CodeGen/CodeGenModule.cpp - platform/external/clang - Gitiles

 //===--- 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 "CodeGenFunction.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Decl.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/TargetInfo.h"
 #include "llvm/Constants.h"
 #include "llvm/DerivedTypes.h"
 #include "llvm/Module.h"
 #include "llvm/Intrinsics.h"
 #include <algorithm>
 using namespace clang;
 using namespace CodeGen;


 CodeGenModule::CodeGenModule(ASTContext &C, const LangOptions &LO,
                              llvm::Module &M, const llvm::TargetData &TD,
                              Diagnostic &diags)
   : Context(C), Features(LO), TheModule(M), TheTargetData(TD), Diags(diags),
     Types(C, M, TD), MemCpyFn(0), MemSetFn(0), CFConstantStringClassRef(0) {
   //TODO: Make this selectable at runtime
   Runtime = CreateObjCRuntime(M);
 }

 CodeGenModule::~CodeGenModule() {
   delete Runtime;
 }

 /// WarnUnsupported - Print out a warning that codegen doesn't support the
 /// specified stmt yet.
 void CodeGenModule::WarnUnsupported(const Stmt *S, const char *Type) {
   unsigned DiagID = getDiags().getCustomDiagID(Diagnostic::Warning,
                                                "cannot codegen this %0 yet");
   SourceRange Range = S->getSourceRange();
   std::string Msg = Type;
   getDiags().Report(Context.getFullLoc(S->getLocStart()), DiagID,
                     &Msg, 1, &Range, 1);
 }

 /// WarnUnsupported - Print out a warning that codegen doesn't support the
 /// specified decl yet.
 void CodeGenModule::WarnUnsupported(const Decl *D, const char *Type) {
   unsigned DiagID = getDiags().getCustomDiagID(Diagnostic::Warning,
                                                "cannot codegen this %0 yet");
   std::string Msg = Type;
   getDiags().Report(Context.getFullLoc(D->getLocation()), DiagID,
                     &Msg, 1);
 }

 /// ReplaceMapValuesWith - This is a really slow and bad function that
 /// searches for any entries in GlobalDeclMap that point to OldVal, changing
 /// them to point to NewVal.  This is badbadbad, FIXME!
 void CodeGenModule::ReplaceMapValuesWith(llvm::Constant *OldVal,
                                          llvm::Constant *NewVal) {
   for (llvm::DenseMap<const Decl*, llvm::Constant*>::iterator
        I = GlobalDeclMap.begin(), E = GlobalDeclMap.end(); I != E; ++I)
     if (I->second == OldVal) I->second = NewVal;
 }


 llvm::Constant *CodeGenModule::GetAddrOfFunctionDecl(const FunctionDecl *D,
                                                      bool isDefinition) {
   // See if it is already in the map.  If so, just return it.
   llvm::Constant *&Entry = GlobalDeclMap[D];
   if (Entry) return Entry;

   const llvm::Type *Ty = getTypes().ConvertType(D->getType());

   // Check to see if the function already exists.
   llvm::Function *F = getModule().getFunction(D->getName());
   const llvm::FunctionType *FTy = cast<llvm::FunctionType>(Ty);

   // If it doesn't already exist, just create and return an entry.
   if (F == 0) {
     // FIXME: param attributes for sext/zext etc.
     return Entry = new llvm::Function(FTy, llvm::Function::ExternalLinkage,
                                       D->getName(), &getModule());
   }

   // If the pointer type matches, just return it.
   llvm::Type *PFTy = llvm::PointerType::getUnqual(Ty);
   if (PFTy == F->getType()) return Entry = F;

   // If this isn't a definition, just return it casted to the right type.
   if (!isDefinition)
     return Entry = llvm::ConstantExpr::getBitCast(F, PFTy);

   // Otherwise, we have a definition after a prototype with the wrong type.
   // 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)").  Start by
   // making a new function of the correct type, RAUW, then steal the name.
   llvm::Function *NewFn = new llvm::Function(FTy,
                                              llvm::Function::ExternalLinkage,
                                              "", &getModule());
   NewFn->takeName(F);

