1 //===--- CGRecordLayoutBuilder.cpp - CGRecordLayout builder ----*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Builder implementation for CGRecordLayout objects.
12 //===----------------------------------------------------------------------===//
14 #include "CGRecordLayout.h"
16 #include "CodeGenTypes.h"
17 #include "clang/AST/ASTContext.h"
18 #include "clang/AST/Attr.h"
19 #include "clang/AST/CXXInheritance.h"
20 #include "clang/AST/DeclCXX.h"
21 #include "clang/AST/Expr.h"
22 #include "clang/AST/RecordLayout.h"
23 #include "clang/Frontend/CodeGenOptions.h"
24 #include "llvm/IR/DataLayout.h"
25 #include "llvm/IR/DerivedTypes.h"
26 #include "llvm/IR/Type.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/MathExtras.h"
29 #include "llvm/Support/raw_ostream.h"
30 using namespace clang;
31 using namespace CodeGen;
34 /// The CGRecordLowering is responsible for lowering an ASTRecordLayout to an
35 /// llvm::Type. Some of the lowering is straightforward, some is not. Here we
36 /// detail some of the complexities and weirdnesses here.
37 /// * LLVM does not have unions - Unions can, in theory be represented by any
38 /// llvm::Type with correct size. We choose a field via a specific heuristic
39 /// and add padding if necessary.
40 /// * LLVM does not have bitfields - Bitfields are collected into contiguous
41 /// runs and allocated as a single storage type for the run. ASTRecordLayout
42 /// contains enough information to determine where the runs break. Microsoft
43 /// and Itanium follow different rules and use different codepaths.
44 /// * It is desired that, when possible, bitfields use the appropriate iN type
45 /// when lowered to llvm types. For example unsigned x : 24 gets lowered to
46 /// i24. This isn't always possible because i24 has storage size of 32 bit
47 /// and if it is possible to use that extra byte of padding we must use
48 /// [i8 x 3] instead of i24. The function clipTailPadding does this.
49 /// C++ examples that require clipping:
50 /// struct { int a : 24; char b; }; // a must be clipped, b goes at offset 3
51 /// struct A { int a : 24; }; // a must be clipped because a struct like B
52 // could exist: struct B : A { char b; }; // b goes at offset 3
53 /// * Clang ignores 0 sized bitfields and 0 sized bases but *not* zero sized
54 /// fields. The existing asserts suggest that LLVM assumes that *every* field
55 /// has an underlying storage type. Therefore empty structures containing
56 /// zero sized subobjects such as empty records or zero sized arrays still get
57 /// a zero sized (empty struct) storage type.
58 /// * Clang reads the complete type rather than the base type when generating
59 /// code to access fields. Bitfields in tail position with tail padding may
60 /// be clipped in the base class but not the complete class (we may discover
61 /// that the tail padding is not used in the complete class.) However,
62 /// because LLVM reads from the complete type it can generate incorrect code
63 /// if we do not clip the tail padding off of the bitfield in the complete
64 /// layout. This introduces a somewhat awkward extra unnecessary clip stage.
65 /// The location of the clip is stored internally as a sentinal of type
66 /// SCISSOR. If LLVM were updated to read base types (which it probably
67 /// should because locations of things such as VBases are bogus in the llvm
68 /// type anyway) then we could eliminate the SCISSOR.
69 /// * Itanium allows nearly empty primary virtual bases. These bases don't get
70 /// get their own storage because they're laid out as part of another base
71 /// or at the beginning of the structure. Determining if a VBase actually
72 /// gets storage awkwardly involves a walk of all bases.
73 /// * VFPtrs and VBPtrs do *not* make a record NotZeroInitializable.
74 struct CGRecordLowering {
75 // MemberInfo is a helper structure that contains information about a record
76 // member. In additional to the standard member types, there exists a
77 // sentinal member type that ensures correct rounding.
80 enum InfoKind { VFPtr, VBPtr, Field, Base, VBase, Scissor } Kind;
84 const CXXRecordDecl *RD;
86 MemberInfo(CharUnits Offset, InfoKind Kind, llvm::Type *Data,
87 const FieldDecl *FD = nullptr)
88 : Offset(Offset), Kind(Kind), Data(Data), FD(FD) {}
89 MemberInfo(CharUnits Offset, InfoKind Kind, llvm::Type *Data,
90 const CXXRecordDecl *RD)
91 : Offset(Offset), Kind(Kind), Data(Data), RD(RD) {}
92 // MemberInfos are sorted so we define a < operator.
