1//===--- CGRecordLayoutBuilder.cpp - CGRecordLayout builder ----*- C++ -*-===//
2//
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
6//
7//===----------------------------------------------------------------------===//
8//
9// Builder implementation for CGRecordLayout objects.
10//
11//===----------------------------------------------------------------------===//
12
13#include "ABIInfoImpl.h"
14#include "CGCXXABI.h"
15#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/Basic/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"
30using namespace clang;
31using namespace CodeGen;
32
33namespace {
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 [i8 x
48/// 3] instead of i24. This is computed when accumulating bitfields in
49/// accumulateBitfields.
50/// C++ examples that require clipping:
51/// struct { int a : 24; char b; }; // a must be clipped, b goes at offset 3
52/// struct A { int a : 24; ~A(); }; // a must be clipped because:
53/// struct B : A { char b; }; // b goes at offset 3
54/// * The allocation of bitfield access units is described in more detail in
55/// CGRecordLowering::accumulateBitFields.
56/// * Clang ignores 0 sized bitfields and 0 sized bases but *not* zero sized
57/// fields. The existing asserts suggest that LLVM assumes that *every* field
58/// has an underlying storage type. Therefore empty structures containing
59/// zero sized subobjects such as empty records or zero sized arrays still get
60/// a zero sized (empty struct) storage type.
61/// * Clang reads the complete type rather than the base type when generating
62/// code to access fields. Bitfields in tail position with tail padding may
63/// be clipped in the base class but not the complete class (we may discover
64/// that the tail padding is not used in the complete class.) However,
65/// because LLVM reads from the complete type it can generate incorrect code
66/// if we do not clip the tail padding off of the bitfield in the complete
67/// layout.
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.
73struct 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.
77 struct MemberInfo {
78 CharUnits Offset;
79 enum InfoKind { VFPtr, VBPtr, Field, Base, VBase } Kind;
80 llvm::Type *Data;
81 union {
82 const FieldDecl *FD;
83 const CXXRecordDecl *RD;
84 };
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; }
93 };
94 // The constructor.
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 static MemberInfo StorageInfo(CharUnits Offset, llvm::Type *Data) {
99 return MemberInfo(Offset, MemberInfo::Field, Data);
100 }
101
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
106 /// continuous run.
107 bool isDiscreteBitFieldABI() const {
108 return Context.getTargetInfo().getCXXABI().isMicrosoft() ||
109 D->isMsStruct(C: Context);
110 }
111
112 /// Helper function to check if we are targeting AAPCS.
113 bool isAAPCS() const {
114 return Context.getTargetInfo().getABI().starts_with(Prefix: "aapcs");
115 }
116
117 /// Helper function to check if the target machine is BigEndian.
118 bool isBE() const { return Context.getTargetInfo().isBigEndian(); }
119
120 /// The Itanium base layout rule allows virtual bases to overlap
121 /// other bases, which complicates layout in specific ways.
122 ///
123 /// Note specifically that the ms_struct attribute doesn't change this.
124 bool isOverlappingVBaseABI() const {
125 return !Context.getTargetInfo().getCXXABI().isMicrosoft();
126 }
127
128 /// Wraps llvm::Type::getIntNTy with some implicit arguments.
129 llvm::Type *getIntNType(uint64_t NumBits) const {
130 unsigned AlignedBits = llvm::alignTo(Value: NumBits, Align: Context.getCharWidth());
131 return llvm::Type::getIntNTy(C&: Types.getLLVMContext(), N: AlignedBits);
132 }
133 /// Get the LLVM type sized as one character unit.
134 llvm::Type *getCharType() const {
135 return llvm::Type::getIntNTy(C&: Types.getLLVMContext(),
136 N: Context.getCharWidth());
137 }
138 /// Gets an llvm type of size NumChars and alignment 1.
139 llvm::Type *getByteArrayType(CharUnits NumChars) const {
140 assert(!NumChars.isZero() && "Empty byte arrays aren't allowed.");
141 llvm::Type *Type = getCharType();
142 return NumChars == CharUnits::One() ? Type :
143 (llvm::Type *)llvm::ArrayType::get(ElementType: Type, NumElements: NumChars.getQuantity());
144 }
145 /// Gets the storage type for a field decl and handles storage
146 /// for itanium bitfields that are smaller than their declared type.
147 llvm::Type *getStorageType(const FieldDecl *FD) const {
148 llvm::Type *Type = Types.ConvertTypeForMem(T: FD->getType());
149 if (!FD->isBitField()) return Type;
150 if (isDiscreteBitFieldABI()) return Type;
151 return getIntNType(NumBits: std::min(a: FD->getBitWidthValue(),
152 b: (unsigned)Context.toBits(CharSize: getSize(Type))));
153 }
154 /// Gets the llvm Basesubobject type from a CXXRecordDecl.
155 llvm::Type *getStorageType(const CXXRecordDecl *RD) const {
156 return Types.getCGRecordLayout(RD).getBaseSubobjectLLVMType();
157 }
158 CharUnits bitsToCharUnits(uint64_t BitOffset) const {
159 return Context.toCharUnitsFromBits(BitSize: BitOffset);
160 }
161 CharUnits getSize(llvm::Type *Type) const {
162 return CharUnits::fromQuantity(Quantity: DataLayout.getTypeAllocSize(Ty: Type));
163 }
164 CharUnits getAlignment(llvm::Type *Type) const {
165 return CharUnits::fromQuantity(Quantity: DataLayout.getABITypeAlign(Ty: Type));
166 }
167 bool isZeroInitializable(const FieldDecl *FD) const {
168 return Types.isZeroInitializable(T: FD->getType());
169 }
170 bool isZeroInitializable(const RecordDecl *RD) const {
171 return Types.isZeroInitializable(RD);
172 }
173 void appendPaddingBytes(CharUnits Size) {
174 if (!Size.isZero())
175 FieldTypes.push_back(Elt: getByteArrayType(NumChars: Size));
176 }
177 uint64_t getFieldBitOffset(const FieldDecl *FD) const {
178 return Layout.getFieldOffset(FieldNo: FD->getFieldIndex());
179 }
180 // Layout routines.
