CodeGenModule.cpp

      WeakRefReferences.erase(Entry);
    }

    if (Entry->getType()->getElementType() == Ty)
      return Entry;

    // Make sure the result is of the correct type.
    return llvm::ConstantExpr::getBitCast(Entry, Ty->getPointerTo());
  }

  // This function doesn't have a complete type (for example, the return
  // type is an incomplete struct). Use a fake type instead, and make
  // sure not to try to set attributes.
  bool IsIncompleteFunction = false;

  llvm::FunctionType *FTy;
  if (isa<llvm::FunctionType>(Ty)) {
    FTy = cast<llvm::FunctionType>(Ty);
  } else {
    FTy = llvm::FunctionType::get(VoidTy, false);
    IsIncompleteFunction = true;
  }
  
  llvm::Function *F = llvm::Function::Create(FTy,
                                             llvm::Function::ExternalLinkage,
                                             MangledName, &getModule());
  assert(F->getName() == MangledName && "name was uniqued!");
  if (D.getDecl())
    SetFunctionAttributes(D, F, IsIncompleteFunction);
  if (ExtraAttrs != llvm::Attribute::None)
    F->addFnAttr(ExtraAttrs);

  // This is the first use or definition of a mangled name.  If there is a
  // deferred decl with this name, remember that we need to emit it at the end
  // of the file.
  llvm::StringMap<GlobalDecl>::iterator DDI = DeferredDecls.find(MangledName);
  if (DDI != DeferredDecls.end()) {
    // Move the potentially referenced deferred decl to the DeferredDeclsToEmit
    // list, and remove it from DeferredDecls (since we don't need it anymore).
    DeferredDeclsToEmit.push_back(DDI->second);
    DeferredDecls.erase(DDI);

  // Otherwise, there are cases we have to worry about where we're
  // using a declaration for which we must emit a definition but where
  // we might not find a top-level definition:
  //   - member functions defined inline in their classes
  //   - friend functions defined inline in some class
  //   - special member functions with implicit definitions
  // If we ever change our AST traversal to walk into class methods,
  // this will be unnecessary.
  //
  // We also don't emit a definition for a function if it's going to be an entry
  // in a vtable, unless it's already marked as used.
  } else if (getLangOpts().CPlusPlus && D.getDecl()) {
    // Look for a declaration that's lexically in a record.
    const FunctionDecl *FD = cast<FunctionDecl>(D.getDecl());
    do {
      if (isa<CXXRecordDecl>(FD->getLexicalDeclContext())) {
        if (FD->isImplicit() && !ForVTable) {
          assert(FD->isUsed() && "Sema didn't mark implicit function as used!");
          DeferredDeclsToEmit.push_back(D.getWithDecl(FD));
          break;
        } else if (FD->doesThisDeclarationHaveABody()) {
          DeferredDeclsToEmit.push_back(D.getWithDecl(FD));
          break;
        }
      }
      FD = FD->getPreviousDecl();
    } while (FD);
  }

  // Make sure the result is of the requested type.
  if (!IsIncompleteFunction) {
    assert(F->getType()->getElementType() == Ty);
    return F;
  }

  llvm::Type *PTy = llvm::PointerType::getUnqual(Ty);
  return llvm::ConstantExpr::getBitCast(F, PTy);
}

/// GetAddrOfFunction - Return the address of the given function.  If Ty is
/// non-null, then this function will use the specified type if it has to
/// create it (this occurs when we see a definition of the function).
llvm::Constant *CodeGenModule::GetAddrOfFunction(GlobalDecl GD,
                                                 llvm::Type *Ty,
                                                 bool ForVTable) {
  // If there was no specific requested type, just convert it now.
  if (!Ty)
    Ty = getTypes().ConvertType(cast<ValueDecl>(GD.getDecl())->getType());
  
  StringRef MangledName = getMangledName(GD);
  return GetOrCreateLLVMFunction(MangledName, Ty, GD, ForVTable);
}

/// CreateRuntimeFunction - Create a new runtime function with the specified
/// type and name.
llvm::Constant *
CodeGenModule::CreateRuntimeFunction(llvm::FunctionType *FTy,
                                     StringRef Name,
                                     llvm::Attributes ExtraAttrs) {
  return GetOrCreateLLVMFunction(Name, FTy, GlobalDecl(), /*ForVTable=*/false,
                                 ExtraAttrs);
}

/// isTypeConstant - Determine whether an object of this type can be emitted
/// as a constant.
///
/// If ExcludeCtor is true, the duration when the object's constructor runs
/// will not be considered. The caller will need to verify that the object is
/// not written to during its construction.
bool CodeGenModule::isTypeConstant(QualType Ty, bool ExcludeCtor) {
  if (!Ty.isConstant(Context) && !Ty->isReferenceType())
    return false;

  if (Context.getLangOpts().CPlusPlus) {
    if (const CXXRecordDecl *Record
          = Context.getBaseElementType(Ty)->getAsCXXRecordDecl())
      return ExcludeCtor && !Record->hasMutableFields() &&
             Record->hasTrivialDestructor();
  }

