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//===--- CGRecordLayoutBuilder.cpp - CGRecordLayout builder ----*- 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
// Builder implementation for CGRecordLayout objects.
#include "CGRecordLayout.h"
#include "CGCXXABI.h"
#include "CodeGenTypes.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Attr.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/Expr.h"
#include "clang/AST/RecordLayout.h"
#include "clang/Basic/CodeGenOptions.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Type.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
using namespace clang;
using namespace CodeGen;
namespace {
/// The CGRecordLowering is responsible for lowering an ASTRecordLayout to an
/// llvm::Type. Some of the lowering is straightforward, some is not. Here we
/// detail some of the complexities and weirdnesses here.
/// * LLVM does not have unions - Unions can, in theory be represented by any
/// llvm::Type with correct size. We choose a field via a specific heuristic
/// and add padding if necessary.
/// * LLVM does not have bitfields - Bitfields are collected into contiguous
/// runs and allocated as a single storage type for the run. ASTRecordLayout
/// contains enough information to determine where the runs break. Microsoft
/// and Itanium follow different rules and use different codepaths.
/// * It is desired that, when possible, bitfields use the appropriate iN type
/// when lowered to llvm types. For example unsigned x : 24 gets lowered to
/// i24. This isn't always possible because i24 has storage size of 32 bit
/// and if it is possible to use that extra byte of padding we must use
/// [i8 x 3] instead of i24. The function clipTailPadding does this.
/// C++ examples that require clipping:
/// struct { int a : 24; char b; }; // a must be clipped, b goes at offset 3
/// struct A { int a : 24; }; // a must be clipped because a struct like B
// could exist: struct B : A { char b; }; // b goes at offset 3
/// * Clang ignores 0 sized bitfields and 0 sized bases but *not* zero sized
/// fields. The existing asserts suggest that LLVM assumes that *every* field
/// has an underlying storage type. Therefore empty structures containing
/// zero sized subobjects such as empty records or zero sized arrays still get
/// a zero sized (empty struct) storage type.
/// * Clang reads the complete type rather than the base type when generating
/// code to access fields. Bitfields in tail position with tail padding may
/// be clipped in the base class but not the complete class (we may discover
/// that the tail padding is not used in the complete class.) However,
/// because LLVM reads from the complete type it can generate incorrect code
/// if we do not clip the tail padding off of the bitfield in the complete
/// layout. This introduces a somewhat awkward extra unnecessary clip stage.
/// The location of the clip is stored internally as a sentinel of type
/// SCISSOR. If LLVM were updated to read base types (which it probably
/// should because locations of things such as VBases are bogus in the llvm
/// type anyway) then we could eliminate the SCISSOR.
/// * Itanium allows nearly empty primary virtual bases. These bases don't get
/// get their own storage because they're laid out as part of another base
/// or at the beginning of the structure. Determining if a VBase actually
/// gets storage awkwardly involves a walk of all bases.
/// * VFPtrs and VBPtrs do *not* make a record NotZeroInitializable.
struct CGRecordLowering {
// MemberInfo is a helper structure that contains information about a record
// member. In additional to the standard member types, there exists a
// sentinel member type that ensures correct rounding.
struct MemberInfo {
CharUnits Offset;
enum InfoKind { VFPtr, VBPtr, Field, Base, VBase, Scissor } Kind;
llvm::Type *Data;
union {
const FieldDecl *FD;
const CXXRecordDecl *RD;
MemberInfo(CharUnits Offset, InfoKind Kind, llvm::Type *Data,
const FieldDecl *FD = nullptr)
: Offset(Offset), Kind(Kind), Data(Data), FD(FD) {}
MemberInfo(CharUnits Offset, InfoKind Kind, llvm::Type *Data,
const CXXRecordDecl *RD)
: Offset(Offset), Kind(Kind), Data(Data), RD(RD) {}
// MemberInfos are sorted so we define a < operator.
bool operator <(const MemberInfo& a) const { return Offset < a.Offset; }
// The constructor.
CGRecordLowering(CodeGenTypes &Types, const RecordDecl *D, bool Packed);
// Short helper routines.
/// Constructs a MemberInfo instance from an offset and llvm::Type *.
MemberInfo StorageInfo(CharUnits Offset, llvm::Type *Data) {
return MemberInfo(Offset, MemberInfo::Field, Data);
/// The Microsoft bitfield layout rule allocates discrete storage
/// units of the field's formal type and only combines adjacent
/// fields of the same formal type. We want to emit a layout with
/// these discrete storage units instead of combining them into a
/// continuous run.
bool isDiscreteBitFieldABI() {
return Context.getTargetInfo().getCXXABI().isMicrosoft() ||
/// Helper function to check if we are targeting AAPCS.
bool isAAPCS() const {
return Context.getTargetInfo().getABI().startswith("aapcs");
/// Helper function to check if the target machine is BigEndian.
bool isBE() const { return Context.getTargetInfo().isBigEndian(); }
/// The Itanium base layout rule allows virtual bases to overlap
/// other bases, which complicates layout in specific ways.
