CodeGenModule.cpp

    
  case TSK_ExplicitInstantiationDeclaration:
    // FIXME: Use available_externally linkage. However, this currently
    // breaks LLVM's build due to undefined symbols.
    //   return llvm::GlobalVariable::AvailableExternallyLinkage;
    return llvm::GlobalVariable::WeakODRLinkage;
  }
  
  // Silence GCC warning.
  return llvm::GlobalVariable::WeakODRLinkage;
}

static CodeGenModule::GVALinkage
GetLinkageForVariable(ASTContext &Context, const VarDecl *VD) {
  // If this is a static data member, compute the kind of template
  // specialization. Otherwise, this variable is not part of a
  // template.
  TemplateSpecializationKind TSK = TSK_Undeclared;
  if (VD->isStaticDataMember())
    TSK = VD->getTemplateSpecializationKind();

  Linkage L = VD->getLinkage();
  if (L == ExternalLinkage && Context.getLangOptions().CPlusPlus &&
      VD->getType()->getLinkage() == UniqueExternalLinkage)
    L = UniqueExternalLinkage;

  switch (L) {
  case NoLinkage:
  case InternalLinkage:
  case UniqueExternalLinkage:
    return CodeGenModule::GVA_Internal;

  case ExternalLinkage:
    switch (TSK) {
    case TSK_Undeclared:
    case TSK_ExplicitSpecialization:
      return CodeGenModule::GVA_StrongExternal;

    case TSK_ExplicitInstantiationDeclaration:
      llvm_unreachable("Variable should not be instantiated");
      // Fall through to treat this like any other instantiation.
        
    case TSK_ExplicitInstantiationDefinition:
      return CodeGenModule::GVA_ExplicitTemplateInstantiation;

    case TSK_ImplicitInstantiation:
      return CodeGenModule::GVA_TemplateInstantiation;      
    }
  }

  return CodeGenModule::GVA_StrongExternal;
}

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

void CodeGenModule::EmitGlobalVarDefinition(const VarDecl *D) {
  llvm::Constant *Init = 0;
  QualType ASTTy = D->getType();
  bool NonConstInit = false;

  const Expr *InitExpr = D->getAnyInitializer();
  
  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 {
    Init = EmitConstantExpr(InitExpr, D->getType());

    if (!Init) {
      QualType T = InitExpr->getType();
      if (getLangOptions().CPlusPlus) {
        EmitCXXGlobalVarDeclInitFunc(D);
        Init = EmitNullConstant(T);
        NonConstInit = true;
      } else {
        ErrorUnsupported(D, "static initializer");
        Init = llvm::UndefValue::get(getTypes().ConvertType(T));
      }
    }
  }

  const 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() != ASTTy.getAddressSpace()) {

    // Move the old entry aside so that we'll create a new one.
    Entry->setName(llvm::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 (const AnnotateAttr *AA = D->getAttr<AnnotateAttr>()) {
    SourceManager &SM = Context.getSourceManager();
    AddAnnotation(EmitAnnotateAttr(GV, AA,
                              SM.getInstantiationLineNumber(D->getLocation())));
  }

  GV->setInitializer(Init);

  // If it is safe to mark the global 'constant', do so now.
  GV->setConstant(false);
  if (!NonConstInit && DeclIsConstantGlobal(Context, D))
    GV->setConstant(true);

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

  // Set the llvm linkage type as appropriate.
  GVALinkage Linkage = GetLinkageForVariable(getContext(), D);
  if (Linkage == GVA_Internal)
    GV->setLinkage(llvm::Function::InternalLinkage);
  else if (D->hasAttr<DLLImportAttr>())
    GV->setLinkage(llvm::Function::DLLImportLinkage);
  else if (D->hasAttr<DLLExportAttr>())
    GV->setLinkage(llvm::Function::DLLExportLinkage);
  else if (D->hasAttr<WeakAttr>()) {
    if (GV->isConstant())
      GV->setLinkage(llvm::GlobalVariable::WeakODRLinkage);
    else
      GV->setLinkage(llvm::GlobalVariable::WeakAnyLinkage);
  } else if (Linkage == GVA_TemplateInstantiation ||
             Linkage == GVA_ExplicitTemplateInstantiation)
    // FIXME: It seems like we can provide more specific linkage here
    // (LinkOnceODR, WeakODR).
    GV->setLinkage(llvm::GlobalVariable::WeakAnyLinkage);   
  else if (!getLangOptions().CPlusPlus && !CodeGenOpts.NoCommon &&
           !D->hasExternalStorage() && !D->getInit() &&
           !D->getAttr<SectionAttr>()) {
    GV->setLinkage(llvm::GlobalVariable::CommonLinkage);
    // common vars aren't constant even if declared const.
    GV->setConstant(false);
  } else
    GV->setLinkage(llvm::GlobalVariable::ExternalLinkage);

