CodeGenModule.cpp

//===--- CodeGenModule.cpp - Emit LLVM Code from ASTs for a Module --------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This coordinates the per-module state used while generating code.
//
//===----------------------------------------------------------------------===//

#include "CodeGenModule.h"
#include "CGDebugInfo.h"
#include "CodeGenFunction.h"
#include "CodeGenTBAA.h"
#include "CGCall.h"
#include "CGCXXABI.h"
#include "CGObjCRuntime.h"
#include "TargetInfo.h"
#include "clang/Frontend/CodeGenOptions.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/CharUnits.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/Mangle.h"
#include "clang/AST/RecordLayout.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Basic/ConvertUTF.h"
#include "llvm/CallingConv.h"
#include "llvm/Module.h"
#include "llvm/Intrinsics.h"
#include "llvm/LLVMContext.h"
#include "llvm/ADT/Triple.h"
#include "llvm/Target/Mangler.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/ErrorHandling.h"
using namespace clang;
using namespace CodeGen;

static const char AnnotationSection[] = "llvm.metadata";

static CGCXXABI &createCXXABI(CodeGenModule &CGM) {
  switch (CGM.getContext().getTargetInfo().getCXXABI()) {
  case CXXABI_ARM: return *CreateARMCXXABI(CGM);
  case CXXABI_Itanium: return *CreateItaniumCXXABI(CGM);
  case CXXABI_Microsoft: return *CreateMicrosoftCXXABI(CGM);
  }

  llvm_unreachable("invalid C++ ABI kind");
  return *CreateItaniumCXXABI(CGM);
}


CodeGenModule::CodeGenModule(ASTContext &C, const CodeGenOptions &CGO,
                             llvm::Module &M, const llvm::TargetData &TD,
                             Diagnostic &diags)
  : Context(C), Features(C.getLangOptions()), CodeGenOpts(CGO), TheModule(M),
    TheTargetData(TD), TheTargetCodeGenInfo(0), Diags(diags),
    ABI(createCXXABI(*this)), 
    Types(C, M, TD, getTargetCodeGenInfo().getABIInfo(), ABI, CGO),
    TBAA(0),
    VTables(*this), ObjCRuntime(0), DebugInfo(0), ARCData(0), RRData(0),
    CFConstantStringClassRef(0), ConstantStringClassRef(0),
    NSConstantStringType(0),
    VMContext(M.getContext()),
    NSConcreteGlobalBlock(0), NSConcreteStackBlock(0),
    BlockObjectAssign(0), BlockObjectDispose(0),
    BlockDescriptorType(0), GenericBlockLiteralType(0) {
  if (Features.ObjC1)
     createObjCRuntime();

  // Enable TBAA unless it's suppressed.
  if (!CodeGenOpts.RelaxedAliasing && CodeGenOpts.OptimizationLevel > 0)
    TBAA = new CodeGenTBAA(Context, VMContext, getLangOptions(),
                           ABI.getMangleContext());

  // If debug info or coverage generation is enabled, create the CGDebugInfo
  // object.
  if (CodeGenOpts.DebugInfo || CodeGenOpts.EmitGcovArcs ||
      CodeGenOpts.EmitGcovNotes)
    DebugInfo = new CGDebugInfo(*this);

  Block.GlobalUniqueCount = 0;

  if (C.getLangOptions().ObjCAutoRefCount)
    ARCData = new ARCEntrypoints();
  RRData = new RREntrypoints();

  // Initialize the type cache.
  llvm::LLVMContext &LLVMContext = M.getContext();
  VoidTy = llvm::Type::getVoidTy(LLVMContext);
  Int8Ty = llvm::Type::getInt8Ty(LLVMContext);
  Int32Ty = llvm::Type::getInt32Ty(LLVMContext);
  Int64Ty = llvm::Type::getInt64Ty(LLVMContext);
  PointerWidthInBits = C.getTargetInfo().getPointerWidth(0);
  PointerAlignInBytes =
    C.toCharUnitsFromBits(C.getTargetInfo().getPointerAlign(0)).getQuantity();
  IntTy = llvm::IntegerType::get(LLVMContext, C.getTargetInfo().getIntWidth());
  IntPtrTy = llvm::IntegerType::get(LLVMContext, PointerWidthInBits);
  Int8PtrTy = Int8Ty->getPointerTo(0);
  Int8PtrPtrTy = Int8PtrTy->getPointerTo(0);
}