181 void setBitFieldInfo(const FieldDecl *FD, CharUnits StartOffset,
182 llvm::Type *StorageType);
183 /// Lowers an ASTRecordLayout to a llvm type.
184 void lower(bool NonVirtualBaseType);
185 void lowerUnion(bool isNonVirtualBaseType);
186 void accumulateFields(bool isNonVirtualBaseType);
187 RecordDecl::field_iterator
188 accumulateBitFields(bool isNonVirtualBaseType,
189 RecordDecl::field_iterator Field,
190 RecordDecl::field_iterator FieldEnd);
191 void computeVolatileBitfields();
192 void accumulateBases();
193 void accumulateVPtrs();
194 void accumulateVBases();
195 /// Recursively searches all of the bases to find out if a vbase is
196 /// not the primary vbase of some base class.
197 bool hasOwnStorage(const CXXRecordDecl *Decl,
198 const CXXRecordDecl *Query) const;
199 void calculateZeroInit();
200 CharUnits calculateTailClippingOffset(bool isNonVirtualBaseType) const;
201 void checkBitfieldClipping(bool isNonVirtualBaseType) const;
202 /// Determines if we need a packed llvm struct.
203 void determinePacked(bool NVBaseType);
204 /// Inserts padding everywhere it's needed.
205 void insertPadding();
206 /// Fills out the structures that are ultimately consumed.
207 void fillOutputFields();
208 // Input memoization fields.
209 CodeGenTypes &Types;
210 const ASTContext &Context;
211 const RecordDecl *D;
212 const CXXRecordDecl *RD;
213 const ASTRecordLayout &Layout;
214 const llvm::DataLayout &DataLayout;
215 // Helpful intermediate data-structures.
216 std::vector<MemberInfo> Members;
217 // Output fields, consumed by CodeGenTypes::ComputeRecordLayout.
218 SmallVector<llvm::Type *, 16> FieldTypes;
219 llvm::DenseMap<const FieldDecl *, unsigned> Fields;
220 llvm::DenseMap<const FieldDecl *, CGBitFieldInfo> BitFields;
221 llvm::DenseMap<const CXXRecordDecl *, unsigned> NonVirtualBases;
222 llvm::DenseMap<const CXXRecordDecl *, unsigned> VirtualBases;
223 bool IsZeroInitializable : 1;
224 bool IsZeroInitializableAsBase : 1;
225 bool Packed : 1;
226private:
227 CGRecordLowering(const CGRecordLowering &) = delete;
228 void operator =(const CGRecordLowering &) = delete;
229};
230} // namespace {
231
232CGRecordLowering::CGRecordLowering(CodeGenTypes &Types, const RecordDecl *D,
233 bool Packed)
234 : Types(Types), Context(Types.getContext()), D(D),
235 RD(dyn_cast<CXXRecordDecl>(Val: D)),
236 Layout(Types.getContext().getASTRecordLayout(D)),
237 DataLayout(Types.getDataLayout()), IsZeroInitializable(true),
238 IsZeroInitializableAsBase(true), Packed(Packed) {}
239
240void CGRecordLowering::setBitFieldInfo(
241 const FieldDecl *FD, CharUnits StartOffset, llvm::Type *StorageType) {
242 CGBitFieldInfo &Info = BitFields[FD->getCanonicalDecl()];
243 Info.IsSigned = FD->getType()->isSignedIntegerOrEnumerationType();
244 Info.Offset = (unsigned)(getFieldBitOffset(FD) - Context.toBits(CharSize: StartOffset));
245 Info.Size = FD->getBitWidthValue();
246 Info.StorageSize = (unsigned)DataLayout.getTypeAllocSizeInBits(Ty: StorageType);
247 Info.StorageOffset = StartOffset;
248 if (Info.Size > Info.StorageSize)
249 Info.Size = Info.StorageSize;
250 // Reverse the bit offsets for big endian machines. Because we represent
251 // a bitfield as a single large integer load, we can imagine the bits
252 // counting from the most-significant-bit instead of the
253 // least-significant-bit.
254 if (DataLayout.isBigEndian())
255 Info.Offset = Info.StorageSize - (Info.Offset + Info.Size);
256
257 Info.VolatileStorageSize = 0;
258 Info.VolatileOffset = 0;
259 Info.VolatileStorageOffset = CharUnits::Zero();
260}
261
262void CGRecordLowering::lower(bool NVBaseType) {
263 // The lowering process implemented in this function takes a variety of
264 // carefully ordered phases.
265 // 1) Store all members (fields and bases) in a list and sort them by offset.
266 // 2) Add a 1-byte capstone member at the Size of the structure.
267 // 3) Clip bitfield storages members if their tail padding is or might be
268 // used by another field or base. The clipping process uses the capstone
269 // by treating it as another object that occurs after the record.
270 // 4) Determine if the llvm-struct requires packing. It's important that this
271 // phase occur after clipping, because clipping changes the llvm type.
272 // This phase reads the offset of the capstone when determining packedness
273 // and updates the alignment of the capstone to be equal of the alignment
274 // of the record after doing so.
275 // 5) Insert padding everywhere it is needed. This phase requires 'Packed' to
276 // have been computed and needs to know the alignment of the record in
277 // order to understand if explicit tail padding is needed.
278 // 6) Remove the capstone, we don't need it anymore.
279 // 7) Determine if this record can be zero-initialized. This phase could have
280 // been placed anywhere after phase 1.
281 // 8) Format the complete list of members in a way that can be consumed by
282 // CodeGenTypes::ComputeRecordLayout.
283 CharUnits Size = NVBaseType ? Layout.getNonVirtualSize() : Layout.getSize();
284 if (D->isUnion()) {
285 lowerUnion(isNonVirtualBaseType: NVBaseType);
286 computeVolatileBitfields();
287 return;
288 }
289 accumulateFields(isNonVirtualBaseType: NVBaseType);
290 // RD implies C++.
