CodeGenModule.cpp

    bool TraverseCallExpr(CallExpr *E) {
      const FunctionDecl *FD = E->getDirectCallee();
      if (!FD)
        return true;
      AsmLabelAttr *Attr = FD->getAttr<AsmLabelAttr>();
      if (Attr && Name == Attr->getLabel()) {
        Result = true;
        return false;
      }
      unsigned BuiltinID = FD->getBuiltinID();
      if (!BuiltinID)
        return true;
      StringRef BuiltinName = BI.GetName(BuiltinID);
      if (BuiltinName.startswith("__builtin_") &&
          Name == BuiltinName.slice(strlen("__builtin_"), StringRef::npos)) {
        Result = true;
        return false;
      }
      return true;
    }
  };
}

// isTriviallyRecursive - Check if this function calls another
// decl that, because of the asm attribute or the other decl being a builtin,
// ends up pointing to itself.
bool
CodeGenModule::isTriviallyRecursive(const FunctionDecl *FD) {
  StringRef Name;
  if (getCXXABI().getMangleContext().shouldMangleDeclName(FD)) {
    // asm labels are a special kind of mangling we have to support.
    AsmLabelAttr *Attr = FD->getAttr<AsmLabelAttr>();
    if (!Attr)
      return false;
    Name = Attr->getLabel();
  } else {
    Name = FD->getName();
  }

  FunctionIsDirectlyRecursive Walker(Name, Context.BuiltinInfo);
  Walker.TraverseFunctionDecl(const_cast<FunctionDecl*>(FD));
  return Walker.Result;
}

bool
CodeGenModule::shouldEmitFunction(const FunctionDecl *F) {
  if (getFunctionLinkage(F) != llvm::Function::AvailableExternallyLinkage)
    return true;
  if (CodeGenOpts.OptimizationLevel == 0 &&
      !F->hasAttr<AlwaysInlineAttr>() && !F->hasAttr<ForceInlineAttr>())
    return false;
  // PR9614. Avoid cases where the source code is lying to us. An available
  // externally function should have an equivalent function somewhere else,
  // but a function that calls itself is clearly not equivalent to the real
  // implementation.
  // This happens in glibc's btowc and in some configure checks.
  return !isTriviallyRecursive(F);
}

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

  PrettyStackTraceDecl CrashInfo(const_cast<ValueDecl *>(D), D->getLocation(), 
                                 Context.getSourceManager(),
                                 "Generating code for declaration");
  
  if (const FunctionDecl *Function = dyn_cast<FunctionDecl>(D)) {
    // At -O0, don't generate IR for functions with available_externally 
    // linkage.
    if (!shouldEmitFunction(Function))
      return;

    if (const CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(D)) {
      // Make sure to emit the definition(s) before we emit the thunks.
      // This is necessary for the generation of certain thunks.
      if (const CXXConstructorDecl *CD = dyn_cast<CXXConstructorDecl>(Method))
        EmitCXXConstructor(CD, GD.getCtorType());
      else if (const CXXDestructorDecl *DD =dyn_cast<CXXDestructorDecl>(Method))
        EmitCXXDestructor(DD, GD.getDtorType());
      else
        EmitGlobalFunctionDefinition(GD);

      if (Method->isVirtual())
        getVTables().EmitThunks(GD);

      return;
    }

    return EmitGlobalFunctionDefinition(GD);
  }
  
  if (const VarDecl *VD = dyn_cast<VarDecl>(D))
    return EmitGlobalVarDefinition(VD);
  
  llvm_unreachable("Invalid argument to EmitGlobalDefinition()");
}

/// GetOrCreateLLVMFunction - If the specified mangled name is not in the
/// module, create and return an llvm Function 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 function when it is first created.
llvm::Constant *
CodeGenModule::GetOrCreateLLVMFunction(StringRef MangledName,
                                       llvm::Type *Ty,
                                       GlobalDecl D, bool ForVTable,
                                       llvm::Attributes ExtraAttrs) {
  // Lookup the entry, lazily creating it if necessary.
  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
  if (Entry) {
    if (WeakRefReferences.erase(Entry)) {
      const FunctionDecl *FD = cast_or_null<FunctionDecl>(D.getDecl());
      if (FD && !FD->hasAttr<WeakAttr>())
        Entry->setLinkage(llvm::Function::ExternalLinkage);
    }

    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.hasAttributes())
    F->addAttribute(llvm::AttributeSet::FunctionIndex, 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());
    FD = FD->getMostRecentDecl();
    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.erase(Entry)) {
      if (D && !D->hasAttr<WeakAttr>())
        Entry->setLinkage(llvm::Function::ExternalLinkage);
    }

    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);
  }

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

  // 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()));
    }

    if (D->isThreadSpecified())
      setTLSMode(GV, *D);
  }

  if (AddrSpace != Ty->getAddressSpace())
    return llvm::ConstantExpr::getBitCast(GV, Ty);
  else
    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 created 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)
    getCXXABI().EmitVTables(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(
      TheDataLayout.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.
  ArrayRef<Expr*> Inits(const_cast<InitListExpr*>(init)->getInits(),
                        init->getNumInits());
  Expr *arrayInit = new (ctx) InitListExpr(ctx, init->getLBraceLoc(), Inits,
                                           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;
}

unsigned CodeGenModule::GetGlobalVarAddressSpace(const VarDecl *D,
                                                 unsigned AddrSpace) {
  if (LangOpts.CUDA && CodeGenOpts.CUDAIsDevice) {
    if (D->hasAttr<CUDAConstantAttr>())
      AddrSpace = getContext().getTargetAddressSpace(LangAS::cuda_constant);
    else if (D->hasAttr<CUDASharedAttr>())
      AddrSpace = getContext().getTargetAddressSpace(LangAS::cuda_shared);
    else
      AddrSpace = getContext().getTargetAddressSpace(LangAS::cuda_device);
  }

  return AddrSpace;
}

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) {
      initializedGlobalDecl = GlobalDecl(D);
      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() !=
       GetGlobalVarAddressSpace(D, 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);

