xref: /llvm-project-15.0.7/clang/lib/CodeGen/CGBlocks.cpp (revision 681c0754)

//===--- CGBlocks.cpp - Emit LLVM Code for declarations -------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This contains code to emit blocks.
//
//===----------------------------------------------------------------------===//

#include "CGDebugInfo.h"
#include "CodeGenFunction.h"
#include "CGObjCRuntime.h"
#include "CodeGenModule.h"
#include "clang/AST/DeclObjC.h"
#include "llvm/Module.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Target/TargetData.h"
#include <algorithm>

using namespace clang;
using namespace CodeGen;

CGBlockInfo::CGBlockInfo(const char *N)
  : Name(N), CXXThisRef(0), NeedsObjCSelf(false) {

  // Skip asm prefix, if any.
  if (Name && Name[0] == '\01')
    ++Name;
}


llvm::Constant *CodeGenFunction::
BuildDescriptorBlockDecl(const BlockExpr *BE, const CGBlockInfo &Info,
                         const llvm::StructType* Ty,
                         llvm::Constant *BlockVarLayout,
                         std::vector<HelperInfo> *NoteForHelper) {
  bool BlockHasCopyDispose = Info.BlockHasCopyDispose;
  CharUnits Size = Info.BlockSize;
  const llvm::Type *UnsignedLongTy
    = CGM.getTypes().ConvertType(getContext().UnsignedLongTy);
  llvm::Constant *C;
  std::vector<llvm::Constant*> Elts;

  // reserved
  C = llvm::ConstantInt::get(UnsignedLongTy, 0);
  Elts.push_back(C);

  // Size
  // FIXME: What is the right way to say this doesn't fit?  We should give
  // a user diagnostic in that case.  Better fix would be to change the
  // API to size_t.
  C = llvm::ConstantInt::get(UnsignedLongTy, Size.getQuantity());
  Elts.push_back(C);

  // optional copy/dispose helpers
  if (BlockHasCopyDispose) {
    // copy_func_helper_decl
    Elts.push_back(BuildCopyHelper(Ty, NoteForHelper));

    // destroy_func_decl
    Elts.push_back(BuildDestroyHelper(Ty, NoteForHelper));
  }

  // Signature.  non-optional ObjC-style method descriptor @encode sequence
  std::string BlockTypeEncoding;
  CGM.getContext().getObjCEncodingForBlock(BE, BlockTypeEncoding);

  Elts.push_back(llvm::ConstantExpr::getBitCast(
          CGM.GetAddrOfConstantCString(BlockTypeEncoding), PtrToInt8Ty));

  // Layout.
  C = BlockVarLayout;

  Elts.push_back(C);

  C = llvm::ConstantStruct::get(VMContext, Elts, false);

  C = new llvm::GlobalVariable(CGM.getModule(), C->getType(), true,
                               llvm::GlobalValue::InternalLinkage,
                               C, "__block_descriptor_tmp");
  return C;
}

static void CollectBlockDeclRefInfo(const Stmt *S, CGBlockInfo &Info) {
  for (Stmt::const_child_iterator I = S->child_begin(), E = S->child_end();
       I != E; ++I)
    if (*I)
      CollectBlockDeclRefInfo(*I, Info);

  // We want to ensure we walk down into block literals so we can find
  // all nested BlockDeclRefExprs.
  if (const BlockExpr *BE = dyn_cast<BlockExpr>(S)) {
    Info.InnerBlocks.insert(BE->getBlockDecl());
    CollectBlockDeclRefInfo(BE->getBody(), Info);
  }

  else if (const BlockDeclRefExpr *BDRE = dyn_cast<BlockDeclRefExpr>(S)) {
    const ValueDecl *D = BDRE->getDecl();
    // FIXME: Handle enums.
    if (isa<FunctionDecl>(D))
      return;

    if (isa<ImplicitParamDecl>(D) &&
        isa<ObjCMethodDecl>(D->getDeclContext()) &&
        cast<ObjCMethodDecl>(D->getDeclContext())->getSelfDecl() == D) {
      Info.NeedsObjCSelf = true;
      return;
    }

    // Only Decls that escape are added.
    if (!Info.InnerBlocks.count(D->getDeclContext()))
      Info.DeclRefs.push_back(BDRE);
  }

  // Make sure to capture implicit 'self' references due to super calls.
  else if (const ObjCMessageExpr *E = dyn_cast<ObjCMessageExpr>(S)) {
    if (E->getReceiverKind() == ObjCMessageExpr::SuperClass ||
        E->getReceiverKind() == ObjCMessageExpr::SuperInstance)
      Info.NeedsObjCSelf = true;
  }
  else if (const ObjCPropertyRefExpr *PE = dyn_cast<ObjCPropertyRefExpr>(S)) {
    // Getter/setter uses may also cause implicit super references,
    // which we can check for with:
    if (PE->isSuperReceiver())
      Info.NeedsObjCSelf = true;
  }
  else if (const ObjCImplicitSetterGetterRefExpr *IE =
           dyn_cast<ObjCImplicitSetterGetterRefExpr>(S)) {
    // Getter/setter uses may also cause implicit super references,
    // which we can check for with:
    if (IE->isSuperReceiver())
      Info.NeedsObjCSelf = true;
  }
  else if (isa<CXXThisExpr>(S))
    Info.CXXThisRef = cast<CXXThisExpr>(S);
}

/// CanBlockBeGlobal - Given a CGBlockInfo struct, determines if a block can be
/// declared as a global variable instead of on the stack.
static bool CanBlockBeGlobal(const CGBlockInfo &Info) {
  return Info.DeclRefs.empty();
}

/// AllocateAllBlockDeclRefs - Preallocate all nested BlockDeclRefExprs to
/// ensure we can generate the debug information for the parameter for the block
/// invoke function.
static void AllocateAllBlockDeclRefs(CodeGenFunction &CGF, CGBlockInfo &Info) {
  if (Info.CXXThisRef)
    CGF.AllocateBlockCXXThisPointer(Info.CXXThisRef);

  for (size_t i = 0; i < Info.DeclRefs.size(); ++i)
    CGF.AllocateBlockDecl(Info.DeclRefs[i]);

  if (Info.NeedsObjCSelf) {
    ValueDecl *Self = cast<ObjCMethodDecl>(CGF.CurFuncDecl)->getSelfDecl();
    BlockDeclRefExpr *BDRE =
      new (CGF.getContext()) BlockDeclRefExpr(Self, Self->getType(),
                                              SourceLocation(), false);
    Info.DeclRefs.push_back(BDRE);
    CGF.AllocateBlockDecl(BDRE);
  }
}

static unsigned computeBlockFlag(CodeGenModule &CGM,
                                 const BlockExpr *BE, unsigned flags) {
  QualType BPT = BE->getType();
  const FunctionType *ftype = BPT->getPointeeType()->getAs<FunctionType>();
  QualType ResultType = ftype->getResultType();