  return true;
}

/// GetOrCreateLLVMGlobal - If the specified mangled name is not in the module,
/// create and return an llvm GlobalVariable with the specified type.  If there
/// is something in the module with the specified name, return it potentially
/// bitcasted to the right type.
///
/// If D is non-null, it specifies a decl that correspond to this.  This is used
/// to set the attributes on the global when it is first created.
llvm::Constant *
CodeGenModule::GetOrCreateLLVMGlobal(StringRef MangledName,
                                     llvm::PointerType *Ty,
                                     const VarDecl *D,
                                     bool UnnamedAddr) {
  // Lookup the entry, lazily creating it if necessary.
  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
  if (Entry) {
    if (WeakRefReferences.count(Entry)) {
      if (D && !D->hasAttr<WeakAttr>())
        Entry->setLinkage(llvm::Function::ExternalLinkage);

      WeakRefReferences.erase(Entry);
    }

    if (UnnamedAddr)
      Entry->setUnnamedAddr(true);

    if (Entry->getType() == Ty)
      return Entry;

    // Make sure the result is of the correct type.
    return llvm::ConstantExpr::getBitCast(Entry, Ty);
  }

  // This is the first use or definition of a mangled name.  If there is a
  // deferred decl with this name, remember that we need to emit it at the end
  // of the file.
  llvm::StringMap<GlobalDecl>::iterator DDI = DeferredDecls.find(MangledName);
  if (DDI != DeferredDecls.end()) {
    // Move the potentially referenced deferred decl to the DeferredDeclsToEmit
    // list, and remove it from DeferredDecls (since we don't need it anymore).
    DeferredDeclsToEmit.push_back(DDI->second);
    DeferredDecls.erase(DDI);
  }

  llvm::GlobalVariable *GV =
    new llvm::GlobalVariable(getModule(), Ty->getElementType(), false,
                             llvm::GlobalValue::ExternalLinkage,
                             0, MangledName, 0,
                             false, Ty->getAddressSpace());

  // Handle things which are present even on external declarations.
  if (D) {
    // FIXME: This code is overly simple and should be merged with other global
    // handling.
    GV->setConstant(isTypeConstant(D->getType(), false));

    // Set linkage and visibility in case we never see a definition.
    NamedDecl::LinkageInfo LV = D->getLinkageAndVisibility();
    if (LV.linkage() != ExternalLinkage) {
      // Don't set internal linkage on declarations.
    } else {
      if (D->hasAttr<DLLImportAttr>())
        GV->setLinkage(llvm::GlobalValue::DLLImportLinkage);
      else if (D->hasAttr<WeakAttr>() || D->isWeakImported())
        GV->setLinkage(llvm::GlobalValue::ExternalWeakLinkage);

      // Set visibility on a declaration only if it's explicit.
      if (LV.visibilityExplicit())
        GV->setVisibility(GetLLVMVisibility(LV.visibility()));
    }

    GV->setThreadLocal(D->isThreadSpecified());
  }

  return GV;
}


llvm::GlobalVariable *
CodeGenModule::CreateOrReplaceCXXRuntimeVariable(StringRef Name, 
                                      llvm::Type *Ty,
                                      llvm::GlobalValue::LinkageTypes Linkage) {
  llvm::GlobalVariable *GV = getModule().getNamedGlobal(Name);
  llvm::GlobalVariable *OldGV = 0;

  
  if (GV) {
    // Check if the variable has the right type.
    if (GV->getType()->getElementType() == Ty)
      return GV;

    // Because C++ name mangling, the only way we can end up with an already
    // existing global with the same name is if it has been declared extern "C".
      assert(GV->isDeclaration() && "Declaration has wrong type!");
    OldGV = GV;
  }
  
  // Create a new variable.
  GV = new llvm::GlobalVariable(getModule(), Ty, /*isConstant=*/true,
                                Linkage, 0, Name);
  
  if (OldGV) {
    // Replace occurrences of the old variable if needed.
    GV->takeName(OldGV);
    
    if (!OldGV->use_empty()) {
      llvm::Constant *NewPtrForOldDecl =
      llvm::ConstantExpr::getBitCast(GV, OldGV->getType());
      OldGV->replaceAllUsesWith(NewPtrForOldDecl);
    }
    
    OldGV->eraseFromParent();
  }
  
  return GV;
}

/// GetAddrOfGlobalVar - Return the llvm::Constant for the address of the
/// given global variable.  If Ty is non-null and if the global doesn't exist,
/// then it will be greated with the specified type instead of whatever the
/// normal requested type would be.
llvm::Constant *CodeGenModule::GetAddrOfGlobalVar(const VarDecl *D,
                                                  llvm::Type *Ty) {
  assert(D->hasGlobalStorage() && "Not a global variable");
  QualType ASTTy = D->getType();
  if (Ty == 0)
    Ty = getTypes().ConvertTypeForMem(ASTTy);

  llvm::PointerType *PTy =
    llvm::PointerType::get(Ty, getContext().getTargetAddressSpace(ASTTy));

  StringRef MangledName = getMangledName(D);
  return GetOrCreateLLVMGlobal(MangledName, PTy, D);
}