291 if (RD) {
292 accumulateVPtrs();
293 accumulateBases();
294 if (Members.empty()) {
295 appendPaddingBytes(Size);
296 computeVolatileBitfields();
297 return;
298 }
299 if (!NVBaseType)
300 accumulateVBases();
301 }
302 llvm::stable_sort(Range&: Members);
303 checkBitfieldClipping(isNonVirtualBaseType: NVBaseType);
304 Members.push_back(x: StorageInfo(Offset: Size, Data: getIntNType(NumBits: 8)));
305 determinePacked(NVBaseType);
306 insertPadding();
307 Members.pop_back();
308 calculateZeroInit();
309 fillOutputFields();
310 computeVolatileBitfields();
311}
312
313void CGRecordLowering::lowerUnion(bool isNonVirtualBaseType) {
314 CharUnits LayoutSize =
315 isNonVirtualBaseType ? Layout.getDataSize() : Layout.getSize();
316 llvm::Type *StorageType = nullptr;
317 bool SeenNamedMember = false;
318 // Iterate through the fields setting bitFieldInfo and the Fields array. Also
319 // locate the "most appropriate" storage type. The heuristic for finding the
320 // storage type isn't necessary, the first (non-0-length-bitfield) field's
321 // type would work fine and be simpler but would be different than what we've
322 // been doing and cause lit tests to change.
323 for (const auto *Field : D->fields()) {
324 if (Field->isBitField()) {
325 if (Field->isZeroLengthBitField())
326 continue;
327 llvm::Type *FieldType = getStorageType(FD: Field);
328 if (LayoutSize < getSize(Type: FieldType))
329 FieldType = getByteArrayType(NumChars: LayoutSize);
330 setBitFieldInfo(FD: Field, StartOffset: CharUnits::Zero(), StorageType: FieldType);
331 }
332 Fields[Field->getCanonicalDecl()] = 0;
333 llvm::Type *FieldType = getStorageType(FD: Field);
334 // Compute zero-initializable status.
335 // This union might not be zero initialized: it may contain a pointer to
336 // data member which might have some exotic initialization sequence.
337 // If this is the case, then we aught not to try and come up with a "better"
338 // type, it might not be very easy to come up with a Constant which
339 // correctly initializes it.
340 if (!SeenNamedMember) {
341 SeenNamedMember = Field->getIdentifier();
342 if (!SeenNamedMember)
343 if (const auto *FieldRD = Field->getType()->getAsRecordDecl())
344 SeenNamedMember = FieldRD->findFirstNamedDataMember();
345 if (SeenNamedMember && !isZeroInitializable(FD: Field)) {
346 IsZeroInitializable = IsZeroInitializableAsBase = false;
347 StorageType = FieldType;
348 }
349 }
350 // Because our union isn't zero initializable, we won't be getting a better
351 // storage type.
352 if (!IsZeroInitializable)
353 continue;
354 // Conditionally update our storage type if we've got a new "better" one.
355 if (!StorageType ||
356 getAlignment(Type: FieldType) > getAlignment(Type: StorageType) ||
357 (getAlignment(Type: FieldType) == getAlignment(Type: StorageType) &&
358 getSize(Type: FieldType) > getSize(Type: StorageType)))
359 StorageType = FieldType;
360 }
361 // If we have no storage type just pad to the appropriate size and return.
362 if (!StorageType)
363 return appendPaddingBytes(Size: LayoutSize);
364 // If our storage size was bigger than our required size (can happen in the
365 // case of packed bitfields on Itanium) then just use an I8 array.
366 if (LayoutSize < getSize(Type: StorageType))
367 StorageType = getByteArrayType(NumChars: LayoutSize);
368 FieldTypes.push_back(Elt: StorageType);
369 appendPaddingBytes(Size: LayoutSize - getSize(Type: StorageType));
370 // Set packed if we need it.
371 const auto StorageAlignment = getAlignment(Type: StorageType);
372 assert((Layout.getSize() % StorageAlignment == 0 ||
373 Layout.getDataSize() % StorageAlignment) &&
374 "Union's standard layout and no_unique_address layout must agree on "
375 "packedness");
376 if (Layout.getDataSize() % StorageAlignment)
377 Packed = true;
378}
379
380void CGRecordLowering::accumulateFields(bool isNonVirtualBaseType) {
381 for (RecordDecl::field_iterator Field = D->field_begin(),
382 FieldEnd = D->field_end();
383 Field != FieldEnd;) {
384 if (Field->isBitField()) {
385 Field = accumulateBitFields(isNonVirtualBaseType, Field, FieldEnd);
386 assert((Field == FieldEnd || !Field->isBitField()) &&
387 "Failed to accumulate all the bitfields");
388 } else if (isEmptyFieldForLayout(Context, FD: *Field)) {
389 // Empty fields have no storage.
390 ++Field;
391 } else {
392 // Use base subobject layout for the potentially-overlapping field,
393 // as it is done in RecordLayoutBuilder
394 Members.push_back(x: MemberInfo(
395 bitsToCharUnits(BitOffset: getFieldBitOffset(FD: *Field)), MemberInfo::Field,
396 Field->isPotentiallyOverlapping()
397 ? getStorageType(RD: Field->getType()->getAsCXXRecordDecl())
398 : getStorageType(FD: *Field),
399 *Field));
400 ++Field;
401 }
402 }
403}
404
405// Create members for bitfields. Field is a bitfield, and FieldEnd is the end
406// iterator of the record. Return the first non-bitfield encountered. We need
407// to know whether this is the base or complete layout, as virtual bases could
408// affect the upper bound of bitfield access unit allocation.
409RecordDecl::field_iterator
410CGRecordLowering::accumulateBitFields(bool isNonVirtualBaseType,
411 RecordDecl::field_iterator Field,
412 RecordDecl::field_iterator FieldEnd) {
413 if (isDiscreteBitFieldABI()) {
414 // Run stores the first element of the current run of bitfields. FieldEnd is
415 // used as a special value to note that we don't have a current run. A
416 // bitfield run is a contiguous collection of bitfields that can be stored
417 // in the same storage block. Zero-sized bitfields and bitfields that would
418 // cross an alignment boundary break a run and start a new one.
419 RecordDecl::field_iterator Run = FieldEnd;
420 // Tail is the offset of the first bit off the end of the current run. It's
421 // used to determine if the ASTRecordLayout is treating these two bitfields
422 // as contiguous. StartBitOffset is offset of the beginning of the Run.
423 uint64_t StartBitOffset, Tail = 0;
424 for (; Field != FieldEnd && Field->isBitField(); ++Field) {
425 // Zero-width bitfields end runs.