CodeGenModule::~CodeGenModule() {
  delete ObjCRuntime;
  delete &ABI;
  delete TBAA;
  delete DebugInfo;
  delete ARCData;
  delete RRData;
}

void CodeGenModule::createObjCRuntime() {
  if (!Features.NeXTRuntime)
    ObjCRuntime = CreateGNUObjCRuntime(*this);
  else
    ObjCRuntime = CreateMacObjCRuntime(*this);
}

void CodeGenModule::Release() {
  EmitDeferred();
  EmitCXXGlobalInitFunc();
  EmitCXXGlobalDtorFunc();
  if (ObjCRuntime)
    if (llvm::Function *ObjCInitFunction = ObjCRuntime->ModuleInitFunction())
      AddGlobalCtor(ObjCInitFunction);
  EmitCtorList(GlobalCtors, "llvm.global_ctors");
  EmitCtorList(GlobalDtors, "llvm.global_dtors");
  EmitGlobalAnnotations();
  EmitLLVMUsed();

  SimplifyPersonality();

  if (getCodeGenOpts().EmitDeclMetadata)
    EmitDeclMetadata();

  if (getCodeGenOpts().EmitGcovArcs || getCodeGenOpts().EmitGcovNotes)
    EmitCoverageFile();

  if (DebugInfo)
    DebugInfo->finalize();
}

void CodeGenModule::UpdateCompletedType(const TagDecl *TD) {
  // Make sure that this type is translated.
  Types.UpdateCompletedType(TD);
  if (DebugInfo)
    DebugInfo->UpdateCompletedType(TD);
}

llvm::MDNode *CodeGenModule::getTBAAInfo(QualType QTy) {
  if (!TBAA)
    return 0;
  return TBAA->getTBAAInfo(QTy);
}

void CodeGenModule::DecorateInstruction(llvm::Instruction *Inst,
                                        llvm::MDNode *TBAAInfo) {
  Inst->setMetadata(llvm::LLVMContext::MD_tbaa, TBAAInfo);
}

bool CodeGenModule::isTargetDarwin() const {
  return getContext().getTargetInfo().getTriple().isOSDarwin();
}

void CodeGenModule::Error(SourceLocation loc, StringRef error) {
  unsigned diagID = getDiags().getCustomDiagID(Diagnostic::Error, error);
  getDiags().Report(Context.getFullLoc(loc), diagID);
}

/// ErrorUnsupported - Print out an error that codegen doesn't support the
/// specified stmt yet.
void CodeGenModule::ErrorUnsupported(const Stmt *S, const char *Type,
                                     bool OmitOnError) {
  if (OmitOnError && getDiags().hasErrorOccurred())
    return;
  unsigned DiagID = getDiags().getCustomDiagID(Diagnostic::Error,
                                               "cannot compile this %0 yet");
  std::string Msg = Type;
  getDiags().Report(Context.getFullLoc(S->getLocStart()), DiagID)
    << Msg << S->getSourceRange();
}

/// ErrorUnsupported - Print out an error that codegen doesn't support the
/// specified decl yet.
void CodeGenModule::ErrorUnsupported(const Decl *D, const char *Type,
                                     bool OmitOnError) {
  if (OmitOnError && getDiags().hasErrorOccurred())
    return;
  unsigned DiagID = getDiags().getCustomDiagID(Diagnostic::Error,
                                               "cannot compile this %0 yet");
  std::string Msg = Type;
  getDiags().Report(Context.getFullLoc(D->getLocation()), DiagID) << Msg;
}

llvm::ConstantInt *CodeGenModule::getSize(CharUnits size) {
  return llvm::ConstantInt::get(SizeTy, size.getQuantity());
}

void CodeGenModule::setGlobalVisibility(llvm::GlobalValue *GV,
                                        const NamedDecl *D) const {
  // Internal definitions always have default visibility.
  if (GV->hasLocalLinkage()) {
    GV->setVisibility(llvm::GlobalValue::DefaultVisibility);
    return;
  }

