clang/lib/CodeGen/MicrosoftCXXABI.cpp

//===--- MicrosoftCXXABI.cpp - Emit LLVM Code from ASTs for a Module ------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This provides C++ code generation targeting the Microsoft Visual C++ ABI.
// The class in this file generates structures that follow the Microsoft
// Visual C++ ABI, which is actually not very well documented at all outside
// of Microsoft.
//
//===----------------------------------------------------------------------===//

#include "CGCXXABI.h"
#include "CGVTables.h"
#include "CodeGenModule.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/VTableBuilder.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/IR/CallSite.h"

using namespace clang;
using namespace CodeGen;

namespace {

/// Holds all the vbtable globals for a given class.
struct VBTableGlobals {
  const VPtrInfoVector *VBTables;
  SmallVector<llvm::GlobalVariable *, 2> Globals;
};

class MicrosoftCXXABI : public CGCXXABI {
public:
  MicrosoftCXXABI(CodeGenModule &CGM)
      : CGCXXABI(CGM), BaseClassDescriptorType(nullptr),
        ClassHierarchyDescriptorType(nullptr),
        CompleteObjectLocatorType(nullptr) {}

  bool HasThisReturn(GlobalDecl GD) const override;

  bool classifyReturnType(CGFunctionInfo &FI) const override;

  RecordArgABI getRecordArgABI(const CXXRecordDecl *RD) const override;

  bool isSRetParameterAfterThis() const override { return true; }

  StringRef GetPureVirtualCallName() override { return "_purecall"; }
  // No known support for deleted functions in MSVC yet, so this choice is
  // arbitrary.
  StringRef GetDeletedVirtualCallName() override { return "_purecall"; }

  llvm::Value *adjustToCompleteObject(CodeGenFunction &CGF,
                                      llvm::Value *ptr,
                                      QualType type) override;

  llvm::GlobalVariable *getMSCompleteObjectLocator(const CXXRecordDecl *RD,
                                                   const VPtrInfo *Info);

  llvm::Constant *getAddrOfRTTIDescriptor(QualType Ty) override;

  bool shouldTypeidBeNullChecked(bool IsDeref, QualType SrcRecordTy) override;
  void EmitBadTypeidCall(CodeGenFunction &CGF) override;
  llvm::Value *EmitTypeid(CodeGenFunction &CGF, QualType SrcRecordTy,
                          llvm::Value *ThisPtr,
                          llvm::Type *StdTypeInfoPtrTy) override;

  bool shouldDynamicCastCallBeNullChecked(bool SrcIsPtr,
                                          QualType SrcRecordTy) override;

  llvm::Value *EmitDynamicCastCall(CodeGenFunction &CGF, llvm::Value *Value,
                                   QualType SrcRecordTy, QualType DestTy,
                                   QualType DestRecordTy,
                                   llvm::BasicBlock *CastEnd) override;

  llvm::Value *EmitDynamicCastToVoid(CodeGenFunction &CGF, llvm::Value *Value,
                                     QualType SrcRecordTy,
                                     QualType DestTy) override;

  bool EmitBadCastCall(CodeGenFunction &CGF) override;

  llvm::Value *
  GetVirtualBaseClassOffset(CodeGenFunction &CGF, llvm::Value *This,
                            const CXXRecordDecl *ClassDecl,
                            const CXXRecordDecl *BaseClassDecl) override;

  llvm::BasicBlock *
  EmitCtorCompleteObjectHandler(CodeGenFunction &CGF,
                                const CXXRecordDecl *RD) override;

  void initializeHiddenVirtualInheritanceMembers(CodeGenFunction &CGF,
                                              const CXXRecordDecl *RD) override;

  void EmitCXXConstructors(const CXXConstructorDecl *D) override;

  // Background on MSVC destructors
  // ==============================
  //
  // Both Itanium and MSVC ABIs have destructor variants.  The variant names
  // roughly correspond in the following way:
  //   Itanium       Microsoft
  //   Base       -> no name, just ~Class
  //   Complete   -> vbase destructor
  //   Deleting   -> scalar deleting destructor
  //                 vector deleting destructor
  //
  // The base and complete destructors are the same as in Itanium, although the
  // complete destructor does not accept a VTT parameter when there are virtual
  // bases.  A separate mechanism involving vtordisps is used to ensure that
  // virtual methods of destroyed subobjects are not called.
  //
  // The deleting destructors accept an i32 bitfield as a second parameter.  Bit
  // 1 indicates if the memory should be deleted.  Bit 2 indicates if the this
  // pointer points to an array.  The scalar deleting destructor assumes that
  // bit 2 is zero, and therefore does not contain a loop.
  //
  // For virtual destructors, only one entry is reserved in the vftable, and it
  // always points to the vector deleting destructor.  The vector deleting
  // destructor is the most general, so it can be used to destroy objects in
  // place, delete single heap objects, or delete arrays.
  //
  // A TU defining a non-inline destructor is only guaranteed to emit a base
  // destructor, and all of the other variants are emitted on an as-needed basis
  // in COMDATs.  Because a non-base destructor can be emitted in a TU that
  // lacks a definition for the destructor, non-base destructors must always
  // delegate to or alias the base destructor.

  void buildStructorSignature(const CXXMethodDecl *MD, StructorType T,
                              SmallVectorImpl<CanQualType> &ArgTys) override;

  /// Non-base dtors should be emitted as delegating thunks in this ABI.
  bool useThunkForDtorVariant(const CXXDestructorDecl *Dtor,
                              CXXDtorType DT) const override {
    return DT != Dtor_Base;
  }

  void EmitCXXDestructors(const CXXDestructorDecl *D) override;

  const CXXRecordDecl *
  getThisArgumentTypeForMethod(const CXXMethodDecl *MD) override {
    MD = MD->getCanonicalDecl();
    if (MD->isVirtual() && !isa<CXXDestructorDecl>(MD)) {
      MicrosoftVTableContext::MethodVFTableLocation ML =
          CGM.getMicrosoftVTableContext().getMethodVFTableLocation(MD);
      // The vbases might be ordered differently in the final overrider object
      // and the complete object, so the "this" argument may sometimes point to
      // memory that has no particular type (e.g. past the complete object).
      // In this case, we just use a generic pointer type.
      // FIXME: might want to have a more precise type in the non-virtual
      // multiple inheritance case.
      if (ML.VBase || !ML.VFPtrOffset.isZero())
        return nullptr;
    }
    return MD->getParent();
  }

  llvm::Value *
  adjustThisArgumentForVirtualFunctionCall(CodeGenFunction &CGF, GlobalDecl GD,
                                           llvm::Value *This,
                                           bool VirtualCall) override;

  void addImplicitStructorParams(CodeGenFunction &CGF, QualType &ResTy,
                                 FunctionArgList &Params) override;

  llvm::Value *adjustThisParameterInVirtualFunctionPrologue(
      CodeGenFunction &CGF, GlobalDecl GD, llvm::Value *This) override;

  void EmitInstanceFunctionProlog(CodeGenFunction &CGF) override;

  unsigned addImplicitConstructorArgs(CodeGenFunction &CGF,
                                      const CXXConstructorDecl *D,
                                      CXXCtorType Type, bool ForVirtualBase,
                                      bool Delegating,
                                      CallArgList &Args) override;

  void EmitDestructorCall(CodeGenFunction &CGF, const CXXDestructorDecl *DD,
                          CXXDtorType Type, bool ForVirtualBase,
                          bool Delegating, llvm::Value *This) override;

  void emitVTableDefinitions(CodeGenVTables &CGVT,
                             const CXXRecordDecl *RD) override;

  llvm::Value *getVTableAddressPointInStructor(
      CodeGenFunction &CGF, const CXXRecordDecl *VTableClass,
      BaseSubobject Base, const CXXRecordDecl *NearestVBase,
      bool &NeedsVirtualOffset) override;

  llvm::Constant *
  getVTableAddressPointForConstExpr(BaseSubobject Base,
                                    const CXXRecordDecl *VTableClass) override;

  llvm::GlobalVariable *getAddrOfVTable(const CXXRecordDecl *RD,
                                        CharUnits VPtrOffset) override;

  llvm::Value *getVirtualFunctionPointer(CodeGenFunction &CGF, GlobalDecl GD,
                                         llvm::Value *This,
                                         llvm::Type *Ty) override;

  void EmitVirtualDestructorCall(CodeGenFunction &CGF,
                                 const CXXDestructorDecl *Dtor,
                                 CXXDtorType DtorType, llvm::Value *This,
                                 const CXXMemberCallExpr *CE) override;

  void adjustCallArgsForDestructorThunk(CodeGenFunction &CGF, GlobalDecl GD,
                                        CallArgList &CallArgs) override {
    assert(GD.getDtorType() == Dtor_Deleting &&
           "Only deleting destructor thunks are available in this ABI");
    CallArgs.add(RValue::get(getStructorImplicitParamValue(CGF)),
                             CGM.getContext().IntTy);
  }

  void emitVirtualInheritanceTables(const CXXRecordDecl *RD) override;

  llvm::GlobalVariable *
  getAddrOfVBTable(const VPtrInfo &VBT, const CXXRecordDecl *RD,
                   llvm::GlobalVariable::LinkageTypes Linkage);

  void emitVBTableDefinition(const VPtrInfo &VBT, const CXXRecordDecl *RD,
                             llvm::GlobalVariable *GV) const;

  void setThunkLinkage(llvm::Function *Thunk, bool ForVTable,
                       GlobalDecl GD, bool ReturnAdjustment) override {
    // Never dllimport/dllexport thunks.
    Thunk->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);

    GVALinkage Linkage =
        getContext().GetGVALinkageForFunction(cast<FunctionDecl>(GD.getDecl()));

    if (Linkage == GVA_Internal)
      Thunk->setLinkage(llvm::GlobalValue::InternalLinkage);
    else if (ReturnAdjustment)
      Thunk->setLinkage(llvm::GlobalValue::WeakODRLinkage);
    else
      Thunk->setLinkage(llvm::GlobalValue::LinkOnceODRLinkage);
  }

  llvm::Value *performThisAdjustment(CodeGenFunction &CGF, llvm::Value *This,
                                     const ThisAdjustment &TA) override;

  llvm::Value *performReturnAdjustment(CodeGenFunction &CGF, llvm::Value *Ret,
                                       const ReturnAdjustment &RA) override;

  void EmitGuardedInit(CodeGenFunction &CGF, const VarDecl &D,
                       llvm::GlobalVariable *DeclPtr,
                       bool PerformInit) override;

  // ==== Notes on array cookies =========
  //
  // MSVC seems to only use cookies when the class has a destructor; a
  // two-argument usual array deallocation function isn't sufficient.
  //
  // For example, this code prints "100" and "1":
  //   struct A {
  //     char x;
  //     void *operator new[](size_t sz) {
  //       printf("%u\n", sz);
  //       return malloc(sz);
  //     }
  //     void operator delete[](void *p, size_t sz) {
  //       printf("%u\n", sz);
  //       free(p);
  //     }
  //   };
  //   int main() {
  //     A *p = new A[100];
  //     delete[] p;
  //   }
  // Whereas it prints "104" and "104" if you give A a destructor.

  bool requiresArrayCookie(const CXXDeleteExpr *expr,
                           QualType elementType) override;
  bool requiresArrayCookie(const CXXNewExpr *expr) override;
  CharUnits getArrayCookieSizeImpl(QualType type) override;
  llvm::Value *InitializeArrayCookie(CodeGenFunction &CGF,
                                     llvm::Value *NewPtr,
                                     llvm::Value *NumElements,
                                     const CXXNewExpr *expr,
                                     QualType ElementType) override;
  llvm::Value *readArrayCookieImpl(CodeGenFunction &CGF,
                                   llvm::Value *allocPtr,
                                   CharUnits cookieSize) override;

  friend struct MSRTTIBuilder;

  bool isImageRelative() const {
    return CGM.getTarget().getPointerWidth(/*AddressSpace=*/0) == 64;
  }

  // 5 routines for constructing the llvm types for MS RTTI structs.
  llvm::StructType *getTypeDescriptorType(StringRef TypeInfoString) {
    llvm::SmallString<32> TDTypeName("rtti.TypeDescriptor");
    TDTypeName += llvm::utostr(TypeInfoString.size());
    llvm::StructType *&TypeDescriptorType =
        TypeDescriptorTypeMap[TypeInfoString.size()];
    if (TypeDescriptorType)
      return TypeDescriptorType;
    llvm::Type *FieldTypes[] = {
        CGM.Int8PtrPtrTy,
        CGM.Int8PtrTy,
        llvm::ArrayType::get(CGM.Int8Ty, TypeInfoString.size() + 1)};
    TypeDescriptorType =
        llvm::StructType::create(CGM.getLLVMContext(), FieldTypes, TDTypeName);
    return TypeDescriptorType;
  }

  llvm::Type *getImageRelativeType(llvm::Type *PtrType) {
    if (!isImageRelative())
      return PtrType;
    return CGM.IntTy;
  }

  llvm::StructType *getBaseClassDescriptorType() {
    if (BaseClassDescriptorType)
      return BaseClassDescriptorType;
    llvm::Type *FieldTypes[] = {
        getImageRelativeType(CGM.Int8PtrTy),
        CGM.IntTy,
        CGM.IntTy,
        CGM.IntTy,
        CGM.IntTy,
        CGM.IntTy,
        getImageRelativeType(getClassHierarchyDescriptorType()->getPointerTo()),
    };
    BaseClassDescriptorType = llvm::StructType::create(
        CGM.getLLVMContext(), FieldTypes, "rtti.BaseClassDescriptor");
    return BaseClassDescriptorType;
  }

  llvm::StructType *getClassHierarchyDescriptorType() {
    if (ClassHierarchyDescriptorType)
      return ClassHierarchyDescriptorType;
    // Forward-declare RTTIClassHierarchyDescriptor to break a cycle.
    ClassHierarchyDescriptorType = llvm::StructType::create(
        CGM.getLLVMContext(), "rtti.ClassHierarchyDescriptor");
    llvm::Type *FieldTypes[] = {
        CGM.IntTy,
        CGM.IntTy,
        CGM.IntTy,
        getImageRelativeType(
            getBaseClassDescriptorType()->getPointerTo()->getPointerTo()),
    };
    ClassHierarchyDescriptorType->setBody(FieldTypes);
    return ClassHierarchyDescriptorType;
  }

  llvm::StructType *getCompleteObjectLocatorType() {
    if (CompleteObjectLocatorType)
      return CompleteObjectLocatorType;
    CompleteObjectLocatorType = llvm::StructType::create(
        CGM.getLLVMContext(), "rtti.CompleteObjectLocator");
    llvm::Type *FieldTypes[] = {
        CGM.IntTy,
        CGM.IntTy,
        CGM.IntTy,
        getImageRelativeType(CGM.Int8PtrTy),
        getImageRelativeType(getClassHierarchyDescriptorType()->getPointerTo()),
        getImageRelativeType(CompleteObjectLocatorType),
    };
    llvm::ArrayRef<llvm::Type *> FieldTypesRef(FieldTypes);
    if (!isImageRelative())
      FieldTypesRef = FieldTypesRef.drop_back();
    CompleteObjectLocatorType->setBody(FieldTypesRef);
    return CompleteObjectLocatorType;
  }

  llvm::GlobalVariable *getImageBase() {
    StringRef Name = "__ImageBase";
    if (llvm::GlobalVariable *GV = CGM.getModule().getNamedGlobal(Name))
      return GV;

    return new llvm::GlobalVariable(CGM.getModule(), CGM.Int8Ty,
                                    /*isConstant=*/true,
                                    llvm::GlobalValue::ExternalLinkage,
                                    /*Initializer=*/nullptr, Name);
  }

  llvm::Constant *getImageRelativeConstant(llvm::Constant *PtrVal) {
    if (!isImageRelative())
      return PtrVal;

    llvm::Constant *ImageBaseAsInt =
        llvm::ConstantExpr::getPtrToInt(getImageBase(), CGM.IntPtrTy);
    llvm::Constant *PtrValAsInt =
        llvm::ConstantExpr::getPtrToInt(PtrVal, CGM.IntPtrTy);
    llvm::Constant *Diff =
        llvm::ConstantExpr::getSub(PtrValAsInt, ImageBaseAsInt,
                                   /*HasNUW=*/true, /*HasNSW=*/true);
    return llvm::ConstantExpr::getTrunc(Diff, CGM.IntTy);
  }

private:
  MicrosoftMangleContext &getMangleContext() {
    return cast<MicrosoftMangleContext>(CodeGen::CGCXXABI::getMangleContext());
  }

  llvm::Constant *getZeroInt() {
    return llvm::ConstantInt::get(CGM.IntTy, 0);
  }

  llvm::Constant *getAllOnesInt() {
    return  llvm::Constant::getAllOnesValue(CGM.IntTy);
  }

  llvm::Constant *getConstantOrZeroInt(llvm::Constant *C) {
    return C ? C : getZeroInt();
  }

  llvm::Value *getValueOrZeroInt(llvm::Value *C) {
    return C ? C : getZeroInt();
  }