93 bool operator <(const MemberInfo& a) const { return Offset < a.Offset; }
96 CGRecordLowering(CodeGenTypes &Types, const RecordDecl *D, bool Packed);
97 // Short helper routines.
98 /// \brief Constructs a MemberInfo instance from an offset and llvm::Type *.
99 MemberInfo StorageInfo(CharUnits Offset, llvm::Type *Data) {
100 return MemberInfo(Offset, MemberInfo::Field, Data);
103 /// The Microsoft bitfield layout rule allocates discrete storage
104 /// units of the field's formal type and only combines adjacent
105 /// fields of the same formal type. We want to emit a layout with
106 /// these discrete storage units instead of combining them into a
108 bool isDiscreteBitFieldABI() {
109 return Context.getTargetInfo().getCXXABI().isMicrosoft() ||
110 D->isMsStruct(Context);
113 /// The Itanium base layout rule allows virtual bases to overlap
114 /// other bases, which complicates layout in specific ways.
116 /// Note specifically that the ms_struct attribute doesn't change this.
117 bool isOverlappingVBaseABI() {
118 return !Context.getTargetInfo().getCXXABI().isMicrosoft();
121 /// \brief Wraps llvm::Type::getIntNTy with some implicit arguments.
122 llvm::Type *getIntNType(uint64_t NumBits) {
123 return llvm::Type::getIntNTy(Types.getLLVMContext(),
124 (unsigned)llvm::RoundUpToAlignment(NumBits, 8));
126 /// \brief Gets an llvm type of size NumBytes and alignment 1.
127 llvm::Type *getByteArrayType(CharUnits NumBytes) {
128 assert(!NumBytes.isZero() && "Empty byte arrays aren't allowed.");
129 llvm::Type *Type = llvm::Type::getInt8Ty(Types.getLLVMContext());
130 return NumBytes == CharUnits::One() ? Type :
131 (llvm::Type *)llvm::ArrayType::get(Type, NumBytes.getQuantity());
133 /// \brief Gets the storage type for a field decl and handles storage
134 /// for itanium bitfields that are smaller than their declared type.
135 llvm::Type *getStorageType(const FieldDecl *FD) {
136 llvm::Type *Type = Types.ConvertTypeForMem(FD->getType());
137 if (!FD->isBitField()) return Type;
138 if (isDiscreteBitFieldABI()) return Type;
139 return getIntNType(std::min(FD->getBitWidthValue(Context),
140 (unsigned)Context.toBits(getSize(Type))));
142 /// \brief Gets the llvm Basesubobject type from a CXXRecordDecl.
143 llvm::Type *getStorageType(const CXXRecordDecl *RD) {
144 return Types.getCGRecordLayout(RD).getBaseSubobjectLLVMType();
146 CharUnits bitsToCharUnits(uint64_t BitOffset) {
147 return Context.toCharUnitsFromBits(BitOffset);
149 CharUnits getSize(llvm::Type *Type) {
150 return CharUnits::fromQuantity(DataLayout.getTypeAllocSize(Type));
152 CharUnits getAlignment(llvm::Type *Type) {
153 return CharUnits::fromQuantity(DataLayout.getABITypeAlignment(Type));
155 bool isZeroInitializable(const FieldDecl *FD) {
156 return Types.isZeroInitializable(FD->getType());
158 bool isZeroInitializable(const RecordDecl *RD) {
159 return Types.isZeroInitializable(RD);
161 void appendPaddingBytes(CharUnits Size) {
163 FieldTypes.push_back(getByteArrayType(Size));
165 uint64_t getFieldBitOffset(const FieldDecl *FD) {
166 return Layout.getFieldOffset(FD->getFieldIndex());
169 void setBitFieldInfo(const FieldDecl *FD, CharUnits StartOffset,
170 llvm::Type *StorageType);
171 /// \brief Lowers an ASTRecordLayout to a llvm type.
