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//===--- CGBlocks.cpp - Emit LLVM Code for declarations ---------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This contains code to emit blocks.
#include "CGBlocks.h"
#include "CGCXXABI.h"
#include "CGDebugInfo.h"
#include "CGObjCRuntime.h"
#include "CGOpenCLRuntime.h"
#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "ConstantEmitter.h"
#include "TargetInfo.h"
#include "clang/AST/Attr.h"
#include "clang/AST/DeclObjC.h"
#include "clang/CodeGen/ConstantInitBuilder.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/ScopedPrinter.h"
#include <algorithm>
#include <cstdio>
using namespace clang;
using namespace CodeGen;
CGBlockInfo::CGBlockInfo(const BlockDecl *block, StringRef name)
: Name(name), CXXThisIndex(0), CanBeGlobal(false), NeedsCopyDispose(false),
HasCXXObject(false), UsesStret(false), HasCapturedVariableLayout(false),
CapturesNonExternalType(false), LocalAddress(Address::invalid()),
StructureType(nullptr), Block(block) {
// Skip asm prefix, if any. 'name' is usually taken directly from
// the mangled name of the enclosing function.
if (!name.empty() && name[0] == '\01')
name = name.substr(1);
// Anchor the vtable to this translation unit.
BlockByrefHelpers::~BlockByrefHelpers() {}
/// Build the given block as a global block.
static llvm::Constant *buildGlobalBlock(CodeGenModule &CGM,
const CGBlockInfo &blockInfo,
llvm::Constant *blockFn);
/// Build the helper function to copy a block.
static llvm::Constant *buildCopyHelper(CodeGenModule &CGM,
const CGBlockInfo &blockInfo) {
return CodeGenFunction(CGM).GenerateCopyHelperFunction(blockInfo);
/// Build the helper function to dispose of a block.
static llvm::Constant *buildDisposeHelper(CodeGenModule &CGM,
const CGBlockInfo &blockInfo) {
return CodeGenFunction(CGM).GenerateDestroyHelperFunction(blockInfo);
namespace {
/// Represents a type of copy/destroy operation that should be performed for an
/// entity that's captured by a block.
enum class BlockCaptureEntityKind {
CXXRecord, // Copy or destroy
BlockObject, // Assign or release
/// Represents a captured entity that requires extra operations in order for
/// this entity to be copied or destroyed correctly.
struct BlockCaptureManagedEntity {
BlockCaptureEntityKind CopyKind, DisposeKind;
BlockFieldFlags CopyFlags, DisposeFlags;
const BlockDecl::Capture *CI;
const CGBlockInfo::Capture *Capture;
BlockCaptureManagedEntity(BlockCaptureEntityKind CopyType,
BlockCaptureEntityKind DisposeType,
BlockFieldFlags CopyFlags,
BlockFieldFlags DisposeFlags,
const BlockDecl::Capture &CI,
const CGBlockInfo::Capture &Capture)
: CopyKind(CopyType), DisposeKind(DisposeType), CopyFlags(CopyFlags),
DisposeFlags(DisposeFlags), CI(&CI), Capture(&Capture) {}
bool operator<(const BlockCaptureManagedEntity &Other) const {
return Capture->getOffset() < Other.Capture->getOffset();
enum class CaptureStrKind {
// String for the copy helper.
// String for the dispose helper.
// Merge the strings for the copy helper and dispose helper.
} // end anonymous namespace
static void findBlockCapturedManagedEntities(
const CGBlockInfo &BlockInfo, const LangOptions &LangOpts,
SmallVectorImpl<BlockCaptureManagedEntity> &ManagedCaptures);
static std::string getBlockCaptureStr(const BlockCaptureManagedEntity &E,
CaptureStrKind StrKind,
CharUnits BlockAlignment,
CodeGenModule &CGM);
static std::string getBlockDescriptorName(const CGBlockInfo &BlockInfo,
CodeGenModule &CGM) {
std::string Name = "__block_descriptor_";
Name += llvm::to_string(BlockInfo.BlockSize.getQuantity()) + "_";
if (BlockInfo.needsCopyDisposeHelpers()) {
if (CGM.getLangOpts().Exceptions)
Name += "e";
if (CGM.getCodeGenOpts().ObjCAutoRefCountExceptions)
Name += "a";
Name += llvm::to_string(BlockInfo.BlockAlign.getQuantity()) + "_";
SmallVector<BlockCaptureManagedEntity, 4> ManagedCaptures;
findBlockCapturedManagedEntities(BlockInfo, CGM.getContext().getLangOpts(),
for (const BlockCaptureManagedEntity &E : ManagedCaptures) {
Name += llvm::to_string(E.Capture->getOffset().getQuantity());
if (E.CopyKind == E.DisposeKind) {
// If CopyKind and DisposeKind are the same, merge the capture
// information.
assert(E.CopyKind != BlockCaptureEntityKind::None &&
"shouldn't see BlockCaptureManagedEntity that is None");
Name += getBlockCaptureStr(E, CaptureStrKind::Merged,
BlockInfo.BlockAlign, CGM);
} else {
// If CopyKind and DisposeKind are not the same, which can happen when
// either Kind is None or the captured object is a __strong block,
// concatenate the copy and dispose strings.
Name += getBlockCaptureStr(E, CaptureStrKind::CopyHelper,
BlockInfo.BlockAlign, CGM);
Name += getBlockCaptureStr(E, CaptureStrKind::DisposeHelper,
BlockInfo.BlockAlign, CGM);
Name += "_";
std::string TypeAtEncoding =
/// Replace occurrences of '@' with '\1'. '@' is reserved on ELF platforms as
/// a separator between symbol name and symbol version.
std::replace(TypeAtEncoding.begin(), TypeAtEncoding.end(), '@', '\1');
Name += "e" + llvm::to_string(TypeAtEncoding.size()) + "_" + TypeAtEncoding;
Name += "l" + CGM.getObjCRuntime().getRCBlockLayoutStr(CGM, BlockInfo);
return Name;
/// buildBlockDescriptor - Build the block descriptor meta-data for a block.
/// buildBlockDescriptor is accessed from 5th field of the Block_literal
/// meta-data and contains stationary information about the block literal.
/// Its definition will have 4 (or optionally 6) words.
/// \code
/// struct Block_descriptor {
/// unsigned long reserved;
/// unsigned long size; // size of Block_literal metadata in bytes.
/// void *copy_func_helper_decl; // optional copy helper.
/// void *destroy_func_decl; // optional destructor helper.
/// void *block_method_encoding_address; // @encode for block literal signature.
/// void *block_layout_info; // encoding of captured block variables.
/// };
/// \endcode
static llvm::Constant *buildBlockDescriptor(CodeGenModule &CGM,
const CGBlockInfo &blockInfo) {
ASTContext &C = CGM.getContext();
llvm::IntegerType *ulong =
llvm::PointerType *i8p = nullptr;
if (CGM.getLangOpts().OpenCL)
i8p =
CGM.getLLVMContext(), C.getTargetAddressSpace(LangAS::opencl_constant));
i8p = CGM.VoidPtrTy;
std::string descName;
// If an equivalent block descriptor global variable exists, return it.
if (C.getLangOpts().ObjC &&
CGM.getLangOpts().getGC() == LangOptions::NonGC) {
descName = getBlockDescriptorName(blockInfo, CGM);
if (llvm::GlobalValue *desc = CGM.getModule().getNamedValue(descName))
return llvm::ConstantExpr::getBitCast(desc,
// If there isn't an equivalent block descriptor global variable, create a new
// one.
ConstantInitBuilder builder(CGM);
auto elements = builder.beginStruct();
// reserved
elements.addInt(ulong, 0);
// 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.
elements.addInt(ulong, blockInfo.BlockSize.getQuantity());
// Optional copy/dispose helpers.
bool hasInternalHelper = false;
if (blockInfo.needsCopyDisposeHelpers()) {
// copy_func_helper_decl
llvm::Constant *copyHelper = buildCopyHelper(CGM, blockInfo);
// destroy_func_decl
llvm::Constant *disposeHelper = buildDisposeHelper(CGM, blockInfo);
if (cast<llvm::Function>(copyHelper->getOperand(0))->hasInternalLinkage() ||
hasInternalHelper = true;
// Signature. Mandatory ObjC-style method descriptor @encode sequence.
std::string typeAtEncoding =
CGM.GetAddrOfConstantCString(typeAtEncoding).getPointer(), i8p));
// GC layout.
if (C.getLangOpts().ObjC) {
if (CGM.getLangOpts().getGC() != LangOptions::NonGC)
elements.add(CGM.getObjCRuntime().BuildGCBlockLayout(CGM, blockInfo));
elements.add(CGM.getObjCRuntime().BuildRCBlockLayout(CGM, blockInfo));
unsigned AddrSpace = 0;
if (C.getLangOpts().OpenCL)
AddrSpace = C.getTargetAddressSpace(LangAS::opencl_constant);
llvm::GlobalValue::LinkageTypes linkage;
if (descName.empty()) {
linkage = llvm::GlobalValue::InternalLinkage;
descName = "__block_descriptor_tmp";
} else if (hasInternalHelper) {
// If either the copy helper or the dispose helper has internal linkage,
// the block descriptor must have internal linkage too.
linkage = llvm::GlobalValue::InternalLinkage;
} else {
linkage = llvm::GlobalValue::LinkOnceODRLinkage;
llvm::GlobalVariable *global =
elements.finishAndCreateGlobal(descName, CGM.getPointerAlign(),
/*constant*/ true, linkage, AddrSpace);
if (linkage == llvm::GlobalValue::LinkOnceODRLinkage) {
if (CGM.supportsCOMDAT())
return llvm::ConstantExpr::getBitCast(global, CGM.getBlockDescriptorType());
Purely notional variadic template describing the layout of a block.
template <class _ResultType, class... _ParamTypes, class... _CaptureTypes>
struct Block_literal {
/// Initialized to one of:
/// extern void *_NSConcreteStackBlock[];
/// extern void *_NSConcreteGlobalBlock[];
/// In theory, we could start one off malloc'ed by setting
/// BLOCK_NEEDS_FREE, giving it a refcount of 1, and using
/// this isa:
/// extern void *_NSConcreteMallocBlock[];
struct objc_class *isa;
/// These are the flags (with corresponding bit number) that the
/// compiler is actually supposed to know about.
/// 23. BLOCK_IS_NOESCAPE - indicates that the block is non-escaping
/// 25. BLOCK_HAS_COPY_DISPOSE - indicates that the block
/// descriptor provides copy and dispose helper functions
/// 26. BLOCK_HAS_CXX_OBJ - indicates that there's a captured
/// object with a nontrivial destructor or copy constructor
/// 28. BLOCK_IS_GLOBAL - indicates that the block is allocated
/// as global memory
/// 29. BLOCK_USE_STRET - indicates that the block function
/// uses stret, which objc_msgSend needs to know about
/// 30. BLOCK_HAS_SIGNATURE - indicates that the block has an
/// @encoded signature string
/// And we're not supposed to manipulate these:
/// 24. BLOCK_NEEDS_FREE - indicates that the block has been moved
/// to malloc'ed memory
/// 27. BLOCK_IS_GC - indicates that the block has been moved to
/// to GC-allocated memory
/// Additionally, the bottom 16 bits are a reference count which
/// should be zero on the stack.
int flags;
/// Reserved; should be zero-initialized.
int reserved;
/// Function pointer generated from block literal.
_ResultType (*invoke)(Block_literal *, _ParamTypes...);
/// Block description metadata generated from block literal.
struct Block_descriptor *block_descriptor;
/// Captured values follow.
