text: //=== RecordLayoutBuilder.cpp - Helper class for building record layouts ---==//
  //
  // 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
  //
  //===----------------------------------------------------------------------===//
  
  #include "clang/AST/RecordLayout.h"
  #include "clang/AST/ASTContext.h"
  #include "clang/AST/ASTDiagnostic.h"
  #include "clang/AST/Attr.h"
  #include "clang/AST/CXXInheritance.h"
  #include "clang/AST/Decl.h"
  #include "clang/AST/DeclCXX.h"
  #include "clang/AST/DeclObjC.h"
  #include "clang/AST/Expr.h"
  #include "clang/Basic/TargetInfo.h"
  #include "llvm/ADT/SmallSet.h"
  #include "llvm/Support/Format.h"
  #include "llvm/Support/MathExtras.h"
  
  using namespace clang;
  
  namespace {
  
  /// BaseSubobjectInfo - Represents a single base subobject in a complete class.
  /// For a class hierarchy like
  ///
  /// class A { };
  /// class B : A { };
  /// class C : A, B { };
  ///
  /// The BaseSubobjectInfo graph for C will have three BaseSubobjectInfo
  /// instances, one for B and two for A.
  ///
  /// If a base is virtual, it will only have one BaseSubobjectInfo allocated.
  struct BaseSubobjectInfo {
    /// Class - The class for this base info.
    const CXXRecordDecl *Class;
  
    /// IsVirtual - Whether the BaseInfo represents a virtual base or not.
    bool IsVirtual;
  
    /// Bases - Information about the base subobjects.
    SmallVector<BaseSubobjectInfo*, 4> Bases;
  
    /// PrimaryVirtualBaseInfo - Holds the base info for the primary virtual base
    /// of this base info (if one exists).
    BaseSubobjectInfo *PrimaryVirtualBaseInfo;
  
    // FIXME: Document.
    const BaseSubobjectInfo *Derived;
  };
  
  /// Externally provided layout. Typically used when the AST source, such
  /// as DWARF, lacks all the information that was available at compile time, such
  /// as alignment attributes on fields and pragmas in effect.
  struct ExternalLayout {
    ExternalLayout() : Size(0), Align(0) {}
  
    /// Overall record size in bits.
    uint64_t Size;
  
    /// Overall record alignment in bits.
    uint64_t Align;
  
    /// Record field offsets in bits.
    llvm::DenseMap<const FieldDecl *, uint64_t> FieldOffsets;
  
    /// Direct, non-virtual base offsets.
    llvm::DenseMap<const CXXRecordDecl *, CharUnits> BaseOffsets;
  
    /// Virtual base offsets.
    llvm::DenseMap<const CXXRecordDecl *, CharUnits> VirtualBaseOffsets;
  
    /// Get the offset of the given field. The external source must provide
    /// entries for all fields in the record.
    uint64_t getExternalFieldOffset(const FieldDecl *FD) {
      assert(FieldOffsets.count(FD) &&
             "Field does not have an external offset");
      return FieldOffsets[FD];
    }
  
    bool getExternalNVBaseOffset(const CXXRecordDecl *RD, CharUnits &BaseOffset) {
      auto Known = BaseOffsets.find(RD);
      if (Known == BaseOffsets.end())
        return false;
      BaseOffset = Known->second;
      return true;
    }
  
    bool getExternalVBaseOffset(const CXXRecordDecl *RD, CharUnits &BaseOffset) {
      auto Known = VirtualBaseOffsets.find(RD);
      if (Known == VirtualBaseOffsets.end())
        return false;
      BaseOffset = Known->second;
      return true;
    }
  };
  
  /// EmptySubobjectMap - Keeps track of which empty subobjects exist at different
  /// offsets while laying out a C++ class.
  class EmptySubobjectMap {
    const ASTContext &Context;
    uint64_t CharWidth;
  
    /// Class - The class whose empty entries we're keeping track of.
    const CXXRecordDecl *Class;
  
    /// EmptyClassOffsets - A map from offsets to empty record decls.
    typedef llvm::TinyPtrVector<const CXXRecordDecl *> ClassVectorTy;
    typedef llvm::DenseMap<CharUnits, ClassVectorTy> EmptyClassOffsetsMapTy;
    EmptyClassOffsetsMapTy EmptyClassOffsets;
  
    /// MaxEmptyClassOffset - The highest offset known to contain an empty
    /// base subobject.
    CharUnits MaxEmptyClassOffset;
  
    /// ComputeEmptySubobjectSizes - Compute the size of the largest base or
    /// member subobject that is empty.
    void ComputeEmptySubobjectSizes();
  
    void AddSubobjectAtOffset(const CXXRecordDecl *RD, CharUnits Offset);
  
    void UpdateEmptyBaseSubobjects(const BaseSubobjectInfo *Info,
                                   CharUnits Offset, bool PlacingEmptyBase);
  
    void UpdateEmptyFieldSubobjects(const CXXRecordDecl *RD,
                                    const CXXRecordDecl *Class, CharUnits Offset,
                                    bool PlacingOverlappingField);
    void UpdateEmptyFieldSubobjects(const FieldDecl *FD, CharUnits Offset,
                                    bool PlacingOverlappingField);
  
    /// AnyEmptySubobjectsBeyondOffset - Returns whether there are any empty
    /// subobjects beyond the given offset.
    bool AnyEmptySubobjectsBeyondOffset(CharUnits Offset) const {
      return Offset <= MaxEmptyClassOffset;
    }
  
    CharUnits
    getFieldOffset(const ASTRecordLayout &Layout, unsigned FieldNo) const {
      uint64_t FieldOffset = Layout.getFieldOffset(FieldNo);
      assert(FieldOffset % CharWidth == 0 &&
             "Field offset not at char boundary!");
  
      return Context.toCharUnitsFromBits(FieldOffset);
    }
  
  protected:
    bool CanPlaceSubobjectAtOffset(const CXXRecordDecl *RD,
                                   CharUnits Offset) const;
  
    bool CanPlaceBaseSubobjectAtOffset(const BaseSubobjectInfo *Info,
                                       CharUnits Offset);
  
    bool CanPlaceFieldSubobjectAtOffset(const CXXRecordDecl *RD,
                                        const CXXRecordDecl *Class,
                                        CharUnits Offset) const;
    bool CanPlaceFieldSubobjectAtOffset(const FieldDecl *FD,
                                        CharUnits Offset) const;
  
  public:
    /// This holds the size of the largest empty subobject (either a base
    /// or a member). Will be zero if the record being built doesn't contain
    /// any empty classes.
    CharUnits SizeOfLargestEmptySubobject;
  
    EmptySubobjectMap(const ASTContext &Context, const CXXRecordDecl *Class)
    : Context(Context), CharWidth(Context.getCharWidth()), Class(Class) {
        ComputeEmptySubobjectSizes();
    }
  
    /// CanPlaceBaseAtOffset - Return whether the given base class can be placed
    /// at the given offset.
    /// Returns false if placing the record will result in two components
    /// (direct or indirect) of the same type having the same offset.
    bool CanPlaceBaseAtOffset(const BaseSubobjectInfo *Info,
                              CharUnits Offset);
  
    /// CanPlaceFieldAtOffset - Return whether a field can be placed at the given
    /// offset.
    bool CanPlaceFieldAtOffset(const FieldDecl *FD, CharUnits Offset);
  };
  
  void EmptySubobjectMap::ComputeEmptySubobjectSizes() {
    // Check the bases.
    for (const CXXBaseSpecifier &Base : Class->bases()) {
      const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
  
      CharUnits EmptySize;
      const ASTRecordLayout &Layout = Context.getASTRecordLayout(BaseDecl);
      if (BaseDecl->isEmpty()) {
        // If the class decl is empty, get its size.
        EmptySize = Layout.getSize();
      } else {
        // Otherwise, we get the largest empty subobject for the decl.
        EmptySize = Layout.getSizeOfLargestEmptySubobject();
      }
  
      if (EmptySize > SizeOfLargestEmptySubobject)
        SizeOfLargestEmptySubobject = EmptySize;
    }
  
    // Check the fields.
    for (const FieldDecl *FD : Class->fields()) {
      const RecordType *RT =
          Context.getBaseElementType(FD->getType())->getAs<RecordType>();
  
      // We only care about record types.
      if (!RT)
        continue;
  
      CharUnits EmptySize;
      const CXXRecordDecl *MemberDecl = RT->getAsCXXRecordDecl();
      const ASTRecordLayout &Layout = Context.getASTRecordLayout(MemberDecl);
      if (MemberDecl->isEmpty()) {
        // If the class decl is empty, get its size.
        EmptySize = Layout.getSize();
      } else {
        // Otherwise, we get the largest empty subobject for the decl.
        EmptySize = Layout.getSizeOfLargestEmptySubobject();
      }
  
      if (EmptySize > SizeOfLargestEmptySubobject)
        SizeOfLargestEmptySubobject = EmptySize;
    }
  }
  
  bool
  EmptySubobjectMap::CanPlaceSubobjectAtOffset(const CXXRecordDecl *RD,
                                               CharUnits Offset) const {
    // We only need to check empty bases.
    if (!RD->isEmpty())
      return true;
  
    EmptyClassOffsetsMapTy::const_iterator I = EmptyClassOffsets.find(Offset);
    if (I == EmptyClassOffsets.end())
      return true;
  
    const ClassVectorTy &Classes = I->second;
    if (llvm::find(Classes, RD) == Classes.end())
      return true;
  
    // There is already an empty class of the same type at this offset.
    return false;
  }
  
  void EmptySubobjectMap::AddSubobjectAtOffset(const CXXRecordDecl *RD,
                                               CharUnits Offset) {
    // We only care about empty bases.
    if (!RD->isEmpty())
      return;
  
    // If we have empty structures inside a union, we can assign both
    // the same offset. Just avoid pushing them twice in the list.
    ClassVectorTy &Classes = EmptyClassOffsets[Offset];
    if (llvm::is_contained(Classes, RD))
      return;
  
    Classes.push_back(RD);
  
    // Update the empty class offset.
    if (Offset > MaxEmptyClassOffset)
      MaxEmptyClassOffset = Offset;
  }
  
  bool
  EmptySubobjectMap::CanPlaceBaseSubobjectAtOffset(const BaseSubobjectInfo *Info,
                                                   CharUnits Offset) {
    // We don't have to keep looking past the maximum offset that's known to
    // contain an empty class.
    if (!AnyEmptySubobjectsBeyondOffset(Offset))
      return true;
  
    if (!CanPlaceSubobjectAtOffset(Info->Class, Offset))
      return false;
  
    // Traverse all non-virtual bases.
    const ASTRecordLayout &Layout = Context.getASTRecordLayout(Info->Class);
    for (const BaseSubobjectInfo *Base : Info->Bases) {
      if (Base->IsVirtual)
        continue;
  
      CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(Base->Class);
  
      if (!CanPlaceBaseSubobjectAtOffset(Base, BaseOffset))
        return false;
    }
  
    if (Info->PrimaryVirtualBaseInfo) {
      BaseSubobjectInfo *PrimaryVirtualBaseInfo = Info->PrimaryVirtualBaseInfo;
  
      if (Info == PrimaryVirtualBaseInfo->Derived) {
        if (!CanPlaceBaseSubobjectAtOffset(PrimaryVirtualBaseInfo, Offset))
          return false;
      }
    }
  
    // Traverse all member variables.
    unsigned FieldNo = 0;
    for (CXXRecordDecl::field_iterator I = Info->Class->field_begin(),
         E = Info->Class->field_end(); I != E; ++I, ++FieldNo) {
      if (I->isBitField())
        continue;
  
      CharUnits FieldOffset = Offset + getFieldOffset(Layout, FieldNo);
      if (!CanPlaceFieldSubobjectAtOffset(*I, FieldOffset))
        return false;
    }
  
    return true;
  }
  
  void EmptySubobjectMap::UpdateEmptyBaseSubobjects(const BaseSubobjectInfo *Info,
                                                    CharUnits Offset,
                                                    bool PlacingEmptyBase) {
    if (!PlacingEmptyBase && Offset >= SizeOfLargestEmptySubobject) {
      // We know that the only empty subobjects that can conflict with empty
      // subobject of non-empty bases, are empty bases that can be placed at
      // offset zero. Because of this, we only need to keep track of empty base
      // subobjects with offsets less than the size of the largest empty
      // subobject for our class.
      return;
    }
  
    AddSubobjectAtOffset(Info->Class, Offset);
  
    // Traverse all non-virtual bases.
    const ASTRecordLayout &Layout = Context.getASTRecordLayout(Info->Class);
    for (const BaseSubobjectInfo *Base : Info->Bases) {
      if (Base->IsVirtual)
        continue;
  
      CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(Base->Class);
      UpdateEmptyBaseSubobjects(Base, BaseOffset, PlacingEmptyBase);
    }
  
    if (Info->PrimaryVirtualBaseInfo) {
      BaseSubobjectInfo *PrimaryVirtualBaseInfo = Info->PrimaryVirtualBaseInfo;
  
      if (Info == PrimaryVirtualBaseInfo->Derived)
        UpdateEmptyBaseSubobjects(PrimaryVirtualBaseInfo, Offset,
                                  PlacingEmptyBase);
    }
  
    // Traverse all member variables.
    unsigned FieldNo = 0;
    for (CXXRecordDecl::field_iterator I = Info->Class->field_begin(),
         E = Info->Class->field_end(); I != E; ++I, ++FieldNo) {
      if (I->isBitField())
        continue;
  
      CharUnits FieldOffset = Offset + getFieldOffset(Layout, FieldNo);
      UpdateEmptyFieldSubobjects(*I, FieldOffset, PlacingEmptyBase);
    }
  }
  
  bool EmptySubobjectMap::CanPlaceBaseAtOffset(const BaseSubobjectInfo *Info,
                                               CharUnits Offset) {
    // If we know this class doesn't have any empty subobjects we don't need to
    // bother checking.
    if (SizeOfLargestEmptySubobject.isZero())
      return true;
  
    if (!CanPlaceBaseSubobjectAtOffset(Info, Offset))
      return false;
  
    // We are able to place the base at this offset. Make sure to update the
    // empty base subobject map.
    UpdateEmptyBaseSubobjects(Info, Offset, Info->Class->isEmpty());
    return true;
  }
  
  bool
  EmptySubobjectMap::CanPlaceFieldSubobjectAtOffset(const CXXRecordDecl *RD,
                                                    const CXXRecordDecl *Class,
                                                    CharUnits Offset) const {
    // We don't have to keep looking past the maximum offset that's known to
    // contain an empty class.
    if (!AnyEmptySubobjectsBeyondOffset(Offset))
      return true;
  
    if (!CanPlaceSubobjectAtOffset(RD, Offset))
      return false;
  
    const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
  
    // Traverse all non-virtual bases.
    for (const CXXBaseSpecifier &Base : RD->bases()) {
      if (Base.isVirtual())
        continue;
  
      const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
  
      CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(BaseDecl);
      if (!CanPlaceFieldSubobjectAtOffset(BaseDecl, Class, BaseOffset))
        return false;
    }
  
    if (RD == Class) {
      // This is the most derived class, traverse virtual bases as well.
      for (const CXXBaseSpecifier &Base : RD->vbases()) {
        const CXXRecordDecl *VBaseDecl = Base.getType()->getAsCXXRecordDecl();
  
        CharUnits VBaseOffset = Offset + Layout.getVBaseClassOffset(VBaseDecl);
        if (!CanPlaceFieldSubobjectAtOffset(VBaseDecl, Class, VBaseOffset))
          return false;
      }
    }
  
    // Traverse all member variables.
    unsigned FieldNo = 0;
    for (CXXRecordDecl::field_iterator I = RD->field_begin(), E = RD->field_end();
         I != E; ++I, ++FieldNo) {
      if (I->isBitField())
        continue;
  
      CharUnits FieldOffset = Offset + getFieldOffset(Layout, FieldNo);
  
      if (!CanPlaceFieldSubobjectAtOffset(*I, FieldOffset))
        return false;
    }
  
    return true;
  }
  
  bool
  EmptySubobjectMap::CanPlaceFieldSubobjectAtOffset(const FieldDecl *FD,
                                                    CharUnits Offset) const {
    // We don't have to keep looking past the maximum offset that's known to
    // contain an empty class.
    if (!AnyEmptySubobjectsBeyondOffset(Offset))
      return true;
  
    QualType T = FD->getType();
    if (const CXXRecordDecl *RD = T->getAsCXXRecordDecl())
      return CanPlaceFieldSubobjectAtOffset(RD, RD, Offset);
  
    // If we have an array type we need to look at every element.
    if (const ConstantArrayType *AT = Context.getAsConstantArrayType(T)) {
      QualType ElemTy = Context.getBaseElementType(AT);
      const RecordType *RT = ElemTy->getAs<RecordType>();
      if (!RT)
        return true;
  
      const CXXRecordDecl *RD = RT->getAsCXXRecordDecl();
      const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
  
      uint64_t NumElements = Context.getConstantArrayElementCount(AT);
      CharUnits ElementOffset = Offset;
      for (uint64_t I = 0; I != NumElements; ++I) {
        // We don't have to keep looking past the maximum offset that's known to
        // contain an empty class.
        if (!AnyEmptySubobjectsBeyondOffset(ElementOffset))
          return true;
  
        if (!CanPlaceFieldSubobjectAtOffset(RD, RD, ElementOffset))
          return false;
  
        ElementOffset += Layout.getSize();
      }
    }
  
    return true;
  }
  
  bool
  EmptySubobjectMap::CanPlaceFieldAtOffset(const FieldDecl *FD,
                                           CharUnits Offset) {
    if (!CanPlaceFieldSubobjectAtOffset(FD, Offset))
      return false;
  
    // We are able to place the member variable at this offset.
    // Make sure to update the empty field subobject map.
    UpdateEmptyFieldSubobjects(FD, Offset, FD->hasAttr<NoUniqueAddressAttr>());
    return true;
  }
  
  void EmptySubobjectMap::UpdateEmptyFieldSubobjects(
      const CXXRecordDecl *RD, const CXXRecordDecl *Class, CharUnits Offset,
      bool PlacingOverlappingField) {
    // We know that the only empty subobjects that can conflict with empty
    // field subobjects are subobjects of empty bases and potentially-overlapping
    // fields that can be placed at offset zero. Because of this, we only need to
    // keep track of empty field subobjects with offsets less than the size of
    // the largest empty subobject for our class.
    //
    // (Proof: we will only consider placing a subobject at offset zero or at
    // >= the current dsize. The only cases where the earlier subobject can be
    // placed beyond the end of dsize is if it's an empty base or a
    // potentially-overlapping field.)
    if (!PlacingOverlappingField && Offset >= SizeOfLargestEmptySubobject)
      return;
  
