lib/CodeGen/CGCXX.cpp - clang - Git at Google

 //===--- CGDecl.cpp - Emit LLVM Code for declarations ---------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This contains code dealing with C++ code generation.
 //
 //===----------------------------------------------------------------------===//

 // We might split this into multiple files if it gets too unwieldy

 #include "CGCXXABI.h"
 #include "CodeGenFunction.h"
 #include "CodeGenModule.h"
 #include "Mangle.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/StmtCXX.h"
 #include "clang/Frontend/CodeGenOptions.h"
 #include "llvm/ADT/StringExtras.h"
 using namespace clang;
 using namespace CodeGen;

 /// Determines whether the given function has a trivial body that does
 /// not require any specific codegen.
 static bool HasTrivialBody(const FunctionDecl *FD) {
   Stmt *S = FD->getBody();
   if (!S)
     return true;
   if (isa<CompoundStmt>(S) && cast<CompoundStmt>(S)->body_empty())
     return true;
   return false;
 }

 /// Try to emit a base destructor as an alias to its primary
 /// base-class destructor.
 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
   if (!getCodeGenOpts().CXXCtorDtorAliases)
     return true;

   // If the destructor doesn't have a trivial body, we have to emit it
   // separately.
   if (!HasTrivialBody(D))
     return true;

   const CXXRecordDecl *Class = D->getParent();

   // If we need to manipulate a VTT parameter, give up.
   if (Class->getNumVBases()) {
     // Extra Credit:  passing extra parameters is perfectly safe
     // in many calling conventions, so only bail out if the ctor's
     // calling convention is nonstandard.
     return true;
   }

   // If any fields have a non-trivial destructor, we have to emit it
   // separately.
   for (CXXRecordDecl::field_iterator I = Class->field_begin(),
          E = Class->field_end(); I != E; ++I)
     if (const RecordType *RT = (*I)->getType()->getAs<RecordType>())
       if (!cast<CXXRecordDecl>(RT->getDecl())->hasTrivialDestructor())
         return true;

   // Try to find a unique base class with a non-trivial destructor.
   const CXXRecordDecl *UniqueBase = 0;
   for (CXXRecordDecl::base_class_const_iterator I = Class->bases_begin(),
          E = Class->bases_end(); I != E; ++I) {

     // We're in the base destructor, so skip virtual bases.
     if (I->isVirtual()) continue;

     // Skip base classes with trivial destructors.
     const CXXRecordDecl *Base
       = cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
     if (Base->hasTrivialDestructor()) continue;

     // If we've already found a base class with a non-trivial
     // destructor, give up.
     if (UniqueBase) return true;
     UniqueBase = Base;
   }

   // If we didn't find any bases with a non-trivial destructor, then
   // the base destructor is actually effectively trivial, which can
   // happen if it was needlessly user-defined or if there are virtual
   // bases with non-trivial destructors.
   if (!UniqueBase)
     return true;

   /// If we don't have a definition for the destructor yet, don't
   /// emit.  We can't emit aliases to declarations; that's just not
   /// how aliases work.
   const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
   if (!BaseD->isImplicit() && !BaseD->hasBody())
     return true;

   // If the base is at a non-zero offset, give up.
   const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
   if (ClassLayout.getBaseClassOffset(UniqueBase) != 0)
     return true;

   return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base),
                                   GlobalDecl(BaseD, Dtor_Base));
 }

 /// Try to emit a definition as a global alias for another definition.
 bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
                                              GlobalDecl TargetDecl) {
   if (!getCodeGenOpts().CXXCtorDtorAliases)
     return true;

   // The alias will use the linkage of the referrent.  If we can't
   // support aliases with that linkage, fail.
   llvm::GlobalValue::LinkageTypes Linkage
     = getFunctionLinkage(cast<FunctionDecl>(AliasDecl.getDecl()));

   switch (Linkage) {
   // We can definitely emit aliases to definitions with external linkage.
   case llvm::GlobalValue::ExternalLinkage:
   case llvm::GlobalValue::ExternalWeakLinkage:
     break;

   // Same with local linkage.
   case llvm::GlobalValue::InternalLinkage:
   case llvm::GlobalValue::PrivateLinkage:
   case llvm::GlobalValue::LinkerPrivateLinkage:
     break;

   // We should try to support linkonce linkages.
   case llvm::GlobalValue::LinkOnceAnyLinkage:
   case llvm::GlobalValue::LinkOnceODRLinkage:
     return true;