  CharUnits getVirtualFunctionPrologueThisAdjustment(GlobalDecl GD);

  void
  GetNullMemberPointerFields(const MemberPointerType *MPT,
                             llvm::SmallVectorImpl<llvm::Constant *> &fields);

  /// \brief Shared code for virtual base adjustment.  Returns the offset from
  /// the vbptr to the virtual base.  Optionally returns the address of the
  /// vbptr itself.
  llvm::Value *GetVBaseOffsetFromVBPtr(CodeGenFunction &CGF,
                                       llvm::Value *Base,
                                       llvm::Value *VBPtrOffset,
                                       llvm::Value *VBTableOffset,
                                       llvm::Value **VBPtr = nullptr);

  llvm::Value *GetVBaseOffsetFromVBPtr(CodeGenFunction &CGF,
                                       llvm::Value *Base,
                                       int32_t VBPtrOffset,
                                       int32_t VBTableOffset,
                                       llvm::Value **VBPtr = nullptr) {
    llvm::Value *VBPOffset = llvm::ConstantInt::get(CGM.IntTy, VBPtrOffset),
                *VBTOffset = llvm::ConstantInt::get(CGM.IntTy, VBTableOffset);
    return GetVBaseOffsetFromVBPtr(CGF, Base, VBPOffset, VBTOffset, VBPtr);
  }

  /// \brief Performs a full virtual base adjustment.  Used to dereference
  /// pointers to members of virtual bases.
  llvm::Value *AdjustVirtualBase(CodeGenFunction &CGF, const Expr *E,
                                 const CXXRecordDecl *RD, llvm::Value *Base,
                                 llvm::Value *VirtualBaseAdjustmentOffset,
                                 llvm::Value *VBPtrOffset /* optional */);

  /// \brief Emits a full member pointer with the fields common to data and
  /// function member pointers.
  llvm::Constant *EmitFullMemberPointer(llvm::Constant *FirstField,
                                        bool IsMemberFunction,
                                        const CXXRecordDecl *RD,
                                        CharUnits NonVirtualBaseAdjustment);

  llvm::Constant *BuildMemberPointer(const CXXRecordDecl *RD,
                                     const CXXMethodDecl *MD,
                                     CharUnits NonVirtualBaseAdjustment);

  bool MemberPointerConstantIsNull(const MemberPointerType *MPT,
                                   llvm::Constant *MP);

  /// \brief - Initialize all vbptrs of 'this' with RD as the complete type.
  void EmitVBPtrStores(CodeGenFunction &CGF, const CXXRecordDecl *RD);

  /// \brief Caching wrapper around VBTableBuilder::enumerateVBTables().
  const VBTableGlobals &enumerateVBTables(const CXXRecordDecl *RD);

  /// \brief Generate a thunk for calling a virtual member function MD.
  llvm::Function *EmitVirtualMemPtrThunk(
      const CXXMethodDecl *MD,
      const MicrosoftVTableContext::MethodVFTableLocation &ML);

public:
  llvm::Type *ConvertMemberPointerType(const MemberPointerType *MPT) override;

  bool isZeroInitializable(const MemberPointerType *MPT) override;

  bool isMemberPointerConvertible(const MemberPointerType *MPT) const override {
    const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
    return RD->getAttr<MSInheritanceAttr>() != nullptr;
  }

  llvm::Constant *EmitNullMemberPointer(const MemberPointerType *MPT) override;

  llvm::Constant *EmitMemberDataPointer(const MemberPointerType *MPT,
                                        CharUnits offset) override;
  llvm::Constant *EmitMemberPointer(const CXXMethodDecl *MD) override;
  llvm::Constant *EmitMemberPointer(const APValue &MP, QualType MPT) override;

  llvm::Value *EmitMemberPointerComparison(CodeGenFunction &CGF,
                                           llvm::Value *L,
                                           llvm::Value *R,
                                           const MemberPointerType *MPT,
                                           bool Inequality) override;

  llvm::Value *EmitMemberPointerIsNotNull(CodeGenFunction &CGF,
                                          llvm::Value *MemPtr,
                                          const MemberPointerType *MPT) override;

  llvm::Value *
  EmitMemberDataPointerAddress(CodeGenFunction &CGF, const Expr *E,
                               llvm::Value *Base, llvm::Value *MemPtr,
                               const MemberPointerType *MPT) override;

  llvm::Value *EmitMemberPointerConversion(CodeGenFunction &CGF,
                                           const CastExpr *E,
                                           llvm::Value *Src) override;

  llvm::Constant *EmitMemberPointerConversion(const CastExpr *E,
                                              llvm::Constant *Src) override;

  llvm::Value *
  EmitLoadOfMemberFunctionPointer(CodeGenFunction &CGF, const Expr *E,
                                  llvm::Value *&This, llvm::Value *MemPtr,
                                  const MemberPointerType *MPT) override;

private:
  typedef std::pair<const CXXRecordDecl *, CharUnits> VFTableIdTy;
  typedef llvm::DenseMap<VFTableIdTy, llvm::GlobalVariable *> VTablesMapTy;
  typedef llvm::DenseMap<VFTableIdTy, llvm::GlobalValue *> VFTablesMapTy;
  /// \brief All the vftables that have been referenced.
  VFTablesMapTy VFTablesMap;
  VTablesMapTy VTablesMap;

  /// \brief This set holds the record decls we've deferred vtable emission for.
  llvm::SmallPtrSet<const CXXRecordDecl *, 4> DeferredVFTables;


  /// \brief All the vbtables which have been referenced.
  llvm::DenseMap<const CXXRecordDecl *, VBTableGlobals> VBTablesMap;

  /// Info on the global variable used to guard initialization of static locals.
  /// The BitIndex field is only used for externally invisible declarations.
  struct GuardInfo {
    GuardInfo() : Guard(nullptr), BitIndex(0) {}
    llvm::GlobalVariable *Guard;
    unsigned BitIndex;
  };

  /// Map from DeclContext to the current guard variable.  We assume that the
  /// AST is visited in source code order.
  llvm::DenseMap<const DeclContext *, GuardInfo> GuardVariableMap;

  llvm::DenseMap<size_t, llvm::StructType *> TypeDescriptorTypeMap;
  llvm::StructType *BaseClassDescriptorType;
  llvm::StructType *ClassHierarchyDescriptorType;
  llvm::StructType *CompleteObjectLocatorType;
};

}

CGCXXABI::RecordArgABI
MicrosoftCXXABI::getRecordArgABI(const CXXRecordDecl *RD) const {
  switch (CGM.getTarget().getTriple().getArch()) {
  default:
    // FIXME: Implement for other architectures.
    return RAA_Default;

  case llvm::Triple::x86:
    // All record arguments are passed in memory on x86.  Decide whether to
    // construct the object directly in argument memory, or to construct the
    // argument elsewhere and copy the bytes during the call.

    // If C++ prohibits us from making a copy, construct the arguments directly
    // into argument memory.
    if (!canCopyArgument(RD))
      return RAA_DirectInMemory;

    // Otherwise, construct the argument into a temporary and copy the bytes
    // into the outgoing argument memory.
    return RAA_Default;

  case llvm::Triple::x86_64:
    // Win64 passes objects with non-trivial copy ctors indirectly.
    if (RD->hasNonTrivialCopyConstructor())
      return RAA_Indirect;

    // Win64 passes objects larger than 8 bytes indirectly.
    if (getContext().getTypeSize(RD->getTypeForDecl()) > 64)
      return RAA_Indirect;

    // We have a trivial copy constructor or no copy constructors, but we have
    // to make sure it isn't deleted.
    bool CopyDeleted = false;
    for (const CXXConstructorDecl *CD : RD->ctors()) {
      if (CD->isCopyConstructor()) {
        assert(CD->isTrivial());
        // We had at least one undeleted trivial copy ctor.  Return directly.
        if (!CD->isDeleted())
          return RAA_Default;
        CopyDeleted = true;
      }
    }

    // The trivial copy constructor was deleted.  Return indirectly.
    if (CopyDeleted)
      return RAA_Indirect;

    // There were no copy ctors.  Return in RAX.
    return RAA_Default;
  }

  llvm_unreachable("invalid enum");
}

llvm::Value *MicrosoftCXXABI::adjustToCompleteObject(CodeGenFunction &CGF,
                                                     llvm::Value *ptr,
                                                     QualType type) {
  // FIXME: implement
  return ptr;
}

/// \brief Gets the offset to the virtual base that contains the vfptr for
/// MS-ABI polymorphic types.
static llvm::Value *getPolymorphicOffset(CodeGenFunction &CGF,
                                         const CXXRecordDecl *RD,
                                         llvm::Value *Value) {
  const ASTContext &Context = RD->getASTContext();
  for (const CXXBaseSpecifier &Base : RD->vbases())
    if (Context.getASTRecordLayout(Base.getType()->getAsCXXRecordDecl())
            .hasExtendableVFPtr())
      return CGF.CGM.getCXXABI().GetVirtualBaseClassOffset(
          CGF, Value, RD, Base.getType()->getAsCXXRecordDecl());
  llvm_unreachable("One of our vbases should be polymorphic.");
}

static std::pair<llvm::Value *, llvm::Value *>
performBaseAdjustment(CodeGenFunction &CGF, llvm::Value *Value,
                      QualType SrcRecordTy) {
  Value = CGF.Builder.CreateBitCast(Value, CGF.Int8PtrTy);
  const CXXRecordDecl *SrcDecl = SrcRecordTy->getAsCXXRecordDecl();

  if (CGF.getContext().getASTRecordLayout(SrcDecl).hasExtendableVFPtr())
    return std::make_pair(Value, llvm::ConstantInt::get(CGF.Int32Ty, 0));

  // Perform a base adjustment.
  llvm::Value *Offset = getPolymorphicOffset(CGF, SrcDecl, Value);
  Value = CGF.Builder.CreateInBoundsGEP(Value, Offset);
  Offset = CGF.Builder.CreateTrunc(Offset, CGF.Int32Ty);
  return std::make_pair(Value, Offset);
}

bool MicrosoftCXXABI::shouldTypeidBeNullChecked(bool IsDeref,
                                                QualType SrcRecordTy) {
  const CXXRecordDecl *SrcDecl = SrcRecordTy->getAsCXXRecordDecl();
  return IsDeref &&
         !CGM.getContext().getASTRecordLayout(SrcDecl).hasExtendableVFPtr();
}

static llvm::CallSite emitRTtypeidCall(CodeGenFunction &CGF,
                                       llvm::Value *Argument) {
  llvm::Type *ArgTypes[] = {CGF.Int8PtrTy};
  llvm::FunctionType *FTy =
      llvm::FunctionType::get(CGF.Int8PtrTy, ArgTypes, false);
  llvm::Value *Args[] = {Argument};
  llvm::Constant *Fn = CGF.CGM.CreateRuntimeFunction(FTy, "__RTtypeid");
  return CGF.EmitRuntimeCallOrInvoke(Fn, Args);
}

void MicrosoftCXXABI::EmitBadTypeidCall(CodeGenFunction &CGF) {
  llvm::CallSite Call =
      emitRTtypeidCall(CGF, llvm::Constant::getNullValue(CGM.VoidPtrTy));
  Call.setDoesNotReturn();
  CGF.Builder.CreateUnreachable();
}

llvm::Value *MicrosoftCXXABI::EmitTypeid(CodeGenFunction &CGF,
                                         QualType SrcRecordTy,
                                         llvm::Value *ThisPtr,
                                         llvm::Type *StdTypeInfoPtrTy) {
  llvm::Value *Offset;
  std::tie(ThisPtr, Offset) = performBaseAdjustment(CGF, ThisPtr, SrcRecordTy);
  return CGF.Builder.CreateBitCast(
      emitRTtypeidCall(CGF, ThisPtr).getInstruction(), StdTypeInfoPtrTy);
}

bool MicrosoftCXXABI::shouldDynamicCastCallBeNullChecked(bool SrcIsPtr,
                                                         QualType SrcRecordTy) {
  const CXXRecordDecl *SrcDecl = SrcRecordTy->getAsCXXRecordDecl();
  return SrcIsPtr &&
         !CGM.getContext().getASTRecordLayout(SrcDecl).hasExtendableVFPtr();
}

llvm::Value *MicrosoftCXXABI::EmitDynamicCastCall(
    CodeGenFunction &CGF, llvm::Value *Value, QualType SrcRecordTy,
    QualType DestTy, QualType DestRecordTy, llvm::BasicBlock *CastEnd) {
  llvm::Type *DestLTy = CGF.ConvertType(DestTy);

  llvm::Value *SrcRTTI =
      CGF.CGM.GetAddrOfRTTIDescriptor(SrcRecordTy.getUnqualifiedType());
  llvm::Value *DestRTTI =
      CGF.CGM.GetAddrOfRTTIDescriptor(DestRecordTy.getUnqualifiedType());

  llvm::Value *Offset;
  std::tie(Value, Offset) = performBaseAdjustment(CGF, Value, SrcRecordTy);

  // PVOID __RTDynamicCast(
  //   PVOID inptr,
  //   LONG VfDelta,
  //   PVOID SrcType,
  //   PVOID TargetType,
  //   BOOL isReference)
  llvm::Type *ArgTypes[] = {CGF.Int8PtrTy, CGF.Int32Ty, CGF.Int8PtrTy,
                            CGF.Int8PtrTy, CGF.Int32Ty};
  llvm::Constant *Function = CGF.CGM.CreateRuntimeFunction(
      llvm::FunctionType::get(CGF.Int8PtrTy, ArgTypes, false),
      "__RTDynamicCast");
  llvm::Value *Args[] = {
      Value, Offset, SrcRTTI, DestRTTI,
      llvm::ConstantInt::get(CGF.Int32Ty, DestTy->isReferenceType())};
  Value = CGF.EmitRuntimeCallOrInvoke(Function, Args).getInstruction();
  return CGF.Builder.CreateBitCast(Value, DestLTy);
}

llvm::Value *
MicrosoftCXXABI::EmitDynamicCastToVoid(CodeGenFunction &CGF, llvm::Value *Value,
                                       QualType SrcRecordTy,
                                       QualType DestTy) {
  llvm::Value *Offset;
  std::tie(Value, Offset) = performBaseAdjustment(CGF, Value, SrcRecordTy);

  // PVOID __RTCastToVoid(
  //   PVOID inptr)
  llvm::Type *ArgTypes[] = {CGF.Int8PtrTy};
  llvm::Constant *Function = CGF.CGM.CreateRuntimeFunction(
      llvm::FunctionType::get(CGF.Int8PtrTy, ArgTypes, false),
      "__RTCastToVoid");
  llvm::Value *Args[] = {Value};
  return CGF.EmitRuntimeCall(Function, Args);
}

bool MicrosoftCXXABI::EmitBadCastCall(CodeGenFunction &CGF) {
  return false;
}

llvm::Value *MicrosoftCXXABI::GetVirtualBaseClassOffset(
    CodeGenFunction &CGF, llvm::Value *This, const CXXRecordDecl *ClassDecl,
    const CXXRecordDecl *BaseClassDecl) {
  int64_t VBPtrChars =
      getContext().getASTRecordLayout(ClassDecl).getVBPtrOffset().getQuantity();
  llvm::Value *VBPtrOffset = llvm::ConstantInt::get(CGM.PtrDiffTy, VBPtrChars);
  CharUnits IntSize = getContext().getTypeSizeInChars(getContext().IntTy);
  CharUnits VBTableChars =
      IntSize *
      CGM.getMicrosoftVTableContext().getVBTableIndex(ClassDecl, BaseClassDecl);
  llvm::Value *VBTableOffset =
      llvm::ConstantInt::get(CGM.IntTy, VBTableChars.getQuantity());

  llvm::Value *VBPtrToNewBase =
      GetVBaseOffsetFromVBPtr(CGF, This, VBPtrOffset, VBTableOffset);
  VBPtrToNewBase =
      CGF.Builder.CreateSExtOrBitCast(VBPtrToNewBase, CGM.PtrDiffTy);
  return CGF.Builder.CreateNSWAdd(VBPtrOffset, VBPtrToNewBase);
}

bool MicrosoftCXXABI::HasThisReturn(GlobalDecl GD) const {
  return isa<CXXConstructorDecl>(GD.getDecl());
}

bool MicrosoftCXXABI::classifyReturnType(CGFunctionInfo &FI) const {
  const CXXRecordDecl *RD = FI.getReturnType()->getAsCXXRecordDecl();
  if (!RD)
    return false;

  if (FI.isInstanceMethod()) {
    // If it's an instance method, aggregates are always returned indirectly via
    // the second parameter.
    FI.getReturnInfo() = ABIArgInfo::getIndirect(0, /*ByVal=*/false);
    FI.getReturnInfo().setSRetAfterThis(FI.isInstanceMethod());
    return true;
  } else if (!RD->isPOD()) {
    // If it's a free function, non-POD types are returned indirectly.
    FI.getReturnInfo() = ABIArgInfo::getIndirect(0, /*ByVal=*/false);
    return true;
  }