/// CreateRuntimeVariable - Create a new runtime global variable with the
/// specified type and name.
llvm::Constant *
CodeGenModule::CreateRuntimeVariable(llvm::Type *Ty,
                                     StringRef Name) {
  return GetOrCreateLLVMGlobal(Name, llvm::PointerType::getUnqual(Ty), 0,
                               true);
}

void CodeGenModule::EmitTentativeDefinition(const VarDecl *D) {
  assert(!D->getInit() && "Cannot emit definite definitions here!");

  if (MayDeferGeneration(D)) {
    // If we have not seen a reference to this variable yet, place it
    // into the deferred declarations table to be emitted if needed
    // later.
    StringRef MangledName = getMangledName(D);
    if (!GetGlobalValue(MangledName)) {
      DeferredDecls[MangledName] = D;
      return;
    }
  }

  // The tentative definition is the only definition.
  EmitGlobalVarDefinition(D);
}

void CodeGenModule::EmitVTable(CXXRecordDecl *Class, bool DefinitionRequired) {
  if (DefinitionRequired)
    getVTables().GenerateClassData(getVTableLinkage(Class), Class);
}

llvm::GlobalVariable::LinkageTypes 
CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
  if (RD->getLinkage() != ExternalLinkage)
    return llvm::GlobalVariable::InternalLinkage;

  if (const CXXMethodDecl *KeyFunction
                                    = RD->getASTContext().getKeyFunction(RD)) {
    // If this class has a key function, use that to determine the linkage of
    // the vtable.
    const FunctionDecl *Def = 0;
    if (KeyFunction->hasBody(Def))
      KeyFunction = cast<CXXMethodDecl>(Def);
    
    switch (KeyFunction->getTemplateSpecializationKind()) {
      case TSK_Undeclared:
      case TSK_ExplicitSpecialization:
        // When compiling with optimizations turned on, we emit all vtables,
        // even if the key function is not defined in the current translation
        // unit. If this is the case, use available_externally linkage.
        if (!Def && CodeGenOpts.OptimizationLevel)
          return llvm::GlobalVariable::AvailableExternallyLinkage;

        if (KeyFunction->isInlined())
          return !Context.getLangOpts().AppleKext ?
                   llvm::GlobalVariable::LinkOnceODRLinkage :
                   llvm::Function::InternalLinkage;
        
        return llvm::GlobalVariable::ExternalLinkage;
        
      case TSK_ImplicitInstantiation:
        return !Context.getLangOpts().AppleKext ?
                 llvm::GlobalVariable::LinkOnceODRLinkage :
                 llvm::Function::InternalLinkage;

      case TSK_ExplicitInstantiationDefinition:
        return !Context.getLangOpts().AppleKext ?
                 llvm::GlobalVariable::WeakODRLinkage :
                 llvm::Function::InternalLinkage;
  
      case TSK_ExplicitInstantiationDeclaration:
        // FIXME: Use available_externally linkage. However, this currently
        // breaks LLVM's build due to undefined symbols.
        //      return llvm::GlobalVariable::AvailableExternallyLinkage;
        return !Context.getLangOpts().AppleKext ?
                 llvm::GlobalVariable::LinkOnceODRLinkage :
                 llvm::Function::InternalLinkage;
    }
  }
  
  if (Context.getLangOpts().AppleKext)
    return llvm::Function::InternalLinkage;
  
  switch (RD->getTemplateSpecializationKind()) {
  case TSK_Undeclared:
  case TSK_ExplicitSpecialization:
  case TSK_ImplicitInstantiation:
    // FIXME: Use available_externally linkage. However, this currently
    // breaks LLVM's build due to undefined symbols.
    //   return llvm::GlobalVariable::AvailableExternallyLinkage;
  case TSK_ExplicitInstantiationDeclaration:
    return llvm::GlobalVariable::LinkOnceODRLinkage;

  case TSK_ExplicitInstantiationDefinition:
      return llvm::GlobalVariable::WeakODRLinkage;
  }

  llvm_unreachable("Invalid TemplateSpecializationKind!");
}

CharUnits CodeGenModule::GetTargetTypeStoreSize(llvm::Type *Ty) const {
    return Context.toCharUnitsFromBits(
      TheTargetData.getTypeStoreSizeInBits(Ty));
}

llvm::Constant *
CodeGenModule::MaybeEmitGlobalStdInitializerListInitializer(const VarDecl *D,
                                                       const Expr *rawInit) {
  ArrayRef<ExprWithCleanups::CleanupObject> cleanups;
  if (const ExprWithCleanups *withCleanups =
          dyn_cast<ExprWithCleanups>(rawInit)) {
    cleanups = withCleanups->getObjects();
    rawInit = withCleanups->getSubExpr();
  }

  const InitListExpr *init = dyn_cast<InitListExpr>(rawInit);
  if (!init || !init->initializesStdInitializerList() ||
      init->getNumInits() == 0)
    return 0;

  ASTContext &ctx = getContext();
  unsigned numInits = init->getNumInits();
  // FIXME: This check is here because we would otherwise silently miscompile
  // nested global std::initializer_lists. Better would be to have a real
  // implementation.
  for (unsigned i = 0; i < numInits; ++i) {
    const InitListExpr *inner = dyn_cast<InitListExpr>(init->getInit(i));
    if (inner && inner->initializesStdInitializerList()) {
      ErrorUnsupported(inner, "nested global std::initializer_list");
      return 0;
    }
  }