426 if (Field->isZeroLengthBitField()) {
427 Run = FieldEnd;
428 continue;
429 }
430 uint64_t BitOffset = getFieldBitOffset(FD: *Field);
431 llvm::Type *Type = Types.ConvertTypeForMem(T: Field->getType());
432 // If we don't have a run yet, or don't live within the previous run's
433 // allocated storage then we allocate some storage and start a new run.
434 if (Run == FieldEnd || BitOffset >= Tail) {
435 Run = Field;
436 StartBitOffset = BitOffset;
437 Tail = StartBitOffset + DataLayout.getTypeAllocSizeInBits(Ty: Type);
438 // Add the storage member to the record. This must be added to the
439 // record before the bitfield members so that it gets laid out before
440 // the bitfields it contains get laid out.
441 Members.push_back(x: StorageInfo(Offset: bitsToCharUnits(BitOffset: StartBitOffset), Data: Type));
442 }
443 // Bitfields get the offset of their storage but come afterward and remain
444 // there after a stable sort.
445 Members.push_back(x: MemberInfo(bitsToCharUnits(BitOffset: StartBitOffset),
446 MemberInfo::Field, nullptr, *Field));
447 }
448 return Field;
449 }
450
451 // The SysV ABI can overlap bitfield storage units with both other bitfield
452 // storage units /and/ other non-bitfield data members. Accessing a sequence
453 // of bitfields mustn't interfere with adjacent non-bitfields -- they're
454 // permitted to be accessed in separate threads for instance.
455
456 // We split runs of bit-fields into a sequence of "access units". When we emit
457 // a load or store of a bit-field, we'll load/store the entire containing
458 // access unit. As mentioned, the standard requires that these loads and
459 // stores must not interfere with accesses to other memory locations, and it
460 // defines the bit-field's memory location as the current run of
461 // non-zero-width bit-fields. So an access unit must never overlap with
462 // non-bit-field storage or cross a zero-width bit-field. Otherwise, we're
463 // free to draw the lines as we see fit.
464
465 // Drawing these lines well can be complicated. LLVM generally can't modify a
466 // program to access memory that it didn't before, so using very narrow access
467 // units can prevent the compiler from using optimal access patterns. For
468 // example, suppose a run of bit-fields occupies four bytes in a struct. If we
469 // split that into four 1-byte access units, then a sequence of assignments
470 // that doesn't touch all four bytes may have to be emitted with multiple
471 // 8-bit stores instead of a single 32-bit store. On the other hand, if we use
472 // very wide access units, we may find ourselves emitting accesses to
473 // bit-fields we didn't really need to touch, just because LLVM was unable to
474 // clean up after us.
475
476 // It is desirable to have access units be aligned powers of 2 no larger than
477 // a register. (On non-strict alignment ISAs, the alignment requirement can be
478 // dropped.) A three byte access unit will be accessed using 2-byte and 1-byte
479 // accesses and bit manipulation. If no bitfield straddles across the two
480 // separate accesses, it is better to have separate 2-byte and 1-byte access
481 // units, as then LLVM will not generate unnecessary memory accesses, or bit
482 // manipulation. Similarly, on a strict-alignment architecture, it is better
483 // to keep access-units naturally aligned, to avoid similar bit
484 // manipulation synthesizing larger unaligned accesses.
485
486 // Bitfields that share parts of a single byte are, of necessity, placed in
487 // the same access unit. That unit will encompass a consecutive run where
488 // adjacent bitfields share parts of a byte. (The first bitfield of such an
489 // access unit will start at the beginning of a byte.)
490
491 // We then try and accumulate adjacent access units when the combined unit is
492 // naturally sized, no larger than a register, and (on a strict alignment
493 // ISA), naturally aligned. Note that this requires lookahead to one or more
494 // subsequent access units. For instance, consider a 2-byte access-unit
495 // followed by 2 1-byte units. We can merge that into a 4-byte access-unit,
496 // but we would not want to merge a 2-byte followed by a single 1-byte (and no
497 // available tail padding). We keep track of the best access unit seen so far,
498 // and use that when we determine we cannot accumulate any more. Then we start
499 // again at the bitfield following that best one.
500
501 // The accumulation is also prevented when:
502 // *) it would cross a character-aigned zero-width bitfield, or
503 // *) fine-grained bitfield access option is in effect.
504
505 CharUnits RegSize =
506 bitsToCharUnits(BitOffset: Context.getTargetInfo().getRegisterWidth());
507 unsigned CharBits = Context.getCharWidth();
508
509 // Limit of useable tail padding at end of the record. Computed lazily and
510 // cached here.
511 CharUnits ScissorOffset = CharUnits::Zero();
512
513 // Data about the start of the span we're accumulating to create an access
514 // unit from. Begin is the first bitfield of the span. If Begin is FieldEnd,
515 // we've not got a current span. The span starts at the BeginOffset character
516 // boundary. BitSizeSinceBegin is the size (in bits) of the span -- this might
517 // include padding when we've advanced to a subsequent bitfield run.
518 RecordDecl::field_iterator Begin = FieldEnd;
519 CharUnits BeginOffset;
520 uint64_t BitSizeSinceBegin;
521
522 // The (non-inclusive) end of the largest acceptable access unit we've found
523 // since Begin. If this is Begin, we're gathering the initial set of bitfields
524 // of a new span. BestEndOffset is the end of that acceptable access unit --
525 // it might extend beyond the last character of the bitfield run, using
526 // available padding characters.
527 RecordDecl::field_iterator BestEnd = Begin;
528 CharUnits BestEndOffset;
529 bool BestClipped; // Whether the representation must be in a byte array.
530
531 for (;;) {
532 // AtAlignedBoundary is true iff Field is the (potential) start of a new
533 // span (or the end of the bitfields). When true, LimitOffset is the
534 // character offset of that span and Barrier indicates whether the new
535 // span cannot be merged into the current one.
536 bool AtAlignedBoundary = false;
537 bool Barrier = false;
538
539 if (Field != FieldEnd && Field->isBitField()) {
540 uint64_t BitOffset = getFieldBitOffset(FD: *Field);
541 if (Begin == FieldEnd) {
542 // Beginning a new span.