  // Set visibility for definitions.
  NamedDecl::LinkageInfo LV = D->getLinkageAndVisibility();
  if (LV.visibilityExplicit() || !GV->hasAvailableExternallyLinkage())
    GV->setVisibility(GetLLVMVisibility(LV.visibility()));
}

/// Set the symbol visibility of type information (vtable and RTTI)
/// associated with the given type.
void CodeGenModule::setTypeVisibility(llvm::GlobalValue *GV,
                                      const CXXRecordDecl *RD,
                                      TypeVisibilityKind TVK) const {
  setGlobalVisibility(GV, RD);

  if (!CodeGenOpts.HiddenWeakVTables)
    return;

  // We never want to drop the visibility for RTTI names.
  if (TVK == TVK_ForRTTIName)
    return;

  // We want to drop the visibility to hidden for weak type symbols.
  // This isn't possible if there might be unresolved references
  // elsewhere that rely on this symbol being visible.

  // This should be kept roughly in sync with setThunkVisibility
  // in CGVTables.cpp.

  // Preconditions.
  if (GV->getLinkage() != llvm::GlobalVariable::LinkOnceODRLinkage ||
      GV->getVisibility() != llvm::GlobalVariable::DefaultVisibility)
    return;

  // Don't override an explicit visibility attribute.
  if (RD->getExplicitVisibility())
    return;

  switch (RD->getTemplateSpecializationKind()) {
  // We have to disable the optimization if this is an EI definition
  // because there might be EI declarations in other shared objects.
  case TSK_ExplicitInstantiationDefinition:
  case TSK_ExplicitInstantiationDeclaration:
    return;

  // Every use of a non-template class's type information has to emit it.
  case TSK_Undeclared:
    break;

  // In theory, implicit instantiations can ignore the possibility of
  // an explicit instantiation declaration because there necessarily
  // must be an EI definition somewhere with default visibility.  In
  // practice, it's possible to have an explicit instantiation for
  // an arbitrary template class, and linkers aren't necessarily able
  // to deal with mixed-visibility symbols.
  case TSK_ExplicitSpecialization:
  case TSK_ImplicitInstantiation:
    if (!CodeGenOpts.HiddenWeakTemplateVTables)
      return;
    break;
  }

  // If there's a key function, there may be translation units
  // that don't have the key function's definition.  But ignore
  // this if we're emitting RTTI under -fno-rtti.
  if (!(TVK != TVK_ForRTTI) || Features.RTTI) {
    if (Context.getKeyFunction(RD))
      return;
  }

  // Otherwise, drop the visibility to hidden.
  GV->setVisibility(llvm::GlobalValue::HiddenVisibility);
  GV->setUnnamedAddr(true);
}

StringRef CodeGenModule::getMangledName(GlobalDecl GD) {
  const NamedDecl *ND = cast<NamedDecl>(GD.getDecl());

  StringRef &Str = MangledDeclNames[GD.getCanonicalDecl()];
  if (!Str.empty())
    return Str;

  if (!getCXXABI().getMangleContext().shouldMangleDeclName(ND)) {
    IdentifierInfo *II = ND->getIdentifier();
    assert(II && "Attempt to mangle unnamed decl.");

    Str = II->getName();
    return Str;
  }
  
  llvm::SmallString<256> Buffer;
  llvm::raw_svector_ostream Out(Buffer);
  if (const CXXConstructorDecl *D = dyn_cast<CXXConstructorDecl>(ND))
    getCXXABI().getMangleContext().mangleCXXCtor(D, GD.getCtorType(), Out);
  else if (const CXXDestructorDecl *D = dyn_cast<CXXDestructorDecl>(ND))
    getCXXABI().getMangleContext().mangleCXXDtor(D, GD.getDtorType(), Out);
  else if (const BlockDecl *BD = dyn_cast<BlockDecl>(ND))
    getCXXABI().getMangleContext().mangleBlock(BD, Out);
  else
    getCXXABI().getMangleContext().mangleName(ND, Out);

  // Allocate space for the mangled name.
  Out.flush();
  size_t Length = Buffer.size();
  char *Name = MangledNamesAllocator.Allocate<char>(Length);
  std::copy(Buffer.begin(), Buffer.end(), Name);
  