  // Synthesize a fake VarDecl for the array and initialize that.
  QualType elementType = init->getInit(0)->getType();
  llvm::APInt numElements(ctx.getTypeSize(ctx.getSizeType()), numInits);
  QualType arrayType = ctx.getConstantArrayType(elementType, numElements,
                                                ArrayType::Normal, 0);

  IdentifierInfo *name = &ctx.Idents.get(D->getNameAsString() + "__initlist");
  TypeSourceInfo *sourceInfo = ctx.getTrivialTypeSourceInfo(
                                              arrayType, D->getLocation());
  VarDecl *backingArray = VarDecl::Create(ctx, const_cast<DeclContext*>(
                                                          D->getDeclContext()),
                                          D->getLocStart(), D->getLocation(),
                                          name, arrayType, sourceInfo,
                                          SC_Static, SC_Static);

  // Now clone the InitListExpr to initialize the array instead.
  // Incredible hack: we want to use the existing InitListExpr here, so we need
  // to tell it that it no longer initializes a std::initializer_list.
  Expr *arrayInit = new (ctx) InitListExpr(ctx, init->getLBraceLoc(),
                                    const_cast<InitListExpr*>(init)->getInits(),
                                                   init->getNumInits(),
                                                   init->getRBraceLoc());
  arrayInit->setType(arrayType);

  if (!cleanups.empty())
    arrayInit = ExprWithCleanups::Create(ctx, arrayInit, cleanups);

  backingArray->setInit(arrayInit);

  // Emit the definition of the array.
  EmitGlobalVarDefinition(backingArray);

  // Inspect the initializer list to validate it and determine its type.
  // FIXME: doing this every time is probably inefficient; caching would be nice
  RecordDecl *record = init->getType()->castAs<RecordType>()->getDecl();
  RecordDecl::field_iterator field = record->field_begin();
  if (field == record->field_end()) {
    ErrorUnsupported(D, "weird std::initializer_list");
    return 0;
  }
  QualType elementPtr = ctx.getPointerType(elementType.withConst());
  // Start pointer.
  if (!ctx.hasSameType(field->getType(), elementPtr)) {
    ErrorUnsupported(D, "weird std::initializer_list");
    return 0;
  }
  ++field;
  if (field == record->field_end()) {
    ErrorUnsupported(D, "weird std::initializer_list");
    return 0;
  }
  bool isStartEnd = false;
  if (ctx.hasSameType(field->getType(), elementPtr)) {
    // End pointer.
    isStartEnd = true;
  } else if(!ctx.hasSameType(field->getType(), ctx.getSizeType())) {
    ErrorUnsupported(D, "weird std::initializer_list");
    return 0;
  }

  // Now build an APValue representing the std::initializer_list.
  APValue initListValue(APValue::UninitStruct(), 0, 2);
  APValue &startField = initListValue.getStructField(0);
  APValue::LValuePathEntry startOffsetPathEntry;
  startOffsetPathEntry.ArrayIndex = 0;
  startField = APValue(APValue::LValueBase(backingArray),
                       CharUnits::fromQuantity(0),
                       llvm::makeArrayRef(startOffsetPathEntry),
                       /*IsOnePastTheEnd=*/false, 0);

  if (isStartEnd) {
    APValue &endField = initListValue.getStructField(1);
    APValue::LValuePathEntry endOffsetPathEntry;
    endOffsetPathEntry.ArrayIndex = numInits;
    endField = APValue(APValue::LValueBase(backingArray),
                       ctx.getTypeSizeInChars(elementType) * numInits,
                       llvm::makeArrayRef(endOffsetPathEntry),
                       /*IsOnePastTheEnd=*/true, 0);
  } else {
    APValue &sizeField = initListValue.getStructField(1);
    sizeField = APValue(llvm::APSInt(numElements));
  }

  // Emit the constant for the initializer_list.
  llvm::Constant *llvmInit =
      EmitConstantValueForMemory(initListValue, D->getType());
  assert(llvmInit && "failed to initialize as constant");
  return llvmInit;
}

void CodeGenModule::EmitGlobalVarDefinition(const VarDecl *D) {
  llvm::Constant *Init = 0;
  QualType ASTTy = D->getType();
  CXXRecordDecl *RD = ASTTy->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
  bool NeedsGlobalCtor = false;
  bool NeedsGlobalDtor = RD && !RD->hasTrivialDestructor();

  const VarDecl *InitDecl;
  const Expr *InitExpr = D->getAnyInitializer(InitDecl);

  if (!InitExpr) {
    // This is a tentative definition; tentative definitions are
    // implicitly initialized with { 0 }.
    //
    // Note that tentative definitions are only emitted at the end of
    // a translation unit, so they should never have incomplete
    // type. In addition, EmitTentativeDefinition makes sure that we
    // never attempt to emit a tentative definition if a real one
    // exists. A use may still exists, however, so we still may need
    // to do a RAUW.
    assert(!ASTTy->isIncompleteType() && "Unexpected incomplete type");
    Init = EmitNullConstant(D->getType());
  } else {
    // If this is a std::initializer_list, emit the special initializer.
    Init = MaybeEmitGlobalStdInitializerListInitializer(D, InitExpr);
    // An empty init list will perform zero-initialization, which happens
    // to be exactly what we want.
    // FIXME: It does so in a global constructor, which is *not* what we
    // want.