172 void lower(bool NonVirtualBaseType);
174 void accumulateFields();
175 void accumulateBitFields(RecordDecl::field_iterator Field,
176 RecordDecl::field_iterator FieldEnd);
177 void accumulateBases();
178 void accumulateVPtrs();
179 void accumulateVBases();
180 /// \brief Recursively searches all of the bases to find out if a vbase is
181 /// not the primary vbase of some base class.
182 bool hasOwnStorage(const CXXRecordDecl *Decl, const CXXRecordDecl *Query);
183 void calculateZeroInit();
184 /// \brief Lowers bitfield storage types to I8 arrays for bitfields with tail
185 /// padding that is or can potentially be used.
186 void clipTailPadding();
187 /// \brief Determines if we need a packed llvm struct.
188 void determinePacked(bool NVBaseType);
189 /// \brief Inserts padding everwhere it's needed.
190 void insertPadding();
191 /// \brief Fills out the structures that are ultimately consumed.
192 void fillOutputFields();
193 // Input memoization fields.
195 const ASTContext &Context;
197 const CXXRecordDecl *RD;
198 const ASTRecordLayout &Layout;
199 const llvm::DataLayout &DataLayout;
200 // Helpful intermediate data-structures.
201 std::vector<MemberInfo> Members;
202 // Output fields, consumed by CodeGenTypes::ComputeRecordLayout.
203 SmallVector<llvm::Type *, 16> FieldTypes;
204 llvm::DenseMap<const FieldDecl *, unsigned> Fields;
205 llvm::DenseMap<const FieldDecl *, CGBitFieldInfo> BitFields;
206 llvm::DenseMap<const CXXRecordDecl *, unsigned> NonVirtualBases;
207 llvm::DenseMap<const CXXRecordDecl *, unsigned> VirtualBases;
208 bool IsZeroInitializable : 1;
209 bool IsZeroInitializableAsBase : 1;
212 CGRecordLowering(const CGRecordLowering &) = delete;
213 void operator =(const CGRecordLowering &) = delete;
217 CGRecordLowering::CGRecordLowering(CodeGenTypes &Types, const RecordDecl *D, bool Packed)
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 std::stable_sort(Members.begin(), Members.end());
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 // Skip 0 sized bitfields.
298 if (Field->getBitWidthValue(Context) == 0)
300 llvm::Type *FieldType = getStorageType(Field);
301 if (LayoutSize < getSize(FieldType))
302 FieldType = getByteArrayType(LayoutSize);
303 setBitFieldInfo(Field, CharUnits::Zero(), FieldType);
305 Fields[Field->getCanonicalDecl()] = 0;
306 llvm::Type *FieldType = getStorageType(Field);
307 // Compute zero-initializable status.
308 // This union might not be zero initialized: it may contain a pointer to
309 // data member which might have some exotic initialization sequence.
310 // If this is the case, then we aught not to try and come up with a "better"
311 // type, it might not be very easy to come up with a Constant which
312 // correctly initializes it.
313 if (!SeenNamedMember) {
314 SeenNamedMember = Field->getIdentifier();
315 if (!SeenNamedMember)
316 if (const auto *FieldRD =
317 dyn_cast_or_null<RecordDecl>(Field->getType()->getAsTagDecl()))
318 SeenNamedMember = FieldRD->findFirstNamedDataMember();
319 if (SeenNamedMember && !isZeroInitializable(Field)) {
320 IsZeroInitializable = IsZeroInitializableAsBase = false;
321 StorageType = FieldType;
324 // Because our union isn't zero initializable, we won't be getting a better
326 if (!IsZeroInitializable)
328 // Conditionally update our storage type if we've got a new "better" one.
330 getAlignment(FieldType) > getAlignment(StorageType) ||
331 (getAlignment(FieldType) == getAlignment(StorageType) &&
332 getSize(FieldType) > getSize(StorageType)))
333 StorageType = FieldType;
335 // If we have no storage type just pad to the appropriate size and return.
337 return appendPaddingBytes(LayoutSize);
338 // If our storage size was bigger than our required size (can happen in the
339 // case of packed bitfields on Itanium) then just use an I8 array.
340 if (LayoutSize < getSize(StorageType))
341 StorageType = getByteArrayType(LayoutSize);
342 FieldTypes.push_back(StorageType);
343 appendPaddingBytes(LayoutSize - getSize(StorageType));
344 // Set packed if we need it.