/// Note specifically that the ms_struct attribute doesn't change this.
bool isOverlappingVBaseABI() {
return !Context.getTargetInfo().getCXXABI().isMicrosoft();
/// Wraps llvm::Type::getIntNTy with some implicit arguments.
llvm::Type *getIntNType(uint64_t NumBits) {
unsigned AlignedBits = llvm::alignTo(NumBits, Context.getCharWidth());
return llvm::Type::getIntNTy(Types.getLLVMContext(), AlignedBits);
/// Get the LLVM type sized as one character unit.
llvm::Type *getCharType() {
return llvm::Type::getIntNTy(Types.getLLVMContext(),
/// Gets an llvm type of size NumChars and alignment 1.
llvm::Type *getByteArrayType(CharUnits NumChars) {
assert(!NumChars.isZero() && "Empty byte arrays aren't allowed.");
llvm::Type *Type = getCharType();
return NumChars == CharUnits::One() ? Type :
(llvm::Type *)llvm::ArrayType::get(Type, NumChars.getQuantity());
/// Gets the storage type for a field decl and handles storage
/// for itanium bitfields that are smaller than their declared type.
llvm::Type *getStorageType(const FieldDecl *FD) {
llvm::Type *Type = Types.ConvertTypeForMem(FD->getType());
if (!FD->isBitField()) return Type;
if (isDiscreteBitFieldABI()) return Type;
return getIntNType(std::min(FD->getBitWidthValue(Context),
/// Gets the llvm Basesubobject type from a CXXRecordDecl.
llvm::Type *getStorageType(const CXXRecordDecl *RD) {
return Types.getCGRecordLayout(RD).getBaseSubobjectLLVMType();
CharUnits bitsToCharUnits(uint64_t BitOffset) {
return Context.toCharUnitsFromBits(BitOffset);
CharUnits getSize(llvm::Type *Type) {
return CharUnits::fromQuantity(DataLayout.getTypeAllocSize(Type));
CharUnits getAlignment(llvm::Type *Type) {
return CharUnits::fromQuantity(DataLayout.getABITypeAlignment(Type));
bool isZeroInitializable(const FieldDecl *FD) {
return Types.isZeroInitializable(FD->getType());
bool isZeroInitializable(const RecordDecl *RD) {
return Types.isZeroInitializable(RD);
void appendPaddingBytes(CharUnits Size) {
if (!Size.isZero())
uint64_t getFieldBitOffset(const FieldDecl *FD) {
return Layout.getFieldOffset(FD->getFieldIndex());
// Layout routines.
void setBitFieldInfo(const FieldDecl *FD, CharUnits StartOffset,
llvm::Type *StorageType);
/// Lowers an ASTRecordLayout to a llvm type.
void lower(bool NonVirtualBaseType);
void lowerUnion();
void accumulateFields();
void accumulateBitFields(RecordDecl::field_iterator Field,
RecordDecl::field_iterator FieldEnd);
void computeVolatileBitfields();
void accumulateBases();
void accumulateVPtrs();
void accumulateVBases();
/// Recursively searches all of the bases to find out if a vbase is
/// not the primary vbase of some base class.
bool hasOwnStorage(const CXXRecordDecl *Decl, const CXXRecordDecl *Query);
void calculateZeroInit();
/// Lowers bitfield storage types to I8 arrays for bitfields with tail
/// padding that is or can potentially be used.
void clipTailPadding();
/// Determines if we need a packed llvm struct.
void determinePacked(bool NVBaseType);
/// Inserts padding everywhere it's needed.
void insertPadding();
/// Fills out the structures that are ultimately consumed.
void fillOutputFields();
// Input memoization fields.
CodeGenTypes &Types;
const ASTContext &Context;
const RecordDecl *D;
const CXXRecordDecl *RD;
const ASTRecordLayout &Layout;
const llvm::DataLayout &DataLayout;
// Helpful intermediate data-structures.
std::vector<MemberInfo> Members;
// Output fields, consumed by CodeGenTypes::ComputeRecordLayout.
SmallVector<llvm::Type *, 16> FieldTypes;
llvm::DenseMap<const FieldDecl *, unsigned> Fields;
llvm::DenseMap<const FieldDecl *, CGBitFieldInfo> BitFields;
llvm::DenseMap<const CXXRecordDecl *, unsigned> NonVirtualBases;
llvm::DenseMap<const CXXRecordDecl *, unsigned> VirtualBases;
bool IsZeroInitializable : 1;
bool IsZeroInitializableAsBase : 1;
bool Packed : 1;
CGRecordLowering(const CGRecordLowering &) = delete;
void operator =(const CGRecordLowering &) = delete;
} // namespace {
CGRecordLowering::CGRecordLowering(CodeGenTypes &Types, const RecordDecl *D,
bool Packed)
: Types(Types), Context(Types.getContext()), D(D),
DataLayout(Types.getDataLayout()), IsZeroInitializable(true),
IsZeroInitializableAsBase(true), Packed(Packed) {}
void CGRecordLowering::setBitFieldInfo(
const FieldDecl *FD, CharUnits StartOffset, llvm::Type *StorageType) {
CGBitFieldInfo &Info = BitFields[FD->getCanonicalDecl()];
Info.IsSigned = FD->getType()->isSignedIntegerOrEnumerationType();
Info.Offset = (unsigned)(getFieldBitOffset(FD) - Context.toBits(StartOffset));
Info.Size = FD->getBitWidthValue(Context);
Info.StorageSize = (unsigned)DataLayout.getTypeAllocSizeInBits(StorageType);
Info.StorageOffset = StartOffset;
if (Info.Size > Info.StorageSize)
Info.Size = Info.StorageSize;
// Reverse the bit offsets for big endian machines. Because we represent
// a bitfield as a single large integer load, we can imagine the bits
// counting from the most-significant-bit instead of the
// least-significant-bit.