    if (!Init)
      Init = EmitConstantInit(*InitDecl);
    if (!Init) {
      QualType T = InitExpr->getType();
      if (D->getType()->isReferenceType())
        T = D->getType();

      if (getLangOpts().CPlusPlus) {
        Init = EmitNullConstant(T);
        NeedsGlobalCtor = true;
      } else {
        ErrorUnsupported(D, "static initializer");
        Init = llvm::UndefValue::get(getTypes().ConvertType(T));
      }
    } else {
      // We don't need an initializer, so remove the entry for the delayed
      // initializer position (just in case this entry was delayed) if we
      // also don't need to register a destructor.
      if (getLangOpts().CPlusPlus && !NeedsGlobalDtor)
        DelayedCXXInitPosition.erase(D);
    }
  }

  llvm::Type* InitType = Init->getType();
  llvm::Constant *Entry = GetAddrOfGlobalVar(D, InitType);

  // Strip off a bitcast if we got one back.
  if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(Entry)) {
    assert(CE->getOpcode() == llvm::Instruction::BitCast ||
           // all zero index gep.
           CE->getOpcode() == llvm::Instruction::GetElementPtr);
    Entry = CE->getOperand(0);
  }

  // Entry is now either a Function or GlobalVariable.
  llvm::GlobalVariable *GV = dyn_cast<llvm::GlobalVariable>(Entry);

  // We have a definition after a declaration with the wrong type.
  // We must make a new GlobalVariable* and update everything that used OldGV
  // (a declaration or tentative definition) with the new GlobalVariable*
  // (which will be a definition).
  //
  // This happens if there is a prototype for a global (e.g.
  // "extern int x[];") and then a definition of a different type (e.g.
  // "int x[10];"). This also happens when an initializer has a different type
  // from the type of the global (this happens with unions).
  if (GV == 0 ||
      GV->getType()->getElementType() != InitType ||
      GV->getType()->getAddressSpace() !=
        getContext().getTargetAddressSpace(ASTTy)) {

    // Move the old entry aside so that we'll create a new one.
    Entry->setName(StringRef());

    // Make a new global with the correct type, this is now guaranteed to work.
    GV = cast<llvm::GlobalVariable>(GetAddrOfGlobalVar(D, InitType));

    // Replace all uses of the old global with the new global
    llvm::Constant *NewPtrForOldDecl =
        llvm::ConstantExpr::getBitCast(GV, Entry->getType());
    Entry->replaceAllUsesWith(NewPtrForOldDecl);

    // Erase the old global, since it is no longer used.
    cast<llvm::GlobalValue>(Entry)->eraseFromParent();
  }

  if (D->hasAttr<AnnotateAttr>())
    AddGlobalAnnotations(D, GV);

  GV->setInitializer(Init);

  // If it is safe to mark the global 'constant', do so now.
  GV->setConstant(!NeedsGlobalCtor && !NeedsGlobalDtor &&
                  isTypeConstant(D->getType(), true));

  GV->setAlignment(getContext().getDeclAlign(D).getQuantity());

  // Set the llvm linkage type as appropriate.
  llvm::GlobalValue::LinkageTypes Linkage = 
    GetLLVMLinkageVarDefinition(D, GV);
  GV->setLinkage(Linkage);
  if (Linkage == llvm::GlobalVariable::CommonLinkage)
    // common vars aren't constant even if declared const.
    GV->setConstant(false);

  SetCommonAttributes(D, GV);

  // Emit the initializer function if necessary.
  if (NeedsGlobalCtor || NeedsGlobalDtor)
    EmitCXXGlobalVarDeclInitFunc(D, GV, NeedsGlobalCtor);

  // Emit global variable debug information.
  if (CGDebugInfo *DI = getModuleDebugInfo())
    DI->EmitGlobalVariable(GV, D);
}

llvm::GlobalValue::LinkageTypes
CodeGenModule::GetLLVMLinkageVarDefinition(const VarDecl *D,
                                           llvm::GlobalVariable *GV) {
  GVALinkage Linkage = getContext().GetGVALinkageForVariable(D);
  if (Linkage == GVA_Internal)
    return llvm::Function::InternalLinkage;
  else if (D->hasAttr<DLLImportAttr>())
    return llvm::Function::DLLImportLinkage;
  else if (D->hasAttr<DLLExportAttr>())
    return llvm::Function::DLLExportLinkage;
  else if (D->hasAttr<WeakAttr>()) {
    if (GV->isConstant())
      return llvm::GlobalVariable::WeakODRLinkage;
    else
      return llvm::GlobalVariable::WeakAnyLinkage;
  } else if (Linkage == GVA_TemplateInstantiation ||
             Linkage == GVA_ExplicitTemplateInstantiation)
    return llvm::GlobalVariable::WeakODRLinkage;
  else if (!getLangOpts().CPlusPlus && 
           ((!CodeGenOpts.NoCommon && !D->getAttr<NoCommonAttr>()) ||
             D->getAttr<CommonAttr>()) &&
           !D->hasExternalStorage() && !D->getInit() &&
           !D->getAttr<SectionAttr>() && !D->isThreadSpecified() &&
           !D->getAttr<WeakImportAttr>()) {
    // Thread local vars aren't considered common linkage.
    return llvm::GlobalVariable::CommonLinkage;
  }
  return llvm::GlobalVariable::ExternalLinkage;
}