345 if (LayoutSize % getAlignment(StorageType))
349 void CGRecordLowering::accumulateFields() {
350 for (RecordDecl::field_iterator Field = D->field_begin(),
351 FieldEnd = D->field_end();
353 if (Field->isBitField()) {
354 RecordDecl::field_iterator Start = Field;
355 // Iterate to gather the list of bitfields.
356 for (++Field; Field != FieldEnd && Field->isBitField(); ++Field);
357 accumulateBitFields(Start, Field);
359 Members.push_back(MemberInfo(
360 bitsToCharUnits(getFieldBitOffset(*Field)), MemberInfo::Field,
361 getStorageType(*Field), *Field));
367 CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field,
368 RecordDecl::field_iterator FieldEnd) {
369 // Run stores the first element of the current run of bitfields. FieldEnd is
370 // used as a special value to note that we don't have a current run. A
371 // bitfield run is a contiguous collection of bitfields that can be stored in
372 // the same storage block. Zero-sized bitfields and bitfields that would
373 // cross an alignment boundary break a run and start a new one.
374 RecordDecl::field_iterator Run = FieldEnd;
375 // Tail is the offset of the first bit off the end of the current run. It's
376 // used to determine if the ASTRecordLayout is treating these two bitfields as
377 // contiguous. StartBitOffset is offset of the beginning of the Run.
378 uint64_t StartBitOffset, Tail = 0;
379 if (isDiscreteBitFieldABI()) {
380 for (; Field != FieldEnd; ++Field) {
381 uint64_t BitOffset = getFieldBitOffset(*Field);
382 // Zero-width bitfields end runs.
383 if (Field->getBitWidthValue(Context) == 0) {
387 llvm::Type *Type = Types.ConvertTypeForMem(Field->getType());
388 // If we don't have a run yet, or don't live within the previous run's
389 // allocated storage then we allocate some storage and start a new run.
390 if (Run == FieldEnd || BitOffset >= Tail) {
392 StartBitOffset = BitOffset;
393 Tail = StartBitOffset + DataLayout.getTypeAllocSizeInBits(Type);
394 // Add the storage member to the record. This must be added to the
395 // record before the bitfield members so that it gets laid out before
396 // the bitfields it contains get laid out.
397 Members.push_back(StorageInfo(bitsToCharUnits(StartBitOffset), Type));
399 // Bitfields get the offset of their storage but come afterward and remain
400 // there after a stable sort.
401 Members.push_back(MemberInfo(bitsToCharUnits(StartBitOffset),
402 MemberInfo::Field, nullptr, *Field));
407 // Check to see if we need to start a new run.
408 if (Run == FieldEnd) {
409 // If we're out of fields, return.
410 if (Field == FieldEnd)
412 // Any non-zero-length bitfield can start a new run.
413 if (Field->getBitWidthValue(Context) != 0) {
415 StartBitOffset = getFieldBitOffset(*Field);
416 Tail = StartBitOffset + Field->getBitWidthValue(Context);
421 // Add bitfields to the run as long as they qualify.
422 if (Field != FieldEnd && Field->getBitWidthValue(Context) != 0 &&
423 Tail == getFieldBitOffset(*Field)) {
424 Tail += Field->getBitWidthValue(Context);
428 // We've hit a break-point in the run and need to emit a storage field.
429 llvm::Type *Type = getIntNType(Tail - StartBitOffset);
430 // Add the storage member to the record and set the bitfield info for all of
431 // the bitfields in the run. Bitfields get the offset of their storage but
432 // come afterward and remain there after a stable sort.
433 Members.push_back(StorageInfo(bitsToCharUnits(StartBitOffset), Type));
434 for (; Run != Field; ++Run)
435 Members.push_back(MemberInfo(bitsToCharUnits(StartBitOffset),
436 MemberInfo::Field, nullptr, *Run));
441 void CGRecordLowering::accumulateBases() {
442 // If we've got a primary virtual base, we need to add it with the bases.
443 if (Layout.isPrimaryBaseVirtual()) {
444 const CXXRecordDecl *BaseDecl = Layout.getPrimaryBase();
445 Members.push_back(MemberInfo(CharUnits::Zero(), MemberInfo::Base,
446 getStorageType(BaseDecl), BaseDecl));
448 // Accumulate the non-virtual bases.