  // Otherwise, use the C ABI rules.
  return false;
}

llvm::BasicBlock *
MicrosoftCXXABI::EmitCtorCompleteObjectHandler(CodeGenFunction &CGF,
                                               const CXXRecordDecl *RD) {
  llvm::Value *IsMostDerivedClass = getStructorImplicitParamValue(CGF);
  assert(IsMostDerivedClass &&
         "ctor for a class with virtual bases must have an implicit parameter");
  llvm::Value *IsCompleteObject =
    CGF.Builder.CreateIsNotNull(IsMostDerivedClass, "is_complete_object");

  llvm::BasicBlock *CallVbaseCtorsBB = CGF.createBasicBlock("ctor.init_vbases");
  llvm::BasicBlock *SkipVbaseCtorsBB = CGF.createBasicBlock("ctor.skip_vbases");
  CGF.Builder.CreateCondBr(IsCompleteObject,
                           CallVbaseCtorsBB, SkipVbaseCtorsBB);

  CGF.EmitBlock(CallVbaseCtorsBB);

  // Fill in the vbtable pointers here.
  EmitVBPtrStores(CGF, RD);

  // CGF will put the base ctor calls in this basic block for us later.

  return SkipVbaseCtorsBB;
}

void MicrosoftCXXABI::initializeHiddenVirtualInheritanceMembers(
    CodeGenFunction &CGF, const CXXRecordDecl *RD) {
  // In most cases, an override for a vbase virtual method can adjust
  // the "this" parameter by applying a constant offset.
  // However, this is not enough while a constructor or a destructor of some
  // class X is being executed if all the following conditions are met:
  //  - X has virtual bases, (1)
  //  - X overrides a virtual method M of a vbase Y, (2)
  //  - X itself is a vbase of the most derived class.
  //
  // If (1) and (2) are true, the vtorDisp for vbase Y is a hidden member of X
  // which holds the extra amount of "this" adjustment we must do when we use
  // the X vftables (i.e. during X ctor or dtor).
  // Outside the ctors and dtors, the values of vtorDisps are zero.

  const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
  typedef ASTRecordLayout::VBaseOffsetsMapTy VBOffsets;
  const VBOffsets &VBaseMap = Layout.getVBaseOffsetsMap();
  CGBuilderTy &Builder = CGF.Builder;

  unsigned AS =
      cast<llvm::PointerType>(getThisValue(CGF)->getType())->getAddressSpace();
  llvm::Value *Int8This = nullptr;  // Initialize lazily.

  for (VBOffsets::const_iterator I = VBaseMap.begin(), E = VBaseMap.end();
        I != E; ++I) {
    if (!I->second.hasVtorDisp())
      continue;

    llvm::Value *VBaseOffset =
        GetVirtualBaseClassOffset(CGF, getThisValue(CGF), RD, I->first);
    // FIXME: it doesn't look right that we SExt in GetVirtualBaseClassOffset()
    // just to Trunc back immediately.
    VBaseOffset = Builder.CreateTruncOrBitCast(VBaseOffset, CGF.Int32Ty);
    uint64_t ConstantVBaseOffset =
        Layout.getVBaseClassOffset(I->first).getQuantity();

    // vtorDisp_for_vbase = vbptr[vbase_idx] - offsetof(RD, vbase).
    llvm::Value *VtorDispValue = Builder.CreateSub(
        VBaseOffset, llvm::ConstantInt::get(CGM.Int32Ty, ConstantVBaseOffset),
        "vtordisp.value");

    if (!Int8This)
      Int8This = Builder.CreateBitCast(getThisValue(CGF),
                                       CGF.Int8Ty->getPointerTo(AS));
    llvm::Value *VtorDispPtr = Builder.CreateInBoundsGEP(Int8This, VBaseOffset);
    // vtorDisp is always the 32-bits before the vbase in the class layout.
    VtorDispPtr = Builder.CreateConstGEP1_32(VtorDispPtr, -4);
    VtorDispPtr = Builder.CreateBitCast(
        VtorDispPtr, CGF.Int32Ty->getPointerTo(AS), "vtordisp.ptr");

    Builder.CreateStore(VtorDispValue, VtorDispPtr);
  }
}

void MicrosoftCXXABI::EmitCXXConstructors(const CXXConstructorDecl *D) {
  // There's only one constructor type in this ABI.
  CGM.EmitGlobal(GlobalDecl(D, Ctor_Complete));
}

void MicrosoftCXXABI::EmitVBPtrStores(CodeGenFunction &CGF,
                                      const CXXRecordDecl *RD) {
  llvm::Value *ThisInt8Ptr =
    CGF.Builder.CreateBitCast(getThisValue(CGF), CGM.Int8PtrTy, "this.int8");
  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);

  const VBTableGlobals &VBGlobals = enumerateVBTables(RD);
  for (unsigned I = 0, E = VBGlobals.VBTables->size(); I != E; ++I) {
    const VPtrInfo *VBT = (*VBGlobals.VBTables)[I];
    llvm::GlobalVariable *GV = VBGlobals.Globals[I];
    const ASTRecordLayout &SubobjectLayout =
        CGM.getContext().getASTRecordLayout(VBT->BaseWithVPtr);
    CharUnits Offs = VBT->NonVirtualOffset;
    Offs += SubobjectLayout.getVBPtrOffset();
    if (VBT->getVBaseWithVPtr())
      Offs += Layout.getVBaseClassOffset(VBT->getVBaseWithVPtr());
    llvm::Value *VBPtr =
        CGF.Builder.CreateConstInBoundsGEP1_64(ThisInt8Ptr, Offs.getQuantity());
    VBPtr = CGF.Builder.CreateBitCast(VBPtr, GV->getType()->getPointerTo(0),
                                      "vbptr." + VBT->ReusingBase->getName());
    CGF.Builder.CreateStore(GV, VBPtr);
  }
}

void
MicrosoftCXXABI::buildStructorSignature(const CXXMethodDecl *MD, StructorType T,
                                        SmallVectorImpl<CanQualType> &ArgTys) {
  // TODO: 'for base' flag
  if (T == StructorType::Deleting) {
    // The scalar deleting destructor takes an implicit int parameter.
    ArgTys.push_back(CGM.getContext().IntTy);
  }
  auto *CD = dyn_cast<CXXConstructorDecl>(MD);
  if (!CD)
    return;

  // All parameters are already in place except is_most_derived, which goes
  // after 'this' if it's variadic and last if it's not.

  const CXXRecordDecl *Class = CD->getParent();
  const FunctionProtoType *FPT = CD->getType()->castAs<FunctionProtoType>();
  if (Class->getNumVBases()) {
    if (FPT->isVariadic())
      ArgTys.insert(ArgTys.begin() + 1, CGM.getContext().IntTy);
    else
      ArgTys.push_back(CGM.getContext().IntTy);
  }
}

void MicrosoftCXXABI::EmitCXXDestructors(const CXXDestructorDecl *D) {
  // The TU defining a dtor is only guaranteed to emit a base destructor.  All
  // other destructor variants are delegating thunks.
  CGM.EmitGlobal(GlobalDecl(D, Dtor_Base));
}

CharUnits
MicrosoftCXXABI::getVirtualFunctionPrologueThisAdjustment(GlobalDecl GD) {
  GD = GD.getCanonicalDecl();
  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());

  GlobalDecl LookupGD = GD;
  if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
    // Complete destructors take a pointer to the complete object as a
    // parameter, thus don't need this adjustment.
    if (GD.getDtorType() == Dtor_Complete)
      return CharUnits();

    // There's no Dtor_Base in vftable but it shares the this adjustment with
    // the deleting one, so look it up instead.
    LookupGD = GlobalDecl(DD, Dtor_Deleting);
  }

  MicrosoftVTableContext::MethodVFTableLocation ML =
      CGM.getMicrosoftVTableContext().getMethodVFTableLocation(LookupGD);
  CharUnits Adjustment = ML.VFPtrOffset;

  // Normal virtual instance methods need to adjust from the vfptr that first
  // defined the virtual method to the virtual base subobject, but destructors
  // do not.  The vector deleting destructor thunk applies this adjustment for
  // us if necessary.
  if (isa<CXXDestructorDecl>(MD))
    Adjustment = CharUnits::Zero();

  if (ML.VBase) {
    const ASTRecordLayout &DerivedLayout =
        CGM.getContext().getASTRecordLayout(MD->getParent());
    Adjustment += DerivedLayout.getVBaseClassOffset(ML.VBase);
  }

  return Adjustment;
}

llvm::Value *MicrosoftCXXABI::adjustThisArgumentForVirtualFunctionCall(
    CodeGenFunction &CGF, GlobalDecl GD, llvm::Value *This, bool VirtualCall) {
  if (!VirtualCall) {
    // If the call of a virtual function is not virtual, we just have to
    // compensate for the adjustment the virtual function does in its prologue.
    CharUnits Adjustment = getVirtualFunctionPrologueThisAdjustment(GD);
    if (Adjustment.isZero())
      return This;

    unsigned AS = cast<llvm::PointerType>(This->getType())->getAddressSpace();
    llvm::Type *charPtrTy = CGF.Int8Ty->getPointerTo(AS);
    This = CGF.Builder.CreateBitCast(This, charPtrTy);
    assert(Adjustment.isPositive());
    return CGF.Builder.CreateConstGEP1_32(This, Adjustment.getQuantity());
  }

  GD = GD.getCanonicalDecl();
  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());

  GlobalDecl LookupGD = GD;
  if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
    // Complete dtors take a pointer to the complete object,
    // thus don't need adjustment.
    if (GD.getDtorType() == Dtor_Complete)
      return This;

    // There's only Dtor_Deleting in vftable but it shares the this adjustment
    // with the base one, so look up the deleting one instead.
    LookupGD = GlobalDecl(DD, Dtor_Deleting);
  }
  MicrosoftVTableContext::MethodVFTableLocation ML =
      CGM.getMicrosoftVTableContext().getMethodVFTableLocation(LookupGD);

  unsigned AS = cast<llvm::PointerType>(This->getType())->getAddressSpace();
  llvm::Type *charPtrTy = CGF.Int8Ty->getPointerTo(AS);
  CharUnits StaticOffset = ML.VFPtrOffset;

  // Base destructors expect 'this' to point to the beginning of the base
  // subobject, not the first vfptr that happens to contain the virtual dtor.
  // However, we still need to apply the virtual base adjustment.
  if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
    StaticOffset = CharUnits::Zero();

  if (ML.VBase) {
    This = CGF.Builder.CreateBitCast(This, charPtrTy);
    llvm::Value *VBaseOffset =
        GetVirtualBaseClassOffset(CGF, This, MD->getParent(), ML.VBase);
    This = CGF.Builder.CreateInBoundsGEP(This, VBaseOffset);
  }
  if (!StaticOffset.isZero()) {
    assert(StaticOffset.isPositive());
    This = CGF.Builder.CreateBitCast(This, charPtrTy);
    if (ML.VBase) {
      // Non-virtual adjustment might result in a pointer outside the allocated
      // object, e.g. if the final overrider class is laid out after the virtual
      // base that declares a method in the most derived class.
      // FIXME: Update the code that emits this adjustment in thunks prologues.
      This = CGF.Builder.CreateConstGEP1_32(This, StaticOffset.getQuantity());
    } else {
      This = CGF.Builder.CreateConstInBoundsGEP1_32(This,
                                                    StaticOffset.getQuantity());
    }
  }
  return This;
}

static bool IsDeletingDtor(GlobalDecl GD) {
  const CXXMethodDecl* MD = cast<CXXMethodDecl>(GD.getDecl());
  if (isa<CXXDestructorDecl>(MD)) {
    return GD.getDtorType() == Dtor_Deleting;
  }
  return false;
}

void MicrosoftCXXABI::addImplicitStructorParams(CodeGenFunction &CGF,
                                                QualType &ResTy,
                                                FunctionArgList &Params) {
  ASTContext &Context = getContext();
  const CXXMethodDecl *MD = cast<CXXMethodDecl>(CGF.CurGD.getDecl());
  assert(isa<CXXConstructorDecl>(MD) || isa<CXXDestructorDecl>(MD));
  if (isa<CXXConstructorDecl>(MD) && MD->getParent()->getNumVBases()) {
    ImplicitParamDecl *IsMostDerived
      = ImplicitParamDecl::Create(Context, nullptr,
                                  CGF.CurGD.getDecl()->getLocation(),
                                  &Context.Idents.get("is_most_derived"),
                                  Context.IntTy);
    // The 'most_derived' parameter goes second if the ctor is variadic and last
    // if it's not.  Dtors can't be variadic.
    const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
    if (FPT->isVariadic())
      Params.insert(Params.begin() + 1, IsMostDerived);
    else
      Params.push_back(IsMostDerived);
    getStructorImplicitParamDecl(CGF) = IsMostDerived;
  } else if (IsDeletingDtor(CGF.CurGD)) {
    ImplicitParamDecl *ShouldDelete
      = ImplicitParamDecl::Create(Context, nullptr,
                                  CGF.CurGD.getDecl()->getLocation(),
                                  &Context.Idents.get("should_call_delete"),
                                  Context.IntTy);
    Params.push_back(ShouldDelete);
    getStructorImplicitParamDecl(CGF) = ShouldDelete;
  }
}

llvm::Value *MicrosoftCXXABI::adjustThisParameterInVirtualFunctionPrologue(
    CodeGenFunction &CGF, GlobalDecl GD, llvm::Value *This) {
  // In this ABI, every virtual function takes a pointer to one of the
  // subobjects that first defines it as the 'this' parameter, rather than a
  // pointer to the final overrider subobject. Thus, we need to adjust it back
  // to the final overrider subobject before use.
  // See comments in the MicrosoftVFTableContext implementation for the details.
  CharUnits Adjustment = getVirtualFunctionPrologueThisAdjustment(GD);
  if (Adjustment.isZero())
    return This;

  unsigned AS = cast<llvm::PointerType>(This->getType())->getAddressSpace();
  llvm::Type *charPtrTy = CGF.Int8Ty->getPointerTo(AS),
             *thisTy = This->getType();

  This = CGF.Builder.CreateBitCast(This, charPtrTy);
  assert(Adjustment.isPositive());
  This =
      CGF.Builder.CreateConstInBoundsGEP1_32(This, -Adjustment.getQuantity());
  return CGF.Builder.CreateBitCast(This, thisTy);
}

void MicrosoftCXXABI::EmitInstanceFunctionProlog(CodeGenFunction &CGF) {
  EmitThisParam(CGF);

  /// If this is a function that the ABI specifies returns 'this', initialize
  /// the return slot to 'this' at the start of the function.
  ///
  /// Unlike the setting of return types, this is done within the ABI
  /// implementation instead of by clients of CGCXXABI because:
  /// 1) getThisValue is currently protected
  /// 2) in theory, an ABI could implement 'this' returns some other way;
  ///    HasThisReturn only specifies a contract, not the implementation    
  if (HasThisReturn(CGF.CurGD))
    CGF.Builder.CreateStore(getThisValue(CGF), CGF.ReturnValue);

  const CXXMethodDecl *MD = cast<CXXMethodDecl>(CGF.CurGD.getDecl());
  if (isa<CXXConstructorDecl>(MD) && MD->getParent()->getNumVBases()) {
    assert(getStructorImplicitParamDecl(CGF) &&
           "no implicit parameter for a constructor with virtual bases?");
    getStructorImplicitParamValue(CGF)
      = CGF.Builder.CreateLoad(
          CGF.GetAddrOfLocalVar(getStructorImplicitParamDecl(CGF)),
          "is_most_derived");
  }

  if (IsDeletingDtor(CGF.CurGD)) {
    assert(getStructorImplicitParamDecl(CGF) &&
           "no implicit parameter for a deleting destructor?");
    getStructorImplicitParamValue(CGF)
      = CGF.Builder.CreateLoad(
          CGF.GetAddrOfLocalVar(getStructorImplicitParamDecl(CGF)),
          "should_call_delete");
  }
}

unsigned MicrosoftCXXABI::addImplicitConstructorArgs(
    CodeGenFunction &CGF, const CXXConstructorDecl *D, CXXCtorType Type,
    bool ForVirtualBase, bool Delegating, CallArgList &Args) {
  assert(Type == Ctor_Complete || Type == Ctor_Base);