543 Begin = Field;
544 BestEnd = Begin;
545
546 assert((BitOffset % CharBits) == 0 && "Not at start of char");
547 BeginOffset = bitsToCharUnits(BitOffset);
548 BitSizeSinceBegin = 0;
549 } else if ((BitOffset % CharBits) != 0) {
550 // Bitfield occupies the same character as previous bitfield, it must be
551 // part of the same span. This can include zero-length bitfields, should
552 // the target not align them to character boundaries. Such non-alignment
553 // is at variance with the standards, which require zero-length
554 // bitfields be a barrier between access units. But of course we can't
555 // achieve that in the middle of a character.
556 assert(BitOffset == Context.toBits(BeginOffset) + BitSizeSinceBegin &&
557 "Concatenating non-contiguous bitfields");
558 } else {
559 // Bitfield potentially begins a new span. This includes zero-length
560 // bitfields on non-aligning targets that lie at character boundaries
561 // (those are barriers to merging).
562 if (Field->isZeroLengthBitField())
563 Barrier = true;
564 AtAlignedBoundary = true;
565 }
566 } else {
567 // We've reached the end of the bitfield run. Either we're done, or this
568 // is a barrier for the current span.
569 if (Begin == FieldEnd)
570 break;
571
572 Barrier = true;
573 AtAlignedBoundary = true;
574 }
575
576 // InstallBest indicates whether we should create an access unit for the
577 // current best span: fields [Begin, BestEnd) occupying characters
578 // [BeginOffset, BestEndOffset).
579 bool InstallBest = false;
580 if (AtAlignedBoundary) {
581 // Field is the start of a new span or the end of the bitfields. The
582 // just-seen span now extends to BitSizeSinceBegin.
583
584 // Determine if we can accumulate that just-seen span into the current
585 // accumulation.
586 CharUnits AccessSize = bitsToCharUnits(BitOffset: BitSizeSinceBegin + CharBits - 1);
587 if (BestEnd == Begin) {
588 // This is the initial run at the start of a new span. By definition,
589 // this is the best seen so far.
590 BestEnd = Field;
591 BestEndOffset = BeginOffset + AccessSize;
592 // Assume clipped until proven not below.
593 BestClipped = true;
594 if (!BitSizeSinceBegin)
595 // A zero-sized initial span -- this will install nothing and reset
596 // for another.
597 InstallBest = true;
598 } else if (AccessSize > RegSize)
599 // Accumulating the just-seen span would create a multi-register access
600 // unit, which would increase register pressure.
601 InstallBest = true;
602
603 if (!InstallBest) {
604 // Determine if accumulating the just-seen span will create an expensive
605 // access unit or not.
606 llvm::Type *Type = getIntNType(NumBits: Context.toBits(CharSize: AccessSize));
607 if (!Context.getTargetInfo().hasCheapUnalignedBitFieldAccess()) {
608 // Unaligned accesses are expensive. Only accumulate if the new unit
609 // is naturally aligned. Otherwise install the best we have, which is
610 // either the initial access unit (can't do better), or a naturally
611 // aligned accumulation (since we would have already installed it if
612 // it wasn't naturally aligned).
613 CharUnits Align = getAlignment(Type);
614 if (Align > Layout.getAlignment())
615 // The alignment required is greater than the containing structure
616 // itself.
617 InstallBest = true;
618 else if (!BeginOffset.isMultipleOf(N: Align))
619 // The access unit is not at a naturally aligned offset within the
620 // structure.
621 InstallBest = true;
622
623 if (InstallBest && BestEnd == Field)
624 // We're installing the first span, whose clipping was presumed
625 // above. Compute it correctly.
626 if (getSize(Type) == AccessSize)
627 BestClipped = false;
628 }
629
630 if (!InstallBest) {
631 // Find the next used storage offset to determine what the limit of
632 // the current span is. That's either the offset of the next field
633 // with storage (which might be Field itself) or the end of the
634 // non-reusable tail padding.
635 CharUnits LimitOffset;
636 for (auto Probe = Field; Probe != FieldEnd; ++Probe)
637 if (!isEmptyFieldForLayout(Context, FD: *Probe)) {
638 // A member with storage sets the limit.
639 assert((getFieldBitOffset(*Probe) % CharBits) == 0 &&
640 "Next storage is not byte-aligned");
641 LimitOffset = bitsToCharUnits(BitOffset: getFieldBitOffset(FD: *Probe));
642 goto FoundLimit;
643 }
644 // We reached the end of the fields, determine the bounds of useable
645 // tail padding. As this can be complex for C++, we cache the result.
646 if (ScissorOffset.isZero()) {
647 ScissorOffset = calculateTailClippingOffset(isNonVirtualBaseType);
648 assert(!ScissorOffset.isZero() && "Tail clipping at zero");
649 }
650
651 LimitOffset = ScissorOffset;
652 FoundLimit:;
653
654 CharUnits TypeSize = getSize(Type);
655 if (BeginOffset + TypeSize <= LimitOffset) {
656 // There is space before LimitOffset to create a naturally-sized
657 // access unit.
658 BestEndOffset = BeginOffset + TypeSize;
659 BestEnd = Field;
660 BestClipped = false;
661 }
662
663 if (Barrier)
664 // The next field is a barrier that we cannot merge across.
665 InstallBest = true;
666 else if (Types.getCodeGenOpts().FineGrainedBitfieldAccesses)
667 // Fine-grained access, so no merging of spans.
668 InstallBest = true;
669 else
670 // Otherwise, we're not installing. Update the bit size
671 // of the current span to go all the way to LimitOffset, which is
672 // the (aligned) offset of next bitfield to consider.
673 BitSizeSinceBegin = Context.toBits(CharSize: LimitOffset - BeginOffset);
674 }
675 }
676 }
677
678 if (InstallBest) {
679 assert((Field == FieldEnd || !Field->isBitField() ||
680 (getFieldBitOffset(*Field) % CharBits) == 0) &&
681 "Installing but not at an aligned bitfield or limit");
682 CharUnits AccessSize = BestEndOffset - BeginOffset;
683 if (!AccessSize.isZero()) {
684 // Add the storage member for the access unit to the record. The
685 // bitfields get the offset of their storage but come afterward and
686 // remain there after a stable sort.