   // Other linkages will probably never be supported.
   default:
     return true;
   }

   llvm::GlobalValue::LinkageTypes TargetLinkage
     = getFunctionLinkage(cast<FunctionDecl>(TargetDecl.getDecl()));

   if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
     return true;

   // Derive the type for the alias.
   const llvm::PointerType *AliasType
     = getTypes().GetFunctionType(AliasDecl)->getPointerTo();

   // Find the referrent.  Some aliases might require a bitcast, in
   // which case the caller is responsible for ensuring the soundness
   // of these semantics.
   llvm::GlobalValue *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
   llvm::Constant *Aliasee = Ref;
   if (Ref->getType() != AliasType)
     Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);

   // Create the alias with no name.
   llvm::GlobalAlias *Alias =
     new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule());

   // Switch any previous uses to the alias.
   llvm::StringRef MangledName = getMangledName(AliasDecl);
   llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
   if (Entry) {
     assert(Entry->isDeclaration() && "definition already exists for alias");
     assert(Entry->getType() == AliasType &&
            "declaration exists with different type");
     Alias->takeName(Entry);
     Entry->replaceAllUsesWith(Alias);
     Entry->eraseFromParent();
   } else {
     Alias->setName(MangledName);
   }

   // Finally, set up the alias with its proper name and attributes.
   SetCommonAttributes(AliasDecl.getDecl(), Alias);

   return false;
 }

 void CodeGenModule::EmitCXXConstructors(const CXXConstructorDecl *D) {
   // The constructor used for constructing this as a complete class;
   // constucts the virtual bases, then calls the base constructor.
   EmitGlobal(GlobalDecl(D, Ctor_Complete));

   // The constructor used for constructing this as a base class;
   // ignores virtual bases.
   EmitGlobal(GlobalDecl(D, Ctor_Base));
 }

 void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *D,
                                        CXXCtorType Type) {
   // The complete constructor is equivalent to the base constructor
   // for classes with no virtual bases.  Try to emit it as an alias.
   if (Type == Ctor_Complete &&
       !D->getParent()->getNumVBases() &&
       !TryEmitDefinitionAsAlias(GlobalDecl(D, Ctor_Complete),
                                 GlobalDecl(D, Ctor_Base)))
     return;

   llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXConstructor(D, Type));
   setFunctionLinkage(D, Fn);

   CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn);

   SetFunctionDefinitionAttributes(D, Fn);
   SetLLVMFunctionAttributesForDefinition(D, Fn);
 }

 llvm::GlobalValue *
 CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *D,
                                        CXXCtorType Type) {
   GlobalDecl GD(D, Type);

   llvm::StringRef Name = getMangledName(GD);
   if (llvm::GlobalValue *V = GetGlobalValue(Name))
     return V;

   const FunctionProtoType *FPT = D->getType()->getAs<FunctionProtoType>();
   const llvm::FunctionType *FTy =
     getTypes().GetFunctionType(getTypes().getFunctionInfo(D, Type),
                                FPT->isVariadic());
   return cast<llvm::Function>(GetOrCreateLLVMFunction(Name, FTy, GD));
 }

 void CodeGenModule::EmitCXXDestructors(const CXXDestructorDecl *D) {
   // The destructor in a virtual table is always a 'deleting'
   // destructor, which calls the complete destructor and then uses the
   // appropriate operator delete.
   if (D->isVirtual())
     EmitGlobal(GlobalDecl(D, Dtor_Deleting));

   // The destructor used for destructing this as a most-derived class;
   // call the base destructor and then destructs any virtual bases.
   EmitGlobal(GlobalDecl(D, Dtor_Complete));

   // The destructor used for destructing this as a base class; ignores
   // virtual bases.
   EmitGlobal(GlobalDecl(D, Dtor_Base));
 }

 void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *D,
                                       CXXDtorType Type) {
   // The complete destructor is equivalent to the base destructor for
   // classes with no virtual bases, so try to emit it as an alias.
   if (Type == Dtor_Complete &&
       !D->getParent()->getNumVBases() &&
       !TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Complete),
                                 GlobalDecl(D, Dtor_Base)))
     return;

   // The base destructor is equivalent to the base destructor of its
   // base class if there is exactly one non-virtual base class with a
   // non-trivial destructor, there are no fields with a non-trivial
   // destructor, and the body of the destructor is trivial.
   if (Type == Dtor_Base && !TryEmitBaseDestructorAsAlias(D))
     return;

   llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXDestructor(D, Type));
   setFunctionLinkage(D, Fn);

   CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn);

   SetFunctionDefinitionAttributes(D, Fn);
   SetLLVMFunctionAttributesForDefinition(D, Fn);
 }

 llvm::GlobalValue *
 CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *D,
                                       CXXDtorType Type) {
   GlobalDecl GD(D, Type);

   llvm::StringRef Name = getMangledName(GD);
   if (llvm::GlobalValue *V = GetGlobalValue(Name))
     return V;

   const llvm::FunctionType *FTy =
     getTypes().GetFunctionType(getTypes().getFunctionInfo(D, Type), false);

   return cast<llvm::Function>(GetOrCreateLLVMFunction(Name, FTy, GD));
 }

 static llvm::Value *BuildVirtualCall(CodeGenFunction &CGF, uint64_t VTableIndex,
                                      llvm::Value *This, const llvm::Type *Ty) {
   Ty = Ty->getPointerTo()->getPointerTo()->getPointerTo();

   llvm::Value *VTable = CGF.Builder.CreateBitCast(This, Ty);
   VTable = CGF.Builder.CreateLoad(VTable);

   llvm::Value *VFuncPtr =
     CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfn");
   return CGF.Builder.CreateLoad(VFuncPtr);
 }

 llvm::Value *
 CodeGenFunction::BuildVirtualCall(const CXXMethodDecl *MD, llvm::Value *This,
                                   const llvm::Type *Ty) {
   MD = MD->getCanonicalDecl();
   uint64_t VTableIndex = CGM.getVTables().getMethodVTableIndex(MD);

   return ::BuildVirtualCall(*this, VTableIndex, This, Ty);
 }

 llvm::Value *
 CodeGenFunction::BuildVirtualCall(const CXXDestructorDecl *DD, CXXDtorType Type,
                                   llvm::Value *&This, const llvm::Type *Ty) {
   DD = cast<CXXDestructorDecl>(DD->getCanonicalDecl());
   uint64_t VTableIndex =
     CGM.getVTables().getMethodVTableIndex(GlobalDecl(DD, Type));

   return ::BuildVirtualCall(*this, VTableIndex, This, Ty);
 }

 /// Implementation for CGCXXABI.  Possibly this should be moved into
 /// the incomplete ABI implementations?

 CGCXXABI::~CGCXXABI() {}

 static void ErrorUnsupportedABI(CodeGenFunction &CGF,
                                 llvm::StringRef S) {
   Diagnostic &Diags = CGF.CGM.getDiags();
   unsigned DiagID = Diags.getCustomDiagID(Diagnostic::Error,
                                           "cannot yet compile %1 in this ABI");
   Diags.Report(CGF.getContext().getFullLoc(CGF.CurCodeDecl->getLocation()),
                DiagID)
     << S;
 }

 static llvm::Constant *GetBogusMemberPointer(CodeGenModule &CGM,
                                              QualType T) {
   return llvm::Constant::getNullValue(CGM.getTypes().ConvertType(T));
 }

 const llvm::Type *
 CGCXXABI::ConvertMemberPointerType(const MemberPointerType *MPT) {
   return CGM.getTypes().ConvertType(CGM.getContext().getPointerDiffType());
 }

 llvm::Value *CGCXXABI::EmitLoadOfMemberFunctionPointer(CodeGenFunction &CGF,
                                                        llvm::Value *&This,
                                                        llvm::Value *MemPtr,
                                                  const MemberPointerType *MPT) {
   ErrorUnsupportedABI(CGF, "calls through member pointers");

   const FunctionProtoType *FPT =
     MPT->getPointeeType()->getAs<FunctionProtoType>();
   const CXXRecordDecl *RD =
     cast<CXXRecordDecl>(MPT->getClass()->getAs<RecordType>()->getDecl());
   const llvm::FunctionType *FTy =
     CGM.getTypes().GetFunctionType(CGM.getTypes().getFunctionInfo(RD, FPT),
                                    FPT->isVariadic());
   return llvm::Constant::getNullValue(FTy->getPointerTo());
 }

 llvm::Value *CGCXXABI::EmitMemberDataPointerAddress(CodeGenFunction &CGF,
                                                     llvm::Value *Base,
                                                     llvm::Value *MemPtr,
                                               const MemberPointerType *MPT) {
   ErrorUnsupportedABI(CGF, "loads of member pointers");
   const llvm::Type *Ty = CGF.ConvertType(MPT->getPointeeType())->getPointerTo();
   return llvm::Constant::getNullValue(Ty);
 }