_CapturesTypes captures...;
namespace {
/// A chunk of data that we actually have to capture in the block.
struct BlockLayoutChunk {
CharUnits Alignment;
CharUnits Size;
Qualifiers::ObjCLifetime Lifetime;
const BlockDecl::Capture *Capture; // null for 'this'
llvm::Type *Type;
QualType FieldType;
BlockLayoutChunk(CharUnits align, CharUnits size,
Qualifiers::ObjCLifetime lifetime,
const BlockDecl::Capture *capture,
llvm::Type *type, QualType fieldType)
: Alignment(align), Size(size), Lifetime(lifetime),
Capture(capture), Type(type), FieldType(fieldType) {}
/// Tell the block info that this chunk has the given field index.
void setIndex(CGBlockInfo &info, unsigned index, CharUnits offset) {
if (!Capture) {
info.CXXThisIndex = index;
info.CXXThisOffset = offset;
} else {
auto C = CGBlockInfo::Capture::makeIndex(index, offset, FieldType);
info.Captures.insert({Capture->getVariable(), C});
/// Order by 1) all __strong together 2) next, all byfref together 3) next,
/// all __weak together. Preserve descending alignment in all situations.
bool operator<(const BlockLayoutChunk &left, const BlockLayoutChunk &right) {
if (left.Alignment != right.Alignment)
return left.Alignment > right.Alignment;
auto getPrefOrder = [](const BlockLayoutChunk &chunk) {
if (chunk.Capture && chunk.Capture->isByRef())
return 1;
if (chunk.Lifetime == Qualifiers::OCL_Strong)
return 0;
if (chunk.Lifetime == Qualifiers::OCL_Weak)
return 2;
return 3;
return getPrefOrder(left) < getPrefOrder(right);
} // end anonymous namespace
/// Determines if the given type is safe for constant capture in C++.
static bool isSafeForCXXConstantCapture(QualType type) {
const RecordType *recordType =
// Only records can be unsafe.
if (!recordType) return true;
const auto *record = cast<CXXRecordDecl>(recordType->getDecl());
// Maintain semantics for classes with non-trivial dtors or copy ctors.
if (!record->hasTrivialDestructor()) return false;
if (record->hasNonTrivialCopyConstructor()) return false;
// Otherwise, we just have to make sure there aren't any mutable
// fields that might have changed since initialization.
return !record->hasMutableFields();
/// It is illegal to modify a const object after initialization.
/// Therefore, if a const object has a constant initializer, we don't
/// actually need to keep storage for it in the block; we'll just
/// rematerialize it at the start of the block function. This is
/// acceptable because we make no promises about address stability of
/// captured variables.
static llvm::Constant *tryCaptureAsConstant(CodeGenModule &CGM,
CodeGenFunction *CGF,
const VarDecl *var) {
// Return if this is a function parameter. We shouldn't try to
// rematerialize default arguments of function parameters.
if (isa<ParmVarDecl>(var))
return nullptr;
QualType type = var->getType();
// We can only do this if the variable is const.
if (!type.isConstQualified()) return nullptr;
// Furthermore, in C++ we have to worry about mutable fields:
// C++ []p4:
// Except that any class member declared mutable can be
// modified, any attempt to modify a const object during its
// lifetime results in undefined behavior.
if (CGM.getLangOpts().CPlusPlus && !isSafeForCXXConstantCapture(type))
return nullptr;
// If the variable doesn't have any initializer (shouldn't this be
// invalid?), it's not clear what we should do. Maybe capture as
// zero?
const Expr *init = var->getInit();
if (!init) return nullptr;
return ConstantEmitter(CGM, CGF).tryEmitAbstractForInitializer(*var);
/// Get the low bit of a nonzero character count. This is the
/// alignment of the nth byte if the 0th byte is universally aligned.
static CharUnits getLowBit(CharUnits v) {
return CharUnits::fromQuantity(v.getQuantity() & (~v.getQuantity() + 1));
static void initializeForBlockHeader(CodeGenModule &CGM, CGBlockInfo &info,
SmallVectorImpl<llvm::Type*> &elementTypes) {
if (CGM.getLangOpts().OpenCL) {
// The header is basically 'struct { int; int; generic void *;
// custom_fields; }'. Assert that struct is packed.
auto GenericAS =
auto GenPtrAlign =
CharUnits::fromQuantity(CGM.getTarget().getPointerAlign(GenericAS) / 8);
auto GenPtrSize =
CharUnits::fromQuantity(CGM.getTarget().getPointerWidth(GenericAS) / 8);
assert(CGM.getIntSize() <= GenPtrSize);
assert(CGM.getIntAlign() <= GenPtrAlign);
assert((2 * CGM.getIntSize()).isMultipleOf(GenPtrAlign));
elementTypes.push_back(CGM.IntTy); /* total size */
elementTypes.push_back(CGM.IntTy); /* align */
.getGenericVoidPointerType()); /* invoke function */
unsigned Offset =
2 * CGM.getIntSize().getQuantity() + GenPtrSize.getQuantity();
unsigned BlockAlign = GenPtrAlign.getQuantity();
if (auto *Helper =
CGM.getTargetCodeGenInfo().getTargetOpenCLBlockHelper()) {
for (auto I : Helper->getCustomFieldTypes()) /* custom fields */ {
// TargetOpenCLBlockHelp needs to make sure the struct is packed.
// If necessary, add padding fields to the custom fields.
unsigned Align = CGM.getDataLayout().getABITypeAlignment(I);
if (BlockAlign < Align)
BlockAlign = Align;
assert(Offset % Align == 0);
Offset += CGM.getDataLayout().getTypeAllocSize(I);
info.BlockAlign = CharUnits::fromQuantity(BlockAlign);
info.BlockSize = CharUnits::fromQuantity(Offset);
} else {
// The header is basically 'struct { void *; int; int; void *; void *; }'.
// Assert that the struct is packed.
assert(CGM.getIntSize() <= CGM.getPointerSize());
assert(CGM.getIntAlign() <= CGM.getPointerAlign());
assert((2 * CGM.getIntSize()).isMultipleOf(CGM.getPointerAlign()));
info.BlockAlign = CGM.getPointerAlign();
info.BlockSize = 3 * CGM.getPointerSize() + 2 * CGM.getIntSize();
static QualType getCaptureFieldType(const CodeGenFunction &CGF,
const BlockDecl::Capture &CI) {
const VarDecl *VD = CI.getVariable();
// If the variable is captured by an enclosing block or lambda expression,
// use the type of the capture field.
if (CGF.BlockInfo && CI.isNested())
return CGF.BlockInfo->getCapture(VD).fieldType();
if (auto *FD = CGF.LambdaCaptureFields.lookup(VD))
return FD->getType();
// If the captured variable is a non-escaping __block variable, the field
// type is the reference type. If the variable is a __block variable that
// already has a reference type, the field type is the variable's type.
return VD->isNonEscapingByref() ?
CGF.getContext().getLValueReferenceType(VD->getType()) : VD->getType();
/// Compute the layout of the given block. Attempts to lay the block
/// out with minimal space requirements.
static void computeBlockInfo(CodeGenModule &CGM, CodeGenFunction *CGF,
CGBlockInfo &info) {
ASTContext &C = CGM.getContext();
const BlockDecl *block = info.getBlockDecl();
SmallVector<llvm::Type*, 8> elementTypes;
initializeForBlockHeader(CGM, info, elementTypes);
bool hasNonConstantCustomFields = false;
if (auto *OpenCLHelper =
hasNonConstantCustomFields =
if (!block->hasCaptures() && !hasNonConstantCustomFields) {
info.StructureType =
llvm::StructType::get(CGM.getLLVMContext(), elementTypes, true);
info.CanBeGlobal = true;
else if (C.getLangOpts().ObjC &&
CGM.getLangOpts().getGC() == LangOptions::NonGC)
info.HasCapturedVariableLayout = true;
// Collect the layout chunks.
SmallVector<BlockLayoutChunk, 16> layout;
layout.reserve(block->capturesCXXThis() +
(block->capture_end() - block->capture_begin()));
CharUnits maxFieldAlign;
// First, 'this'.
if (block->capturesCXXThis()) {
assert(CGF && CGF->CurFuncDecl && isa<CXXMethodDecl>(CGF->CurFuncDecl) &&
"Can't capture 'this' outside a method");
QualType thisType = cast<CXXMethodDecl>(CGF->CurFuncDecl)->getThisType();
// Theoretically, this could be in a different address space, so
// don't assume standard pointer size/align.
llvm::Type *llvmType = CGM.getTypes().ConvertType(thisType);
auto TInfo = CGM.getContext().getTypeInfoInChars(thisType);
maxFieldAlign = std::max(maxFieldAlign, TInfo.Align);
layout.push_back(BlockLayoutChunk(TInfo.Align, TInfo.Width,
nullptr, llvmType, thisType));
// Next, all the block captures.
for (const auto &CI : block->captures()) {
const VarDecl *variable = CI.getVariable();
if (CI.isEscapingByref()) {
// We have to copy/dispose of the __block reference.
info.NeedsCopyDispose = true;
// Just use void* instead of a pointer to the byref type.
CharUnits align = CGM.getPointerAlign();
maxFieldAlign = std::max(maxFieldAlign, align);
// Since a __block variable cannot be captured by lambdas, its type and
// the capture field type should always match.
assert(CGF && getCaptureFieldType(*CGF, CI) == variable->getType() &&
"capture type differs from the variable type");
layout.push_back(BlockLayoutChunk(align, CGM.getPointerSize(),
Qualifiers::OCL_None, &CI,
CGM.VoidPtrTy, variable->getType()));
// Otherwise, build a layout chunk with the size and alignment of
// the declaration.
if (llvm::Constant *constant = tryCaptureAsConstant(CGM, CGF, variable)) {
info.Captures[variable] = CGBlockInfo::Capture::makeConstant(constant);
QualType VT = getCaptureFieldType(*CGF, CI);
// If we have a lifetime qualifier, honor it for capture purposes.
// That includes *not* copying it if it's __unsafe_unretained.
Qualifiers::ObjCLifetime lifetime = VT.getObjCLifetime();
if (lifetime) {
switch (lifetime) {
case Qualifiers::OCL_None: llvm_unreachable("impossible");
case Qualifiers::OCL_ExplicitNone:
case Qualifiers::OCL_Autoreleasing:
case Qualifiers::OCL_Strong:
case Qualifiers::OCL_Weak:
info.NeedsCopyDispose = true;
// Block pointers require copy/dispose. So do Objective-C pointers.
} else if (VT->isObjCRetainableType()) {
// But honor the inert __unsafe_unretained qualifier, which doesn't
// actually make it into the type system.
if (VT->isObjCInertUnsafeUnretainedType()) {
lifetime = Qualifiers::OCL_ExplicitNone;
} else {
info.NeedsCopyDispose = true;
// used for mrr below.
lifetime = Qualifiers::OCL_Strong;
// So do types that require non-trivial copy construction.
} else if (CI.hasCopyExpr()) {
info.NeedsCopyDispose = true;
info.HasCXXObject = true;
if (!VT->getAsCXXRecordDecl()->isExternallyVisible())
info.CapturesNonExternalType = true;
// So do C structs that require non-trivial copy construction or
// destruction.
} else if (VT.isNonTrivialToPrimitiveCopy() == QualType::PCK_Struct ||
VT.isDestructedType() == QualType::DK_nontrivial_c_struct) {
info.NeedsCopyDispose = true;
// And so do types with destructors.
} else if (CGM.getLangOpts().CPlusPlus) {
if (const CXXRecordDecl *record = VT->getAsCXXRecordDecl()) {
if (!record->hasTrivialDestructor()) {
info.HasCXXObject = true;
info.NeedsCopyDispose = true;
if (!record->isExternallyVisible())
info.CapturesNonExternalType = true;
CharUnits size = C.getTypeSizeInChars(VT);
CharUnits align = C.getDeclAlign(variable);
maxFieldAlign = std::max(maxFieldAlign, align);
llvm::Type *llvmType =
BlockLayoutChunk(align, size, lifetime, &CI, llvmType, VT));
// If that was everything, we're done here.
if (layout.empty()) {
info.StructureType =
llvm::StructType::get(CGM.getLLVMContext(), elementTypes, true);
info.CanBeGlobal = true;
// Sort the layout by alignment. We have to use a stable sort here
// to get reproducible results. There should probably be an
// llvm::array_pod_stable_sort.
// Needed for blocks layout info.
info.BlockHeaderForcedGapOffset = info.BlockSize;
info.BlockHeaderForcedGapSize = CharUnits::Zero();
CharUnits &blockSize = info.BlockSize;
info.BlockAlign = std::max(maxFieldAlign, info.BlockAlign);
// Assuming that the first byte in the header is maximally aligned,
// get the alignment of the first byte following the header.
