1 //===--- CGRecordLayoutBuilder.cpp - CGRecordLayout builder ----*- C++ -*-===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // Builder implementation for CGRecordLayout objects.
11 //===----------------------------------------------------------------------===//
13 #include "CGRecordLayout.h"
15 #include "CodeGenTypes.h"
16 #include "clang/AST/ASTContext.h"
17 #include "clang/AST/Attr.h"
18 #include "clang/AST/CXXInheritance.h"
19 #include "clang/AST/DeclCXX.h"
20 #include "clang/AST/Expr.h"
21 #include "clang/AST/RecordLayout.h"
22 #include "clang/Basic/CodeGenOptions.h"
23 #include "llvm/IR/DataLayout.h"
24 #include "llvm/IR/DerivedTypes.h"
25 #include "llvm/IR/Type.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/MathExtras.h"
28 #include "llvm/Support/raw_ostream.h"
29 using namespace clang;
30 using namespace CodeGen;
33 /// The CGRecordLowering is responsible for lowering an ASTRecordLayout to an
34 /// llvm::Type. Some of the lowering is straightforward, some is not. Here we
35 /// detail some of the complexities and weirdnesses here.
36 /// * LLVM does not have unions - Unions can, in theory be represented by any
37 /// llvm::Type with correct size. We choose a field via a specific heuristic
38 /// and add padding if necessary.
39 /// * LLVM does not have bitfields - Bitfields are collected into contiguous
40 /// runs and allocated as a single storage type for the run. ASTRecordLayout
41 /// contains enough information to determine where the runs break. Microsoft
42 /// and Itanium follow different rules and use different codepaths.
43 /// * It is desired that, when possible, bitfields use the appropriate iN type
44 /// when lowered to llvm types. For example unsigned x : 24 gets lowered to
45 /// i24. This isn't always possible because i24 has storage size of 32 bit
46 /// and if it is possible to use that extra byte of padding we must use
47 /// [i8 x 3] instead of i24. The function clipTailPadding does this.
48 /// C++ examples that require clipping:
49 /// struct { int a : 24; char b; }; // a must be clipped, b goes at offset 3
50 /// struct A { int a : 24; }; // a must be clipped because a struct like B
51 // could exist: struct B : A { char b; }; // b goes at offset 3
52 /// * Clang ignores 0 sized bitfields and 0 sized bases but *not* zero sized
53 /// fields. The existing asserts suggest that LLVM assumes that *every* field
54 /// has an underlying storage type. Therefore empty structures containing
55 /// zero sized subobjects such as empty records or zero sized arrays still get
56 /// a zero sized (empty struct) storage type.
57 /// * Clang reads the complete type rather than the base type when generating
58 /// code to access fields. Bitfields in tail position with tail padding may
59 /// be clipped in the base class but not the complete class (we may discover
60 /// that the tail padding is not used in the complete class.) However,
61 /// because LLVM reads from the complete type it can generate incorrect code
62 /// if we do not clip the tail padding off of the bitfield in the complete
63 /// layout. This introduces a somewhat awkward extra unnecessary clip stage.
64 /// The location of the clip is stored internally as a sentinel of type
65 /// SCISSOR. If LLVM were updated to read base types (which it probably
66 /// should because locations of things such as VBases are bogus in the llvm
67 /// type anyway) then we could eliminate the SCISSOR.
68 /// * Itanium allows nearly empty primary virtual bases. These bases don't get
69 /// get their own storage because they're laid out as part of another base
70 /// or at the beginning of the structure. Determining if a VBase actually
71 /// gets storage awkwardly involves a walk of all bases.
72 /// * VFPtrs and VBPtrs do *not* make a record NotZeroInitializable.
73 struct CGRecordLowering {
74 // MemberInfo is a helper structure that contains information about a record
75 // member. In additional to the standard member types, there exists a
76 // sentinel member type that ensures correct rounding.
79 enum InfoKind { VFPtr, VBPtr, Field, Base, VBase, Scissor } Kind;
83 const CXXRecordDecl *RD;
85 MemberInfo(CharUnits Offset, InfoKind Kind, llvm::Type *Data,
86 const FieldDecl *FD = nullptr)
87 : Offset(Offset), Kind(Kind), Data(Data), FD(FD) {}
88 MemberInfo(CharUnits Offset, InfoKind Kind, llvm::Type *Data,
89 const CXXRecordDecl *RD)
90 : Offset(Offset), Kind(Kind), Data(Data), RD(RD) {}
91 // MemberInfos are sorted so we define a < operator.
92 bool operator <(const MemberInfo& a) const { return Offset < a.Offset; }
95 CGRecordLowering(CodeGenTypes &Types, const RecordDecl *D, bool Packed);
96 // Short helper routines.
97 /// Constructs a MemberInfo instance from an offset and llvm::Type *.