if (DataLayout.isBigEndian())
Info.Offset = Info.StorageSize - (Info.Offset + Info.Size);
Info.VolatileStorageSize = 0;
Info.VolatileOffset = 0;
Info.VolatileStorageOffset = CharUnits::Zero();
void CGRecordLowering::lower(bool NVBaseType) {
// The lowering process implemented in this function takes a variety of
// carefully ordered phases.
// 1) Store all members (fields and bases) in a list and sort them by offset.
// 2) Add a 1-byte capstone member at the Size of the structure.
// 3) Clip bitfield storages members if their tail padding is or might be
// used by another field or base. The clipping process uses the capstone
// by treating it as another object that occurs after the record.
// 4) Determine if the llvm-struct requires packing. It's important that this
// phase occur after clipping, because clipping changes the llvm type.
// This phase reads the offset of the capstone when determining packedness
// and updates the alignment of the capstone to be equal of the alignment
// of the record after doing so.
// 5) Insert padding everywhere it is needed. This phase requires 'Packed' to
// have been computed and needs to know the alignment of the record in
// order to understand if explicit tail padding is needed.
// 6) Remove the capstone, we don't need it anymore.
// 7) Determine if this record can be zero-initialized. This phase could have
// been placed anywhere after phase 1.
// 8) Format the complete list of members in a way that can be consumed by
// CodeGenTypes::ComputeRecordLayout.
CharUnits Size = NVBaseType ? Layout.getNonVirtualSize() : Layout.getSize();
if (D->isUnion()) {
// RD implies C++.
if (RD) {
if (Members.empty()) {
if (!NVBaseType)
Members.push_back(StorageInfo(Size, getIntNType(8)));
void CGRecordLowering::lowerUnion() {
CharUnits LayoutSize = Layout.getSize();
llvm::Type *StorageType = nullptr;
bool SeenNamedMember = false;
// Iterate through the fields setting bitFieldInfo and the Fields array. Also
// locate the "most appropriate" storage type. The heuristic for finding the
// storage type isn't necessary, the first (non-0-length-bitfield) field's
// type would work fine and be simpler but would be different than what we've
// been doing and cause lit tests to change.
for (const auto *Field : D->fields()) {
if (Field->isBitField()) {
if (Field->isZeroLengthBitField(Context))
llvm::Type *FieldType = getStorageType(Field);
if (LayoutSize < getSize(FieldType))
FieldType = getByteArrayType(LayoutSize);
setBitFieldInfo(Field, CharUnits::Zero(), FieldType);
Fields[Field->getCanonicalDecl()] = 0;
llvm::Type *FieldType = getStorageType(Field);
// Compute zero-initializable status.
// This union might not be zero initialized: it may contain a pointer to
// data member which might have some exotic initialization sequence.
// If this is the case, then we aught not to try and come up with a "better"
// type, it might not be very easy to come up with a Constant which
// correctly initializes it.
if (!SeenNamedMember) {
SeenNamedMember = Field->getIdentifier();
if (!SeenNamedMember)
if (const auto *FieldRD = Field->getType()->getAsRecordDecl())
SeenNamedMember = FieldRD->findFirstNamedDataMember();
if (SeenNamedMember && !isZeroInitializable(Field)) {
IsZeroInitializable = IsZeroInitializableAsBase = false;
StorageType = FieldType;
// Because our union isn't zero initializable, we won't be getting a better
// storage type.
if (!IsZeroInitializable)
// Conditionally update our storage type if we've got a new "better" one.
if (!StorageType ||
getAlignment(FieldType) > getAlignment(StorageType) ||
(getAlignment(FieldType) == getAlignment(StorageType) &&
getSize(FieldType) > getSize(StorageType)))
StorageType = FieldType;
// If we have no storage type just pad to the appropriate size and return.
if (!StorageType)
return appendPaddingBytes(LayoutSize);
// If our storage size was bigger than our required size (can happen in the
// case of packed bitfields on Itanium) then just use an I8 array.
if (LayoutSize < getSize(StorageType))
StorageType = getByteArrayType(LayoutSize);
appendPaddingBytes(LayoutSize - getSize(StorageType));
// Set packed if we need it.