    AddSubobjectAtOffset(RD, Offset);
  
    const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
  
    // Traverse all non-virtual bases.
    for (const CXXBaseSpecifier &Base : RD->bases()) {
      if (Base.isVirtual())
        continue;
  
      const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
  
      CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(BaseDecl);
      UpdateEmptyFieldSubobjects(BaseDecl, Class, BaseOffset,
                                 PlacingOverlappingField);
    }
  
    if (RD == Class) {
      // This is the most derived class, traverse virtual bases as well.
      for (const CXXBaseSpecifier &Base : RD->vbases()) {
        const CXXRecordDecl *VBaseDecl = Base.getType()->getAsCXXRecordDecl();
  
        CharUnits VBaseOffset = Offset + Layout.getVBaseClassOffset(VBaseDecl);
        UpdateEmptyFieldSubobjects(VBaseDecl, Class, VBaseOffset,
                                   PlacingOverlappingField);
      }
    }
  
    // Traverse all member variables.
    unsigned FieldNo = 0;
    for (CXXRecordDecl::field_iterator I = RD->field_begin(), E = RD->field_end();
         I != E; ++I, ++FieldNo) {
      if (I->isBitField())
        continue;
  
      CharUnits FieldOffset = Offset + getFieldOffset(Layout, FieldNo);
  
      UpdateEmptyFieldSubobjects(*I, FieldOffset, PlacingOverlappingField);
    }
  }
  
  void EmptySubobjectMap::UpdateEmptyFieldSubobjects(
      const FieldDecl *FD, CharUnits Offset, bool PlacingOverlappingField) {
    QualType T = FD->getType();
    if (const CXXRecordDecl *RD = T->getAsCXXRecordDecl()) {
      UpdateEmptyFieldSubobjects(RD, RD, Offset, PlacingOverlappingField);
      return;
    }
  
    // If we have an array type we need to update every element.
    if (const ConstantArrayType *AT = Context.getAsConstantArrayType(T)) {
      QualType ElemTy = Context.getBaseElementType(AT);
      const RecordType *RT = ElemTy->getAs<RecordType>();
      if (!RT)
        return;
  
      const CXXRecordDecl *RD = RT->getAsCXXRecordDecl();
      const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
  
      uint64_t NumElements = Context.getConstantArrayElementCount(AT);
      CharUnits ElementOffset = Offset;
  
      for (uint64_t I = 0; I != NumElements; ++I) {
        // We know that the only empty subobjects that can conflict with empty
        // field subobjects are subobjects of empty bases that can be placed at
        // offset zero. Because of this, we only need to keep track of empty field
        // subobjects with offsets less than the size of the largest empty
        // subobject for our class.
        if (!PlacingOverlappingField &&
            ElementOffset >= SizeOfLargestEmptySubobject)
          return;
  
        UpdateEmptyFieldSubobjects(RD, RD, ElementOffset,
                                   PlacingOverlappingField);
        ElementOffset += Layout.getSize();
      }
    }
  }
  
  typedef llvm::SmallPtrSet<const CXXRecordDecl*, 4> ClassSetTy;
  
  class ItaniumRecordLayoutBuilder {
  protected:
    // FIXME: Remove this and make the appropriate fields public.
    friend class clang::ASTContext;
  
    const ASTContext &Context;
  
    EmptySubobjectMap *EmptySubobjects;
  
    /// Size - The current size of the record layout.
    uint64_t Size;
  
    /// Alignment - The current alignment of the record layout.
    CharUnits Alignment;
  
    /// The alignment if attribute packed is not used.
    CharUnits UnpackedAlignment;
  
    /// \brief The maximum of the alignments of top-level members.
    CharUnits UnadjustedAlignment;
  
    SmallVector<uint64_t, 16> FieldOffsets;
  
    /// Whether the external AST source has provided a layout for this
    /// record.
    unsigned UseExternalLayout : 1;
  
    /// Whether we need to infer alignment, even when we have an
    /// externally-provided layout.
    unsigned InferAlignment : 1;
  
    /// Packed - Whether the record is packed or not.
    unsigned Packed : 1;
  
    unsigned IsUnion : 1;
  
    unsigned IsMac68kAlign : 1;
  
    unsigned IsMsStruct : 1;
  
    /// UnfilledBitsInLastUnit - If the last field laid out was a bitfield,
    /// this contains the number of bits in the last unit that can be used for
    /// an adjacent bitfield if necessary.  The unit in question is usually
    /// a byte, but larger units are used if IsMsStruct.
    unsigned char UnfilledBitsInLastUnit;
    /// LastBitfieldTypeSize - If IsMsStruct, represents the size of the type
    /// of the previous field if it was a bitfield.
    unsigned char LastBitfieldTypeSize;
  
    /// MaxFieldAlignment - The maximum allowed field alignment. This is set by
    /// #pragma pack.
    CharUnits MaxFieldAlignment;
  
    /// DataSize - The data size of the record being laid out.
    uint64_t DataSize;
  
    CharUnits NonVirtualSize;
    CharUnits NonVirtualAlignment;
  
    /// If we've laid out a field but not included its tail padding in Size yet,
    /// this is the size up to the end of that field.
    CharUnits PaddedFieldSize;
  
    /// PrimaryBase - the primary base class (if one exists) of the class
    /// we're laying out.
    const CXXRecordDecl *PrimaryBase;
  
    /// PrimaryBaseIsVirtual - Whether the primary base of the class we're laying
    /// out is virtual.
    bool PrimaryBaseIsVirtual;
  
    /// HasOwnVFPtr - Whether the class provides its own vtable/vftbl
    /// pointer, as opposed to inheriting one from a primary base class.
    bool HasOwnVFPtr;
  
    /// the flag of field offset changing due to packed attribute.
    bool HasPackedField;
  
    typedef llvm::DenseMap<const CXXRecordDecl *, CharUnits> BaseOffsetsMapTy;
  
    /// Bases - base classes and their offsets in the record.
    BaseOffsetsMapTy Bases;
  
    // VBases - virtual base classes and their offsets in the record.
    ASTRecordLayout::VBaseOffsetsMapTy VBases;
  
    /// IndirectPrimaryBases - Virtual base classes, direct or indirect, that are
    /// primary base classes for some other direct or indirect base class.
    CXXIndirectPrimaryBaseSet IndirectPrimaryBases;
  
    /// FirstNearlyEmptyVBase - The first nearly empty virtual base class in
    /// inheritance graph order. Used for determining the primary base class.
    const CXXRecordDecl *FirstNearlyEmptyVBase;
  
    /// VisitedVirtualBases - A set of all the visited virtual bases, used to
    /// avoid visiting virtual bases more than once.
    llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedVirtualBases;
  
    /// Valid if UseExternalLayout is true.
    ExternalLayout External;
  
    ItaniumRecordLayoutBuilder(const ASTContext &Context,
                               EmptySubobjectMap *EmptySubobjects)
        : Context(Context), EmptySubobjects(EmptySubobjects), Size(0),
          Alignment(CharUnits::One()), UnpackedAlignment(CharUnits::One()),
          UnadjustedAlignment(CharUnits::One()),
          UseExternalLayout(false), InferAlignment(false), Packed(false),
          IsUnion(false), IsMac68kAlign(false), IsMsStruct(false),
          UnfilledBitsInLastUnit(0), LastBitfieldTypeSize(0),
          MaxFieldAlignment(CharUnits::Zero()), DataSize(0),
          NonVirtualSize(CharUnits::Zero()),
          NonVirtualAlignment(CharUnits::One()),
          PaddedFieldSize(CharUnits::Zero()), PrimaryBase(nullptr),
          PrimaryBaseIsVirtual(false), HasOwnVFPtr(false),
          HasPackedField(false), FirstNearlyEmptyVBase(nullptr) {}
  
    void Layout(const RecordDecl *D);
    void Layout(const CXXRecordDecl *D);
    void Layout(const ObjCInterfaceDecl *D);
  
    void LayoutFields(const RecordDecl *D);
    void LayoutField(const FieldDecl *D, bool InsertExtraPadding);
    void LayoutWideBitField(uint64_t FieldSize, uint64_t TypeSize,
                            bool FieldPacked, const FieldDecl *D);
    void LayoutBitField(const FieldDecl *D);
  
    TargetCXXABI getCXXABI() const {
      return Context.getTargetInfo().getCXXABI();
    }
  
    /// BaseSubobjectInfoAllocator - Allocator for BaseSubobjectInfo objects.
    llvm::SpecificBumpPtrAllocator<BaseSubobjectInfo> BaseSubobjectInfoAllocator;
  
    typedef llvm::DenseMap<const CXXRecordDecl *, BaseSubobjectInfo *>
      BaseSubobjectInfoMapTy;
  
    /// VirtualBaseInfo - Map from all the (direct or indirect) virtual bases
    /// of the class we're laying out to their base subobject info.
    BaseSubobjectInfoMapTy VirtualBaseInfo;
  
    /// NonVirtualBaseInfo - Map from all the direct non-virtual bases of the
    /// class we're laying out to their base subobject info.
    BaseSubobjectInfoMapTy NonVirtualBaseInfo;
  
    /// ComputeBaseSubobjectInfo - Compute the base subobject information for the
    /// bases of the given class.
    void ComputeBaseSubobjectInfo(const CXXRecordDecl *RD);
  
    /// ComputeBaseSubobjectInfo - Compute the base subobject information for a
    /// single class and all of its base classes.
    BaseSubobjectInfo *ComputeBaseSubobjectInfo(const CXXRecordDecl *RD,
                                                bool IsVirtual,
                                                BaseSubobjectInfo *Derived);
  
    /// DeterminePrimaryBase - Determine the primary base of the given class.
    void DeterminePrimaryBase(const CXXRecordDecl *RD);
  
    void SelectPrimaryVBase(const CXXRecordDecl *RD);
  
    void EnsureVTablePointerAlignment(CharUnits UnpackedBaseAlign);
  
    /// LayoutNonVirtualBases - Determines the primary base class (if any) and
    /// lays it out. Will then proceed to lay out all non-virtual base clasess.
    void LayoutNonVirtualBases(const CXXRecordDecl *RD);
  
    /// LayoutNonVirtualBase - Lays out a single non-virtual base.
    void LayoutNonVirtualBase(const BaseSubobjectInfo *Base);
  
    void AddPrimaryVirtualBaseOffsets(const BaseSubobjectInfo *Info,
                                      CharUnits Offset);
  
    /// LayoutVirtualBases - Lays out all the virtual bases.
    void LayoutVirtualBases(const CXXRecordDecl *RD,
                            const CXXRecordDecl *MostDerivedClass);
  
    /// LayoutVirtualBase - Lays out a single virtual base.
    void LayoutVirtualBase(const BaseSubobjectInfo *Base);
  
    /// LayoutBase - Will lay out a base and return the offset where it was
    /// placed, in chars.
    CharUnits LayoutBase(const BaseSubobjectInfo *Base);
  
    /// InitializeLayout - Initialize record layout for the given record decl.
    void InitializeLayout(const Decl *D);
  
    /// FinishLayout - Finalize record layout. Adjust record size based on the
    /// alignment.
    void FinishLayout(const NamedDecl *D);
  
    void UpdateAlignment(CharUnits NewAlignment, CharUnits UnpackedNewAlignment);
    void UpdateAlignment(CharUnits NewAlignment) {
      UpdateAlignment(NewAlignment, NewAlignment);
    }
  
    /// Retrieve the externally-supplied field offset for the given
    /// field.
    ///
    /// \param Field The field whose offset is being queried.
    /// \param ComputedOffset The offset that we've computed for this field.
    uint64_t updateExternalFieldOffset(const FieldDecl *Field,
                                       uint64_t ComputedOffset);
  
    void CheckFieldPadding(uint64_t Offset, uint64_t UnpaddedOffset,
                            uint64_t UnpackedOffset, unsigned UnpackedAlign,
                            bool isPacked, const FieldDecl *D);
  
    DiagnosticBuilder Diag(SourceLocation Loc, unsigned DiagID);
  
    CharUnits getSize() const {
      assert(Size % Context.getCharWidth() == 0);
      return Context.toCharUnitsFromBits(Size);
    }
    uint64_t getSizeInBits() const { return Size; }
  
    void setSize(CharUnits NewSize) { Size = Context.toBits(NewSize); }
    void setSize(uint64_t NewSize) { Size = NewSize; }
  
    CharUnits getAligment() const { return Alignment; }
  
    CharUnits getDataSize() const {
      assert(DataSize % Context.getCharWidth() == 0);
      return Context.toCharUnitsFromBits(DataSize);
    }
    uint64_t getDataSizeInBits() const { return DataSize; }
  
    void setDataSize(CharUnits NewSize) { DataSize = Context.toBits(NewSize); }
    void setDataSize(uint64_t NewSize) { DataSize = NewSize; }
  
    ItaniumRecordLayoutBuilder(const ItaniumRecordLayoutBuilder &) = delete;
    void operator=(const ItaniumRecordLayoutBuilder &) = delete;
  };
  } // end anonymous namespace
  
  void ItaniumRecordLayoutBuilder::SelectPrimaryVBase(const CXXRecordDecl *RD) {
    for (const auto &I : RD->bases()) {
      assert(!I.getType()->isDependentType() &&
             "Cannot layout class with dependent bases.");
  
      const CXXRecordDecl *Base = I.getType()->getAsCXXRecordDecl();
  
      // Check if this is a nearly empty virtual base.
      if (I.isVirtual() && Context.isNearlyEmpty(Base)) {
        // If it's not an indirect primary base, then we've found our primary
        // base.
        if (!IndirectPrimaryBases.count(Base)) {
          PrimaryBase = Base;
          PrimaryBaseIsVirtual = true;
          return;
        }
  
        // Is this the first nearly empty virtual base?
        if (!FirstNearlyEmptyVBase)
          FirstNearlyEmptyVBase = Base;
      }
  
      SelectPrimaryVBase(Base);
      if (PrimaryBase)
        return;
    }
  }
  
  /// DeterminePrimaryBase - Determine the primary base of the given class.
  void ItaniumRecordLayoutBuilder::DeterminePrimaryBase(const CXXRecordDecl *RD) {
    // If the class isn't dynamic, it won't have a primary base.
    if (!RD->isDynamicClass())
      return;
  
    // Compute all the primary virtual bases for all of our direct and
    // indirect bases, and record all their primary virtual base classes.
    RD->getIndirectPrimaryBases(IndirectPrimaryBases);
  
    // If the record has a dynamic base class, attempt to choose a primary base
    // class. It is the first (in direct base class order) non-virtual dynamic
    // base class, if one exists.
    for (const auto &I : RD->bases()) {
      // Ignore virtual bases.
      if (I.isVirtual())
        continue;
  
      const CXXRecordDecl *Base = I.getType()->getAsCXXRecordDecl();
  
      if (Base->isDynamicClass()) {
        // We found it.
        PrimaryBase = Base;
        PrimaryBaseIsVirtual = false;
        return;
      }
    }
  
    // Under the Itanium ABI, if there is no non-virtual primary base class,
    // try to compute the primary virtual base.  The primary virtual base is
    // the first nearly empty virtual base that is not an indirect primary
    // virtual base class, if one exists.
    if (RD->getNumVBases() != 0) {
      SelectPrimaryVBase(RD);
      if (PrimaryBase)
        return;
    }
  
    // Otherwise, it is the first indirect primary base class, if one exists.
    if (FirstNearlyEmptyVBase) {
      PrimaryBase = FirstNearlyEmptyVBase;
      PrimaryBaseIsVirtual = true;
      return;
    }
  
    assert(!PrimaryBase && "Should not get here with a primary base!");
  }
  
  BaseSubobjectInfo *ItaniumRecordLayoutBuilder::ComputeBaseSubobjectInfo(
      const CXXRecordDecl *RD, bool IsVirtual, BaseSubobjectInfo *Derived) {
    BaseSubobjectInfo *Info;
  
    if (IsVirtual) {
      // Check if we already have info about this virtual base.
      BaseSubobjectInfo *&InfoSlot = VirtualBaseInfo[RD];
      if (InfoSlot) {
        assert(InfoSlot->Class == RD && "Wrong class for virtual base info!");
        return InfoSlot;
      }
  
      // We don't, create it.
      InfoSlot = new (BaseSubobjectInfoAllocator.Allocate()) BaseSubobjectInfo;
      Info = InfoSlot;
    } else {
      Info = new (BaseSubobjectInfoAllocator.Allocate()) BaseSubobjectInfo;
    }
  
    Info->Class = RD;
    Info->IsVirtual = IsVirtual;
    Info->Derived = nullptr;
    Info->PrimaryVirtualBaseInfo = nullptr;
  
    const CXXRecordDecl *PrimaryVirtualBase = nullptr;
    BaseSubobjectInfo *PrimaryVirtualBaseInfo = nullptr;
  
    // Check if this base has a primary virtual base.
    if (RD->getNumVBases()) {
      const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
      if (Layout.isPrimaryBaseVirtual()) {
        // This base does have a primary virtual base.
        PrimaryVirtualBase = Layout.getPrimaryBase();
        assert(PrimaryVirtualBase && "Didn't have a primary virtual base!");
  
        // Now check if we have base subobject info about this primary base.
        PrimaryVirtualBaseInfo = VirtualBaseInfo.lookup(PrimaryVirtualBase);
  
        if (PrimaryVirtualBaseInfo) {
          if (PrimaryVirtualBaseInfo->Derived) {
            // We did have info about this primary base, and it turns out that it
            // has already been claimed as a primary virtual base for another
            // base.
            PrimaryVirtualBase = nullptr;
          } else {
            // We can claim this base as our primary base.
            Info->PrimaryVirtualBaseInfo = PrimaryVirtualBaseInfo;
            PrimaryVirtualBaseInfo->Derived = Info;
          }
        }
      }
    }
  
    // Now go through all direct bases.
    for (const auto &I : RD->bases()) {
      bool IsVirtual = I.isVirtual();
  
      const CXXRecordDecl *BaseDecl = I.getType()->getAsCXXRecordDecl();
  