449 for (const auto &Base : RD->bases()) {
450 if (Base.isVirtual())
453 // Bases can be zero-sized even if not technically empty if they
454 // contain only a trailing array member.
455 const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
456 if (!BaseDecl->isEmpty() &&
457 !Context.getASTRecordLayout(BaseDecl).getSize().isZero())
458 Members.push_back(MemberInfo(Layout.getBaseClassOffset(BaseDecl),
459 MemberInfo::Base, getStorageType(BaseDecl), BaseDecl));
463 void CGRecordLowering::accumulateVPtrs() {
464 if (Layout.hasOwnVFPtr())
465 Members.push_back(MemberInfo(CharUnits::Zero(), MemberInfo::VFPtr,
466 llvm::FunctionType::get(getIntNType(32), /*isVarArg=*/true)->
467 getPointerTo()->getPointerTo()));
468 if (Layout.hasOwnVBPtr())
469 Members.push_back(MemberInfo(Layout.getVBPtrOffset(), MemberInfo::VBPtr,
470 llvm::Type::getInt32PtrTy(Types.getLLVMContext())));
473 void CGRecordLowering::accumulateVBases() {
474 CharUnits ScissorOffset = Layout.getNonVirtualSize();
475 // In the itanium ABI, it's possible to place a vbase at a dsize that is
476 // smaller than the nvsize. Here we check to see if such a base is placed
477 // before the nvsize and set the scissor offset to that, instead of the
479 if (isOverlappingVBaseABI())
480 for (const auto &Base : RD->vbases()) {
481 const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
482 if (BaseDecl->isEmpty())
484 // If the vbase is a primary virtual base of some base, then it doesn't
485 // get its own storage location but instead lives inside of that base.
486 if (Context.isNearlyEmpty(BaseDecl) && !hasOwnStorage(RD, BaseDecl))
488 ScissorOffset = std::min(ScissorOffset,
489 Layout.getVBaseClassOffset(BaseDecl));
491 Members.push_back(MemberInfo(ScissorOffset, MemberInfo::Scissor, nullptr,
493 for (const auto &Base : RD->vbases()) {
494 const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
495 if (BaseDecl->isEmpty())
497 CharUnits Offset = Layout.getVBaseClassOffset(BaseDecl);
498 // If the vbase is a primary virtual base of some base, then it doesn't
499 // get its own storage location but instead lives inside of that base.
500 if (isOverlappingVBaseABI() &&
501 Context.isNearlyEmpty(BaseDecl) &&
502 !hasOwnStorage(RD, BaseDecl)) {
503 Members.push_back(MemberInfo(Offset, MemberInfo::VBase, nullptr,
507 // If we've got a vtordisp, add it as a storage type.
508 if (Layout.getVBaseOffsetsMap().find(BaseDecl)->second.hasVtorDisp())
509 Members.push_back(StorageInfo(Offset - CharUnits::fromQuantity(4),
511 Members.push_back(MemberInfo(Offset, MemberInfo::VBase,
512 getStorageType(BaseDecl), BaseDecl));
516 bool CGRecordLowering::hasOwnStorage(const CXXRecordDecl *Decl,
517 const CXXRecordDecl *Query) {
518 const ASTRecordLayout &DeclLayout = Context.getASTRecordLayout(Decl);
519 if (DeclLayout.isPrimaryBaseVirtual() && DeclLayout.getPrimaryBase() == Query)
521 for (const auto &Base : Decl->bases())
522 if (!hasOwnStorage(Base.getType()->getAsCXXRecordDecl(), Query))
527 void CGRecordLowering::calculateZeroInit() {
528 for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
529 MemberEnd = Members.end();
530 IsZeroInitializableAsBase && Member != MemberEnd; ++Member) {
531 if (Member->Kind == MemberInfo::Field) {
532 if (!Member->FD || isZeroInitializable(Member->FD))
534 IsZeroInitializable = IsZeroInitializableAsBase = false;
535 } else if (Member->Kind == MemberInfo::Base ||
536 Member->Kind == MemberInfo::VBase) {
537 if (isZeroInitializable(Member->RD))
539 IsZeroInitializable = false;
540 if (Member->Kind == MemberInfo::Base)
541 IsZeroInitializableAsBase = false;
546 void CGRecordLowering::clipTailPadding() {
547 std::vector<MemberInfo>::iterator Prior = Members.begin();
548 CharUnits Tail = getSize(Prior->Data);
549 for (std::vector<MemberInfo>::iterator Member = Prior + 1,
550 MemberEnd = Members.end();
551 Member != MemberEnd; ++Member) {
552 // Only members with data and the scissor can cut into tail padding.