if (LayoutSize % getAlignment(StorageType))
Packed = true;
void CGRecordLowering::accumulateFields() {
for (RecordDecl::field_iterator Field = D->field_begin(),
FieldEnd = D->field_end();
Field != FieldEnd;) {
if (Field->isBitField()) {
RecordDecl::field_iterator Start = Field;
// Iterate to gather the list of bitfields.
for (++Field; Field != FieldEnd && Field->isBitField(); ++Field);
accumulateBitFields(Start, Field);
} else if (!Field->isZeroSize(Context)) {
bitsToCharUnits(getFieldBitOffset(*Field)), MemberInfo::Field,
getStorageType(*Field), *Field));
} else {
CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field,
RecordDecl::field_iterator FieldEnd) {
// Run stores the first element of the current run of bitfields. FieldEnd is
// used as a special value to note that we don't have a current run. A
// bitfield run is a contiguous collection of bitfields that can be stored in
// the same storage block. Zero-sized bitfields and bitfields that would
// cross an alignment boundary break a run and start a new one.
RecordDecl::field_iterator Run = FieldEnd;
// Tail is the offset of the first bit off the end of the current run. It's
// used to determine if the ASTRecordLayout is treating these two bitfields as
// contiguous. StartBitOffset is offset of the beginning of the Run.
uint64_t StartBitOffset, Tail = 0;
if (isDiscreteBitFieldABI()) {
for (; Field != FieldEnd; ++Field) {
uint64_t BitOffset = getFieldBitOffset(*Field);
// Zero-width bitfields end runs.
if (Field->isZeroLengthBitField(Context)) {
Run = FieldEnd;
llvm::Type *Type =
Types.ConvertTypeForMem(Field->getType(), /*ForBitFields=*/true);
// If we don't have a run yet, or don't live within the previous run's
// allocated storage then we allocate some storage and start a new run.
if (Run == FieldEnd || BitOffset >= Tail) {
Run = Field;
StartBitOffset = BitOffset;
Tail = StartBitOffset + DataLayout.getTypeAllocSizeInBits(Type);
// Add the storage member to the record. This must be added to the
// record before the bitfield members so that it gets laid out before
// the bitfields it contains get laid out.
Members.push_back(StorageInfo(bitsToCharUnits(StartBitOffset), Type));
// Bitfields get the offset of their storage but come afterward and remain
// there after a stable sort.
MemberInfo::Field, nullptr, *Field));
// Check if OffsetInRecord (the size in bits of the current run) is better
// as a single field run. When OffsetInRecord has legal integer width, and
// its bitfield offset is naturally aligned, it is better to make the
// bitfield a separate storage component so as it can be accessed directly
// with lower cost.
auto IsBetterAsSingleFieldRun = [&](uint64_t OffsetInRecord,
uint64_t StartBitOffset) {
if (!Types.getCodeGenOpts().FineGrainedBitfieldAccesses)
return false;
if (OffsetInRecord < 8 || !llvm::isPowerOf2_64(OffsetInRecord) ||
return false;
// Make sure StartBitOffset is naturally aligned if it is treated as an
// IType integer.
if (StartBitOffset %
Context.toBits(getAlignment(getIntNType(OffsetInRecord))) !=
return false;
return true;
// The start field is better as a single field run.
bool StartFieldAsSingleRun = false;
for (;;) {
// Check to see if we need to start a new run.
if (Run == FieldEnd) {
// If we're out of fields, return.
if (Field == FieldEnd)
// Any non-zero-length bitfield can start a new run.
if (!Field->isZeroLengthBitField(Context)) {
Run = Field;
StartBitOffset = getFieldBitOffset(*Field);
Tail = StartBitOffset + Field->getBitWidthValue(Context);
StartFieldAsSingleRun = IsBetterAsSingleFieldRun(Tail - StartBitOffset,
// If the start field of a new run is better as a single run, or
// if current field (or consecutive fields) is better as a single run, or
// if current field has zero width bitfield and either
// UseZeroLengthBitfieldAlignment or UseBitFieldTypeAlignment is set to
// true, or
// if the offset of current field is inconsistent with the offset of
// previous field plus its offset,
// skip the block below and go ahead to emit the storage.
// Otherwise, try to add bitfields to the run.
if (!StartFieldAsSingleRun && Field != FieldEnd &&
!IsBetterAsSingleFieldRun(Tail - StartBitOffset, StartBitOffset) &&
(!Field->isZeroLengthBitField(Context) ||
(!Context.getTargetInfo().useZeroLengthBitfieldAlignment() &&
!Context.getTargetInfo().useBitFieldTypeAlignment())) &&
Tail == getFieldBitOffset(*Field)) {
Tail += Field->getBitWidthValue(Context);
// We've hit a break-point in the run and need to emit a storage field.
llvm::Type *Type = getIntNType(Tail - StartBitOffset);
// Add the storage member to the record and set the bitfield info for all of
// the bitfields in the run. Bitfields get the offset of their storage but
// come afterward and remain there after a stable sort.