98 MemberInfo StorageInfo(CharUnits Offset, llvm::Type *Data) {
99 return MemberInfo(Offset, MemberInfo::Field, Data);
102 /// The Microsoft bitfield layout rule allocates discrete storage
103 /// units of the field's formal type and only combines adjacent
104 /// fields of the same formal type. We want to emit a layout with
105 /// these discrete storage units instead of combining them into a
107 bool isDiscreteBitFieldABI() {
108 return Context.getTargetInfo().getCXXABI().isMicrosoft() ||
109 D->isMsStruct(Context);
112 /// The Itanium base layout rule allows virtual bases to overlap
113 /// other bases, which complicates layout in specific ways.
115 /// Note specifically that the ms_struct attribute doesn't change this.
116 bool isOverlappingVBaseABI() {
117 return !Context.getTargetInfo().getCXXABI().isMicrosoft();
120 /// Wraps llvm::Type::getIntNTy with some implicit arguments.
121 llvm::Type *getIntNType(uint64_t NumBits) {
122 return llvm::Type::getIntNTy(Types.getLLVMContext(),
123 (unsigned)llvm::alignTo(NumBits, 8));
125 /// Gets an llvm type of size NumBytes and alignment 1.
126 llvm::Type *getByteArrayType(CharUnits NumBytes) {
127 assert(!NumBytes.isZero() && "Empty byte arrays aren't allowed.");
128 llvm::Type *Type = llvm::Type::getInt8Ty(Types.getLLVMContext());
129 return NumBytes == CharUnits::One() ? Type :
130 (llvm::Type *)llvm::ArrayType::get(Type, NumBytes.getQuantity());
132 /// Gets the storage type for a field decl and handles storage
133 /// for itanium bitfields that are smaller than their declared type.
134 llvm::Type *getStorageType(const FieldDecl *FD) {
135 llvm::Type *Type = Types.ConvertTypeForMem(FD->getType());
136 if (!FD->isBitField()) return Type;
137 if (isDiscreteBitFieldABI()) return Type;
138 return getIntNType(std::min(FD->getBitWidthValue(Context),
139 (unsigned)Context.toBits(getSize(Type))));
141 /// Gets the llvm Basesubobject type from a CXXRecordDecl.
142 llvm::Type *getStorageType(const CXXRecordDecl *RD) {
143 return Types.getCGRecordLayout(RD).getBaseSubobjectLLVMType();
145 CharUnits bitsToCharUnits(uint64_t BitOffset) {
146 return Context.toCharUnitsFromBits(BitOffset);
148 CharUnits getSize(llvm::Type *Type) {
149 return CharUnits::fromQuantity(DataLayout.getTypeAllocSize(Type));
151 CharUnits getAlignment(llvm::Type *Type) {
152 return CharUnits::fromQuantity(DataLayout.getABITypeAlignment(Type));
154 bool isZeroInitializable(const FieldDecl *FD) {
155 return Types.isZeroInitializable(FD->getType());
157 bool isZeroInitializable(const RecordDecl *RD) {
158 return Types.isZeroInitializable(RD);
160 void appendPaddingBytes(CharUnits Size) {
162 FieldTypes.push_back(getByteArrayType(Size));
164 uint64_t getFieldBitOffset(const FieldDecl *FD) {
165 return Layout.getFieldOffset(FD->getFieldIndex());
168 void setBitFieldInfo(const FieldDecl *FD, CharUnits StartOffset,
169 llvm::Type *StorageType);
170 /// Lowers an ASTRecordLayout to a llvm type.
171 void lower(bool NonVirtualBaseType);
173 void accumulateFields();
174 void accumulateBitFields(RecordDecl::field_iterator Field,
175 RecordDecl::field_iterator FieldEnd);
176 void accumulateBases();
177 void accumulateVPtrs();
178 void accumulateVBases();
179 /// Recursively searches all of the bases to find out if a vbase is
180 /// not the primary vbase of some base class.
181 bool hasOwnStorage(const CXXRecordDecl *Decl, const CXXRecordDecl *Query);
182 void calculateZeroInit();
183 /// Lowers bitfield storage types to I8 arrays for bitfields with tail
184 /// padding that is or can potentially be used.
185 void clipTailPadding();
186 /// Determines if we need a packed llvm struct.
187 void determinePacked(bool NVBaseType);
188 /// Inserts padding everywhere it's needed.
189 void insertPadding();
190 /// Fills out the structures that are ultimately consumed.
191 void fillOutputFields();
192 // Input memoization fields.
194 const ASTContext &Context;
196 const CXXRecordDecl *RD;
197 const ASTRecordLayout &Layout;
198 const llvm::DataLayout &DataLayout;
199 // Helpful intermediate data-structures.
200 std::vector<MemberInfo> Members;
201 // Output fields, consumed by CodeGenTypes::ComputeRecordLayout.