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

   // FIXME: Update the globaldeclmap for the previous decl of this name.  We
   // really want a way to walk all of these, but we don't have it yet.  This
   // is incredibly slow!
   ReplaceMapValuesWith(F, NewPtrForOldDecl);

   // Ok, delete the old function now, which is dead.
   assert(F->isDeclaration() && "Shouldn't replace non-declaration");
   F->eraseFromParent();

   // Return the new function which has the right type.
   return Entry = NewFn;
 }

 static bool IsZeroElementArray(const llvm::Type *Ty) {
   if (const llvm::ArrayType *ATy = dyn_cast<llvm::ArrayType>(Ty))
     return ATy->getNumElements() == 0;
   return false;
 }

 llvm::Constant *CodeGenModule::GetAddrOfGlobalVar(const VarDecl *D,
                                                   bool isDefinition) {
   assert(D->hasGlobalStorage() && "Not a global variable");

   // See if it is already in the map.
   llvm::Constant *&Entry = GlobalDeclMap[D];
   if (Entry) return Entry;

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

   // Check to see if the global already exists.
   llvm::GlobalVariable *GV = getModule().getGlobalVariable(D->getName(), true);

   // If it doesn't already exist, just create and return an entry.
   if (GV == 0) {
     return Entry = new llvm::GlobalVariable(Ty, false,
                                             llvm::GlobalValue::ExternalLinkage,
                                             0, D->getName(), &getModule(), 0,
                                             ASTTy.getAddressSpace());
   }

   // If the pointer type matches, just return it.
   llvm::Type *PTy = llvm::PointerType::getUnqual(Ty);
   if (PTy == GV->getType()) return Entry = GV;

   // If this isn't a definition, just return it casted to the right type.
   if (!isDefinition)
     return Entry = llvm::ConstantExpr::getBitCast(GV, PTy);


   // Otherwise, we have a definition after a prototype with the wrong type.
   // GV is the GlobalVariable* for the one with the wrong type, we must make a
   /// new GlobalVariable* and update everything that used GV (a declaration)
   // 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];").  Start by
   // making a new global of the correct type, RAUW, then steal the name.
   llvm::GlobalVariable *NewGV =
     new llvm::GlobalVariable(Ty, false, llvm::GlobalValue::ExternalLinkage,
                              0, D->getName(), &getModule(), 0,
                              ASTTy.getAddressSpace());
   NewGV->takeName(GV);

   // Replace uses of GV with the globalvalue we will endow with a body.
   llvm::Constant *NewPtrForOldDecl =
     llvm::ConstantExpr::getBitCast(NewGV, GV->getType());
   GV->replaceAllUsesWith(NewPtrForOldDecl);

   // FIXME: Update the globaldeclmap for the previous decl of this name.  We
   // really want a way to walk all of these, but we don't have it yet.  This
   // is incredibly slow!
   ReplaceMapValuesWith(GV, NewPtrForOldDecl);

   // Verify that GV was a declaration or something like x[] which turns into
   // [0 x type].
   assert((GV->isDeclaration() ||
           IsZeroElementArray(GV->getType()->getElementType())) &&
          "Shouldn't replace non-declaration");

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

   // Return the new global which has the right type.
   return Entry = NewGV;
 }


 void CodeGenModule::EmitFunction(const FunctionDecl *FD) {
   // If this is not a prototype, emit the body.
   if (FD->getBody())
     CodeGenFunction(*this).GenerateCode(FD);
 }

 llvm::Constant *CodeGenModule::EmitGlobalInit(const Expr *Expr) {
   return EmitConstantExpr(Expr);
 }

 void CodeGenModule::EmitGlobalVar(const FileVarDecl *D) {
   // If this is just a forward declaration of the variable, don't emit it now,
   // allow it to be emitted lazily on its first use.
   if (D->getStorageClass() == VarDecl::Extern && D->getInit() == 0)
     return;

   // Get the global, forcing it to be a direct reference.
   llvm::GlobalVariable *GV =
     cast<llvm::GlobalVariable>(GetAddrOfGlobalVar(D, true));