Members.push_back(StorageInfo(bitsToCharUnits(StartBitOffset), Type));
for (; Run != Field; ++Run)
MemberInfo::Field, nullptr, *Run));
Run = FieldEnd;
StartFieldAsSingleRun = false;
void CGRecordLowering::accumulateBases() {
// If we've got a primary virtual base, we need to add it with the bases.
if (Layout.isPrimaryBaseVirtual()) {
const CXXRecordDecl *BaseDecl = Layout.getPrimaryBase();
Members.push_back(MemberInfo(CharUnits::Zero(), MemberInfo::Base,
getStorageType(BaseDecl), BaseDecl));
// Accumulate the non-virtual bases.
for (const auto &Base : RD->bases()) {
if (Base.isVirtual())
// Bases can be zero-sized even if not technically empty if they
// contain only a trailing array member.
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
if (!BaseDecl->isEmpty() &&
MemberInfo::Base, getStorageType(BaseDecl), BaseDecl));
/// The AAPCS that defines that, when possible, bit-fields should
/// be accessed using containers of the declared type width:
/// When a volatile bit-field is read, and its container does not overlap with
/// any non-bit-field member or any zero length bit-field member, its container
/// must be read exactly once using the access width appropriate to the type of
/// the container. When a volatile bit-field is written, and its container does
/// not overlap with any non-bit-field member or any zero-length bit-field
/// member, its container must be read exactly once and written exactly once
/// using the access width appropriate to the type of the container. The two
/// accesses are not atomic.
/// Enforcing the width restriction can be disabled using
/// -fno-aapcs-bitfield-width.
void CGRecordLowering::computeVolatileBitfields() {
if (!isAAPCS() || !Types.getCodeGenOpts().AAPCSBitfieldWidth)
for (auto &I : BitFields) {
const FieldDecl *Field = I.first;
CGBitFieldInfo &Info = I.second;
llvm::Type *ResLTy = Types.ConvertTypeForMem(Field->getType());
// If the record alignment is less than the type width, we can't enforce a
// aligned load, bail out.
if ((uint64_t)(Context.toBits(Layout.getAlignment())) <
// CGRecordLowering::setBitFieldInfo() pre-adjusts the bit-field offsets
// for big-endian targets, but it assumes a container of width
// Info.StorageSize. Since AAPCS uses a different container size (width
// of the type), we first undo that calculation here and redo it once
// the bit-field offset within the new container is calculated.
const unsigned OldOffset =
isBE() ? Info.StorageSize - (Info.Offset + Info.Size) : Info.Offset;
// Offset to the bit-field from the beginning of the struct.
const unsigned AbsoluteOffset =
Context.toBits(Info.StorageOffset) + OldOffset;
// Container size is the width of the bit-field type.
const unsigned StorageSize = ResLTy->getPrimitiveSizeInBits();
// Nothing to do if the access uses the desired
// container width and is naturally aligned.
if (Info.StorageSize == StorageSize && (OldOffset % StorageSize == 0))
// Offset within the container.
unsigned Offset = AbsoluteOffset & (StorageSize - 1);
// Bail out if an aligned load of the container cannot cover the entire
// bit-field. This can happen for example, if the bit-field is part of a
// packed struct. AAPCS does not define access rules for such cases, we let
// clang to follow its own rules.
if (Offset + Info.Size > StorageSize)
// Re-adjust offsets for big-endian targets.
if (isBE())
Offset = StorageSize - (Offset + Info.Size);
const CharUnits StorageOffset =
Context.toCharUnitsFromBits(AbsoluteOffset & ~(StorageSize - 1));
const CharUnits End = StorageOffset +
Context.toCharUnitsFromBits(StorageSize) -
const ASTRecordLayout &Layout =
// If we access outside memory outside the record, than bail out.
const CharUnits RecordSize = Layout.getSize();
if (End >= RecordSize)
// Bail out if performing this load would access non-bit-fields members.
bool Conflict = false;
for (const auto *F : D->fields()) {
// Allow sized bit-fields overlaps.
if (F->isBitField() && !F->isZeroLengthBitField(Context))
const CharUnits FOffset = Context.toCharUnitsFromBits(
// As C11 defines, a zero sized bit-field defines a barrier, so
// fields after and before it should be race condition free.
// The AAPCS acknowledges it and imposes no restritions when the
// natural container overlaps a zero-length bit-field.
if (F->isZeroLengthBitField(Context)) {
if (End > FOffset && StorageOffset < FOffset) {
Conflict = true;
const CharUnits FEnd =
FOffset +
Types.ConvertTypeForMem(F->getType())->getPrimitiveSizeInBits()) -
// If no overlap, continue.
if (End < FOffset || FEnd < StorageOffset)
// The desired load overlaps a non-bit-field member, bail out.
Conflict = true;
if (Conflict)
// Write the new bit-field access parameters.
// As the storage offset now is defined as the number of elements from the
// start of the structure, we should divide the Offset by the element size.
