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 "Mangle.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/RecordLayout.h"
#include "clang/Basic/Builtins.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/TargetData.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/ErrorHandling.h"
using namespace clang;
using namespace CodeGen;

static CGCXXABI &createCXXABI(CodeGenModule &CGM) {
  switch (CGM.getContext().Target.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)
  : BlockModule(C, M, TD, Types, *this), 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),
    TBAA(0),
    VTables(*this), Runtime(0),
    CFConstantStringClassRef(0), ConstantStringClassRef(0),
    VMContext(M.getContext()),
    NSConcreteGlobalBlockDecl(0), NSConcreteStackBlockDecl(0),
    NSConcreteGlobalBlock(0), NSConcreteStackBlock(0),
    BlockObjectAssignDecl(0), BlockObjectDisposeDecl(0),
    BlockObjectAssign(0), BlockObjectDispose(0){

  if (!Features.ObjC1)
    Runtime = 0;
  else if (!Features.NeXTRuntime)
    Runtime = CreateGNUObjCRuntime(*this);
  else if (Features.ObjCNonFragileABI)
    Runtime = CreateMacNonFragileABIObjCRuntime(*this);
  else
    Runtime = CreateMacObjCRuntime(*this);

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

  // If debug info generation is enabled, create the CGDebugInfo object.
  DebugInfo = CodeGenOpts.DebugInfo ? new CGDebugInfo(*this) : 0;
}

CodeGenModule::~CodeGenModule() {
  delete Runtime;
  delete &ABI;
  delete TBAA;
  delete DebugInfo;
}

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

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

  SimplifyPersonality();

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

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().Target.getTriple().getOS() == llvm::Triple::Darwin;
}

/// 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;
}

static llvm::GlobalValue::VisibilityTypes GetLLVMVisibility(Visibility V) {
  switch (V) {
  case DefaultVisibility:   return llvm::GlobalValue::DefaultVisibility;
  case HiddenVisibility:    return llvm::GlobalValue::HiddenVisibility;
  case ProtectedVisibility: return llvm::GlobalValue::ProtectedVisibility;
  }
  llvm_unreachable("unknown visibility!");
  return llvm::GlobalValue::DefaultVisibility;
}


void CodeGenModule::setGlobalVisibility(llvm::GlobalValue *GV,
                                        const NamedDecl *D,
                                        bool IsForDefinition) 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() ||
      (IsForDefinition && !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,
                                      bool IsForRTTI,
                                      bool IsForDefinition) const {
  setGlobalVisibility(GV, RD, IsForDefinition);

  if (!CodeGenOpts.HiddenWeakVTables)
    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::WeakODRLinkage ||
      GV->getVisibility() != llvm::GlobalVariable::DefaultVisibility)
    return;

  // Don't override an explicit visibility attribute.
  if (RD->hasAttr<VisibilityAttr>())
    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 (!IsForRTTI || Features.RTTI)
    if (Context.getKeyFunction(RD))
      return;

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

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

  llvm::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;
  if (const CXXConstructorDecl *D = dyn_cast<CXXConstructorDecl>(ND))
    getCXXABI().getMangleContext().mangleCXXCtor(D, GD.getCtorType(), Buffer);
  else if (const CXXDestructorDecl *D = dyn_cast<CXXDestructorDecl>(ND))
    getCXXABI().getMangleContext().mangleCXXDtor(D, GD.getDtorType(), Buffer);
  else if (const BlockDecl *BD = dyn_cast<BlockDecl>(ND))
    getCXXABI().getMangleContext().mangleBlock(GD, BD, Buffer);
  else
    getCXXABI().getMangleContext().mangleName(ND, Buffer);

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

void CodeGenModule::getMangledName(GlobalDecl GD, MangleBuffer &Buffer,
                                   const BlockDecl *BD) {
  getCXXABI().getMangleContext().mangleBlock(GD, BD, Buffer.getBuffer());
}

llvm::GlobalValue *CodeGenModule::GetGlobalValue(llvm::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(llvm::Type::getVoidTy(VMContext),
                            std::vector<const llvm::Type*>(),
                            false);
  llvm::Type *CtorPFTy = llvm::PointerType::getUnqual(CtorFTy);