  // Check if we need a 'most_derived' parameter.
  if (!D->getParent()->getNumVBases())
    return 0;

  // Add the 'most_derived' argument second if we are variadic or last if not.
  const FunctionProtoType *FPT = D->getType()->castAs<FunctionProtoType>();
  llvm::Value *MostDerivedArg =
      llvm::ConstantInt::get(CGM.Int32Ty, Type == Ctor_Complete);
  RValue RV = RValue::get(MostDerivedArg);
  if (MostDerivedArg) {
    if (FPT->isVariadic())
      Args.insert(Args.begin() + 1,
                  CallArg(RV, getContext().IntTy, /*needscopy=*/false));
    else
      Args.add(RV, getContext().IntTy);
  }

  return 1;  // Added one arg.
}

void MicrosoftCXXABI::EmitDestructorCall(CodeGenFunction &CGF,
                                         const CXXDestructorDecl *DD,
                                         CXXDtorType Type, bool ForVirtualBase,
                                         bool Delegating, llvm::Value *This) {
  llvm::Value *Callee = CGM.GetAddrOfCXXDestructor(DD, Type);

  if (DD->isVirtual()) {
    assert(Type != CXXDtorType::Dtor_Deleting &&
           "The deleting destructor should only be called via a virtual call");
    This = adjustThisArgumentForVirtualFunctionCall(CGF, GlobalDecl(DD, Type),
                                                    This, false);
  }

  CGF.EmitCXXMemberOrOperatorCall(DD, Callee, ReturnValueSlot(), This,
                                  /*ImplicitParam=*/nullptr,
                                  /*ImplicitParamTy=*/QualType(), nullptr);
}

void MicrosoftCXXABI::emitVTableDefinitions(CodeGenVTables &CGVT,
                                            const CXXRecordDecl *RD) {
  MicrosoftVTableContext &VFTContext = CGM.getMicrosoftVTableContext();
  VPtrInfoVector VFPtrs = VFTContext.getVFPtrOffsets(RD);

  for (VPtrInfo *Info : VFPtrs) {
    llvm::GlobalVariable *VTable = getAddrOfVTable(RD, Info->FullOffsetInMDC);
    if (VTable->hasInitializer())
      continue;

    llvm::Constant *RTTI = getContext().getLangOpts().RTTIData
                               ? getMSCompleteObjectLocator(RD, Info)
                               : nullptr;

    const VTableLayout &VTLayout =
      VFTContext.getVFTableLayout(RD, Info->FullOffsetInMDC);
    llvm::Constant *Init = CGVT.CreateVTableInitializer(
        RD, VTLayout.vtable_component_begin(),
        VTLayout.getNumVTableComponents(), VTLayout.vtable_thunk_begin(),
        VTLayout.getNumVTableThunks(), RTTI);

    VTable->setInitializer(Init);
  }
}

llvm::Value *MicrosoftCXXABI::getVTableAddressPointInStructor(
    CodeGenFunction &CGF, const CXXRecordDecl *VTableClass, BaseSubobject Base,
    const CXXRecordDecl *NearestVBase, bool &NeedsVirtualOffset) {
  NeedsVirtualOffset = (NearestVBase != nullptr);

  (void)getAddrOfVTable(VTableClass, Base.getBaseOffset());
  VFTableIdTy ID(VTableClass, Base.getBaseOffset());
  llvm::GlobalValue *VTableAddressPoint = VFTablesMap[ID];
  if (!VTableAddressPoint) {
    assert(Base.getBase()->getNumVBases() &&
           !CGM.getContext().getASTRecordLayout(Base.getBase()).hasOwnVFPtr());
  }
  return VTableAddressPoint;
}

static void mangleVFTableName(MicrosoftMangleContext &MangleContext,
                              const CXXRecordDecl *RD, const VPtrInfo *VFPtr,
                              SmallString<256> &Name) {
  llvm::raw_svector_ostream Out(Name);
  MangleContext.mangleCXXVFTable(RD, VFPtr->MangledPath, Out);
}

llvm::Constant *MicrosoftCXXABI::getVTableAddressPointForConstExpr(
    BaseSubobject Base, const CXXRecordDecl *VTableClass) {
  (void)getAddrOfVTable(VTableClass, Base.getBaseOffset());
  VFTableIdTy ID(VTableClass, Base.getBaseOffset());
  llvm::GlobalValue *VFTable = VFTablesMap[ID];
  assert(VFTable && "Couldn't find a vftable for the given base?");
  return VFTable;
}

llvm::GlobalVariable *MicrosoftCXXABI::getAddrOfVTable(const CXXRecordDecl *RD,
                                                       CharUnits VPtrOffset) {
  // getAddrOfVTable may return 0 if asked to get an address of a vtable which
  // shouldn't be used in the given record type. We want to cache this result in
  // VFTablesMap, thus a simple zero check is not sufficient.
  VFTableIdTy ID(RD, VPtrOffset);
  VTablesMapTy::iterator I;
  bool Inserted;
  std::tie(I, Inserted) = VTablesMap.insert(std::make_pair(ID, nullptr));
  if (!Inserted)
    return I->second;

  llvm::GlobalVariable *&VTable = I->second;

  MicrosoftVTableContext &VTContext = CGM.getMicrosoftVTableContext();
  const VPtrInfoVector &VFPtrs = VTContext.getVFPtrOffsets(RD);

  if (DeferredVFTables.insert(RD)) {
    // We haven't processed this record type before.
    // Queue up this v-table for possible deferred emission.
    CGM.addDeferredVTable(RD);

#ifndef NDEBUG
    // Create all the vftables at once in order to make sure each vftable has
    // a unique mangled name.
    llvm::StringSet<> ObservedMangledNames;
    for (size_t J = 0, F = VFPtrs.size(); J != F; ++J) {
      SmallString<256> Name;
      mangleVFTableName(getMangleContext(), RD, VFPtrs[J], Name);
      if (!ObservedMangledNames.insert(Name.str()))
        llvm_unreachable("Already saw this mangling before?");
    }
#endif
  }

  for (size_t J = 0, F = VFPtrs.size(); J != F; ++J) {
    if (VFPtrs[J]->FullOffsetInMDC != VPtrOffset)
      continue;
    SmallString<256> VFTableName;
    mangleVFTableName(getMangleContext(), RD, VFPtrs[J], VFTableName);
    StringRef VTableName = VFTableName;

    uint64_t NumVTableSlots =
        VTContext.getVFTableLayout(RD, VFPtrs[J]->FullOffsetInMDC)
            .getNumVTableComponents();
    llvm::GlobalValue::LinkageTypes VTableLinkage =
        llvm::GlobalValue::ExternalLinkage;
    llvm::ArrayType *VTableType =
        llvm::ArrayType::get(CGM.Int8PtrTy, NumVTableSlots);
    if (getContext().getLangOpts().RTTIData) {
      VTableLinkage = llvm::GlobalValue::PrivateLinkage;
      VTableName = "";
    }

    VTable = CGM.getModule().getNamedGlobal(VFTableName);
    if (!VTable) {
      // Create a backing variable for the contents of VTable.  The VTable may
      // or may not include space for a pointer to RTTI data.
      llvm::GlobalValue *VFTable = VTable = new llvm::GlobalVariable(
          CGM.getModule(), VTableType, /*isConstant=*/true, VTableLinkage,
          /*Initializer=*/nullptr, VTableName);
      VTable->setUnnamedAddr(true);

      // Only insert a pointer into the VFTable for RTTI data if we are not
      // importing it.  We never reference the RTTI data directly so there is no
      // need to make room for it.
      if (getContext().getLangOpts().RTTIData &&
          !RD->hasAttr<DLLImportAttr>()) {
        llvm::Value *GEPIndices[] = {llvm::ConstantInt::get(CGM.IntTy, 0),
                                     llvm::ConstantInt::get(CGM.IntTy, 1)};
        // Create a GEP which points just after the first entry in the VFTable,
        // this should be the location of the first virtual method.
        llvm::Constant *VTableGEP =
            llvm::ConstantExpr::getInBoundsGetElementPtr(VTable, GEPIndices);
        // The symbol for the VFTable is an alias to the GEP.  It is
        // transparent, to other modules, what the nature of this symbol is; all
        // that matters is that the alias be the address of the first virtual
        // method.
        VFTable = llvm::GlobalAlias::create(
            cast<llvm::SequentialType>(VTableGEP->getType())->getElementType(),
            /*AddressSpace=*/0, llvm::GlobalValue::ExternalLinkage,
            VFTableName.str(), VTableGEP, &CGM.getModule());
      } else {
        // We don't need a GlobalAlias to be a symbol for the VTable if we won't
        // be referencing any RTTI data.  The GlobalVariable will end up being
        // an appropriate definition of the VFTable.
        VTable->setName(VFTableName.str());
      }

      VFTable->setUnnamedAddr(true);
      if (RD->hasAttr<DLLImportAttr>())
        VFTable->setDLLStorageClass(llvm::GlobalValue::DLLImportStorageClass);
      else if (RD->hasAttr<DLLExportAttr>())
        VFTable->setDLLStorageClass(llvm::GlobalValue::DLLExportStorageClass);

      llvm::GlobalValue::LinkageTypes VFTableLinkage = CGM.getVTableLinkage(RD);
      if (VFTable != VTable) {
        if (llvm::GlobalValue::isAvailableExternallyLinkage(VFTableLinkage)) {
          // AvailableExternally implies that we grabbed the data from another
          // executable.  No need to stick the alias in a Comdat.
        } else if (llvm::GlobalValue::isInternalLinkage(VFTableLinkage) ||
                   llvm::GlobalValue::isWeakODRLinkage(VFTableLinkage) ||
                   llvm::GlobalValue::isLinkOnceODRLinkage(VFTableLinkage)) {
          // The alias is going to be dropped into a Comdat, no need to make it
          // weak.
          if (!llvm::GlobalValue::isInternalLinkage(VFTableLinkage))
            VFTableLinkage = llvm::GlobalValue::ExternalLinkage;
          llvm::Comdat *C =
              CGM.getModule().getOrInsertComdat(VFTable->getName());
          // We must indicate which VFTable is larger to support linking between
          // translation units which do and do not have RTTI data.  The largest
          // VFTable contains the RTTI data; translation units which reference
          // the smaller VFTable always reference it relative to the first
          // virtual method.
          C->setSelectionKind(llvm::Comdat::Largest);
          VTable->setComdat(C);
        } else {
          llvm_unreachable("unexpected linkage for vftable!");
        }
      }
      VFTable->setLinkage(VFTableLinkage);
      CGM.setGlobalVisibility(VFTable, RD);
      VFTablesMap[ID] = VFTable;
    }
    break;
  }

  return VTable;
}

llvm::Value *MicrosoftCXXABI::getVirtualFunctionPointer(CodeGenFunction &CGF,
                                                        GlobalDecl GD,
                                                        llvm::Value *This,
                                                        llvm::Type *Ty) {
  GD = GD.getCanonicalDecl();
  CGBuilderTy &Builder = CGF.Builder;

  Ty = Ty->getPointerTo()->getPointerTo();
  llvm::Value *VPtr =
      adjustThisArgumentForVirtualFunctionCall(CGF, GD, This, true);
  llvm::Value *VTable = CGF.GetVTablePtr(VPtr, Ty);

  MicrosoftVTableContext::MethodVFTableLocation ML =
      CGM.getMicrosoftVTableContext().getMethodVFTableLocation(GD);
  llvm::Value *VFuncPtr =
      Builder.CreateConstInBoundsGEP1_64(VTable, ML.Index, "vfn");
  return Builder.CreateLoad(VFuncPtr);
}

void MicrosoftCXXABI::EmitVirtualDestructorCall(CodeGenFunction &CGF,
                                                const CXXDestructorDecl *Dtor,
                                                CXXDtorType DtorType,
                                                llvm::Value *This,
                                                const CXXMemberCallExpr *CE) {
  assert(CE == nullptr || CE->arg_begin() == CE->arg_end());
  assert(DtorType == Dtor_Deleting || DtorType == Dtor_Complete);

  // We have only one destructor in the vftable but can get both behaviors
  // by passing an implicit int parameter.
  GlobalDecl GD(Dtor, Dtor_Deleting);
  const CGFunctionInfo *FInfo = &CGM.getTypes().arrangeCXXStructorDeclaration(
      Dtor, StructorType::Deleting);
  llvm::Type *Ty = CGF.CGM.getTypes().GetFunctionType(*FInfo);
  llvm::Value *Callee = getVirtualFunctionPointer(CGF, GD, This, Ty);

  ASTContext &Context = CGF.getContext();
  llvm::Value *ImplicitParam =
      llvm::ConstantInt::get(llvm::IntegerType::getInt32Ty(CGF.getLLVMContext()),
                             DtorType == Dtor_Deleting);

  This = adjustThisArgumentForVirtualFunctionCall(CGF, GD, This, true);
  CGF.EmitCXXMemberOrOperatorCall(Dtor, Callee, ReturnValueSlot(), This,
                                  ImplicitParam, Context.IntTy, CE);
}

const VBTableGlobals &
MicrosoftCXXABI::enumerateVBTables(const CXXRecordDecl *RD) {
  // At this layer, we can key the cache off of a single class, which is much
  // easier than caching each vbtable individually.
  llvm::DenseMap<const CXXRecordDecl*, VBTableGlobals>::iterator Entry;
  bool Added;
  std::tie(Entry, Added) =
      VBTablesMap.insert(std::make_pair(RD, VBTableGlobals()));
  VBTableGlobals &VBGlobals = Entry->second;
  if (!Added)
    return VBGlobals;

  MicrosoftVTableContext &Context = CGM.getMicrosoftVTableContext();
  VBGlobals.VBTables = &Context.enumerateVBTables(RD);

  // Cache the globals for all vbtables so we don't have to recompute the
  // mangled names.
  llvm::GlobalVariable::LinkageTypes Linkage = CGM.getVTableLinkage(RD);
  for (VPtrInfoVector::const_iterator I = VBGlobals.VBTables->begin(),
                                      E = VBGlobals.VBTables->end();
       I != E; ++I) {
    VBGlobals.Globals.push_back(getAddrOfVBTable(**I, RD, Linkage));
  }

  return VBGlobals;
}

llvm::Function *MicrosoftCXXABI::EmitVirtualMemPtrThunk(
    const CXXMethodDecl *MD,
    const MicrosoftVTableContext::MethodVFTableLocation &ML) {
  assert(!isa<CXXConstructorDecl>(MD) && !isa<CXXDestructorDecl>(MD) &&
         "can't form pointers to ctors or virtual dtors");

  // Calculate the mangled name.
  SmallString<256> ThunkName;
  llvm::raw_svector_ostream Out(ThunkName);
  getMangleContext().mangleVirtualMemPtrThunk(MD, Out);
  Out.flush();

  // If the thunk has been generated previously, just return it.
  if (llvm::GlobalValue *GV = CGM.getModule().getNamedValue(ThunkName))
    return cast<llvm::Function>(GV);

  // Create the llvm::Function.
  const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeMSMemberPointerThunk(MD);
  llvm::FunctionType *ThunkTy = CGM.getTypes().GetFunctionType(FnInfo);
  llvm::Function *ThunkFn =
      llvm::Function::Create(ThunkTy, llvm::Function::ExternalLinkage,
                             ThunkName.str(), &CGM.getModule());
  assert(ThunkFn->getName() == ThunkName && "name was uniqued!");

  ThunkFn->setLinkage(MD->isExternallyVisible()
                          ? llvm::GlobalValue::LinkOnceODRLinkage
                          : llvm::GlobalValue::InternalLinkage);

  CGM.SetLLVMFunctionAttributes(MD, FnInfo, ThunkFn);
  CGM.SetLLVMFunctionAttributesForDefinition(MD, ThunkFn);

  // These thunks can be compared, so they are not unnamed.
  ThunkFn->setUnnamedAddr(false);

  // Start codegen.
  CodeGenFunction CGF(CGM);
  CGF.CurGD = GlobalDecl(MD);
  CGF.CurFuncIsThunk = true;

  // Build FunctionArgs, but only include the implicit 'this' parameter
  // declaration.
  FunctionArgList FunctionArgs;
  buildThisParam(CGF, FunctionArgs);

