamed value of the given type. This applies in particular to function
  /// calls and casts.
  static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {
    // In C, function calls are always rvalues.
    if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
  
    // C++ [expr.call]p10: A function call is an lvalue if the result type is an
    //   lvalue reference type or an rvalue reference to function type, an xvalue
    //   if the result type is an rvalue reference to object type, and a prvalue
    //   otherwise.
    if (T->isLValueReferenceType())
      return Cl::CL_LValue;
    const auto *RV = T->getAs<RValueReferenceType>();
    if (!RV) // Could still be a class temporary, though.
      return ClassifyTemporary(T);
  
    return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
  }
  
  static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
    if (E->getType() == Ctx.UnknownAnyTy)
      return (isa<FunctionDecl>(E->getMemberDecl())
                ? Cl::CL_PRValue : Cl::CL_LValue);
  
    // Handle C first, it's easier.
    if (!Ctx.getLangOpts().CPlusPlus) {
      // C99 6.5.2.3p3
      // For dot access, the expression is an lvalue if the first part is. For
      // arrow access, it always is an lvalue.
      if (E->isArrow())
        return Cl::CL_LValue;
      // ObjC property accesses are not lvalues, but get special treatment.
      Expr *Base = E->getBase()->IgnoreParens();
      if (isa<ObjCPropertyRefExpr>(Base))
        return Cl::CL_SubObjCPropertySetting;
      return ClassifyInternal(Ctx, Base);
    }
  
    NamedDecl *Member = E->getMemberDecl();
    // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
    // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
    //   E1.E2 is an lvalue.
    if (const auto *Value = dyn_cast<ValueDecl>(Member))
      if (Value->getType()->isReferenceType())
        return Cl::CL_LValue;
  
    //   Otherwise, one of the following rules applies.
    //   -- If E2 is a static member [...] then E1.E2 is an lvalue.
    if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
      return Cl::CL_LValue;
  
    //   -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
    //      E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
    //      otherwise, it is a prvalue.
    if (isa<FieldDecl>(Member)) {
      // *E1 is an lvalue
      if (E->isArrow())
        return Cl::CL_LValue;
      Expr *Base = E->getBase()->IgnoreParenImpCasts();
      if (isa<ObjCPropertyRefExpr>(Base))
        return Cl::CL_SubObjCPropertySetting;
      return ClassifyInternal(Ctx, E->getBase());
    }
  
    //   -- If E2 is a [...] member function, [...]
    //      -- If it refers to a static member function [...], then E1.E2 is an
    //         lvalue; [...]
    //      -- Otherwise [...] E1.E2 is a prvalue.
    if (const auto *Method = dyn_cast<CXXMethodDecl>(Member))
      return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
  
    //   -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
    // So is everything else we haven't handled yet.
    return Cl::CL_PRValue;
  }
  
  static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) {
    assert(Ctx.getLangOpts().CPlusPlus &&
           "This is only relevant for C++.");
    // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
    // Except we override this for writes to ObjC properties.
    if (E->isAssignmentOp())
      return (E->getLHS()->getObjectKind() == OK_ObjCProperty
                ? Cl::CL_PRValue : Cl::CL_LValue);
  
    // C++ [expr.comma]p1: the result is of the same value category as its right
    //   operand, [...].
    if (E->getOpcode() == BO_Comma)
      return ClassifyInternal(Ctx, E->getRHS());
  
    // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
    //   is a pointer to a data member is of the same value category as its first
    //   operand.
    if (E->getOpcode() == BO_PtrMemD)
      return (E->getType()->isFunctionType() ||
              E->hasPlaceholderType(BuiltinType::BoundMember))
               ? Cl::CL_MemberFunction
               : ClassifyInternal(Ctx, E->getLHS());
  
    // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
    //   second operand is a pointer to data member and a prvalue otherwise.
    if (E->getOpcode() == BO_PtrMemI)
      return (E->getType()->isFunctionType() ||
              E->hasPlaceholderType(BuiltinType::BoundMember))
               ? Cl::CL_MemberFunction
               : Cl::CL_LValue;
  
    // All other binary operations are prvalues.
    return Cl::CL_PRValue;
  }
  
  static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
                                       const Expr *False) {
    assert(Ctx.getLangOpts().CPlusPlus &&
           "This is only relevant for C++.");
  
    // C++ [expr.cond]p2
    //   If either the second or the third operand has type (cv) void,
    //   one of the following shall hold:
    if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
      // The second or the third operand (but not both) is a (possibly
      // parenthesized) throw-expression; the result is of the [...] value
      // category of the other.
      bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());
      bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());
      if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
                                             : (FalseIsThrow ? True : nullptr))
        return ClassifyInternal(Ctx, NonThrow);
  