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

void CodeGenModule::EmitAnnotations() {
  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(TheModule, Array->getType(), false,
                           llvm::GlobalValue::AppendingLinkage, Array,
                           "llvm.global.annotations");
  gv->setSection("llvm.metadata");
}

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 llvm::Function::LinkOnceODRLinkage;
  
  // 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 llvm::Function::WeakODRLinkage;
  
  // 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 (!Features.Exceptions && !Features.ObjCNonFragileABI)
    F->addFnAttr(llvm::Attribute::NoUnwind);

  if (D->hasAttr<AlwaysInlineAttr>())
    F->addFnAttr(llvm::Attribute::AlwaysInline);

  if (D->hasAttr<NakedAttr>())
    F->addFnAttr(llvm::Attribute::Naked);

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

  if (Features.getStackProtectorMode() == LangOptions::SSPOn)
    F->addFnAttr(llvm::Attribute::StackProtect);
  else if (Features.getStackProtectorMode() == 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 (isa<NamedDecl>(D))
    setGlobalVisibility(GV, cast<NamedDecl>(D), /*ForDef*/ true);
  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) {
  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->hasAttr<WeakImportAttr>()) {
    // "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;

  const 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.
    llvm::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);
  }
}

/// EmitAnnotateAttr - Generate the llvm::ConstantStruct which contains the
/// annotation information for a given GlobalValue.  The annotation struct is
/// {i8 *, i8 *, i8 *, i32}.  The first field is a constant expression, the
/// GlobalValue being annotated.  The second field is the constant string
/// created from the AnnotateAttr's annotation.  The third field is a constant
/// string containing the name of the translation unit.  The fourth field is
/// the line number in the file of the annotated value declaration.
///
/// FIXME: this does not unique the annotation string constants, as llvm-gcc
///        appears to.
///
llvm::Constant *CodeGenModule::EmitAnnotateAttr(llvm::GlobalValue *GV,
                                                const AnnotateAttr *AA,
                                                unsigned LineNo) {
  llvm::Module *M = &getModule();

  // get [N x i8] constants for the annotation string, and the filename string
  // which are the 2nd and 3rd elements of the global annotation structure.
  const llvm::Type *SBP = llvm::Type::getInt8PtrTy(VMContext);
  llvm::Constant *anno = llvm::ConstantArray::get(VMContext,
                                                  AA->getAnnotation(), true);
  llvm::Constant *unit = llvm::ConstantArray::get(VMContext,
                                                  M->getModuleIdentifier(),
                                                  true);

  // Get the two global values corresponding to the ConstantArrays we just
  // created to hold the bytes of the strings.
  llvm::GlobalValue *annoGV =
    new llvm::GlobalVariable(*M, anno->getType(), false,
                             llvm::GlobalValue::PrivateLinkage, anno,
                             GV->getName());
  // translation unit name string, emitted into the llvm.metadata section.
  llvm::GlobalValue *unitGV =
    new llvm::GlobalVariable(*M, unit->getType(), false,
                             llvm::GlobalValue::PrivateLinkage, unit,
                             ".str");

  // Create the ConstantStruct for the global annotation.
  llvm::Constant *Fields[4] = {
    llvm::ConstantExpr::getBitCast(GV, SBP),
    llvm::ConstantExpr::getBitCast(annoGV, SBP),
    llvm::ConstantExpr::getBitCast(unitGV, SBP),
    llvm::ConstantInt::get(llvm::Type::getInt32Ty(VMContext), LineNo)
  };
  return llvm::ConstantStruct::get(VMContext, Fields, 4, false);
}

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?");

  const 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());
  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)) {
    if (FD->getIdentifier()) {
      llvm::StringRef Name = FD->getName();
      if (Name == "_Block_object_assign") {
        BlockObjectAssignDecl = FD;
      } else if (Name == "_Block_object_dispose") {
        BlockObjectDisposeDecl = FD;
      }
    }