  Str = StringRef(Name, Length);
  
  return Str;
}

void CodeGenModule::getBlockMangledName(GlobalDecl GD, MangleBuffer &Buffer,
                                        const BlockDecl *BD) {
  MangleContext &MangleCtx = getCXXABI().getMangleContext();
  const Decl *D = GD.getDecl();
  llvm::raw_svector_ostream Out(Buffer.getBuffer());
  if (D == 0)
    MangleCtx.mangleGlobalBlock(BD, Out);
  else if (const CXXConstructorDecl *CD = dyn_cast<CXXConstructorDecl>(D))
    MangleCtx.mangleCtorBlock(CD, GD.getCtorType(), BD, Out);
  else if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(D))
    MangleCtx.mangleDtorBlock(DD, GD.getDtorType(), BD, Out);
  else
    MangleCtx.mangleBlock(cast<DeclContext>(D), BD, Out);
}

llvm::GlobalValue *CodeGenModule::GetGlobalValue(StringRef Name) {
  return getModule().getNamedValue(Name);
}

/// AddGlobalCtor - Add a function to the list that will be called before
/// main() runs.
void CodeGenModule::AddGlobalCtor(llvm::Function * Ctor, int Priority) {
  // FIXME: Type coercion of void()* types.
  GlobalCtors.push_back(std::make_pair(Ctor, Priority));
}

/// AddGlobalDtor - Add a function to the list that will be called
/// when the module is unloaded.
void CodeGenModule::AddGlobalDtor(llvm::Function * Dtor, int Priority) {
  // FIXME: Type coercion of void()* types.
  GlobalDtors.push_back(std::make_pair(Dtor, Priority));
}

void CodeGenModule::EmitCtorList(const CtorList &Fns, const char *GlobalName) {
  // Ctor function type is void()*.
  llvm::FunctionType* CtorFTy = llvm::FunctionType::get(VoidTy, false);
  llvm::Type *CtorPFTy = llvm::PointerType::getUnqual(CtorFTy);

  // Get the type of a ctor entry, { i32, void ()* }.
  llvm::StructType *CtorStructTy =
    llvm::StructType::get(llvm::Type::getInt32Ty(VMContext),
                          llvm::PointerType::getUnqual(CtorFTy), NULL);

  // Construct the constructor and destructor arrays.
  std::vector<llvm::Constant*> Ctors;
  for (CtorList::const_iterator I = Fns.begin(), E = Fns.end(); I != E; ++I) {
    std::vector<llvm::Constant*> S;
    S.push_back(llvm::ConstantInt::get(llvm::Type::getInt32Ty(VMContext),
                I->second, false));
    S.push_back(llvm::ConstantExpr::getBitCast(I->first, CtorPFTy));
    Ctors.push_back(llvm::ConstantStruct::get(CtorStructTy, S));
  }

  if (!Ctors.empty()) {
    llvm::ArrayType *AT = llvm::ArrayType::get(CtorStructTy, Ctors.size());
    new llvm::GlobalVariable(TheModule, AT, false,
                             llvm::GlobalValue::AppendingLinkage,
                             llvm::ConstantArray::get(AT, Ctors),
                             GlobalName);
  }
}

llvm::GlobalValue::LinkageTypes
CodeGenModule::getFunctionLinkage(const FunctionDecl *D) {
  GVALinkage Linkage = getContext().GetGVALinkageForFunction(D);

  if (Linkage == GVA_Internal)
    return llvm::Function::InternalLinkage;
  
  if (D->hasAttr<DLLExportAttr>())
    return llvm::Function::DLLExportLinkage;
  
  if (D->hasAttr<WeakAttr>())
    return llvm::Function::WeakAnyLinkage;
  
  // In C99 mode, 'inline' functions are guaranteed to have a strong
  // definition somewhere else, so we can use available_externally linkage.
  if (Linkage == GVA_C99Inline)
    return llvm::Function::AvailableExternallyLinkage;
  