  CallArgList Args;
  CodeGenTypes &Types = CGM.getTypes();
  const CGFunctionInfo &FnInfo = Types.getFunctionInfo(ResultType, Args,
                                                       FunctionType::ExtInfo());
  if (CGM.ReturnTypeUsesSRet(FnInfo))
    flags |= CodeGenFunction::BLOCK_USE_STRET;
  return flags;
}

// FIXME: Push most into CGM, passing down a few bits, like current function
// name.
llvm::Value *CodeGenFunction::BuildBlockLiteralTmp(const BlockExpr *BE) {
  std::string Name = CurFn->getName();
  CGBlockInfo Info(Name.c_str());
  Info.InnerBlocks.insert(BE->getBlockDecl());
  CollectBlockDeclRefInfo(BE->getBody(), Info);

  // Check if the block can be global.
  // FIXME: This test doesn't work for nested blocks yet.  Longer term, I'd like
  // to just have one code path.  We should move this function into CGM and pass
  // CGF, then we can just check to see if CGF is 0.
  if (0 && CanBlockBeGlobal(Info))
    return CGM.GetAddrOfGlobalBlock(BE, Name.c_str());

  size_t BlockFields = 5;

  std::vector<llvm::Constant*> Elts(BlockFields);

  llvm::Constant *C;
  llvm::Value *V;

  {
    llvm::Constant *BlockVarLayout;
    // C = BuildBlockStructInitlist();
    unsigned int flags = BLOCK_HAS_SIGNATURE;

    // We run this first so that we set BlockHasCopyDispose from the entire
    // block literal.
    // __invoke
    llvm::Function *Fn
      = CodeGenFunction(CGM).GenerateBlockFunction(CurGD, BE, Info, CurFuncDecl,
                                                   BlockVarLayout,
                                                   LocalDeclMap);
    BlockHasCopyDispose |= Info.BlockHasCopyDispose;
    Elts[3] = Fn;

    // FIXME: Don't use BlockHasCopyDispose, it is set more often then
    // necessary, for example: { ^{ __block int i; ^{ i = 1; }(); }(); }
    if (Info.BlockHasCopyDispose)
      flags |= BLOCK_HAS_COPY_DISPOSE;

    // __isa
    C = CGM.getNSConcreteStackBlock();
    C = llvm::ConstantExpr::getBitCast(C, PtrToInt8Ty);
    Elts[0] = C;

    // __flags
    flags = computeBlockFlag(CGM, BE, flags);
    const llvm::IntegerType *IntTy = cast<llvm::IntegerType>(
      CGM.getTypes().ConvertType(CGM.getContext().IntTy));
    C = llvm::ConstantInt::get(IntTy, flags);
    Elts[1] = C;

    // __reserved
    C = llvm::ConstantInt::get(IntTy, 0);
    Elts[2] = C;

    if (Info.BlockLayout.empty()) {
      // __descriptor
      C = llvm::Constant::getNullValue(PtrToInt8Ty);
      Elts[4] = BuildDescriptorBlockDecl(BE, Info, 0, C, 0);

      // Optimize to being a global block.
      Elts[0] = CGM.getNSConcreteGlobalBlock();

      Elts[1] = llvm::ConstantInt::get(IntTy, flags|BLOCK_IS_GLOBAL);

      C = llvm::ConstantStruct::get(VMContext, Elts, false);

      C = new llvm::GlobalVariable(CGM.getModule(), C->getType(), true,
                                   llvm::GlobalValue::InternalLinkage, C,
                                   "__block_holder_tmp_" +
                                   llvm::Twine(CGM.getGlobalUniqueCount()));
      QualType BPT = BE->getType();
      C = llvm::ConstantExpr::getBitCast(C, ConvertType(BPT));
      return C;
    }

    std::vector<const llvm::Type *> Types(BlockFields+Info.BlockLayout.size());
    for (int i=0; i<4; ++i)
      Types[i] = Elts[i]->getType();
    Types[4] = PtrToInt8Ty;

    for (unsigned i = 0, n = Info.BlockLayout.size(); i != n; ++i) {
      const Expr *E = Info.BlockLayout[i];
      const BlockDeclRefExpr *BDRE = dyn_cast<BlockDeclRefExpr>(E);
      QualType Ty = E->getType();
      if (BDRE && BDRE->isByRef()) {
        Types[i+BlockFields] =
          llvm::PointerType::get(BuildByRefType(BDRE->getDecl()), 0);
      } else if (BDRE && BDRE->getDecl()->getType()->isReferenceType()) {
         Types[i+BlockFields] = llvm::PointerType::get(ConvertType(Ty), 0);
      } else
        Types[i+BlockFields] = ConvertType(Ty);
    }

    llvm::StructType *Ty = llvm::StructType::get(VMContext, Types, true);

    llvm::AllocaInst *A = CreateTempAlloca(Ty);
    A->setAlignment(Info.BlockAlign.getQuantity());
    V = A;

    // Build layout / cleanup information for all the data entries in the
    // layout, and write the enclosing fields into the type.
    std::vector<HelperInfo> NoteForHelper(Info.BlockLayout.size());
    unsigned NumHelpers = 0;

    for (unsigned i=0; i<4; ++i)
      Builder.CreateStore(Elts[i], Builder.CreateStructGEP(V, i, "block.tmp"));

    for (unsigned i=0; i < Info.BlockLayout.size(); ++i) {
      const Expr *E = Info.BlockLayout[i];

      // Skip padding.
      if (isa<DeclRefExpr>(E)) continue;

      llvm::Value* Addr = Builder.CreateStructGEP(V, i+BlockFields, "tmp");
      HelperInfo &Note = NoteForHelper[NumHelpers++];

      Note.index = i+5;

      if (isa<CXXThisExpr>(E)) {
        Note.RequiresCopying = false;
        Note.flag = BLOCK_FIELD_IS_OBJECT;

        Builder.CreateStore(LoadCXXThis(), Addr);
        continue;
      }

      const BlockDeclRefExpr *BDRE = cast<BlockDeclRefExpr>(E);
      const ValueDecl *VD = BDRE->getDecl();
      QualType T = VD->getType();