   // Convert the initializer, or use zero if appropriate.
   llvm::Constant *Init = 0;
   if (D->getInit() == 0) {
     Init = llvm::Constant::getNullValue(GV->getType()->getElementType());
   } else if (D->getType()->isIntegerType()) {
     llvm::APSInt Value(static_cast<uint32_t>(
       getContext().getTypeSize(D->getInit()->getType())));
     if (D->getInit()->isIntegerConstantExpr(Value, Context))
       Init = llvm::ConstantInt::get(Value);
   }

   if (!Init)
     Init = EmitGlobalInit(D->getInit());

   assert(GV->getType()->getElementType() == Init->getType() &&
          "Initializer codegen type mismatch!");
   GV->setInitializer(Init);

   if (const VisibilityAttr *attr = D->getAttr<VisibilityAttr>())
     GV->setVisibility(attr->getVisibility());
   // FIXME: else handle -fvisibility

   // Set the llvm linkage type as appropriate.
   if (D->getAttr<DLLImportAttr>())
     GV->setLinkage(llvm::Function::DLLImportLinkage);
   else if (D->getAttr<DLLExportAttr>())
     GV->setLinkage(llvm::Function::DLLExportLinkage);
   else if (D->getAttr<WeakAttr>()) {
     GV->setLinkage(llvm::GlobalVariable::WeakLinkage);

   } else {
     // FIXME: This isn't right.  This should handle common linkage and other
     // stuff.
     switch (D->getStorageClass()) {
     case VarDecl::Auto:
     case VarDecl::Register:
       assert(0 && "Can't have auto or register globals");
     case VarDecl::None:
       if (!D->getInit())
         GV->setLinkage(llvm::GlobalVariable::WeakLinkage);
       break;
     case VarDecl::Extern:
     case VarDecl::PrivateExtern:
       // todo: common
       break;
     case VarDecl::Static:
       GV->setLinkage(llvm::GlobalVariable::InternalLinkage);
       break;
     }
   }
 }

 /// EmitGlobalVarDeclarator - Emit all the global vars attached to the specified
 /// declarator chain.
 void CodeGenModule::EmitGlobalVarDeclarator(const FileVarDecl *D) {
   for (; D; D = cast_or_null<FileVarDecl>(D->getNextDeclarator()))
     EmitGlobalVar(D);
 }

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


 /// getBuiltinLibFunction
 llvm::Function *CodeGenModule::getBuiltinLibFunction(unsigned BuiltinID) {
   if (BuiltinID > BuiltinFunctions.size())
     BuiltinFunctions.resize(BuiltinID);

   // Cache looked up functions.  Since builtin id #0 is invalid we don't reserve
   // a slot for it.
   assert(BuiltinID && "Invalid Builtin ID");
   llvm::Function *&FunctionSlot = BuiltinFunctions[BuiltinID-1];
   if (FunctionSlot)
     return FunctionSlot;

   assert(Context.BuiltinInfo.isLibFunction(BuiltinID) && "isn't a lib fn");

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

   // Get the type for the builtin.
   QualType Type = Context.BuiltinInfo.GetBuiltinType(BuiltinID, Context);
   const llvm::FunctionType *Ty =
     cast<llvm::FunctionType>(getTypes().ConvertType(Type));

   // FIXME: This has a serious problem with code like this:
   //  void abs() {}
   //    ... __builtin_abs(x);
   // The two versions of abs will collide.  The fix is for the builtin to win,
   // and for the existing one to be turned into a constantexpr cast of the
   // builtin.  In the case where the existing one is a static function, it
   // should just be renamed.
   if (llvm::Function *Existing = getModule().getFunction(Name)) {
     if (Existing->getFunctionType() == Ty && Existing->hasExternalLinkage())
       return FunctionSlot = Existing;
     assert(Existing == 0 && "FIXME: Name collision");
   }

   // FIXME: param attributes for sext/zext etc.
   return FunctionSlot = new llvm::Function(Ty, llvm::Function::ExternalLinkage,
                                            Name, &getModule());
 }