  // Start defining the function.
  CGF.StartFunction(GlobalDecl(), FnInfo.getReturnType(), ThunkFn, FnInfo,
                    FunctionArgs, MD->getLocation(), SourceLocation());
  EmitThisParam(CGF);

  // Load the vfptr and then callee from the vftable.  The callee should have
  // adjusted 'this' so that the vfptr is at offset zero.
  llvm::Value *VTable = CGF.GetVTablePtr(
      getThisValue(CGF), ThunkTy->getPointerTo()->getPointerTo());
  llvm::Value *VFuncPtr =
      CGF.Builder.CreateConstInBoundsGEP1_64(VTable, ML.Index, "vfn");
  llvm::Value *Callee = CGF.Builder.CreateLoad(VFuncPtr);

  CGF.EmitMustTailThunk(MD, getThisValue(CGF), Callee);

  return ThunkFn;
}

void MicrosoftCXXABI::emitVirtualInheritanceTables(const CXXRecordDecl *RD) {
  const VBTableGlobals &VBGlobals = enumerateVBTables(RD);
  for (unsigned I = 0, E = VBGlobals.VBTables->size(); I != E; ++I) {
    const VPtrInfo *VBT = (*VBGlobals.VBTables)[I];
    llvm::GlobalVariable *GV = VBGlobals.Globals[I];
    emitVBTableDefinition(*VBT, RD, GV);
  }
}

llvm::GlobalVariable *
MicrosoftCXXABI::getAddrOfVBTable(const VPtrInfo &VBT, const CXXRecordDecl *RD,
                                  llvm::GlobalVariable::LinkageTypes Linkage) {
  SmallString<256> OutName;
  llvm::raw_svector_ostream Out(OutName);
  getMangleContext().mangleCXXVBTable(RD, VBT.MangledPath, Out);
  Out.flush();
  StringRef Name = OutName.str();

  llvm::ArrayType *VBTableType =
      llvm::ArrayType::get(CGM.IntTy, 1 + VBT.ReusingBase->getNumVBases());

  assert(!CGM.getModule().getNamedGlobal(Name) &&
         "vbtable with this name already exists: mangling bug?");
  llvm::GlobalVariable *GV =
      CGM.CreateOrReplaceCXXRuntimeVariable(Name, VBTableType, Linkage);
  GV->setUnnamedAddr(true);

  if (RD->hasAttr<DLLImportAttr>())
    GV->setDLLStorageClass(llvm::GlobalValue::DLLImportStorageClass);
  else if (RD->hasAttr<DLLExportAttr>())
    GV->setDLLStorageClass(llvm::GlobalValue::DLLExportStorageClass);

  return GV;
}

void MicrosoftCXXABI::emitVBTableDefinition(const VPtrInfo &VBT,
                                            const CXXRecordDecl *RD,
                                            llvm::GlobalVariable *GV) const {
  const CXXRecordDecl *ReusingBase = VBT.ReusingBase;

  assert(RD->getNumVBases() && ReusingBase->getNumVBases() &&
         "should only emit vbtables for classes with vbtables");

  const ASTRecordLayout &BaseLayout =
      CGM.getContext().getASTRecordLayout(VBT.BaseWithVPtr);
  const ASTRecordLayout &DerivedLayout =
    CGM.getContext().getASTRecordLayout(RD);

  SmallVector<llvm::Constant *, 4> Offsets(1 + ReusingBase->getNumVBases(),
                                           nullptr);

  // The offset from ReusingBase's vbptr to itself always leads.
  CharUnits VBPtrOffset = BaseLayout.getVBPtrOffset();
  Offsets[0] = llvm::ConstantInt::get(CGM.IntTy, -VBPtrOffset.getQuantity());

  MicrosoftVTableContext &Context = CGM.getMicrosoftVTableContext();
  for (const auto &I : ReusingBase->vbases()) {
    const CXXRecordDecl *VBase = I.getType()->getAsCXXRecordDecl();
    CharUnits Offset = DerivedLayout.getVBaseClassOffset(VBase);
    assert(!Offset.isNegative());

    // Make it relative to the subobject vbptr.
    CharUnits CompleteVBPtrOffset = VBT.NonVirtualOffset + VBPtrOffset;
    if (VBT.getVBaseWithVPtr())
      CompleteVBPtrOffset +=
          DerivedLayout.getVBaseClassOffset(VBT.getVBaseWithVPtr());
    Offset -= CompleteVBPtrOffset;

    unsigned VBIndex = Context.getVBTableIndex(ReusingBase, VBase);
    assert(Offsets[VBIndex] == nullptr && "The same vbindex seen twice?");
    Offsets[VBIndex] = llvm::ConstantInt::get(CGM.IntTy, Offset.getQuantity());
  }

  assert(Offsets.size() ==
         cast<llvm::ArrayType>(cast<llvm::PointerType>(GV->getType())
                               ->getElementType())->getNumElements());
  llvm::ArrayType *VBTableType =
    llvm::ArrayType::get(CGM.IntTy, Offsets.size());
  llvm::Constant *Init = llvm::ConstantArray::get(VBTableType, Offsets);
  GV->setInitializer(Init);

  // Set the right visibility.
  CGM.setGlobalVisibility(GV, RD);
}

llvm::Value *MicrosoftCXXABI::performThisAdjustment(CodeGenFunction &CGF,
                                                    llvm::Value *This,
                                                    const ThisAdjustment &TA) {
  if (TA.isEmpty())
    return This;

  llvm::Value *V = CGF.Builder.CreateBitCast(This, CGF.Int8PtrTy);

  if (!TA.Virtual.isEmpty()) {
    assert(TA.Virtual.Microsoft.VtordispOffset < 0);
    // Adjust the this argument based on the vtordisp value.
    llvm::Value *VtorDispPtr =
        CGF.Builder.CreateConstGEP1_32(V, TA.Virtual.Microsoft.VtordispOffset);
    VtorDispPtr =
        CGF.Builder.CreateBitCast(VtorDispPtr, CGF.Int32Ty->getPointerTo());
    llvm::Value *VtorDisp = CGF.Builder.CreateLoad(VtorDispPtr, "vtordisp");
    V = CGF.Builder.CreateGEP(V, CGF.Builder.CreateNeg(VtorDisp));

    if (TA.Virtual.Microsoft.VBPtrOffset) {
      // If the final overrider is defined in a virtual base other than the one
      // that holds the vfptr, we have to use a vtordispex thunk which looks up
      // the vbtable of the derived class.
      assert(TA.Virtual.Microsoft.VBPtrOffset > 0);
      assert(TA.Virtual.Microsoft.VBOffsetOffset >= 0);
      llvm::Value *VBPtr;
      llvm::Value *VBaseOffset =
          GetVBaseOffsetFromVBPtr(CGF, V, -TA.Virtual.Microsoft.VBPtrOffset,
                                  TA.Virtual.Microsoft.VBOffsetOffset, &VBPtr);
      V = CGF.Builder.CreateInBoundsGEP(VBPtr, VBaseOffset);
    }
  }

  if (TA.NonVirtual) {
    // Non-virtual adjustment might result in a pointer outside the allocated
    // object, e.g. if the final overrider class is laid out after the virtual
    // base that declares a method in the most derived class.
    V = CGF.Builder.CreateConstGEP1_32(V, TA.NonVirtual);
  }

  // Don't need to bitcast back, the call CodeGen will handle this.
  return V;
}

llvm::Value *
MicrosoftCXXABI::performReturnAdjustment(CodeGenFunction &CGF, llvm::Value *Ret,
                                         const ReturnAdjustment &RA) {
  if (RA.isEmpty())
    return Ret;

  llvm::Value *V = CGF.Builder.CreateBitCast(Ret, CGF.Int8PtrTy);

  if (RA.Virtual.Microsoft.VBIndex) {
    assert(RA.Virtual.Microsoft.VBIndex > 0);
    int32_t IntSize =
        getContext().getTypeSizeInChars(getContext().IntTy).getQuantity();
    llvm::Value *VBPtr;
    llvm::Value *VBaseOffset =
        GetVBaseOffsetFromVBPtr(CGF, V, RA.Virtual.Microsoft.VBPtrOffset,
                                IntSize * RA.Virtual.Microsoft.VBIndex, &VBPtr);
    V = CGF.Builder.CreateInBoundsGEP(VBPtr, VBaseOffset);
  }

  if (RA.NonVirtual)
    V = CGF.Builder.CreateConstInBoundsGEP1_32(V, RA.NonVirtual);

  // Cast back to the original type.
  return CGF.Builder.CreateBitCast(V, Ret->getType());
}

bool MicrosoftCXXABI::requiresArrayCookie(const CXXDeleteExpr *expr,
                                   QualType elementType) {
  // Microsoft seems to completely ignore the possibility of a
  // two-argument usual deallocation function.
  return elementType.isDestructedType();
}

bool MicrosoftCXXABI::requiresArrayCookie(const CXXNewExpr *expr) {
  // Microsoft seems to completely ignore the possibility of a
  // two-argument usual deallocation function.
  return expr->getAllocatedType().isDestructedType();
}

CharUnits MicrosoftCXXABI::getArrayCookieSizeImpl(QualType type) {
  // The array cookie is always a size_t; we then pad that out to the
  // alignment of the element type.
  ASTContext &Ctx = getContext();
  return std::max(Ctx.getTypeSizeInChars(Ctx.getSizeType()),
                  Ctx.getTypeAlignInChars(type));
}

llvm::Value *MicrosoftCXXABI::readArrayCookieImpl(CodeGenFunction &CGF,
                                                  llvm::Value *allocPtr,
                                                  CharUnits cookieSize) {
  unsigned AS = allocPtr->getType()->getPointerAddressSpace();
  llvm::Value *numElementsPtr =
    CGF.Builder.CreateBitCast(allocPtr, CGF.SizeTy->getPointerTo(AS));
  return CGF.Builder.CreateLoad(numElementsPtr);
}

llvm::Value* MicrosoftCXXABI::InitializeArrayCookie(CodeGenFunction &CGF,
                                                    llvm::Value *newPtr,
                                                    llvm::Value *numElements,
                                                    const CXXNewExpr *expr,
                                                    QualType elementType) {
  assert(requiresArrayCookie(expr));

  // The size of the cookie.
  CharUnits cookieSize = getArrayCookieSizeImpl(elementType);

  // Compute an offset to the cookie.
  llvm::Value *cookiePtr = newPtr;

  // Write the number of elements into the appropriate slot.
  unsigned AS = newPtr->getType()->getPointerAddressSpace();
  llvm::Value *numElementsPtr
    = CGF.Builder.CreateBitCast(cookiePtr, CGF.SizeTy->getPointerTo(AS));
  CGF.Builder.CreateStore(numElements, numElementsPtr);

  // Finally, compute a pointer to the actual data buffer by skipping
  // over the cookie completely.
  return CGF.Builder.CreateConstInBoundsGEP1_64(newPtr,
                                                cookieSize.getQuantity());
}

void MicrosoftCXXABI::EmitGuardedInit(CodeGenFunction &CGF, const VarDecl &D,
                                      llvm::GlobalVariable *GV,
                                      bool PerformInit) {
  // MSVC only uses guards for static locals.
  if (!D.isStaticLocal()) {
    assert(GV->hasWeakLinkage() || GV->hasLinkOnceLinkage());
    // GlobalOpt is allowed to discard the initializer, so use linkonce_odr.
    CGF.CurFn->setLinkage(llvm::GlobalValue::LinkOnceODRLinkage);
    CGF.EmitCXXGlobalVarDeclInit(D, GV, PerformInit);
    return;
  }

  // MSVC always uses an i32 bitfield to guard initialization, which is *not*
  // threadsafe.  Since the user may be linking in inline functions compiled by
  // cl.exe, there's no reason to provide a false sense of security by using
  // critical sections here.

  if (D.getTLSKind())
    CGM.ErrorUnsupported(&D, "dynamic TLS initialization");

  CGBuilderTy &Builder = CGF.Builder;
  llvm::IntegerType *GuardTy = CGF.Int32Ty;
  llvm::ConstantInt *Zero = llvm::ConstantInt::get(GuardTy, 0);

  // Get the guard variable for this function if we have one already.
  GuardInfo *GI = &GuardVariableMap[D.getDeclContext()];

  unsigned BitIndex;
  if (D.isStaticLocal() && D.isExternallyVisible()) {
    // Externally visible variables have to be numbered in Sema to properly
    // handle unreachable VarDecls.
    BitIndex = getContext().getStaticLocalNumber(&D);
    assert(BitIndex > 0);
    BitIndex--;
  } else {
    // Non-externally visible variables are numbered here in CodeGen.
    BitIndex = GI->BitIndex++;
  }

  if (BitIndex >= 32) {
    if (D.isExternallyVisible())
      ErrorUnsupportedABI(CGF, "more than 32 guarded initializations");
    BitIndex %= 32;
    GI->Guard = nullptr;
  }

  // Lazily create the i32 bitfield for this function.
  if (!GI->Guard) {
    // Mangle the name for the guard.
    SmallString<256> GuardName;
    {
      llvm::raw_svector_ostream Out(GuardName);
      getMangleContext().mangleStaticGuardVariable(&D, Out);
      Out.flush();
    }

    // Create the guard variable with a zero-initializer. Just absorb linkage,
    // visibility and dll storage class from the guarded variable.
    GI->Guard =
        new llvm::GlobalVariable(CGM.getModule(), GuardTy, false,
                                 GV->getLinkage(), Zero, GuardName.str());
    GI->Guard->setVisibility(GV->getVisibility());
    GI->Guard->setDLLStorageClass(GV->getDLLStorageClass());
  } else {
    assert(GI->Guard->getLinkage() == GV->getLinkage() &&
           "static local from the same function had different linkage");
  }

  // Pseudo code for the test:
  // if (!(GuardVar & MyGuardBit)) {
  //   GuardVar |= MyGuardBit;
  //   ... initialize the object ...;
  // }

  // Test our bit from the guard variable.
  llvm::ConstantInt *Bit = llvm::ConstantInt::get(GuardTy, 1U << BitIndex);
  llvm::LoadInst *LI = Builder.CreateLoad(GI->Guard);
  llvm::Value *IsInitialized =
      Builder.CreateICmpNE(Builder.CreateAnd(LI, Bit), Zero);
  llvm::BasicBlock *InitBlock = CGF.createBasicBlock("init");
  llvm::BasicBlock *EndBlock = CGF.createBasicBlock("init.end");
  Builder.CreateCondBr(IsInitialized, EndBlock, InitBlock);

  // Set our bit in the guard variable and emit the initializer and add a global
  // destructor if appropriate.
  CGF.EmitBlock(InitBlock);
  Builder.CreateStore(Builder.CreateOr(LI, Bit), GI->Guard);
  CGF.EmitCXXGlobalVarDeclInit(D, GV, PerformInit);
  Builder.CreateBr(EndBlock);

  // Continue.
  CGF.EmitBlock(EndBlock);
}

bool MicrosoftCXXABI::isZeroInitializable(const MemberPointerType *MPT) {
  // Null-ness for function memptrs only depends on the first field, which is
  // the function pointer.  The rest don't matter, so we can zero initialize.
  if (MPT->isMemberFunctionPointer())
    return true;