202 SmallVector<llvm::Type *, 16> FieldTypes;
203 llvm::DenseMap<const FieldDecl *, unsigned> Fields;
204 llvm::DenseMap<const FieldDecl *, CGBitFieldInfo> BitFields;
205 llvm::DenseMap<const CXXRecordDecl *, unsigned> NonVirtualBases;
206 llvm::DenseMap<const CXXRecordDecl *, unsigned> VirtualBases;
207 bool IsZeroInitializable : 1;
208 bool IsZeroInitializableAsBase : 1;
211 CGRecordLowering(const CGRecordLowering &) = delete;
212 void operator =(const CGRecordLowering &) = delete;
216 CGRecordLowering::CGRecordLowering(CodeGenTypes &Types, const RecordDecl *D,
218 : Types(Types), Context(Types.getContext()), D(D),
219 RD(dyn_cast<CXXRecordDecl>(D)),
220 Layout(Types.getContext().getASTRecordLayout(D)),
221 DataLayout(Types.getDataLayout()), IsZeroInitializable(true),
222 IsZeroInitializableAsBase(true), Packed(Packed) {}
224 void CGRecordLowering::setBitFieldInfo(
225 const FieldDecl *FD, CharUnits StartOffset, llvm::Type *StorageType) {
226 CGBitFieldInfo &Info = BitFields[FD->getCanonicalDecl()];
227 Info.IsSigned = FD->getType()->isSignedIntegerOrEnumerationType();
228 Info.Offset = (unsigned)(getFieldBitOffset(FD) - Context.toBits(StartOffset));
229 Info.Size = FD->getBitWidthValue(Context);
230 Info.StorageSize = (unsigned)DataLayout.getTypeAllocSizeInBits(StorageType);
231 Info.StorageOffset = StartOffset;
232 if (Info.Size > Info.StorageSize)
233 Info.Size = Info.StorageSize;
234 // Reverse the bit offsets for big endian machines. Because we represent
235 // a bitfield as a single large integer load, we can imagine the bits
236 // counting from the most-significant-bit instead of the
237 // least-significant-bit.
238 if (DataLayout.isBigEndian())
239 Info.Offset = Info.StorageSize - (Info.Offset + Info.Size);
242 void CGRecordLowering::lower(bool NVBaseType) {
243 // The lowering process implemented in this function takes a variety of
244 // carefully ordered phases.
245 // 1) Store all members (fields and bases) in a list and sort them by offset.
246 // 2) Add a 1-byte capstone member at the Size of the structure.
247 // 3) Clip bitfield storages members if their tail padding is or might be
248 // used by another field or base. The clipping process uses the capstone
249 // by treating it as another object that occurs after the record.
250 // 4) Determine if the llvm-struct requires packing. It's important that this
251 // phase occur after clipping, because clipping changes the llvm type.
252 // This phase reads the offset of the capstone when determining packedness
253 // and updates the alignment of the capstone to be equal of the alignment
254 // of the record after doing so.
255 // 5) Insert padding everywhere it is needed. This phase requires 'Packed' to
256 // have been computed and needs to know the alignment of the record in
257 // order to understand if explicit tail padding is needed.
258 // 6) Remove the capstone, we don't need it anymore.
259 // 7) Determine if this record can be zero-initialized. This phase could have
260 // been placed anywhere after phase 1.
261 // 8) Format the complete list of members in a way that can be consumed by
262 // CodeGenTypes::ComputeRecordLayout.
263 CharUnits Size = NVBaseType ? Layout.getNonVirtualSize() : Layout.getSize();
272 return appendPaddingBytes(Size);
276 llvm::stable_sort(Members);
277 Members.push_back(StorageInfo(Size, getIntNType(8)));
279 determinePacked(NVBaseType);
286 void CGRecordLowering::lowerUnion() {
287 CharUnits LayoutSize = Layout.getSize();
288 llvm::Type *StorageType = nullptr;
289 bool SeenNamedMember = false;
290 // Iterate through the fields setting bitFieldInfo and the Fields array. Also
291 // locate the "most appropriate" storage type. The heuristic for finding the
292 // storage type isn't necessary, the first (non-0-length-bitfield) field's
293 // type would work fine and be simpler but would be different than what we've
294 // been doing and cause lit tests to change.
295 for (const auto *Field : D->fields()) {
296 if (Field->isBitField()) {
297 if (Field->isZeroLengthBitField(Context))
299 llvm::Type *FieldType = getStorageType(Field);
300 if (LayoutSize < getSize(FieldType))
301 FieldType = getByteArrayType(LayoutSize);
302 setBitFieldInfo(Field, CharUnits::Zero(), FieldType);
304 Fields[Field->getCanonicalDecl()] = 0;
305 llvm::Type *FieldType = getStorageType(Field);
306 // Compute zero-initializable status.
307 // This union might not be zero initialized: it may contain a pointer to
308 // data member which might have some exotic initialization sequence.
309 // If this is the case, then we aught not to try and come up with a "better"
310 // type, it might not be very easy to come up with a Constant which
311 // correctly initializes it.
