CodeGenModule.cpp

    // __CFConstantStringClassReference is already defined, in that it
    // will get renamed and the user will most likely see an opaque
    // error message. This is a general issue with relying on
    // particular names.
    llvm::GlobalVariable *GV = 
      new llvm::GlobalVariable(Ty, false,
                               llvm::GlobalVariable::ExternalLinkage, 0, 
                               "__CFConstantStringClassReference", 
                               &getModule());
    
    // Decay array -> ptr
    CFConstantStringClassRef =
      llvm::ConstantExpr::getGetElementPtr(GV, Zeros, 2);
  }
  
  QualType CFTy = getContext().getCFConstantStringType();
  RecordDecl *CFRD = CFTy->getAsRecordType()->getDecl();

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

  std::vector<llvm::Constant*> Fields;
  RecordDecl::field_iterator Field = CFRD->field_begin();

  // Class pointer.
  FieldDecl *CurField = *Field++;
  FieldDecl *NextField = *Field++;
  appendFieldAndPadding(*this, Fields, CurField, NextField,
                        CFConstantStringClassRef, CFRD, STy);
  
  // Flags.
  CurField = NextField;
  NextField = *Field++;
  const llvm::Type *Ty = getTypes().ConvertType(getContext().UnsignedIntTy);
  appendFieldAndPadding(*this, Fields, CurField, NextField,
                        llvm::ConstantInt::get(Ty, 0x07C8), CFRD, STy);
    
  // String pointer.
  CurField = NextField;
  NextField = *Field++;
  llvm::Constant *C = llvm::ConstantArray::get(str);
  C = new llvm::GlobalVariable(C->getType(), true, 
                               llvm::GlobalValue::InternalLinkage,
                               C, ".str", &getModule());
  appendFieldAndPadding(*this, Fields, CurField, NextField,
                        llvm::ConstantExpr::getGetElementPtr(C, Zeros, 2),
                        CFRD, STy);
  
  // String length.
  CurField = NextField;
  NextField = 0;
  Ty = getTypes().ConvertType(getContext().LongTy);
  appendFieldAndPadding(*this, Fields, CurField, NextField,
                        llvm::ConstantInt::get(Ty, str.length()), CFRD, STy);
  
  // The struct.
  C = llvm::ConstantStruct::get(STy, Fields);
  llvm::GlobalVariable *GV = 
    new llvm::GlobalVariable(C->getType(), true, 
                             llvm::GlobalVariable::InternalLinkage, 
                             C, "", &getModule());
  
  GV->setSection("__DATA,__cfstring");
  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.
  return GetAddrOfConstantString(GetStringForStringLiteral(S));
}

/// 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);
  
  llvm::Constant *C = llvm::ConstantArray::get(Str);
  C = new llvm::GlobalVariable(C->getType(), true, 
                               llvm::GlobalValue::InternalLinkage,
                               C, ".str", &getModule());
  return C;
}


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

/// 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) {
  // Don't share any string literals if writable-strings is turned on.
  if (Features.WritableStrings)
    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);
    }
  }
}

/// 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;

  switch (D->getKind()) {
  case Decl::Function:
  case Decl::Var:
    EmitGlobal(cast<ValueDecl>(D));
    break;

  case Decl::Namespace:
    ErrorUnsupported(D, "namespace");
    break;

    // Objective-C Decls
    
    // Forward declarations, no (immediate) code generation.
  case Decl::ObjCClass:
  case Decl::ObjCCategory:
  case Decl::ObjCForwardProtocol:
  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: {
    LinkageSpecDecl *LSD = cast<LinkageSpecDecl>(D);
    if (LSD->getLanguage() == LinkageSpecDecl::lang_cxx)
      ErrorUnsupported(LSD, "linkage spec");
    // FIXME: implement C++ linkage, C linkage works mostly by C
    // language reuse already.
    break;
  }

  case Decl::FileScopeAsm: {
    FileScopeAsmDecl *AD = cast<FileScopeAsmDecl>(D);
    std::string AsmString(AD->getAsmString()->getStrData(),
                          AD->getAsmString()->getByteLength());
    
    const std::string &S = getModule().getModuleInlineAsm();
    if (S.empty())
      getModule().setModuleInlineAsm(AsmString);
    else
      getModule().setModuleInlineAsm(S + '\n' + AsmString);
    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");
  }
}