  // In C++, the compiler has to emit a definition in every translation unit
  // that references the function.  We should use linkonce_odr because
  // a) if all references in this translation unit are optimized away, we
  // don't need to codegen it.  b) if the function persists, it needs to be
  // merged with other definitions. c) C++ has the ODR, so we know the
  // definition is dependable.
  if (Linkage == GVA_CXXInline || Linkage == GVA_TemplateInstantiation)
    return !Context.getLangOptions().AppleKext 
             ? llvm::Function::LinkOnceODRLinkage 
             : llvm::Function::InternalLinkage;
  
  // An explicit instantiation of a template has weak linkage, since
  // explicit instantiations can occur in multiple translation units
  // and must all be equivalent. However, we are not allowed to
  // throw away these explicit instantiations.
  if (Linkage == GVA_ExplicitTemplateInstantiation)
    return !Context.getLangOptions().AppleKext
             ? llvm::Function::WeakODRLinkage
             : llvm::Function::InternalLinkage;
  
  // Otherwise, we have strong external linkage.
  assert(Linkage == GVA_StrongExternal);
  return llvm::Function::ExternalLinkage;
}


/// SetFunctionDefinitionAttributes - Set attributes for a global.
///
/// FIXME: This is currently only done for aliases and functions, but not for
/// variables (these details are set in EmitGlobalVarDefinition for variables).
void CodeGenModule::SetFunctionDefinitionAttributes(const FunctionDecl *D,
                                                    llvm::GlobalValue *GV) {
  SetCommonAttributes(D, GV);
}

void CodeGenModule::SetLLVMFunctionAttributes(const Decl *D,
                                              const CGFunctionInfo &Info,
                                              llvm::Function *F) {
  unsigned CallingConv;
  AttributeListType AttributeList;
  ConstructAttributeList(Info, D, AttributeList, CallingConv);
  F->setAttributes(llvm::AttrListPtr::get(AttributeList.begin(),
                                          AttributeList.size()));
  F->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
}

void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
                                                           llvm::Function *F) {
  if (CodeGenOpts.UnwindTables)
    F->setHasUWTable();

  if (!Features.Exceptions && !Features.ObjCNonFragileABI)
    F->addFnAttr(llvm::Attribute::NoUnwind);

  if (D->hasAttr<NakedAttr>()) {
    // Naked implies noinline: we should not be inlining such functions.
    F->addFnAttr(llvm::Attribute::Naked);
    F->addFnAttr(llvm::Attribute::NoInline);
  }

  if (D->hasAttr<NoInlineAttr>())
    F->addFnAttr(llvm::Attribute::NoInline);

  // (noinline wins over always_inline, and we can't specify both in IR)
  if (D->hasAttr<AlwaysInlineAttr>() &&
      !F->hasFnAttr(llvm::Attribute::NoInline))
    F->addFnAttr(llvm::Attribute::AlwaysInline);

  if (isa<CXXConstructorDecl>(D) || isa<CXXDestructorDecl>(D))
    F->setUnnamedAddr(true);

  if (Features.getStackProtector() == LangOptions::SSPOn)
    F->addFnAttr(llvm::Attribute::StackProtect);
  else if (Features.getStackProtector() == LangOptions::SSPReq)
    F->addFnAttr(llvm::Attribute::StackProtectReq);
  
  unsigned alignment = D->getMaxAlignment() / Context.getCharWidth();
  if (alignment)
    F->setAlignment(alignment);

  // C++ ABI requires 2-byte alignment for member functions.
  if (F->getAlignment() < 2 && isa<CXXMethodDecl>(D))
    F->setAlignment(2);
}

void CodeGenModule::SetCommonAttributes(const Decl *D,
                                        llvm::GlobalValue *GV) {
  if (const NamedDecl *ND = dyn_cast<NamedDecl>(D))
    setGlobalVisibility(GV, ND);
  else
    GV->setVisibility(llvm::GlobalValue::DefaultVisibility);

  if (D->hasAttr<UsedAttr>())
    AddUsedGlobal(GV);

  if (const SectionAttr *SA = D->getAttr<SectionAttr>())
    GV->setSection(SA->getName());

  getTargetCodeGenInfo().SetTargetAttributes(D, GV, *this);
}

void CodeGenModule::SetInternalFunctionAttributes(const Decl *D,
                                                  llvm::Function *F,
                                                  const CGFunctionInfo &FI) {
  SetLLVMFunctionAttributes(D, FI, F);
  SetLLVMFunctionAttributesForDefinition(D, F);