  SetCommonAttributes(D, GV);

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

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

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

  for (llvm::Value::use_iterator UI = OldFn->use_begin(), E = OldFn->use_end();
       UI != E; ) {
    // TODO: Do invokes ever occur in C code?  If so, we should handle them too.
    unsigned OpNo = UI.getOperandNo();
    llvm::CallInst *CI = dyn_cast<llvm::CallInst>(*UI++);
    if (!CI || OpNo != 0) continue;

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

    // If the function was passed too few arguments, don't transform.  If extra
    // arguments were passed, we silently drop them.  If any of the types
    // mismatch, we don't transform.
    unsigned ArgNo = 0;
    bool DontTransform = false;
    for (llvm::Function::arg_iterator AI = NewFn->arg_begin(),
         E = NewFn->arg_end(); AI != E; ++AI, ++ArgNo) {
      if (CI->getNumOperands()-1 == ArgNo ||
          CI->getOperand(ArgNo+1)->getType() != AI->getType()) {
        DontTransform = true;
        break;
      }
    }
    if (DontTransform)
      continue;

    // Okay, we can transform this.  Create the new call instruction and copy
    // over the required information.
    ArgList.append(CI->op_begin()+1, CI->op_begin()+1+ArgNo);
    llvm::CallInst *NewCall = llvm::CallInst::Create(NewFn, ArgList.begin(),
                                                     ArgList.end(), "", CI);
    ArgList.clear();
    if (!NewCall->getType()->isVoidTy())
      NewCall->takeName(CI);
    NewCall->setAttributes(CI->getAttributes());
    NewCall->setCallingConv(CI->getCallingConv());

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

    // Copy any custom metadata attached with CI.
    if (llvm::MDNode *DbgNode = CI->getDbgMetadata())
      NewCall->setDbgMetadata(DbgNode);
    CI->eraseFromParent();
  }
}


void CodeGenModule::EmitGlobalFunctionDefinition(GlobalDecl GD) {
  const FunctionDecl *D = cast<FunctionDecl>(GD.getDecl());
  const llvm::FunctionType *Ty = getTypes().GetFunctionType(GD);
  getMangleContext().mangleInitDiscriminator();
  // 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(llvm::StringRef());
    llvm::Function *NewFn = cast<llvm::Function>(GetAddrOfFunction(GD, Ty));

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

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

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

    Entry = NewFn;
  }

  llvm::Function *Fn = cast<llvm::Function>(Entry);

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

  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());
}

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

  MangleBuffer MangledName;
  getMangledName(MangledName, GD);

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

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

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

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

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

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

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

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

  SetCommonAttributes(D, GA);
}

/// getBuiltinLibFunction - Given a builtin id for a function like
/// "__builtin_fabsf", return a Function* for "fabsf".
llvm::Value *CodeGenModule::getBuiltinLibFunction(const FunctionDecl *FD,
                                                  unsigned BuiltinID) {
  assert((Context.BuiltinInfo.isLibFunction(BuiltinID) ||
          Context.BuiltinInfo.isPredefinedLibFunction(BuiltinID)) &&
         "isn't a lib fn");

  // Get the name, skip over the __builtin_ prefix (if necessary).
  const char *Name = Context.BuiltinInfo.GetName(BuiltinID);
  if (Context.BuiltinInfo.isLibFunction(BuiltinID))
    Name += 10;

  const llvm::FunctionType *Ty =
    cast<llvm::FunctionType>(getTypes().ConvertType(FD->getType()));

  return GetOrCreateLLVMFunction(Name, Ty, GlobalDecl(FD));
}

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

llvm::Function *CodeGenModule::getMemCpyFn() {
  if (MemCpyFn) return MemCpyFn;
  const llvm::Type *IntPtr = TheTargetData.getIntPtrType(VMContext);
  return MemCpyFn = getIntrinsic(llvm::Intrinsic::memcpy, &IntPtr, 1);
}

llvm::Function *CodeGenModule::getMemMoveFn() {
  if (MemMoveFn) return MemMoveFn;
  const llvm::Type *IntPtr = TheTargetData.getIntPtrType(VMContext);
  return MemMoveFn = getIntrinsic(llvm::Intrinsic::memmove, &IntPtr, 1);
}

llvm::Function *CodeGenModule::getMemSetFn() {
  if (MemSetFn) return MemSetFn;
  const llvm::Type *IntPtr = TheTargetData.getIntPtrType(VMContext);
  return MemSetFn = getIntrinsic(llvm::Intrinsic::memset, &IntPtr, 1);
}