      Info->Bases.push_back(ComputeBaseSubobjectInfo(BaseDecl, IsVirtual, Info));
    }
  
    if (PrimaryVirtualBase && !PrimaryVirtualBaseInfo) {
      // Traversing the bases must have created the base info for our primary
      // virtual base.
      PrimaryVirtualBaseInfo = VirtualBaseInfo.lookup(PrimaryVirtualBase);
      assert(PrimaryVirtualBaseInfo &&
             "Did not create a primary virtual base!");
  
      // Claim the primary virtual base as our primary virtual base.
      Info->PrimaryVirtualBaseInfo = PrimaryVirtualBaseInfo;
      PrimaryVirtualBaseInfo->Derived = Info;
    }
  
    return Info;
  }
  
  void ItaniumRecordLayoutBuilder::ComputeBaseSubobjectInfo(
      const CXXRecordDecl *RD) {
    for (const auto &I : RD->bases()) {
      bool IsVirtual = I.isVirtual();
  
      const CXXRecordDecl *BaseDecl = I.getType()->getAsCXXRecordDecl();
  
      // Compute the base subobject info for this base.
      BaseSubobjectInfo *Info = ComputeBaseSubobjectInfo(BaseDecl, IsVirtual,
                                                         nullptr);
  
      if (IsVirtual) {
        // ComputeBaseInfo has already added this base for us.
        assert(VirtualBaseInfo.count(BaseDecl) &&
               "Did not add virtual base!");
      } else {
        // Add the base info to the map of non-virtual bases.
        assert(!NonVirtualBaseInfo.count(BaseDecl) &&
               "Non-virtual base already exists!");
        NonVirtualBaseInfo.insert(std::make_pair(BaseDecl, Info));
      }
    }
  }
  
  void ItaniumRecordLayoutBuilder::EnsureVTablePointerAlignment(
      CharUnits UnpackedBaseAlign) {
    CharUnits BaseAlign = Packed ? CharUnits::One() : UnpackedBaseAlign;
  
    // The maximum field alignment overrides base align.
    if (!MaxFieldAlignment.isZero()) {
      BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
      UnpackedBaseAlign = std::min(UnpackedBaseAlign, MaxFieldAlignment);
    }
  
    // Round up the current record size to pointer alignment.
    setSize(getSize().alignTo(BaseAlign));
  
    // Update the alignment.
    UpdateAlignment(BaseAlign, UnpackedBaseAlign);
  }
  
  void ItaniumRecordLayoutBuilder::LayoutNonVirtualBases(
      const CXXRecordDecl *RD) {
    // Then, determine the primary base class.
    DeterminePrimaryBase(RD);
  
    // Compute base subobject info.
    ComputeBaseSubobjectInfo(RD);
  
    // If we have a primary base class, lay it out.
    if (PrimaryBase) {
      if (PrimaryBaseIsVirtual) {
        // If the primary virtual base was a primary virtual base of some other
        // base class we'll have to steal it.
        BaseSubobjectInfo *PrimaryBaseInfo = VirtualBaseInfo.lookup(PrimaryBase);
        PrimaryBaseInfo->Derived = nullptr;
  
        // We have a virtual primary base, insert it as an indirect primary base.
        IndirectPrimaryBases.insert(PrimaryBase);
  
        assert(!VisitedVirtualBases.count(PrimaryBase) &&
               "vbase already visited!");
        VisitedVirtualBases.insert(PrimaryBase);
  
        LayoutVirtualBase(PrimaryBaseInfo);
      } else {
        BaseSubobjectInfo *PrimaryBaseInfo =
          NonVirtualBaseInfo.lookup(PrimaryBase);
        assert(PrimaryBaseInfo &&
               "Did not find base info for non-virtual primary base!");
  
        LayoutNonVirtualBase(PrimaryBaseInfo);
      }
  
    // If this class needs a vtable/vf-table and didn't get one from a
    // primary base, add it in now.
    } else if (RD->isDynamicClass()) {
      assert(DataSize == 0 && "Vtable pointer must be at offset zero!");
      CharUnits PtrWidth =
        Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
      CharUnits PtrAlign =
        Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerAlign(0));
      EnsureVTablePointerAlignment(PtrAlign);
      HasOwnVFPtr = true;
      setSize(getSize() + PtrWidth);
      setDataSize(getSize());
    }
  
    // Now lay out the non-virtual bases.
    for (const auto &I : RD->bases()) {
  
      // Ignore virtual bases.
      if (I.isVirtual())
        continue;
  
      const CXXRecordDecl *BaseDecl = I.getType()->getAsCXXRecordDecl();
  
      // Skip the primary base, because we've already laid it out.  The
      // !PrimaryBaseIsVirtual check is required because we might have a
      // non-virtual base of the same type as a primary virtual base.
      if (BaseDecl == PrimaryBase && !PrimaryBaseIsVirtual)
        continue;
  
      // Lay out the base.
      BaseSubobjectInfo *BaseInfo = NonVirtualBaseInfo.lookup(BaseDecl);
      assert(BaseInfo && "Did not find base info for non-virtual base!");
  
      LayoutNonVirtualBase(BaseInfo);
    }
  }
  
  void ItaniumRecordLayoutBuilder::LayoutNonVirtualBase(
      const BaseSubobjectInfo *Base) {
    // Layout the base.
    CharUnits Offset = LayoutBase(Base);
  
    // Add its base class offset.
    assert(!Bases.count(Base->Class) && "base offset already exists!");
    Bases.insert(std::make_pair(Base->Class, Offset));
  
    AddPrimaryVirtualBaseOffsets(Base, Offset);
  }
  
  void ItaniumRecordLayoutBuilder::AddPrimaryVirtualBaseOffsets(
      const BaseSubobjectInfo *Info, CharUnits Offset) {
    // This base isn't interesting, it has no virtual bases.
    if (!Info->Class->getNumVBases())
      return;
  
    // First, check if we have a virtual primary base to add offsets for.
    if (Info->PrimaryVirtualBaseInfo) {
      assert(Info->PrimaryVirtualBaseInfo->IsVirtual &&
             "Primary virtual base is not virtual!");
      if (Info->PrimaryVirtualBaseInfo->Derived == Info) {
        // Add the offset.
        assert(!VBases.count(Info->PrimaryVirtualBaseInfo->Class) &&
               "primary vbase offset already exists!");
        VBases.insert(std::make_pair(Info->PrimaryVirtualBaseInfo->Class,
                                     ASTRecordLayout::VBaseInfo(Offset, false)));
  
        // Traverse the primary virtual base.
        AddPrimaryVirtualBaseOffsets(Info->PrimaryVirtualBaseInfo, Offset);
      }
    }
  
    // Now go through all direct non-virtual bases.
    const ASTRecordLayout &Layout = Context.getASTRecordLayout(Info->Class);
    for (const BaseSubobjectInfo *Base : Info->Bases) {
      if (Base->IsVirtual)
        continue;
  
      CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(Base->Class);
      AddPrimaryVirtualBaseOffsets(Base, BaseOffset);
    }
  }
  
  void ItaniumRecordLayoutBuilder::LayoutVirtualBases(
      const CXXRecordDecl *RD, const CXXRecordDecl *MostDerivedClass) {
    const CXXRecordDecl *PrimaryBase;
    bool PrimaryBaseIsVirtual;
  
    if (MostDerivedClass == RD) {
      PrimaryBase = this->PrimaryBase;
      PrimaryBaseIsVirtual = this->PrimaryBaseIsVirtual;
    } else {
      const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
      PrimaryBase = Layout.getPrimaryBase();
      PrimaryBaseIsVirtual = Layout.isPrimaryBaseVirtual();
    }
  
    for (const CXXBaseSpecifier &Base : RD->bases()) {
      assert(!Base.getType()->isDependentType() &&
             "Cannot layout class with dependent bases.");
  
      const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
  
      if (Base.isVirtual()) {
        if (PrimaryBase != BaseDecl || !PrimaryBaseIsVirtual) {
          bool IndirectPrimaryBase = IndirectPrimaryBases.count(BaseDecl);
  
          // Only lay out the virtual base if it's not an indirect primary base.
          if (!IndirectPrimaryBase) {
            // Only visit virtual bases once.
            if (!VisitedVirtualBases.insert(BaseDecl).second)
              continue;
  
            const BaseSubobjectInfo *BaseInfo = VirtualBaseInfo.lookup(BaseDecl);
            assert(BaseInfo && "Did not find virtual base info!");
            LayoutVirtualBase(BaseInfo);
          }
        }
      }
  
      if (!BaseDecl->getNumVBases()) {
        // This base isn't interesting since it doesn't have any virtual bases.
        continue;
      }
  
      LayoutVirtualBases(BaseDecl, MostDerivedClass);
    }
  }
  
  void ItaniumRecordLayoutBuilder::LayoutVirtualBase(
      const BaseSubobjectInfo *Base) {
    assert(!Base->Derived && "Trying to lay out a primary virtual base!");
  
    // Layout the base.
    CharUnits Offset = LayoutBase(Base);
  
    // Add its base class offset.
    assert(!VBases.count(Base->Class) && "vbase offset already exists!");
    VBases.insert(std::make_pair(Base->Class,
                         ASTRecordLayout::VBaseInfo(Offset, false)));
  
    AddPrimaryVirtualBaseOffsets(Base, Offset);
  }
  
  CharUnits
  ItaniumRecordLayoutBuilder::LayoutBase(const BaseSubobjectInfo *Base) {
    const ASTRecordLayout &Layout = Context.getASTRecordLayout(Base->Class);
  
  
    CharUnits Offset;
  
    // Query the external layout to see if it provides an offset.
    bool HasExternalLayout = false;
    if (UseExternalLayout) {
      // FIXME: This appears to be reversed.
      if (Base->IsVirtual)
        HasExternalLayout = External.getExternalNVBaseOffset(Base->Class, Offset);
      else
        HasExternalLayout = External.getExternalVBaseOffset(Base->Class, Offset);
    }
  
    // Clang <= 6 incorrectly applied the 'packed' attribute to base classes.
    // Per GCC's documentation, it only applies to non-static data members.
    CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlignment();
    CharUnits BaseAlign =
        (Packed && ((Context.getLangOpts().getClangABICompat() <=
                     LangOptions::ClangABI::Ver6) ||
                    Context.getTargetInfo().getTriple().isPS4()))
            ? CharUnits::One()
            : UnpackedBaseAlign;
  
    // If we have an empty base class, try to place it at offset 0.
    if (Base->Class->isEmpty() &&
        (!HasExternalLayout || Offset == CharUnits::Zero()) &&
        EmptySubobjects->CanPlaceBaseAtOffset(Base, CharUnits::Zero())) {
      setSize(std::max(getSize(), Layout.getSize()));
      UpdateAlignment(BaseAlign, UnpackedBaseAlign);
  
      return CharUnits::Zero();
    }
  
    // The maximum field alignment overrides base align.
    if (!MaxFieldAlignment.isZero()) {
      BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
      UnpackedBaseAlign = std::min(UnpackedBaseAlign, MaxFieldAlignment);
    }
  
    if (!HasExternalLayout) {
      // Round up the current record size to the base's alignment boundary.
      Offset = getDataSize().alignTo(BaseAlign);
  
      // Try to place the base.
      while (!EmptySubobjects->CanPlaceBaseAtOffset(Base, Offset))
        Offset += BaseAlign;
    } else {
      bool Allowed = EmptySubobjects->CanPlaceBaseAtOffset(Base, Offset);
      (void)Allowed;
      assert(Allowed && "Base subobject externally placed at overlapping offset");
  
      if (InferAlignment && Offset < getDataSize().alignTo(BaseAlign)) {
        // The externally-supplied base offset is before the base offset we
        // computed. Assume that the structure is packed.
        Alignment = CharUnits::One();
        InferAlignment = false;
      }
    }
  
    if (!Base->Class->isEmpty()) {
      // Update the data size.
      setDataSize(Offset + Layout.getNonVirtualSize());
  
      setSize(std::max(getSize(), getDataSize()));
    } else
      setSize(std::max(getSize(), Offset + Layout.getSize()));
  
    // Remember max struct/class alignment.
    UpdateAlignment(BaseAlign, UnpackedBaseAlign);
  
    return Offset;
  }
  
  void ItaniumRecordLayoutBuilder::InitializeLayout(const Decl *D) {
    if (const RecordDecl *RD = dyn_cast<RecordDecl>(D)) {
      IsUnion = RD->isUnion();
      IsMsStruct = RD->isMsStruct(Context);
    }
  
    Packed = D->hasAttr<PackedAttr>();
  
    // Honor the default struct packing maximum alignment flag.
    if (unsigned DefaultMaxFieldAlignment = Context.getLangOpts().PackStruct) {
      MaxFieldAlignment = CharUnits::fromQuantity(DefaultMaxFieldAlignment);
    }
  
    // mac68k alignment supersedes maximum field alignment and attribute aligned,
    // and forces all structures to have 2-byte alignment. The IBM docs on it
    // allude to additional (more complicated) semantics, especially with regard
    // to bit-fields, but gcc appears not to follow that.
    if (D->hasAttr<AlignMac68kAttr>()) {
      IsMac68kAlign = true;
      MaxFieldAlignment = CharUnits::fromQuantity(2);
      Alignment = CharUnits::fromQuantity(2);
    } else {
      if (const MaxFieldAlignmentAttr *MFAA = D->getAttr<MaxFieldAlignmentAttr>())
        MaxFieldAlignment = Context.toCharUnitsFromBits(MFAA->getAlignment());
  
      if (unsigned MaxAlign = D->getMaxAlignment())
        UpdateAlignment(Context.toCharUnitsFromBits(MaxAlign));
    }
  
    // If there is an external AST source, ask it for the various offsets.
    if (const RecordDecl *RD = dyn_cast<RecordDecl>(D))
      if (ExternalASTSource *Source = Context.getExternalSource()) {
        UseExternalLayout = Source->layoutRecordType(
            RD, External.Size, External.Align, External.FieldOffsets,
            External.BaseOffsets, External.VirtualBaseOffsets);
  
        // Update based on external alignment.
        if (UseExternalLayout) {
          if (External.Align > 0) {
            Alignment = Context.toCharUnitsFromBits(External.Align);
          } else {
            // The external source didn't have alignment information; infer it.
            InferAlignment = true;
          }
        }
      }
  }
  
  void ItaniumRecordLayoutBuilder::Layout(const RecordDecl *D) {
    InitializeLayout(D);
    LayoutFields(D);
  
    // Finally, round the size of the total struct up to the alignment of the
    // struct itself.
    FinishLayout(D);
  }
  
  void ItaniumRecordLayoutBuilder::Layout(const CXXRecordDecl *RD) {
    InitializeLayout(RD);
  
    // Lay out the vtable and the non-virtual bases.
    LayoutNonVirtualBases(RD);
  
    LayoutFields(RD);
  
    NonVirtualSize = Context.toCharUnitsFromBits(
        llvm::alignTo(getSizeInBits(), Context.getTargetInfo().getCharAlign()));
    NonVirtualAlignment = Alignment;
  
    // Lay out the virtual bases and add the primary virtual base offsets.
    LayoutVirtualBases(RD, RD);
  
    // Finally, round the size of the total struct up to the alignment
    // of the struct itself.
    FinishLayout(RD);
  
  #ifndef NDEBUG
    // Check that we have base offsets for all bases.
    for (const CXXBaseSpecifier &Base : RD->bases()) {
      if (Base.isVirtual())
        continue;
  
      const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
  
      assert(Bases.count(BaseDecl) && "Did not find base offset!");
    }
  
    // And all virtual bases.
    for (const CXXBaseSpecifier &Base : RD->vbases()) {
      const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
  
      assert(VBases.count(BaseDecl) && "Did not find base offset!");
    }
  #endif
  }
  
  void ItaniumRecordLayoutBuilder::Layout(const ObjCInterfaceDecl *D) {
    if (ObjCInterfaceDecl *SD = D->getSuperClass()) {
      const ASTRecordLayout &SL = Context.getASTObjCInterfaceLayout(SD);
  
      UpdateAlignment(SL.getAlignment());
  
      // We start laying out ivars not at the end of the superclass
      // structure, but at the next byte following the last field.
      setDataSize(SL.getDataSize());
      setSize(getDataSize());
    }
  
    InitializeLayout(D);
    // Layout each ivar sequentially.
    for (const ObjCIvarDecl *IVD = D->all_declared_ivar_begin(); IVD;
         IVD = IVD->getNextIvar())
      LayoutField(IVD, false);
  
    // Finally, round the size of the total struct up to the alignment of the
    // struct itself.
    FinishLayout(D);
  }
  
  void ItaniumRecordLayoutBuilder::LayoutFields(const RecordDecl *D) {
    // Layout each field, for now, just sequentially, respecting alignment.  In
    // the future, this will need to be tweakable by targets.
    bool InsertExtraPadding = D->mayInsertExtraPadding(/*EmitRemark=*/true);
    bool HasFlexibleArrayMember = D->hasFlexibleArrayMember();
    for (auto I = D->field_begin(), End = D->field_end(); I != End; ++I) {
      auto Next(I);
      ++Next;
      LayoutField(*I,
                  InsertExtraPadding && (Next != End || !HasFlexibleArrayMember));
    }
  }
  
  // Rounds the specified size to have it a multiple of the char size.
  static uint64_t
  roundUpSizeToCharAlignment(uint64_t Size,
                             const ASTContext &Context) {
    uint64_t CharAlignment = Context.getTargetInfo().getCharAlign();
    return llvm::alignTo(Size, CharAlignment);
  }
  
  void ItaniumRecordLayoutBuilder::LayoutWideBitField(uint64_t FieldSize,
                                                      uint64_t TypeSize,
                                                      bool FieldPacked,
                                                      const FieldDecl *D) {
    assert(Context.getLangOpts().CPlusPlus &&
           "Can only have wide bit-fields in C++!");
  
    // Itanium C++ ABI 2.4:
    //   If sizeof(T)*8 < n, let T' be the largest integral POD type with
    //   sizeof(T')*8 <= n.
  