      Note.RequiresCopying = BlockRequiresCopying(T);

      if (BDRE->isByRef()) {
        Note.flag = BLOCK_FIELD_IS_BYREF;
        if (T.isObjCGCWeak())
          Note.flag |= BLOCK_FIELD_IS_WEAK;
      } else if (T->isBlockPointerType()) {
        Note.flag = BLOCK_FIELD_IS_BLOCK;
      } else {
        Note.flag = BLOCK_FIELD_IS_OBJECT;
      }

      if (LocalDeclMap[VD]) {
        if (BDRE->isByRef()) {
          llvm::Value *Loc = LocalDeclMap[VD];
          Loc = Builder.CreateStructGEP(Loc, 1, "forwarding");
          Loc = Builder.CreateLoad(Loc);
          Builder.CreateStore(Loc, Addr);
          continue;
        } else {
          if (BDRE->getCopyConstructorExpr()) {
            E = BDRE->getCopyConstructorExpr();
            PushDestructorCleanup(E->getType(), Addr);
          }
            else {
              E = new (getContext()) DeclRefExpr(const_cast<ValueDecl*>(VD),
                                            VD->getType().getNonReferenceType(),
                                            SourceLocation());
              if (VD->getType()->isReferenceType()) {
                E = new (getContext())
                    UnaryOperator(const_cast<Expr*>(E), UO_AddrOf,
                                getContext().getPointerType(E->getType()),
                                SourceLocation());
              }
            }
          }
        }

      if (BDRE->isByRef()) {
        E = new (getContext())
          UnaryOperator(const_cast<Expr*>(E), UO_AddrOf,
                        getContext().getPointerType(E->getType()),
                        SourceLocation());
      }

      RValue r = EmitAnyExpr(E, AggValueSlot::forAddr(Addr, false, true));
      if (r.isScalar()) {
        llvm::Value *Loc = r.getScalarVal();
        const llvm::Type *Ty = Types[i+BlockFields];
        if  (BDRE->isByRef()) {
          // E is now the address of the value field, instead, we want the
          // address of the actual ByRef struct.  We optimize this slightly
          // compared to gcc by not grabbing the forwarding slot as this must
          // be done during Block_copy for us, and we can postpone the work
          // until then.
          CharUnits offset = BlockDecls[BDRE->getDecl()];

          llvm::Value *BlockLiteral = LoadBlockStruct();

          Loc = Builder.CreateGEP(BlockLiteral,
                     llvm::ConstantInt::get(Int64Ty, offset.getQuantity()),
                                  "block.literal");
          Ty = llvm::PointerType::get(Ty, 0);
          Loc = Builder.CreateBitCast(Loc, Ty);
          Loc = Builder.CreateLoad(Loc);
          // Loc = Builder.CreateBitCast(Loc, Ty);
        }
        Builder.CreateStore(Loc, Addr);
      } else if (r.isComplex())
        // FIXME: implement
        ErrorUnsupported(BE, "complex in block literal");
      else if (r.isAggregate())
        ; // Already created into the destination
      else
        assert (0 && "bad block variable");
      // FIXME: Ensure that the offset created by the backend for
      // the struct matches the previously computed offset in BlockDecls.
    }
    NoteForHelper.resize(NumHelpers);

    // __descriptor
    llvm::Value *Descriptor = BuildDescriptorBlockDecl(BE, Info, Ty,
                                                       BlockVarLayout,
                                                       &NoteForHelper);
    Descriptor = Builder.CreateBitCast(Descriptor, PtrToInt8Ty);
    Builder.CreateStore(Descriptor, Builder.CreateStructGEP(V, 4, "block.tmp"));
  }

  QualType BPT = BE->getType();
  V = Builder.CreateBitCast(V, ConvertType(BPT));
  // See if this is a __weak block variable and the must call objc_read_weak
  // on it.
  const FunctionType *ftype = BPT->getPointeeType()->getAs<FunctionType>();
  QualType RES = ftype->getResultType();
  if (RES.isObjCGCWeak()) {
    // Must cast argument to id*
    const llvm::Type *ObjectPtrTy =
      ConvertType(CGM.getContext().getObjCIdType());
    const llvm::Type *PtrObjectPtrTy =
      llvm::PointerType::getUnqual(ObjectPtrTy);
    V = Builder.CreateBitCast(V, PtrObjectPtrTy);
    V =  CGM.getObjCRuntime().EmitObjCWeakRead(*this, V);
  }
  return V;
}


const llvm::Type *BlockModule::getBlockDescriptorType() {
  if (BlockDescriptorType)
    return BlockDescriptorType;

  const llvm::Type *UnsignedLongTy =
    getTypes().ConvertType(getContext().UnsignedLongTy);

  // struct __block_descriptor {
  //   unsigned long reserved;
  //   unsigned long block_size;
  //
  //   // later, the following will be added
  //
  //   struct {
  //     void (*copyHelper)();
  //     void (*copyHelper)();
  //   } helpers;                // !!! optional
  //
  //   const char *signature;   // the block signature
  //   const char *layout;      // reserved
  // };
  BlockDescriptorType = llvm::StructType::get(UnsignedLongTy->getContext(),
                                              UnsignedLongTy,
                                              UnsignedLongTy,
                                              NULL);

  getModule().addTypeName("struct.__block_descriptor",
                          BlockDescriptorType);

  return BlockDescriptorType;
}

const llvm::Type *BlockModule::getGenericBlockLiteralType() {
  if (GenericBlockLiteralType)
    return GenericBlockLiteralType;

  const llvm::Type *BlockDescPtrTy =
    llvm::PointerType::getUnqual(getBlockDescriptorType());

  const llvm::IntegerType *IntTy = cast<llvm::IntegerType>(
    getTypes().ConvertType(getContext().IntTy));

  // struct __block_literal_generic {
  //   void *__isa;
  //   int __flags;
  //   int __reserved;
  //   void (*__invoke)(void *);
  //   struct __block_descriptor *__descriptor;
  // };
  GenericBlockLiteralType = llvm::StructType::get(IntTy->getContext(),
                                                  PtrToInt8Ty,
                                                  IntTy,
                                                  IntTy,
                                                  PtrToInt8Ty,
                                                  BlockDescPtrTy,
                                                  NULL);

  getModule().addTypeName("struct.__block_literal_generic",
                          GenericBlockLiteralType);

  return GenericBlockLiteralType;
}


RValue CodeGenFunction::EmitBlockCallExpr(const CallExpr* E,
                                          ReturnValueSlot ReturnValue) {
  const BlockPointerType *BPT =
    E->getCallee()->getType()->getAs<BlockPointerType>();

  llvm::Value *Callee = EmitScalarExpr(E->getCallee());

  // Get a pointer to the generic block literal.
  const llvm::Type *BlockLiteralTy =
    llvm::PointerType::getUnqual(CGM.getGenericBlockLiteralType());