 llvm::Value *CGCXXABI::EmitMemberPointerConversion(CodeGenFunction &CGF,
                                                    const CastExpr *E,
                                                    llvm::Value *Src) {
   ErrorUnsupportedABI(CGF, "member function pointer conversions");
   return GetBogusMemberPointer(CGM, E->getType());
 }

 llvm::Value *
 CGCXXABI::EmitMemberPointerComparison(CodeGenFunction &CGF,
                                       llvm::Value *L,
                                       llvm::Value *R,
                                       const MemberPointerType *MPT,
                                       bool Inequality) {
   ErrorUnsupportedABI(CGF, "member function pointer comparison");
   return CGF.Builder.getFalse();
 }

 llvm::Value *
 CGCXXABI::EmitMemberPointerIsNotNull(CodeGenFunction &CGF,
                                      llvm::Value *MemPtr,
                                      const MemberPointerType *MPT) {
   ErrorUnsupportedABI(CGF, "member function pointer null testing");
   return CGF.Builder.getFalse();
 }

 llvm::Constant *
 CGCXXABI::EmitMemberPointerConversion(llvm::Constant *C, const CastExpr *E) {
   return GetBogusMemberPointer(CGM, E->getType());
 }

 llvm::Constant *
 CGCXXABI::EmitNullMemberPointer(const MemberPointerType *MPT) {
   return GetBogusMemberPointer(CGM, QualType(MPT, 0));
 }

 llvm::Constant *CGCXXABI::EmitMemberPointer(const CXXMethodDecl *MD) {
   return GetBogusMemberPointer(CGM,
                          CGM.getContext().getMemberPointerType(MD->getType(),
                                          MD->getParent()->getTypeForDecl()));
 }

 llvm::Constant *CGCXXABI::EmitMemberPointer(const FieldDecl *FD) {
   return GetBogusMemberPointer(CGM,
                          CGM.getContext().getMemberPointerType(FD->getType(),
                                          FD->getParent()->getTypeForDecl()));
 }

 bool CGCXXABI::isZeroInitializable(const MemberPointerType *MPT) {
   // Fake answer.
   return true;
 }

 void CGCXXABI::BuildThisParam(CodeGenFunction &CGF, FunctionArgList &Params) {
   const CXXMethodDecl *MD = cast<CXXMethodDecl>(CGF.CurGD.getDecl());

   // FIXME: I'm not entirely sure I like using a fake decl just for code
   // generation. Maybe we can come up with a better way?
   ImplicitParamDecl *ThisDecl
     = ImplicitParamDecl::Create(CGM.getContext(), 0, MD->getLocation(),
                                 &CGM.getContext().Idents.get("this"),
                                 MD->getThisType(CGM.getContext()));
   Params.push_back(std::make_pair(ThisDecl, ThisDecl->getType()));
   getThisDecl(CGF) = ThisDecl;
 }

 void CGCXXABI::EmitThisParam(CodeGenFunction &CGF) {
   /// Initialize the 'this' slot.
   assert(getThisDecl(CGF) && "no 'this' variable for function");
   getThisValue(CGF)
     = CGF.Builder.CreateLoad(CGF.GetAddrOfLocalVar(getThisDecl(CGF)),
                              "this");
 }

 void CGCXXABI::EmitReturnFromThunk(CodeGenFunction &CGF,
                                    RValue RV, QualType ResultType) {
   CGF.EmitReturnOfRValue(RV, ResultType);
 }

 CharUnits CGCXXABI::GetArrayCookieSize(QualType ElementType) {
   return CharUnits::Zero();
 }

 llvm::Value *CGCXXABI::InitializeArrayCookie(CodeGenFunction &CGF,
                                              llvm::Value *NewPtr,
                                              llvm::Value *NumElements,
                                              QualType ElementType) {
   // Should never be called.
   ErrorUnsupportedABI(CGF, "array cookie initialization");
   return 0;
 }

 void CGCXXABI::ReadArrayCookie(CodeGenFunction &CGF, llvm::Value *Ptr,
                                QualType ElementType, llvm::Value *&NumElements,
                                llvm::Value *&AllocPtr, CharUnits &CookieSize) {
   ErrorUnsupportedABI(CGF, "array cookie reading");