312 if (!SeenNamedMember) {
313 SeenNamedMember = Field->getIdentifier();
314 if (!SeenNamedMember)
315 if (const auto *FieldRD = Field->getType()->getAsRecordDecl())
316 SeenNamedMember = FieldRD->findFirstNamedDataMember();
317 if (SeenNamedMember && !isZeroInitializable(Field)) {
318 IsZeroInitializable = IsZeroInitializableAsBase = false;
319 StorageType = FieldType;
322 // Because our union isn't zero initializable, we won't be getting a better
324 if (!IsZeroInitializable)
326 // Conditionally update our storage type if we've got a new "better" one.
328 getAlignment(FieldType) > getAlignment(StorageType) ||
329 (getAlignment(FieldType) == getAlignment(StorageType) &&
330 getSize(FieldType) > getSize(StorageType)))
331 StorageType = FieldType;
333 // If we have no storage type just pad to the appropriate size and return.
335 return appendPaddingBytes(LayoutSize);
336 // If our storage size was bigger than our required size (can happen in the
337 // case of packed bitfields on Itanium) then just use an I8 array.
338 if (LayoutSize < getSize(StorageType))
339 StorageType = getByteArrayType(LayoutSize);
340 FieldTypes.push_back(StorageType);
341 appendPaddingBytes(LayoutSize - getSize(StorageType));
342 // Set packed if we need it.
343 if (LayoutSize % getAlignment(StorageType))
347 void CGRecordLowering::accumulateFields() {
348 for (RecordDecl::field_iterator Field = D->field_begin(),
349 FieldEnd = D->field_end();
350 Field != FieldEnd;) {
351 if (Field->isBitField()) {
352 RecordDecl::field_iterator Start = Field;
353 // Iterate to gather the list of bitfields.
354 for (++Field; Field != FieldEnd && Field->isBitField(); ++Field);
355 accumulateBitFields(Start, Field);
356 } else if (!Field->isZeroSize(Context)) {
357 Members.push_back(MemberInfo(
358 bitsToCharUnits(getFieldBitOffset(*Field)), MemberInfo::Field,
359 getStorageType(*Field), *Field));
368 CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field,
369 RecordDecl::field_iterator FieldEnd) {
370 // Run stores the first element of the current run of bitfields. FieldEnd is
371 // used as a special value to note that we don't have a current run. A
372 // bitfield run is a contiguous collection of bitfields that can be stored in
373 // the same storage block. Zero-sized bitfields and bitfields that would
374 // cross an alignment boundary break a run and start a new one.
375 RecordDecl::field_iterator Run = FieldEnd;
376 // Tail is the offset of the first bit off the end of the current run. It's
377 // used to determine if the ASTRecordLayout is treating these two bitfields as
378 // contiguous. StartBitOffset is offset of the beginning of the Run.
379 uint64_t StartBitOffset, Tail = 0;
380 if (isDiscreteBitFieldABI()) {
381 for (; Field != FieldEnd; ++Field) {
382 uint64_t BitOffset = getFieldBitOffset(*Field);
383 // Zero-width bitfields end runs.
384 if (Field->isZeroLengthBitField(Context)) {
388 llvm::Type *Type = Types.ConvertTypeForMem(Field->getType());
389 // If we don't have a run yet, or don't live within the previous run's
390 // allocated storage then we allocate some storage and start a new run.
391 if (Run == FieldEnd || BitOffset >= Tail) {
393 StartBitOffset = BitOffset;
394 Tail = StartBitOffset + DataLayout.getTypeAllocSizeInBits(Type);
395 // Add the storage member to the record. This must be added to the
396 // record before the bitfield members so that it gets laid out before
397 // the bitfields it contains get laid out.
398 Members.push_back(StorageInfo(bitsToCharUnits(StartBitOffset), Type));
400 // Bitfields get the offset of their storage but come afterward and remain
401 // there after a stable sort.
402 Members.push_back(MemberInfo(bitsToCharUnits(StartBitOffset),
403 MemberInfo::Field, nullptr, *Field));
408 // Check if OffsetInRecord is better as a single field run. When OffsetInRecord
409 // has legal integer width, and its bitfield offset is naturally aligned, it
410 // is better to make the bitfield a separate storage component so as it can be
411 // accessed directly with lower cost.
412 auto IsBetterAsSingleFieldRun = [&](uint64_t OffsetInRecord,
413 uint64_t StartBitOffset) {
414 if (!Types.getCodeGenOpts().FineGrainedBitfieldAccesses)
416 if (!DataLayout.isLegalInteger(OffsetInRecord))
418 // Make sure StartBitOffset is natually aligned if it is treated as an
421 Context.toBits(getAlignment(getIntNType(OffsetInRecord))) !=
427 // The start field is better as a single field run.
428 bool StartFieldAsSingleRun = false;
430 // Check to see if we need to start a new run.
431 if (Run == FieldEnd) {
432 // If we're out of fields, return.