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

  // Check for simple case.
  if (!Literal->containsNonAsciiOrNull()) {
    StringLength = NumBytes;
    return Map.GetOrCreateValue(llvm::StringRef(Literal->getStrData(),
                                                StringLength));
  }

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

  ConversionResult Result = ConvertUTF8toUTF16(&FromPtr, FromPtr + NumBytes,
                                               &ToPtr, ToPtr + NumBytes,
                                               strictConversion);

  // Check for conversion failure.
  if (Result != conversionOK) {
    // FIXME: Have Sema::CheckObjCString() validate the UTF-8 string and remove
    // this duplicate code.
    assert(Result == sourceIllegal && "UTF-8 to UTF-16 conversion failed");
    StringLength = NumBytes;
    return Map.GetOrCreateValue(llvm::StringRef(Literal->getStrData(),
                                                StringLength));
  }

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

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

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

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

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

  llvm::Constant *Zero =
      llvm::Constant::getNullValue(llvm::Type::getInt32Ty(VMContext));
  llvm::Constant *Zeros[] = { Zero, Zero };

  // If we don't already have it, get __CFConstantStringClassReference.
  if (!CFConstantStringClassRef) {
    const llvm::Type *Ty = getTypes().ConvertType(getContext().IntTy);
    Ty = llvm::ArrayType::get(Ty, 0);
    llvm::Constant *GV = CreateRuntimeVariable(Ty,
                                           "__CFConstantStringClassReference");
    // Decay array -> ptr
    CFConstantStringClassRef =
      llvm::ConstantExpr::getGetElementPtr(GV, Zeros, 2);
  }

  QualType CFTy = getContext().getCFConstantStringType();

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

  std::vector<llvm::Constant*> Fields(4);

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

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

  // String pointer.
  llvm::Constant *C = llvm::ConstantArray::get(VMContext, Entry.getKey().str());

  llvm::GlobalValue::LinkageTypes Linkage;
  bool isConstant;
  if (isUTF16) {
    // FIXME: why do utf strings get "_" labels instead of "L" labels?
    Linkage = llvm::GlobalValue::InternalLinkage;
    // Note: -fwritable-strings doesn't make unicode CFStrings writable, but
    // does make plain ascii ones writable.
    isConstant = true;
  } else {
    Linkage = llvm::GlobalValue::PrivateLinkage;
    isConstant = !Features.WritableStrings;
  }
  
  llvm::GlobalVariable *GV =
    new llvm::GlobalVariable(getModule(), C->getType(), isConstant, Linkage, C,
                             ".str");
  if (isUTF16) {
    CharUnits Align = getContext().getTypeAlignInChars(getContext().ShortTy);
    GV->setAlignment(Align.getQuantity());
  }
  Fields[2] = llvm::ConstantExpr::getGetElementPtr(GV, Zeros, 2);

  // String length.
  Ty = getTypes().ConvertType(getContext().LongTy);
  Fields[3] = llvm::ConstantInt::get(Ty, StringLength);

  // The struct.
  C = llvm::ConstantStruct::get(STy, Fields);
  GV = new llvm::GlobalVariable(getModule(), C->getType(), true,
                                llvm::GlobalVariable::PrivateLinkage, C,
                                "_unnamed_cfstring_");
  if (const char *Sect = getContext().Target.getCFStringSection())
    GV->setSection(Sect);
  Entry.setValue(GV);

  return GV;
}

/// GetStringForStringLiteral - Return the appropriate bytes for a
/// string literal, properly padded to match the literal type.
std::string CodeGenModule::GetStringForStringLiteral(const StringLiteral *E) {
  const char *StrData = E->getStrData();
  unsigned Len = E->getByteLength();

  const ConstantArrayType *CAT =
    getContext().getAsConstantArrayType(E->getType());
  assert(CAT && "String isn't pointer or array!");

  // Resize the string to the right size.
  std::string Str(StrData, StrData+Len);
  uint64_t RealLen = CAT->getSize().getZExtValue();

  if (E->isWide())
    RealLen *= getContext().Target.getWCharWidth()/8;