  // If we are compiling with ASan, add metadata indicating dynamically
  // initialized globals.
  if (LangOpts.SanitizeAddress && NeedsGlobalCtor) {
    llvm::Module &M = getModule();

    llvm::NamedMDNode *DynamicInitializers =
        M.getOrInsertNamedMetadata("llvm.asan.dynamically_initialized_globals");
    llvm::Value *GlobalToAdd[] = { GV };
    llvm::MDNode *ThisGlobal = llvm::MDNode::get(VMContext, GlobalToAdd);
    DynamicInitializers->addOperand(ThisGlobal);
  }

  // Emit global variable debug information.
  if (CGDebugInfo *DI = getModuleDebugInfo())
    if (getCodeGenOpts().getDebugInfo() >= CodeGenOptions::LimitedDebugInfo)
      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;
}

/// Replace the uses of a function that was declared with a non-proto type.
/// We want to silently drop extra arguments from call sites
static void replaceUsesOfNonProtoConstant(llvm::Constant *old,
                                          llvm::Function *newFn) {
  // Fast path.
  if (old->use_empty()) return;

  llvm::Type *newRetTy = newFn->getReturnType();
  SmallVector<llvm::Value*, 4> newArgs;

  for (llvm::Value::use_iterator ui = old->use_begin(), ue = old->use_end();
         ui != ue; ) {
    llvm::Value::use_iterator use = ui++; // Increment before the use is erased.
    llvm::User *user = *use;

    // Recognize and replace uses of bitcasts.  Most calls to
    // unprototyped functions will use bitcasts.
    if (llvm::ConstantExpr *bitcast = dyn_cast<llvm::ConstantExpr>(user)) {
      if (bitcast->getOpcode() == llvm::Instruction::BitCast)
        replaceUsesOfNonProtoConstant(bitcast, newFn);
      continue;
    }

    // Recognize calls to the function.
    llvm::CallSite callSite(user);
    if (!callSite) continue;
    if (!callSite.isCallee(use)) continue;

    // If the return types don't match exactly, then we can't
    // transform this call unless it's dead.
    if (callSite->getType() != newRetTy && !callSite->use_empty())
      continue;

    // Get the call site's attribute list.
    llvm::SmallVector<llvm::AttributeWithIndex, 8> newAttrs;
    llvm::AttributeSet oldAttrs = callSite.getAttributes();

    // Collect any return attributes from the call.
    llvm::Attributes returnAttrs = oldAttrs.getRetAttributes();
    if (returnAttrs.hasAttributes())
      newAttrs.push_back(llvm::AttributeWithIndex::get(
                                llvm::AttributeSet::ReturnIndex, returnAttrs));

    // If the function was passed too few arguments, don't transform.
    unsigned newNumArgs = newFn->arg_size();
    if (callSite.arg_size() < newNumArgs) continue;

    // 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(),
           ae = newFn->arg_end(); ai != ae; ++ai, ++argNo) {
      if (callSite.getArgument(argNo)->getType() != ai->getType()) {
        dontTransform = true;
        break;
      }

      // Add any parameter attributes.
      llvm::Attributes pAttrs = oldAttrs.getParamAttributes(argNo + 1);
      if (pAttrs.hasAttributes())
        newAttrs.push_back(llvm::AttributeWithIndex::get(argNo + 1, pAttrs));
    }
    if (dontTransform)
      continue;

    llvm::Attributes fnAttrs = oldAttrs.getFnAttributes();
    if (fnAttrs.hasAttributes())
      newAttrs.push_back(llvm::
                       AttributeWithIndex::get(llvm::AttributeSet::FunctionIndex,
                                               fnAttrs));

    // Okay, we can transform this.  Create the new call instruction and copy
    // over the required information.
    newArgs.append(callSite.arg_begin(), callSite.arg_begin() + argNo);

    llvm::CallSite newCall;
    if (callSite.isCall()) {
      newCall = llvm::CallInst::Create(newFn, newArgs, "",
                                       callSite.getInstruction());
    } else {
      llvm::InvokeInst *oldInvoke =
        cast<llvm::InvokeInst>(callSite.getInstruction());
      newCall = llvm::InvokeInst::Create(newFn,
                                         oldInvoke->getNormalDest(),
                                         oldInvoke->getUnwindDest(),
                                         newArgs, "",
                                         callSite.getInstruction());
    }
    newArgs.clear(); // for the next iteration

    if (!newCall->getType()->isVoidTy())
      newCall->takeName(callSite.getInstruction());
    newCall.setAttributes(
                     llvm::AttributeSet::get(newFn->getContext(), newAttrs));
    newCall.setCallingConv(callSite.getCallingConv());

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

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

/// 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.
  if (!isa<llvm::Function>(Old)) return;

  replaceUsesOfNonProtoConstant(Old, NewFn);
}

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));

    // This might be an implementation of a function without a
    // prototype, in which case, try to do special replacement of
    // calls which match the new prototype.  The really key thing here
    // is that we also potentially drop arguments from the call site
    // so as to make a direct call, which makes the inliner happier
    // and suppresses a number of optimizer warnings (!) about
    // dropping arguments.
    if (!OldFn->use_empty()) {
      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>())