 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;
   llvm::Intrinsic::ID IID;
   uint64_t Size; unsigned Align;
   Context.Target.getPointerInfo(Size, Align);
   switch (Size) {
   default: assert(0 && "Unknown ptr width");
   case 32: IID = llvm::Intrinsic::memcpy_i32; break;
   case 64: IID = llvm::Intrinsic::memcpy_i64; break;
   }
   return MemCpyFn = getIntrinsic(IID);
 }

 llvm::Function *CodeGenModule::getMemSetFn() {
   if (MemSetFn) return MemSetFn;
   llvm::Intrinsic::ID IID;
   uint64_t Size; unsigned Align;
   Context.Target.getPointerInfo(Size, Align);
   switch (Size) {
   default: assert(0 && "Unknown ptr width");
   case 32: IID = llvm::Intrinsic::memset_i32; break;
   case 64: IID = llvm::Intrinsic::memset_i64; break;
   }
   return MemSetFn = getIntrinsic(IID);
 }

 llvm::Constant *CodeGenModule::
 GetAddrOfConstantCFString(const std::string &str) {
   llvm::StringMapEntry<llvm::Constant *> &Entry =
     CFConstantStringMap.GetOrCreateValue(&str[0], &str[str.length()]);

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

   std::vector<llvm::Constant*> Fields;

   if (!CFConstantStringClassRef) {
     const llvm::Type *Ty = getTypes().ConvertType(getContext().IntTy);
     Ty = llvm::ArrayType::get(Ty, 0);

     CFConstantStringClassRef =
       new llvm::GlobalVariable(Ty, false,
                                llvm::GlobalVariable::ExternalLinkage, 0,
                                "__CFConstantStringClassReference",
                                &getModule());
   }

   // Class pointer.
   llvm::Constant *Zero = llvm::Constant::getNullValue(llvm::Type::Int32Ty);
   llvm::Constant *Zeros[] = { Zero, Zero };
   llvm::Constant *C =
     llvm::ConstantExpr::getGetElementPtr(CFConstantStringClassRef, Zeros, 2);
   Fields.push_back(C);

   // Flags.
   const llvm::Type *Ty = getTypes().ConvertType(getContext().IntTy);
   Fields.push_back(llvm::ConstantInt::get(Ty, 1992));

   // String pointer.
   C = llvm::ConstantArray::get(str);
   C = new llvm::GlobalVariable(C->getType(), true,
                                llvm::GlobalValue::InternalLinkage,
                                C, ".str", &getModule());

   C = llvm::ConstantExpr::getGetElementPtr(C, Zeros, 2);
   Fields.push_back(C);

   // String length.
   Ty = getTypes().ConvertType(getContext().LongTy);
   Fields.push_back(llvm::ConstantInt::get(Ty, str.length()));

   // The struct.
   Ty = getTypes().ConvertType(getContext().getCFConstantStringType());
   C = llvm::ConstantStruct::get(cast<llvm::StructType>(Ty), Fields);
   llvm::GlobalVariable *GV =
     new llvm::GlobalVariable(C->getType(), true,
                              llvm::GlobalVariable::InternalLinkage,
                              C, "", &getModule());
   GV->setSection("__DATA,__cfstring");
   Entry.setValue(GV);
   return GV;
 }

 /// GenerateWritableString -- Creates storage for a string literal.
 static llvm::Constant *GenerateStringLiteral(const std::string &str,
                                              bool constant,
                                              CodeGenModule &CGM) {
   // Create Constant for this string literal
   llvm::Constant *C=llvm::ConstantArray::get(str);

   // Create a global variable for this string
   C = new llvm::GlobalVariable(C->getType(), constant,
                                llvm::GlobalValue::InternalLinkage,
                                C, ".str", &CGM.getModule());
   return C;
 }

 /// CodeGenModule::GetAddrOfConstantString -- returns a pointer to the character
 /// array containing the literal.  The result is pointer to array type.
 llvm::Constant *CodeGenModule::GetAddrOfConstantString(const std::string &str) {
   // Don't share any string literals if writable-strings is turned on.
   if (Features.WritableStrings)
     return GenerateStringLiteral(str, false, *this);