   // This should be enough to avoid assertions.
   NumElements = 0;
   AllocPtr = llvm::Constant::getNullValue(CGF.Builder.getInt8PtrTy());
   CookieSize = CharUnits::Zero();
 }
	//===--- CGDecl.cpp - Emit LLVM Code for declarations ---------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This contains code dealing with C++ code generation.
	//
	//===----------------------------------------------------------------------===//

	// We might split this into multiple files if it gets too unwieldy

	#include "CGCXXABI.h"
	#include "CodeGenFunction.h"
	#include "CodeGenModule.h"
	#include "Mangle.h"
	#include "clang/AST/ASTContext.h"
	#include "clang/AST/RecordLayout.h"
	#include "clang/AST/Decl.h"
	#include "clang/AST/DeclCXX.h"
	#include "clang/AST/DeclObjC.h"
	#include "clang/AST/StmtCXX.h"
	#include "clang/Frontend/CodeGenOptions.h"
	#include "llvm/ADT/StringExtras.h"
	using namespace clang;
	using namespace CodeGen;

	/// Determines whether the given function has a trivial body that does
	/// not require any specific codegen.
	static bool HasTrivialBody(const FunctionDecl *FD) {
	Stmt *S = FD->getBody();
	if (!S)
	return true;
	if (isa<CompoundStmt>(S) && cast<CompoundStmt>(S)->body_empty())
	return true;
	return false;
	}

	/// Try to emit a base destructor as an alias to its primary
	/// base-class destructor.
	bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
	if (!getCodeGenOpts().CXXCtorDtorAliases)
	return true;

	// If the destructor doesn't have a trivial body, we have to emit it
	// separately.
	if (!HasTrivialBody(D))
	return true;

	const CXXRecordDecl *Class = D->getParent();

	// If we need to manipulate a VTT parameter, give up.
	if (Class->getNumVBases()) {
	// Extra Credit: passing extra parameters is perfectly safe
	// in many calling conventions, so only bail out if the ctor's
	// calling convention is nonstandard.
	return true;
	}

	// If any fields have a non-trivial destructor, we have to emit it
	// separately.
	for (CXXRecordDecl::field_iterator I = Class->field_begin(),
	E = Class->field_end(); I != E; ++I)
	if (const RecordType RT = (I)->getType()->getAs<RecordType>())
	if (!cast<CXXRecordDecl>(RT->getDecl())->hasTrivialDestructor())
	return true;

	// Try to find a unique base class with a non-trivial destructor.
	const CXXRecordDecl *UniqueBase = 0;
	for (CXXRecordDecl::base_class_const_iterator I = Class->bases_begin(),
	E = Class->bases_end(); I != E; ++I) {

	// We're in the base destructor, so skip virtual bases.
	if (I->isVirtual()) continue;

	// Skip base classes with trivial destructors.
	const CXXRecordDecl *Base
	= cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
	if (Base->hasTrivialDestructor()) continue;

	// If we've already found a base class with a non-trivial
	// destructor, give up.
	if (UniqueBase) return true;
	UniqueBase = Base;
	}

	// If we didn't find any bases with a non-trivial destructor, then
	// the base destructor is actually effectively trivial, which can
	// happen if it was needlessly user-defined or if there are virtual
	// bases with non-trivial destructors.
	if (!UniqueBase)
	return true;

	/// If we don't have a definition for the destructor yet, don't
	/// emit. We can't emit aliases to declarations; that's just not
	/// how aliases work.
	const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
	if (!BaseD->isImplicit() && !BaseD->hasBody())
	return true;

	// If the base is at a non-zero offset, give up.
	const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
	if (ClassLayout.getBaseClassOffset(UniqueBase) != 0)
	return true;

	return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base),
	GlobalDecl(BaseD, Dtor_Base));
	}

	/// Try to emit a definition as a global alias for another definition.
	bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
	GlobalDecl TargetDecl) {
	if (!getCodeGenOpts().CXXCtorDtorAliases)
	return true;

	// The alias will use the linkage of the referrent. If we can't
	// support aliases with that linkage, fail.
	llvm::GlobalValue::LinkageTypes Linkage
	= getFunctionLinkage(cast<FunctionDecl>(AliasDecl.getDecl()));

	switch (Linkage) {
	// We can definitely emit aliases to definitions with external linkage.
	case llvm::GlobalValue::ExternalLinkage:
	case llvm::GlobalValue::ExternalWeakLinkage:
	break;

	// Same with local linkage.
	case llvm::GlobalValue::InternalLinkage:
	case llvm::GlobalValue::PrivateLinkage:
	case llvm::GlobalValue::LinkerPrivateLinkage:
	break;