553 if (!Member->Data && Member->Kind != MemberInfo::Scissor)
555 if (Member->Offset < Tail) {
556 assert(Prior->Kind == MemberInfo::Field && !Prior->FD &&
557 "Only storage fields have tail padding!");
558 Prior->Data = getByteArrayType(bitsToCharUnits(llvm::RoundUpToAlignment(
559 cast<llvm::IntegerType>(Prior->Data)->getIntegerBitWidth(), 8)));
563 Tail = Prior->Offset + getSize(Prior->Data);
567 void CGRecordLowering::determinePacked(bool NVBaseType) {
570 CharUnits Alignment = CharUnits::One();
571 CharUnits NVAlignment = CharUnits::One();
573 !NVBaseType && RD ? Layout.getNonVirtualSize() : CharUnits::Zero();
574 for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
575 MemberEnd = Members.end();
576 Member != MemberEnd; ++Member) {
579 // If any member falls at an offset that it not a multiple of its alignment,
580 // then the entire record must be packed.
581 if (Member->Offset % getAlignment(Member->Data))
583 if (Member->Offset < NVSize)
584 NVAlignment = std::max(NVAlignment, getAlignment(Member->Data));
585 Alignment = std::max(Alignment, getAlignment(Member->Data));
587 // If the size of the record (the capstone's offset) is not a multiple of the
588 // record's alignment, it must be packed.
589 if (Members.back().Offset % Alignment)
591 // If the non-virtual sub-object is not a multiple of the non-virtual
592 // sub-object's alignment, it must be packed. We cannot have a packed
593 // non-virtual sub-object and an unpacked complete object or vise versa.
594 if (NVSize % NVAlignment)
596 // Update the alignment of the sentinal.
598 Members.back().Data = getIntNType(Context.toBits(Alignment));
601 void CGRecordLowering::insertPadding() {
602 std::vector<std::pair<CharUnits, CharUnits> > Padding;
603 CharUnits Size = CharUnits::Zero();
604 for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
605 MemberEnd = Members.end();
606 Member != MemberEnd; ++Member) {
609 CharUnits Offset = Member->Offset;
610 assert(Offset >= Size);
611 // Insert padding if we need to.
612 if (Offset != Size.RoundUpToAlignment(Packed ? CharUnits::One() :
613 getAlignment(Member->Data)))
614 Padding.push_back(std::make_pair(Size, Offset - Size));
615 Size = Offset + getSize(Member->Data);
619 // Add the padding to the Members list and sort it.
620 for (std::vector<std::pair<CharUnits, CharUnits> >::const_iterator
621 Pad = Padding.begin(), PadEnd = Padding.end();
622 Pad != PadEnd; ++Pad)
623 Members.push_back(StorageInfo(Pad->first, getByteArrayType(Pad->second)));
624 std::stable_sort(Members.begin(), Members.end());
627 void CGRecordLowering::fillOutputFields() {
628 for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
629 MemberEnd = Members.end();
630 Member != MemberEnd; ++Member) {
632 FieldTypes.push_back(Member->Data);
633 if (Member->Kind == MemberInfo::Field) {
635 Fields[Member->FD->getCanonicalDecl()] = FieldTypes.size() - 1;
636 // A field without storage must be a bitfield.
638 setBitFieldInfo(Member->FD, Member->Offset, FieldTypes.back());
639 } else if (Member->Kind == MemberInfo::Base)
640 NonVirtualBases[Member->RD] = FieldTypes.size() - 1;
641 else if (Member->Kind == MemberInfo::VBase)
642 VirtualBases[Member->RD] = FieldTypes.size() - 1;
646 CGBitFieldInfo CGBitFieldInfo::MakeInfo(CodeGenTypes &Types,
648 uint64_t Offset, uint64_t Size,
649 uint64_t StorageSize,
650 CharUnits StorageOffset) {
651 // This function is vestigial from CGRecordLayoutBuilder days but is still
652 // used in GCObjCRuntime.cpp. That usage has a "fixme" attached to it that
653 // when addressed will allow for the removal of this function.