  Str.resize(RealLen, '\0');

  return Str;
}

/// GetAddrOfConstantStringFromLiteral - Return a pointer to a
/// constant array for the given string literal.
llvm::Constant *
CodeGenModule::GetAddrOfConstantStringFromLiteral(const StringLiteral *S) {
  // FIXME: This can be more efficient.
  // FIXME: We shouldn't need to bitcast the constant in the wide string case.
  llvm::Constant *C = GetAddrOfConstantString(GetStringForStringLiteral(S));
  if (S->isWide()) {
    llvm::Type *DestTy =
        llvm::PointerType::getUnqual(getTypes().ConvertType(S->getType()));
    C = llvm::ConstantExpr::getBitCast(C, DestTy);
  }
  return C;
}

/// GetAddrOfConstantStringFromObjCEncode - Return a pointer to a constant
/// array for the given ObjCEncodeExpr node.
llvm::Constant *
CodeGenModule::GetAddrOfConstantStringFromObjCEncode(const ObjCEncodeExpr *E) {
  std::string Str;
  getContext().getObjCEncodingForType(E->getEncodedType(), Str);

  return GetAddrOfConstantCString(Str);
}


/// GenerateWritableString -- Creates storage for a string literal.
static llvm::Constant *GenerateStringLiteral(const std::string &str,
                                             bool constant,
                                             CodeGenModule &CGM,
                                             const char *GlobalName) {
  // Create Constant for this string literal. Don't add a '\0'.
  llvm::Constant *C =
      llvm::ConstantArray::get(CGM.getLLVMContext(), str, false);

  // Create a global variable for this string
  return new llvm::GlobalVariable(CGM.getModule(), C->getType(), constant,
                                  llvm::GlobalValue::PrivateLinkage,
                                  C, GlobalName);
}

/// GetAddrOfConstantString - Returns a pointer to a character array
/// containing the literal. This contents are exactly that of the
/// given string, i.e. it will not be null terminated automatically;
/// see GetAddrOfConstantCString. Note that whether the result is
/// actually a pointer to an LLVM constant depends on
/// Feature.WriteableStrings.
///
/// The result has pointer to array type.
llvm::Constant *CodeGenModule::GetAddrOfConstantString(const std::string &str,
                                                       const char *GlobalName) {
  bool IsConstant = !Features.WritableStrings;

  // Get the default prefix if a name wasn't specified.
  if (!GlobalName)
    GlobalName = ".str";

  // Don't share any string literals if strings aren't constant.
  if (!IsConstant)
    return GenerateStringLiteral(str, false, *this, GlobalName);

  llvm::StringMapEntry<llvm::Constant *> &Entry =
    ConstantStringMap.GetOrCreateValue(&str[0], &str[str.length()]);

  if (Entry.getValue())
    return Entry.getValue();

  // Create a global variable for this.
  llvm::Constant *C = GenerateStringLiteral(str, true, *this, GlobalName);
  Entry.setValue(C);
  return C;
}

/// GetAddrOfConstantCString - Returns a pointer to a character
/// array containing the literal and a terminating '\-'
/// character. The result has pointer to array type.
llvm::Constant *CodeGenModule::GetAddrOfConstantCString(const std::string &str,
                                                        const char *GlobalName){
  return GetAddrOfConstantString(str + '\0', GlobalName);
}

/// EmitObjCPropertyImplementations - Emit information for synthesized
/// properties for an implementation.
void CodeGenModule::EmitObjCPropertyImplementations(const
                                                    ObjCImplementationDecl *D) {
  for (ObjCImplementationDecl::propimpl_iterator
         i = D->propimpl_begin(), e = D->propimpl_end(); i != e; ++i) {
    ObjCPropertyImplDecl *PID = *i;

    // Dynamic is just for type-checking.
    if (PID->getPropertyImplementation() == ObjCPropertyImplDecl::Synthesize) {
      ObjCPropertyDecl *PD = PID->getPropertyDecl();

      // Determine which methods need to be implemented, some may have
      // been overridden. Note that ::isSynthesized is not the method
      // we want, that just indicates if the decl came from a
      // property. What we want to know is if the method is defined in
      // this implementation.
      if (!D->getInstanceMethod(PD->getGetterName()))
        CodeGenFunction(*this).GenerateObjCGetter(
                                 const_cast<ObjCImplementationDecl *>(D), PID);
      if (!PD->isReadOnly() &&
          !D->getInstanceMethod(PD->getSetterName()))
        CodeGenFunction(*this).GenerateObjCSetter(
                                 const_cast<ObjCImplementationDecl *>(D), PID);
    }
  }
}