  // Bitcast the callee to a block literal.
  llvm::Value *BlockLiteral =
    Builder.CreateBitCast(Callee, BlockLiteralTy, "block.literal");

  // Get the function pointer from the literal.
  llvm::Value *FuncPtr = Builder.CreateStructGEP(BlockLiteral, 3, "tmp");

  BlockLiteral =
    Builder.CreateBitCast(BlockLiteral,
                          llvm::Type::getInt8PtrTy(VMContext),
                          "tmp");

  // Add the block literal.
  QualType VoidPtrTy = getContext().getPointerType(getContext().VoidTy);
  CallArgList Args;
  Args.push_back(std::make_pair(RValue::get(BlockLiteral), VoidPtrTy));

  QualType FnType = BPT->getPointeeType();

  // And the rest of the arguments.
  EmitCallArgs(Args, FnType->getAs<FunctionProtoType>(),
               E->arg_begin(), E->arg_end());

  // Load the function.
  llvm::Value *Func = Builder.CreateLoad(FuncPtr, "tmp");

  const FunctionType *FuncTy = FnType->getAs<FunctionType>();
  QualType ResultType = FuncTy->getResultType();

  const CGFunctionInfo &FnInfo =
    CGM.getTypes().getFunctionInfo(ResultType, Args,
                                   FuncTy->getExtInfo());

  // Cast the function pointer to the right type.
  const llvm::Type *BlockFTy =
    CGM.getTypes().GetFunctionType(FnInfo, false);

  const llvm::Type *BlockFTyPtr = llvm::PointerType::getUnqual(BlockFTy);
  Func = Builder.CreateBitCast(Func, BlockFTyPtr);

  // And call the block.
  return EmitCall(FnInfo, Func, ReturnValue, Args);
}

void CodeGenFunction::AllocateBlockCXXThisPointer(const CXXThisExpr *E) {
  assert(BlockCXXThisOffset.isZero() && "already computed 'this' pointer");

  // Figure out what the offset is.
  QualType T = E->getType();
  std::pair<CharUnits,CharUnits> TypeInfo = getContext().getTypeInfoInChars(T);
  CharUnits Offset = getBlockOffset(TypeInfo.first, TypeInfo.second);

  BlockCXXThisOffset = Offset;
  BlockLayout.push_back(E);
}

void CodeGenFunction::AllocateBlockDecl(const BlockDeclRefExpr *E) {
  const ValueDecl *VD = E->getDecl();
  CharUnits &Offset = BlockDecls[VD];

  // See if we have already allocated an offset for this variable.
  if (!Offset.isZero())
    return;

  // Don't run the expensive check, unless we have to.
  if (!BlockHasCopyDispose)
    if (E->isByRef()
        || BlockRequiresCopying(E->getType()))
      BlockHasCopyDispose = true;

  const ValueDecl *D = cast<ValueDecl>(E->getDecl());

  CharUnits Size;
  CharUnits Align;

  if (E->isByRef()) {
    llvm::tie(Size,Align) =
      getContext().getTypeInfoInChars(getContext().VoidPtrTy);
  } else {
    Size = getContext().getTypeSizeInChars(D->getType());
    Align = getContext().getDeclAlign(D);
  }

  Offset = getBlockOffset(Size, Align);
  BlockLayout.push_back(E);
}

llvm::Value *CodeGenFunction::GetAddrOfBlockDecl(const ValueDecl *VD,
                                                 bool IsByRef) {

  CharUnits offset = BlockDecls[VD];
  assert(!offset.isZero() && "getting address of unallocated decl");

  llvm::Value *BlockLiteral = LoadBlockStruct();
  llvm::Value *V = Builder.CreateGEP(BlockLiteral,
                       llvm::ConstantInt::get(Int64Ty, offset.getQuantity()),
                                     "block.literal");
  if (IsByRef) {
    const llvm::Type *PtrStructTy
      = llvm::PointerType::get(BuildByRefType(VD), 0);
    // The block literal will need a copy/destroy helper.
    BlockHasCopyDispose = true;

    const llvm::Type *Ty = PtrStructTy;
    Ty = llvm::PointerType::get(Ty, 0);
    V = Builder.CreateBitCast(V, Ty);
    V = Builder.CreateLoad(V);
    V = Builder.CreateStructGEP(V, 1, "forwarding");
    V = Builder.CreateLoad(V);
    V = Builder.CreateBitCast(V, PtrStructTy);
    V = Builder.CreateStructGEP(V, getByRefValueLLVMField(VD),
                                VD->getNameAsString());
    if (VD->getType()->isReferenceType())
      V = Builder.CreateLoad(V);
  } else {
    const llvm::Type *Ty = CGM.getTypes().ConvertType(VD->getType());
    Ty = llvm::PointerType::get(Ty, 0);
    V = Builder.CreateBitCast(V, Ty);
    if (VD->getType()->isReferenceType())
      V = Builder.CreateLoad(V, "ref.tmp");
  }
  return V;
}

llvm::Constant *
BlockModule::GetAddrOfGlobalBlock(const BlockExpr *BE, const char * n) {
  // Generate the block descriptor.
  const llvm::Type *UnsignedLongTy = Types.ConvertType(Context.UnsignedLongTy);
  const llvm::IntegerType *IntTy = cast<llvm::IntegerType>(
    getTypes().ConvertType(getContext().IntTy));

  llvm::Constant *DescriptorFields[4];

  // Reserved
  DescriptorFields[0] = llvm::Constant::getNullValue(UnsignedLongTy);

  // Block literal size. For global blocks we just use the size of the generic
  // block literal struct.
  CharUnits BlockLiteralSize =
    CGM.GetTargetTypeStoreSize(getGenericBlockLiteralType());
  DescriptorFields[1] =
    llvm::ConstantInt::get(UnsignedLongTy,BlockLiteralSize.getQuantity());

  // signature.  non-optional ObjC-style method descriptor @encode sequence
  std::string BlockTypeEncoding;
  CGM.getContext().getObjCEncodingForBlock(BE, BlockTypeEncoding);

  DescriptorFields[2] = llvm::ConstantExpr::getBitCast(
          CGM.GetAddrOfConstantCString(BlockTypeEncoding), PtrToInt8Ty);

  // layout
  DescriptorFields[3] =
    llvm::ConstantInt::get(UnsignedLongTy,0);

  // build the structure from the 4 elements
  llvm::Constant *DescriptorStruct =
    llvm::ConstantStruct::get(VMContext, &DescriptorFields[0], 4, false);

  llvm::GlobalVariable *Descriptor =
    new llvm::GlobalVariable(getModule(), DescriptorStruct->getType(), true,
                             llvm::GlobalVariable::InternalLinkage,
                             DescriptorStruct, "__block_descriptor_global");

  int FieldCount = 5;
  // Generate the constants for the block literal.