   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);
   Entry.setValue(C);
   return C;
 }
	//===--- 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 "CodeGenFunction.h"
	#include "clang/AST/ASTContext.h"
	#include "clang/AST/Decl.h"
	#include "clang/Basic/Diagnostic.h"
	#include "clang/Basic/LangOptions.h"
	#include "clang/Basic/TargetInfo.h"
	#include "llvm/Constants.h"
	#include "llvm/DerivedTypes.h"
	#include "llvm/Module.h"
	#include "llvm/Intrinsics.h"
	#include <algorithm>
	using namespace clang;
	using namespace CodeGen;


	CodeGenModule::CodeGenModule(ASTContext &C, const LangOptions &LO,
	llvm::Module &M, const llvm::TargetData &TD,
	Diagnostic &diags)
	: Context(C), Features(LO), TheModule(M), TheTargetData(TD), Diags(diags),
	Types(C, M, TD), MemCpyFn(0), MemSetFn(0), CFConstantStringClassRef(0) {
	//TODO: Make this selectable at runtime
	Runtime = CreateObjCRuntime(M);
	}

	CodeGenModule::~CodeGenModule() {
	delete Runtime;
	}

	/// WarnUnsupported - Print out a warning that codegen doesn't support the
	/// specified stmt yet.
	void CodeGenModule::WarnUnsupported(const Stmt S, const char Type) {
	unsigned DiagID = getDiags().getCustomDiagID(Diagnostic::Warning,
	"cannot codegen this %0 yet");
	SourceRange Range = S->getSourceRange();
	std::string Msg = Type;
	getDiags().Report(Context.getFullLoc(S->getLocStart()), DiagID,
	&Msg, 1, &Range, 1);
	}

	/// WarnUnsupported - Print out a warning that codegen doesn't support the
	/// specified decl yet.
	void CodeGenModule::WarnUnsupported(const Decl D, const char Type) {
	unsigned DiagID = getDiags().getCustomDiagID(Diagnostic::Warning,
	"cannot codegen this %0 yet");
	std::string Msg = Type;
	getDiags().Report(Context.getFullLoc(D->getLocation()), DiagID,
	&Msg, 1);
	}

	/// ReplaceMapValuesWith - This is a really slow and bad function that
	/// searches for any entries in GlobalDeclMap that point to OldVal, changing
	/// them to point to NewVal. This is badbadbad, FIXME!
	void CodeGenModule::ReplaceMapValuesWith(llvm::Constant *OldVal,
	llvm::Constant *NewVal) {
	for (llvm::DenseMap<const Decl, llvm::Constant>::iterator
	I = GlobalDeclMap.begin(), E = GlobalDeclMap.end(); I != E; ++I)
	if (I->second == OldVal) I->second = NewVal;
	}


	llvm::Constant CodeGenModule::GetAddrOfFunctionDecl(const FunctionDecl D,
	bool isDefinition) {
	// See if it is already in the map. If so, just return it.
	llvm::Constant *&Entry = GlobalDeclMap[D];
	if (Entry) return Entry;

	const llvm::Type *Ty = getTypes().ConvertType(D->getType());

	// Check to see if the function already exists.
	llvm::Function *F = getModule().getFunction(D->getName());
	const llvm::FunctionType *FTy = cast<llvm::FunctionType>(Ty);

	// If it doesn't already exist, just create and return an entry.
	if (F == 0) {
	// FIXME: param attributes for sext/zext etc.
	return Entry = new llvm::Function(FTy, llvm::Function::ExternalLinkage,
	D->getName(), &getModule());
	}

	// If the pointer type matches, just return it.
	llvm::Type *PFTy = llvm::PointerType::getUnqual(Ty);
	if (PFTy == F->getType()) return Entry = F;

	// If this isn't a definition, just return it casted to the right type.
	if (!isDefinition)
	return Entry = llvm::ConstantExpr::getBitCast(F, PFTy);

	// Otherwise, we have a definition after a prototype with the wrong type.
	// 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)"). Start by
	// making a new function of the correct type, RAUW, then steal the name.
	llvm::Function *NewFn = new llvm::Function(FTy,
	llvm::Function::ExternalLinkage,
	"", &getModule());
	NewFn->takeName(F);