433 if (Field == FieldEnd)
435 // Any non-zero-length bitfield can start a new run.
436 if (!Field->isZeroLengthBitField(Context)) {
438 StartBitOffset = getFieldBitOffset(*Field);
439 Tail = StartBitOffset + Field->getBitWidthValue(Context);
440 StartFieldAsSingleRun = IsBetterAsSingleFieldRun(Tail - StartBitOffset,
447 // If the start field of a new run is better as a single run, or
448 // if current field (or consecutive fields) is better as a single run, or
449 // if current field has zero width bitfield and either
450 // UseZeroLengthBitfieldAlignment or UseBitFieldTypeAlignment is set to
452 // if the offset of current field is inconsistent with the offset of
453 // previous field plus its offset,
454 // skip the block below and go ahead to emit the storage.
455 // Otherwise, try to add bitfields to the run.
456 if (!StartFieldAsSingleRun && Field != FieldEnd &&
457 !IsBetterAsSingleFieldRun(Tail - StartBitOffset, StartBitOffset) &&
458 (!Field->isZeroLengthBitField(Context) ||
459 (!Context.getTargetInfo().useZeroLengthBitfieldAlignment() &&
460 !Context.getTargetInfo().useBitFieldTypeAlignment())) &&
461 Tail == getFieldBitOffset(*Field)) {
462 Tail += Field->getBitWidthValue(Context);
467 // We've hit a break-point in the run and need to emit a storage field.
468 llvm::Type *Type = getIntNType(Tail - StartBitOffset);
469 // Add the storage member to the record and set the bitfield info for all of
470 // the bitfields in the run. Bitfields get the offset of their storage but
471 // come afterward and remain there after a stable sort.
472 Members.push_back(StorageInfo(bitsToCharUnits(StartBitOffset), Type));
473 for (; Run != Field; ++Run)
474 Members.push_back(MemberInfo(bitsToCharUnits(StartBitOffset),
475 MemberInfo::Field, nullptr, *Run));
477 StartFieldAsSingleRun = false;
481 void CGRecordLowering::accumulateBases() {
482 // If we've got a primary virtual base, we need to add it with the bases.
483 if (Layout.isPrimaryBaseVirtual()) {
484 const CXXRecordDecl *BaseDecl = Layout.getPrimaryBase();
485 Members.push_back(MemberInfo(CharUnits::Zero(), MemberInfo::Base,
486 getStorageType(BaseDecl), BaseDecl));
488 // Accumulate the non-virtual bases.
489 for (const auto &Base : RD->bases()) {
490 if (Base.isVirtual())
493 // Bases can be zero-sized even if not technically empty if they
494 // contain only a trailing array member.
495 const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
496 if (!BaseDecl->isEmpty() &&
497 !Context.getASTRecordLayout(BaseDecl).getNonVirtualSize().isZero())
498 Members.push_back(MemberInfo(Layout.getBaseClassOffset(BaseDecl),
499 MemberInfo::Base, getStorageType(BaseDecl), BaseDecl));
503 void CGRecordLowering::accumulateVPtrs() {
504 if (Layout.hasOwnVFPtr())
505 Members.push_back(MemberInfo(CharUnits::Zero(), MemberInfo::VFPtr,
506 llvm::FunctionType::get(getIntNType(32), /*isVarArg=*/true)->
507 getPointerTo()->getPointerTo()));
508 if (Layout.hasOwnVBPtr())
509 Members.push_back(MemberInfo(Layout.getVBPtrOffset(), MemberInfo::VBPtr,
510 llvm::Type::getInt32PtrTy(Types.getLLVMContext())));
513 void CGRecordLowering::accumulateVBases() {
514 CharUnits ScissorOffset = Layout.getNonVirtualSize();
515 // In the itanium ABI, it's possible to place a vbase at a dsize that is
516 // smaller than the nvsize. Here we check to see if such a base is placed
517 // before the nvsize and set the scissor offset to that, instead of the
519 if (isOverlappingVBaseABI())
520 for (const auto &Base : RD->vbases()) {
521 const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
522 if (BaseDecl->isEmpty())
524 // If the vbase is a primary virtual base of some base, then it doesn't
525 // get its own storage location but instead lives inside of that base.
526 if (Context.isNearlyEmpty(BaseDecl) && !hasOwnStorage(RD, BaseDecl))
528 ScissorOffset = std::min(ScissorOffset,
529 Layout.getVBaseClassOffset(BaseDecl));
531 Members.push_back(MemberInfo(ScissorOffset, MemberInfo::Scissor, nullptr,
533 for (const auto &Base : RD->vbases()) {
534 const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
535 if (BaseDecl->isEmpty())
537 CharUnits Offset = Layout.getVBaseClassOffset(BaseDecl);
538 // If the vbase is a primary virtual base of some base, then it doesn't
539 // get its own storage location but instead lives inside of that base.