  std::vector<llvm::Constant*> LiteralFields(FieldCount);

  CGBlockInfo Info(n);
  llvm::Constant *BlockVarLayout;
  llvm::DenseMap<const Decl*, llvm::Value*> LocalDeclMap;
  llvm::Function *Fn
    = CodeGenFunction(CGM).GenerateBlockFunction(GlobalDecl(), BE,
                                                 Info, 0, BlockVarLayout,
                                                 LocalDeclMap);
  assert(Info.BlockSize == BlockLiteralSize
         && "no imports allowed for global block");

  // isa
  LiteralFields[0] = CGM.getNSConcreteGlobalBlock();

  // __flags
  unsigned flags = computeBlockFlag(CGM, BE,
                                    (BLOCK_IS_GLOBAL | BLOCK_HAS_SIGNATURE));
  LiteralFields[1] =
    llvm::ConstantInt::get(IntTy, flags);

  // Reserved
  LiteralFields[2] = llvm::Constant::getNullValue(IntTy);

  // Function
  LiteralFields[3] = Fn;

  // Descriptor
  LiteralFields[4] = Descriptor;

  llvm::Constant *BlockLiteralStruct =
    llvm::ConstantStruct::get(VMContext, LiteralFields, false);

  llvm::GlobalVariable *BlockLiteral =
    new llvm::GlobalVariable(getModule(), BlockLiteralStruct->getType(), true,
                             llvm::GlobalVariable::InternalLinkage,
                             BlockLiteralStruct, "__block_literal_global");

  return BlockLiteral;
}

llvm::Value *CodeGenFunction::LoadBlockStruct() {
  llvm::Value *V = Builder.CreateLoad(LocalDeclMap[getBlockStructDecl()],
                                      "self");
  // For now, we codegen based upon byte offsets.
  return Builder.CreateBitCast(V, PtrToInt8Ty);
}

llvm::Function *
CodeGenFunction::GenerateBlockFunction(GlobalDecl GD, const BlockExpr *BExpr,
                                       CGBlockInfo &Info,
                                       const Decl *OuterFuncDecl,
                                       llvm::Constant *& BlockVarLayout,
                                  llvm::DenseMap<const Decl*, llvm::Value*> ldm) {

  // Check if we should generate debug info for this block.
  if (CGM.getDebugInfo())
    DebugInfo = CGM.getDebugInfo();

  // Arrange for local static and local extern declarations to appear
  // to be local to this function as well, as they are directly referenced
  // in a block.
  for (llvm::DenseMap<const Decl *, llvm::Value*>::iterator i = ldm.begin();
       i != ldm.end();
       ++i) {
    const VarDecl *VD = dyn_cast<VarDecl>(i->first);

    if (VD->getStorageClass() == SC_Static || VD->hasExternalStorage())
      LocalDeclMap[VD] = i->second;
  }

  BlockOffset =
      CGM.GetTargetTypeStoreSize(CGM.getGenericBlockLiteralType());
  BlockAlign = getContext().getTypeAlignInChars(getContext().VoidPtrTy);

  const FunctionType *BlockFunctionType = BExpr->getFunctionType();
  QualType ResultType;
  FunctionType::ExtInfo EInfo = getFunctionExtInfo(*BlockFunctionType);
  bool IsVariadic;
  if (const FunctionProtoType *FTy =
      dyn_cast<FunctionProtoType>(BlockFunctionType)) {
    ResultType = FTy->getResultType();
    IsVariadic = FTy->isVariadic();
  } else {
    // K&R style block.
    ResultType = BlockFunctionType->getResultType();
    IsVariadic = false;
  }

  FunctionArgList Args;

  CurFuncDecl = OuterFuncDecl;

  const BlockDecl *BD = BExpr->getBlockDecl();

  IdentifierInfo *II = &CGM.getContext().Idents.get(".block_descriptor");

  // Build the block struct now.
  AllocateAllBlockDeclRefs(*this, Info);

  // Capture block layout info. here.
  if (CGM.getContext().getLangOptions().ObjC1)
    BlockVarLayout = CGM.getObjCRuntime().GCBlockLayout(*this, BlockLayout);
  else
    BlockVarLayout = llvm::Constant::getNullValue(PtrToInt8Ty);

  QualType ParmTy = getContext().getBlockParmType(BlockHasCopyDispose,
                                                  BlockLayout);

  // FIXME: This leaks
  ImplicitParamDecl *SelfDecl =
    ImplicitParamDecl::Create(getContext(), const_cast<BlockDecl*>(BD),
                              SourceLocation(), II,
                              ParmTy);

  Args.push_back(std::make_pair(SelfDecl, SelfDecl->getType()));
  BlockStructDecl = SelfDecl;

  for (BlockDecl::param_const_iterator i = BD->param_begin(),
       e = BD->param_end(); i != e; ++i)
    Args.push_back(std::make_pair(*i, (*i)->getType()));

  const CGFunctionInfo &FI =
    CGM.getTypes().getFunctionInfo(ResultType, Args, EInfo);

  CodeGenTypes &Types = CGM.getTypes();
  const llvm::FunctionType *LTy = Types.GetFunctionType(FI, IsVariadic);

  MangleBuffer Name;
  CGM.getMangledName(GD, Name, BD);
  llvm::Function *Fn =
    llvm::Function::Create(LTy, llvm::GlobalValue::InternalLinkage,
                           Name.getString(), &CGM.getModule());

  CGM.SetInternalFunctionAttributes(BD, Fn, FI);
  StartFunction(BD, ResultType, Fn, Args,
                BExpr->getBody()->getLocEnd());

  CurFuncDecl = OuterFuncDecl;

  QualType FnType(BlockFunctionType, 0);
  bool HasPrototype = isa<FunctionProtoType>(BlockFunctionType);

  IdentifierInfo *ID = &getContext().Idents.get(Name.getString());
  CurCodeDecl = FunctionDecl::Create(getContext(),
                                     getContext().getTranslationUnitDecl(),
                                     SourceLocation(), ID, FnType,
                                     0,
                                     SC_Static,
                                     SC_None,
                                     false, HasPrototype);
  if (FunctionProtoType *FT = dyn_cast<FunctionProtoType>(FnType)) {
    const FunctionDecl *CFD = dyn_cast<FunctionDecl>(CurCodeDecl);
    FunctionDecl *FD = const_cast<FunctionDecl *>(CFD);
    llvm::SmallVector<ParmVarDecl*, 16> Params;
    for (unsigned i = 0, e = FT->getNumArgs(); i != e; ++i)
      Params.push_back(ParmVarDecl::Create(getContext(), FD,
                                           SourceLocation(), 0,
                                           FT->getArgType(i), /*TInfo=*/0,
                                           SC_None, SC_None, 0));
    FD->setParams(Params.data(), Params.size());
  }