  F->setLinkage(llvm::Function::InternalLinkage);

  SetCommonAttributes(D, F);
}

void CodeGenModule::SetFunctionAttributes(GlobalDecl GD,
                                          llvm::Function *F,
                                          bool IsIncompleteFunction) {
  if (unsigned IID = F->getIntrinsicID()) {
    // If this is an intrinsic function, set the function's attributes
    // to the intrinsic's attributes.
    F->setAttributes(llvm::Intrinsic::getAttributes((llvm::Intrinsic::ID)IID));
    return;
  }

  const FunctionDecl *FD = cast<FunctionDecl>(GD.getDecl());

  if (!IsIncompleteFunction)
    SetLLVMFunctionAttributes(FD, getTypes().getFunctionInfo(GD), F);

  // Only a few attributes are set on declarations; these may later be
  // overridden by a definition.

  if (FD->hasAttr<DLLImportAttr>()) {
    F->setLinkage(llvm::Function::DLLImportLinkage);
  } else if (FD->hasAttr<WeakAttr>() ||
             FD->isWeakImported()) {
    // "extern_weak" is overloaded in LLVM; we probably should have
    // separate linkage types for this.
    F->setLinkage(llvm::Function::ExternalWeakLinkage);
  } else {
    F->setLinkage(llvm::Function::ExternalLinkage);

    NamedDecl::LinkageInfo LV = FD->getLinkageAndVisibility();
    if (LV.linkage() == ExternalLinkage && LV.visibilityExplicit()) {
      F->setVisibility(GetLLVMVisibility(LV.visibility()));
    }
  }

  if (const SectionAttr *SA = FD->getAttr<SectionAttr>())
    F->setSection(SA->getName());
}

void CodeGenModule::AddUsedGlobal(llvm::GlobalValue *GV) {
  assert(!GV->isDeclaration() &&
         "Only globals with definition can force usage.");
  LLVMUsed.push_back(GV);
}

void CodeGenModule::EmitLLVMUsed() {
  // Don't create llvm.used if there is no need.
  if (LLVMUsed.empty())
    return;

  llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(VMContext);

  // Convert LLVMUsed to what ConstantArray needs.
  std::vector<llvm::Constant*> UsedArray;
  UsedArray.resize(LLVMUsed.size());
  for (unsigned i = 0, e = LLVMUsed.size(); i != e; ++i) {
    UsedArray[i] =
     llvm::ConstantExpr::getBitCast(cast<llvm::Constant>(&*LLVMUsed[i]),
                                      i8PTy);
  }

  if (UsedArray.empty())
    return;
  llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, UsedArray.size());

  llvm::GlobalVariable *GV =
    new llvm::GlobalVariable(getModule(), ATy, false,
                             llvm::GlobalValue::AppendingLinkage,
                             llvm::ConstantArray::get(ATy, UsedArray),
                             "llvm.used");

  GV->setSection("llvm.metadata");
}

void CodeGenModule::EmitDeferred() {
  // Emit code for any potentially referenced deferred decls.  Since a
  // previously unused static decl may become used during the generation of code
  // for a static function, iterate until no changes are made.

  while (!DeferredDeclsToEmit.empty() || !DeferredVTables.empty()) {
    if (!DeferredVTables.empty()) {
      const CXXRecordDecl *RD = DeferredVTables.back();
      DeferredVTables.pop_back();
      getVTables().GenerateClassData(getVTableLinkage(RD), RD);
      continue;
    }

    GlobalDecl D = DeferredDeclsToEmit.back();
    DeferredDeclsToEmit.pop_back();

    // Check to see if we've already emitted this.  This is necessary
    // for a couple of reasons: first, decls can end up in the
    // deferred-decls queue multiple times, and second, decls can end
    // up with definitions in unusual ways (e.g. by an extern inline
    // function acquiring a strong function redefinition).  Just
    // ignore these cases.
    //
    // TODO: That said, looking this up multiple times is very wasteful.
    StringRef Name = getMangledName(D);
    llvm::GlobalValue *CGRef = GetGlobalValue(Name);
    assert(CGRef && "Deferred decl wasn't referenced?");

    if (!CGRef->isDeclaration())
      continue;