687 llvm::Type *Type;
688 if (BestClipped) {
689 assert(getSize(getIntNType(Context.toBits(AccessSize))) >
690 AccessSize &&
691 "Clipped access need not be clipped");
692 Type = getByteArrayType(NumChars: AccessSize);
693 } else {
694 Type = getIntNType(NumBits: Context.toBits(CharSize: AccessSize));
695 assert(getSize(Type) == AccessSize &&
696 "Unclipped access must be clipped");
697 }
698 Members.push_back(x: StorageInfo(Offset: BeginOffset, Data: Type));
699 for (; Begin != BestEnd; ++Begin)
700 if (!Begin->isZeroLengthBitField())
701 Members.push_back(
702 x: MemberInfo(BeginOffset, MemberInfo::Field, nullptr, *Begin));
703 }
704 // Reset to start a new span.
705 Field = BestEnd;
706 Begin = FieldEnd;
707 } else {
708 assert(Field != FieldEnd && Field->isBitField() &&
709 "Accumulating past end of bitfields");
710 assert(!Barrier && "Accumulating across barrier");
711 // Accumulate this bitfield into the current (potential) span.
712 BitSizeSinceBegin += Field->getBitWidthValue();
713 ++Field;
714 }
715 }
716
717 return Field;
718}
719
720void CGRecordLowering::accumulateBases() {
721 // If we've got a primary virtual base, we need to add it with the bases.
722 if (Layout.isPrimaryBaseVirtual()) {
723 const CXXRecordDecl *BaseDecl = Layout.getPrimaryBase();
724 Members.push_back(x: MemberInfo(CharUnits::Zero(), MemberInfo::Base,
725 getStorageType(RD: BaseDecl), BaseDecl));
726 }
727 // Accumulate the non-virtual bases.
728 for (const auto &Base : RD->bases()) {
729 if (Base.isVirtual())
730 continue;
731
732 // Bases can be zero-sized even if not technically empty if they
733 // contain only a trailing array member.
734 const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
735 if (!isEmptyRecordForLayout(Context, T: Base.getType()) &&
736 !Context.getASTRecordLayout(D: BaseDecl).getNonVirtualSize().isZero())
737 Members.push_back(x: MemberInfo(Layout.getBaseClassOffset(Base: BaseDecl),
738 MemberInfo::Base, getStorageType(RD: BaseDecl), BaseDecl));
739 }
740}
741
742/// The AAPCS that defines that, when possible, bit-fields should
743/// be accessed using containers of the declared type width:
744/// When a volatile bit-field is read, and its container does not overlap with
745/// any non-bit-field member or any zero length bit-field member, its container
746/// must be read exactly once using the access width appropriate to the type of
747/// the container. When a volatile bit-field is written, and its container does
748/// not overlap with any non-bit-field member or any zero-length bit-field
749/// member, its container must be read exactly once and written exactly once
750/// using the access width appropriate to the type of the container. The two
751/// accesses are not atomic.
752///
753/// Enforcing the width restriction can be disabled using
754/// -fno-aapcs-bitfield-width.
755void CGRecordLowering::computeVolatileBitfields() {
756 if (!isAAPCS() || !Types.getCodeGenOpts().AAPCSBitfieldWidth)
757 return;
758
759 for (auto &I : BitFields) {
760 const FieldDecl *Field = I.first;
761 CGBitFieldInfo &Info = I.second;
762 llvm::Type *ResLTy = Types.ConvertTypeForMem(T: Field->getType());
763 // If the record alignment is less than the type width, we can't enforce a
764 // aligned load, bail out.
765 if ((uint64_t)(Context.toBits(CharSize: Layout.getAlignment())) <
766 ResLTy->getPrimitiveSizeInBits())
767 continue;
768 // CGRecordLowering::setBitFieldInfo() pre-adjusts the bit-field offsets
769 // for big-endian targets, but it assumes a container of width
770 // Info.StorageSize. Since AAPCS uses a different container size (width
771 // of the type), we first undo that calculation here and redo it once
772 // the bit-field offset within the new container is calculated.
773 const unsigned OldOffset =
774 isBE() ? Info.StorageSize - (Info.Offset + Info.Size) : Info.Offset;
775 // Offset to the bit-field from the beginning of the struct.
776 const unsigned AbsoluteOffset =
777 Context.toBits(CharSize: Info.StorageOffset) + OldOffset;
778
779 // Container size is the width of the bit-field type.
780 const unsigned StorageSize = ResLTy->getPrimitiveSizeInBits();
781 // Nothing to do if the access uses the desired
782 // container width and is naturally aligned.
783 if (Info.StorageSize == StorageSize && (OldOffset % StorageSize == 0))
784 continue;
785
786 // Offset within the container.
787 unsigned Offset = AbsoluteOffset & (StorageSize - 1);
788 // Bail out if an aligned load of the container cannot cover the entire
789 // bit-field. This can happen for example, if the bit-field is part of a
790 // packed struct. AAPCS does not define access rules for such cases, we let
791 // clang to follow its own rules.
792 if (Offset + Info.Size > StorageSize)
793 continue;
794
795 // Re-adjust offsets for big-endian targets.
796 if (isBE())
797 Offset = StorageSize - (Offset + Info.Size);
798
799 const CharUnits StorageOffset =
800 Context.toCharUnitsFromBits(BitSize: AbsoluteOffset & ~(StorageSize - 1));
801 const CharUnits End = StorageOffset +
802 Context.toCharUnitsFromBits(BitSize: StorageSize) -
803 CharUnits::One();
804
805 const ASTRecordLayout &Layout =
806 Context.getASTRecordLayout(D: Field->getParent());
807 // If we access outside memory outside the record, than bail out.
808 const CharUnits RecordSize = Layout.getSize();
809 if (End >= RecordSize)
810 continue;
811
812 // Bail out if performing this load would access non-bit-fields members.
813 bool Conflict = false;
814 for (const auto *F : D->fields()) {
815 // Allow sized bit-fields overlaps.