  // If we have a C++ 'this' reference, go ahead and force it into
  // existence now.
  if (Info.CXXThisRef) {
    assert(!BlockCXXThisOffset.isZero() &&
           "haven't yet allocated 'this' reference");

    // TODO: I have a dream that one day this will be typed.
    llvm::Value *BlockLiteral = LoadBlockStruct();
    llvm::Value *ThisPtrRaw =
      Builder.CreateConstInBoundsGEP1_64(BlockLiteral,
                                         BlockCXXThisOffset.getQuantity(),
                                         "this.ptr.raw");

    const llvm::Type *Ty =
      CGM.getTypes().ConvertType(Info.CXXThisRef->getType());
    Ty = llvm::PointerType::get(Ty, 0);
    llvm::Value *ThisPtr = Builder.CreateBitCast(ThisPtrRaw, Ty, "this.ptr");

    CXXThisValue = Builder.CreateLoad(ThisPtr, "this");
  }

  // If we have an Objective C 'self' reference, go ahead and force it
  // into existence now.
  if (Info.NeedsObjCSelf) {
    ValueDecl *Self = cast<ObjCMethodDecl>(CurFuncDecl)->getSelfDecl();
    LocalDeclMap[Self] = GetAddrOfBlockDecl(Self, false);
  }

  // Save a spot to insert the debug information for all the BlockDeclRefDecls.
  llvm::BasicBlock *entry = Builder.GetInsertBlock();
  llvm::BasicBlock::iterator entry_ptr = Builder.GetInsertPoint();
  --entry_ptr;

  EmitStmt(BExpr->getBody());

  // Remember where we were...
  llvm::BasicBlock *resume = Builder.GetInsertBlock();

  // Go back to the entry.
  ++entry_ptr;
  Builder.SetInsertPoint(entry, entry_ptr);

  if (CGDebugInfo *DI = getDebugInfo()) {
    // Emit debug information for all the BlockDeclRefDecls.
    // FIXME: also for 'this'
    for (unsigned i = 0, e = BlockLayout.size(); i != e; ++i) {
      if (const BlockDeclRefExpr *BDRE =
            dyn_cast<BlockDeclRefExpr>(BlockLayout[i])) {
        const ValueDecl *D = BDRE->getDecl();
        DI->setLocation(D->getLocation());
        DI->EmitDeclareOfBlockDeclRefVariable(BDRE,
                                             LocalDeclMap[getBlockStructDecl()],
                                              Builder, this);
      }
    }
  }
  // And resume where we left off.
  if (resume == 0)
    Builder.ClearInsertionPoint();
  else
    Builder.SetInsertPoint(resume);

  FinishFunction(cast<CompoundStmt>(BExpr->getBody())->getRBracLoc());

  // The runtime needs a minimum alignment of a void *.
  CharUnits MinAlign = getContext().getTypeAlignInChars(getContext().VoidPtrTy);
  BlockOffset = CharUnits::fromQuantity(
      llvm::RoundUpToAlignment(BlockOffset.getQuantity(),
                               MinAlign.getQuantity()));

  Info.BlockSize = BlockOffset;
  Info.BlockAlign = BlockAlign;
  Info.BlockLayout = BlockLayout;
  Info.BlockHasCopyDispose = BlockHasCopyDispose;
  return Fn;
}

CharUnits BlockFunction::getBlockOffset(CharUnits Size, CharUnits Align) {
  assert((Align.isPositive()) && "alignment must be 1 byte or more");

  CharUnits OldOffset = BlockOffset;

  // Ensure proper alignment, even if it means we have to have a gap
  BlockOffset = CharUnits::fromQuantity(
      llvm::RoundUpToAlignment(BlockOffset.getQuantity(), Align.getQuantity()));
  BlockAlign = std::max(Align, BlockAlign);

  CharUnits Pad = BlockOffset - OldOffset;
  if (Pad.isPositive()) {
    QualType PadTy = getContext().getConstantArrayType(getContext().CharTy,
                                                       llvm::APInt(32,
                                                         Pad.getQuantity()),
                                                       ArrayType::Normal, 0);
    ValueDecl *PadDecl = VarDecl::Create(getContext(),
                                         getContext().getTranslationUnitDecl(),
                                         SourceLocation(),
                                         0, QualType(PadTy), 0,
                                         SC_None, SC_None);
    Expr *E = new (getContext()) DeclRefExpr(PadDecl, PadDecl->getType(),
                                             SourceLocation());
    BlockLayout.push_back(E);
  }

  BlockOffset += Size;
  return BlockOffset - Size;
}

llvm::Constant *BlockFunction::
GenerateCopyHelperFunction(bool BlockHasCopyDispose, const llvm::StructType *T,
                           std::vector<HelperInfo> *NoteForHelperp) {
  QualType R = getContext().VoidTy;

  FunctionArgList Args;
  // FIXME: This leaks
  ImplicitParamDecl *Dst =
    ImplicitParamDecl::Create(getContext(), 0,
                              SourceLocation(), 0,
                              getContext().getPointerType(getContext().VoidTy));
  Args.push_back(std::make_pair(Dst, Dst->getType()));
  ImplicitParamDecl *Src =
    ImplicitParamDecl::Create(getContext(), 0,
                              SourceLocation(), 0,
                              getContext().getPointerType(getContext().VoidTy));
  Args.push_back(std::make_pair(Src, Src->getType()));

  const CGFunctionInfo &FI =
      CGM.getTypes().getFunctionInfo(R, Args, FunctionType::ExtInfo());

  // FIXME: We'd like to put these into a mergable by content, with
  // internal linkage.
  CodeGenTypes &Types = CGM.getTypes();
  const llvm::FunctionType *LTy = Types.GetFunctionType(FI, false);

  llvm::Function *Fn =
    llvm::Function::Create(LTy, llvm::GlobalValue::InternalLinkage,
                           "__copy_helper_block_", &CGM.getModule());

  IdentifierInfo *II
    = &CGM.getContext().Idents.get("__copy_helper_block_");