CharUnits endAlign = getLowBit(blockSize);
// If the end of the header isn't satisfactorily aligned for the
// maximum thing, look for things that are okay with the header-end
// alignment, and keep appending them until we get something that's
// aligned right. This algorithm is only guaranteed optimal if
// that condition is satisfied at some point; otherwise we can get
// things like:
// header // next byte has alignment 4
// something_with_size_5; // next byte has alignment 1
// something_with_alignment_8;
// which has 7 bytes of padding, as opposed to the naive solution
// which might have less (?).
if (endAlign < maxFieldAlign) {
li = layout.begin() + 1, le = layout.end();
// Look for something that the header end is already
// satisfactorily aligned for.
for (; li != le && endAlign < li->Alignment; ++li)
// If we found something that's naturally aligned for the end of
// the header, keep adding things...
if (li != le) {
SmallVectorImpl<BlockLayoutChunk>::iterator first = li;
for (; li != le; ++li) {
assert(endAlign >= li->Alignment);
li->setIndex(info, elementTypes.size(), blockSize);
blockSize += li->Size;
endAlign = getLowBit(blockSize);
// ...until we get to the alignment of the maximum field.
if (endAlign >= maxFieldAlign) {
// Don't re-append everything we just appended.
layout.erase(first, li);
assert(endAlign == getLowBit(blockSize));
// At this point, we just have to add padding if the end align still
// isn't aligned right.
if (endAlign < maxFieldAlign) {
CharUnits newBlockSize = blockSize.alignTo(maxFieldAlign);
CharUnits padding = newBlockSize - blockSize;
// If we haven't yet added any fields, remember that there was an
// initial gap; this need to go into the block layout bit map.
if (blockSize == info.BlockHeaderForcedGapOffset) {
info.BlockHeaderForcedGapSize = padding;
blockSize = newBlockSize;
endAlign = getLowBit(blockSize); // might be > maxFieldAlign
assert(endAlign >= maxFieldAlign);
assert(endAlign == getLowBit(blockSize));
// Slam everything else on now. This works because they have
// strictly decreasing alignment and we expect that size is always a
// multiple of alignment.
for (SmallVectorImpl<BlockLayoutChunk>::iterator
li = layout.begin(), le = layout.end(); li != le; ++li) {
if (endAlign < li->Alignment) {
// size may not be multiple of alignment. This can only happen with
// an over-aligned variable. We will be adding a padding field to
// make the size be multiple of alignment.
CharUnits padding = li->Alignment - endAlign;
blockSize += padding;
endAlign = getLowBit(blockSize);
assert(endAlign >= li->Alignment);
li->setIndex(info, elementTypes.size(), blockSize);
blockSize += li->Size;
endAlign = getLowBit(blockSize);
info.StructureType =
llvm::StructType::get(CGM.getLLVMContext(), elementTypes, true);
/// Emit a block literal expression in the current function.
llvm::Value *CodeGenFunction::EmitBlockLiteral(const BlockExpr *blockExpr) {
// If the block has no captures, we won't have a pre-computed
// layout for it.
if (!blockExpr->getBlockDecl()->hasCaptures())
// The block literal is emitted as a global variable, and the block invoke
// function has to be extracted from its initializer.
if (llvm::Constant *Block = CGM.getAddrOfGlobalBlockIfEmitted(blockExpr))
return Block;
CGBlockInfo blockInfo(blockExpr->getBlockDecl(), CurFn->getName());
computeBlockInfo(CGM, this, blockInfo);
blockInfo.BlockExpression = blockExpr;
if (!blockInfo.CanBeGlobal)
blockInfo.LocalAddress = CreateTempAlloca(blockInfo.StructureType,
blockInfo.BlockAlign, "block");
return EmitBlockLiteral(blockInfo);
llvm::Value *CodeGenFunction::EmitBlockLiteral(const CGBlockInfo &blockInfo) {
bool IsOpenCL = CGM.getContext().getLangOpts().OpenCL;
auto GenVoidPtrTy =
IsOpenCL ? CGM.getOpenCLRuntime().getGenericVoidPointerType() : VoidPtrTy;
LangAS GenVoidPtrAddr = IsOpenCL ? LangAS::opencl_generic : LangAS::Default;
auto GenVoidPtrSize = CharUnits::fromQuantity(
CGM.getContext().getTargetAddressSpace(GenVoidPtrAddr)) /
// Using the computed layout, generate the actual block function.
bool isLambdaConv = blockInfo.getBlockDecl()->isConversionFromLambda();
CodeGenFunction BlockCGF{CGM, true};
BlockCGF.SanOpts = SanOpts;
auto *InvokeFn = BlockCGF.GenerateBlockFunction(
CurGD, blockInfo, LocalDeclMap, isLambdaConv, blockInfo.CanBeGlobal);
auto *blockFn = llvm::ConstantExpr::getPointerCast(InvokeFn, GenVoidPtrTy);
// If there is nothing to capture, we can emit this as a global block.
if (blockInfo.CanBeGlobal)
return CGM.getAddrOfGlobalBlockIfEmitted(blockInfo.BlockExpression);
// Otherwise, we have to emit this as a local block.
Address blockAddr = blockInfo.LocalAddress;
assert(blockAddr.isValid() && "block has no address!");
llvm::Constant *isa;
llvm::Constant *descriptor;
BlockFlags flags;
if (!IsOpenCL) {
// If the block is non-escaping, set field 'isa 'to NSConcreteGlobalBlock
// and set the BLOCK_IS_GLOBAL bit of field 'flags'. Copying a non-escaping
// block just returns the original block and releasing it is a no-op.
llvm::Constant *blockISA = blockInfo.getBlockDecl()->doesNotEscape()
? CGM.getNSConcreteGlobalBlock()
: CGM.getNSConcreteStackBlock();
isa = llvm::ConstantExpr::getBitCast(blockISA, VoidPtrTy);
// Build the block descriptor.
descriptor = buildBlockDescriptor(CGM, blockInfo);
// Compute the initial on-stack block flags.
if (blockInfo.HasCapturedVariableLayout)
if (blockInfo.needsCopyDisposeHelpers())
if (blockInfo.HasCXXObject)
if (blockInfo.UsesStret)
if (blockInfo.getBlockDecl()->doesNotEscape())
auto projectField = [&](unsigned index, const Twine &name) -> Address {
return Builder.CreateStructGEP(blockAddr, index, name);
auto storeField = [&](llvm::Value *value, unsigned index, const Twine &name) {
Builder.CreateStore(value, projectField(index, name));
// Initialize the block header.
// We assume all the header fields are densely packed.
unsigned index = 0;
CharUnits offset;
auto addHeaderField = [&](llvm::Value *value, CharUnits size,
const Twine &name) {
storeField(value, index, name);
offset += size;
if (!IsOpenCL) {
addHeaderField(isa, getPointerSize(), "block.isa");
addHeaderField(llvm::ConstantInt::get(IntTy, flags.getBitMask()),
getIntSize(), "block.flags");
addHeaderField(llvm::ConstantInt::get(IntTy, 0), getIntSize(),
} else {
llvm::ConstantInt::get(IntTy, blockInfo.BlockSize.getQuantity()),
getIntSize(), "block.size");
llvm::ConstantInt::get(IntTy, blockInfo.BlockAlign.getQuantity()),
getIntSize(), "block.align");
addHeaderField(blockFn, GenVoidPtrSize, "block.invoke");
if (!IsOpenCL)
addHeaderField(descriptor, getPointerSize(), "block.descriptor");
else if (auto *Helper =
CGM.getTargetCodeGenInfo().getTargetOpenCLBlockHelper()) {
for (auto I : Helper->getCustomFieldValues(*this, blockInfo)) {
// Finally, capture all the values into the block.
const BlockDecl *blockDecl = blockInfo.getBlockDecl();
// First, 'this'.
if (blockDecl->capturesCXXThis()) {
Address addr =
projectField(blockInfo.CXXThisIndex, "block.captured-this.addr");
Builder.CreateStore(LoadCXXThis(), addr);
// Next, captured variables.
for (const auto &CI : blockDecl->captures()) {
const VarDecl *variable = CI.getVariable();
const CGBlockInfo::Capture &capture = blockInfo.getCapture(variable);
// Ignore constant captures.
if (capture.isConstant()) continue;
QualType type = capture.fieldType();
// This will be a [[type]]*, except that a byref entry will just be
// an i8**.
Address blockField = projectField(capture.getIndex(), "block.captured");
// Compute the address of the thing we're going to move into the
// block literal.
Address src = Address::invalid();
if (blockDecl->isConversionFromLambda()) {
// The lambda capture in a lambda's conversion-to-block-pointer is
// special; we'll simply emit it directly.
src = Address::invalid();
} else if (CI.isEscapingByref()) {
if (BlockInfo && CI.isNested()) {
// We need to use the capture from the enclosing block.
const CGBlockInfo::Capture &enclosingCapture =
// This is a [[type]]*, except that a byref entry will just be an i8**.
src = Builder.CreateStructGEP(LoadBlockStruct(),
} else {
auto I = LocalDeclMap.find(variable);
assert(I != LocalDeclMap.end());
src = I->second;
} else {
DeclRefExpr declRef(getContext(), const_cast<VarDecl *>(variable),
/*RefersToEnclosingVariableOrCapture*/ CI.isNested(),
type.getNonReferenceType(), VK_LValue,
src = EmitDeclRefLValue(&declRef).getAddress(*this);
// For byrefs, we just write the pointer to the byref struct into
// the block field. There's no need to chase the forwarding
// pointer at this point, since we're building something that will
// live a shorter life than the stack byref anyway.
if (CI.isEscapingByref()) {
// Get a void* that points to the byref struct.
llvm::Value *byrefPointer;
if (CI.isNested())
byrefPointer = Builder.CreateLoad(src, "byref.capture");
byrefPointer = Builder.CreateBitCast(src.getPointer(), VoidPtrTy);
// Write that void* into the capture field.
Builder.CreateStore(byrefPointer, blockField);
// If we have a copy constructor, evaluate that into the block field.
} else if (const Expr *copyExpr = CI.getCopyExpr()) {
if (blockDecl->isConversionFromLambda()) {
// If we have a lambda conversion, emit the expression
// directly into the block instead.
AggValueSlot Slot =
AggValueSlot::forAddr(blockField, Qualifiers(),
EmitAggExpr(copyExpr, Slot);
} else {
EmitSynthesizedCXXCopyCtor(blockField, src, copyExpr);
// If it's a reference variable, copy the reference into the block field.
} else if (type->isReferenceType()) {
Builder.CreateStore(src.getPointer(), blockField);
// If type is const-qualified, copy the value into the block field.
} else if (type.isConstQualified() &&
type.getObjCLifetime() == Qualifiers::OCL_Strong &&
CGM.getCodeGenOpts().OptimizationLevel != 0) {
llvm::Value *value = Builder.CreateLoad(src, "captured");
Builder.CreateStore(value, blockField);
// If this is an ARC __strong block-pointer variable, don't do a
// block copy.
// TODO: this can be generalized into the normal initialization logic:
// we should never need to do a block-copy when initializing a local
// variable, because the local variable's lifetime should be strictly
// contained within the stack block's.
} else if (type.getObjCLifetime() == Qualifiers::OCL_Strong &&
type->isBlockPointerType()) {
// Load the block and do a simple retain.
llvm::Value *value = Builder.CreateLoad(src, "block.captured_block");
value = EmitARCRetainNonBlock(value);
// Do a primitive store to the block field.
Builder.CreateStore(value, blockField);
// Otherwise, fake up a POD copy into the block field.
} else {
// Fake up a new variable so that EmitScalarInit doesn't think
// we're referring to the variable in its own initializer.
ImplicitParamDecl BlockFieldPseudoVar(getContext(), type,
// We use one of these or the other depending on whether the
// reference is nested.
DeclRefExpr declRef(getContext(), const_cast<VarDecl *>(variable),
/*RefersToEnclosingVariableOrCapture*/ CI.isNested(),
type, VK_LValue, SourceLocation());
ImplicitCastExpr l2r(ImplicitCastExpr::OnStack, type, CK_LValueToRValue,
&declRef, VK_PRValue, FPOptionsOverride());
// FIXME: Pass a specific location for the expr init so that the store is
// attributed to a reasonable location - otherwise it may be attributed to
// locations of subexpressions in the initialization.