      //   [Otherwise] the result [...] is a prvalue.
      return Cl::CL_PRValue;
    }
  
    // Note that at this point, we have already performed all conversions
    // according to [expr.cond]p3.
    // C++ [expr.cond]p4: If the second and third operands are glvalues of the
    //   same value category [...], the result is of that [...] value category.
    // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
    Cl::Kinds LCl = ClassifyInternal(Ctx, True),
              RCl = ClassifyInternal(Ctx, False);
    return LCl == RCl ? LCl : Cl::CL_PRValue;
  }
  
  static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
                                         Cl::Kinds Kind, SourceLocation &Loc) {
    // As a general rule, we only care about lvalues. But there are some rvalues
    // for which we want to generate special results.
    if (Kind == Cl::CL_PRValue) {
      // For the sake of better diagnostics, we want to specifically recognize
      // use of the GCC cast-as-lvalue extension.
      if (const auto *CE = dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
        if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
          Loc = CE->getExprLoc();
          return Cl::CM_LValueCast;
        }
      }
    }
    if (Kind != Cl::CL_LValue)
      return Cl::CM_RValue;
  
    // This is the lvalue case.
    // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
    if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
      return Cl::CM_Function;
  
    // Assignment to a property in ObjC is an implicit setter access. But a
    // setter might not exist.
    if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
      if (Expr->isImplicitProperty() &&
          Expr->getImplicitPropertySetter() == nullptr)
        return Cl::CM_NoSetterProperty;
    }
  
    CanQualType CT = Ctx.getCanonicalType(E->getType());
    // Const stuff is obviously not modifiable.
    if (CT.isConstQualified())
      return Cl::CM_ConstQualified;
    if (Ctx.getLangOpts().OpenCL &&
        CT.getQualifiers().getAddressSpace() == LangAS::opencl_constant)
      return Cl::CM_ConstAddrSpace;
  
    // Arrays are not modifiable, only their elements are.
    if (CT->isArrayType())
      return Cl::CM_ArrayType;
    // Incomplete types are not modifiable.
    if (CT->isIncompleteType())
      return Cl::CM_IncompleteType;
  
    // Records with any const fields (recursively) are not modifiable.
    if (const RecordType *R = CT->getAs<RecordType>())
      if (R->hasConstFields())
        return Cl::CM_ConstQualifiedField;
  
    return Cl::CM_Modifiable;
  }
  
  Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {
    Classification VC = Classify(Ctx);
    switch (VC.getKind()) {
    case Cl::CL_LValue: return LV_Valid;
    case Cl::CL_XValue: return LV_InvalidExpression;
    case Cl::CL_Function: return LV_NotObjectType;
    case Cl::CL_Void: return LV_InvalidExpression;
    case Cl::CL_AddressableVoid: return LV_IncompleteVoidType;
    case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents;
    case Cl::CL_MemberFunction: return LV_MemberFunction;
    case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;
    case Cl::CL_ClassTemporary: return LV_ClassTemporary;
    case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;
    case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;
    case Cl::CL_PRValue: return LV_InvalidExpression;
    }
    llvm_unreachable("Unhandled kind");
  }
  
  Expr::isModifiableLvalueResult
  Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {
    SourceLocation dummy;
    Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
    switch (VC.getKind()) {
    case Cl::CL_LValue: break;
    case Cl::CL_XValue: return MLV_InvalidExpression;
    case Cl::CL_Function: return MLV_NotObjectType;
    case Cl::CL_Void: return MLV_InvalidExpression;
    case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType;
    case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents;
    case Cl::CL_MemberFunction: return MLV_MemberFunction;
    case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;
    case Cl::CL_ClassTemporary: return MLV_ClassTemporary;
    case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;
    case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;
    case Cl::CL_PRValue:
      return VC.getModifiable() == Cl::CM_LValueCast ?
        MLV_LValueCast : MLV_InvalidExpression;
    }
    assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
    switch (VC.getModifiable()) {
    case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
    case Cl::CM_Modifiable: return MLV_Valid;
    case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
    case Cl::CM_Function: return MLV_NotObjectType;
    case Cl::CM_LValueCast:
      llvm_unreachable("CM_LValueCast and CL_LValue don't match");
    case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;
    case Cl::CM_ConstQualified: return MLV_ConstQualified;
    case Cl::CM_ConstQualifiedField: return MLV_ConstQualifiedField;
    case Cl::CM_ConstAddrSpace: return MLV_ConstAddrSpace;
    case Cl::CM_ArrayType: return MLV_ArrayType;
    case Cl::CM_IncompleteType: return MLV_IncompleteType;
    }
    llvm_unreachable("Unhandled modifiable type");
  }
  