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

	// FIXME: Update the globaldeclmap for the previous decl of this name. We
	// really want a way to walk all of these, but we don't have it yet. This
	// is incredibly slow!
	ReplaceMapValuesWith(F, NewPtrForOldDecl);

	// Ok, delete the old function now, which is dead.
	assert(F->isDeclaration() && "Shouldn't replace non-declaration");
	F->eraseFromParent();

	// Return the new function which has the right type.
	return Entry = NewFn;
	}

	static bool IsZeroElementArray(const llvm::Type *Ty) {
	if (const llvm::ArrayType *ATy = dyn_cast<llvm::ArrayType>(Ty))
	return ATy->getNumElements() == 0;
	return false;
	}

	llvm::Constant CodeGenModule::GetAddrOfGlobalVar(const VarDecl D,
	bool isDefinition) {
	assert(D->hasGlobalStorage() && "Not a global variable");

	// See if it is already in the map.
	llvm::Constant *&Entry = GlobalDeclMap[D];
	if (Entry) return Entry;

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

	// Check to see if the global already exists.
	llvm::GlobalVariable *GV = getModule().getGlobalVariable(D->getName(), true);

	// If it doesn't already exist, just create and return an entry.
	if (GV == 0) {
	return Entry = new llvm::GlobalVariable(Ty, false,
	llvm::GlobalValue::ExternalLinkage,
	0, D->getName(), &getModule(), 0,
	ASTTy.getAddressSpace());
	}

	// If the pointer type matches, just return it.
	llvm::Type *PTy = llvm::PointerType::getUnqual(Ty);
	if (PTy == GV->getType()) return Entry = GV;

	// If this isn't a definition, just return it casted to the right type.
	if (!isDefinition)
	return Entry = llvm::ConstantExpr::getBitCast(GV, PTy);


	// Otherwise, we have a definition after a prototype with the wrong type.
	// GV is the GlobalVariable* for the one with the wrong type, we must make a
	/// new GlobalVariable* and update everything that used GV (a declaration)
	// 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];"). Start by
	// making a new global of the correct type, RAUW, then steal the name.
	llvm::GlobalVariable *NewGV =
	new llvm::GlobalVariable(Ty, false, llvm::GlobalValue::ExternalLinkage,
	0, D->getName(), &getModule(), 0,
	ASTTy.getAddressSpace());
	NewGV->takeName(GV);

	// Replace uses of GV with the globalvalue we will endow with a body.
	llvm::Constant *NewPtrForOldDecl =
	llvm::ConstantExpr::getBitCast(NewGV, GV->getType());
	GV->replaceAllUsesWith(NewPtrForOldDecl);

	// FIXME: Update the globaldeclmap for the previous decl of this name. We
	// really want a way to walk all of these, but we don't have it yet. This
	// is incredibly slow!
	ReplaceMapValuesWith(GV, NewPtrForOldDecl);

	// Verify that GV was a declaration or something like x[] which turns into
	// [0 x type].
	assert((GV->isDeclaration() \|\|
	IsZeroElementArray(GV->getType()->getElementType())) &&
	"Shouldn't replace non-declaration");

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

	// Return the new global which has the right type.
	return Entry = NewGV;
	}


	void CodeGenModule::EmitFunction(const FunctionDecl *FD) {
	// If this is not a prototype, emit the body.
	if (FD->getBody())
	CodeGenFunction(*this).GenerateCode(FD);
	}

	llvm::Constant CodeGenModule::EmitGlobalInit(const Expr Expr) {
	return EmitConstantExpr(Expr);
	}

	void CodeGenModule::EmitGlobalVar(const FileVarDecl *D) {
	// If this is just a forward declaration of the variable, don't emit it now,
	// allow it to be emitted lazily on its first use.
	if (D->getStorageClass() == VarDecl::Extern && D->getInit() == 0)
	return;

	// Get the global, forcing it to be a direct reference.
	llvm::GlobalVariable *GV =
	cast<llvm::GlobalVariable>(GetAddrOfGlobalVar(D, true));