816 if (F->isBitField() && !F->isZeroLengthBitField())
817 continue;
818
819 const CharUnits FOffset = Context.toCharUnitsFromBits(
820 BitSize: Layout.getFieldOffset(FieldNo: F->getFieldIndex()));
821
822 // As C11 defines, a zero sized bit-field defines a barrier, so
823 // fields after and before it should be race condition free.
824 // The AAPCS acknowledges it and imposes no restritions when the
825 // natural container overlaps a zero-length bit-field.
826 if (F->isZeroLengthBitField()) {
827 if (End > FOffset && StorageOffset < FOffset) {
828 Conflict = true;
829 break;
830 }
831 }
832
833 const CharUnits FEnd =
834 FOffset +
835 Context.toCharUnitsFromBits(
836 BitSize: Types.ConvertTypeForMem(T: F->getType())->getPrimitiveSizeInBits()) -
837 CharUnits::One();
838 // If no overlap, continue.
839 if (End < FOffset || FEnd < StorageOffset)
840 continue;
841
842 // The desired load overlaps a non-bit-field member, bail out.
843 Conflict = true;
844 break;
845 }
846
847 if (Conflict)
848 continue;
849 // Write the new bit-field access parameters.
850 // As the storage offset now is defined as the number of elements from the
851 // start of the structure, we should divide the Offset by the element size.
852 Info.VolatileStorageOffset =
853 StorageOffset / Context.toCharUnitsFromBits(BitSize: StorageSize).getQuantity();
854 Info.VolatileStorageSize = StorageSize;
855 Info.VolatileOffset = Offset;
856 }
857}
858
859void CGRecordLowering::accumulateVPtrs() {
860 if (Layout.hasOwnVFPtr())
861 Members.push_back(
862 x: MemberInfo(CharUnits::Zero(), MemberInfo::VFPtr,
863 llvm::PointerType::getUnqual(C&: Types.getLLVMContext())));
864 if (Layout.hasOwnVBPtr())
865 Members.push_back(
866 x: MemberInfo(Layout.getVBPtrOffset(), MemberInfo::VBPtr,
867 llvm::PointerType::getUnqual(C&: Types.getLLVMContext())));
868}
869
870CharUnits
871CGRecordLowering::calculateTailClippingOffset(bool isNonVirtualBaseType) const {
872 if (!RD)
873 return Layout.getDataSize();
874
875 CharUnits ScissorOffset = Layout.getNonVirtualSize();
876 // In the itanium ABI, it's possible to place a vbase at a dsize that is
877 // smaller than the nvsize. Here we check to see if such a base is placed
878 // before the nvsize and set the scissor offset to that, instead of the
879 // nvsize.
880 if (!isNonVirtualBaseType && isOverlappingVBaseABI())
881 for (const auto &Base : RD->vbases()) {
882 const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
883 if (isEmptyRecordForLayout(Context, T: Base.getType()))
884 continue;
885 // If the vbase is a primary virtual base of some base, then it doesn't
886 // get its own storage location but instead lives inside of that base.
887 if (Context.isNearlyEmpty(RD: BaseDecl) && !hasOwnStorage(Decl: RD, Query: BaseDecl))
888 continue;
889 ScissorOffset = std::min(a: ScissorOffset,
890 b: Layout.getVBaseClassOffset(VBase: BaseDecl));
891 }
892
893 return ScissorOffset;
894}
895
896void CGRecordLowering::accumulateVBases() {
897 for (const auto &Base : RD->vbases()) {
898 const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
899 if (isEmptyRecordForLayout(Context, T: Base.getType()))
900 continue;
901 CharUnits Offset = Layout.getVBaseClassOffset(VBase: BaseDecl);
902 // If the vbase is a primary virtual base of some base, then it doesn't
903 // get its own storage location but instead lives inside of that base.
904 if (isOverlappingVBaseABI() &&
905 Context.isNearlyEmpty(RD: BaseDecl) &&
906 !hasOwnStorage(Decl: RD, Query: BaseDecl)) {
907 Members.push_back(x: MemberInfo(Offset, MemberInfo::VBase, nullptr,
908 BaseDecl));
909 continue;
910 }
911 // If we've got a vtordisp, add it as a storage type.
912 if (Layout.getVBaseOffsetsMap().find(Val: BaseDecl)->second.hasVtorDisp())
913 Members.push_back(x: StorageInfo(Offset: Offset - CharUnits::fromQuantity(Quantity: 4),
914 Data: getIntNType(NumBits: 32)));
915 Members.push_back(x: MemberInfo(Offset, MemberInfo::VBase,
916 getStorageType(RD: BaseDecl), BaseDecl));
917 }
918}
919
920bool CGRecordLowering::hasOwnStorage(const CXXRecordDecl *Decl,
921 const CXXRecordDecl *Query) const {
922 const ASTRecordLayout &DeclLayout = Context.getASTRecordLayout(D: Decl);
923 if (DeclLayout.isPrimaryBaseVirtual() && DeclLayout.getPrimaryBase() == Query)
924 return false;
925 for (const auto &Base : Decl->bases())
926 if (!hasOwnStorage(Decl: Base.getType()->getAsCXXRecordDecl(), Query))
927 return false;
928 return true;
929}
930
931void CGRecordLowering::calculateZeroInit() {
932 for (std::vector<MemberInfo>::const_iterator Member = Members.begin(),
933 MemberEnd = Members.end();
934 IsZeroInitializableAsBase && Member != MemberEnd; ++Member) {
935 if (Member->Kind == MemberInfo::Field) {
936 if (!Member->FD || isZeroInitializable(FD: Member->FD))
937 continue;
938 IsZeroInitializable = IsZeroInitializableAsBase = false;
939 } else if (Member->Kind == MemberInfo::Base ||
940 Member->Kind == MemberInfo::VBase) {
941 if (isZeroInitializable(RD: Member->RD))
942 continue;
943 IsZeroInitializable = false;
944 if (Member->Kind == MemberInfo::Base)
945 IsZeroInitializableAsBase = false;
946 }
947 }
948}
949
950// Verify accumulateBitfields computed the correct storage representations.
951void CGRecordLowering::checkBitfieldClipping(bool IsNonVirtualBaseType) const {
952#ifndef NDEBUG
953 auto ScissorOffset = calculateTailClippingOffset(IsNonVirtualBaseType);
954 auto Tail = CharUnits::Zero();
955 for (const auto &M : Members) {
956 // Only members with data could possibly overlap.