654 llvm::Type *Ty = Types.ConvertTypeForMem(FD->getType());
655 CharUnits TypeSizeInBytes =
656 CharUnits::fromQuantity(Types.getDataLayout().getTypeAllocSize(Ty));
657 uint64_t TypeSizeInBits = Types.getContext().toBits(TypeSizeInBytes);
659 bool IsSigned = FD->getType()->isSignedIntegerOrEnumerationType();
661 if (Size > TypeSizeInBits) {
662 // We have a wide bit-field. The extra bits are only used for padding, so
663 // if we have a bitfield of type T, with size N:
667 // We can just assume that it's:
671 Size = TypeSizeInBits;
674 // Reverse the bit offsets for big endian machines. Because we represent
675 // a bitfield as a single large integer load, we can imagine the bits
676 // counting from the most-significant-bit instead of the
677 // least-significant-bit.
678 if (Types.getDataLayout().isBigEndian()) {
679 Offset = StorageSize - (Offset + Size);
682 return CGBitFieldInfo(Offset, Size, IsSigned, StorageSize, StorageOffset);
685 CGRecordLayout *CodeGenTypes::ComputeRecordLayout(const RecordDecl *D,
686 llvm::StructType *Ty) {
687 CGRecordLowering Builder(*this, D, /*Packed=*/false);
689 Builder.lower(/*NonVirtualBaseType=*/false);
691 // If we're in C++, compute the base subobject type.
692 llvm::StructType *BaseTy = nullptr;
693 if (isa<CXXRecordDecl>(D) && !D->isUnion() && !D->hasAttr<FinalAttr>()) {
695 if (Builder.Layout.getNonVirtualSize() != Builder.Layout.getSize()) {
696 CGRecordLowering BaseBuilder(*this, D, /*Packed=*/Builder.Packed);
697 BaseBuilder.lower(/*NonVirtualBaseType=*/true);
698 BaseTy = llvm::StructType::create(
699 getLLVMContext(), BaseBuilder.FieldTypes, "", BaseBuilder.Packed);
700 addRecordTypeName(D, BaseTy, ".base");
701 // BaseTy and Ty must agree on their packedness for getLLVMFieldNo to work
702 // on both of them with the same index.
703 assert(Builder.Packed == BaseBuilder.Packed &&
704 "Non-virtual and complete types must agree on packedness");
708 // Fill in the struct *after* computing the base type. Filling in the body
709 // signifies that the type is no longer opaque and record layout is complete,
710 // but we may need to recursively layout D while laying D out as a base type.
711 Ty->setBody(Builder.FieldTypes, Builder.Packed);
714 new CGRecordLayout(Ty, BaseTy, Builder.IsZeroInitializable,
715 Builder.IsZeroInitializableAsBase);
717 RL->NonVirtualBases.swap(Builder.NonVirtualBases);
718 RL->CompleteObjectVirtualBases.swap(Builder.VirtualBases);
720 // Add all the field numbers.
721 RL->FieldInfo.swap(Builder.Fields);
723 // Add bitfield info.
724 RL->BitFields.swap(Builder.BitFields);
726 // Dump the layout, if requested.
727 if (getContext().getLangOpts().DumpRecordLayouts) {
728 llvm::outs() << "\n*** Dumping IRgen Record Layout\n";
729 llvm::outs() << "Record: ";
730 D->dump(llvm::outs());
731 llvm::outs() << "\nLayout: ";
732 RL->print(llvm::outs());
736 // Verify that the computed LLVM struct size matches the AST layout size.
737 const ASTRecordLayout &Layout = getContext().getASTRecordLayout(D);
739 uint64_t TypeSizeInBits = getContext().toBits(Layout.getSize());
740 assert(TypeSizeInBits == getDataLayout().getTypeAllocSizeInBits(Ty) &&
741 "Type size mismatch!");
744 CharUnits NonVirtualSize = Layout.getNonVirtualSize();
746 uint64_t AlignedNonVirtualTypeSizeInBits =
747 getContext().toBits(NonVirtualSize);
749 assert(AlignedNonVirtualTypeSizeInBits ==
750 getDataLayout().getTypeAllocSizeInBits(BaseTy) &&
751 "Type size mismatch!");
754 // Verify that the LLVM and AST field offsets agree.