	// We should try to support linkonce linkages.
	case llvm::GlobalValue::LinkOnceAnyLinkage:
	case llvm::GlobalValue::LinkOnceODRLinkage:
	return true;

	// Other linkages will probably never be supported.
	default:
	return true;
	}

	llvm::GlobalValue::LinkageTypes TargetLinkage
	= getFunctionLinkage(cast<FunctionDecl>(TargetDecl.getDecl()));

	if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
	return true;

	// Derive the type for the alias.
	const llvm::PointerType *AliasType
	= getTypes().GetFunctionType(AliasDecl)->getPointerTo();

	// Find the referrent. Some aliases might require a bitcast, in
	// which case the caller is responsible for ensuring the soundness
	// of these semantics.
	llvm::GlobalValue *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
	llvm::Constant *Aliasee = Ref;
	if (Ref->getType() != AliasType)
	Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);

	// Create the alias with no name.
	llvm::GlobalAlias *Alias =
	new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule());

	// Switch any previous uses to the alias.
	llvm::StringRef MangledName = getMangledName(AliasDecl);
	llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
	if (Entry) {
	assert(Entry->isDeclaration() && "definition already exists for alias");
	assert(Entry->getType() == AliasType &&
	"declaration exists with different type");
	Alias->takeName(Entry);
	Entry->replaceAllUsesWith(Alias);
	Entry->eraseFromParent();
	} else {
	Alias->setName(MangledName);
	}

	// Finally, set up the alias with its proper name and attributes.
	SetCommonAttributes(AliasDecl.getDecl(), Alias);

	return false;
	}

	void CodeGenModule::EmitCXXConstructors(const CXXConstructorDecl *D) {
	// The constructor used for constructing this as a complete class;
	// constucts the virtual bases, then calls the base constructor.
	EmitGlobal(GlobalDecl(D, Ctor_Complete));

	// The constructor used for constructing this as a base class;
	// ignores virtual bases.
	EmitGlobal(GlobalDecl(D, Ctor_Base));
	}

	void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *D,
	CXXCtorType Type) {
	// The complete constructor is equivalent to the base constructor
	// for classes with no virtual bases. Try to emit it as an alias.
	if (Type == Ctor_Complete &&
	!D->getParent()->getNumVBases() &&
	!TryEmitDefinitionAsAlias(GlobalDecl(D, Ctor_Complete),
	GlobalDecl(D, Ctor_Base)))
	return;

	llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXConstructor(D, Type));
	setFunctionLinkage(D, Fn);

	CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn);

	SetFunctionDefinitionAttributes(D, Fn);
	SetLLVMFunctionAttributesForDefinition(D, Fn);
	}

	llvm::GlobalValue *
	CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *D,
	CXXCtorType Type) {
	GlobalDecl GD(D, Type);

	llvm::StringRef Name = getMangledName(GD);
	if (llvm::GlobalValue *V = GetGlobalValue(Name))
	return V;

	const FunctionProtoType *FPT = D->getType()->getAs<FunctionProtoType>();
	const llvm::FunctionType *FTy =
	getTypes().GetFunctionType(getTypes().getFunctionInfo(D, Type),
	FPT->isVariadic());
	return cast<llvm::Function>(GetOrCreateLLVMFunction(Name, FTy, GD));
	}

	void CodeGenModule::EmitCXXDestructors(const CXXDestructorDecl *D) {
	// The destructor in a virtual table is always a 'deleting'
	// destructor, which calls the complete destructor and then uses the
	// appropriate operator delete.
	if (D->isVirtual())
	EmitGlobal(GlobalDecl(D, Dtor_Deleting));

	// The destructor used for destructing this as a most-derived class;
	// call the base destructor and then destructs any virtual bases.
	EmitGlobal(GlobalDecl(D, Dtor_Complete));

	// The destructor used for destructing this as a base class; ignores
	// virtual bases.
	EmitGlobal(GlobalDecl(D, Dtor_Base));
	}

	void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *D,
	CXXDtorType Type) {
	// The complete destructor is equivalent to the base destructor for
	// classes with no virtual bases, so try to emit it as an alias.
	if (Type == Dtor_Complete &&
	!D->getParent()->getNumVBases() &&
	!TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Complete),
	GlobalDecl(D, Dtor_Base)))
	return;