	// Convert the initializer, or use zero if appropriate.
	llvm::Constant *Init = 0;
	if (D->getInit() == 0) {
	Init = llvm::Constant::getNullValue(GV->getType()->getElementType());
	} else if (D->getType()->isIntegerType()) {
	llvm::APSInt Value(static_cast<uint32_t>(
	getContext().getTypeSize(D->getInit()->getType())));
	if (D->getInit()->isIntegerConstantExpr(Value, Context))
	Init = llvm::ConstantInt::get(Value);
	}

	if (!Init)
	Init = EmitGlobalInit(D->getInit());

	assert(GV->getType()->getElementType() == Init->getType() &&
	"Initializer codegen type mismatch!");
	GV->setInitializer(Init);

	if (const VisibilityAttr *attr = D->getAttr<VisibilityAttr>())
	GV->setVisibility(attr->getVisibility());
	// FIXME: else handle -fvisibility

	// Set the llvm linkage type as appropriate.
	if (D->getAttr<DLLImportAttr>())
	GV->setLinkage(llvm::Function::DLLImportLinkage);
	else if (D->getAttr<DLLExportAttr>())
	GV->setLinkage(llvm::Function::DLLExportLinkage);
	else if (D->getAttr<WeakAttr>()) {
	GV->setLinkage(llvm::GlobalVariable::WeakLinkage);

	} else {
	// FIXME: This isn't right. This should handle common linkage and other
	// stuff.
	switch (D->getStorageClass()) {
	case VarDecl::Auto:
	case VarDecl::Register:
	assert(0 && "Can't have auto or register globals");
	case VarDecl::None:
	if (!D->getInit())
	GV->setLinkage(llvm::GlobalVariable::WeakLinkage);
	break;
	case VarDecl::Extern:
	case VarDecl::PrivateExtern:
	// todo: common
	break;
	case VarDecl::Static:
	GV->setLinkage(llvm::GlobalVariable::InternalLinkage);
	break;
	}
	}
	}

	/// EmitGlobalVarDeclarator - Emit all the global vars attached to the specified
	/// declarator chain.
	void CodeGenModule::EmitGlobalVarDeclarator(const FileVarDecl *D) {
	for (; D; D = cast_or_null<FileVarDecl>(D->getNextDeclarator()))
	EmitGlobalVar(D);
	}

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


	/// getBuiltinLibFunction
	llvm::Function *CodeGenModule::getBuiltinLibFunction(unsigned BuiltinID) {
	if (BuiltinID > BuiltinFunctions.size())
	BuiltinFunctions.resize(BuiltinID);

	// Cache looked up functions. Since builtin id #0 is invalid we don't reserve
	// a slot for it.
	assert(BuiltinID && "Invalid Builtin ID");
	llvm::Function *&FunctionSlot = BuiltinFunctions[BuiltinID-1];
	if (FunctionSlot)
	return FunctionSlot;

	assert(Context.BuiltinInfo.isLibFunction(BuiltinID) && "isn't a lib fn");

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

	// Get the type for the builtin.
	QualType Type = Context.BuiltinInfo.GetBuiltinType(BuiltinID, Context);
	const llvm::FunctionType *Ty =
	cast<llvm::FunctionType>(getTypes().ConvertType(Type));

	// FIXME: This has a serious problem with code like this:
	// void abs() {}
	// ... __builtin_abs(x);
	// The two versions of abs will collide. The fix is for the builtin to win,
	// and for the existing one to be turned into a constantexpr cast of the
	// builtin. In the case where the existing one is a static function, it
	// should just be renamed.
	if (llvm::Function *Existing = getModule().getFunction(Name)) {
	if (Existing->getFunctionType() == Ty && Existing->hasExternalLinkage())
	return FunctionSlot = Existing;
	assert(Existing == 0 && "FIXME: Name collision");
	}

	// FIXME: param attributes for sext/zext etc.
	return FunctionSlot = new llvm::Function(Ty, llvm::Function::ExternalLinkage,
	Name, &getModule());
	}