Info.VolatileStorageOffset =
StorageOffset / Context.toCharUnitsFromBits(StorageSize).getQuantity();
Info.VolatileStorageSize = StorageSize;
Info.VolatileOffset = Offset;
void CGRecordLowering::accumulateVPtrs() {
if (Layout.hasOwnVFPtr())
Members.push_back(MemberInfo(CharUnits::Zero(), MemberInfo::VFPtr,
llvm::FunctionType::get(getIntNType(32), /*isVarArg=*/true)->
if (Layout.hasOwnVBPtr())
Members.push_back(MemberInfo(Layout.getVBPtrOffset(), MemberInfo::VBPtr,
void CGRecordLowering::accumulateVBases() {
CharUnits ScissorOffset = Layout.getNonVirtualSize();
// In the itanium ABI, it's possible to place a vbase at a dsize that is
// smaller than the nvsize. Here we check to see if such a base is placed
// before the nvsize and set the scissor offset to that, instead of the
// nvsize.
if (isOverlappingVBaseABI())
for (const auto &Base : RD->vbases()) {
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
if (BaseDecl->isEmpty())
// If the vbase is a primary virtual base of some base, then it doesn't
// get its own storage location but instead lives inside of that base.
if (Context.isNearlyEmpty(BaseDecl) && !hasOwnStorage(RD, BaseDecl))
ScissorOffset = std::min(ScissorOffset,
Members.push_back(MemberInfo(ScissorOffset, MemberInfo::Scissor, nullptr,
for (const auto &Base : RD->vbases()) {
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
if (BaseDecl->isEmpty())
CharUnits Offset = Layout.getVBaseClassOffset(BaseDecl);
// If the vbase is a primary virtual base of some base, then it doesn't
// get its own storage location but instead lives inside of that base.
if (isOverlappingVBaseABI() &&
Context.isNearlyEmpty(BaseDecl) &&
!hasOwnStorage(RD, BaseDecl)) {
Members.push_back(MemberInfo(Offset, MemberInfo::VBase, nullptr,
// If we've got a vtordisp, add it as a storage type.
if (Layout.getVBaseOffsetsMap().find(BaseDecl)->second.hasVtorDisp())
Members.push_back(StorageInfo(Offset - CharUnits::fromQuantity(4),
Members.push_back(MemberInfo(Offset, MemberInfo::VBase,
getStorageType(BaseDecl), BaseDecl));
bool CGRecordLowering::hasOwnStorage(const CXXRecordDecl *Decl,
const CXXRecordDecl *Query) {
const ASTRecordLayout &DeclLayout = Context.getASTRecordLayout(Decl);
if (DeclLayout.isPrimaryBaseVirtual() && DeclLayout.getPrimaryBase() == Query)
return false;
for (const auto &Base : Decl->bases())
if (!hasOwnStorage(Base.getType()->getAsCXXRecordDecl(), Query))
return false;
return true;
void CGRecordLowering::calculateZeroInit() {
for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
MemberEnd = Members.end();
IsZeroInitializableAsBase && Member != MemberEnd; ++Member) {
if (Member->Kind == MemberInfo::Field) {
if (!Member->FD || isZeroInitializable(Member->FD))
IsZeroInitializable = IsZeroInitializableAsBase = false;
} else if (Member->Kind == MemberInfo::Base ||
Member->Kind == MemberInfo::VBase) {
if (isZeroInitializable(Member->RD))
IsZeroInitializable = false;
if (Member->Kind == MemberInfo::Base)
IsZeroInitializableAsBase = false;
void CGRecordLowering::clipTailPadding() {
std::vector<MemberInfo>::iterator Prior = Members.begin();
CharUnits Tail = getSize(Prior->Data);
for (std::vector<MemberInfo>::iterator Member = Prior + 1,
MemberEnd = Members.end();
Member != MemberEnd; ++Member) {
// Only members with data and the scissor can cut into tail padding.
if (!Member->Data && Member->Kind != MemberInfo::Scissor)
if (Member->Offset < Tail) {
assert(Prior->Kind == MemberInfo::Field &&
"Only storage fields have tail padding!");
if (!Prior->FD || Prior->FD->isBitField())
Prior->Data = getByteArrayType(bitsToCharUnits(llvm::alignTo(
cast<llvm::IntegerType>(Prior->Data)->getIntegerBitWidth(), 8)));
else {
assert(Prior->FD->hasAttr<NoUniqueAddressAttr>() &&
"should not have reused this field's tail padding");
Prior->Data = getByteArrayType(
if (Member->Data)
Prior = Member;
Tail = Prior->Offset + getSize(Prior->Data);
void CGRecordLowering::determinePacked(bool NVBaseType) {
if (Packed)
CharUnits Alignment = CharUnits::One();
CharUnits NVAlignment = CharUnits::One();
CharUnits NVSize =
!NVBaseType && RD ? Layout.getNonVirtualSize() : CharUnits::Zero();
for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
MemberEnd = Members.end();
Member != MemberEnd; ++Member) {
if (!Member->Data)
// If any member falls at an offset that it not a multiple of its alignment,
// then the entire record must be packed.
if (Member->Offset % getAlignment(Member->Data))
Packed = true;
if (Member->Offset < NVSize)
NVAlignment = std::max(NVAlignment, getAlignment(Member->Data));
Alignment = std::max(Alignment, getAlignment(Member->Data));
// If the size of the record (the capstone's offset) is not a multiple of the
// record's alignment, it must be packed.