	// The base destructor is equivalent to the base destructor of its
	// base class if there is exactly one non-virtual base class with a
	// non-trivial destructor, there are no fields with a non-trivial
	// destructor, and the body of the destructor is trivial.
	if (Type == Dtor_Base && !TryEmitBaseDestructorAsAlias(D))
	return;

	llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXDestructor(D, Type));
	setFunctionLinkage(D, Fn);

	CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn);

	SetFunctionDefinitionAttributes(D, Fn);
	SetLLVMFunctionAttributesForDefinition(D, Fn);
	}

	llvm::GlobalValue *
	CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *D,
	CXXDtorType Type) {
	GlobalDecl GD(D, Type);

	llvm::StringRef Name = getMangledName(GD);
	if (llvm::GlobalValue *V = GetGlobalValue(Name))
	return V;

	const llvm::FunctionType *FTy =
	getTypes().GetFunctionType(getTypes().getFunctionInfo(D, Type), false);

	return cast<llvm::Function>(GetOrCreateLLVMFunction(Name, FTy, GD));
	}

	static llvm::Value *BuildVirtualCall(CodeGenFunction &CGF, uint64_t VTableIndex,
	llvm::Value This, const llvm::Type Ty) {
	Ty = Ty->getPointerTo()->getPointerTo()->getPointerTo();

	llvm::Value *VTable = CGF.Builder.CreateBitCast(This, Ty);
	VTable = CGF.Builder.CreateLoad(VTable);

	llvm::Value *VFuncPtr =
	CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfn");
	return CGF.Builder.CreateLoad(VFuncPtr);
	}

	llvm::Value *
	CodeGenFunction::BuildVirtualCall(const CXXMethodDecl MD, llvm::Value This,
	const llvm::Type *Ty) {
	MD = MD->getCanonicalDecl();
	uint64_t VTableIndex = CGM.getVTables().getMethodVTableIndex(MD);

	return ::BuildVirtualCall(*this, VTableIndex, This, Ty);
	}

	llvm::Value *
	CodeGenFunction::BuildVirtualCall(const CXXDestructorDecl *DD, CXXDtorType Type,
	llvm::Value &This, const llvm::Type Ty) {
	DD = cast<CXXDestructorDecl>(DD->getCanonicalDecl());
	uint64_t VTableIndex =
	CGM.getVTables().getMethodVTableIndex(GlobalDecl(DD, Type));

	return ::BuildVirtualCall(*this, VTableIndex, This, Ty);
	}

	/// Implementation for CGCXXABI. Possibly this should be moved into
	/// the incomplete ABI implementations?

	CGCXXABI::~CGCXXABI() {}

	static void ErrorUnsupportedABI(CodeGenFunction &CGF,
	llvm::StringRef S) {
	Diagnostic &Diags = CGF.CGM.getDiags();
	unsigned DiagID = Diags.getCustomDiagID(Diagnostic::Error,
	"cannot yet compile %1 in this ABI");
	Diags.Report(CGF.getContext().getFullLoc(CGF.CurCodeDecl->getLocation()),
	DiagID)
	<< S;
	}

	static llvm::Constant *GetBogusMemberPointer(CodeGenModule &CGM,
	QualType T) {
	return llvm::Constant::getNullValue(CGM.getTypes().ConvertType(T));
	}

	const llvm::Type *
	CGCXXABI::ConvertMemberPointerType(const MemberPointerType *MPT) {
	return CGM.getTypes().ConvertType(CGM.getContext().getPointerDiffType());
	}

	llvm::Value *CGCXXABI::EmitLoadOfMemberFunctionPointer(CodeGenFunction &CGF,
	llvm::Value *&This,
	llvm::Value *MemPtr,
	const MemberPointerType *MPT) {
	ErrorUnsupportedABI(CGF, "calls through member pointers");

	const FunctionProtoType *FPT =
	MPT->getPointeeType()->getAs<FunctionProtoType>();
	const CXXRecordDecl *RD =
	cast<CXXRecordDecl>(MPT->getClass()->getAs<RecordType>()->getDecl());
	const llvm::FunctionType *FTy =
	CGM.getTypes().GetFunctionType(CGM.getTypes().getFunctionInfo(RD, FPT),
	FPT->isVariadic());
	return llvm::Constant::getNullValue(FTy->getPointerTo());
	}

	llvm::Value *CGCXXABI::EmitMemberDataPointerAddress(CodeGenFunction &CGF,
	llvm::Value *Base,
	llvm::Value *MemPtr,
	const MemberPointerType *MPT) {
	ErrorUnsupportedABI(CGF, "loads of member pointers");
	const llvm::Type *Ty = CGF.ConvertType(MPT->getPointeeType())->getPointerTo();
	return llvm::Constant::getNullValue(Ty);
	}