    QualType IntegralPODTypes[] = {
      Context.UnsignedCharTy, Context.UnsignedShortTy, Context.UnsignedIntTy,
      Context.UnsignedLongTy, Context.UnsignedLongLongTy
    };
  
    QualType Type;
    for (const QualType &QT : IntegralPODTypes) {
      uint64_t Size = Context.getTypeSize(QT);
  
      if (Size > FieldSize)
        break;
  
      Type = QT;
    }
    assert(!Type.isNull() && "Did not find a type!");
  
    CharUnits TypeAlign = Context.getTypeAlignInChars(Type);
  
    // We're not going to use any of the unfilled bits in the last byte.
    UnfilledBitsInLastUnit = 0;
    LastBitfieldTypeSize = 0;
  
    uint64_t FieldOffset;
    uint64_t UnpaddedFieldOffset = getDataSizeInBits() - UnfilledBitsInLastUnit;
  
    if (IsUnion) {
      uint64_t RoundedFieldSize = roundUpSizeToCharAlignment(FieldSize,
                                                             Context);
      setDataSize(std::max(getDataSizeInBits(), RoundedFieldSize));
      FieldOffset = 0;
    } else {
      // The bitfield is allocated starting at the next offset aligned
      // appropriately for T', with length n bits.
      FieldOffset = llvm::alignTo(getDataSizeInBits(), Context.toBits(TypeAlign));
  
      uint64_t NewSizeInBits = FieldOffset + FieldSize;
  
      setDataSize(
          llvm::alignTo(NewSizeInBits, Context.getTargetInfo().getCharAlign()));
      UnfilledBitsInLastUnit = getDataSizeInBits() - NewSizeInBits;
    }
  
    // Place this field at the current location.
    FieldOffsets.push_back(FieldOffset);
  
    CheckFieldPadding(FieldOffset, UnpaddedFieldOffset, FieldOffset,
                      Context.toBits(TypeAlign), FieldPacked, D);
  
    // Update the size.
    setSize(std::max(getSizeInBits(), getDataSizeInBits()));
  
    // Remember max struct/class alignment.
    UpdateAlignment(TypeAlign);
  }
  
  void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
    bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
    uint64_t FieldSize = D->getBitWidthValue(Context);
    TypeInfo FieldInfo = Context.getTypeInfo(D->getType());
    uint64_t TypeSize = FieldInfo.Width;
    unsigned FieldAlign = FieldInfo.Align;
  
    // UnfilledBitsInLastUnit is the difference between the end of the
    // last allocated bitfield (i.e. the first bit offset available for
    // bitfields) and the end of the current data size in bits (i.e. the
    // first bit offset available for non-bitfields).  The current data
    // size in bits is always a multiple of the char size; additionally,
    // for ms_struct records it's also a multiple of the
    // LastBitfieldTypeSize (if set).
  
    // The struct-layout algorithm is dictated by the platform ABI,
    // which in principle could use almost any rules it likes.  In
    // practice, UNIXy targets tend to inherit the algorithm described
    // in the System V generic ABI.  The basic bitfield layout rule in
    // System V is to place bitfields at the next available bit offset
    // where the entire bitfield would fit in an aligned storage unit of
    // the declared type; it's okay if an earlier or later non-bitfield
    // is allocated in the same storage unit.  However, some targets
    // (those that !useBitFieldTypeAlignment(), e.g. ARM APCS) don't
    // require this storage unit to be aligned, and therefore always put
    // the bitfield at the next available bit offset.
  
    // ms_struct basically requests a complete replacement of the
    // platform ABI's struct-layout algorithm, with the high-level goal
    // of duplicating MSVC's layout.  For non-bitfields, this follows
    // the standard algorithm.  The basic bitfield layout rule is to
    // allocate an entire unit of the bitfield's declared type
    // (e.g. 'unsigned long'), then parcel it up among successive
    // bitfields whose declared types have the same size, making a new
    // unit as soon as the last can no longer store the whole value.
    // Since it completely replaces the platform ABI's algorithm,
    // settings like !useBitFieldTypeAlignment() do not apply.
  
    // A zero-width bitfield forces the use of a new storage unit for
    // later bitfields.  In general, this occurs by rounding up the
    // current size of the struct as if the algorithm were about to
    // place a non-bitfield of the field's formal type.  Usually this
    // does not change the alignment of the struct itself, but it does
    // on some targets (those that useZeroLengthBitfieldAlignment(),
    // e.g. ARM).  In ms_struct layout, zero-width bitfields are
    // ignored unless they follow a non-zero-width bitfield.
  
    // A field alignment restriction (e.g. from #pragma pack) or
    // specification (e.g. from __attribute__((aligned))) changes the
    // formal alignment of the field.  For System V, this alters the
    // required alignment of the notional storage unit that must contain
    // the bitfield.  For ms_struct, this only affects the placement of
    // new storage units.  In both cases, the effect of #pragma pack is
    // ignored on zero-width bitfields.
  
    // On System V, a packed field (e.g. from #pragma pack or
    // __attribute__((packed))) always uses the next available bit
    // offset.
  
    // In an ms_struct struct, the alignment of a fundamental type is
    // always equal to its size.  This is necessary in order to mimic
    // the i386 alignment rules on targets which might not fully align
    // all types (e.g. Darwin PPC32, where alignof(long long) == 4).
  
    // First, some simple bookkeeping to perform for ms_struct structs.
    if (IsMsStruct) {
      // The field alignment for integer types is always the size.
      FieldAlign = TypeSize;
  
      // If the previous field was not a bitfield, or was a bitfield
      // with a different storage unit size, or if this field doesn't fit into
      // the current storage unit, we're done with that storage unit.
      if (LastBitfieldTypeSize != TypeSize ||
          UnfilledBitsInLastUnit < FieldSize) {
        // Also, ignore zero-length bitfields after non-bitfields.
        if (!LastBitfieldTypeSize && !FieldSize)
          FieldAlign = 1;
  
        UnfilledBitsInLastUnit = 0;
        LastBitfieldTypeSize = 0;
      }
    }
  
    // If the field is wider than its declared type, it follows
    // different rules in all cases.
    if (FieldSize > TypeSize) {
      LayoutWideBitField(FieldSize, TypeSize, FieldPacked, D);
      return;
    }
  
    // Compute the next available bit offset.
    uint64_t FieldOffset =
      IsUnion ? 0 : (getDataSizeInBits() - UnfilledBitsInLastUnit);
  
    // Handle targets that don't honor bitfield type alignment.
    if (!IsMsStruct && !Context.getTargetInfo().useBitFieldTypeAlignment()) {
      // Some such targets do honor it on zero-width bitfields.
      if (FieldSize == 0 &&
          Context.getTargetInfo().useZeroLengthBitfieldAlignment()) {
        // The alignment to round up to is the max of the field's natural
        // alignment and a target-specific fixed value (sometimes zero).
        unsigned ZeroLengthBitfieldBoundary =
          Context.getTargetInfo().getZeroLengthBitfieldBoundary();
        FieldAlign = std::max(FieldAlign, ZeroLengthBitfieldBoundary);
  
      // If that doesn't apply, just ignore the field alignment.
      } else {
        FieldAlign = 1;
      }
    }
  
    // Remember the alignment we would have used if the field were not packed.
    unsigned UnpackedFieldAlign = FieldAlign;
  
    // Ignore the field alignment if the field is packed unless it has zero-size.
    if (!IsMsStruct && FieldPacked && FieldSize != 0)
      FieldAlign = 1;
  
    // But, if there's an 'aligned' attribute on the field, honor that.
    unsigned ExplicitFieldAlign = D->getMaxAlignment();
    if (ExplicitFieldAlign) {
      FieldAlign = std::max(FieldAlign, ExplicitFieldAlign);
      UnpackedFieldAlign = std::max(UnpackedFieldAlign, ExplicitFieldAlign);
    }
  
    // But, if there's a #pragma pack in play, that takes precedent over
    // even the 'aligned' attribute, for non-zero-width bitfields.
    unsigned MaxFieldAlignmentInBits = Context.toBits(MaxFieldAlignment);
    if (!MaxFieldAlignment.isZero() && FieldSize) {
      UnpackedFieldAlign = std::min(UnpackedFieldAlign, MaxFieldAlignmentInBits);
      if (FieldPacked)
        FieldAlign = UnpackedFieldAlign;
      else
        FieldAlign = std::min(FieldAlign, MaxFieldAlignmentInBits);
    }
  
    // But, ms_struct just ignores all of that in unions, even explicit
    // alignment attributes.
    if (IsMsStruct && IsUnion) {
      FieldAlign = UnpackedFieldAlign = 1;
    }
  
    // For purposes of diagnostics, we're going to simultaneously
    // compute the field offsets that we would have used if we weren't
    // adding any alignment padding or if the field weren't packed.
    uint64_t UnpaddedFieldOffset = FieldOffset;
    uint64_t UnpackedFieldOffset = FieldOffset;
  
    // Check if we need to add padding to fit the bitfield within an
    // allocation unit with the right size and alignment.  The rules are
    // somewhat different here for ms_struct structs.
    if (IsMsStruct) {
      // If it's not a zero-width bitfield, and we can fit the bitfield
      // into the active storage unit (and we haven't already decided to
      // start a new storage unit), just do so, regardless of any other
      // other consideration.  Otherwise, round up to the right alignment.
      if (FieldSize == 0 || FieldSize > UnfilledBitsInLastUnit) {
        FieldOffset = llvm::alignTo(FieldOffset, FieldAlign);
        UnpackedFieldOffset =
            llvm::alignTo(UnpackedFieldOffset, UnpackedFieldAlign);
        UnfilledBitsInLastUnit = 0;
      }
  
    } else {
      // #pragma pack, with any value, suppresses the insertion of padding.
      bool AllowPadding = MaxFieldAlignment.isZero();
  
      // Compute the real offset.
      if (FieldSize == 0 ||
          (AllowPadding &&
           (FieldOffset & (FieldAlign-1)) + FieldSize > TypeSize)) {
        FieldOffset = llvm::alignTo(FieldOffset, FieldAlign);
      } else if (ExplicitFieldAlign &&
                 (MaxFieldAlignmentInBits == 0 ||
                  ExplicitFieldAlign <= MaxFieldAlignmentInBits) &&
                 Context.getTargetInfo().useExplicitBitFieldAlignment()) {
        // TODO: figure it out what needs to be done on targets that don't honor
        // bit-field type alignment like ARM APCS ABI.
        FieldOffset = llvm::alignTo(FieldOffset, ExplicitFieldAlign);
      }
  
      // Repeat the computation for diagnostic purposes.
      if (FieldSize == 0 ||
          (AllowPadding &&
           (UnpackedFieldOffset & (UnpackedFieldAlign-1)) + FieldSize > TypeSize))
        UnpackedFieldOffset =
            llvm::alignTo(UnpackedFieldOffset, UnpackedFieldAlign);
      else if (ExplicitFieldAlign &&
               (MaxFieldAlignmentInBits == 0 ||
                ExplicitFieldAlign <= MaxFieldAlignmentInBits) &&
               Context.getTargetInfo().useExplicitBitFieldAlignment())
        UnpackedFieldOffset =
            llvm::alignTo(UnpackedFieldOffset, ExplicitFieldAlign);
    }
  
    // If we're using external layout, give the external layout a chance
    // to override this information.
    if (UseExternalLayout)
      FieldOffset = updateExternalFieldOffset(D, FieldOffset);
  
    // Okay, place the bitfield at the calculated offset.
    FieldOffsets.push_back(FieldOffset);
  
    // Bookkeeping:
  
    // Anonymous members don't affect the overall record alignment,
    // except on targets where they do.
    if (!IsMsStruct &&
        !Context.getTargetInfo().useZeroLengthBitfieldAlignment() &&
        !D->getIdentifier())
      FieldAlign = UnpackedFieldAlign = 1;
  
    // Diagnose differences in layout due to padding or packing.
    if (!UseExternalLayout)
      CheckFieldPadding(FieldOffset, UnpaddedFieldOffset, UnpackedFieldOffset,
                        UnpackedFieldAlign, FieldPacked, D);
  
    // Update DataSize to include the last byte containing (part of) the bitfield.
  
    // For unions, this is just a max operation, as usual.
    if (IsUnion) {
      // For ms_struct, allocate the entire storage unit --- unless this
      // is a zero-width bitfield, in which case just use a size of 1.
      uint64_t RoundedFieldSize;
      if (IsMsStruct) {
        RoundedFieldSize =
          (FieldSize ? TypeSize : Context.getTargetInfo().getCharWidth());
  
      // Otherwise, allocate just the number of bytes required to store
      // the bitfield.
      } else {
        RoundedFieldSize = roundUpSizeToCharAlignment(FieldSize, Context);
      }
      setDataSize(std::max(getDataSizeInBits(), RoundedFieldSize));
  
    // For non-zero-width bitfields in ms_struct structs, allocate a new
    // storage unit if necessary.
    } else if (IsMsStruct && FieldSize) {
      // We should have cleared UnfilledBitsInLastUnit in every case
      // where we changed storage units.
      if (!UnfilledBitsInLastUnit) {
        setDataSize(FieldOffset + TypeSize);
        UnfilledBitsInLastUnit = TypeSize;
      }
      UnfilledBitsInLastUnit -= FieldSize;
      LastBitfieldTypeSize = TypeSize;
  
    // Otherwise, bump the data size up to include the bitfield,
    // including padding up to char alignment, and then remember how
    // bits we didn't use.
    } else {
      uint64_t NewSizeInBits = FieldOffset + FieldSize;
      uint64_t CharAlignment = Context.getTargetInfo().getCharAlign();
      setDataSize(llvm::alignTo(NewSizeInBits, CharAlignment));
      UnfilledBitsInLastUnit = getDataSizeInBits() - NewSizeInBits;
  
      // The only time we can get here for an ms_struct is if this is a
      // zero-width bitfield, which doesn't count as anything for the
      // purposes of unfilled bits.
      LastBitfieldTypeSize = 0;
    }
  
    // Update the size.
    setSize(std::max(getSizeInBits(), getDataSizeInBits()));
  
    // Remember max struct/class alignment.
    UnadjustedAlignment =
        std::max(UnadjustedAlignment, Context.toCharUnitsFromBits(FieldAlign));
    UpdateAlignment(Context.toCharUnitsFromBits(FieldAlign),
                    Context.toCharUnitsFromBits(UnpackedFieldAlign));
  }
  
  void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
                                               bool InsertExtraPadding) {
    if (D->isBitField()) {
      LayoutBitField(D);
      return;
    }
  
    uint64_t UnpaddedFieldOffset = getDataSizeInBits() - UnfilledBitsInLastUnit;
  
    // Reset the unfilled bits.
    UnfilledBitsInLastUnit = 0;
    LastBitfieldTypeSize = 0;
  
    auto *FieldClass = D->getType()->getAsCXXRecordDecl();
    bool PotentiallyOverlapping = D->hasAttr<NoUniqueAddressAttr>() && FieldClass;
    bool IsOverlappingEmptyField = PotentiallyOverlapping && FieldClass->isEmpty();
    bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
  
    CharUnits FieldOffset = (IsUnion || IsOverlappingEmptyField)
                                ? CharUnits::Zero()
                                : getDataSize();
    CharUnits FieldSize;
    CharUnits FieldAlign;
    // The amount of this class's dsize occupied by the field.
    // This is equal to FieldSize unless we're permitted to pack
    // into the field's tail padding.
    CharUnits EffectiveFieldSize;
  
    if (D->getType()->isIncompleteArrayType()) {
      // This is a flexible array member; we can't directly
      // query getTypeInfo about these, so we figure it out here.
      // Flexible array members don't have any size, but they
      // have to be aligned appropriately for their element type.
      EffectiveFieldSize = FieldSize = CharUnits::Zero();
      const ArrayType* ATy = Context.getAsArrayType(D->getType());
      FieldAlign = Context.getTypeAlignInChars(ATy->getElementType());
    } else if (const ReferenceType *RT = D->getType()->getAs<ReferenceType>()) {
      unsigned AS = Context.getTargetAddressSpace(RT->getPointeeType());
      EffectiveFieldSize = FieldSize =
        Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(AS));
      FieldAlign =
        Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerAlign(AS));
    } else {
      std::pair<CharUnits, CharUnits> FieldInfo =
        Context.getTypeInfoInChars(D->getType());
      EffectiveFieldSize = FieldSize = FieldInfo.first;
      FieldAlign = FieldInfo.second;
  
      // A potentially-overlapping field occupies its dsize or nvsize, whichever
      // is larger.
      if (PotentiallyOverlapping) {
        const ASTRecordLayout &Layout = Context.getASTRecordLayout(FieldClass);
        EffectiveFieldSize =
            std::max(Layout.getNonVirtualSize(), Layout.getDataSize());
      }
  
      if (IsMsStruct) {
        // If MS bitfield layout is required, figure out what type is being
        // laid out and align the field to the width of that type.
  
        // Resolve all typedefs down to their base type and round up the field
        // alignment if necessary.
        QualType T = Context.getBaseElementType(D->getType());
        if (const BuiltinType *BTy = T->getAs<BuiltinType>()) {
          CharUnits TypeSize = Context.getTypeSizeInChars(BTy);
  
          if (!llvm::isPowerOf2_64(TypeSize.getQuantity())) {
            assert(
                !Context.getTargetInfo().getTriple().isWindowsMSVCEnvironment() &&
                "Non PowerOf2 size in MSVC mode");
            // Base types with sizes that aren't a power of two don't work
            // with the layout rules for MS structs. This isn't an issue in
            // MSVC itself since there are no such base data types there.
            // On e.g. x86_32 mingw and linux, long double is 12 bytes though.
            // Any structs involving that data type obviously can't be ABI
            // compatible with MSVC regardless of how it is laid out.
  
            // Since ms_struct can be mass enabled (via a pragma or via the
            // -mms-bitfields command line parameter), this can trigger for
            // structs that don't actually need MSVC compatibility, so we
            // need to be able to sidestep the ms_struct layout for these types.
  