/// ReplaceUsesOfNonProtoTypeWithRealFunction - This function is called when we
/// implement a function with no prototype, e.g. "int foo() {}".  If there are
/// existing call uses of the old function in the module, this adjusts them to
/// call the new function directly.
///
/// This is not just a cleanup: the always_inline pass requires direct calls to
/// functions to be able to inline them.  If there is a bitcast in the way, it
/// won't inline them.  Instcombine normally deletes these calls, but it isn't
/// run at -O0.
static void ReplaceUsesOfNonProtoTypeWithRealFunction(llvm::GlobalValue *Old,
                                                      llvm::Function *NewFn) {
  // If we're redefining a global as a function, don't transform it.
  llvm::Function *OldFn = dyn_cast<llvm::Function>(Old);
  if (OldFn == 0) return;

  llvm::Type *NewRetTy = NewFn->getReturnType();
  SmallVector<llvm::Value*, 4> ArgList;

  for (llvm::Value::use_iterator UI = OldFn->use_begin(), E = OldFn->use_end();
       UI != E; ) {
    // TODO: Do invokes ever occur in C code?  If so, we should handle them too.
    llvm::Value::use_iterator I = UI++; // Increment before the CI is erased.
    llvm::CallInst *CI = dyn_cast<llvm::CallInst>(*I);
    if (!CI) continue; // FIXME: when we allow Invoke, just do CallSite CS(*I)
    llvm::CallSite CS(CI);
    if (!CI || !CS.isCallee(I)) continue;

    // If the return types don't match exactly, and if the call isn't dead, then
    // we can't transform this call.
    if (CI->getType() != NewRetTy && !CI->use_empty())
      continue;

    // Get the attribute list.
    llvm::SmallVector<llvm::AttributeWithIndex, 8> AttrVec;
    llvm::AttrListPtr AttrList = CI->getAttributes();

    // Get any return attributes.
    llvm::Attributes RAttrs = AttrList.getRetAttributes();

    // Add the return attributes.
    if (RAttrs)
      AttrVec.push_back(llvm::AttributeWithIndex::get(0, RAttrs));

    // If the function was passed too few arguments, don't transform.  If extra
    // arguments were passed, we silently drop them.  If any of the types
    // mismatch, we don't transform.
    unsigned ArgNo = 0;
    bool DontTransform = false;
    for (llvm::Function::arg_iterator AI = NewFn->arg_begin(),
         E = NewFn->arg_end(); AI != E; ++AI, ++ArgNo) {
      if (CS.arg_size() == ArgNo ||
          CS.getArgument(ArgNo)->getType() != AI->getType()) {
        DontTransform = true;
        break;
      }

      // Add any parameter attributes.
      if (llvm::Attributes PAttrs = AttrList.getParamAttributes(ArgNo + 1))
        AttrVec.push_back(llvm::AttributeWithIndex::get(ArgNo + 1, PAttrs));
    }
    if (DontTransform)
      continue;

    if (llvm::Attributes FnAttrs =  AttrList.getFnAttributes())
      AttrVec.push_back(llvm::AttributeWithIndex::get(~0, FnAttrs));

    // Okay, we can transform this.  Create the new call instruction and copy
    // over the required information.
    ArgList.append(CS.arg_begin(), CS.arg_begin() + ArgNo);
    llvm::CallInst *NewCall = llvm::CallInst::Create(NewFn, ArgList, "", CI);
    ArgList.clear();
    if (!NewCall->getType()->isVoidTy())
      NewCall->takeName(CI);
    NewCall->setAttributes(llvm::AttrListPtr::get(AttrVec.begin(),
                                                  AttrVec.end()));
    NewCall->setCallingConv(CI->getCallingConv());

    // Finally, remove the old call, replacing any uses with the new one.
    if (!CI->use_empty())
      CI->replaceAllUsesWith(NewCall);

    // Copy debug location attached to CI.
    if (!CI->getDebugLoc().isUnknown())
      NewCall->setDebugLoc(CI->getDebugLoc());
    CI->eraseFromParent();
  }
}

void CodeGenModule::HandleCXXStaticMemberVarInstantiation(VarDecl *VD) {
  TemplateSpecializationKind TSK = VD->getTemplateSpecializationKind();
  // If we have a definition, this might be a deferred decl. If the
  // instantiation is explicit, make sure we emit it at the end.
  if (VD->getDefinition() && TSK == TSK_ExplicitInstantiationDefinition)
    GetAddrOfGlobalVar(VD);
}

void CodeGenModule::EmitGlobalFunctionDefinition(GlobalDecl GD) {
  const FunctionDecl *D = cast<FunctionDecl>(GD.getDecl());