	llvm::Value *CGCXXABI::EmitMemberPointerConversion(CodeGenFunction &CGF,
	const CastExpr *E,
	llvm::Value *Src) {
	ErrorUnsupportedABI(CGF, "member function pointer conversions");
	return GetBogusMemberPointer(CGM, E->getType());
	}

	llvm::Value *
	CGCXXABI::EmitMemberPointerComparison(CodeGenFunction &CGF,
	llvm::Value *L,
	llvm::Value *R,
	const MemberPointerType *MPT,
	bool Inequality) {
	ErrorUnsupportedABI(CGF, "member function pointer comparison");
	return CGF.Builder.getFalse();
	}

	llvm::Value *
	CGCXXABI::EmitMemberPointerIsNotNull(CodeGenFunction &CGF,
	llvm::Value *MemPtr,
	const MemberPointerType *MPT) {
	ErrorUnsupportedABI(CGF, "member function pointer null testing");
	return CGF.Builder.getFalse();
	}

	llvm::Constant *
	CGCXXABI::EmitMemberPointerConversion(llvm::Constant C, const CastExpr E) {
	return GetBogusMemberPointer(CGM, E->getType());
	}

	llvm::Constant *
	CGCXXABI::EmitNullMemberPointer(const MemberPointerType *MPT) {
	return GetBogusMemberPointer(CGM, QualType(MPT, 0));
	}

	llvm::Constant CGCXXABI::EmitMemberPointer(const CXXMethodDecl MD) {
	return GetBogusMemberPointer(CGM,
	CGM.getContext().getMemberPointerType(MD->getType(),
	MD->getParent()->getTypeForDecl()));
	}

	llvm::Constant CGCXXABI::EmitMemberPointer(const FieldDecl FD) {
	return GetBogusMemberPointer(CGM,
	CGM.getContext().getMemberPointerType(FD->getType(),
	FD->getParent()->getTypeForDecl()));
	}

	bool CGCXXABI::isZeroInitializable(const MemberPointerType *MPT) {
	// Fake answer.
	return true;
	}

	void CGCXXABI::BuildThisParam(CodeGenFunction &CGF, FunctionArgList &Params) {
	const CXXMethodDecl *MD = cast<CXXMethodDecl>(CGF.CurGD.getDecl());

	// FIXME: I'm not entirely sure I like using a fake decl just for code
	// generation. Maybe we can come up with a better way?
	ImplicitParamDecl *ThisDecl
	= ImplicitParamDecl::Create(CGM.getContext(), 0, MD->getLocation(),
	&CGM.getContext().Idents.get("this"),
	MD->getThisType(CGM.getContext()));
	Params.push_back(std::make_pair(ThisDecl, ThisDecl->getType()));
	getThisDecl(CGF) = ThisDecl;
	}

	void CGCXXABI::EmitThisParam(CodeGenFunction &CGF) {
	/// Initialize the 'this' slot.
	assert(getThisDecl(CGF) && "no 'this' variable for function");
	getThisValue(CGF)
	= CGF.Builder.CreateLoad(CGF.GetAddrOfLocalVar(getThisDecl(CGF)),
	"this");
	}

	void CGCXXABI::EmitReturnFromThunk(CodeGenFunction &CGF,
	RValue RV, QualType ResultType) {
	CGF.EmitReturnOfRValue(RV, ResultType);
	}

	CharUnits CGCXXABI::GetArrayCookieSize(QualType ElementType) {
	return CharUnits::Zero();
	}

	llvm::Value *CGCXXABI::InitializeArrayCookie(CodeGenFunction &CGF,
	llvm::Value *NewPtr,
	llvm::Value *NumElements,
	QualType ElementType) {
	// Should never be called.
	ErrorUnsupportedABI(CGF, "array cookie initialization");
	return 0;
	}

	void CGCXXABI::ReadArrayCookie(CodeGenFunction &CGF, llvm::Value *Ptr,
	QualType ElementType, llvm::Value *&NumElements,
	llvm::Value *&AllocPtr, CharUnits &CookieSize) {
	ErrorUnsupportedABI(CGF, "array cookie reading");

	// This should be enough to avoid assertions.
	NumElements = 0;
	AllocPtr = llvm::Constant::getNullValue(CGF.Builder.getInt8PtrTy());
	CookieSize = CharUnits::Zero();
	}