            // Since the combination of -mms-bitfields together with structs
            // like max_align_t (which contains a long double) for mingw is
            // quite comon (and GCC handles it silently), just handle it
            // silently there. For other targets that have ms_struct enabled
            // (most probably via a pragma or attribute), trigger a diagnostic
            // that defaults to an error.
            if (!Context.getTargetInfo().getTriple().isWindowsGNUEnvironment())
              Diag(D->getLocation(), diag::warn_npot_ms_struct);
          }
          if (TypeSize > FieldAlign &&
              llvm::isPowerOf2_64(TypeSize.getQuantity()))
            FieldAlign = TypeSize;
        }
      }
    }
  
    // The align if the field is not packed. This is to check if the attribute
    // was unnecessary (-Wpacked).
    CharUnits UnpackedFieldAlign = FieldAlign;
    CharUnits UnpackedFieldOffset = FieldOffset;
  
    if (FieldPacked)
      FieldAlign = CharUnits::One();
    CharUnits MaxAlignmentInChars =
      Context.toCharUnitsFromBits(D->getMaxAlignment());
    FieldAlign = std::max(FieldAlign, MaxAlignmentInChars);
    UnpackedFieldAlign = std::max(UnpackedFieldAlign, MaxAlignmentInChars);
  
    // The maximum field alignment overrides the aligned attribute.
    if (!MaxFieldAlignment.isZero()) {
      FieldAlign = std::min(FieldAlign, MaxFieldAlignment);
      UnpackedFieldAlign = std::min(UnpackedFieldAlign, MaxFieldAlignment);
    }
  
    // Round up the current record size to the field's alignment boundary.
    FieldOffset = FieldOffset.alignTo(FieldAlign);
    UnpackedFieldOffset = UnpackedFieldOffset.alignTo(UnpackedFieldAlign);
  
    if (UseExternalLayout) {
      FieldOffset = Context.toCharUnitsFromBits(
                      updateExternalFieldOffset(D, Context.toBits(FieldOffset)));
  
      if (!IsUnion && EmptySubobjects) {
        // Record the fact that we're placing a field at this offset.
        bool Allowed = EmptySubobjects->CanPlaceFieldAtOffset(D, FieldOffset);
        (void)Allowed;
        assert(Allowed && "Externally-placed field cannot be placed here");
      }
    } else {
      if (!IsUnion && EmptySubobjects) {
        // Check if we can place the field at this offset.
        while (!EmptySubobjects->CanPlaceFieldAtOffset(D, FieldOffset)) {
          // We couldn't place the field at the offset. Try again at a new offset.
          // We try offset 0 (for an empty field) and then dsize(C) onwards.
          if (FieldOffset == CharUnits::Zero() &&
              getDataSize() != CharUnits::Zero())
            FieldOffset = getDataSize().alignTo(FieldAlign);
          else
            FieldOffset += FieldAlign;
        }
      }
    }
  
    // Place this field at the current location.
    FieldOffsets.push_back(Context.toBits(FieldOffset));
  
    if (!UseExternalLayout)
      CheckFieldPadding(Context.toBits(FieldOffset), UnpaddedFieldOffset,
                        Context.toBits(UnpackedFieldOffset),
                        Context.toBits(UnpackedFieldAlign), FieldPacked, D);
  
    if (InsertExtraPadding) {
      CharUnits ASanAlignment = CharUnits::fromQuantity(8);
      CharUnits ExtraSizeForAsan = ASanAlignment;
      if (FieldSize % ASanAlignment)
        ExtraSizeForAsan +=
            ASanAlignment - CharUnits::fromQuantity(FieldSize % ASanAlignment);
      EffectiveFieldSize = FieldSize = FieldSize + ExtraSizeForAsan;
    }
  
    // Reserve space for this field.
    if (!IsOverlappingEmptyField) {
      uint64_t EffectiveFieldSizeInBits = Context.toBits(EffectiveFieldSize);
      if (IsUnion)
        setDataSize(std::max(getDataSizeInBits(), EffectiveFieldSizeInBits));
      else
        setDataSize(FieldOffset + EffectiveFieldSize);
  
      PaddedFieldSize = std::max(PaddedFieldSize, FieldOffset + FieldSize);
      setSize(std::max(getSizeInBits(), getDataSizeInBits()));
    } else {
      setSize(std::max(getSizeInBits(),
                       (uint64_t)Context.toBits(FieldOffset + FieldSize)));
    }
  
    // Remember max struct/class alignment.
    UnadjustedAlignment = std::max(UnadjustedAlignment, FieldAlign);
    UpdateAlignment(FieldAlign, UnpackedFieldAlign);
  }
  
  void ItaniumRecordLayoutBuilder::FinishLayout(const NamedDecl *D) {
    // In C++, records cannot be of size 0.
    if (Context.getLangOpts().CPlusPlus && getSizeInBits() == 0) {
      if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D)) {
        // Compatibility with gcc requires a class (pod or non-pod)
        // which is not empty but of size 0; such as having fields of
        // array of zero-length, remains of Size 0
        if (RD->isEmpty())
          setSize(CharUnits::One());
      }
      else
        setSize(CharUnits::One());
    }
  
    // If we have any remaining field tail padding, include that in the overall
    // size.
    setSize(std::max(getSizeInBits(), (uint64_t)Context.toBits(PaddedFieldSize)));
  
    // Finally, round the size of the record up to the alignment of the
    // record itself.
    uint64_t UnpaddedSize = getSizeInBits() - UnfilledBitsInLastUnit;
    uint64_t UnpackedSizeInBits =
        llvm::alignTo(getSizeInBits(), Context.toBits(UnpackedAlignment));
    uint64_t RoundedSize =
        llvm::alignTo(getSizeInBits(), Context.toBits(Alignment));
  
    if (UseExternalLayout) {
      // If we're inferring alignment, and the external size is smaller than
      // our size after we've rounded up to alignment, conservatively set the
      // alignment to 1.
      if (InferAlignment && External.Size < RoundedSize) {
        Alignment = CharUnits::One();
        InferAlignment = false;
      }
      setSize(External.Size);
      return;
    }
  
    // Set the size to the final size.
    setSize(RoundedSize);
  
    unsigned CharBitNum = Context.getTargetInfo().getCharWidth();
    if (const RecordDecl *RD = dyn_cast<RecordDecl>(D)) {
      // Warn if padding was introduced to the struct/class/union.
      if (getSizeInBits() > UnpaddedSize) {
        unsigned PadSize = getSizeInBits() - UnpaddedSize;
        bool InBits = true;
        if (PadSize % CharBitNum == 0) {
          PadSize = PadSize / CharBitNum;
          InBits = false;
        }
        Diag(RD->getLocation(), diag::warn_padded_struct_size)
            << Context.getTypeDeclType(RD)
            << PadSize
            << (InBits ? 1 : 0); // (byte|bit)
      }
  
      // Warn if we packed it unnecessarily, when the unpacked alignment is not
      // greater than the one after packing, the size in bits doesn't change and
      // the offset of each field is identical.
      if (Packed && UnpackedAlignment <= Alignment &&
          UnpackedSizeInBits == getSizeInBits() && !HasPackedField)
        Diag(D->getLocation(), diag::warn_unnecessary_packed)
            << Context.getTypeDeclType(RD);
    }
  }
  
  void ItaniumRecordLayoutBuilder::UpdateAlignment(
      CharUnits NewAlignment, CharUnits UnpackedNewAlignment) {
    // The alignment is not modified when using 'mac68k' alignment or when
    // we have an externally-supplied layout that also provides overall alignment.
    if (IsMac68kAlign || (UseExternalLayout && !InferAlignment))
      return;
  
    if (NewAlignment > Alignment) {
      assert(llvm::isPowerOf2_64(NewAlignment.getQuantity()) &&
             "Alignment not a power of 2");
      Alignment = NewAlignment;
    }
  
    if (UnpackedNewAlignment > UnpackedAlignment) {
      assert(llvm::isPowerOf2_64(UnpackedNewAlignment.getQuantity()) &&
             "Alignment not a power of 2");
      UnpackedAlignment = UnpackedNewAlignment;
    }
  }
  
  uint64_t
  ItaniumRecordLayoutBuilder::updateExternalFieldOffset(const FieldDecl *Field,
                                                        uint64_t ComputedOffset) {
    uint64_t ExternalFieldOffset = External.getExternalFieldOffset(Field);
  
    if (InferAlignment && ExternalFieldOffset < ComputedOffset) {
      // The externally-supplied field offset is before the field offset we
      // computed. Assume that the structure is packed.
      Alignment = CharUnits::One();
      InferAlignment = false;
    }
  
    // Use the externally-supplied field offset.
    return ExternalFieldOffset;
  }
  
  /// Get diagnostic %select index for tag kind for
  /// field padding diagnostic message.
  /// WARNING: Indexes apply to particular diagnostics only!
  ///
  /// \returns diagnostic %select index.
  static unsigned getPaddingDiagFromTagKind(TagTypeKind Tag) {
    switch (Tag) {
    case TTK_Struct: return 0;
    case TTK_Interface: return 1;
    case TTK_Class: return 2;
    default: llvm_unreachable("Invalid tag kind for field padding diagnostic!");
    }
  }
  
  void ItaniumRecordLayoutBuilder::CheckFieldPadding(
      uint64_t Offset, uint64_t UnpaddedOffset, uint64_t UnpackedOffset,
      unsigned UnpackedAlign, bool isPacked, const FieldDecl *D) {
    // We let objc ivars without warning, objc interfaces generally are not used
    // for padding tricks.
    if (isa<ObjCIvarDecl>(D))
      return;
  
    // Don't warn about structs created without a SourceLocation.  This can
    // be done by clients of the AST, such as codegen.
    if (D->getLocation().isInvalid())
      return;
  
    unsigned CharBitNum = Context.getTargetInfo().getCharWidth();
  
    // Warn if padding was introduced to the struct/class.
    if (!IsUnion && Offset > UnpaddedOffset) {
      unsigned PadSize = Offset - UnpaddedOffset;
      bool InBits = true;
      if (PadSize % CharBitNum == 0) {
        PadSize = PadSize / CharBitNum;
        InBits = false;
      }
      if (D->getIdentifier())
        Diag(D->getLocation(), diag::warn_padded_struct_field)
            << getPaddingDiagFromTagKind(D->getParent()->getTagKind())
            << Context.getTypeDeclType(D->getParent())
            << PadSize
            << (InBits ? 1 : 0) // (byte|bit)
            << D->getIdentifier();
      else
        Diag(D->getLocation(), diag::warn_padded_struct_anon_field)
            << getPaddingDiagFromTagKind(D->getParent()->getTagKind())
            << Context.getTypeDeclType(D->getParent())
            << PadSize
            << (InBits ? 1 : 0); // (byte|bit)
   }
   if (isPacked && Offset != UnpackedOffset) {
     HasPackedField = true;
   }
  }
  
  static const CXXMethodDecl *computeKeyFunction(ASTContext &Context,
                                                 const CXXRecordDecl *RD) {
    // If a class isn't polymorphic it doesn't have a key function.
    if (!RD->isPolymorphic())
      return nullptr;
  
    // A class that is not externally visible doesn't have a key function. (Or
    // at least, there's no point to assigning a key function to such a class;
    // this doesn't affect the ABI.)
    if (!RD->isExternallyVisible())
      return nullptr;
  
    // Template instantiations don't have key functions per Itanium C++ ABI 5.2.6.
    // Same behavior as GCC.
    TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
    if (TSK == TSK_ImplicitInstantiation ||
        TSK == TSK_ExplicitInstantiationDeclaration ||
        TSK == TSK_ExplicitInstantiationDefinition)
      return nullptr;
  
    bool allowInlineFunctions =
      Context.getTargetInfo().getCXXABI().canKeyFunctionBeInline();
  
    for (const CXXMethodDecl *MD : RD->methods()) {
      if (!MD->isVirtual())
        continue;
  
      if (MD->isPure())
        continue;
  
      // Ignore implicit member functions, they are always marked as inline, but
      // they don't have a body until they're defined.
      if (MD->isImplicit())
        continue;
  
      if (MD->isInlineSpecified())
        continue;
  
      if (MD->hasInlineBody())
        continue;
  
      // Ignore inline deleted or defaulted functions.
      if (!MD->isUserProvided())
        continue;
  
      // In certain ABIs, ignore functions with out-of-line inline definitions.
      if (!allowInlineFunctions) {
        const FunctionDecl *Def;
        if (MD->hasBody(Def) && Def->isInlineSpecified())
          continue;
      }
  
      if (Context.getLangOpts().CUDA) {
        // While compiler may see key method in this TU, during CUDA
        // compilation we should ignore methods that are not accessible
        // on this side of compilation.
        if (Context.getLangOpts().CUDAIsDevice) {
          // In device mode ignore methods without __device__ attribute.
          if (!MD->hasAttr<CUDADeviceAttr>())
            continue;
        } else {
          // In host mode ignore __device__-only methods.
          if (!MD->hasAttr<CUDAHostAttr>() && MD->hasAttr<CUDADeviceAttr>())
            continue;
        }
      }
  
      // If the key function is dllimport but the class isn't, then the class has
      // no key function. The DLL that exports the key function won't export the
      // vtable in this case.
      if (MD->hasAttr<DLLImportAttr>() && !RD->hasAttr<DLLImportAttr>())
        return nullptr;
  
      // We found it.
      return MD;
    }
  
    return nullptr;
  }
  
  DiagnosticBuilder ItaniumRecordLayoutBuilder::Diag(SourceLocation Loc,
                                                     unsigned DiagID) {
    return Context.getDiagnostics().Report(Loc, DiagID);
  }
  
  /// Does the target C++ ABI require us to skip over the tail-padding
  /// of the given class (considering it as a base class) when allocating
  /// objects?
  static bool mustSkipTailPadding(TargetCXXABI ABI, const CXXRecordDecl *RD) {
    switch (ABI.getTailPaddingUseRules()) {
    case TargetCXXABI::AlwaysUseTailPadding:
      return false;
  
    case TargetCXXABI::UseTailPaddingUnlessPOD03:
      // FIXME: To the extent that this is meant to cover the Itanium ABI
      // rules, we should implement the restrictions about over-sized
      // bitfields:
      //
      // http://itanium-cxx-abi.github.io/cxx-abi/abi.html#POD :
      //   In general, a type is considered a POD for the purposes of
      //   layout if it is a POD type (in the sense of ISO C++
      //   [basic.types]). However, a POD-struct or POD-union (in the
      //   sense of ISO C++ [class]) with a bitfield member whose
      //   declared width is wider than the declared type of the
      //   bitfield is not a POD for the purpose of layout.  Similarly,
      //   an array type is not a POD for the purpose of layout if the
      //   element type of the array is not a POD for the purpose of
      //   layout.
      //
      //   Where references to the ISO C++ are made in this paragraph,
      //   the Technical Corrigendum 1 version of the standard is
      //   intended.
      return RD->isPOD();
  
    case TargetCXXABI::UseTailPaddingUnlessPOD11:
      // This is equivalent to RD->getTypeForDecl().isCXX11PODType(),
      // but with a lot of abstraction penalty stripped off.  This does
      // assume that these properties are set correctly even in C++98
      // mode; fortunately, that is true because we want to assign
      // consistently semantics to the type-traits intrinsics (or at
      // least as many of them as possible).
      return RD->isTrivial() && RD->isCXX11StandardLayout();
    }
  
    llvm_unreachable("bad tail-padding use kind");
  }
  
  static bool isMsLayout(const ASTContext &Context, bool CheckAuxABI = false) {
    return (CheckAuxABI) ? Context.getAuxTargetInfo()->getCXXABI().isMicrosoft()
                         : Context.getTargetInfo().getCXXABI().isMicrosoft();
  }
  
  // This section contains an implementation of struct layout that is, up to the
  // included tests, compatible with cl.exe (2013).  The layout produced is
  // significantly different than those produced by the Itanium ABI.  Here we note
  // the most important differences.
  //
  // * The alignment of bitfields in unions is ignored when computing the
  //   alignment of the union.
  // * The existence of zero-width bitfield that occurs after anything other than
  //   a non-zero length bitfield is ignored.
  // * There is no explicit primary base for the purposes of layout.  All bases
  //   with vfptrs are laid out first, followed by all bases without vfptrs.
  // * The Itanium equivalent vtable pointers are split into a vfptr (virtual
  //   function pointer) and a vbptr (virtual base pointer).  They can each be
  //   shared with a, non-virtual bases. These bases need not be the same.  vfptrs
  //   always occur at offset 0.  vbptrs can occur at an arbitrary offset and are
  //   placed after the lexicographically last non-virtual base.  This placement
  //   is always before fields but can be in the middle of the non-virtual bases
  //   due to the two-pass layout scheme for non-virtual-bases.
  // * Virtual bases sometimes require a 'vtordisp' field that is laid out before
  //   the virtual base and is used in conjunction with virtual overrides during
  //   construction and destruction.  This is always a 4 byte value and is used as
  //   an alternative to constructor vtables.
  // * vtordisps are allocated in a block of memory with size and alignment equal
  //   to the alignment of the completed structure (before applying __declspec(
  //   align())).  The vtordisp always occur at the end of the allocation block,
  //   immediately prior to the virtual base.
  // * vfptrs are injected after all bases and fields have been laid out.  In
  //   order to guarantee proper alignment of all fields, the vfptr injection
  //   pushes all bases and fields back by the alignment imposed by those bases
  //   and fields.  This can potentially add a significant amount of padding.
  //   vfptrs are always injected at offset 0.
  // * vbptrs are injected after all bases and fields have been laid out.  In
  //   order to guarantee proper alignment of all fields, the vfptr injection
  //   pushes all bases and fields back by the alignment imposed by those bases
  //   and fields.  This can potentially add a significant amount of padding.
  //   vbptrs are injected immediately after the last non-virtual base as
  //   lexicographically ordered in the code.  If this site isn't pointer aligned
  //   the vbptr is placed at the next properly aligned location.  Enough padding
  //   is added to guarantee a fit.
  // * The last zero sized non-virtual base can be placed at the end of the
  //   struct (potentially aliasing another object), or may alias with the first
  //   field, even if they are of the same type.
  // * The last zero size virtual base may be placed at the end of the struct
  //   potentially aliasing another object.
  // * The ABI attempts to avoid aliasing of zero sized bases by adding padding
  //   between bases or vbases with specific properties.  The criteria for
  //   additional padding between two bases is that the first base is zero sized
  //   or ends with a zero sized subobject and the second base is zero sized or
  //   trails with a zero sized base or field (sharing of vfptrs can reorder the
  //   layout of the so the leading base is not always the first one declared).
  //   This rule does take into account fields that are not records, so padding
  //   will occur even if the last field is, e.g. an int. The padding added for
  //   bases is 1 byte.  The padding added between vbases depends on the alignment
  //   of the object but is at least 4 bytes (in both 32 and 64 bit modes).
  // * There is no concept of non-virtual alignment, non-virtual alignment and
  //   alignment are always identical.
  // * There is a distinction between alignment and required alignment.
  //   __declspec(align) changes the required alignment of a struct.  This
  //   alignment is _always_ obeyed, even in the presence of #pragma pack. A
  //   record inherits required alignment from all of its fields and bases.
  // * __declspec(align) on bitfields has the effect of changing the bitfield's
  //   alignment instead of its required alignment.  This is the only known way
  //   to make the alignment of a struct bigger than 8.  Interestingly enough
  //   this alignment is also immune to the effects of #pragma pack and can be
  //   used to create structures with large alignment under #pragma pack.
  //   However, because it does not impact required alignment, such a structure,
  //   when used as a field or base, will not be aligned if #pragma pack is
  //   still active at the time of use.
  //
  // Known incompatibilities:
  // * all: #pragma pack between fields in a record
  // * 2010 and back: If the last field in a record is a bitfield, every object
  //   laid out after the record will have extra padding inserted before it.  The
  //   extra padding will have size equal to the size of the storage class of the
  //   bitfield.  0 sized bitfields don't exhibit this behavior and the extra
  //   padding can be avoided by adding a 0 sized bitfield after the non-zero-
  //   sized bitfield.
  // * 2012 and back: In 64-bit mode, if the alignment of a record is 16 or
  //   greater due to __declspec(align()) then a second layout phase occurs after
  //   The locations of the vf and vb pointers are known.  This layout phase
  //   suffers from the "last field is a bitfield" bug in 2010 and results in
  //   _every_ field getting padding put in front of it, potentially including the
  //   vfptr, leaving the vfprt at a non-zero location which results in a fault if
  //   anything tries to read the vftbl.  The second layout phase also treats
  //   bitfields as separate entities and gives them each storage rather than
  //   packing them.  Additionally, because this phase appears to perform a
  //   (an unstable) sort on the members before laying them out and because merged
  //   bitfields have the same address, the bitfields end up in whatever order
  //   the sort left them in, a behavior we could never hope to replicate.
  