/// EmitNamespace - Emit all declarations in a namespace.
void CodeGenModule::EmitNamespace(const NamespaceDecl *ND) {
  for (RecordDecl::decl_iterator I = ND->decls_begin(), E = ND->decls_end();
       I != E; ++I)
    EmitTopLevelDecl(*I);
}

// EmitLinkageSpec - Emit all declarations in a linkage spec.
void CodeGenModule::EmitLinkageSpec(const LinkageSpecDecl *LSD) {
  if (LSD->getLanguage() != LinkageSpecDecl::lang_c &&
      LSD->getLanguage() != LinkageSpecDecl::lang_cxx) {
    ErrorUnsupported(LSD, "linkage spec");
    return;
  }

  for (RecordDecl::decl_iterator I = LSD->decls_begin(), E = LSD->decls_end();
       I != E; ++I)
    EmitTopLevelDecl(*I);
}

/// EmitTopLevelDecl - Emit code for a single top level declaration.
void CodeGenModule::EmitTopLevelDecl(Decl *D) {
  // If an error has occurred, stop code generation, but continue
  // parsing and semantic analysis (to ensure all warnings and errors
  // are emitted).
  if (Diags.hasErrorOccurred())
    return;

  // Ignore dependent declarations.
  if (D->getDeclContext() && D->getDeclContext()->isDependentContext())
    return;

  switch (D->getKind()) {
  case Decl::CXXConversion:
  case Decl::CXXMethod:
  case Decl::Function:
    // Skip function templates
    if (cast<FunctionDecl>(D)->getDescribedFunctionTemplate())
      return;

    EmitGlobal(cast<FunctionDecl>(D));
    break;
      
  case Decl::Var:
    EmitGlobal(cast<VarDecl>(D));
    break;

  // C++ Decls
  case Decl::Namespace:
    EmitNamespace(cast<NamespaceDecl>(D));
    break;
    // No code generation needed.
  case Decl::UsingShadow:
  case Decl::Using:
  case Decl::UsingDirective:
  case Decl::ClassTemplate:
  case Decl::FunctionTemplate:
  case Decl::NamespaceAlias:
    break;
  case Decl::CXXConstructor:
    // Skip function templates
    if (cast<FunctionDecl>(D)->getDescribedFunctionTemplate())
      return;
      
    EmitCXXConstructors(cast<CXXConstructorDecl>(D));
    break;
  case Decl::CXXDestructor:
    EmitCXXDestructors(cast<CXXDestructorDecl>(D));
    break;

  case Decl::StaticAssert:
    // Nothing to do.
    break;

  // Objective-C Decls

  // Forward declarations, no (immediate) code generation.
  case Decl::ObjCClass:
  case Decl::ObjCForwardProtocol:
  case Decl::ObjCCategory:
  case Decl::ObjCInterface:
    break;

  case Decl::ObjCProtocol:
    Runtime->GenerateProtocol(cast<ObjCProtocolDecl>(D));
    break;

  case Decl::ObjCCategoryImpl:
    // Categories have properties but don't support synthesize so we
    // can ignore them here.
    Runtime->GenerateCategory(cast<ObjCCategoryImplDecl>(D));
    break;

  case Decl::ObjCImplementation: {
    ObjCImplementationDecl *OMD = cast<ObjCImplementationDecl>(D);
    EmitObjCPropertyImplementations(OMD);
    Runtime->GenerateClass(OMD);
    break;
  }
  case Decl::ObjCMethod: {
    ObjCMethodDecl *OMD = cast<ObjCMethodDecl>(D);
    // If this is not a prototype, emit the body.
    if (OMD->getBody())
      CodeGenFunction(*this).GenerateObjCMethod(OMD);
    break;
  }
  case Decl::ObjCCompatibleAlias:
    // compatibility-alias is a directive and has no code gen.
    break;

  case Decl::LinkageSpec:
    EmitLinkageSpec(cast<LinkageSpecDecl>(D));
    break;

  case Decl::FileScopeAsm: {
    FileScopeAsmDecl *AD = cast<FileScopeAsmDecl>(D);
    llvm::StringRef AsmString = AD->getAsmString()->getString();

    const std::string &S = getModule().getModuleInlineAsm();
    if (S.empty())
      getModule().setModuleInlineAsm(AsmString);
    else
      getModule().setModuleInlineAsm(S + '\n' + AsmString.str());
    break;
  }

  default:
    // Make sure we handled everything we should, every other kind is a
    // non-top-level decl.  FIXME: Would be nice to have an isTopLevelDeclKind
    // function. Need to recode Decl::Kind to do that easily.
    assert(isa<TypeDecl>(D) && "Unsupported decl kind");
  }
}