  // Compute the function info and LLVM type.
  const CGFunctionInfo &FI = getTypes().arrangeGlobalDeclaration(GD);
  llvm::FunctionType *Ty = getTypes().GetFunctionType(FI);

  // Get or create the prototype for the function.
  llvm::Constant *Entry = GetAddrOfFunction(GD, Ty);

  // Strip off a bitcast if we got one back.
  if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(Entry)) {
    assert(CE->getOpcode() == llvm::Instruction::BitCast);
    Entry = CE->getOperand(0);
  }


  if (cast<llvm::GlobalValue>(Entry)->getType()->getElementType() != Ty) {
    llvm::GlobalValue *OldFn = cast<llvm::GlobalValue>(Entry);

    // If the types mismatch then we have to rewrite the definition.
    assert(OldFn->isDeclaration() &&
           "Shouldn't replace non-declaration");

    // F is the Function* for the one with the wrong type, we must make a new
    // Function* and update everything that used F (a declaration) with the new
    // Function* (which will be a definition).
    //
    // This happens if there is a prototype for a function
    // (e.g. "int f()") and then a definition of a different type
    // (e.g. "int f(int x)").  Move the old function aside so that it
    // doesn't interfere with GetAddrOfFunction.
    OldFn->setName(StringRef());
    llvm::Function *NewFn = cast<llvm::Function>(GetAddrOfFunction(GD, Ty));

    // If this is an implementation of a function without a prototype, try to
    // replace any existing uses of the function (which may be calls) with uses
    // of the new function
    if (D->getType()->isFunctionNoProtoType()) {
      ReplaceUsesOfNonProtoTypeWithRealFunction(OldFn, NewFn);
      OldFn->removeDeadConstantUsers();
    }

    // Replace uses of F with the Function we will endow with a body.
    if (!Entry->use_empty()) {
      llvm::Constant *NewPtrForOldDecl =
        llvm::ConstantExpr::getBitCast(NewFn, Entry->getType());
      Entry->replaceAllUsesWith(NewPtrForOldDecl);
    }

    // Ok, delete the old function now, which is dead.
    OldFn->eraseFromParent();

    Entry = NewFn;
  }

  // We need to set linkage and visibility on the function before
  // generating code for it because various parts of IR generation
  // want to propagate this information down (e.g. to local static
  // declarations).
  llvm::Function *Fn = cast<llvm::Function>(Entry);
  setFunctionLinkage(D, Fn);

  // FIXME: this is redundant with part of SetFunctionDefinitionAttributes
  setGlobalVisibility(Fn, D);

  CodeGenFunction(*this).GenerateCode(D, Fn, FI);

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

  if (const ConstructorAttr *CA = D->getAttr<ConstructorAttr>())
    AddGlobalCtor(Fn, CA->getPriority());
  if (const DestructorAttr *DA = D->getAttr<DestructorAttr>())
    AddGlobalDtor(Fn, DA->getPriority());
  if (D->hasAttr<AnnotateAttr>())
    AddGlobalAnnotations(D, Fn);
}

void CodeGenModule::EmitAliasDefinition(GlobalDecl GD) {
  const ValueDecl *D = cast<ValueDecl>(GD.getDecl());
  const AliasAttr *AA = D->getAttr<AliasAttr>();
  assert(AA && "Not an alias?");

  StringRef MangledName = getMangledName(GD);

  // If there is a definition in the module, then it wins over the alias.
  // This is dubious, but allow it to be safe.  Just ignore the alias.
  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
  if (Entry && !Entry->isDeclaration())
    return;

  llvm::Type *DeclTy = getTypes().ConvertTypeForMem(D->getType());

  // Create a reference to the named value.  This ensures that it is emitted
  // if a deferred decl.
  llvm::Constant *Aliasee;
  if (isa<llvm::FunctionType>(DeclTy))
    Aliasee = GetOrCreateLLVMFunction(AA->getAliasee(), DeclTy, GlobalDecl(),
                                      /*ForVTable=*/false);
  else
    Aliasee = GetOrCreateLLVMGlobal(AA->getAliasee(),
                                    llvm::PointerType::getUnqual(DeclTy), 0);

  // Create the new alias itself, but don't set a name yet.
  llvm::GlobalValue *GA =
    new llvm::GlobalAlias(Aliasee->getType(),
                          llvm::Function::ExternalLinkage,
                          "", Aliasee, &getModule());

  if (Entry) {
    assert(Entry->isDeclaration());

    // If there is a declaration in the module, then we had an extern followed
    // by the alias, as in:
    //   extern int test6();
    //   ...
    //   int test6() __attribute__((alias("test7")));
    //
    // Remove it and replace uses of it with the alias.
    GA->takeName(Entry);

    Entry->replaceAllUsesWith(llvm::ConstantExpr::getBitCast(GA,
                                                          Entry->getType()));
    Entry->eraseFromParent();
  } else {
    GA->setName(MangledName);
  }