    // GlobalAlias::isDeclaration() defers to the aliasee, but for our
    // purposes an alias counts as a definition.
    if (isa<llvm::GlobalAlias>(CGRef))
      continue;

    // Otherwise, emit the definition and move on to the next one.
    EmitGlobalDefinition(D);
  }
}

void CodeGenModule::EmitGlobalAnnotations() {
  if (Annotations.empty())
    return;

  // Create a new global variable for the ConstantStruct in the Module.
  llvm::Constant *Array = llvm::ConstantArray::get(llvm::ArrayType::get(
    Annotations[0]->getType(), Annotations.size()), Annotations);
  llvm::GlobalValue *gv = new llvm::GlobalVariable(getModule(),
    Array->getType(), false, llvm::GlobalValue::AppendingLinkage, Array,
    "llvm.global.annotations");
  gv->setSection(AnnotationSection);
}

llvm::Constant *CodeGenModule::EmitAnnotationString(llvm::StringRef Str) {
  llvm::StringMap<llvm::Constant*>::iterator i = AnnotationStrings.find(Str);
  if (i != AnnotationStrings.end())
    return i->second;

  // Not found yet, create a new global.
  llvm::Constant *s = llvm::ConstantArray::get(getLLVMContext(), Str, true);
  llvm::GlobalValue *gv = new llvm::GlobalVariable(getModule(), s->getType(),
    true, llvm::GlobalValue::PrivateLinkage, s, ".str");
  gv->setSection(AnnotationSection);
  gv->setUnnamedAddr(true);
  AnnotationStrings[Str] = gv;
  return gv;
}

llvm::Constant *CodeGenModule::EmitAnnotationUnit(SourceLocation Loc) {
  SourceManager &SM = getContext().getSourceManager();
  PresumedLoc PLoc = SM.getPresumedLoc(Loc);
  if (PLoc.isValid())
    return EmitAnnotationString(PLoc.getFilename());
  return EmitAnnotationString(SM.getBufferName(Loc));
}

llvm::Constant *CodeGenModule::EmitAnnotationLineNo(SourceLocation L) {
  SourceManager &SM = getContext().getSourceManager();
  PresumedLoc PLoc = SM.getPresumedLoc(L);
  unsigned LineNo = PLoc.isValid() ? PLoc.getLine() :
    SM.getExpansionLineNumber(L);
  return llvm::ConstantInt::get(Int32Ty, LineNo);
}

llvm::Constant *CodeGenModule::EmitAnnotateAttr(llvm::GlobalValue *GV,
                                                const AnnotateAttr *AA,
                                                SourceLocation L) {
  // Get the globals for file name, annotation, and the line number.
  llvm::Constant *AnnoGV = EmitAnnotationString(AA->getAnnotation()),
                 *UnitGV = EmitAnnotationUnit(L),
                 *LineNoCst = EmitAnnotationLineNo(L);

  // Create the ConstantStruct for the global annotation.
  llvm::Constant *Fields[4] = {
    llvm::ConstantExpr::getBitCast(GV, Int8PtrTy),
    llvm::ConstantExpr::getBitCast(AnnoGV, Int8PtrTy),
    llvm::ConstantExpr::getBitCast(UnitGV, Int8PtrTy),
    LineNoCst
  };
  return llvm::ConstantStruct::getAnon(Fields);
}

void CodeGenModule::AddGlobalAnnotations(const ValueDecl *D,
                                         llvm::GlobalValue *GV) {
  assert(D->hasAttr<AnnotateAttr>() && "no annotate attribute");
  // Get the struct elements for these annotations.
  for (specific_attr_iterator<AnnotateAttr>
       ai = D->specific_attr_begin<AnnotateAttr>(),
       ae = D->specific_attr_end<AnnotateAttr>(); ai != ae; ++ai)
    Annotations.push_back(EmitAnnotateAttr(GV, *ai, D->getLocation()));
}

bool CodeGenModule::MayDeferGeneration(const ValueDecl *Global) {
  // Never defer when EmitAllDecls is specified.
  if (Features.EmitAllDecls)
    return false;

  return !getContext().DeclMustBeEmitted(Global);
}

llvm::Constant *CodeGenModule::GetWeakRefReference(const ValueDecl *VD) {
  const AliasAttr *AA = VD->getAttr<AliasAttr>();
  assert(AA && "No alias?");