EmitExprAsInit(&l2r, &BlockFieldPseudoVar,
MakeAddrLValue(blockField, type, AlignmentSource::Decl),
/*captured by init*/ false);
// Push a cleanup for the capture if necessary.
if (!blockInfo.NeedsCopyDispose)
// Ignore __block captures; there's nothing special in the on-stack block
// that we need to do for them.
if (CI.isByRef())
// Ignore objects that aren't destructed.
QualType::DestructionKind dtorKind = type.isDestructedType();
if (dtorKind == QualType::DK_none)
CodeGenFunction::Destroyer *destroyer;
// Block captures count as local values and have imprecise semantics.
// They also can't be arrays, so need to worry about that.
// For const-qualified captures, emit clang.arc.use to ensure the captured
// object doesn't get released while we are still depending on its validity
// within the block.
if (type.isConstQualified() &&
type.getObjCLifetime() == Qualifiers::OCL_Strong &&
CGM.getCodeGenOpts().OptimizationLevel != 0) {
assert(CGM.getLangOpts().ObjCAutoRefCount &&
"expected ObjC ARC to be enabled");
destroyer = emitARCIntrinsicUse;
} else if (dtorKind == QualType::DK_objc_strong_lifetime) {
destroyer = destroyARCStrongImprecise;
} else {
destroyer = getDestroyer(dtorKind);
CleanupKind cleanupKind = NormalCleanup;
bool useArrayEHCleanup = needsEHCleanup(dtorKind);
if (useArrayEHCleanup)
cleanupKind = NormalAndEHCleanup;
// Extend the lifetime of the capture to the end of the scope enclosing the
// block expression except when the block decl is in the list of RetExpr's
// cleanup objects, in which case its lifetime ends after the full
// expression.
auto IsBlockDeclInRetExpr = [&]() {
auto *EWC = llvm::dyn_cast_or_null<ExprWithCleanups>(RetExpr);
if (EWC)
for (auto &C : EWC->getObjects())
if (auto *BD = C.dyn_cast<BlockDecl *>())
if (BD == blockDecl)
return true;
return false;
if (IsBlockDeclInRetExpr())
pushDestroy(cleanupKind, blockField, type, destroyer, useArrayEHCleanup);
pushLifetimeExtendedDestroy(cleanupKind, blockField, type, destroyer,
// Cast to the converted block-pointer type, which happens (somewhat
// unfortunately) to be a pointer to function type.
llvm::Value *result = Builder.CreatePointerCast(
blockAddr.getPointer(), ConvertType(blockInfo.getBlockExpr()->getType()));
if (IsOpenCL) {
CGM.getOpenCLRuntime().recordBlockInfo(blockInfo.BlockExpression, InvokeFn,
return result;
llvm::Type *CodeGenModule::getBlockDescriptorType() {
if (BlockDescriptorType)
return BlockDescriptorType;
llvm::Type *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::create(
"struct.__block_descriptor", UnsignedLongTy, UnsignedLongTy);
// Now form a pointer to that.
unsigned AddrSpace = 0;
if (getLangOpts().OpenCL)
AddrSpace = getContext().getTargetAddressSpace(LangAS::opencl_constant);
BlockDescriptorType = llvm::PointerType::get(BlockDescriptorType, AddrSpace);
return BlockDescriptorType;
llvm::Type *CodeGenModule::getGenericBlockLiteralType() {
if (GenericBlockLiteralType)
return GenericBlockLiteralType;
llvm::Type *BlockDescPtrTy = getBlockDescriptorType();
if (getLangOpts().OpenCL) {
// struct __opencl_block_literal_generic {
// int __size;
// int __align;
// __generic void *__invoke;
// /* custom fields */
// };
SmallVector<llvm::Type *, 8> StructFields(
{IntTy, IntTy, getOpenCLRuntime().getGenericVoidPointerType()});
if (auto *Helper = getTargetCodeGenInfo().getTargetOpenCLBlockHelper()) {
for (auto I : Helper->getCustomFieldTypes())
GenericBlockLiteralType = llvm::StructType::create(
StructFields, "struct.__opencl_block_literal_generic");
} else {
// struct __block_literal_generic {
// void *__isa;
// int __flags;
// int __reserved;
// void (*__invoke)(void *);
// struct __block_descriptor *__descriptor;
// };
GenericBlockLiteralType =
llvm::StructType::create("struct.__block_literal_generic", VoidPtrTy,
IntTy, IntTy, VoidPtrTy, BlockDescPtrTy);
return GenericBlockLiteralType;
RValue CodeGenFunction::EmitBlockCallExpr(const CallExpr *E,
ReturnValueSlot ReturnValue) {
const auto *BPT = E->getCallee()->getType()->castAs<BlockPointerType>();
llvm::Value *BlockPtr = EmitScalarExpr(E->getCallee());
llvm::Type *GenBlockTy = CGM.getGenericBlockLiteralType();
llvm::Value *Func = nullptr;
QualType FnType = BPT->getPointeeType();
ASTContext &Ctx = getContext();
CallArgList Args;
if (getLangOpts().OpenCL) {
// For OpenCL, BlockPtr is already casted to generic block literal.
// First argument of a block call is a generic block literal casted to
// generic void pointer, i.e. i8 addrspace(4)*
llvm::Type *GenericVoidPtrTy =
llvm::Value *BlockDescriptor = Builder.CreatePointerCast(
BlockPtr, GenericVoidPtrTy);
QualType VoidPtrQualTy = Ctx.getPointerType(
Ctx.getAddrSpaceQualType(Ctx.VoidTy, LangAS::opencl_generic));
Args.add(RValue::get(BlockDescriptor), VoidPtrQualTy);
// And the rest of the arguments.
EmitCallArgs(Args, FnType->getAs<FunctionProtoType>(), E->arguments());
// We *can* call the block directly unless it is a function argument.
if (!isa<ParmVarDecl>(E->getCalleeDecl()))
Func = CGM.getOpenCLRuntime().getInvokeFunction(E->getCallee());
else {
llvm::Value *FuncPtr = Builder.CreateStructGEP(GenBlockTy, BlockPtr, 2);
Func = Builder.CreateAlignedLoad(GenericVoidPtrTy, FuncPtr,
} else {
// Bitcast the block literal to a generic block literal.
BlockPtr = Builder.CreatePointerCast(
BlockPtr, llvm::PointerType::get(GenBlockTy, 0), "block.literal");
// Get pointer to the block invoke function
llvm::Value *FuncPtr = Builder.CreateStructGEP(GenBlockTy, BlockPtr, 3);
// First argument is a block literal casted to a void pointer
BlockPtr = Builder.CreatePointerCast(BlockPtr, VoidPtrTy);
Args.add(RValue::get(BlockPtr), Ctx.VoidPtrTy);
// And the rest of the arguments.
EmitCallArgs(Args, FnType->getAs<FunctionProtoType>(), E->arguments());
// Load the function.
Func = Builder.CreateAlignedLoad(VoidPtrTy, FuncPtr, getPointerAlign());
const FunctionType *FuncTy = FnType->castAs<FunctionType>();
const CGFunctionInfo &FnInfo =
CGM.getTypes().arrangeBlockFunctionCall(Args, FuncTy);
// Cast the function pointer to the right type.
llvm::Type *BlockFTy = CGM.getTypes().GetFunctionType(FnInfo);
llvm::Type *BlockFTyPtr = llvm::PointerType::getUnqual(BlockFTy);
Func = Builder.CreatePointerCast(Func, BlockFTyPtr);
// Prepare the callee.
CGCallee Callee(CGCalleeInfo(), Func);
// And call the block.
return EmitCall(FnInfo, Callee, ReturnValue, Args);
Address CodeGenFunction::GetAddrOfBlockDecl(const VarDecl *variable) {
assert(BlockInfo && "evaluating block ref without block information?");
const CGBlockInfo::Capture &capture = BlockInfo->getCapture(variable);
// Handle constant captures.
if (capture.isConstant()) return LocalDeclMap.find(variable)->second;
Address addr = Builder.CreateStructGEP(LoadBlockStruct(), capture.getIndex(),
if (variable->isEscapingByref()) {
// addr should be a void** right now. Load, then cast the result
// to byref*.
auto &byrefInfo = getBlockByrefInfo(variable);
addr = Address(Builder.CreateLoad(addr), byrefInfo.ByrefAlignment);
auto byrefPointerType = llvm::PointerType::get(byrefInfo.Type, 0);
addr = Builder.CreateBitCast(addr, byrefPointerType, "byref.addr");
addr = emitBlockByrefAddress(addr, byrefInfo, /*follow*/ true,
assert((!variable->isNonEscapingByref() ||
capture.fieldType()->isReferenceType()) &&
"the capture field of a non-escaping variable should have a "
"reference type");
if (capture.fieldType()->isReferenceType())
addr = EmitLoadOfReference(MakeAddrLValue(addr, capture.fieldType()));
return addr;
void CodeGenModule::setAddrOfGlobalBlock(const BlockExpr *BE,
llvm::Constant *Addr) {
bool Ok = EmittedGlobalBlocks.insert(std::make_pair(BE, Addr)).second;
assert(Ok && "Trying to replace an already-existing global block!");
llvm::Constant *
CodeGenModule::GetAddrOfGlobalBlock(const BlockExpr *BE,
StringRef Name) {
if (llvm::Constant *Block = getAddrOfGlobalBlockIfEmitted(BE))
return Block;
CGBlockInfo blockInfo(BE->getBlockDecl(), Name);
blockInfo.BlockExpression = BE;
// Compute information about the layout, etc., of this block.
computeBlockInfo(*this, nullptr, blockInfo);
// Using that metadata, generate the actual block function.
CodeGenFunction::DeclMapTy LocalDeclMap;
GlobalDecl(), blockInfo, LocalDeclMap,
/*IsLambdaConversionToBlock*/ false, /*BuildGlobalBlock*/ true);
return getAddrOfGlobalBlockIfEmitted(BE);
static llvm::Constant *buildGlobalBlock(CodeGenModule &CGM,
const CGBlockInfo &blockInfo,
llvm::Constant *blockFn) {
// Callers should detect this case on their own: calling this function
// generally requires computing layout information, which is a waste of time
// if we've already emitted this block.
assert(!CGM.getAddrOfGlobalBlockIfEmitted(blockInfo.BlockExpression) &&
"Refusing to re-emit a global block.");
// Generate the constants for the block literal initializer.
ConstantInitBuilder builder(CGM);
auto fields = builder.beginStruct();
bool IsOpenCL = CGM.getLangOpts().OpenCL;
bool IsWindows = CGM.getTarget().getTriple().isOSWindows();
if (!IsOpenCL) {
// isa
if (IsWindows)
// __flags
if (blockInfo.UsesStret)
fields.addInt(CGM.IntTy, flags.getBitMask());
// Reserved
fields.addInt(CGM.IntTy, 0);
} else {
fields.addInt(CGM.IntTy, blockInfo.BlockSize.getQuantity());
fields.addInt(CGM.IntTy, blockInfo.BlockAlign.getQuantity());
// Function
if (!IsOpenCL) {
// Descriptor
fields.add(buildBlockDescriptor(CGM, blockInfo));
} else if (auto *Helper =
CGM.getTargetCodeGenInfo().getTargetOpenCLBlockHelper()) {
for (auto I : Helper->getCustomFieldValues(CGM, blockInfo)) {
unsigned AddrSpace = 0;
if (CGM.getContext().getLangOpts().OpenCL)
AddrSpace = CGM.getContext().getTargetAddressSpace(LangAS::opencl_global);
llvm::GlobalVariable *literal = fields.finishAndCreateGlobal(
"__block_literal_global", blockInfo.BlockAlign,
/*constant*/ !IsWindows, llvm::GlobalVariable::InternalLinkage, AddrSpace);
// Windows does not allow globals to be initialised to point to globals in
// different DLLs. Any such variables must run code to initialise them.
if (IsWindows) {
auto *Init = llvm::Function::Create(llvm::FunctionType::get(CGM.VoidTy,
{}), llvm::GlobalValue::InternalLinkage, ".block_isa_init",
llvm::IRBuilder<> b(llvm::BasicBlock::Create(CGM.getLLVMContext(), "entry",
b.CreateStructGEP(literal->getValueType(), literal, 0),
// We can't use the normal LLVM global initialisation array, because we
// need to specify that this runs early in library initialisation.
auto *InitVar = new llvm::GlobalVariable(CGM.getModule(), Init->getType(),
/*isConstant*/true, llvm::GlobalValue::InternalLinkage,
Init, ".block_isa_init_ptr");
// Return a constant of the appropriately-casted type.
llvm::Type *RequiredType =
llvm::Constant *Result =
llvm::ConstantExpr::getPointerCast(literal, RequiredType);
CGM.setAddrOfGlobalBlock(blockInfo.BlockExpression, Result);
if (CGM.getContext().getLangOpts().OpenCL)
cast<llvm::Function>(blockFn->stripPointerCasts()), Result);
return Result;
void CodeGenFunction::setBlockContextParameter(const ImplicitParamDecl *D,
unsigned argNum,
llvm::Value *arg) {
assert(BlockInfo && "not emitting prologue of block invocation function?!");
// Allocate a stack slot like for any local variable to guarantee optimal
// debug info at -O0. The mem2reg pass will eliminate it when optimizing.