  // The virtual base adjustment field is always -1 for null, so if we have one
  // we can't zero initialize.  The field offset is sometimes also -1 if 0 is a
  // valid field offset.
  const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
  MSInheritanceAttr::Spelling Inheritance = RD->getMSInheritanceModel();
  return (!MSInheritanceAttr::hasVBTableOffsetField(Inheritance) &&
          RD->nullFieldOffsetIsZero());
}

llvm::Type *
MicrosoftCXXABI::ConvertMemberPointerType(const MemberPointerType *MPT) {
  const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
  MSInheritanceAttr::Spelling Inheritance = RD->getMSInheritanceModel();
  llvm::SmallVector<llvm::Type *, 4> fields;
  if (MPT->isMemberFunctionPointer())
    fields.push_back(CGM.VoidPtrTy);  // FunctionPointerOrVirtualThunk
  else
    fields.push_back(CGM.IntTy);  // FieldOffset

  if (MSInheritanceAttr::hasNVOffsetField(MPT->isMemberFunctionPointer(),
                                          Inheritance))
    fields.push_back(CGM.IntTy);
  if (MSInheritanceAttr::hasVBPtrOffsetField(Inheritance))
    fields.push_back(CGM.IntTy);
  if (MSInheritanceAttr::hasVBTableOffsetField(Inheritance))
    fields.push_back(CGM.IntTy);  // VirtualBaseAdjustmentOffset

  if (fields.size() == 1)
    return fields[0];
  return llvm::StructType::get(CGM.getLLVMContext(), fields);
}

void MicrosoftCXXABI::
GetNullMemberPointerFields(const MemberPointerType *MPT,
                           llvm::SmallVectorImpl<llvm::Constant *> &fields) {
  assert(fields.empty());
  const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
  MSInheritanceAttr::Spelling Inheritance = RD->getMSInheritanceModel();
  if (MPT->isMemberFunctionPointer()) {
    // FunctionPointerOrVirtualThunk
    fields.push_back(llvm::Constant::getNullValue(CGM.VoidPtrTy));
  } else {
    if (RD->nullFieldOffsetIsZero())
      fields.push_back(getZeroInt());  // FieldOffset
    else
      fields.push_back(getAllOnesInt());  // FieldOffset
  }

  if (MSInheritanceAttr::hasNVOffsetField(MPT->isMemberFunctionPointer(),
                                          Inheritance))
    fields.push_back(getZeroInt());
  if (MSInheritanceAttr::hasVBPtrOffsetField(Inheritance))
    fields.push_back(getZeroInt());
  if (MSInheritanceAttr::hasVBTableOffsetField(Inheritance))
    fields.push_back(getAllOnesInt());
}

llvm::Constant *
MicrosoftCXXABI::EmitNullMemberPointer(const MemberPointerType *MPT) {
  llvm::SmallVector<llvm::Constant *, 4> fields;
  GetNullMemberPointerFields(MPT, fields);
  if (fields.size() == 1)
    return fields[0];
  llvm::Constant *Res = llvm::ConstantStruct::getAnon(fields);
  assert(Res->getType() == ConvertMemberPointerType(MPT));
  return Res;
}

llvm::Constant *
MicrosoftCXXABI::EmitFullMemberPointer(llvm::Constant *FirstField,
                                       bool IsMemberFunction,
                                       const CXXRecordDecl *RD,
                                       CharUnits NonVirtualBaseAdjustment)
{
  MSInheritanceAttr::Spelling Inheritance = RD->getMSInheritanceModel();

  // Single inheritance class member pointer are represented as scalars instead
  // of aggregates.
  if (MSInheritanceAttr::hasOnlyOneField(IsMemberFunction, Inheritance))
    return FirstField;

  llvm::SmallVector<llvm::Constant *, 4> fields;
  fields.push_back(FirstField);

  if (MSInheritanceAttr::hasNVOffsetField(IsMemberFunction, Inheritance))
    fields.push_back(llvm::ConstantInt::get(
      CGM.IntTy, NonVirtualBaseAdjustment.getQuantity()));

  if (MSInheritanceAttr::hasVBPtrOffsetField(Inheritance)) {
    CharUnits Offs = CharUnits::Zero();
    if (RD->getNumVBases())
      Offs = getContext().getASTRecordLayout(RD).getVBPtrOffset();
    fields.push_back(llvm::ConstantInt::get(CGM.IntTy, Offs.getQuantity()));
  }

  // The rest of the fields are adjusted by conversions to a more derived class.
  if (MSInheritanceAttr::hasVBTableOffsetField(Inheritance))
    fields.push_back(getZeroInt());

  return llvm::ConstantStruct::getAnon(fields);
}

llvm::Constant *
MicrosoftCXXABI::EmitMemberDataPointer(const MemberPointerType *MPT,
                                       CharUnits offset) {
  const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
  llvm::Constant *FirstField =
    llvm::ConstantInt::get(CGM.IntTy, offset.getQuantity());
  return EmitFullMemberPointer(FirstField, /*IsMemberFunction=*/false, RD,
                               CharUnits::Zero());
}

llvm::Constant *MicrosoftCXXABI::EmitMemberPointer(const CXXMethodDecl *MD) {
  return BuildMemberPointer(MD->getParent(), MD, CharUnits::Zero());
}

llvm::Constant *MicrosoftCXXABI::EmitMemberPointer(const APValue &MP,
                                                   QualType MPType) {
  const MemberPointerType *MPT = MPType->castAs<MemberPointerType>();
  const ValueDecl *MPD = MP.getMemberPointerDecl();
  if (!MPD)
    return EmitNullMemberPointer(MPT);

  CharUnits ThisAdjustment = getMemberPointerPathAdjustment(MP);

  // FIXME PR15713: Support virtual inheritance paths.

  if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(MPD))
    return BuildMemberPointer(MPT->getMostRecentCXXRecordDecl(), MD,
                              ThisAdjustment);

  CharUnits FieldOffset =
    getContext().toCharUnitsFromBits(getContext().getFieldOffset(MPD));
  return EmitMemberDataPointer(MPT, ThisAdjustment + FieldOffset);
}

llvm::Constant *
MicrosoftCXXABI::BuildMemberPointer(const CXXRecordDecl *RD,
                                    const CXXMethodDecl *MD,
                                    CharUnits NonVirtualBaseAdjustment) {
  assert(MD->isInstance() && "Member function must not be static!");
  MD = MD->getCanonicalDecl();
  RD = RD->getMostRecentDecl();
  CodeGenTypes &Types = CGM.getTypes();

  llvm::Constant *FirstField;
  const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
  if (!MD->isVirtual()) {
    llvm::Type *Ty;
    // Check whether the function has a computable LLVM signature.
    if (Types.isFuncTypeConvertible(FPT)) {
      // The function has a computable LLVM signature; use the correct type.
      Ty = Types.GetFunctionType(Types.arrangeCXXMethodDeclaration(MD));
    } else {
      // Use an arbitrary non-function type to tell GetAddrOfFunction that the
      // function type is incomplete.
      Ty = CGM.PtrDiffTy;
    }
    FirstField = CGM.GetAddrOfFunction(MD, Ty);
    FirstField = llvm::ConstantExpr::getBitCast(FirstField, CGM.VoidPtrTy);
  } else {
    MicrosoftVTableContext::MethodVFTableLocation ML =
        CGM.getMicrosoftVTableContext().getMethodVFTableLocation(MD);
    if (!CGM.getTypes().isFuncTypeConvertible(
            MD->getType()->castAs<FunctionType>())) {
      CGM.ErrorUnsupported(MD, "pointer to virtual member function with "
                               "incomplete return or parameter type");
      FirstField = llvm::Constant::getNullValue(CGM.VoidPtrTy);
    } else if (FPT->getCallConv() == CC_X86FastCall) {
      CGM.ErrorUnsupported(MD, "pointer to fastcall virtual member function");
      FirstField = llvm::Constant::getNullValue(CGM.VoidPtrTy);
    } else if (ML.VBase) {
      CGM.ErrorUnsupported(MD, "pointer to virtual member function overriding "
                               "member function in virtual base class");
      FirstField = llvm::Constant::getNullValue(CGM.VoidPtrTy);
    } else {
      llvm::Function *Thunk = EmitVirtualMemPtrThunk(MD, ML);
      FirstField = llvm::ConstantExpr::getBitCast(Thunk, CGM.VoidPtrTy);
      // Include the vfptr adjustment if the method is in a non-primary vftable.
      NonVirtualBaseAdjustment += ML.VFPtrOffset;
    }
  }

  // The rest of the fields are common with data member pointers.
  return EmitFullMemberPointer(FirstField, /*IsMemberFunction=*/true, RD,
                               NonVirtualBaseAdjustment);
}

/// Member pointers are the same if they're either bitwise identical *or* both
/// null.  Null-ness for function members is determined by the first field,
/// while for data member pointers we must compare all fields.
llvm::Value *
MicrosoftCXXABI::EmitMemberPointerComparison(CodeGenFunction &CGF,
                                             llvm::Value *L,
                                             llvm::Value *R,
                                             const MemberPointerType *MPT,
                                             bool Inequality) {
  CGBuilderTy &Builder = CGF.Builder;

  // Handle != comparisons by switching the sense of all boolean operations.
  llvm::ICmpInst::Predicate Eq;
  llvm::Instruction::BinaryOps And, Or;
  if (Inequality) {
    Eq = llvm::ICmpInst::ICMP_NE;
    And = llvm::Instruction::Or;
    Or = llvm::Instruction::And;
  } else {
    Eq = llvm::ICmpInst::ICMP_EQ;
    And = llvm::Instruction::And;
    Or = llvm::Instruction::Or;
  }

  // If this is a single field member pointer (single inheritance), this is a
  // single icmp.
  const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
  MSInheritanceAttr::Spelling Inheritance = RD->getMSInheritanceModel();
  if (MSInheritanceAttr::hasOnlyOneField(MPT->isMemberFunctionPointer(),
                                         Inheritance))
    return Builder.CreateICmp(Eq, L, R);

  // Compare the first field.
  llvm::Value *L0 = Builder.CreateExtractValue(L, 0, "lhs.0");
  llvm::Value *R0 = Builder.CreateExtractValue(R, 0, "rhs.0");
  llvm::Value *Cmp0 = Builder.CreateICmp(Eq, L0, R0, "memptr.cmp.first");

  // Compare everything other than the first field.
  llvm::Value *Res = nullptr;
  llvm::StructType *LType = cast<llvm::StructType>(L->getType());
  for (unsigned I = 1, E = LType->getNumElements(); I != E; ++I) {
    llvm::Value *LF = Builder.CreateExtractValue(L, I);
    llvm::Value *RF = Builder.CreateExtractValue(R, I);
    llvm::Value *Cmp = Builder.CreateICmp(Eq, LF, RF, "memptr.cmp.rest");
    if (Res)
      Res = Builder.CreateBinOp(And, Res, Cmp);
    else
      Res = Cmp;
  }

  // Check if the first field is 0 if this is a function pointer.
  if (MPT->isMemberFunctionPointer()) {
    // (l1 == r1 && ...) || l0 == 0
    llvm::Value *Zero = llvm::Constant::getNullValue(L0->getType());
    llvm::Value *IsZero = Builder.CreateICmp(Eq, L0, Zero, "memptr.cmp.iszero");
    Res = Builder.CreateBinOp(Or, Res, IsZero);
  }

  // Combine the comparison of the first field, which must always be true for
  // this comparison to succeeed.
  return Builder.CreateBinOp(And, Res, Cmp0, "memptr.cmp");
}

llvm::Value *
MicrosoftCXXABI::EmitMemberPointerIsNotNull(CodeGenFunction &CGF,
                                            llvm::Value *MemPtr,
                                            const MemberPointerType *MPT) {
  CGBuilderTy &Builder = CGF.Builder;
  llvm::SmallVector<llvm::Constant *, 4> fields;
  // We only need one field for member functions.
  if (MPT->isMemberFunctionPointer())
    fields.push_back(llvm::Constant::getNullValue(CGM.VoidPtrTy));
  else
    GetNullMemberPointerFields(MPT, fields);
  assert(!fields.empty());
  llvm::Value *FirstField = MemPtr;
  if (MemPtr->getType()->isStructTy())
    FirstField = Builder.CreateExtractValue(MemPtr, 0);
  llvm::Value *Res = Builder.CreateICmpNE(FirstField, fields[0], "memptr.cmp0");

  // For function member pointers, we only need to test the function pointer
  // field.  The other fields if any can be garbage.
  if (MPT->isMemberFunctionPointer())
    return Res;

  // Otherwise, emit a series of compares and combine the results.
  for (int I = 1, E = fields.size(); I < E; ++I) {
    llvm::Value *Field = Builder.CreateExtractValue(MemPtr, I);
    llvm::Value *Next = Builder.CreateICmpNE(Field, fields[I], "memptr.cmp");
    Res = Builder.CreateOr(Res, Next, "memptr.tobool");
  }
  return Res;
}

bool MicrosoftCXXABI::MemberPointerConstantIsNull(const MemberPointerType *MPT,
                                                  llvm::Constant *Val) {
  // Function pointers are null if the pointer in the first field is null.
  if (MPT->isMemberFunctionPointer()) {
    llvm::Constant *FirstField = Val->getType()->isStructTy() ?
      Val->getAggregateElement(0U) : Val;
    return FirstField->isNullValue();
  }

  // If it's not a function pointer and it's zero initializable, we can easily
  // check zero.
  if (isZeroInitializable(MPT) && Val->isNullValue())
    return true;

  // Otherwise, break down all the fields for comparison.  Hopefully these
  // little Constants are reused, while a big null struct might not be.
  llvm::SmallVector<llvm::Constant *, 4> Fields;
  GetNullMemberPointerFields(MPT, Fields);
  if (Fields.size() == 1) {
    assert(Val->getType()->isIntegerTy());
    return Val == Fields[0];
  }

  unsigned I, E;
  for (I = 0, E = Fields.size(); I != E; ++I) {
    if (Val->getAggregateElement(I) != Fields[I])
      break;
  }
  return I == E;
}

llvm::Value *
MicrosoftCXXABI::GetVBaseOffsetFromVBPtr(CodeGenFunction &CGF,
                                         llvm::Value *This,
                                         llvm::Value *VBPtrOffset,
                                         llvm::Value *VBTableOffset,
                                         llvm::Value **VBPtrOut) {
  CGBuilderTy &Builder = CGF.Builder;
  // Load the vbtable pointer from the vbptr in the instance.
  This = Builder.CreateBitCast(This, CGM.Int8PtrTy);
  llvm::Value *VBPtr =
    Builder.CreateInBoundsGEP(This, VBPtrOffset, "vbptr");
  if (VBPtrOut) *VBPtrOut = VBPtr;
  VBPtr = Builder.CreateBitCast(VBPtr, CGM.Int8PtrTy->getPointerTo(0));
  llvm::Value *VBTable = Builder.CreateLoad(VBPtr, "vbtable");

  // Load an i32 offset from the vb-table.
  llvm::Value *VBaseOffs = Builder.CreateInBoundsGEP(VBTable, VBTableOffset);
  VBaseOffs = Builder.CreateBitCast(VBaseOffs, CGM.Int32Ty->getPointerTo(0));
  return Builder.CreateLoad(VBaseOffs, "vbase_offs");
}

// Returns an adjusted base cast to i8*, since we do more address arithmetic on
// it.
llvm::Value *MicrosoftCXXABI::AdjustVirtualBase(
    CodeGenFunction &CGF, const Expr *E, const CXXRecordDecl *RD,
    llvm::Value *Base, llvm::Value *VBTableOffset, llvm::Value *VBPtrOffset) {
  CGBuilderTy &Builder = CGF.Builder;
  Base = Builder.CreateBitCast(Base, CGM.Int8PtrTy);
  llvm::BasicBlock *OriginalBB = nullptr;
  llvm::BasicBlock *SkipAdjustBB = nullptr;
  llvm::BasicBlock *VBaseAdjustBB = nullptr;

  // In the unspecified inheritance model, there might not be a vbtable at all,
  // in which case we need to skip the virtual base lookup.  If there is a
  // vbtable, the first entry is a no-op entry that gives back the original
  // base, so look for a virtual base adjustment offset of zero.
  if (VBPtrOffset) {
    OriginalBB = Builder.GetInsertBlock();
    VBaseAdjustBB = CGF.createBasicBlock("memptr.vadjust");
    SkipAdjustBB = CGF.createBasicBlock("memptr.skip_vadjust");
    llvm::Value *IsVirtual =
      Builder.CreateICmpNE(VBTableOffset, getZeroInt(),
                           "memptr.is_vbase");
    Builder.CreateCondBr(IsVirtual, VBaseAdjustBB, SkipAdjustBB);
    CGF.EmitBlock(VBaseAdjustBB);
  }

  // If we weren't given a dynamic vbptr offset, RD should be complete and we'll
  // know the vbptr offset.
  if (!VBPtrOffset) {
    CharUnits offs = CharUnits::Zero();
    if (!RD->hasDefinition()) {
      DiagnosticsEngine &Diags = CGF.CGM.getDiags();
      unsigned DiagID = Diags.getCustomDiagID(
          DiagnosticsEngine::Error,
          "member pointer representation requires a "
          "complete class type for %0 to perform this expression");
      Diags.Report(E->getExprLoc(), DiagID) << RD << E->getSourceRange();
    } else if (RD->getNumVBases())
      offs = getContext().getASTRecordLayout(RD).getVBPtrOffset();
    VBPtrOffset = llvm::ConstantInt::get(CGM.IntTy, offs.getQuantity());
  }
  llvm::Value *VBPtr = nullptr;
  llvm::Value *VBaseOffs =
    GetVBaseOffsetFromVBPtr(CGF, Base, VBPtrOffset, VBTableOffset, &VBPtr);
  llvm::Value *AdjustedBase = Builder.CreateInBoundsGEP(VBPtr, VBaseOffs);