  namespace {
  struct MicrosoftRecordLayoutBuilder {
    struct ElementInfo {
      CharUnits Size;
      CharUnits Alignment;
    };
    typedef llvm::DenseMap<const CXXRecordDecl *, CharUnits> BaseOffsetsMapTy;
    MicrosoftRecordLayoutBuilder(const ASTContext &Context) : Context(Context) {}
  private:
    MicrosoftRecordLayoutBuilder(const MicrosoftRecordLayoutBuilder &) = delete;
    void operator=(const MicrosoftRecordLayoutBuilder &) = delete;
  public:
    void layout(const RecordDecl *RD);
    void cxxLayout(const CXXRecordDecl *RD);
    /// Initializes size and alignment and honors some flags.
    void initializeLayout(const RecordDecl *RD);
    /// Initialized C++ layout, compute alignment and virtual alignment and
    /// existence of vfptrs and vbptrs.  Alignment is needed before the vfptr is
    /// laid out.
    void initializeCXXLayout(const CXXRecordDecl *RD);
    void layoutNonVirtualBases(const CXXRecordDecl *RD);
    void layoutNonVirtualBase(const CXXRecordDecl *RD,
                              const CXXRecordDecl *BaseDecl,
                              const ASTRecordLayout &BaseLayout,
                              const ASTRecordLayout *&PreviousBaseLayout);
    void injectVFPtr(const CXXRecordDecl *RD);
    void injectVBPtr(const CXXRecordDecl *RD);
    /// Lays out the fields of the record.  Also rounds size up to
    /// alignment.
    void layoutFields(const RecordDecl *RD);
    void layoutField(const FieldDecl *FD);
    void layoutBitField(const FieldDecl *FD);
    /// Lays out a single zero-width bit-field in the record and handles
    /// special cases associated with zero-width bit-fields.
    void layoutZeroWidthBitField(const FieldDecl *FD);
    void layoutVirtualBases(const CXXRecordDecl *RD);
    void finalizeLayout(const RecordDecl *RD);
    /// Gets the size and alignment of a base taking pragma pack and
    /// __declspec(align) into account.
    ElementInfo getAdjustedElementInfo(const ASTRecordLayout &Layout);
    /// Gets the size and alignment of a field taking pragma  pack and
    /// __declspec(align) into account.  It also updates RequiredAlignment as a
    /// side effect because it is most convenient to do so here.
    ElementInfo getAdjustedElementInfo(const FieldDecl *FD);
    /// Places a field at an offset in CharUnits.
    void placeFieldAtOffset(CharUnits FieldOffset) {
      FieldOffsets.push_back(Context.toBits(FieldOffset));
    }
    /// Places a bitfield at a bit offset.
    void placeFieldAtBitOffset(uint64_t FieldOffset) {
      FieldOffsets.push_back(FieldOffset);
    }
    /// Compute the set of virtual bases for which vtordisps are required.
    void computeVtorDispSet(
        llvm::SmallPtrSetImpl<const CXXRecordDecl *> &HasVtorDispSet,
        const CXXRecordDecl *RD) const;
    const ASTContext &Context;
    /// The size of the record being laid out.
    CharUnits Size;
    /// The non-virtual size of the record layout.
    CharUnits NonVirtualSize;
    /// The data size of the record layout.
    CharUnits DataSize;
    /// The current alignment of the record layout.
    CharUnits Alignment;
    /// The maximum allowed field alignment. This is set by #pragma pack.
    CharUnits MaxFieldAlignment;
    /// The alignment that this record must obey.  This is imposed by
    /// __declspec(align()) on the record itself or one of its fields or bases.
    CharUnits RequiredAlignment;
    /// The size of the allocation of the currently active bitfield.
    /// This value isn't meaningful unless LastFieldIsNonZeroWidthBitfield
    /// is true.
    CharUnits CurrentBitfieldSize;
    /// Offset to the virtual base table pointer (if one exists).
    CharUnits VBPtrOffset;
    /// Minimum record size possible.
    CharUnits MinEmptyStructSize;
    /// The size and alignment info of a pointer.
    ElementInfo PointerInfo;
    /// The primary base class (if one exists).
    const CXXRecordDecl *PrimaryBase;
    /// The class we share our vb-pointer with.
    const CXXRecordDecl *SharedVBPtrBase;
    /// The collection of field offsets.
    SmallVector<uint64_t, 16> FieldOffsets;
    /// Base classes and their offsets in the record.
    BaseOffsetsMapTy Bases;
    /// virtual base classes and their offsets in the record.
    ASTRecordLayout::VBaseOffsetsMapTy VBases;
    /// The number of remaining bits in our last bitfield allocation.
    /// This value isn't meaningful unless LastFieldIsNonZeroWidthBitfield is
    /// true.
    unsigned RemainingBitsInField;
    bool IsUnion : 1;
    /// True if the last field laid out was a bitfield and was not 0
    /// width.
    bool LastFieldIsNonZeroWidthBitfield : 1;
    /// True if the class has its own vftable pointer.
    bool HasOwnVFPtr : 1;
    /// True if the class has a vbtable pointer.
    bool HasVBPtr : 1;
    /// True if the last sub-object within the type is zero sized or the
    /// object itself is zero sized.  This *does not* count members that are not
    /// records.  Only used for MS-ABI.
    bool EndsWithZeroSizedObject : 1;
    /// True if this class is zero sized or first base is zero sized or
    /// has this property.  Only used for MS-ABI.
    bool LeadsWithZeroSizedBase : 1;
  
    /// True if the external AST source provided a layout for this record.
    bool UseExternalLayout : 1;
  
    /// The layout provided by the external AST source. Only active if
    /// UseExternalLayout is true.
    ExternalLayout External;
  };
  } // namespace
  
  MicrosoftRecordLayoutBuilder::ElementInfo
  MicrosoftRecordLayoutBuilder::getAdjustedElementInfo(
      const ASTRecordLayout &Layout) {
    ElementInfo Info;
    Info.Alignment = Layout.getAlignment();
    // Respect pragma pack.
    if (!MaxFieldAlignment.isZero())
      Info.Alignment = std::min(Info.Alignment, MaxFieldAlignment);
    // Track zero-sized subobjects here where it's already available.
    EndsWithZeroSizedObject = Layout.endsWithZeroSizedObject();
    // Respect required alignment, this is necessary because we may have adjusted
    // the alignment in the case of pragam pack.  Note that the required alignment
    // doesn't actually apply to the struct alignment at this point.
    Alignment = std::max(Alignment, Info.Alignment);
    RequiredAlignment = std::max(RequiredAlignment, Layout.getRequiredAlignment());
    Info.Alignment = std::max(Info.Alignment, Layout.getRequiredAlignment());
    Info.Size = Layout.getNonVirtualSize();
    return Info;
  }
  
  MicrosoftRecordLayoutBuilder::ElementInfo
  MicrosoftRecordLayoutBuilder::getAdjustedElementInfo(
      const FieldDecl *FD) {
    // Get the alignment of the field type's natural alignment, ignore any
    // alignment attributes.
    ElementInfo Info;
    std::tie(Info.Size, Info.Alignment) =
        Context.getTypeInfoInChars(FD->getType()->getUnqualifiedDesugaredType());
    // Respect align attributes on the field.
    CharUnits FieldRequiredAlignment =
        Context.toCharUnitsFromBits(FD->getMaxAlignment());
    // Respect align attributes on the type.
    if (Context.isAlignmentRequired(FD->getType()))
      FieldRequiredAlignment = std::max(
          Context.getTypeAlignInChars(FD->getType()), FieldRequiredAlignment);
    // Respect attributes applied to subobjects of the field.
    if (FD->isBitField())
      // For some reason __declspec align impacts alignment rather than required
      // alignment when it is applied to bitfields.
      Info.Alignment = std::max(Info.Alignment, FieldRequiredAlignment);
    else {
      if (auto RT =
              FD->getType()->getBaseElementTypeUnsafe()->getAs<RecordType>()) {
        auto const &Layout = Context.getASTRecordLayout(RT->getDecl());
        EndsWithZeroSizedObject = Layout.endsWithZeroSizedObject();
        FieldRequiredAlignment = std::max(FieldRequiredAlignment,
                                          Layout.getRequiredAlignment());
      }
      // Capture required alignment as a side-effect.
      RequiredAlignment = std::max(RequiredAlignment, FieldRequiredAlignment);
    }
    // Respect pragma pack, attribute pack and declspec align
    if (!MaxFieldAlignment.isZero())
      Info.Alignment = std::min(Info.Alignment, MaxFieldAlignment);
    if (FD->hasAttr<PackedAttr>())
      Info.Alignment = CharUnits::One();
    Info.Alignment = std::max(Info.Alignment, FieldRequiredAlignment);
    return Info;
  }
  
  void MicrosoftRecordLayoutBuilder::layout(const RecordDecl *RD) {
    // For C record layout, zero-sized records always have size 4.
    MinEmptyStructSize = CharUnits::fromQuantity(4);
    initializeLayout(RD);
    layoutFields(RD);
    DataSize = Size = Size.alignTo(Alignment);
    RequiredAlignment = std::max(
        RequiredAlignment, Context.toCharUnitsFromBits(RD->getMaxAlignment()));
    finalizeLayout(RD);
  }
  
  void MicrosoftRecordLayoutBuilder::cxxLayout(const CXXRecordDecl *RD) {
    // The C++ standard says that empty structs have size 1.
    MinEmptyStructSize = CharUnits::One();
    initializeLayout(RD);
    initializeCXXLayout(RD);
    layoutNonVirtualBases(RD);
    layoutFields(RD);
    injectVBPtr(RD);
    injectVFPtr(RD);
    if (HasOwnVFPtr || (HasVBPtr && !SharedVBPtrBase))
      Alignment = std::max(Alignment, PointerInfo.Alignment);
    auto RoundingAlignment = Alignment;
    if (!MaxFieldAlignment.isZero())
      RoundingAlignment = std::min(RoundingAlignment, MaxFieldAlignment);
    if (!UseExternalLayout)
      Size = Size.alignTo(RoundingAlignment);
    NonVirtualSize = Size;
    RequiredAlignment = std::max(
        RequiredAlignment, Context.toCharUnitsFromBits(RD->getMaxAlignment()));
    layoutVirtualBases(RD);
    finalizeLayout(RD);
  }
  
  void MicrosoftRecordLayoutBuilder::initializeLayout(const RecordDecl *RD) {
    IsUnion = RD->isUnion();
    Size = CharUnits::Zero();
    Alignment = CharUnits::One();
    // In 64-bit mode we always perform an alignment step after laying out vbases.
    // In 32-bit mode we do not.  The check to see if we need to perform alignment
    // checks the RequiredAlignment field and performs alignment if it isn't 0.
    RequiredAlignment = Context.getTargetInfo().getTriple().isArch64Bit()
                            ? CharUnits::One()
                            : CharUnits::Zero();
    // Compute the maximum field alignment.
    MaxFieldAlignment = CharUnits::Zero();
    // Honor the default struct packing maximum alignment flag.
    if (unsigned DefaultMaxFieldAlignment = Context.getLangOpts().PackStruct)
        MaxFieldAlignment = CharUnits::fromQuantity(DefaultMaxFieldAlignment);
    // Honor the packing attribute.  The MS-ABI ignores pragma pack if its larger
    // than the pointer size.
    if (const MaxFieldAlignmentAttr *MFAA = RD->getAttr<MaxFieldAlignmentAttr>()){
      unsigned PackedAlignment = MFAA->getAlignment();
      if (PackedAlignment <= Context.getTargetInfo().getPointerWidth(0))
        MaxFieldAlignment = Context.toCharUnitsFromBits(PackedAlignment);
    }
    // Packed attribute forces max field alignment to be 1.
    if (RD->hasAttr<PackedAttr>())
      MaxFieldAlignment = CharUnits::One();
  
    // Try to respect the external layout if present.
    UseExternalLayout = false;
    if (ExternalASTSource *Source = Context.getExternalSource())
      UseExternalLayout = Source->layoutRecordType(
          RD, External.Size, External.Align, External.FieldOffsets,
          External.BaseOffsets, External.VirtualBaseOffsets);
  }
  
  void
  MicrosoftRecordLayoutBuilder::initializeCXXLayout(const CXXRecordDecl *RD) {
    EndsWithZeroSizedObject = false;
    LeadsWithZeroSizedBase = false;
    HasOwnVFPtr = false;
    HasVBPtr = false;
    PrimaryBase = nullptr;
    SharedVBPtrBase = nullptr;
    // Calculate pointer size and alignment.  These are used for vfptr and vbprt
    // injection.
    PointerInfo.Size =
        Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
    PointerInfo.Alignment =
        Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerAlign(0));
    // Respect pragma pack.
    if (!MaxFieldAlignment.isZero())
      PointerInfo.Alignment = std::min(PointerInfo.Alignment, MaxFieldAlignment);
  }
  
  void
  MicrosoftRecordLayoutBuilder::layoutNonVirtualBases(const CXXRecordDecl *RD) {
    // The MS-ABI lays out all bases that contain leading vfptrs before it lays
    // out any bases that do not contain vfptrs.  We implement this as two passes
    // over the bases.  This approach guarantees that the primary base is laid out
    // first.  We use these passes to calculate some additional aggregated
    // information about the bases, such as required alignment and the presence of
    // zero sized members.
    const ASTRecordLayout *PreviousBaseLayout = nullptr;
    // Iterate through the bases and lay out the non-virtual ones.
    for (const CXXBaseSpecifier &Base : RD->bases()) {
      const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
      const ASTRecordLayout &BaseLayout = Context.getASTRecordLayout(BaseDecl);
      // Mark and skip virtual bases.
      if (Base.isVirtual()) {
        HasVBPtr = true;
        continue;
      }
      // Check for a base to share a VBPtr with.
      if (!SharedVBPtrBase && BaseLayout.hasVBPtr()) {
        SharedVBPtrBase = BaseDecl;
        HasVBPtr = true;
      }
      // Only lay out bases with extendable VFPtrs on the first pass.
      if (!BaseLayout.hasExtendableVFPtr())
        continue;
      // If we don't have a primary base, this one qualifies.
      if (!PrimaryBase) {
        PrimaryBase = BaseDecl;
        LeadsWithZeroSizedBase = BaseLayout.leadsWithZeroSizedBase();
      }
      // Lay out the base.
      layoutNonVirtualBase(RD, BaseDecl, BaseLayout, PreviousBaseLayout);
    }
    // Figure out if we need a fresh VFPtr for this class.
    if (!PrimaryBase && RD->isDynamicClass())
      for (CXXRecordDecl::method_iterator i = RD->method_begin(),
                                          e = RD->method_end();
           !HasOwnVFPtr && i != e; ++i)
        HasOwnVFPtr = i->isVirtual() && i->size_overridden_methods() == 0;
    // If we don't have a primary base then we have a leading object that could
    // itself lead with a zero-sized object, something we track.
    bool CheckLeadingLayout = !PrimaryBase;
    // Iterate through the bases and lay out the non-virtual ones.
    for (const CXXBaseSpecifier &Base : RD->bases()) {
      if (Base.isVirtual())
        continue;
      const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
      const ASTRecordLayout &BaseLayout = Context.getASTRecordLayout(BaseDecl);
      // Only lay out bases without extendable VFPtrs on the second pass.
      if (BaseLayout.hasExtendableVFPtr()) {
        VBPtrOffset = Bases[BaseDecl] + BaseLayout.getNonVirtualSize();
        continue;
      }
      // If this is the first layout, check to see if it leads with a zero sized
      // object.  If it does, so do we.
      if (CheckLeadingLayout) {
        CheckLeadingLayout = false;
        LeadsWithZeroSizedBase = BaseLayout.leadsWithZeroSizedBase();
      }
      // Lay out the base.
      layoutNonVirtualBase(RD, BaseDecl, BaseLayout, PreviousBaseLayout);
      VBPtrOffset = Bases[BaseDecl] + BaseLayout.getNonVirtualSize();
    }
    // Set our VBPtroffset if we know it at this point.
    if (!HasVBPtr)
      VBPtrOffset = CharUnits::fromQuantity(-1);
    else if (SharedVBPtrBase) {
      const ASTRecordLayout &Layout = Context.getASTRecordLayout(SharedVBPtrBase);
      VBPtrOffset = Bases[SharedVBPtrBase] + Layout.getVBPtrOffset();
    }
  }
  
  static bool recordUsesEBO(const RecordDecl *RD) {
    if (!isa<CXXRecordDecl>(RD))
      return false;
    if (RD->hasAttr<EmptyBasesAttr>())
      return true;
    if (auto *LVA = RD->getAttr<LayoutVersionAttr>())
      // TODO: Double check with the next version of MSVC.
      if (LVA->getVersion() <= LangOptions::MSVC2015)
        return false;
    // TODO: Some later version of MSVC will change the default behavior of the
    // compiler to enable EBO by default.  When this happens, we will need an
    // additional isCompatibleWithMSVC check.
    return false;
  }
  
  void MicrosoftRecordLayoutBuilder::layoutNonVirtualBase(
      const CXXRecordDecl *RD,
      const CXXRecordDecl *BaseDecl,
      const ASTRecordLayout &BaseLayout,
      const ASTRecordLayout *&PreviousBaseLayout) {
    // Insert padding between two bases if the left first one is zero sized or
    // contains a zero sized subobject and the right is zero sized or one leads
    // with a zero sized base.
    bool MDCUsesEBO = recordUsesEBO(RD);
    if (PreviousBaseLayout && PreviousBaseLayout->endsWithZeroSizedObject() &&
        BaseLayout.leadsWithZeroSizedBase() && !MDCUsesEBO)
      Size++;
    ElementInfo Info = getAdjustedElementInfo(BaseLayout);
    CharUnits BaseOffset;
  