Address alloc = CreateMemTemp(D->getType(), D->getName() + ".addr");
Builder.CreateStore(arg, alloc);
if (CGDebugInfo *DI = getDebugInfo()) {
if (CGM.getCodeGenOpts().hasReducedDebugInfo()) {
*BlockInfo, D->getName(), argNum,
cast<llvm::AllocaInst>(alloc.getPointer()), Builder);
SourceLocation StartLoc = BlockInfo->getBlockExpr()->getBody()->getBeginLoc();
ApplyDebugLocation Scope(*this, StartLoc);
// Instead of messing around with LocalDeclMap, just set the value
// directly as BlockPointer.
BlockPointer = Builder.CreatePointerCast(
? getContext().getTargetAddressSpace(LangAS::opencl_generic)
: 0),
Address CodeGenFunction::LoadBlockStruct() {
assert(BlockInfo && "not in a block invocation function!");
assert(BlockPointer && "no block pointer set!");
return Address(BlockPointer, BlockInfo->BlockAlign);
llvm::Function *
CodeGenFunction::GenerateBlockFunction(GlobalDecl GD,
const CGBlockInfo &blockInfo,
const DeclMapTy &ldm,
bool IsLambdaConversionToBlock,
bool BuildGlobalBlock) {
const BlockDecl *blockDecl = blockInfo.getBlockDecl();
CurGD = GD;
CurEHLocation = blockInfo.getBlockExpr()->getEndLoc();
BlockInfo = &blockInfo;
// Arrange for local static and local extern declarations to appear
// to be local to this function as well, in case they're directly
// referenced in a block.
for (DeclMapTy::const_iterator i = ldm.begin(), e = ldm.end(); i != e; ++i) {
const auto *var = dyn_cast<VarDecl>(i->first);
if (var && !var->hasLocalStorage())
setAddrOfLocalVar(var, i->second);
// Begin building the function declaration.
// Build the argument list.
FunctionArgList args;
// The first argument is the block pointer. Just take it as a void*
// and cast it later.
QualType selfTy = getContext().VoidPtrTy;
// For OpenCL passed block pointer can be private AS local variable or
// global AS program scope variable (for the case with and without captures).
// Generic AS is used therefore to be able to accommodate both private and
// generic AS in one implementation.
if (getLangOpts().OpenCL)
selfTy = getContext().getPointerType(getContext().getAddrSpaceQualType(
getContext().VoidTy, LangAS::opencl_generic));
IdentifierInfo *II = &CGM.getContext().Idents.get(".block_descriptor");
ImplicitParamDecl SelfDecl(getContext(), const_cast<BlockDecl *>(blockDecl),
SourceLocation(), II, selfTy,
// Now add the rest of the parameters.
args.append(blockDecl->param_begin(), blockDecl->param_end());
// Create the function declaration.
const FunctionProtoType *fnType = blockInfo.getBlockExpr()->getFunctionType();
const CGFunctionInfo &fnInfo =
CGM.getTypes().arrangeBlockFunctionDeclaration(fnType, args);
if (CGM.ReturnSlotInterferesWithArgs(fnInfo))
blockInfo.UsesStret = true;
llvm::FunctionType *fnLLVMType = CGM.getTypes().GetFunctionType(fnInfo);
StringRef name = CGM.getBlockMangledName(GD, blockDecl);
llvm::Function *fn = llvm::Function::Create(
fnLLVMType, llvm::GlobalValue::InternalLinkage, name, &CGM.getModule());
CGM.SetInternalFunctionAttributes(blockDecl, fn, fnInfo);
if (BuildGlobalBlock) {
auto GenVoidPtrTy = getContext().getLangOpts().OpenCL
? CGM.getOpenCLRuntime().getGenericVoidPointerType()
: VoidPtrTy;
buildGlobalBlock(CGM, blockInfo,
llvm::ConstantExpr::getPointerCast(fn, GenVoidPtrTy));
// Begin generating the function.
StartFunction(blockDecl, fnType->getReturnType(), fn, fnInfo, args,
// Okay. Undo some of what StartFunction did.
// At -O0 we generate an explicit alloca for the BlockPointer, so the RA
// won't delete the dbg.declare intrinsics for captured variables.
llvm::Value *BlockPointerDbgLoc = BlockPointer;
if (CGM.getCodeGenOpts().OptimizationLevel == 0) {
// Allocate a stack slot for it, so we can point the debugger to it
Address Alloca = CreateTempAlloca(BlockPointer->getType(),
// Set the DebugLocation to empty, so the store is recognized as a
// frame setup instruction by llvm::DwarfDebug::beginFunction().
auto NL = ApplyDebugLocation::CreateEmpty(*this);
Builder.CreateStore(BlockPointer, Alloca);
BlockPointerDbgLoc = Alloca.getPointer();
// If we have a C++ 'this' reference, go ahead and force it into
// existence now.
if (blockDecl->capturesCXXThis()) {
Address addr = Builder.CreateStructGEP(
LoadBlockStruct(), blockInfo.CXXThisIndex, "block.captured-this");
CXXThisValue = Builder.CreateLoad(addr, "this");
// Also force all the constant captures.
for (const auto &CI : blockDecl->captures()) {
const VarDecl *variable = CI.getVariable();
const CGBlockInfo::Capture &capture = blockInfo.getCapture(variable);
if (!capture.isConstant()) continue;
CharUnits align = getContext().getDeclAlign(variable);
Address alloca =
CreateMemTemp(variable->getType(), align, "block.captured-const");
Builder.CreateStore(capture.getConstant(), alloca);
setAddrOfLocalVar(variable, alloca);
// Save a spot to insert the debug information for all the DeclRefExprs.
llvm::BasicBlock *entry = Builder.GetInsertBlock();
llvm::BasicBlock::iterator entry_ptr = Builder.GetInsertPoint();
if (IsLambdaConversionToBlock)
else {
PGO.assignRegionCounters(GlobalDecl(blockDecl), fn);
// Remember where we were...
llvm::BasicBlock *resume = Builder.GetInsertBlock();
// Go back to the entry.
Builder.SetInsertPoint(entry, entry_ptr);
// Emit debug information for all the DeclRefExprs.
// FIXME: also for 'this'
if (CGDebugInfo *DI = getDebugInfo()) {
for (const auto &CI : blockDecl->captures()) {
const VarDecl *variable = CI.getVariable();
DI->EmitLocation(Builder, variable->getLocation());
if (CGM.getCodeGenOpts().hasReducedDebugInfo()) {
const CGBlockInfo::Capture &capture = blockInfo.getCapture(variable);
if (capture.isConstant()) {
auto addr = LocalDeclMap.find(variable)->second;
(void)DI->EmitDeclareOfAutoVariable(variable, addr.getPointer(),
variable, BlockPointerDbgLoc, Builder, blockInfo,
entry_ptr == entry->end() ? nullptr : &*entry_ptr);
// Recover location if it was changed in the above loop.
// And resume where we left off.
if (resume == nullptr)
return fn;
static std::pair<BlockCaptureEntityKind, BlockFieldFlags>
computeCopyInfoForBlockCapture(const BlockDecl::Capture &CI, QualType T,
const LangOptions &LangOpts) {
if (CI.getCopyExpr()) {
// don't bother computing flags
return std::make_pair(BlockCaptureEntityKind::CXXRecord, BlockFieldFlags());
BlockFieldFlags Flags;
if (CI.isEscapingByref()) {
if (T.isObjCGCWeak())
return std::make_pair(BlockCaptureEntityKind::BlockObject, Flags);
bool isBlockPointer = T->isBlockPointerType();
if (isBlockPointer)
switch (T.isNonTrivialToPrimitiveCopy()) {
case QualType::PCK_Struct:
return std::make_pair(BlockCaptureEntityKind::NonTrivialCStruct,
case QualType::PCK_ARCWeak:
// We need to register __weak direct captures with the runtime.
return std::make_pair(BlockCaptureEntityKind::ARCWeak, Flags);
case QualType::PCK_ARCStrong:
// We need to retain the copied value for __strong direct captures.
// If it's a block pointer, we have to copy the block and assign that to
// the destination pointer, so we might as well use _Block_object_assign.
// Otherwise we can avoid that.
return std::make_pair(!isBlockPointer ? BlockCaptureEntityKind::ARCStrong
: BlockCaptureEntityKind::BlockObject,
case QualType::PCK_Trivial:
case QualType::PCK_VolatileTrivial: {
if (!T->isObjCRetainableType())
// For all other types, the memcpy is fine.
return std::make_pair(BlockCaptureEntityKind::None, BlockFieldFlags());
// Special rules for ARC captures:
Qualifiers QS = T.getQualifiers();
// Non-ARC captures of retainable pointers are strong and
// therefore require a call to _Block_object_assign.
if (!QS.getObjCLifetime() && !LangOpts.ObjCAutoRefCount)
return std::make_pair(BlockCaptureEntityKind::BlockObject, Flags);
// Otherwise the memcpy is fine.
return std::make_pair(BlockCaptureEntityKind::None, BlockFieldFlags());
llvm_unreachable("after exhaustive PrimitiveCopyKind switch");
static std::pair<BlockCaptureEntityKind, BlockFieldFlags>
computeDestroyInfoForBlockCapture(const BlockDecl::Capture &CI, QualType T,
const LangOptions &LangOpts);
/// Find the set of block captures that need to be explicitly copied or destroy.
static void findBlockCapturedManagedEntities(
const CGBlockInfo &BlockInfo, const LangOptions &LangOpts,
SmallVectorImpl<BlockCaptureManagedEntity> &ManagedCaptures) {
for (const auto &CI : BlockInfo.getBlockDecl()->captures()) {
const VarDecl *Variable = CI.getVariable();
const CGBlockInfo::Capture &Capture = BlockInfo.getCapture(Variable);
if (Capture.isConstant())
QualType VT = Capture.fieldType();
auto CopyInfo = computeCopyInfoForBlockCapture(CI, VT, LangOpts);
auto DisposeInfo = computeDestroyInfoForBlockCapture(CI, VT, LangOpts);
if (CopyInfo.first != BlockCaptureEntityKind::None ||
DisposeInfo.first != BlockCaptureEntityKind::None)
ManagedCaptures.emplace_back(CopyInfo.first, DisposeInfo.first,
CopyInfo.second, DisposeInfo.second, CI,
// Sort the captures by offset.
namespace {
/// Release a __block variable.
struct CallBlockRelease final : EHScopeStack::Cleanup {
Address Addr;
BlockFieldFlags FieldFlags;
bool LoadBlockVarAddr, CanThrow;
CallBlockRelease(Address Addr, BlockFieldFlags Flags, bool LoadValue,
bool CT)
: Addr(Addr), FieldFlags(Flags), LoadBlockVarAddr(LoadValue),
CanThrow(CT) {}
void Emit(CodeGenFunction &CGF, Flags flags) override {
llvm::Value *BlockVarAddr;
if (LoadBlockVarAddr) {
BlockVarAddr = CGF.Builder.CreateLoad(Addr);
BlockVarAddr = CGF.Builder.CreateBitCast(BlockVarAddr, CGF.VoidPtrTy);
} else {
BlockVarAddr = Addr.getPointer();
CGF.BuildBlockRelease(BlockVarAddr, FieldFlags, CanThrow);
} // end anonymous namespace
/// Check if \p T is a C++ class that has a destructor that can throw.