  // Merge control flow with the case where we didn't have to adjust.
  if (VBaseAdjustBB) {
    Builder.CreateBr(SkipAdjustBB);
    CGF.EmitBlock(SkipAdjustBB);
    llvm::PHINode *Phi = Builder.CreatePHI(CGM.Int8PtrTy, 2, "memptr.base");
    Phi->addIncoming(Base, OriginalBB);
    Phi->addIncoming(AdjustedBase, VBaseAdjustBB);
    return Phi;
  }
  return AdjustedBase;
}

llvm::Value *MicrosoftCXXABI::EmitMemberDataPointerAddress(
    CodeGenFunction &CGF, const Expr *E, llvm::Value *Base, llvm::Value *MemPtr,
    const MemberPointerType *MPT) {
  assert(MPT->isMemberDataPointer());
  unsigned AS = Base->getType()->getPointerAddressSpace();
  llvm::Type *PType =
      CGF.ConvertTypeForMem(MPT->getPointeeType())->getPointerTo(AS);
  CGBuilderTy &Builder = CGF.Builder;
  const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
  MSInheritanceAttr::Spelling Inheritance = RD->getMSInheritanceModel();

  // Extract the fields we need, regardless of model.  We'll apply them if we
  // have them.
  llvm::Value *FieldOffset = MemPtr;
  llvm::Value *VirtualBaseAdjustmentOffset = nullptr;
  llvm::Value *VBPtrOffset = nullptr;
  if (MemPtr->getType()->isStructTy()) {
    // We need to extract values.
    unsigned I = 0;
    FieldOffset = Builder.CreateExtractValue(MemPtr, I++);
    if (MSInheritanceAttr::hasVBPtrOffsetField(Inheritance))
      VBPtrOffset = Builder.CreateExtractValue(MemPtr, I++);
    if (MSInheritanceAttr::hasVBTableOffsetField(Inheritance))
      VirtualBaseAdjustmentOffset = Builder.CreateExtractValue(MemPtr, I++);
  }

  if (VirtualBaseAdjustmentOffset) {
    Base = AdjustVirtualBase(CGF, E, RD, Base, VirtualBaseAdjustmentOffset,
                             VBPtrOffset);
  }

  // Cast to char*.
  Base = Builder.CreateBitCast(Base, Builder.getInt8Ty()->getPointerTo(AS));

  // Apply the offset, which we assume is non-null.
  llvm::Value *Addr =
    Builder.CreateInBoundsGEP(Base, FieldOffset, "memptr.offset");

  // Cast the address to the appropriate pointer type, adopting the address
  // space of the base pointer.
  return Builder.CreateBitCast(Addr, PType);
}

static MSInheritanceAttr::Spelling
getInheritanceFromMemptr(const MemberPointerType *MPT) {
  return MPT->getMostRecentCXXRecordDecl()->getMSInheritanceModel();
}

llvm::Value *
MicrosoftCXXABI::EmitMemberPointerConversion(CodeGenFunction &CGF,
                                             const CastExpr *E,
                                             llvm::Value *Src) {
  assert(E->getCastKind() == CK_DerivedToBaseMemberPointer ||
         E->getCastKind() == CK_BaseToDerivedMemberPointer ||
         E->getCastKind() == CK_ReinterpretMemberPointer);

  // Use constant emission if we can.
  if (isa<llvm::Constant>(Src))
    return EmitMemberPointerConversion(E, cast<llvm::Constant>(Src));

  // We may be adding or dropping fields from the member pointer, so we need
  // both types and the inheritance models of both records.
  const MemberPointerType *SrcTy =
    E->getSubExpr()->getType()->castAs<MemberPointerType>();
  const MemberPointerType *DstTy = E->getType()->castAs<MemberPointerType>();
  bool IsFunc = SrcTy->isMemberFunctionPointer();

  // If the classes use the same null representation, reinterpret_cast is a nop.
  bool IsReinterpret = E->getCastKind() == CK_ReinterpretMemberPointer;
  if (IsReinterpret && IsFunc)
    return Src;

  CXXRecordDecl *SrcRD = SrcTy->getMostRecentCXXRecordDecl();
  CXXRecordDecl *DstRD = DstTy->getMostRecentCXXRecordDecl();
  if (IsReinterpret &&
      SrcRD->nullFieldOffsetIsZero() == DstRD->nullFieldOffsetIsZero())
    return Src;

  CGBuilderTy &Builder = CGF.Builder;

  // Branch past the conversion if Src is null.
  llvm::Value *IsNotNull = EmitMemberPointerIsNotNull(CGF, Src, SrcTy);
  llvm::Constant *DstNull = EmitNullMemberPointer(DstTy);

  // C++ 5.2.10p9: The null member pointer value is converted to the null member
  //   pointer value of the destination type.
  if (IsReinterpret) {
    // For reinterpret casts, sema ensures that src and dst are both functions
    // or data and have the same size, which means the LLVM types should match.
    assert(Src->getType() == DstNull->getType());
    return Builder.CreateSelect(IsNotNull, Src, DstNull);
  }

  llvm::BasicBlock *OriginalBB = Builder.GetInsertBlock();
  llvm::BasicBlock *ConvertBB = CGF.createBasicBlock("memptr.convert");
  llvm::BasicBlock *ContinueBB = CGF.createBasicBlock("memptr.converted");
  Builder.CreateCondBr(IsNotNull, ConvertBB, ContinueBB);
  CGF.EmitBlock(ConvertBB);

  // Decompose src.
  llvm::Value *FirstField = Src;
  llvm::Value *NonVirtualBaseAdjustment = nullptr;
  llvm::Value *VirtualBaseAdjustmentOffset = nullptr;
  llvm::Value *VBPtrOffset = nullptr;
  MSInheritanceAttr::Spelling SrcInheritance = SrcRD->getMSInheritanceModel();
  if (!MSInheritanceAttr::hasOnlyOneField(IsFunc, SrcInheritance)) {
    // We need to extract values.
    unsigned I = 0;
    FirstField = Builder.CreateExtractValue(Src, I++);
    if (MSInheritanceAttr::hasNVOffsetField(IsFunc, SrcInheritance))
      NonVirtualBaseAdjustment = Builder.CreateExtractValue(Src, I++);
    if (MSInheritanceAttr::hasVBPtrOffsetField(SrcInheritance))
      VBPtrOffset = Builder.CreateExtractValue(Src, I++);
    if (MSInheritanceAttr::hasVBTableOffsetField(SrcInheritance))
      VirtualBaseAdjustmentOffset = Builder.CreateExtractValue(Src, I++);
  }

  // For data pointers, we adjust the field offset directly.  For functions, we
  // have a separate field.
  llvm::Constant *Adj = getMemberPointerAdjustment(E);
  if (Adj) {
    Adj = llvm::ConstantExpr::getTruncOrBitCast(Adj, CGM.IntTy);
    llvm::Value *&NVAdjustField = IsFunc ? NonVirtualBaseAdjustment : FirstField;
    bool isDerivedToBase = (E->getCastKind() == CK_DerivedToBaseMemberPointer);
    if (!NVAdjustField)  // If this field didn't exist in src, it's zero.
      NVAdjustField = getZeroInt();
    if (isDerivedToBase)
      NVAdjustField = Builder.CreateNSWSub(NVAdjustField, Adj, "adj");
    else
      NVAdjustField = Builder.CreateNSWAdd(NVAdjustField, Adj, "adj");
  }

  // FIXME PR15713: Support conversions through virtually derived classes.

  // Recompose dst from the null struct and the adjusted fields from src.
  MSInheritanceAttr::Spelling DstInheritance = DstRD->getMSInheritanceModel();
  llvm::Value *Dst;
  if (MSInheritanceAttr::hasOnlyOneField(IsFunc, DstInheritance)) {
    Dst = FirstField;
  } else {
    Dst = llvm::UndefValue::get(DstNull->getType());
    unsigned Idx = 0;
    Dst = Builder.CreateInsertValue(Dst, FirstField, Idx++);
    if (MSInheritanceAttr::hasNVOffsetField(IsFunc, DstInheritance))
      Dst = Builder.CreateInsertValue(
        Dst, getValueOrZeroInt(NonVirtualBaseAdjustment), Idx++);
    if (MSInheritanceAttr::hasVBPtrOffsetField(DstInheritance))
      Dst = Builder.CreateInsertValue(
        Dst, getValueOrZeroInt(VBPtrOffset), Idx++);
    if (MSInheritanceAttr::hasVBTableOffsetField(DstInheritance))
      Dst = Builder.CreateInsertValue(
        Dst, getValueOrZeroInt(VirtualBaseAdjustmentOffset), Idx++);
  }
  Builder.CreateBr(ContinueBB);

  // In the continuation, choose between DstNull and Dst.
  CGF.EmitBlock(ContinueBB);
  llvm::PHINode *Phi = Builder.CreatePHI(DstNull->getType(), 2, "memptr.converted");
  Phi->addIncoming(DstNull, OriginalBB);
  Phi->addIncoming(Dst, ConvertBB);
  return Phi;
}

llvm::Constant *
MicrosoftCXXABI::EmitMemberPointerConversion(const CastExpr *E,
                                             llvm::Constant *Src) {
  const MemberPointerType *SrcTy =
    E->getSubExpr()->getType()->castAs<MemberPointerType>();
  const MemberPointerType *DstTy = E->getType()->castAs<MemberPointerType>();

  // If src is null, emit a new null for dst.  We can't return src because dst
  // might have a new representation.
  if (MemberPointerConstantIsNull(SrcTy, Src))
    return EmitNullMemberPointer(DstTy);

  // We don't need to do anything for reinterpret_casts of non-null member
  // pointers.  We should only get here when the two type representations have
  // the same size.
  if (E->getCastKind() == CK_ReinterpretMemberPointer)
    return Src;

  MSInheritanceAttr::Spelling SrcInheritance = getInheritanceFromMemptr(SrcTy);
  MSInheritanceAttr::Spelling DstInheritance = getInheritanceFromMemptr(DstTy);

  // Decompose src.
  llvm::Constant *FirstField = Src;
  llvm::Constant *NonVirtualBaseAdjustment = nullptr;
  llvm::Constant *VirtualBaseAdjustmentOffset = nullptr;
  llvm::Constant *VBPtrOffset = nullptr;
  bool IsFunc = SrcTy->isMemberFunctionPointer();
  if (!MSInheritanceAttr::hasOnlyOneField(IsFunc, SrcInheritance)) {
    // We need to extract values.
    unsigned I = 0;
    FirstField = Src->getAggregateElement(I++);
    if (MSInheritanceAttr::hasNVOffsetField(IsFunc, SrcInheritance))
      NonVirtualBaseAdjustment = Src->getAggregateElement(I++);
    if (MSInheritanceAttr::hasVBPtrOffsetField(SrcInheritance))
      VBPtrOffset = Src->getAggregateElement(I++);
    if (MSInheritanceAttr::hasVBTableOffsetField(SrcInheritance))
      VirtualBaseAdjustmentOffset = Src->getAggregateElement(I++);
  }

  // For data pointers, we adjust the field offset directly.  For functions, we
  // have a separate field.
  llvm::Constant *Adj = getMemberPointerAdjustment(E);
  if (Adj) {
    Adj = llvm::ConstantExpr::getTruncOrBitCast(Adj, CGM.IntTy);
    llvm::Constant *&NVAdjustField =
      IsFunc ? NonVirtualBaseAdjustment : FirstField;
    bool IsDerivedToBase = (E->getCastKind() == CK_DerivedToBaseMemberPointer);
    if (!NVAdjustField)  // If this field didn't exist in src, it's zero.
      NVAdjustField = getZeroInt();
    if (IsDerivedToBase)
      NVAdjustField = llvm::ConstantExpr::getNSWSub(NVAdjustField, Adj);
    else
      NVAdjustField = llvm::ConstantExpr::getNSWAdd(NVAdjustField, Adj);
  }

  // FIXME PR15713: Support conversions through virtually derived classes.

  // Recompose dst from the null struct and the adjusted fields from src.
  if (MSInheritanceAttr::hasOnlyOneField(IsFunc, DstInheritance))
    return FirstField;

  llvm::SmallVector<llvm::Constant *, 4> Fields;
  Fields.push_back(FirstField);
  if (MSInheritanceAttr::hasNVOffsetField(IsFunc, DstInheritance))
    Fields.push_back(getConstantOrZeroInt(NonVirtualBaseAdjustment));
  if (MSInheritanceAttr::hasVBPtrOffsetField(DstInheritance))
    Fields.push_back(getConstantOrZeroInt(VBPtrOffset));
  if (MSInheritanceAttr::hasVBTableOffsetField(DstInheritance))
    Fields.push_back(getConstantOrZeroInt(VirtualBaseAdjustmentOffset));
  return llvm::ConstantStruct::getAnon(Fields);
}

llvm::Value *MicrosoftCXXABI::EmitLoadOfMemberFunctionPointer(
    CodeGenFunction &CGF, const Expr *E, llvm::Value *&This,
    llvm::Value *MemPtr, const MemberPointerType *MPT) {
  assert(MPT->isMemberFunctionPointer());
  const FunctionProtoType *FPT =
    MPT->getPointeeType()->castAs<FunctionProtoType>();
  const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
  llvm::FunctionType *FTy =
    CGM.getTypes().GetFunctionType(
      CGM.getTypes().arrangeCXXMethodType(RD, FPT));
  CGBuilderTy &Builder = CGF.Builder;

  MSInheritanceAttr::Spelling Inheritance = RD->getMSInheritanceModel();

  // Extract the fields we need, regardless of model.  We'll apply them if we
  // have them.
  llvm::Value *FunctionPointer = MemPtr;
  llvm::Value *NonVirtualBaseAdjustment = nullptr;
  llvm::Value *VirtualBaseAdjustmentOffset = nullptr;
  llvm::Value *VBPtrOffset = nullptr;
  if (MemPtr->getType()->isStructTy()) {
    // We need to extract values.
    unsigned I = 0;
    FunctionPointer = Builder.CreateExtractValue(MemPtr, I++);
    if (MSInheritanceAttr::hasNVOffsetField(MPT, Inheritance))
      NonVirtualBaseAdjustment = Builder.CreateExtractValue(MemPtr, I++);
    if (MSInheritanceAttr::hasVBPtrOffsetField(Inheritance))
      VBPtrOffset = Builder.CreateExtractValue(MemPtr, I++);
    if (MSInheritanceAttr::hasVBTableOffsetField(Inheritance))
      VirtualBaseAdjustmentOffset = Builder.CreateExtractValue(MemPtr, I++);
  }

  if (VirtualBaseAdjustmentOffset) {
    This = AdjustVirtualBase(CGF, E, RD, This, VirtualBaseAdjustmentOffset,
                             VBPtrOffset);
  }

  if (NonVirtualBaseAdjustment) {
    // Apply the adjustment and cast back to the original struct type.
    llvm::Value *Ptr = Builder.CreateBitCast(This, Builder.getInt8PtrTy());
    Ptr = Builder.CreateInBoundsGEP(Ptr, NonVirtualBaseAdjustment);
    This = Builder.CreateBitCast(Ptr, This->getType(), "this.adjusted");
  }

  return Builder.CreateBitCast(FunctionPointer, FTy->getPointerTo());
}

CGCXXABI *clang::CodeGen::CreateMicrosoftCXXABI(CodeGenModule &CGM) {
  return new MicrosoftCXXABI(CGM);
}

// MS RTTI Overview:
// The run time type information emitted by cl.exe contains 5 distinct types of
// structures.  Many of them reference each other.
//
// TypeInfo:  Static classes that are returned by typeid.
//
// CompleteObjectLocator:  Referenced by vftables.  They contain information
//   required for dynamic casting, including OffsetFromTop.  They also contain
//   a reference to the TypeInfo for the type and a reference to the
//   CompleteHierarchyDescriptor for the type.
//
// ClassHieararchyDescriptor: Contains information about a class hierarchy.
//   Used during dynamic_cast to walk a class hierarchy.  References a base
//   class array and the size of said array.
//
// BaseClassArray: Contains a list of classes in a hierarchy.  BaseClassArray is
//   somewhat of a misnomer because the most derived class is also in the list
//   as well as multiple copies of virtual bases (if they occur multiple times
//   in the hiearchy.)  The BaseClassArray contains one BaseClassDescriptor for
//   every path in the hierarchy, in pre-order depth first order.  Note, we do
//   not declare a specific llvm type for BaseClassArray, it's merely an array
//   of BaseClassDescriptor pointers.
//
// BaseClassDescriptor: Contains information about a class in a class hierarchy.
//   BaseClassDescriptor is also somewhat of a misnomer for the same reason that
//   BaseClassArray is.  It contains information about a class within a
//   hierarchy such as: is this base is ambiguous and what is its offset in the
//   vbtable.  The names of the BaseClassDescriptors have all of their fields
//   mangled into them so they can be aggressively deduplicated by the linker.