540 if (isOverlappingVBaseABI() &&
541 Context.isNearlyEmpty(BaseDecl) &&
542 !hasOwnStorage(RD, BaseDecl)) {
543 Members.push_back(MemberInfo(Offset, MemberInfo::VBase, nullptr,
547 // If we've got a vtordisp, add it as a storage type.
548 if (Layout.getVBaseOffsetsMap().find(BaseDecl)->second.hasVtorDisp())
549 Members.push_back(StorageInfo(Offset - CharUnits::fromQuantity(4),
551 Members.push_back(MemberInfo(Offset, MemberInfo::VBase,
552 getStorageType(BaseDecl), BaseDecl));
556 bool CGRecordLowering::hasOwnStorage(const CXXRecordDecl *Decl,
557 const CXXRecordDecl *Query) {
558 const ASTRecordLayout &DeclLayout = Context.getASTRecordLayout(Decl);
559 if (DeclLayout.isPrimaryBaseVirtual() && DeclLayout.getPrimaryBase() == Query)
561 for (const auto &Base : Decl->bases())
562 if (!hasOwnStorage(Base.getType()->getAsCXXRecordDecl(), Query))
567 void CGRecordLowering::calculateZeroInit() {
568 for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
569 MemberEnd = Members.end();
570 IsZeroInitializableAsBase && Member != MemberEnd; ++Member) {
571 if (Member->Kind == MemberInfo::Field) {
572 if (!Member->FD || isZeroInitializable(Member->FD))
574 IsZeroInitializable = IsZeroInitializableAsBase = false;
575 } else if (Member->Kind == MemberInfo::Base ||
576 Member->Kind == MemberInfo::VBase) {
577 if (isZeroInitializable(Member->RD))
579 IsZeroInitializable = false;
580 if (Member->Kind == MemberInfo::Base)
581 IsZeroInitializableAsBase = false;
586 void CGRecordLowering::clipTailPadding() {
587 std::vector<MemberInfo>::iterator Prior = Members.begin();
588 CharUnits Tail = getSize(Prior->Data);
589 for (std::vector<MemberInfo>::iterator Member = Prior + 1,
590 MemberEnd = Members.end();
591 Member != MemberEnd; ++Member) {
592 // Only members with data and the scissor can cut into tail padding.
593 if (!Member->Data && Member->Kind != MemberInfo::Scissor)
595 if (Member->Offset < Tail) {
596 assert(Prior->Kind == MemberInfo::Field &&
597 "Only storage fields have tail padding!");
598 if (!Prior->FD || Prior->FD->isBitField())
599 Prior->Data = getByteArrayType(bitsToCharUnits(llvm::alignTo(
600 cast<llvm::IntegerType>(Prior->Data)->getIntegerBitWidth(), 8)));
602 assert(Prior->FD->hasAttr<NoUniqueAddressAttr>() &&
603 "should not have reused this field's tail padding");
604 Prior->Data = getByteArrayType(
605 Context.getTypeInfoDataSizeInChars(Prior->FD->getType()).first);
610 Tail = Prior->Offset + getSize(Prior->Data);
614 void CGRecordLowering::determinePacked(bool NVBaseType) {
617 CharUnits Alignment = CharUnits::One();
618 CharUnits NVAlignment = CharUnits::One();
620 !NVBaseType && RD ? Layout.getNonVirtualSize() : CharUnits::Zero();
621 for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
622 MemberEnd = Members.end();
623 Member != MemberEnd; ++Member) {
626 // If any member falls at an offset that it not a multiple of its alignment,
627 // then the entire record must be packed.
628 if (Member->Offset % getAlignment(Member->Data))
630 if (Member->Offset < NVSize)
631 NVAlignment = std::max(NVAlignment, getAlignment(Member->Data));
632 Alignment = std::max(Alignment, getAlignment(Member->Data));
634 // If the size of the record (the capstone's offset) is not a multiple of the
635 // record's alignment, it must be packed.
636 if (Members.back().Offset % Alignment)
638 // If the non-virtual sub-object is not a multiple of the non-virtual
639 // sub-object's alignment, it must be packed. We cannot have a packed
640 // non-virtual sub-object and an unpacked complete object or vise versa.
641 if (NVSize % NVAlignment)
643 // Update the alignment of the sentinel.
645 Members.back().Data = getIntNType(Context.toBits(Alignment));
648 void CGRecordLowering::insertPadding() {
649 std::vector<std::pair<CharUnits, CharUnits> > Padding;
650 CharUnits Size = CharUnits::Zero();
651 for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
652 MemberEnd = Members.end();
653 Member != MemberEnd; ++Member) {
656 CharUnits Offset = Member->Offset;
657 assert(Offset >= Size);
658 // Insert padding if we need to.
660 Size.alignTo(Packed ? CharUnits::One() : getAlignment(Member->Data)))
661 Padding.push_back(std::make_pair(Size, Offset - Size));
662 Size = Offset + getSize(Member->Data);
666 // Add the padding to the Members list and sort it.