bool CodeGenFunction::cxxDestructorCanThrow(QualType T) {
if (const auto *RD = T->getAsCXXRecordDecl())
if (const CXXDestructorDecl *DD = RD->getDestructor())
return DD->getType()->castAs<FunctionProtoType>()->canThrow();
return false;
// Return a string that has the information about a capture.
static std::string getBlockCaptureStr(const BlockCaptureManagedEntity &E,
CaptureStrKind StrKind,
CharUnits BlockAlignment,
CodeGenModule &CGM) {
std::string Str;
ASTContext &Ctx = CGM.getContext();
const BlockDecl::Capture &CI = *E.CI;
QualType CaptureTy = CI.getVariable()->getType();
BlockCaptureEntityKind Kind;
BlockFieldFlags Flags;
// CaptureStrKind::Merged should be passed only when the operations and the
// flags are the same for copy and dispose.
assert((StrKind != CaptureStrKind::Merged ||
(E.CopyKind == E.DisposeKind && E.CopyFlags == E.DisposeFlags)) &&
"different operations and flags");
if (StrKind == CaptureStrKind::DisposeHelper) {
Kind = E.DisposeKind;
Flags = E.DisposeFlags;
} else {
Kind = E.CopyKind;
Flags = E.CopyFlags;
switch (Kind) {
case BlockCaptureEntityKind::CXXRecord: {
Str += "c";
SmallString<256> TyStr;
llvm::raw_svector_ostream Out(TyStr);
CGM.getCXXABI().getMangleContext().mangleTypeName(CaptureTy, Out);
Str += llvm::to_string(TyStr.size()) + TyStr.c_str();
case BlockCaptureEntityKind::ARCWeak:
Str += "w";
case BlockCaptureEntityKind::ARCStrong:
Str += "s";
case BlockCaptureEntityKind::BlockObject: {
const VarDecl *Var = CI.getVariable();
unsigned F = Flags.getBitMask();
Str += "r";
Str += "w";
else {
// If CaptureStrKind::Merged is passed, check both the copy expression
// and the destructor.
if (StrKind != CaptureStrKind::DisposeHelper) {
if (Ctx.getBlockVarCopyInit(Var).canThrow())
Str += "c";
if (StrKind != CaptureStrKind::CopyHelper) {
if (CodeGenFunction::cxxDestructorCanThrow(CaptureTy))
Str += "d";
} else {
assert((F & BLOCK_FIELD_IS_OBJECT) && "unexpected flag value");
Str += "b";
Str += "o";
case BlockCaptureEntityKind::NonTrivialCStruct: {
bool IsVolatile = CaptureTy.isVolatileQualified();
CharUnits Alignment =
Str += "n";
std::string FuncStr;
if (StrKind == CaptureStrKind::DisposeHelper)
FuncStr = CodeGenFunction::getNonTrivialDestructorStr(
CaptureTy, Alignment, IsVolatile, Ctx);
// If CaptureStrKind::Merged is passed, use the copy constructor string.
// It has all the information that the destructor string has.
FuncStr = CodeGenFunction::getNonTrivialCopyConstructorStr(
CaptureTy, Alignment, IsVolatile, Ctx);
// The underscore is necessary here because non-trivial copy constructor
// and destructor strings can start with a number.
Str += llvm::to_string(FuncStr.size()) + "_" + FuncStr;
case BlockCaptureEntityKind::None:
return Str;
static std::string getCopyDestroyHelperFuncName(
const SmallVectorImpl<BlockCaptureManagedEntity> &Captures,
CharUnits BlockAlignment, CaptureStrKind StrKind, CodeGenModule &CGM) {
assert((StrKind == CaptureStrKind::CopyHelper ||
StrKind == CaptureStrKind::DisposeHelper) &&
"unexpected CaptureStrKind");
std::string Name = StrKind == CaptureStrKind::CopyHelper
? "__copy_helper_block_"
: "__destroy_helper_block_";
if (CGM.getLangOpts().Exceptions)
Name += "e";
if (CGM.getCodeGenOpts().ObjCAutoRefCountExceptions)
Name += "a";
Name += llvm::to_string(BlockAlignment.getQuantity()) + "_";
for (const BlockCaptureManagedEntity &E : Captures) {
Name += llvm::to_string(E.Capture->getOffset().getQuantity());
Name += getBlockCaptureStr(E, StrKind, BlockAlignment, CGM);
return Name;
static void pushCaptureCleanup(BlockCaptureEntityKind CaptureKind,
Address Field, QualType CaptureType,
BlockFieldFlags Flags, bool ForCopyHelper,
VarDecl *Var, CodeGenFunction &CGF) {
bool EHOnly = ForCopyHelper;
switch (CaptureKind) {
case BlockCaptureEntityKind::CXXRecord:
case BlockCaptureEntityKind::ARCWeak:
case BlockCaptureEntityKind::NonTrivialCStruct:
case BlockCaptureEntityKind::ARCStrong: {
if (CaptureType.isDestructedType() &&
(!EHOnly || CGF.needsEHCleanup(CaptureType.isDestructedType()))) {
CodeGenFunction::Destroyer *Destroyer =
CaptureKind == BlockCaptureEntityKind::ARCStrong
? CodeGenFunction::destroyARCStrongImprecise
: CGF.getDestroyer(CaptureType.isDestructedType());
CleanupKind Kind =
EHOnly ? EHCleanup
: CGF.getCleanupKind(CaptureType.isDestructedType());
CGF.pushDestroy(Kind, Field, CaptureType, Destroyer, Kind & EHCleanup);
case BlockCaptureEntityKind::BlockObject: {
if (!EHOnly || CGF.getLangOpts().Exceptions) {
CleanupKind Kind = EHOnly ? EHCleanup : NormalAndEHCleanup;
// Calls to _Block_object_dispose along the EH path in the copy helper
// function don't throw as newly-copied __block variables always have a
// reference count of 2.
bool CanThrow =
!ForCopyHelper && CGF.cxxDestructorCanThrow(CaptureType);
CGF.enterByrefCleanup(Kind, Field, Flags, /*LoadBlockVarAddr*/ true,
case BlockCaptureEntityKind::None:
static void setBlockHelperAttributesVisibility(bool CapturesNonExternalType,
llvm::Function *Fn,
const CGFunctionInfo &FI,
CodeGenModule &CGM) {
if (CapturesNonExternalType) {
CGM.SetInternalFunctionAttributes(GlobalDecl(), Fn, FI);
} else {
CGM.SetLLVMFunctionAttributes(GlobalDecl(), FI, Fn, /*IsThunk=*/false);
CGM.SetLLVMFunctionAttributesForDefinition(nullptr, Fn);
/// Generate the copy-helper function for a block closure object:
/// static void block_copy_helper(block_t *dst, block_t *src);
/// The runtime will have previously initialized 'dst' by doing a
/// bit-copy of 'src'.
/// Note that this copies an entire block closure object to the heap;
/// it should not be confused with a 'byref copy helper', which moves
/// the contents of an individual __block variable to the heap.
llvm::Constant *
CodeGenFunction::GenerateCopyHelperFunction(const CGBlockInfo &blockInfo) {
SmallVector<BlockCaptureManagedEntity, 4> CopiedCaptures;
findBlockCapturedManagedEntities(blockInfo, getLangOpts(), CopiedCaptures);
std::string FuncName =
getCopyDestroyHelperFuncName(CopiedCaptures, blockInfo.BlockAlign,
CaptureStrKind::CopyHelper, CGM);
if (llvm::GlobalValue *Func = CGM.getModule().getNamedValue(FuncName))
return llvm::ConstantExpr::getBitCast(Func, VoidPtrTy);
ASTContext &C = getContext();
QualType ReturnTy = C.VoidTy;
FunctionArgList args;
ImplicitParamDecl DstDecl(C, C.VoidPtrTy, ImplicitParamDecl::Other);
ImplicitParamDecl SrcDecl(C, C.VoidPtrTy, ImplicitParamDecl::Other);
const CGFunctionInfo &FI =
CGM.getTypes().arrangeBuiltinFunctionDeclaration(ReturnTy, args);
// FIXME: it would be nice if these were mergeable with things with
// identical semantics.
llvm::FunctionType *LTy = CGM.getTypes().GetFunctionType(FI);
llvm::Function *Fn =
llvm::Function::Create(LTy, llvm::GlobalValue::LinkOnceODRLinkage,
FuncName, &CGM.getModule());
if (CGM.supportsCOMDAT())
SmallVector<QualType, 2> ArgTys;
setBlockHelperAttributesVisibility(blockInfo.CapturesNonExternalType, Fn, FI,
StartFunction(GlobalDecl(), ReturnTy, Fn, FI, args);
auto AL = ApplyDebugLocation::CreateArtificial(*this);
llvm::Type *structPtrTy = blockInfo.StructureType->getPointerTo();
Address src = GetAddrOfLocalVar(&SrcDecl);
src = Address(Builder.CreateLoad(src), blockInfo.BlockAlign);
src = Builder.CreateBitCast(src, structPtrTy, "block.source");
Address dst = GetAddrOfLocalVar(&DstDecl);
dst = Address(Builder.CreateLoad(dst), blockInfo.BlockAlign);
dst = Builder.CreateBitCast(dst, structPtrTy, "block.dest");
for (const auto &CopiedCapture : CopiedCaptures) {
const BlockDecl::Capture &CI = *CopiedCapture.CI;
const CGBlockInfo::Capture &capture = *CopiedCapture.Capture;
QualType captureType = CI.getVariable()->getType();
BlockFieldFlags flags = CopiedCapture.CopyFlags;
unsigned index = capture.getIndex();
Address srcField = Builder.CreateStructGEP(src, index);
Address dstField = Builder.CreateStructGEP(dst, index);
switch (CopiedCapture.CopyKind) {
case BlockCaptureEntityKind::CXXRecord:
// If there's an explicit copy expression, we do that.
assert(CI.getCopyExpr() && "copy expression for variable is missing");
EmitSynthesizedCXXCopyCtor(dstField, srcField, CI.getCopyExpr());
case BlockCaptureEntityKind::ARCWeak:
EmitARCCopyWeak(dstField, srcField);
case BlockCaptureEntityKind::NonTrivialCStruct: {
// If this is a C struct that requires non-trivial copy construction,
// emit a call to its copy constructor.
QualType varType = CI.getVariable()->getType();
callCStructCopyConstructor(MakeAddrLValue(dstField, varType),
MakeAddrLValue(srcField, varType));
case BlockCaptureEntityKind::ARCStrong: {
llvm::Value *srcValue = Builder.CreateLoad(srcField, "blockcopy.src");
// At -O0, store null into the destination field (so that the
// storeStrong doesn't over-release) and then call storeStrong.
// This is a workaround to not having an initStrong call.
if (CGM.getCodeGenOpts().OptimizationLevel == 0) {
auto *ty = cast<llvm::PointerType>(srcValue->getType());
llvm::Value *null = llvm::ConstantPointerNull::get(ty);
Builder.CreateStore(null, dstField);
EmitARCStoreStrongCall(dstField, srcValue, true);
// With optimization enabled, take advantage of the fact that
// the blocks runtime guarantees a memcpy of the block data, and
// just emit a retain of the src field.