static llvm::GlobalVariable *getTypeInfoVTable(CodeGenModule &CGM) {
  StringRef MangledName("\01??_7type_info@@6B@");
  if (auto VTable = CGM.getModule().getNamedGlobal(MangledName))
    return VTable;
  return new llvm::GlobalVariable(CGM.getModule(), CGM.Int8PtrTy,
                                  /*Constant=*/true,
                                  llvm::GlobalVariable::ExternalLinkage,
                                  /*Initializer=*/nullptr, MangledName);
}

namespace {

/// \brief A Helper struct that stores information about a class in a class
/// hierarchy.  The information stored in these structs struct is used during
/// the generation of ClassHierarchyDescriptors and BaseClassDescriptors.
// During RTTI creation, MSRTTIClasses are stored in a contiguous array with
// implicit depth first pre-order tree connectivity.  getFirstChild and
// getNextSibling allow us to walk the tree efficiently.
struct MSRTTIClass {
  enum {
    IsPrivateOnPath = 1 | 8,
    IsAmbiguous = 2,
    IsPrivate = 4,
    IsVirtual = 16,
    HasHierarchyDescriptor = 64
  };
  MSRTTIClass(const CXXRecordDecl *RD) : RD(RD) {}
  uint32_t initialize(const MSRTTIClass *Parent,
                      const CXXBaseSpecifier *Specifier);

  MSRTTIClass *getFirstChild() { return this + 1; }
  static MSRTTIClass *getNextChild(MSRTTIClass *Child) {
    return Child + 1 + Child->NumBases;
  }

  const CXXRecordDecl *RD, *VirtualRoot;
  uint32_t Flags, NumBases, OffsetInVBase;
};

/// \brief Recursively initialize the base class array.
uint32_t MSRTTIClass::initialize(const MSRTTIClass *Parent,
                                 const CXXBaseSpecifier *Specifier) {
  Flags = HasHierarchyDescriptor;
  if (!Parent) {
    VirtualRoot = nullptr;
    OffsetInVBase = 0;
  } else {
    if (Specifier->getAccessSpecifier() != AS_public)
      Flags |= IsPrivate | IsPrivateOnPath;
    if (Specifier->isVirtual()) {
      Flags |= IsVirtual;
      VirtualRoot = RD;
      OffsetInVBase = 0;
    } else {
      if (Parent->Flags & IsPrivateOnPath)
        Flags |= IsPrivateOnPath;
      VirtualRoot = Parent->VirtualRoot;
      OffsetInVBase = Parent->OffsetInVBase + RD->getASTContext()
          .getASTRecordLayout(Parent->RD).getBaseClassOffset(RD).getQuantity();
    }
  }
  NumBases = 0;
  MSRTTIClass *Child = getFirstChild();
  for (const CXXBaseSpecifier &Base : RD->bases()) {
    NumBases += Child->initialize(this, &Base) + 1;
    Child = getNextChild(Child);
  }
  return NumBases;
}

static llvm::GlobalValue::LinkageTypes getLinkageForRTTI(QualType Ty) {
  switch (Ty->getLinkage()) {
  case NoLinkage:
  case InternalLinkage:
  case UniqueExternalLinkage:
    return llvm::GlobalValue::InternalLinkage;

  case VisibleNoLinkage:
  case ExternalLinkage:
    return llvm::GlobalValue::LinkOnceODRLinkage;
  }
  llvm_unreachable("Invalid linkage!");
}

/// \brief An ephemeral helper class for building MS RTTI types.  It caches some
/// calls to the module and information about the most derived class in a
/// hierarchy.
struct MSRTTIBuilder {
  enum {
    HasBranchingHierarchy = 1,
    HasVirtualBranchingHierarchy = 2,
    HasAmbiguousBases = 4
  };

  MSRTTIBuilder(MicrosoftCXXABI &ABI, const CXXRecordDecl *RD)
      : CGM(ABI.CGM), Context(CGM.getContext()),
        VMContext(CGM.getLLVMContext()), Module(CGM.getModule()), RD(RD),
        Linkage(getLinkageForRTTI(CGM.getContext().getTagDeclType(RD))),
        ABI(ABI) {}

  llvm::GlobalVariable *getBaseClassDescriptor(const MSRTTIClass &Classes);
  llvm::GlobalVariable *
  getBaseClassArray(SmallVectorImpl<MSRTTIClass> &Classes);
  llvm::GlobalVariable *getClassHierarchyDescriptor();
  llvm::GlobalVariable *getCompleteObjectLocator(const VPtrInfo *Info);

  CodeGenModule &CGM;
  ASTContext &Context;
  llvm::LLVMContext &VMContext;
  llvm::Module &Module;
  const CXXRecordDecl *RD;
  llvm::GlobalVariable::LinkageTypes Linkage;
  MicrosoftCXXABI &ABI;
};

} // namespace

/// \brief Recursively serializes a class hierarchy in pre-order depth first
/// order.
static void serializeClassHierarchy(SmallVectorImpl<MSRTTIClass> &Classes,
                                    const CXXRecordDecl *RD) {
  Classes.push_back(MSRTTIClass(RD));
  for (const CXXBaseSpecifier &Base : RD->bases())
    serializeClassHierarchy(Classes, Base.getType()->getAsCXXRecordDecl());
}

/// \brief Find ambiguity among base classes.
static void
detectAmbiguousBases(SmallVectorImpl<MSRTTIClass> &Classes) {
  llvm::SmallPtrSet<const CXXRecordDecl *, 8> VirtualBases;
  llvm::SmallPtrSet<const CXXRecordDecl *, 8> UniqueBases;
  llvm::SmallPtrSet<const CXXRecordDecl *, 8> AmbiguousBases;
  for (MSRTTIClass *Class = &Classes.front(); Class <= &Classes.back();) {
    if ((Class->Flags & MSRTTIClass::IsVirtual) &&
        !VirtualBases.insert(Class->RD)) {
      Class = MSRTTIClass::getNextChild(Class);
      continue;
    }
    if (!UniqueBases.insert(Class->RD))
      AmbiguousBases.insert(Class->RD);
    Class++;
  }
  if (AmbiguousBases.empty())
    return;
  for (MSRTTIClass &Class : Classes)
    if (AmbiguousBases.count(Class.RD))
      Class.Flags |= MSRTTIClass::IsAmbiguous;
}

llvm::GlobalVariable *MSRTTIBuilder::getClassHierarchyDescriptor() {
  SmallString<256> MangledName;
  {
    llvm::raw_svector_ostream Out(MangledName);
    ABI.getMangleContext().mangleCXXRTTIClassHierarchyDescriptor(RD, Out);
  }

  // Check to see if we've already declared this ClassHierarchyDescriptor.
  if (auto CHD = Module.getNamedGlobal(MangledName))
    return CHD;

  // Serialize the class hierarchy and initialize the CHD Fields.
  SmallVector<MSRTTIClass, 8> Classes;
  serializeClassHierarchy(Classes, RD);
  Classes.front().initialize(/*Parent=*/nullptr, /*Specifier=*/nullptr);
  detectAmbiguousBases(Classes);
  int Flags = 0;
  for (auto Class : Classes) {
    if (Class.RD->getNumBases() > 1)
      Flags |= HasBranchingHierarchy;
    // Note: cl.exe does not calculate "HasAmbiguousBases" correctly.  We
    // believe the field isn't actually used.
    if (Class.Flags & MSRTTIClass::IsAmbiguous)
      Flags |= HasAmbiguousBases;
  }
  if ((Flags & HasBranchingHierarchy) && RD->getNumVBases() != 0)
    Flags |= HasVirtualBranchingHierarchy;
  // These gep indices are used to get the address of the first element of the
  // base class array.
  llvm::Value *GEPIndices[] = {llvm::ConstantInt::get(CGM.IntTy, 0),
                               llvm::ConstantInt::get(CGM.IntTy, 0)};

  // Forward-declare the class hierarchy descriptor
  auto Type = ABI.getClassHierarchyDescriptorType();
  auto CHD = new llvm::GlobalVariable(Module, Type, /*Constant=*/true, Linkage,
                                      /*Initializer=*/nullptr,
                                      MangledName.c_str());

  // Initialize the base class ClassHierarchyDescriptor.
  llvm::Constant *Fields[] = {
      llvm::ConstantInt::get(CGM.IntTy, 0), // Unknown
      llvm::ConstantInt::get(CGM.IntTy, Flags),
      llvm::ConstantInt::get(CGM.IntTy, Classes.size()),
      ABI.getImageRelativeConstant(llvm::ConstantExpr::getInBoundsGetElementPtr(
          getBaseClassArray(Classes),
          llvm::ArrayRef<llvm::Value *>(GEPIndices))),
  };
  CHD->setInitializer(llvm::ConstantStruct::get(Type, Fields));
  return CHD;
}

llvm::GlobalVariable *
MSRTTIBuilder::getBaseClassArray(SmallVectorImpl<MSRTTIClass> &Classes) {
  SmallString<256> MangledName;
  {
    llvm::raw_svector_ostream Out(MangledName);
    ABI.getMangleContext().mangleCXXRTTIBaseClassArray(RD, Out);
  }

  // Forward-declare the base class array.
  // cl.exe pads the base class array with 1 (in 32 bit mode) or 4 (in 64 bit
  // mode) bytes of padding.  We provide a pointer sized amount of padding by
  // adding +1 to Classes.size().  The sections have pointer alignment and are
  // marked pick-any so it shouldn't matter.
  llvm::Type *PtrType = ABI.getImageRelativeType(
      ABI.getBaseClassDescriptorType()->getPointerTo());
  auto *ArrType = llvm::ArrayType::get(PtrType, Classes.size() + 1);
  auto *BCA = new llvm::GlobalVariable(
      Module, ArrType,
      /*Constant=*/true, Linkage, /*Initializer=*/nullptr, MangledName.c_str());

  // Initialize the BaseClassArray.
  SmallVector<llvm::Constant *, 8> BaseClassArrayData;
  for (MSRTTIClass &Class : Classes)
    BaseClassArrayData.push_back(
        ABI.getImageRelativeConstant(getBaseClassDescriptor(Class)));
  BaseClassArrayData.push_back(llvm::Constant::getNullValue(PtrType));
  BCA->setInitializer(llvm::ConstantArray::get(ArrType, BaseClassArrayData));
  return BCA;
}

llvm::GlobalVariable *
MSRTTIBuilder::getBaseClassDescriptor(const MSRTTIClass &Class) {
  // Compute the fields for the BaseClassDescriptor.  They are computed up front
  // because they are mangled into the name of the object.
  uint32_t OffsetInVBTable = 0;
  int32_t VBPtrOffset = -1;
  if (Class.VirtualRoot) {
    auto &VTableContext = CGM.getMicrosoftVTableContext();
    OffsetInVBTable = VTableContext.getVBTableIndex(RD, Class.VirtualRoot) * 4;
    VBPtrOffset = Context.getASTRecordLayout(RD).getVBPtrOffset().getQuantity();
  }

  SmallString<256> MangledName;
  {
    llvm::raw_svector_ostream Out(MangledName);
    ABI.getMangleContext().mangleCXXRTTIBaseClassDescriptor(
        Class.RD, Class.OffsetInVBase, VBPtrOffset, OffsetInVBTable,
        Class.Flags, Out);
  }

  // Check to see if we've already declared this object.
  if (auto BCD = Module.getNamedGlobal(MangledName))
    return BCD;

  // Forward-declare the base class descriptor.
  auto Type = ABI.getBaseClassDescriptorType();
  auto BCD = new llvm::GlobalVariable(Module, Type, /*Constant=*/true, Linkage,
                                      /*Initializer=*/nullptr,
                                      MangledName.c_str());

  // Initialize the BaseClassDescriptor.
  llvm::Constant *Fields[] = {
      ABI.getImageRelativeConstant(
          ABI.getAddrOfRTTIDescriptor(Context.getTypeDeclType(Class.RD))),
      llvm::ConstantInt::get(CGM.IntTy, Class.NumBases),
      llvm::ConstantInt::get(CGM.IntTy, Class.OffsetInVBase),
      llvm::ConstantInt::get(CGM.IntTy, VBPtrOffset),
      llvm::ConstantInt::get(CGM.IntTy, OffsetInVBTable),
      llvm::ConstantInt::get(CGM.IntTy, Class.Flags),
      ABI.getImageRelativeConstant(
          MSRTTIBuilder(ABI, Class.RD).getClassHierarchyDescriptor()),
  };
  BCD->setInitializer(llvm::ConstantStruct::get(Type, Fields));
  return BCD;
}

llvm::GlobalVariable *
MSRTTIBuilder::getCompleteObjectLocator(const VPtrInfo *Info) {
  SmallString<256> MangledName;
  {
    llvm::raw_svector_ostream Out(MangledName);
    ABI.getMangleContext().mangleCXXRTTICompleteObjectLocator(RD, Info->MangledPath, Out);
  }

  // Check to see if we've already computed this complete object locator.
  if (auto COL = Module.getNamedGlobal(MangledName))
    return COL;

  // Compute the fields of the complete object locator.
  int OffsetToTop = Info->FullOffsetInMDC.getQuantity();
  int VFPtrOffset = 0;
  // The offset includes the vtordisp if one exists.
  if (const CXXRecordDecl *VBase = Info->getVBaseWithVPtr())
    if (Context.getASTRecordLayout(RD)
      .getVBaseOffsetsMap()
      .find(VBase)
      ->second.hasVtorDisp())
      VFPtrOffset = Info->NonVirtualOffset.getQuantity() + 4;

  // Forward-declare the complete object locator.
  llvm::StructType *Type = ABI.getCompleteObjectLocatorType();
  auto COL = new llvm::GlobalVariable(Module, Type, /*Constant=*/true, Linkage,
    /*Initializer=*/nullptr, MangledName.c_str());

  // Initialize the CompleteObjectLocator.
  llvm::Constant *Fields[] = {
      llvm::ConstantInt::get(CGM.IntTy, ABI.isImageRelative()),
      llvm::ConstantInt::get(CGM.IntTy, OffsetToTop),
      llvm::ConstantInt::get(CGM.IntTy, VFPtrOffset),
      ABI.getImageRelativeConstant(
          CGM.GetAddrOfRTTIDescriptor(Context.getTypeDeclType(RD))),
      ABI.getImageRelativeConstant(getClassHierarchyDescriptor()),
      ABI.getImageRelativeConstant(COL),
  };
  llvm::ArrayRef<llvm::Constant *> FieldsRef(Fields);
  if (!ABI.isImageRelative())
    FieldsRef = FieldsRef.drop_back();
  COL->setInitializer(llvm::ConstantStruct::get(Type, FieldsRef));
  return COL;
}

/// \brief Gets a TypeDescriptor.  Returns a llvm::Constant * rather than a
/// llvm::GlobalVariable * because different type descriptors have different
/// types, and need to be abstracted.  They are abstracting by casting the
/// address to an Int8PtrTy.
llvm::Constant *MicrosoftCXXABI::getAddrOfRTTIDescriptor(QualType Type) {
  SmallString<256> MangledName, TypeInfoString;
  {
    llvm::raw_svector_ostream Out(MangledName);
    getMangleContext().mangleCXXRTTI(Type, Out);
  }

  // Check to see if we've already declared this TypeDescriptor.
  if (llvm::GlobalVariable *GV = CGM.getModule().getNamedGlobal(MangledName))
    return llvm::ConstantExpr::getBitCast(GV, CGM.Int8PtrTy);

  // Compute the fields for the TypeDescriptor.
  {
    llvm::raw_svector_ostream Out(TypeInfoString);
    getMangleContext().mangleCXXRTTIName(Type, Out);
  }

  // Declare and initialize the TypeDescriptor.
  llvm::Constant *Fields[] = {
    getTypeInfoVTable(CGM),                        // VFPtr
    llvm::ConstantPointerNull::get(CGM.Int8PtrTy), // Runtime data
    llvm::ConstantDataArray::getString(CGM.getLLVMContext(), TypeInfoString)};
  llvm::StructType *TypeDescriptorType =
      getTypeDescriptorType(TypeInfoString);
  return llvm::ConstantExpr::getBitCast(
      new llvm::GlobalVariable(
          CGM.getModule(), TypeDescriptorType, /*Constant=*/false,
          getLinkageForRTTI(Type),
          llvm::ConstantStruct::get(TypeDescriptorType, Fields),
          MangledName.c_str()),
      CGM.Int8PtrTy);
}

/// \brief Gets or a creates a Microsoft CompleteObjectLocator.
llvm::GlobalVariable *
MicrosoftCXXABI::getMSCompleteObjectLocator(const CXXRecordDecl *RD,
                                            const VPtrInfo *Info) {
  return MSRTTIBuilder(*this, RD).getCompleteObjectLocator(Info);
}