if (Members.back().Offset % Alignment)
Packed = true;
// If the non-virtual sub-object is not a multiple of the non-virtual
// sub-object's alignment, it must be packed. We cannot have a packed
// non-virtual sub-object and an unpacked complete object or vise versa.
if (NVSize % NVAlignment)
Packed = true;
// Update the alignment of the sentinel.
if (!Packed)
Members.back().Data = getIntNType(Context.toBits(Alignment));
void CGRecordLowering::insertPadding() {
std::vector<std::pair<CharUnits, CharUnits> > Padding;
CharUnits Size = CharUnits::Zero();
for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
MemberEnd = Members.end();
Member != MemberEnd; ++Member) {
if (!Member->Data)
CharUnits Offset = Member->Offset;
assert(Offset >= Size);
// Insert padding if we need to.
if (Offset !=
Size.alignTo(Packed ? CharUnits::One() : getAlignment(Member->Data)))
Padding.push_back(std::make_pair(Size, Offset - Size));
Size = Offset + getSize(Member->Data);
if (Padding.empty())
// Add the padding to the Members list and sort it.
for (std::vector<std::pair<CharUnits, CharUnits> >::const_iterator
Pad = Padding.begin(), PadEnd = Padding.end();
Pad != PadEnd; ++Pad)
Members.push_back(StorageInfo(Pad->first, getByteArrayType(Pad->second)));
void CGRecordLowering::fillOutputFields() {
for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
MemberEnd = Members.end();
Member != MemberEnd; ++Member) {
if (Member->Data)
if (Member->Kind == MemberInfo::Field) {
if (Member->FD)
Fields[Member->FD->getCanonicalDecl()] = FieldTypes.size() - 1;
// A field without storage must be a bitfield.
if (!Member->Data)
setBitFieldInfo(Member->FD, Member->Offset, FieldTypes.back());
} else if (Member->Kind == MemberInfo::Base)
NonVirtualBases[Member->RD] = FieldTypes.size() - 1;
else if (Member->Kind == MemberInfo::VBase)
VirtualBases[Member->RD] = FieldTypes.size() - 1;
CGBitFieldInfo CGBitFieldInfo::MakeInfo(CodeGenTypes &Types,
const FieldDecl *FD,
uint64_t Offset, uint64_t Size,
uint64_t StorageSize,
CharUnits StorageOffset) {
// This function is vestigial from CGRecordLayoutBuilder days but is still
// used in GCObjCRuntime.cpp. That usage has a "fixme" attached to it that
// when addressed will allow for the removal of this function.
llvm::Type *Ty = Types.ConvertTypeForMem(FD->getType());
CharUnits TypeSizeInBytes =
uint64_t TypeSizeInBits = Types.getContext().toBits(TypeSizeInBytes);
bool IsSigned = FD->getType()->isSignedIntegerOrEnumerationType();
if (Size > TypeSizeInBits) {
// We have a wide bit-field. The extra bits are only used for padding, so
// if we have a bitfield of type T, with size N:
// T t : N;
// We can just assume that it's:
// T t : sizeof(T);
Size = TypeSizeInBits;
// Reverse the bit offsets for big endian machines. Because we represent
// a bitfield as a single large integer load, we can imagine the bits
// counting from the most-significant-bit instead of the
// least-significant-bit.
if (Types.getDataLayout().isBigEndian()) {
Offset = StorageSize - (Offset + Size);
return CGBitFieldInfo(Offset, Size, IsSigned, StorageSize, StorageOffset);
CodeGenTypes::ComputeRecordLayout(const RecordDecl *D, llvm::StructType *Ty) {
CGRecordLowering Builder(*this, D, /*Packed=*/false);
// If we're in C++, compute the base subobject type.
llvm::StructType *BaseTy = nullptr;
if (isa<CXXRecordDecl>(D) && !D->isUnion() && !D->hasAttr<FinalAttr>()) {
BaseTy = Ty;
if (Builder.Layout.getNonVirtualSize() != Builder.Layout.getSize()) {
CGRecordLowering BaseBuilder(*this, D, /*Packed=*/Builder.Packed);
BaseTy = llvm::StructType::create(
getLLVMContext(), BaseBuilder.FieldTypes, "", BaseBuilder.Packed);
addRecordTypeName(D, BaseTy, ".base");
// BaseTy and Ty must agree on their packedness for getLLVMFieldNo to work
// on both of them with the same index.
assert(Builder.Packed == BaseBuilder.Packed &&
"Non-virtual and complete types must agree on packedness");
// Fill in the struct *after* computing the base type. Filling in the body
// signifies that the type is no longer opaque and record layout is complete,
// but we may need to recursively layout D while laying D out as a base type.
Ty->setBody(Builder.FieldTypes, Builder.Packed);
auto RL = std::make_unique<CGRecordLayout>(
Ty, BaseTy, (bool)Builder.IsZeroInitializable,
// Add all the field numbers.
// Add bitfield info.