} else {
// Unless EH cleanup is required, we don't need this anymore, so kill
// it. It's not quite worth the annoyance to avoid creating it in the
// first place.
if (!needsEHCleanup(captureType.isDestructedType()))
case BlockCaptureEntityKind::BlockObject: {
llvm::Value *srcValue = Builder.CreateLoad(srcField, "blockcopy.src");
srcValue = Builder.CreateBitCast(srcValue, VoidPtrTy);
llvm::Value *dstAddr =
Builder.CreateBitCast(dstField.getPointer(), VoidPtrTy);
llvm::Value *args[] = {
dstAddr, srcValue, llvm::ConstantInt::get(Int32Ty, flags.getBitMask())
if (CI.isByRef() && C.getBlockVarCopyInit(CI.getVariable()).canThrow())
EmitRuntimeCallOrInvoke(CGM.getBlockObjectAssign(), args);
EmitNounwindRuntimeCall(CGM.getBlockObjectAssign(), args);
case BlockCaptureEntityKind::None:
// Ensure that we destroy the copied object if an exception is thrown later
// in the helper function.
pushCaptureCleanup(CopiedCapture.CopyKind, dstField, captureType, flags,
/*ForCopyHelper*/ true, CI.getVariable(), *this);
return llvm::ConstantExpr::getBitCast(Fn, VoidPtrTy);
static BlockFieldFlags
getBlockFieldFlagsForObjCObjectPointer(const BlockDecl::Capture &CI,
QualType T) {
BlockFieldFlags Flags = BLOCK_FIELD_IS_OBJECT;
if (T->isBlockPointerType())
return Flags;
static std::pair<BlockCaptureEntityKind, BlockFieldFlags>
computeDestroyInfoForBlockCapture(const BlockDecl::Capture &CI, QualType T,
const LangOptions &LangOpts) {
if (CI.isEscapingByref()) {
BlockFieldFlags Flags = BLOCK_FIELD_IS_BYREF;
if (T.isObjCGCWeak())
return std::make_pair(BlockCaptureEntityKind::BlockObject, Flags);
switch (T.isDestructedType()) {
case QualType::DK_cxx_destructor:
return std::make_pair(BlockCaptureEntityKind::CXXRecord, BlockFieldFlags());
case QualType::DK_objc_strong_lifetime:
// Use objc_storeStrong for __strong direct captures; the
// dynamic tools really like it when we do this.
return std::make_pair(BlockCaptureEntityKind::ARCStrong,
getBlockFieldFlagsForObjCObjectPointer(CI, T));
case QualType::DK_objc_weak_lifetime:
// Support __weak direct captures.
return std::make_pair(BlockCaptureEntityKind::ARCWeak,
getBlockFieldFlagsForObjCObjectPointer(CI, T));
case QualType::DK_nontrivial_c_struct:
return std::make_pair(BlockCaptureEntityKind::NonTrivialCStruct,
case QualType::DK_none: {
// Non-ARC captures are strong, and we need to use _Block_object_dispose.
if (T->isObjCRetainableType() && !T.getQualifiers().hasObjCLifetime() &&
return std::make_pair(BlockCaptureEntityKind::BlockObject,
getBlockFieldFlagsForObjCObjectPointer(CI, T));
// Otherwise, we have nothing to do.
return std::make_pair(BlockCaptureEntityKind::None, BlockFieldFlags());
llvm_unreachable("after exhaustive DestructionKind switch");
/// Generate the destroy-helper function for a block closure object:
/// static void block_destroy_helper(block_t *theBlock);
/// Note that this destroys a heap-allocated block closure object;
/// it should not be confused with a 'byref destroy helper', which
/// destroys the heap-allocated contents of an individual __block
/// variable.
llvm::Constant *
CodeGenFunction::GenerateDestroyHelperFunction(const CGBlockInfo &blockInfo) {
SmallVector<BlockCaptureManagedEntity, 4> DestroyedCaptures;
findBlockCapturedManagedEntities(blockInfo, getLangOpts(), DestroyedCaptures);
std::string FuncName =
getCopyDestroyHelperFuncName(DestroyedCaptures, blockInfo.BlockAlign,
CaptureStrKind::DisposeHelper, CGM);
if (llvm::GlobalValue *Func = CGM.getModule().getNamedValue(FuncName))
return llvm::ConstantExpr::getBitCast(Func, VoidPtrTy);
ASTContext &C = getContext();
QualType ReturnTy = C.VoidTy;
FunctionArgList args;
ImplicitParamDecl SrcDecl(C, C.VoidPtrTy, ImplicitParamDecl::Other);
const CGFunctionInfo &FI =
CGM.getTypes().arrangeBuiltinFunctionDeclaration(ReturnTy, args);
// FIXME: We'd like to put these into a mergable by content, with
// internal linkage.
llvm::FunctionType *LTy = CGM.getTypes().GetFunctionType(FI);
llvm::Function *Fn =
llvm::Function::Create(LTy, llvm::GlobalValue::LinkOnceODRLinkage,
FuncName, &CGM.getModule());
if (CGM.supportsCOMDAT())
SmallVector<QualType, 1> ArgTys;
setBlockHelperAttributesVisibility(blockInfo.CapturesNonExternalType, Fn, FI,
StartFunction(GlobalDecl(), ReturnTy, Fn, FI, args);
auto AL = ApplyDebugLocation::CreateArtificial(*this);
llvm::Type *structPtrTy = blockInfo.StructureType->getPointerTo();
Address src = GetAddrOfLocalVar(&SrcDecl);
src = Address(Builder.CreateLoad(src), blockInfo.BlockAlign);
src = Builder.CreateBitCast(src, structPtrTy, "block");
CodeGenFunction::RunCleanupsScope cleanups(*this);
for (const auto &DestroyedCapture : DestroyedCaptures) {
const BlockDecl::Capture &CI = *DestroyedCapture.CI;
const CGBlockInfo::Capture &capture = *DestroyedCapture.Capture;
BlockFieldFlags flags = DestroyedCapture.DisposeFlags;
Address srcField = Builder.CreateStructGEP(src, capture.getIndex());
pushCaptureCleanup(DestroyedCapture.DisposeKind, srcField,
CI.getVariable()->getType(), flags,
/*ForCopyHelper*/ false, CI.getVariable(), *this);
return llvm::ConstantExpr::getBitCast(Fn, VoidPtrTy);
namespace {
/// Emits the copy/dispose helper functions for a __block object of id type.
class ObjectByrefHelpers final : public BlockByrefHelpers {
BlockFieldFlags Flags;
ObjectByrefHelpers(CharUnits alignment, BlockFieldFlags flags)
: BlockByrefHelpers(alignment), Flags(flags) {}
void emitCopy(CodeGenFunction &CGF, Address destField,
Address srcField) override {
destField = CGF.Builder.CreateBitCast(destField, CGF.VoidPtrTy);
srcField = CGF.Builder.CreateBitCast(srcField, CGF.VoidPtrPtrTy);
llvm::Value *srcValue = CGF.Builder.CreateLoad(srcField);
unsigned flags = (Flags | BLOCK_BYREF_CALLER).getBitMask();
llvm::Value *flagsVal = llvm::ConstantInt::get(CGF.Int32Ty, flags);
llvm::FunctionCallee fn = CGF.CGM.getBlockObjectAssign();
llvm::Value *args[] = { destField.getPointer(), srcValue, flagsVal };
CGF.EmitNounwindRuntimeCall(fn, args);
void emitDispose(CodeGenFunction &CGF, Address field) override {
field = CGF.Builder.CreateBitCast(field, CGF.Int8PtrTy->getPointerTo(0));
llvm::Value *value = CGF.Builder.CreateLoad(field);
CGF.BuildBlockRelease(value, Flags | BLOCK_BYREF_CALLER, false);
void profileImpl(llvm::FoldingSetNodeID &id) const override {
/// Emits the copy/dispose helpers for an ARC __block __weak variable.
class ARCWeakByrefHelpers final : public BlockByrefHelpers {
ARCWeakByrefHelpers(CharUnits alignment) : BlockByrefHelpers(alignment) {}
void emitCopy(CodeGenFunction &CGF, Address destField,
Address srcField) override {
CGF.EmitARCMoveWeak(destField, srcField);
void emitDispose(CodeGenFunction &CGF, Address field) override {
void profileImpl(llvm::FoldingSetNodeID &id) const override {
// 0 is distinguishable from all pointers and byref flags
/// Emits the copy/dispose helpers for an ARC __block __strong variable
/// that's not of block-pointer type.
class ARCStrongByrefHelpers final : public BlockByrefHelpers {
ARCStrongByrefHelpers(CharUnits alignment) : BlockByrefHelpers(alignment) {}
void emitCopy(CodeGenFunction &CGF, Address destField,
Address srcField) override {
// Do a "move" by copying the value and then zeroing out the old
// variable.
llvm::Value *value = CGF.Builder.CreateLoad(srcField);
llvm::Value *null =
if (CGF.CGM.getCodeGenOpts().OptimizationLevel == 0) {
CGF.Builder.CreateStore(null, destField);
CGF.EmitARCStoreStrongCall(destField, value, /*ignored*/ true);
CGF.EmitARCStoreStrongCall(srcField, null, /*ignored*/ true);
CGF.Builder.CreateStore(value, destField);
CGF.Builder.CreateStore(null, srcField);
void emitDispose(CodeGenFunction &CGF, Address field) override {
CGF.EmitARCDestroyStrong(field, ARCImpreciseLifetime);
void profileImpl(llvm::FoldingSetNodeID &id) const override {
// 1 is distinguishable from all pointers and byref flags
/// Emits the copy/dispose helpers for an ARC __block __strong
/// variable that's of block-pointer type.
class ARCStrongBlockByrefHelpers final : public BlockByrefHelpers {
ARCStrongBlockByrefHelpers(CharUnits alignment)
: BlockByrefHelpers(alignment) {}
void emitCopy(CodeGenFunction &CGF, Address destField,
Address srcField) override {
// Do the copy with objc_retainBlock; that's all that
// _Block_object_assign would do anyway, and we'd have to pass the
// right arguments to make sure it doesn't get no-op'ed.
llvm::Value *oldValue = CGF.Builder.CreateLoad(srcField);
llvm::Value *copy = CGF.EmitARCRetainBlock(oldValue, /*mandatory*/ true);
CGF.Builder.CreateStore(copy, destField);
void emitDispose(CodeGenFunction &CGF, Address field) override {
CGF.EmitARCDestroyStrong(field, ARCImpreciseLifetime);
void profileImpl(llvm::FoldingSetNodeID &id) const override {
// 2 is distinguishable from all pointers and byref flags
/// Emits the copy/dispose helpers for a __block variable with a
/// nontrivial copy constructor or destructor.
class CXXByrefHelpers final : public BlockByrefHelpers {
QualType VarType;
const Expr *CopyExpr;
CXXByrefHelpers(CharUnits alignment, QualType type,
const Expr *copyExpr)
: BlockByrefHelpers(alignment), VarType(type), CopyExpr(copyExpr) {}
bool needsCopy() const override { return CopyExpr != nullptr; }
void emitCopy(CodeGenFunction &CGF, Address destField,
Address srcField) override {
if (!CopyExpr) return;
CGF.EmitSynthesizedCXXCopyCtor(destField, srcField, CopyExpr);
void emitDispose(CodeGenFunction &CGF, Address field) override {
EHScopeStack::stable_iterator cleanupDepth = CGF.EHStack.stable_begin();
CGF.PushDestructorCleanup(VarType, field);
void profileImpl(llvm::FoldingSetNodeID &id) const override {
/// Emits the copy/dispose helpers for a __block variable that is a non-trivial
/// C struct.
class NonTrivialCStructByrefHelpers final : public BlockByrefHelpers {
QualType VarType;
NonTrivialCStructByrefHelpers(CharUnits alignment, QualType type)
: BlockByrefHelpers(alignment), VarType(type) {}
void emitCopy(CodeGenFunction &CGF, Address destField,
Address srcField) override {
CGF.callCStructMoveConstructor(CGF.MakeAddrLValue(destField, VarType),
CGF.MakeAddrLValue(srcField, VarType));
bool needsDispose() const override {
return VarType.isDestructedType();
void emitDispose(CodeGenFunction &CGF, Address field) override {
EHScopeStack::stable_iterator cleanupDepth = CGF.EHStack.stable_begin();
CGF.pushDestroy(VarType.isDestructedType(), field, VarType);
void profileImpl(llvm::FoldingSetNodeID &id) const override {
} // end anonymous namespace
static llvm::Constant *
generateByrefCopyHelper(CodeGenFunction &CGF, const BlockByrefInfo &byrefInfo,
BlockByrefHelpers &generator) {
ASTContext &Context = CGF.getContext();
QualType ReturnTy = Context.VoidTy;
FunctionArgList args;
ImplicitParamDecl Dst(Context, Context.VoidPtrTy, ImplicitParamDecl::Other);
ImplicitParamDecl Src(Context, Context.VoidPtrTy, ImplicitParamDecl::Other);
const CGFunctionInfo &FI =
CGF.CGM.getTypes().arrangeBuiltinFunctionDeclaration(ReturnTy, args);
llvm::FunctionType *LTy = CGF.CGM.getTypes().GetFunctionType(FI);
// 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_object_copy_", &CGF.CGM.getModule());
SmallVector<QualType, 2> ArgTys;
CGF.CGM.SetInternalFunctionAttributes(GlobalDecl(), Fn, FI);
CGF.StartFunction(GlobalDecl(), ReturnTy, Fn, FI, args);
// Create a scope with an artificial location for the body of this function.