    // Respect the external AST source base offset, if present.
    bool FoundBase = false;
    if (UseExternalLayout) {
      FoundBase = External.getExternalNVBaseOffset(BaseDecl, BaseOffset);
      if (FoundBase) {
        assert(BaseOffset >= Size && "base offset already allocated");
        Size = BaseOffset;
      }
    }
  
    if (!FoundBase) {
      if (MDCUsesEBO && BaseDecl->isEmpty()) {
        assert(BaseLayout.getNonVirtualSize() == CharUnits::Zero());
        BaseOffset = CharUnits::Zero();
      } else {
        // Otherwise, lay the base out at the end of the MDC.
        BaseOffset = Size = Size.alignTo(Info.Alignment);
      }
    }
    Bases.insert(std::make_pair(BaseDecl, BaseOffset));
    Size += BaseLayout.getNonVirtualSize();
    PreviousBaseLayout = &BaseLayout;
  }
  
  void MicrosoftRecordLayoutBuilder::layoutFields(const RecordDecl *RD) {
    LastFieldIsNonZeroWidthBitfield = false;
    for (const FieldDecl *Field : RD->fields())
      layoutField(Field);
  }
  
  void MicrosoftRecordLayoutBuilder::layoutField(const FieldDecl *FD) {
    if (FD->isBitField()) {
      layoutBitField(FD);
      return;
    }
    LastFieldIsNonZeroWidthBitfield = false;
    ElementInfo Info = getAdjustedElementInfo(FD);
    Alignment = std::max(Alignment, Info.Alignment);
    CharUnits FieldOffset;
    if (UseExternalLayout)
      FieldOffset =
          Context.toCharUnitsFromBits(External.getExternalFieldOffset(FD));
    else if (IsUnion)
      FieldOffset = CharUnits::Zero();
    else
      FieldOffset = Size.alignTo(Info.Alignment);
    placeFieldAtOffset(FieldOffset);
    Size = std::max(Size, FieldOffset + Info.Size);
  }
  
  void MicrosoftRecordLayoutBuilder::layoutBitField(const FieldDecl *FD) {
    unsigned Width = FD->getBitWidthValue(Context);
    if (Width == 0) {
      layoutZeroWidthBitField(FD);
      return;
    }
    ElementInfo Info = getAdjustedElementInfo(FD);
    // Clamp the bitfield to a containable size for the sake of being able
    // to lay them out.  Sema will throw an error.
    if (Width > Context.toBits(Info.Size))
      Width = Context.toBits(Info.Size);
    // Check to see if this bitfield fits into an existing allocation.  Note:
    // MSVC refuses to pack bitfields of formal types with different sizes
    // into the same allocation.
    if (!UseExternalLayout && !IsUnion && LastFieldIsNonZeroWidthBitfield &&
        CurrentBitfieldSize == Info.Size && Width <= RemainingBitsInField) {
      placeFieldAtBitOffset(Context.toBits(Size) - RemainingBitsInField);
      RemainingBitsInField -= Width;
      return;
    }
    LastFieldIsNonZeroWidthBitfield = true;
    CurrentBitfieldSize = Info.Size;
    if (UseExternalLayout) {
      auto FieldBitOffset = External.getExternalFieldOffset(FD);
      placeFieldAtBitOffset(FieldBitOffset);
      auto NewSize = Context.toCharUnitsFromBits(
          llvm::alignDown(FieldBitOffset, Context.toBits(Info.Alignment)) +
          Context.toBits(Info.Size));
      Size = std::max(Size, NewSize);
      Alignment = std::max(Alignment, Info.Alignment);
    } else if (IsUnion) {
      placeFieldAtOffset(CharUnits::Zero());
      Size = std::max(Size, Info.Size);
      // TODO: Add a Sema warning that MS ignores bitfield alignment in unions.
    } else {
      // Allocate a new block of memory and place the bitfield in it.
      CharUnits FieldOffset = Size.alignTo(Info.Alignment);
      placeFieldAtOffset(FieldOffset);
      Size = FieldOffset + Info.Size;
      Alignment = std::max(Alignment, Info.Alignment);
      RemainingBitsInField = Context.toBits(Info.Size) - Width;
    }
  }
  
  void
  MicrosoftRecordLayoutBuilder::layoutZeroWidthBitField(const FieldDecl *FD) {
    // Zero-width bitfields are ignored unless they follow a non-zero-width
    // bitfield.
    if (!LastFieldIsNonZeroWidthBitfield) {
      placeFieldAtOffset(IsUnion ? CharUnits::Zero() : Size);
      // TODO: Add a Sema warning that MS ignores alignment for zero
      // sized bitfields that occur after zero-size bitfields or non-bitfields.
      return;
    }
    LastFieldIsNonZeroWidthBitfield = false;
    ElementInfo Info = getAdjustedElementInfo(FD);
    if (IsUnion) {
      placeFieldAtOffset(CharUnits::Zero());
      Size = std::max(Size, Info.Size);
      // TODO: Add a Sema warning that MS ignores bitfield alignment in unions.
    } else {
      // Round up the current record size to the field's alignment boundary.
      CharUnits FieldOffset = Size.alignTo(Info.Alignment);
      placeFieldAtOffset(FieldOffset);
      Size = FieldOffset;
      Alignment = std::max(Alignment, Info.Alignment);
    }
  }
  
  void MicrosoftRecordLayoutBuilder::injectVBPtr(const CXXRecordDecl *RD) {
    if (!HasVBPtr || SharedVBPtrBase)
      return;
    // Inject the VBPointer at the injection site.
    CharUnits InjectionSite = VBPtrOffset;
    // But before we do, make sure it's properly aligned.
    VBPtrOffset = VBPtrOffset.alignTo(PointerInfo.Alignment);
    // Determine where the first field should be laid out after the vbptr.
    CharUnits FieldStart = VBPtrOffset + PointerInfo.Size;
    // Shift everything after the vbptr down, unless we're using an external
    // layout.
    if (UseExternalLayout) {
      // It is possible that there were no fields or bases located after vbptr,
      // so the size was not adjusted before.
      if (Size < FieldStart)
        Size = FieldStart;
      return;
    }
    // Make sure that the amount we push the fields back by is a multiple of the
    // alignment.
    CharUnits Offset = (FieldStart - InjectionSite)
                           .alignTo(std::max(RequiredAlignment, Alignment));
    Size += Offset;
    for (uint64_t &FieldOffset : FieldOffsets)
      FieldOffset += Context.toBits(Offset);
    for (BaseOffsetsMapTy::value_type &Base : Bases)
      if (Base.second >= InjectionSite)
        Base.second += Offset;
  }
  
  void MicrosoftRecordLayoutBuilder::injectVFPtr(const CXXRecordDecl *RD) {
    if (!HasOwnVFPtr)
      return;
    // Make sure that the amount we push the struct back by is a multiple of the
    // alignment.
    CharUnits Offset =
        PointerInfo.Size.alignTo(std::max(RequiredAlignment, Alignment));
    // Push back the vbptr, but increase the size of the object and push back
    // regular fields by the offset only if not using external record layout.
    if (HasVBPtr)
      VBPtrOffset += Offset;
  
    if (UseExternalLayout) {
      // The class may have no bases or fields, but still have a vfptr
      // (e.g. it's an interface class). The size was not correctly set before
      // in this case.
      if (FieldOffsets.empty() && Bases.empty())
        Size += Offset;
      return;
    }
  
    Size += Offset;
  
    // If we're using an external layout, the fields offsets have already
    // accounted for this adjustment.
    for (uint64_t &FieldOffset : FieldOffsets)
      FieldOffset += Context.toBits(Offset);
    for (BaseOffsetsMapTy::value_type &Base : Bases)
      Base.second += Offset;
  }
  
  void MicrosoftRecordLayoutBuilder::layoutVirtualBases(const CXXRecordDecl *RD) {
    if (!HasVBPtr)
      return;
    // Vtordisps are always 4 bytes (even in 64-bit mode)
    CharUnits VtorDispSize = CharUnits::fromQuantity(4);
    CharUnits VtorDispAlignment = VtorDispSize;
    // vtordisps respect pragma pack.
    if (!MaxFieldAlignment.isZero())
      VtorDispAlignment = std::min(VtorDispAlignment, MaxFieldAlignment);
    // The alignment of the vtordisp is at least the required alignment of the
    // entire record.  This requirement may be present to support vtordisp
    // injection.
    for (const CXXBaseSpecifier &VBase : RD->vbases()) {
      const CXXRecordDecl *BaseDecl = VBase.getType()->getAsCXXRecordDecl();
      const ASTRecordLayout &BaseLayout = Context.getASTRecordLayout(BaseDecl);
      RequiredAlignment =
          std::max(RequiredAlignment, BaseLayout.getRequiredAlignment());
    }
    VtorDispAlignment = std::max(VtorDispAlignment, RequiredAlignment);
    // Compute the vtordisp set.
    llvm::SmallPtrSet<const CXXRecordDecl *, 2> HasVtorDispSet;
    computeVtorDispSet(HasVtorDispSet, RD);
    // Iterate through the virtual bases and lay them out.
    const ASTRecordLayout *PreviousBaseLayout = nullptr;
    for (const CXXBaseSpecifier &VBase : RD->vbases()) {
      const CXXRecordDecl *BaseDecl = VBase.getType()->getAsCXXRecordDecl();
      const ASTRecordLayout &BaseLayout = Context.getASTRecordLayout(BaseDecl);
      bool HasVtordisp = HasVtorDispSet.count(BaseDecl) > 0;
      // Insert padding between two bases if the left first one is zero sized or
      // contains a zero sized subobject and the right is zero sized or one leads
      // with a zero sized base.  The padding between virtual bases is 4
      // bytes (in both 32 and 64 bits modes) and always involves rounding up to
      // the required alignment, we don't know why.
      if ((PreviousBaseLayout && PreviousBaseLayout->endsWithZeroSizedObject() &&
           BaseLayout.leadsWithZeroSizedBase() && !recordUsesEBO(RD)) ||
          HasVtordisp) {
        Size = Size.alignTo(VtorDispAlignment) + VtorDispSize;
        Alignment = std::max(VtorDispAlignment, Alignment);
      }
      // Insert the virtual base.
      ElementInfo Info = getAdjustedElementInfo(BaseLayout);
      CharUnits BaseOffset;
  
      // Respect the external AST source base offset, if present.
      if (UseExternalLayout) {
        if (!External.getExternalVBaseOffset(BaseDecl, BaseOffset))
          BaseOffset = Size;
      } else
        BaseOffset = Size.alignTo(Info.Alignment);
  
      assert(BaseOffset >= Size && "base offset already allocated");
  
      VBases.insert(std::make_pair(BaseDecl,
          ASTRecordLayout::VBaseInfo(BaseOffset, HasVtordisp)));
      Size = BaseOffset + BaseLayout.getNonVirtualSize();
      PreviousBaseLayout = &BaseLayout;
    }
  }
  
  void MicrosoftRecordLayoutBuilder::finalizeLayout(const RecordDecl *RD) {
    // Respect required alignment.  Note that in 32-bit mode Required alignment
    // may be 0 and cause size not to be updated.
    DataSize = Size;
    if (!RequiredAlignment.isZero()) {
      Alignment = std::max(Alignment, RequiredAlignment);
      auto RoundingAlignment = Alignment;
      if (!MaxFieldAlignment.isZero())
        RoundingAlignment = std::min(RoundingAlignment, MaxFieldAlignment);
      RoundingAlignment = std::max(RoundingAlignment, RequiredAlignment);
      Size = Size.alignTo(RoundingAlignment);
    }
    if (Size.isZero()) {
      if (!recordUsesEBO(RD) || !cast<CXXRecordDecl>(RD)->isEmpty()) {
        EndsWithZeroSizedObject = true;
        LeadsWithZeroSizedBase = true;
      }
      // Zero-sized structures have size equal to their alignment if a
      // __declspec(align) came into play.
      if (RequiredAlignment >= MinEmptyStructSize)
        Size = Alignment;
      else
        Size = MinEmptyStructSize;
    }
  
    if (UseExternalLayout) {
      Size = Context.toCharUnitsFromBits(External.Size);
      if (External.Align)
        Alignment = Context.toCharUnitsFromBits(External.Align);
    }
  }
  
  // Recursively walks the non-virtual bases of a class and determines if any of
  // them are in the bases with overridden methods set.
  static bool
  RequiresVtordisp(const llvm::SmallPtrSetImpl<const CXXRecordDecl *> &
                       BasesWithOverriddenMethods,
                   const CXXRecordDecl *RD) {
    if (BasesWithOverriddenMethods.count(RD))
      return true;
    // If any of a virtual bases non-virtual bases (recursively) requires a
    // vtordisp than so does this virtual base.
    for (const CXXBaseSpecifier &Base : RD->bases())
      if (!Base.isVirtual() &&
          RequiresVtordisp(BasesWithOverriddenMethods,
                           Base.getType()->getAsCXXRecordDecl()))
        return true;
    return false;
  }
  
  void MicrosoftRecordLayoutBuilder::computeVtorDispSet(
      llvm::SmallPtrSetImpl<const CXXRecordDecl *> &HasVtordispSet,
      const CXXRecordDecl *RD) const {
    // /vd2 or #pragma vtordisp(2): Always use vtordisps for virtual bases with
    // vftables.
    if (RD->getMSVtorDispMode() == MSVtorDispMode::ForVFTable) {
      for (const CXXBaseSpecifier &Base : RD->vbases()) {
        const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
        const ASTRecordLayout &Layout = Context.getASTRecordLayout(BaseDecl);
        if (Layout.hasExtendableVFPtr())
          HasVtordispSet.insert(BaseDecl);
      }
      return;
    }
  
    // If any of our bases need a vtordisp for this type, so do we.  Check our
    // direct bases for vtordisp requirements.
    for (const CXXBaseSpecifier &Base : RD->bases()) {
      const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
      const ASTRecordLayout &Layout = Context.getASTRecordLayout(BaseDecl);
      for (const auto &bi : Layout.getVBaseOffsetsMap())
        if (bi.second.hasVtorDisp())
          HasVtordispSet.insert(bi.first);
    }
    // We don't introduce any additional vtordisps if either:
    // * A user declared constructor or destructor aren't declared.
    // * #pragma vtordisp(0) or the /vd0 flag are in use.
    if ((!RD->hasUserDeclaredConstructor() && !RD->hasUserDeclaredDestructor()) ||
        RD->getMSVtorDispMode() == MSVtorDispMode::Never)
      return;
    // /vd1 or #pragma vtordisp(1): Try to guess based on whether we think it's
    // possible for a partially constructed object with virtual base overrides to
    // escape a non-trivial constructor.
    assert(RD->getMSVtorDispMode() == MSVtorDispMode::ForVBaseOverride);
    // Compute a set of base classes which define methods we override.  A virtual
    // base in this set will require a vtordisp.  A virtual base that transitively
    // contains one of these bases as a non-virtual base will also require a
    // vtordisp.
    llvm::SmallPtrSet<const CXXMethodDecl *, 8> Work;
    llvm::SmallPtrSet<const CXXRecordDecl *, 2> BasesWithOverriddenMethods;
    // Seed the working set with our non-destructor, non-pure virtual methods.
    for (const CXXMethodDecl *MD : RD->methods())
      if (MD->isVirtual() && !isa<CXXDestructorDecl>(MD) && !MD->isPure())
        Work.insert(MD);
    while (!Work.empty()) {
      const CXXMethodDecl *MD = *Work.begin();
      auto MethodRange = MD->overridden_methods();
      // If a virtual method has no-overrides it lives in its parent's vtable.
      if (MethodRange.begin() == MethodRange.end())
        BasesWithOverriddenMethods.insert(MD->getParent());
      else
        Work.insert(MethodRange.begin(), MethodRange.end());
      // We've finished processing this element, remove it from the working set.
      Work.erase(MD);
    }
    // For each of our virtual bases, check if it is in the set of overridden
    // bases or if it transitively contains a non-virtual base that is.
    for (const CXXBaseSpecifier &Base : RD->vbases()) {
      const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
      if (!HasVtordispSet.count(BaseDecl) &&
          RequiresVtordisp(BasesWithOverriddenMethods, BaseDecl))
        HasVtordispSet.insert(BaseDecl);
    }
  }
  
  /// getASTRecordLayout - Get or compute information about the layout of the
  /// specified record (struct/union/class), which indicates its size and field
  /// position information.
  const ASTRecordLayout &
  ASTContext::getASTRecordLayout(const RecordDecl *D) const {
    // These asserts test different things.  A record has a definition
    // as soon as we begin to parse the definition.  That definition is
    // not a complete definition (which is what isDefinition() tests)
    // until we *finish* parsing the definition.
    bool CheckAuxABI = false;
    if (getLangOpts().SYCLIsDevice && (getAuxTargetInfo() != nullptr))
      CheckAuxABI = true;
  
    if (D->hasExternalLexicalStorage() && !D->getDefinition())
      getExternalSource()->CompleteType(const_cast<RecordDecl*>(D));
  