  FunctionDecl *FD = FunctionDecl::Create(getContext(),
                                          getContext().getTranslationUnitDecl(),
                                          SourceLocation(), II, R, 0,
                                          SC_Static,
                                          SC_None,
                                          false,
                                          true);
  CGF.StartFunction(FD, R, Fn, Args, SourceLocation());

  llvm::Value *SrcObj = CGF.GetAddrOfLocalVar(Src);
  llvm::Type *PtrPtrT;

  if (NoteForHelperp) {
    std::vector<HelperInfo> &NoteForHelper = *NoteForHelperp;

    PtrPtrT = llvm::PointerType::get(llvm::PointerType::get(T, 0), 0);
    SrcObj = Builder.CreateBitCast(SrcObj, PtrPtrT);
    SrcObj = Builder.CreateLoad(SrcObj);

    llvm::Value *DstObj = CGF.GetAddrOfLocalVar(Dst);
    llvm::Type *PtrPtrT;
    PtrPtrT = llvm::PointerType::get(llvm::PointerType::get(T, 0), 0);
    DstObj = Builder.CreateBitCast(DstObj, PtrPtrT);
    DstObj = Builder.CreateLoad(DstObj);

    for (unsigned i=0; i < NoteForHelper.size(); ++i) {
      int flag = NoteForHelper[i].flag;
      int index = NoteForHelper[i].index;

      if ((NoteForHelper[i].flag & BLOCK_FIELD_IS_BYREF)
          || NoteForHelper[i].RequiresCopying) {
        llvm::Value *Srcv = SrcObj;
        Srcv = Builder.CreateStructGEP(Srcv, index);
        Srcv = Builder.CreateBitCast(Srcv,
                                     llvm::PointerType::get(PtrToInt8Ty, 0));
        Srcv = Builder.CreateLoad(Srcv);

        llvm::Value *Dstv = Builder.CreateStructGEP(DstObj, index);
        Dstv = Builder.CreateBitCast(Dstv, PtrToInt8Ty);

        llvm::Value *N = llvm::ConstantInt::get(CGF.Int32Ty, flag);
        llvm::Value *F = CGM.getBlockObjectAssign();
        Builder.CreateCall3(F, Dstv, Srcv, N);
      }
    }
  }

  CGF.FinishFunction();

  return llvm::ConstantExpr::getBitCast(Fn, PtrToInt8Ty);
}

llvm::Constant *BlockFunction::
GenerateDestroyHelperFunction(bool BlockHasCopyDispose,
                              const llvm::StructType* T,
                              std::vector<HelperInfo> *NoteForHelperp) {
  QualType R = getContext().VoidTy;

  FunctionArgList Args;
  // FIXME: This leaks
  ImplicitParamDecl *Src =
    ImplicitParamDecl::Create(getContext(), 0,
                              SourceLocation(), 0,
                              getContext().getPointerType(getContext().VoidTy));

  Args.push_back(std::make_pair(Src, Src->getType()));

  const CGFunctionInfo &FI =
      CGM.getTypes().getFunctionInfo(R, Args, FunctionType::ExtInfo());

  // FIXME: We'd like to put these into a mergable by content, with
  // internal linkage.
  CodeGenTypes &Types = CGM.getTypes();
  const llvm::FunctionType *LTy = Types.GetFunctionType(FI, false);

  llvm::Function *Fn =
    llvm::Function::Create(LTy, llvm::GlobalValue::InternalLinkage,
                           "__destroy_helper_block_", &CGM.getModule());

  IdentifierInfo *II
    = &CGM.getContext().Idents.get("__destroy_helper_block_");

  FunctionDecl *FD = FunctionDecl::Create(getContext(),
                                          getContext().getTranslationUnitDecl(),
                                          SourceLocation(), II, R, 0,
                                          SC_Static,
                                          SC_None,
                                          false, true);
  CGF.StartFunction(FD, R, Fn, Args, SourceLocation());

  if (NoteForHelperp) {
    std::vector<HelperInfo> &NoteForHelper = *NoteForHelperp;

    llvm::Value *SrcObj = CGF.GetAddrOfLocalVar(Src);
    llvm::Type *PtrPtrT;
    PtrPtrT = llvm::PointerType::get(llvm::PointerType::get(T, 0), 0);
    SrcObj = Builder.CreateBitCast(SrcObj, PtrPtrT);
    SrcObj = Builder.CreateLoad(SrcObj);

    for (unsigned i=0; i < NoteForHelper.size(); ++i) {
      int flag = NoteForHelper[i].flag;
      int index = NoteForHelper[i].index;

      if ((NoteForHelper[i].flag & BLOCK_FIELD_IS_BYREF)
          || NoteForHelper[i].RequiresCopying) {
        llvm::Value *Srcv = SrcObj;
        Srcv = Builder.CreateStructGEP(Srcv, index);
        Srcv = Builder.CreateBitCast(Srcv,
                                     llvm::PointerType::get(PtrToInt8Ty, 0));
        Srcv = Builder.CreateLoad(Srcv);

        BuildBlockRelease(Srcv, flag);
      }
    }
  }

  CGF.FinishFunction();

  return llvm::ConstantExpr::getBitCast(Fn, PtrToInt8Ty);
}

llvm::Constant *BlockFunction::BuildCopyHelper(const llvm::StructType *T,
                                       std::vector<HelperInfo> *NoteForHelper) {
  return CodeGenFunction(CGM).GenerateCopyHelperFunction(BlockHasCopyDispose,
                                                         T, NoteForHelper);
}

llvm::Constant *BlockFunction::BuildDestroyHelper(const llvm::StructType *T,
                                      std::vector<HelperInfo> *NoteForHelperp) {
  return CodeGenFunction(CGM).GenerateDestroyHelperFunction(BlockHasCopyDispose,
                                                            T, NoteForHelperp);
}

llvm::Constant *BlockFunction::
GeneratebyrefCopyHelperFunction(const llvm::Type *T, int flag) {
  QualType R = getContext().VoidTy;

  FunctionArgList Args;
  // FIXME: This leaks
  ImplicitParamDecl *Dst =
    ImplicitParamDecl::Create(getContext(), 0,
                              SourceLocation(), 0,
                              getContext().getPointerType(getContext().VoidTy));
  Args.push_back(std::make_pair(Dst, Dst->getType()));

  // FIXME: This leaks
  ImplicitParamDecl *Src =
    ImplicitParamDecl::Create(getContext(), 0,
                              SourceLocation(), 0,
                              getContext().getPointerType(getContext().VoidTy));
  Args.push_back(std::make_pair(Src, Src->getType()));

  const CGFunctionInfo &FI =
      CGM.getTypes().getFunctionInfo(R, Args, FunctionType::ExtInfo());

  CodeGenTypes &Types = CGM.getTypes();
  const llvm::FunctionType *LTy = Types.GetFunctionType(FI, false);