auto AL = ApplyDebugLocation::CreateArtificial(CGF);
if (generator.needsCopy()) {
llvm::Type *byrefPtrType = byrefInfo.Type->getPointerTo(0);
// dst->x
Address destField = CGF.GetAddrOfLocalVar(&Dst);
destField = Address(CGF.Builder.CreateLoad(destField),
destField = CGF.Builder.CreateBitCast(destField, byrefPtrType);
destField = CGF.emitBlockByrefAddress(destField, byrefInfo, false,
// src->x
Address srcField = CGF.GetAddrOfLocalVar(&Src);
srcField = Address(CGF.Builder.CreateLoad(srcField),
srcField = CGF.Builder.CreateBitCast(srcField, byrefPtrType);
srcField = CGF.emitBlockByrefAddress(srcField, byrefInfo, false,
generator.emitCopy(CGF, destField, srcField);
return llvm::ConstantExpr::getBitCast(Fn, CGF.Int8PtrTy);
/// Build the copy helper for a __block variable.
static llvm::Constant *buildByrefCopyHelper(CodeGenModule &CGM,
const BlockByrefInfo &byrefInfo,
BlockByrefHelpers &generator) {
CodeGenFunction CGF(CGM);
return generateByrefCopyHelper(CGF, byrefInfo, generator);
/// Generate code for a __block variable's dispose helper.
static llvm::Constant *
generateByrefDisposeHelper(CodeGenFunction &CGF,
const BlockByrefInfo &byrefInfo,
BlockByrefHelpers &generator) {
ASTContext &Context = CGF.getContext();
QualType R = Context.VoidTy;
FunctionArgList args;
ImplicitParamDecl Src(CGF.getContext(), Context.VoidPtrTy,
const CGFunctionInfo &FI =
CGF.CGM.getTypes().arrangeBuiltinFunctionDeclaration(R, args);
llvm::FunctionType *LTy = CGF.CGM.getTypes().GetFunctionType(FI);
// 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,
SmallVector<QualType, 1> ArgTys;
CGF.CGM.SetInternalFunctionAttributes(GlobalDecl(), Fn, FI);
CGF.StartFunction(GlobalDecl(), R, Fn, FI, args);
// Create a scope with an artificial location for the body of this function.
auto AL = ApplyDebugLocation::CreateArtificial(CGF);
if (generator.needsDispose()) {
Address addr = CGF.GetAddrOfLocalVar(&Src);
addr = Address(CGF.Builder.CreateLoad(addr), byrefInfo.ByrefAlignment);
auto byrefPtrType = byrefInfo.Type->getPointerTo(0);
addr = CGF.Builder.CreateBitCast(addr, byrefPtrType);
addr = CGF.emitBlockByrefAddress(addr, byrefInfo, false, "object");
generator.emitDispose(CGF, addr);
return llvm::ConstantExpr::getBitCast(Fn, CGF.Int8PtrTy);
/// Build the dispose helper for a __block variable.
static llvm::Constant *buildByrefDisposeHelper(CodeGenModule &CGM,
const BlockByrefInfo &byrefInfo,
BlockByrefHelpers &generator) {
CodeGenFunction CGF(CGM);
return generateByrefDisposeHelper(CGF, byrefInfo, generator);
/// Lazily build the copy and dispose helpers for a __block variable
/// with the given information.
template <class T>
static T *buildByrefHelpers(CodeGenModule &CGM, const BlockByrefInfo &byrefInfo,
T &&generator) {
llvm::FoldingSetNodeID id;
void *insertPos;
BlockByrefHelpers *node
= CGM.ByrefHelpersCache.FindNodeOrInsertPos(id, insertPos);
if (node) return static_cast<T*>(node);
generator.CopyHelper = buildByrefCopyHelper(CGM, byrefInfo, generator);
generator.DisposeHelper = buildByrefDisposeHelper(CGM, byrefInfo, generator);
T *copy = new (CGM.getContext()) T(std::forward<T>(generator));
CGM.ByrefHelpersCache.InsertNode(copy, insertPos);
return copy;
/// Build the copy and dispose helpers for the given __block variable
/// emission. Places the helpers in the global cache. Returns null
/// if no helpers are required.
BlockByrefHelpers *
CodeGenFunction::buildByrefHelpers(llvm::StructType &byrefType,
const AutoVarEmission &emission) {
const VarDecl &var = *emission.Variable;
assert(var.isEscapingByref() &&
"only escaping __block variables need byref helpers");
QualType type = var.getType();
auto &byrefInfo = getBlockByrefInfo(&var);
// The alignment we care about for the purposes of uniquing byref
// helpers is the alignment of the actual byref value field.
CharUnits valueAlignment =
if (const CXXRecordDecl *record = type->getAsCXXRecordDecl()) {
const Expr *copyExpr =
if (!copyExpr && record->hasTrivialDestructor()) return nullptr;
return ::buildByrefHelpers(
CGM, byrefInfo, CXXByrefHelpers(valueAlignment, type, copyExpr));
// If type is a non-trivial C struct type that is non-trivial to
// destructly move or destroy, build the copy and dispose helpers.
if (type.isNonTrivialToPrimitiveDestructiveMove() == QualType::PCK_Struct ||
type.isDestructedType() == QualType::DK_nontrivial_c_struct)
return ::buildByrefHelpers(
CGM, byrefInfo, NonTrivialCStructByrefHelpers(valueAlignment, type));
// Otherwise, if we don't have a retainable type, there's nothing to do.
// that the runtime does extra copies.
if (!type->isObjCRetainableType()) return nullptr;
Qualifiers qs = type.getQualifiers();
// If we have lifetime, that dominates.
if (Qualifiers::ObjCLifetime lifetime = qs.getObjCLifetime()) {
switch (lifetime) {
case Qualifiers::OCL_None: llvm_unreachable("impossible");
// These are just bits as far as the runtime is concerned.
case Qualifiers::OCL_ExplicitNone:
case Qualifiers::OCL_Autoreleasing:
return nullptr;
// Tell the runtime that this is ARC __weak, called by the
// byref routines.
case Qualifiers::OCL_Weak:
return ::buildByrefHelpers(CGM, byrefInfo,
// ARC __strong __block variables need to be retained.
case Qualifiers::OCL_Strong:
// Block pointers need to be copied, and there's no direct
// transfer possible.
if (type->isBlockPointerType()) {
return ::buildByrefHelpers(CGM, byrefInfo,
// Otherwise, we transfer ownership of the retain from the stack
// to the heap.
} else {
return ::buildByrefHelpers(CGM, byrefInfo,
llvm_unreachable("fell out of lifetime switch!");
BlockFieldFlags flags;
if (type->isBlockPointerType()) {
} else if (CGM.getContext().isObjCNSObjectType(type) ||
type->isObjCObjectPointerType()) {
} else {
return nullptr;
if (type.isObjCGCWeak())
return ::buildByrefHelpers(CGM, byrefInfo,
ObjectByrefHelpers(valueAlignment, flags));
Address CodeGenFunction::emitBlockByrefAddress(Address baseAddr,
const VarDecl *var,
bool followForward) {
auto &info = getBlockByrefInfo(var);
return emitBlockByrefAddress(baseAddr, info, followForward, var->getName());
Address CodeGenFunction::emitBlockByrefAddress(Address baseAddr,
const BlockByrefInfo &info,
bool followForward,
const llvm::Twine &name) {
// Chase the forwarding address if requested.
if (followForward) {
Address forwardingAddr = Builder.CreateStructGEP(baseAddr, 1, "forwarding");
baseAddr = Address(Builder.CreateLoad(forwardingAddr), info.ByrefAlignment);
return Builder.CreateStructGEP(baseAddr, info.FieldIndex, name);
/// BuildByrefInfo - This routine changes a __block variable declared as T x
/// into:
/// struct {
/// void *__isa;
/// void *__forwarding;
/// int32_t __flags;
/// int32_t __size;
/// void *__copy_helper; // only if needed
/// void *__destroy_helper; // only if needed
/// void *__byref_variable_layout;// only if needed
/// char padding[X]; // only if needed
/// T x;
/// } x
const BlockByrefInfo &CodeGenFunction::getBlockByrefInfo(const VarDecl *D) {
auto it = BlockByrefInfos.find(D);
if (it != BlockByrefInfos.end())
return it->second;
llvm::StructType *byrefType =
"struct.__block_byref_" + D->getNameAsString());
QualType Ty = D->getType();
CharUnits size;
SmallVector<llvm::Type *, 8> types;
// void *__isa;
size += getPointerSize();
// void *__forwarding;
size += getPointerSize();
// int32_t __flags;
size += CharUnits::fromQuantity(4);
// int32_t __size;
size += CharUnits::fromQuantity(4);
// Note that this must match *exactly* the logic in buildByrefHelpers.
bool hasCopyAndDispose = getContext().BlockRequiresCopying(Ty, D);
if (hasCopyAndDispose) {
/// void *__copy_helper;
size += getPointerSize();
/// void *__destroy_helper;
size += getPointerSize();
bool HasByrefExtendedLayout = false;
Qualifiers::ObjCLifetime Lifetime = Qualifiers::OCL_None;
if (getContext().getByrefLifetime(Ty, Lifetime, HasByrefExtendedLayout) &&
HasByrefExtendedLayout) {
/// void *__byref_variable_layout;
size += CharUnits::fromQuantity(PointerSizeInBytes);
// T x;
llvm::Type *varTy = ConvertTypeForMem(Ty);
bool packed = false;
CharUnits varAlign = getContext().getDeclAlign(D);
CharUnits varOffset = size.alignTo(varAlign);
// We may have to insert padding.
if (varOffset != size) {
llvm::Type *paddingTy =
llvm::ArrayType::get(Int8Ty, (varOffset - size).getQuantity());
size = varOffset;
// Conversely, we might have to prevent LLVM from inserting padding.
} else if (CGM.getDataLayout().getABITypeAlignment(varTy) >
uint64_t(varAlign.getQuantity())) {
packed = true;
byrefType->setBody(types, packed);
BlockByrefInfo info;
info.Type = byrefType;
info.FieldIndex = types.size() - 1;
info.FieldOffset = varOffset;
info.ByrefAlignment = std::max(varAlign, getPointerAlign());
auto pair = BlockByrefInfos.insert({D, info});
assert(pair.second && "info was inserted recursively?");
return pair.first->second;
/// Initialize the structural components of a __block variable, i.e.
/// everything but the actual object.
void CodeGenFunction::emitByrefStructureInit(const AutoVarEmission &emission) {
// Find the address of the local.
Address addr = emission.Addr;
// That's an alloca of the byref structure type.
llvm::StructType *byrefType = cast<llvm::StructType>(
unsigned nextHeaderIndex = 0;
CharUnits nextHeaderOffset;
auto storeHeaderField = [&](llvm::Value *value, CharUnits fieldSize,
const Twine &name) {
auto fieldAddr = Builder.CreateStructGEP(addr, nextHeaderIndex, name);
Builder.CreateStore(value, fieldAddr);
nextHeaderOffset += fieldSize;
// Build the byref helpers if necessary. This is null if we don't need any.
BlockByrefHelpers *helpers = buildByrefHelpers(*byrefType, emission);
const VarDecl &D = *emission.Variable;
QualType type = D.getType();
bool HasByrefExtendedLayout = false;
Qualifiers::ObjCLifetime ByrefLifetime = Qualifiers::OCL_None;
bool ByRefHasLifetime =
getContext().getByrefLifetime(type, ByrefLifetime, HasByrefExtendedLayout);
llvm::Value *V;
// Initialize the 'isa', which is just 0 or 1.
int isa = 0;
if (type.isObjCGCWeak())
isa = 1;
V = Builder.CreateIntToPtr(Builder.getInt32(isa), Int8PtrTy, "isa");
storeHeaderField(V, getPointerSize(), "byref.isa");
// Store the address of the variable into its own forwarding pointer.
storeHeaderField(addr.getPointer(), getPointerSize(), "byref.forwarding");
// Blocks ABI:
// c) the flags field is set to either 0 if no helper functions are
// needed or BLOCK_BYREF_HAS_COPY_DISPOSE if they are,
BlockFlags flags;