	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;
	llvm::Intrinsic::ID IID;
	uint64_t Size; unsigned Align;
	Context.Target.getPointerInfo(Size, Align);
	switch (Size) {
	default: assert(0 && "Unknown ptr width");
	case 32: IID = llvm::Intrinsic::memcpy_i32; break;
	case 64: IID = llvm::Intrinsic::memcpy_i64; break;
	}
	return MemCpyFn = getIntrinsic(IID);
	}

	llvm::Function *CodeGenModule::getMemSetFn() {
	if (MemSetFn) return MemSetFn;
	llvm::Intrinsic::ID IID;
	uint64_t Size; unsigned Align;
	Context.Target.getPointerInfo(Size, Align);
	switch (Size) {
	default: assert(0 && "Unknown ptr width");
	case 32: IID = llvm::Intrinsic::memset_i32; break;
	case 64: IID = llvm::Intrinsic::memset_i64; break;
	}
	return MemSetFn = getIntrinsic(IID);
	}

	llvm::Constant *CodeGenModule::
	GetAddrOfConstantCFString(const std::string &str) {
	llvm::StringMapEntry<llvm::Constant *> &Entry =
	CFConstantStringMap.GetOrCreateValue(&str[0], &str[str.length()]);

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

	std::vector<llvm::Constant*> Fields;

	if (!CFConstantStringClassRef) {
	const llvm::Type *Ty = getTypes().ConvertType(getContext().IntTy);
	Ty = llvm::ArrayType::get(Ty, 0);

	CFConstantStringClassRef =
	new llvm::GlobalVariable(Ty, false,
	llvm::GlobalVariable::ExternalLinkage, 0,
	"__CFConstantStringClassReference",
	&getModule());
	}

	// Class pointer.
	llvm::Constant *Zero = llvm::Constant::getNullValue(llvm::Type::Int32Ty);
	llvm::Constant *Zeros[] = { Zero, Zero };
	llvm::Constant *C =
	llvm::ConstantExpr::getGetElementPtr(CFConstantStringClassRef, Zeros, 2);
	Fields.push_back(C);

	// Flags.
	const llvm::Type *Ty = getTypes().ConvertType(getContext().IntTy);
	Fields.push_back(llvm::ConstantInt::get(Ty, 1992));

	// String pointer.
	C = llvm::ConstantArray::get(str);
	C = new llvm::GlobalVariable(C->getType(), true,
	llvm::GlobalValue::InternalLinkage,
	C, ".str", &getModule());

	C = llvm::ConstantExpr::getGetElementPtr(C, Zeros, 2);
	Fields.push_back(C);

	// String length.
	Ty = getTypes().ConvertType(getContext().LongTy);
	Fields.push_back(llvm::ConstantInt::get(Ty, str.length()));

	// The struct.
	Ty = getTypes().ConvertType(getContext().getCFConstantStringType());
	C = llvm::ConstantStruct::get(cast<llvm::StructType>(Ty), Fields);
	llvm::GlobalVariable *GV =
	new llvm::GlobalVariable(C->getType(), true,
	llvm::GlobalVariable::InternalLinkage,
	C, "", &getModule());
	GV->setSection("__DATA,__cfstring");
	Entry.setValue(GV);
	return GV;
	}

	/// GenerateWritableString -- Creates storage for a string literal.
	static llvm::Constant *GenerateStringLiteral(const std::string &str,
	bool constant,
	CodeGenModule &CGM) {
	// Create Constant for this string literal
	llvm::Constant *C=llvm::ConstantArray::get(str);

	// Create a global variable for this string
	C = new llvm::GlobalVariable(C->getType(), constant,
	llvm::GlobalValue::InternalLinkage,
	C, ".str", &CGM.getModule());
	return C;
	}

	/// CodeGenModule::GetAddrOfConstantString -- returns a pointer to the character
	/// array containing the literal. The result is pointer to array type.
	llvm::Constant *CodeGenModule::GetAddrOfConstantString(const std::string &str) {
	// Don't share any string literals if writable-strings is turned on.
	if (Features.WritableStrings)
	return GenerateStringLiteral(str, false, *this);

	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);
	Entry.setValue(C);
	return C;
	}