667 for (std::vector<std::pair<CharUnits, CharUnits> >::const_iterator
668 Pad = Padding.begin(), PadEnd = Padding.end();
669 Pad != PadEnd; ++Pad)
670 Members.push_back(StorageInfo(Pad->first, getByteArrayType(Pad->second)));
671 llvm::stable_sort(Members);
674 void CGRecordLowering::fillOutputFields() {
675 for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
676 MemberEnd = Members.end();
677 Member != MemberEnd; ++Member) {
679 FieldTypes.push_back(Member->Data);
680 if (Member->Kind == MemberInfo::Field) {
682 Fields[Member->FD->getCanonicalDecl()] = FieldTypes.size() - 1;
683 // A field without storage must be a bitfield.
685 setBitFieldInfo(Member->FD, Member->Offset, FieldTypes.back());
686 } else if (Member->Kind == MemberInfo::Base)
687 NonVirtualBases[Member->RD] = FieldTypes.size() - 1;
688 else if (Member->Kind == MemberInfo::VBase)
689 VirtualBases[Member->RD] = FieldTypes.size() - 1;
693 CGBitFieldInfo CGBitFieldInfo::MakeInfo(CodeGenTypes &Types,
695 uint64_t Offset, uint64_t Size,
696 uint64_t StorageSize,
697 CharUnits StorageOffset) {
698 // This function is vestigial from CGRecordLayoutBuilder days but is still
699 // used in GCObjCRuntime.cpp. That usage has a "fixme" attached to it that
700 // when addressed will allow for the removal of this function.
701 llvm::Type *Ty = Types.ConvertTypeForMem(FD->getType());
702 CharUnits TypeSizeInBytes =
703 CharUnits::fromQuantity(Types.getDataLayout().getTypeAllocSize(Ty));
704 uint64_t TypeSizeInBits = Types.getContext().toBits(TypeSizeInBytes);
706 bool IsSigned = FD->getType()->isSignedIntegerOrEnumerationType();
708 if (Size > TypeSizeInBits) {
709 // We have a wide bit-field. The extra bits are only used for padding, so
710 // if we have a bitfield of type T, with size N:
714 // We can just assume that it's:
718 Size = TypeSizeInBits;
721 // Reverse the bit offsets for big endian machines. Because we represent
722 // a bitfield as a single large integer load, we can imagine the bits
723 // counting from the most-significant-bit instead of the
724 // least-significant-bit.
725 if (Types.getDataLayout().isBigEndian()) {
726 Offset = StorageSize - (Offset + Size);
729 return CGBitFieldInfo(Offset, Size, IsSigned, StorageSize, StorageOffset);
732 CGRecordLayout *CodeGenTypes::ComputeRecordLayout(const RecordDecl *D,
733 llvm::StructType *Ty) {
734 CGRecordLowering Builder(*this, D, /*Packed=*/false);
736 Builder.lower(/*NonVirtualBaseType=*/false);
738 // If we're in C++, compute the base subobject type.
739 llvm::StructType *BaseTy = nullptr;
740 if (isa<CXXRecordDecl>(D) && !D->isUnion() && !D->hasAttr<FinalAttr>()) {
742 if (Builder.Layout.getNonVirtualSize() != Builder.Layout.getSize()) {
743 CGRecordLowering BaseBuilder(*this, D, /*Packed=*/Builder.Packed);
744 BaseBuilder.lower(/*NonVirtualBaseType=*/true);
745 BaseTy = llvm::StructType::create(
746 getLLVMContext(), BaseBuilder.FieldTypes, "", BaseBuilder.Packed);
747 addRecordTypeName(D, BaseTy, ".base");
748 // BaseTy and Ty must agree on their packedness for getLLVMFieldNo to work
749 // on both of them with the same index.
750 assert(Builder.Packed == BaseBuilder.Packed &&
751 "Non-virtual and complete types must agree on packedness");
755 // Fill in the struct *after* computing the base type. Filling in the body
756 // signifies that the type is no longer opaque and record layout is complete,
757 // but we may need to recursively layout D while laying D out as a base type.
758 Ty->setBody(Builder.FieldTypes, Builder.Packed);
761 new CGRecordLayout(Ty, BaseTy, Builder.IsZeroInitializable,
762 Builder.IsZeroInitializableAsBase);
764 RL->NonVirtualBases.swap(Builder.NonVirtualBases);
765 RL->CompleteObjectVirtualBases.swap(Builder.VirtualBases);
767 // Add all the field numbers.
768 RL->FieldInfo.swap(Builder.Fields);
770 // Add bitfield info.
771 RL->BitFields.swap(Builder.BitFields);
773 // Dump the layout, if requested.