  // Set attributes which are particular to an alias; this is a
  // specialization of the attributes which may be set on a global
  // variable/function.
  if (D->hasAttr<DLLExportAttr>()) {
    if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
      // The dllexport attribute is ignored for undefined symbols.
      if (FD->hasBody())
        GA->setLinkage(llvm::Function::DLLExportLinkage);
    } else {
      GA->setLinkage(llvm::Function::DLLExportLinkage);
    }
  } else if (D->hasAttr<WeakAttr>() ||
             D->hasAttr<WeakRefAttr>() ||
             D->isWeakImported()) {
    GA->setLinkage(llvm::Function::WeakAnyLinkage);
  }

  SetCommonAttributes(D, GA);
}

llvm::Function *CodeGenModule::getIntrinsic(unsigned IID,
                                            ArrayRef<llvm::Type*> Tys) {
  return llvm::Intrinsic::getDeclaration(&getModule(), (llvm::Intrinsic::ID)IID,
                                         Tys);
}

static llvm::StringMapEntry<llvm::Constant*> &
GetConstantCFStringEntry(llvm::StringMap<llvm::Constant*> &Map,
                         const StringLiteral *Literal,
                         bool TargetIsLSB,
                         bool &IsUTF16,
                         unsigned &StringLength) {
  StringRef String = Literal->getString();
  unsigned NumBytes = String.size();

  // Check for simple case.
  if (!Literal->containsNonAsciiOrNull()) {
    StringLength = NumBytes;
    return Map.GetOrCreateValue(String);
  }

  // Otherwise, convert the UTF8 literals into a byte string.
  SmallVector<UTF16, 128> ToBuf(NumBytes);
  const UTF8 *FromPtr = (UTF8 *)String.data();
  UTF16 *ToPtr = &ToBuf[0];

  (void)ConvertUTF8toUTF16(&FromPtr, FromPtr + NumBytes,
                           &ToPtr, ToPtr + NumBytes,
                           strictConversion);

  // ConvertUTF8toUTF16 returns the length in ToPtr.
  StringLength = ToPtr - &ToBuf[0];

  // Render the UTF-16 string into a byte array and convert to the target byte
  // order.
  //
  // FIXME: This isn't something we should need to do here.
  SmallString<128> AsBytes;
  AsBytes.reserve(StringLength * 2);
  for (unsigned i = 0; i != StringLength; ++i) {
    unsigned short Val = ToBuf[i];
    if (TargetIsLSB) {
      AsBytes.push_back(Val & 0xFF);
      AsBytes.push_back(Val >> 8);
    } else {
      AsBytes.push_back(Val >> 8);
      AsBytes.push_back(Val & 0xFF);
    }
  }
  // Append one extra null character, the second is automatically added by our
  // caller.
  AsBytes.push_back(0);

  IsUTF16 = true;
  return Map.GetOrCreateValue(StringRef(AsBytes.data(), AsBytes.size()));
}

static llvm::StringMapEntry<llvm::Constant*> &
GetConstantStringEntry(llvm::StringMap<llvm::Constant*> &Map,
                       const StringLiteral *Literal,
                       unsigned &StringLength) {
  StringRef String = Literal->getString();
  StringLength = String.size();
  return Map.GetOrCreateValue(String);
}

llvm::Constant *
CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
  unsigned StringLength = 0;
  bool isUTF16 = false;
  llvm::StringMapEntry<llvm::Constant*> &Entry =
    GetConstantCFStringEntry(CFConstantStringMap, Literal,
                             getTargetData().isLittleEndian(),
                             isUTF16, StringLength);

  if (llvm::Constant *C = Entry.getValue())
    return C;

  llvm::Constant *Zero = llvm::Constant::getNullValue(Int32Ty);
  llvm::Constant *Zeros[] = { Zero, Zero };

  // If we don't already have it, get __CFConstantStringClassReference.
  if (!CFConstantStringClassRef) {
    llvm::Type *Ty = getTypes().ConvertType(getContext().IntTy);
    Ty = llvm::ArrayType::get(Ty, 0);
    llvm::Constant *GV = CreateRuntimeVariable(Ty,
                                           "__CFConstantStringClassReference");
    // Decay array -> ptr
    CFConstantStringClassRef =
      llvm::ConstantExpr::getGetElementPtr(GV, Zeros);
  }

  QualType CFTy = getContext().getCFConstantStringType();

  llvm::StructType *STy =
    cast<llvm::StructType>(getTypes().ConvertType(CFTy));

  llvm::Constant *Fields[4];

  // Class pointer.
  Fields[0] = CFConstantStringClassRef;

  // Flags.
  llvm::Type *Ty = getTypes().ConvertType(getContext().UnsignedIntTy);
  Fields[1] = isUTF16 ? llvm::ConstantInt::get(Ty, 0x07d0) :
    llvm::ConstantInt::get(Ty, 0x07C8);

  // String pointer.
  llvm::Constant *C = llvm::ConstantDataArray::getString(VMContext,
                                                         Entry.getKey());

  llvm::GlobalValue::LinkageTypes Linkage;
  if (isUTF16)
    // FIXME: why do utf strings get "_" labels instead of "L" labels?
    Linkage = llvm::GlobalValue::InternalLinkage;
  else