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

  // See if there is already something with the target's name in the module.
  llvm::GlobalValue *Entry = GetGlobalValue(AA->getAliasee());

  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);
  if (!Entry) {
    llvm::GlobalValue* F = cast<llvm::GlobalValue>(Aliasee);
    F->setLinkage(llvm::Function::ExternalWeakLinkage);    
    WeakRefReferences.insert(F);
  }

  return Aliasee;
}

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

  // Weak references don't produce any output by themselves.
  if (Global->hasAttr<WeakRefAttr>())
    return;

  // If this is an alias definition (which otherwise looks like a declaration)
  // emit it now.
  if (Global->hasAttr<AliasAttr>())
    return EmitAliasDefinition(GD);

  // Ignore declarations, they will be emitted on their first use.
  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Global)) {
    // Forward declarations are emitted lazily on first use.
    if (!FD->doesThisDeclarationHaveABody()) {
      if (!FD->doesDeclarationForceExternallyVisibleDefinition())
        return;

      const FunctionDecl *InlineDefinition = 0;
      FD->getBody(InlineDefinition);

      StringRef MangledName = getMangledName(GD);
      llvm::StringMap<GlobalDecl>::iterator DDI =
          DeferredDecls.find(MangledName);
      if (DDI != DeferredDecls.end())
        DeferredDecls.erase(DDI);
      EmitGlobalDefinition(InlineDefinition);
      return;
    }
  } else {
    const VarDecl *VD = cast<VarDecl>(Global);
    assert(VD->isFileVarDecl() && "Cannot emit local var decl as global.");

    if (VD->isThisDeclarationADefinition() != VarDecl::Definition)
      return;
  }

  // Defer code generation when possible if this is a static definition, inline
  // function etc.  These we only want to emit if they are used.
  if (!MayDeferGeneration(Global)) {
    // Emit the definition if it can't be deferred.
    EmitGlobalDefinition(GD);
    return;
  }

  // If we're deferring emission of a C++ variable with an
  // initializer, remember the order in which it appeared in the file.
  if (getLangOptions().CPlusPlus && isa<VarDecl>(Global) &&
      cast<VarDecl>(Global)->hasInit()) {
    DelayedCXXInitPosition[Global] = CXXGlobalInits.size();
    CXXGlobalInits.push_back(0);
  }
  
  // If the value has already been used, add it directly to the
  // DeferredDeclsToEmit list.
  StringRef MangledName = getMangledName(GD);
  if (GetGlobalValue(MangledName))
    DeferredDeclsToEmit.push_back(GD);
  else {
    // Otherwise, remember that we saw a deferred decl with this name.  The
    // first use of the mangled name will cause it to move into
    // DeferredDeclsToEmit.
    DeferredDecls[MangledName] = GD;
  }
}

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 (CodeGenOpts.OptimizationLevel == 0 && 
        !Function->hasAttr<AlwaysInlineAttr>() &&
        getFunctionLinkage(Function) 
                                  == llvm::Function::AvailableExternallyLinkage)
      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);
  
  assert(0 && "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.count(Entry)) {
      const FunctionDecl *FD = cast_or_null<FunctionDecl>(D.getDecl());
      if (FD && !FD->hasAttr<WeakAttr>())
        Entry->setLinkage(llvm::Function::ExternalLinkage);

      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 (getLangOptions().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->getPreviousDeclaration();
    } 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);
}

static bool DeclIsConstantGlobal(ASTContext &Context, const VarDecl *D,
                                 bool ConstantInit) {
  if (!D->getType().isConstant(Context) && !D->getType()->isReferenceType())
    return false;
  
  if (Context.getLangOptions().CPlusPlus) {
    if (const RecordType *Record 
          = Context.getBaseElementType(D->getType())->getAs<RecordType>())
      return ConstantInit && 
             cast<CXXRecordDecl>(Record->getDecl())->isPOD() &&
             !cast<CXXRecordDecl>(Record->getDecl())->hasMutableFields();
  }
  
  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>())