    D = D->getDefinition();
    assert(D && "Cannot get layout of forward declarations!");
    assert(!D->isInvalidDecl() && "Cannot get layout of invalid decl!");
    assert(D->isCompleteDefinition() && "Cannot layout type before complete!");
  
    // Look up this layout, if already laid out, return what we have.
    // Note that we can't save a reference to the entry because this function
    // is recursive.
    const ASTRecordLayout *Entry = ASTRecordLayouts[D];
    if (Entry) return *Entry;
  
    const ASTRecordLayout *NewEntry = nullptr;
  
    if (isMsLayout(*this, CheckAuxABI)) {
      MicrosoftRecordLayoutBuilder Builder(*this);
      if (const auto *RD = dyn_cast<CXXRecordDecl>(D)) {
        Builder.cxxLayout(RD);
        NewEntry = new (*this) ASTRecordLayout(
            *this, Builder.Size, Builder.Alignment, Builder.Alignment,
            Builder.RequiredAlignment,
            Builder.HasOwnVFPtr, Builder.HasOwnVFPtr || Builder.PrimaryBase,
            Builder.VBPtrOffset, Builder.DataSize, Builder.FieldOffsets,
            Builder.NonVirtualSize, Builder.Alignment, CharUnits::Zero(),
            Builder.PrimaryBase, false, Builder.SharedVBPtrBase,
            Builder.EndsWithZeroSizedObject, Builder.LeadsWithZeroSizedBase,
            Builder.Bases, Builder.VBases);
      } else {
        Builder.layout(D);
        NewEntry = new (*this) ASTRecordLayout(
            *this, Builder.Size, Builder.Alignment, Builder.Alignment,
            Builder.RequiredAlignment,
            Builder.Size, Builder.FieldOffsets);
      }
    } else {
      if (const auto *RD = dyn_cast<CXXRecordDecl>(D)) {
        EmptySubobjectMap EmptySubobjects(*this, RD);
        ItaniumRecordLayoutBuilder Builder(*this, &EmptySubobjects);
        Builder.Layout(RD);
  
        // In certain situations, we are allowed to lay out objects in the
        // tail-padding of base classes.  This is ABI-dependent.
        // FIXME: this should be stored in the record layout.
        bool skipTailPadding =
            mustSkipTailPadding(getTargetInfo().getCXXABI(), RD);
  
        // FIXME: This should be done in FinalizeLayout.
        CharUnits DataSize =
            skipTailPadding ? Builder.getSize() : Builder.getDataSize();
        CharUnits NonVirtualSize =
            skipTailPadding ? DataSize : Builder.NonVirtualSize;
        NewEntry = new (*this) ASTRecordLayout(
            *this, Builder.getSize(), Builder.Alignment, Builder.UnadjustedAlignment,
            /*RequiredAlignment : used by MS-ABI)*/
            Builder.Alignment, Builder.HasOwnVFPtr, RD->isDynamicClass(),
            CharUnits::fromQuantity(-1), DataSize, Builder.FieldOffsets,
            NonVirtualSize, Builder.NonVirtualAlignment,
            EmptySubobjects.SizeOfLargestEmptySubobject, Builder.PrimaryBase,
            Builder.PrimaryBaseIsVirtual, nullptr, false, false, Builder.Bases,
            Builder.VBases);
      } else {
        ItaniumRecordLayoutBuilder Builder(*this, /*EmptySubobjects=*/nullptr);
        Builder.Layout(D);
  
        NewEntry = new (*this) ASTRecordLayout(
            *this, Builder.getSize(), Builder.Alignment, Builder.UnadjustedAlignment,
            /*RequiredAlignment : used by MS-ABI)*/
            Builder.Alignment, Builder.getSize(), Builder.FieldOffsets);
      }
    }
  
    ASTRecordLayouts[D] = NewEntry;
  
    if (getLangOpts().DumpRecordLayouts) {
      llvm::outs() << "\n*** Dumping AST Record Layout\n";
      DumpRecordLayout(D, llvm::outs(), getLangOpts().DumpRecordLayoutsSimple);
    }
  
    return *NewEntry;
  }
  
  const CXXMethodDecl *ASTContext::getCurrentKeyFunction(const CXXRecordDecl *RD) {
    if (!getTargetInfo().getCXXABI().hasKeyFunctions())
      return nullptr;
  
    assert(RD->getDefinition() && "Cannot get key function for forward decl!");
    RD = RD->getDefinition();
  
    // Beware:
    //  1) computing the key function might trigger deserialization, which might
    //     invalidate iterators into KeyFunctions
    //  2) 'get' on the LazyDeclPtr might also trigger deserialization and
    //     invalidate the LazyDeclPtr within the map itself
    LazyDeclPtr Entry = KeyFunctions[RD];
    const Decl *Result =
        Entry ? Entry.get(getExternalSource()) : computeKeyFunction(*this, RD);
  
    // Store it back if it changed.
    if (Entry.isOffset() || Entry.isValid() != bool(Result))
      KeyFunctions[RD] = const_cast<Decl*>(Result);
  
    return cast_or_null<CXXMethodDecl>(Result);
  }
  
  void ASTContext::setNonKeyFunction(const CXXMethodDecl *Method) {
    assert(Method == Method->getFirstDecl() &&
           "not working with method declaration from class definition");
  
    // Look up the cache entry.  Since we're working with the first
    // declaration, its parent must be the class definition, which is
    // the correct key for the KeyFunctions hash.
    const auto &Map = KeyFunctions;
    auto I = Map.find(Method->getParent());
  
    // If it's not cached, there's nothing to do.
    if (I == Map.end()) return;
  
    // If it is cached, check whether it's the target method, and if so,
    // remove it from the cache. Note, the call to 'get' might invalidate
    // the iterator and the LazyDeclPtr object within the map.
    LazyDeclPtr Ptr = I->second;
    if (Ptr.get(getExternalSource()) == Method) {
      // FIXME: remember that we did this for module / chained PCH state?
      KeyFunctions.erase(Method->getParent());
    }
  }
  
  static uint64_t getFieldOffset(const ASTContext &C, const FieldDecl *FD) {
    const ASTRecordLayout &Layout = C.getASTRecordLayout(FD->getParent());
    return Layout.getFieldOffset(FD->getFieldIndex());
  }
  
  uint64_t ASTContext::getFieldOffset(const ValueDecl *VD) const {
    uint64_t OffsetInBits;
    if (const FieldDecl *FD = dyn_cast<FieldDecl>(VD)) {
      OffsetInBits = ::getFieldOffset(*this, FD);
    } else {
      const IndirectFieldDecl *IFD = cast<IndirectFieldDecl>(VD);
  
      OffsetInBits = 0;
      for (const NamedDecl *ND : IFD->chain())
        OffsetInBits += ::getFieldOffset(*this, cast<FieldDecl>(ND));
    }
  
    return OffsetInBits;
  }
  
  uint64_t ASTContext::lookupFieldBitOffset(const ObjCInterfaceDecl *OID,
                                            const ObjCImplementationDecl *ID,
                                            const ObjCIvarDecl *Ivar) const {
    const ObjCInterfaceDecl *Container = Ivar->getContainingInterface();
  
    // FIXME: We should eliminate the need to have ObjCImplementationDecl passed
    // in here; it should never be necessary because that should be the lexical
    // decl context for the ivar.
  
    // If we know have an implementation (and the ivar is in it) then
    // look up in the implementation layout.
    const ASTRecordLayout *RL;
    if (ID && declaresSameEntity(ID->getClassInterface(), Container))
      RL = &getASTObjCImplementationLayout(ID);
    else
      RL = &getASTObjCInterfaceLayout(Container);
  
    // Compute field index.
    //
    // FIXME: The index here is closely tied to how ASTContext::getObjCLayout is
    // implemented. This should be fixed to get the information from the layout
    // directly.
    unsigned Index = 0;
  
    for (const ObjCIvarDecl *IVD = Container->all_declared_ivar_begin();
         IVD; IVD = IVD->getNextIvar()) {
      if (Ivar == IVD)
        break;
      ++Index;
    }
    assert(Index < RL->getFieldCount() && "Ivar is not inside record layout!");
  
    return RL->getFieldOffset(Index);
  }
  
  /// getObjCLayout - Get or compute information about the layout of the
  /// given interface.
  ///
  /// \param Impl - If given, also include the layout of the interface's
  /// implementation. This may differ by including synthesized ivars.
  const ASTRecordLayout &
  ASTContext::getObjCLayout(const ObjCInterfaceDecl *D,
                            const ObjCImplementationDecl *Impl) const {
    // Retrieve the definition
    if (D->hasExternalLexicalStorage() && !D->getDefinition())
      getExternalSource()->CompleteType(const_cast<ObjCInterfaceDecl*>(D));
    D = D->getDefinition();
    assert(D && D->isThisDeclarationADefinition() && "Invalid interface decl!");
  
    // Look up this layout, if already laid out, return what we have.
    const ObjCContainerDecl *Key =
      Impl ? (const ObjCContainerDecl*) Impl : (const ObjCContainerDecl*) D;
    if (const ASTRecordLayout *Entry = ObjCLayouts[Key])
      return *Entry;
  
    // Add in synthesized ivar count if laying out an implementation.
    if (Impl) {
      unsigned SynthCount = CountNonClassIvars(D);
      // If there aren't any synthesized ivars then reuse the interface
      // entry. Note we can't cache this because we simply free all
      // entries later; however we shouldn't look up implementations
      // frequently.
      if (SynthCount == 0)
        return getObjCLayout(D, nullptr);
    }
  
    ItaniumRecordLayoutBuilder Builder(*this, /*EmptySubobjects=*/nullptr);
    Builder.Layout(D);
  
    const ASTRecordLayout *NewEntry =
      new (*this) ASTRecordLayout(*this, Builder.getSize(),
                                  Builder.Alignment,
                                  Builder.UnadjustedAlignment,
                                  /*RequiredAlignment : used by MS-ABI)*/
                                  Builder.Alignment,
                                  Builder.getDataSize(),
                                  Builder.FieldOffsets);
  
    ObjCLayouts[Key] = NewEntry;
  
    return *NewEntry;
  }
  
  static void PrintOffset(raw_ostream &OS,
                          CharUnits Offset, unsigned IndentLevel) {
    OS << llvm::format("%10" PRId64 " | ", (int64_t)Offset.getQuantity());
    OS.indent(IndentLevel * 2);
  }
  
  static void PrintBitFieldOffset(raw_ostream &OS, CharUnits Offset,
                                  unsigned Begin, unsigned Width,
                                  unsigned IndentLevel) {
    llvm::SmallString<10> Buffer;
    {
      llvm::raw_svector_ostream BufferOS(Buffer);
      BufferOS << Offset.getQuantity() << ':';
      if (Width == 0) {
        BufferOS << '-';
      } else {
        BufferOS << Begin << '-' << (Begin + Width - 1);
      }
    }
  
    OS << llvm::right_justify(Buffer, 10) << " | ";
    OS.indent(IndentLevel * 2);
  }
  
  static void PrintIndentNoOffset(raw_ostream &OS, unsigned IndentLevel) {
    OS << "           | ";
    OS.indent(IndentLevel * 2);
  }
  
  static void DumpRecordLayout(raw_ostream &OS, const RecordDecl *RD,
                               const ASTContext &C,
                               CharUnits Offset,
                               unsigned IndentLevel,
                               const char* Description,
                               bool PrintSizeInfo,
                               bool IncludeVirtualBases) {
    const ASTRecordLayout &Layout = C.getASTRecordLayout(RD);
    auto CXXRD = dyn_cast<CXXRecordDecl>(RD);
  
    PrintOffset(OS, Offset, IndentLevel);
    OS << C.getTypeDeclType(const_cast<RecordDecl*>(RD)).getAsString();
    if (Description)
      OS << ' ' << Description;
    if (CXXRD && CXXRD->isEmpty())
      OS << " (empty)";
    OS << '\n';
  
    IndentLevel++;
  
    // Dump bases.
    if (CXXRD) {
      const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
      bool HasOwnVFPtr = Layout.hasOwnVFPtr();
      bool HasOwnVBPtr = Layout.hasOwnVBPtr();
  
      // Vtable pointer.
      if (CXXRD->isDynamicClass() && !PrimaryBase && !isMsLayout(C)) {
        PrintOffset(OS, Offset, IndentLevel);
        OS << '(' << *RD << " vtable pointer)\n";
      } else if (HasOwnVFPtr) {
        PrintOffset(OS, Offset, IndentLevel);
        // vfptr (for Microsoft C++ ABI)
        OS << '(' << *RD << " vftable pointer)\n";
      }
  
      // Collect nvbases.
      SmallVector<const CXXRecordDecl *, 4> Bases;
      for (const CXXBaseSpecifier &Base : CXXRD->bases()) {
        assert(!Base.getType()->isDependentType() &&
               "Cannot layout class with dependent bases.");
        if (!Base.isVirtual())
          Bases.push_back(Base.getType()->getAsCXXRecordDecl());
      }
  
      // Sort nvbases by offset.
      llvm::stable_sort(
          Bases, [&](const CXXRecordDecl *L, const CXXRecordDecl *R) {
            return Layout.getBaseClassOffset(L) < Layout.getBaseClassOffset(R);
          });
  
      // Dump (non-virtual) bases
      for (const CXXRecordDecl *Base : Bases) {
        CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(Base);
        DumpRecordLayout(OS, Base, C, BaseOffset, IndentLevel,
                         Base == PrimaryBase ? "(primary base)" : "(base)",
                         /*PrintSizeInfo=*/false,
                         /*IncludeVirtualBases=*/false);
      }
  
      // vbptr (for Microsoft C++ ABI)
      if (HasOwnVBPtr) {
        PrintOffset(OS, Offset + Layout.getVBPtrOffset(), IndentLevel);
        OS << '(' << *RD << " vbtable pointer)\n";
      }
    }
  
    // Dump fields.
    uint64_t FieldNo = 0;
    for (RecordDecl::field_iterator I = RD->field_begin(),
           E = RD->field_end(); I != E; ++I, ++FieldNo) {
      const FieldDecl &Field = **I;
      uint64_t LocalFieldOffsetInBits = Layout.getFieldOffset(FieldNo);
      CharUnits FieldOffset =
        Offset + C.toCharUnitsFromBits(LocalFieldOffsetInBits);
  
      // Recursively dump fields of record type.
      if (auto RT = Field.getType()->getAs<RecordType>()) {
        DumpRecordLayout(OS, RT->getDecl(), C, FieldOffset, IndentLevel,
                         Field.getName().data(),
                         /*PrintSizeInfo=*/false,
                         /*IncludeVirtualBases=*/true);
        continue;
      }
  
      if (Field.isBitField()) {
        uint64_t LocalFieldByteOffsetInBits = C.toBits(FieldOffset - Offset);
        unsigned Begin = LocalFieldOffsetInBits - LocalFieldByteOffsetInBits;
        unsigned Width = Field.getBitWidthValue(C);
        PrintBitFieldOffset(OS, FieldOffset, Begin, Width, IndentLevel);
      } else {
        PrintOffset(OS, FieldOffset, IndentLevel);
      }
      OS << Field.getType().getAsString() << ' ' << Field << '\n';
    }
  
    // Dump virtual bases.
    if (CXXRD && IncludeVirtualBases) {
      const ASTRecordLayout::VBaseOffsetsMapTy &VtorDisps =
        Layout.getVBaseOffsetsMap();
  
      for (const CXXBaseSpecifier &Base : CXXRD->vbases()) {
        assert(Base.isVirtual() && "Found non-virtual class!");
        const CXXRecordDecl *VBase = Base.getType()->getAsCXXRecordDecl();
  
        CharUnits VBaseOffset = Offset + Layout.getVBaseClassOffset(VBase);
  
        if (VtorDisps.find(VBase)->second.hasVtorDisp()) {
          PrintOffset(OS, VBaseOffset - CharUnits::fromQuantity(4), IndentLevel);
          OS << "(vtordisp for vbase " << *VBase << ")\n";
        }
  
        DumpRecordLayout(OS, VBase, C, VBaseOffset, IndentLevel,
                         VBase == Layout.getPrimaryBase() ?
                           "(primary virtual base)" : "(virtual base)",
                         /*PrintSizeInfo=*/false,
                         /*IncludeVirtualBases=*/false);
      }
    }
  
    if (!PrintSizeInfo) return;
  
    PrintIndentNoOffset(OS, IndentLevel - 1);
    OS << "[sizeof=" << Layout.getSize().getQuantity();
    if (CXXRD && !isMsLayout(C))
      OS << ", dsize=" << Layout.getDataSize().getQuantity();
    OS << ", align=" << Layout.getAlignment().getQuantity();
  
    if (CXXRD) {
      OS << ",\n";
      PrintIndentNoOffset(OS, IndentLevel - 1);
      OS << " nvsize=" << Layout.getNonVirtualSize().getQuantity();
      OS << ", nvalign=" << Layout.getNonVirtualAlignment().getQuantity();
    }
    OS << "]\n";
  }
  
  void ASTContext::DumpRecordLayout(const RecordDecl *RD,
                                    raw_ostream &OS,
                                    bool Simple) const {
    if (!Simple) {
      ::DumpRecordLayout(OS, RD, *this, CharUnits(), 0, nullptr,
                         /*PrintSizeInfo*/true,
                         /*IncludeVirtualBases=*/true);
      return;
    }
  
    // The "simple" format is designed to be parsed by the
    // layout-override testing code.  There shouldn't be any external
    // uses of this format --- when LLDB overrides a layout, it sets up
    // the data structures directly --- so feel free to adjust this as
    // you like as long as you also update the rudimentary parser for it
    // in libFrontend.
  
    const ASTRecordLayout &Info = getASTRecordLayout(RD);
    OS << "Type: " << getTypeDeclType(RD).getAsString() << "\n";
    OS << "\nLayout: ";
    OS << "<ASTRecordLayout\n";
    OS << "  Size:" << toBits(Info.getSize()) << "\n";
    if (!isMsLayout(*this))
      OS << "  DataSize:" << toBits(Info.getDataSize()) << "\n";
    OS << "  Alignment:" << toBits(Info.getAlignment()) << "\n";
    OS << "  FieldOffsets: [";
    for (unsigned i = 0, e = Info.getFieldCount(); i != e; ++i) {
      if (i) OS << ", ";
      OS << Info.getFieldOffset(i);
    }
    OS << "]>\n";
  }
  