    // Forward declarations are emitted lazily on first use.
    if (!FD->isThisDeclarationADefinition())
      return;
  } else {
    const VarDecl *VD = cast<VarDecl>(Global);
    assert(VD->isFileVarDecl() && "Cannot emit local var decl as global.");

    if (VD->getIdentifier()) {
      llvm::StringRef Name = VD->getName();
      if (Name == "_NSConcreteGlobalBlock") {
        NSConcreteGlobalBlockDecl = VD;
      } else if (Name == "_NSConcreteStackBlock") {
        NSConcreteStackBlockDecl = VD;
      }
    }


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

      if (const CXXConstructorDecl *CD = dyn_cast<CXXConstructorDecl>(Method))
        return EmitCXXConstructor(CD, GD.getCtorType());
  
      if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(Method))
        return EmitCXXDestructor(DD, GD.getDtorType());
    }

    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(llvm::StringRef MangledName,
                                       const llvm::Type *Ty,
                                       GlobalDecl D) {
  // 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.
    const llvm::Type *PTy = llvm::PointerType::getUnqual(Ty);
    return llvm::ConstantExpr::getBitCast(Entry, PTy);
  }

  // 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;

  const llvm::FunctionType *FTy;
  if (isa<llvm::FunctionType>(Ty)) {
    FTy = cast<llvm::FunctionType>(Ty);
  } else {
    FTy = llvm::FunctionType::get(llvm::Type::getVoidTy(VMContext),
                                  std::vector<const llvm::Type*>(), 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);

  // 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.
  } 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()) {
          assert(FD->isUsed() && "Sema didn't mark implicit function as used!");
          DeferredDeclsToEmit.push_back(D);
          break;
        } else if (FD->isThisDeclarationADefinition()) {
          DeferredDeclsToEmit.push_back(D);
          break;
        }
      }
      FD = FD->getPreviousDeclaration();
    } while (FD);
  }

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

  const 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,
                                                 const llvm::Type *Ty) {
  // If there was no specific requested type, just convert it now.
  if (!Ty)
    Ty = getTypes().ConvertType(cast<ValueDecl>(GD.getDecl())->getType());
  
  llvm::StringRef MangledName = getMangledName(GD);
  return GetOrCreateLLVMFunction(MangledName, Ty, GD);
}

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

static bool DeclIsConstantGlobal(ASTContext &Context, const VarDecl *D) {
  if (!D->getType().isConstant(Context) && !D->getType()->isReferenceType())
    return false;
  if (Context.getLangOptions().CPlusPlus &&
      Context.getBaseElementType(D->getType())->getAs<RecordType>()) {
    // FIXME: We should do something fancier here!
    return false;
  }
  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(llvm::StringRef MangledName,
                                     const llvm::PointerType *Ty,
                                     const VarDecl *D) {
  // 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 (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(DeclIsConstantGlobal(Context, D));

    // Set linkage and visibility in case we never see a definition.
    NamedDecl::LinkageInfo LV = D->getLinkageAndVisibility();
    if (LV.linkage() != ExternalLinkage) {
      GV->setLinkage(llvm::GlobalValue::InternalLinkage);
    } else {
      if (D->hasAttr<DLLImportAttr>())
        GV->setLinkage(llvm::GlobalValue::DLLImportLinkage);
      else if (D->hasAttr<WeakAttr>() || D->hasAttr<WeakImportAttr>())
        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;
}


/// 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,
                                                  const llvm::Type *Ty) {
  assert(D->hasGlobalStorage() && "Not a global variable");
  QualType ASTTy = D->getType();
  if (Ty == 0)
    Ty = getTypes().ConvertTypeForMem(ASTTy);

  const llvm::PointerType *PTy =
    llvm::PointerType::get(Ty, ASTTy.getAddressSpace());

  llvm::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(const llvm::Type *Ty,
                                     llvm::StringRef Name) {
  return GetOrCreateLLVMGlobal(Name, llvm::PointerType::getUnqual(Ty), 0);
}

void CodeGenModule::EmitTentativeDefinition(const VarDecl *D) {