// Dump the layout, if requested.
if (getContext().getLangOpts().DumpRecordLayouts) {
llvm::outs() << "\n*** Dumping IRgen Record Layout\n";
llvm::outs() << "Record: ";
llvm::outs() << "\nLayout: ";
#ifndef NDEBUG
// Verify that the computed LLVM struct size matches the AST layout size.
const ASTRecordLayout &Layout = getContext().getASTRecordLayout(D);
uint64_t TypeSizeInBits = getContext().toBits(Layout.getSize());
assert(TypeSizeInBits == getDataLayout().getTypeAllocSizeInBits(Ty) &&
"Type size mismatch!");
if (BaseTy) {
CharUnits NonVirtualSize = Layout.getNonVirtualSize();
uint64_t AlignedNonVirtualTypeSizeInBits =
assert(AlignedNonVirtualTypeSizeInBits ==
getDataLayout().getTypeAllocSizeInBits(BaseTy) &&
"Type size mismatch!");
// Verify that the LLVM and AST field offsets agree.
llvm::StructType *ST = RL->getLLVMType();
const llvm::StructLayout *SL = getDataLayout().getStructLayout(ST);
const ASTRecordLayout &AST_RL = getContext().getASTRecordLayout(D);
RecordDecl::field_iterator it = D->field_begin();
for (unsigned i = 0, e = AST_RL.getFieldCount(); i != e; ++i, ++it) {
const FieldDecl *FD = *it;
// Ignore zero-sized fields.
if (FD->isZeroSize(getContext()))
// For non-bit-fields, just check that the LLVM struct offset matches the
// AST offset.
if (!FD->isBitField()) {
unsigned FieldNo = RL->getLLVMFieldNo(FD);
assert(AST_RL.getFieldOffset(i) == SL->getElementOffsetInBits(FieldNo) &&
"Invalid field offset!");
// Ignore unnamed bit-fields.
if (!FD->getDeclName())
const CGBitFieldInfo &Info = RL->getBitFieldInfo(FD);
llvm::Type *ElementTy = ST->getTypeAtIndex(RL->getLLVMFieldNo(FD));
// Unions have overlapping elements dictating their layout, but for
// non-unions we can verify that this section of the layout is the exact
// expected size.
if (D->isUnion()) {
// For unions we verify that the start is zero and the size
// is in-bounds. However, on BE systems, the offset may be non-zero, but
// the size + offset should match the storage size in that case as it
// "starts" at the back.
if (getDataLayout().isBigEndian())
assert(static_cast<unsigned>(Info.Offset + Info.Size) ==
Info.StorageSize &&
"Big endian union bitfield does not end at the back");
assert(Info.Offset == 0 &&
"Little endian union bitfield with a non-zero offset");
assert(Info.StorageSize <= SL->getSizeInBits() &&
"Union not large enough for bitfield storage");
} else {
assert((Info.StorageSize ==
getDataLayout().getTypeAllocSizeInBits(ElementTy) ||
Info.VolatileStorageSize ==
getDataLayout().getTypeAllocSizeInBits(ElementTy)) &&
"Storage size does not match the element type size");
assert(Info.Size > 0 && "Empty bitfield!");
assert(static_cast<unsigned>(Info.Offset) + Info.Size <= Info.StorageSize &&
"Bitfield outside of its allocated storage");
return RL;
void CGRecordLayout::print(raw_ostream &OS) const {
OS << "<CGRecordLayout\n";
OS << " LLVMType:" << *CompleteObjectType << "\n";
if (BaseSubobjectType)
OS << " NonVirtualBaseLLVMType:" << *BaseSubobjectType << "\n";
OS << " IsZeroInitializable:" << IsZeroInitializable << "\n";
OS << " BitFields:[\n";
// Print bit-field infos in declaration order.
std::vector<std::pair<unsigned, const CGBitFieldInfo*> > BFIs;
for (llvm::DenseMap<const FieldDecl*, CGBitFieldInfo>::const_iterator
it = BitFields.begin(), ie = BitFields.end();
it != ie; ++it) {
const RecordDecl *RD = it->first->getParent();
unsigned Index = 0;
for (RecordDecl::field_iterator
it2 = RD->field_begin(); *it2 != it->first; ++it2)
BFIs.push_back(std::make_pair(Index, &it->second));
llvm::array_pod_sort(BFIs.begin(), BFIs.end());
for (unsigned i = 0, e = BFIs.size(); i != e; ++i) {
OS << "\n";
OS << "]>\n";
LLVM_DUMP_METHOD void CGRecordLayout::dump() const {
void CGBitFieldInfo::print(raw_ostream &OS) const {
OS << "<CGBitFieldInfo"
<< " Offset:" << Offset << " Size:" << Size << " IsSigned:" << IsSigned
<< " StorageSize:" << StorageSize
<< " StorageOffset:" << StorageOffset.getQuantity()
<< " VolatileOffset:" << VolatileOffset
<< " VolatileStorageSize:" << VolatileStorageSize
<< " VolatileStorageOffset:" << VolatileStorageOffset.getQuantity() << ">";
LLVM_DUMP_METHOD void CGBitFieldInfo::dump() const {