774 if (getContext().getLangOpts().DumpRecordLayouts) {
775 llvm::outs() << "\n*** Dumping IRgen Record Layout\n";
776 llvm::outs() << "Record: ";
777 D->dump(llvm::outs());
778 llvm::outs() << "\nLayout: ";
779 RL->print(llvm::outs());
783 // Verify that the computed LLVM struct size matches the AST layout size.
784 const ASTRecordLayout &Layout = getContext().getASTRecordLayout(D);
786 uint64_t TypeSizeInBits = getContext().toBits(Layout.getSize());
787 assert(TypeSizeInBits == getDataLayout().getTypeAllocSizeInBits(Ty) &&
788 "Type size mismatch!");
791 CharUnits NonVirtualSize = Layout.getNonVirtualSize();
793 uint64_t AlignedNonVirtualTypeSizeInBits =
794 getContext().toBits(NonVirtualSize);
796 assert(AlignedNonVirtualTypeSizeInBits ==
797 getDataLayout().getTypeAllocSizeInBits(BaseTy) &&
798 "Type size mismatch!");
801 // Verify that the LLVM and AST field offsets agree.
802 llvm::StructType *ST = RL->getLLVMType();
803 const llvm::StructLayout *SL = getDataLayout().getStructLayout(ST);
805 const ASTRecordLayout &AST_RL = getContext().getASTRecordLayout(D);
806 RecordDecl::field_iterator it = D->field_begin();
807 for (unsigned i = 0, e = AST_RL.getFieldCount(); i != e; ++i, ++it) {
808 const FieldDecl *FD = *it;
810 // Ignore zero-sized fields.
811 if (FD->isZeroSize(getContext()))
814 // For non-bit-fields, just check that the LLVM struct offset matches the
816 if (!FD->isBitField()) {
817 unsigned FieldNo = RL->getLLVMFieldNo(FD);
818 assert(AST_RL.getFieldOffset(i) == SL->getElementOffsetInBits(FieldNo) &&
819 "Invalid field offset!");
823 // Ignore unnamed bit-fields.
824 if (!FD->getDeclName())
827 const CGBitFieldInfo &Info = RL->getBitFieldInfo(FD);
828 llvm::Type *ElementTy = ST->getTypeAtIndex(RL->getLLVMFieldNo(FD));
830 // Unions have overlapping elements dictating their layout, but for
831 // non-unions we can verify that this section of the layout is the exact
834 // For unions we verify that the start is zero and the size
835 // is in-bounds. However, on BE systems, the offset may be non-zero, but
836 // the size + offset should match the storage size in that case as it
837 // "starts" at the back.
838 if (getDataLayout().isBigEndian())
839 assert(static_cast<unsigned>(Info.Offset + Info.Size) ==
841 "Big endian union bitfield does not end at the back");
843 assert(Info.Offset == 0 &&
844 "Little endian union bitfield with a non-zero offset");
845 assert(Info.StorageSize <= SL->getSizeInBits() &&
846 "Union not large enough for bitfield storage");
848 assert(Info.StorageSize ==
849 getDataLayout().getTypeAllocSizeInBits(ElementTy) &&
850 "Storage size does not match the element type size");
852 assert(Info.Size > 0 && "Empty bitfield!");
853 assert(static_cast<unsigned>(Info.Offset) + Info.Size <= Info.StorageSize &&
854 "Bitfield outside of its allocated storage");
861 void CGRecordLayout::print(raw_ostream &OS) const {
862 OS << "<CGRecordLayout\n";
863 OS << " LLVMType:" << *CompleteObjectType << "\n";
864 if (BaseSubobjectType)
865 OS << " NonVirtualBaseLLVMType:" << *BaseSubobjectType << "\n";
866 OS << " IsZeroInitializable:" << IsZeroInitializable << "\n";
867 OS << " BitFields:[\n";
869 // Print bit-field infos in declaration order.
870 std::vector<std::pair<unsigned, const CGBitFieldInfo*> > BFIs;
871 for (llvm::DenseMap<const FieldDecl*, CGBitFieldInfo>::const_iterator
872 it = BitFields.begin(), ie = BitFields.end();
874 const RecordDecl *RD = it->first->getParent();
876 for (RecordDecl::field_iterator
877 it2 = RD->field_begin(); *it2 != it->first; ++it2)
879 BFIs.push_back(std::make_pair(Index, &it->second));
881 llvm::array_pod_sort(BFIs.begin(), BFIs.end());
882 for (unsigned i = 0, e = BFIs.size(); i != e; ++i) {
884 BFIs[i].second->print(OS);
891 LLVM_DUMP_METHOD void CGRecordLayout::dump() const {
895 void CGBitFieldInfo::print(raw_ostream &OS) const {
896 OS << "<CGBitFieldInfo"
897 << " Offset:" << Offset
899 << " IsSigned:" << IsSigned
900 << " StorageSize:" << StorageSize
901 << " StorageOffset:" << StorageOffset.getQuantity() << ">";
904 LLVM_DUMP_METHOD void CGBitFieldInfo::dump() const {