755 llvm::StructType *ST =
756 dyn_cast<llvm::StructType>(RL->getLLVMType());
757 const llvm::StructLayout *SL = getDataLayout().getStructLayout(ST);
759 const ASTRecordLayout &AST_RL = getContext().getASTRecordLayout(D);
760 RecordDecl::field_iterator it = D->field_begin();
761 for (unsigned i = 0, e = AST_RL.getFieldCount(); i != e; ++i, ++it) {
762 const FieldDecl *FD = *it;
764 // For non-bit-fields, just check that the LLVM struct offset matches the
766 if (!FD->isBitField()) {
767 unsigned FieldNo = RL->getLLVMFieldNo(FD);
768 assert(AST_RL.getFieldOffset(i) == SL->getElementOffsetInBits(FieldNo) &&
769 "Invalid field offset!");
773 // Ignore unnamed bit-fields.
774 if (!FD->getDeclName())
777 // Don't inspect zero-length bitfields.
778 if (FD->getBitWidthValue(getContext()) == 0)
781 const CGBitFieldInfo &Info = RL->getBitFieldInfo(FD);
782 llvm::Type *ElementTy = ST->getTypeAtIndex(RL->getLLVMFieldNo(FD));
784 // Unions have overlapping elements dictating their layout, but for
785 // non-unions we can verify that this section of the layout is the exact
788 // For unions we verify that the start is zero and the size
789 // is in-bounds. However, on BE systems, the offset may be non-zero, but
790 // the size + offset should match the storage size in that case as it
791 // "starts" at the back.
792 if (getDataLayout().isBigEndian())
793 assert(static_cast<unsigned>(Info.Offset + Info.Size) ==
795 "Big endian union bitfield does not end at the back");
797 assert(Info.Offset == 0 &&
798 "Little endian union bitfield with a non-zero offset");
799 assert(Info.StorageSize <= SL->getSizeInBits() &&
800 "Union not large enough for bitfield storage");
802 assert(Info.StorageSize ==
803 getDataLayout().getTypeAllocSizeInBits(ElementTy) &&
804 "Storage size does not match the element type size");
806 assert(Info.Size > 0 && "Empty bitfield!");
807 assert(static_cast<unsigned>(Info.Offset) + Info.Size <= Info.StorageSize &&
808 "Bitfield outside of its allocated storage");
815 void CGRecordLayout::print(raw_ostream &OS) const {
816 OS << "<CGRecordLayout\n";
817 OS << " LLVMType:" << *CompleteObjectType << "\n";
818 if (BaseSubobjectType)
819 OS << " NonVirtualBaseLLVMType:" << *BaseSubobjectType << "\n";
820 OS << " IsZeroInitializable:" << IsZeroInitializable << "\n";
821 OS << " BitFields:[\n";
823 // Print bit-field infos in declaration order.
824 std::vector<std::pair<unsigned, const CGBitFieldInfo*> > BFIs;
825 for (llvm::DenseMap<const FieldDecl*, CGBitFieldInfo>::const_iterator
826 it = BitFields.begin(), ie = BitFields.end();
828 const RecordDecl *RD = it->first->getParent();
830 for (RecordDecl::field_iterator
831 it2 = RD->field_begin(); *it2 != it->first; ++it2)
833 BFIs.push_back(std::make_pair(Index, &it->second));
835 llvm::array_pod_sort(BFIs.begin(), BFIs.end());
836 for (unsigned i = 0, e = BFIs.size(); i != e; ++i) {
838 BFIs[i].second->print(OS);
845 void CGRecordLayout::dump() const {
849 void CGBitFieldInfo::print(raw_ostream &OS) const {
850 OS << "<CGBitFieldInfo"
851 << " Offset:" << Offset
853 << " IsSigned:" << IsSigned
854 << " StorageSize:" << StorageSize
855 << " StorageOffset:" << StorageOffset.getQuantity() << ">";
858 void CGBitFieldInfo::dump() const {