  // FIXME: We'd like to put these into a mergable by content, with
  // internal linkage.
  llvm::Function *Fn =
    llvm::Function::Create(LTy, llvm::GlobalValue::InternalLinkage,
                           "__Block_byref_id_object_copy_", &CGM.getModule());

  IdentifierInfo *II
    = &CGM.getContext().Idents.get("__Block_byref_id_object_copy_");

  FunctionDecl *FD = FunctionDecl::Create(getContext(),
                                          getContext().getTranslationUnitDecl(),
                                          SourceLocation(), II, R, 0,
                                          SC_Static,
                                          SC_None,
                                          false, true);
  CGF.StartFunction(FD, R, Fn, Args, SourceLocation());

  // dst->x
  llvm::Value *V = CGF.GetAddrOfLocalVar(Dst);
  V = Builder.CreateBitCast(V, llvm::PointerType::get(T, 0));
  V = Builder.CreateLoad(V);
  V = Builder.CreateStructGEP(V, 6, "x");
  llvm::Value *DstObj = Builder.CreateBitCast(V, PtrToInt8Ty);

  // src->x
  V = CGF.GetAddrOfLocalVar(Src);
  V = Builder.CreateLoad(V);
  V = Builder.CreateBitCast(V, T);
  V = Builder.CreateStructGEP(V, 6, "x");
  V = Builder.CreateBitCast(V, llvm::PointerType::get(PtrToInt8Ty, 0));
  llvm::Value *SrcObj = Builder.CreateLoad(V);

  flag |= BLOCK_BYREF_CALLER;

  llvm::Value *N = llvm::ConstantInt::get(CGF.Int32Ty, flag);
  llvm::Value *F = CGM.getBlockObjectAssign();
  Builder.CreateCall3(F, DstObj, SrcObj, N);

  CGF.FinishFunction();

  return llvm::ConstantExpr::getBitCast(Fn, PtrToInt8Ty);
}

llvm::Constant *
BlockFunction::GeneratebyrefDestroyHelperFunction(const llvm::Type *T,
                                                  int flag) {
  QualType R = getContext().VoidTy;

  FunctionArgList Args;
  // FIXME: This leaks
  ImplicitParamDecl *Src =
    ImplicitParamDecl::Create(getContext(), 0,
                              SourceLocation(), 0,
                              getContext().getPointerType(getContext().VoidTy));

  Args.push_back(std::make_pair(Src, Src->getType()));

  const CGFunctionInfo &FI =
      CGM.getTypes().getFunctionInfo(R, Args, FunctionType::ExtInfo());

  CodeGenTypes &Types = CGM.getTypes();
  const llvm::FunctionType *LTy = Types.GetFunctionType(FI, false);

  // FIXME: We'd like to put these into a mergable by content, with
  // internal linkage.
  llvm::Function *Fn =
    llvm::Function::Create(LTy, llvm::GlobalValue::InternalLinkage,
                           "__Block_byref_id_object_dispose_",
                           &CGM.getModule());

  IdentifierInfo *II
    = &CGM.getContext().Idents.get("__Block_byref_id_object_dispose_");

  FunctionDecl *FD = FunctionDecl::Create(getContext(),
                                          getContext().getTranslationUnitDecl(),
                                          SourceLocation(), II, R, 0,
                                          SC_Static,
                                          SC_None,
                                          false, true);
  CGF.StartFunction(FD, R, Fn, Args, SourceLocation());

  llvm::Value *V = CGF.GetAddrOfLocalVar(Src);
  V = Builder.CreateBitCast(V, llvm::PointerType::get(T, 0));
  V = Builder.CreateLoad(V);
  V = Builder.CreateStructGEP(V, 6, "x");
  V = Builder.CreateBitCast(V, llvm::PointerType::get(PtrToInt8Ty, 0));
  V = Builder.CreateLoad(V);

  flag |= BLOCK_BYREF_CALLER;
  BuildBlockRelease(V, flag);
  CGF.FinishFunction();

  return llvm::ConstantExpr::getBitCast(Fn, PtrToInt8Ty);
}

llvm::Constant *BlockFunction::BuildbyrefCopyHelper(const llvm::Type *T,
                                                    int Flag, unsigned Align) {
  // All alignments below that of pointer alignment collapse down to just
  // pointer alignment, as we always have at least that much alignment to begin
  // with.
  Align /= unsigned(CGF.Target.getPointerAlign(0)/8);

  // As an optimization, we only generate a single function of each kind we
  // might need.  We need a different one for each alignment and for each
  // setting of flags.  We mix Align and flag to get the kind.
  uint64_t Kind = (uint64_t)Align*BLOCK_BYREF_CURRENT_MAX + Flag;
  llvm::Constant *&Entry = CGM.AssignCache[Kind];
  if (Entry)
    return Entry;
  return Entry = CodeGenFunction(CGM).GeneratebyrefCopyHelperFunction(T, Flag);
}

llvm::Constant *BlockFunction::BuildbyrefDestroyHelper(const llvm::Type *T,
                                                       int Flag,
                                                       unsigned Align) {
  // All alignments below that of pointer alignment collpase down to just
  // pointer alignment, as we always have at least that much alignment to begin
  // with.
  Align /= unsigned(CGF.Target.getPointerAlign(0)/8);

  // As an optimization, we only generate a single function of each kind we
  // might need.  We need a different one for each alignment and for each
  // setting of flags.  We mix Align and flag to get the kind.
  uint64_t Kind = (uint64_t)Align*BLOCK_BYREF_CURRENT_MAX + Flag;
  llvm::Constant *&Entry = CGM.DestroyCache[Kind];
  if (Entry)
    return Entry;
  return Entry=CodeGenFunction(CGM).GeneratebyrefDestroyHelperFunction(T, Flag);
}

void BlockFunction::BuildBlockRelease(llvm::Value *V, int flag) {
  llvm::Value *F = CGM.getBlockObjectDispose();
  llvm::Value *N;
  V = Builder.CreateBitCast(V, PtrToInt8Ty);
  N = llvm::ConstantInt::get(CGF.Int32Ty, flag);
  Builder.CreateCall2(F, V, N);
}

ASTContext &BlockFunction::getContext() const { return CGM.getContext(); }

BlockFunction::BlockFunction(CodeGenModule &cgm, CodeGenFunction &cgf,
                             CGBuilderTy &B)
  : CGM(cgm), VMContext(cgm.getLLVMContext()), CGF(cgf), Builder(B) {
  PtrToInt8Ty = llvm::PointerType::getUnqual(
            llvm::Type::getInt8Ty(VMContext));

  BlockHasCopyDispose = false;
}