957 if (!M.Data)
958 continue;
959
960 assert(M.Offset >= Tail && "Bitfield access unit is not clipped");
961 Tail = M.Offset + getSize(M.Data);
962 assert((Tail <= ScissorOffset || M.Offset >= ScissorOffset) &&
963 "Bitfield straddles scissor offset");
964 }
965#endif
966}
967
968void CGRecordLowering::determinePacked(bool NVBaseType) {
969 if (Packed)
970 return;
971 CharUnits Alignment = CharUnits::One();
972 CharUnits NVAlignment = CharUnits::One();
973 CharUnits NVSize =
974 !NVBaseType && RD ? Layout.getNonVirtualSize() : CharUnits::Zero();
975 for (const MemberInfo &Member : Members) {
976 if (!Member.Data)
977 continue;
978 // If any member falls at an offset that it not a multiple of its alignment,
979 // then the entire record must be packed.
980 if (Member.Offset % getAlignment(Type: Member.Data))
981 Packed = true;
982 if (Member.Offset < NVSize)
983 NVAlignment = std::max(a: NVAlignment, b: getAlignment(Type: Member.Data));
984 Alignment = std::max(a: Alignment, b: getAlignment(Type: Member.Data));
985 }
986 // If the size of the record (the capstone's offset) is not a multiple of the
987 // record's alignment, it must be packed.
988 if (Members.back().Offset % Alignment)
989 Packed = true;
990 // If the non-virtual sub-object is not a multiple of the non-virtual
991 // sub-object's alignment, it must be packed. We cannot have a packed
992 // non-virtual sub-object and an unpacked complete object or vise versa.
993 if (NVSize % NVAlignment)
994 Packed = true;
995 // Update the alignment of the sentinel.
996 if (!Packed)
997 Members.back().Data = getIntNType(NumBits: Context.toBits(CharSize: Alignment));
998}
999
1000void CGRecordLowering::insertPadding() {
1001 std::vector<std::pair<CharUnits, CharUnits> > Padding;
1002 CharUnits Size = CharUnits::Zero();
1003 for (const MemberInfo &Member : Members) {
1004 if (!Member.Data)
1005 continue;
1006 CharUnits Offset = Member.Offset;
1007 assert(Offset >= Size);
1008 // Insert padding if we need to.
1009 if (Offset !=
1010 Size.alignTo(Align: Packed ? CharUnits::One() : getAlignment(Type: Member.Data)))
1011 Padding.push_back(x: std::make_pair(x&: Size, y: Offset - Size));
1012 Size = Offset + getSize(Type: Member.Data);
1013 }
1014 if (Padding.empty())
1015 return;
1016 // Add the padding to the Members list and sort it.
1017 for (const auto &Pad : Padding)
1018 Members.push_back(x: StorageInfo(Offset: Pad.first, Data: getByteArrayType(NumChars: Pad.second)));
1019 llvm::stable_sort(Range&: Members);
1020}
1021
1022void CGRecordLowering::fillOutputFields() {
1023 for (const MemberInfo &Member : Members) {
1024 if (Member.Data)
1025 FieldTypes.push_back(Elt: Member.Data);
1026 if (Member.Kind == MemberInfo::Field) {
1027 if (Member.FD)
1028 Fields[Member.FD->getCanonicalDecl()] = FieldTypes.size() - 1;
1029 // A field without storage must be a bitfield.
1030 if (!Member.Data)
1031 setBitFieldInfo(FD: Member.FD, StartOffset: Member.Offset, StorageType: FieldTypes.back());
1032 } else if (Member.Kind == MemberInfo::Base)
1033 NonVirtualBases[Member.RD] = FieldTypes.size() - 1;
1034 else if (Member.Kind == MemberInfo::VBase)
1035 VirtualBases[Member.RD] = FieldTypes.size() - 1;
1036 }
1037}
1038
1039CGBitFieldInfo CGBitFieldInfo::MakeInfo(CodeGenTypes &Types,
1040 const FieldDecl *FD,
1041 uint64_t Offset, uint64_t Size,
1042 uint64_t StorageSize,
1043 CharUnits StorageOffset) {
1044 // This function is vestigial from CGRecordLayoutBuilder days but is still
1045 // used in GCObjCRuntime.cpp. That usage has a "fixme" attached to it that
1046 // when addressed will allow for the removal of this function.
1047 llvm::Type *Ty = Types.ConvertTypeForMem(T: FD->getType());
1048 CharUnits TypeSizeInBytes =
1049 CharUnits::fromQuantity(Quantity: Types.getDataLayout().getTypeAllocSize(Ty));
1050 uint64_t TypeSizeInBits = Types.getContext().toBits(CharSize: TypeSizeInBytes);
1051
1052 bool IsSigned = FD->getType()->isSignedIntegerOrEnumerationType();
1053
1054 if (Size > TypeSizeInBits) {
1055 // We have a wide bit-field. The extra bits are only used for padding, so
1056 // if we have a bitfield of type T, with size N:
1057 //
1058 // T t : N;
1059 //
1060 // We can just assume that it's:
1061 //
1062 // T t : sizeof(T);
1063 //
1064 Size = TypeSizeInBits;
1065 }
1066
1067 // Reverse the bit offsets for big endian machines. Because we represent
1068 // a bitfield as a single large integer load, we can imagine the bits
1069 // counting from the most-significant-bit instead of the
1070 // least-significant-bit.
1071 if (Types.getDataLayout().isBigEndian()) {
1072 Offset = StorageSize - (Offset + Size);
1073 }
1074
1075 return CGBitFieldInfo(Offset, Size, IsSigned, StorageSize, StorageOffset);
1076}
1077
1078std::unique_ptr<CGRecordLayout>
1079CodeGenTypes::ComputeRecordLayout(const RecordDecl *D, llvm::StructType *Ty) {
1080 CGRecordLowering Builder(*this, D, /*Packed=*/false);
1081
1082 Builder.lower(/*NonVirtualBaseType=*/NVBaseType: false);
1083
1084 // If we're in C++, compute the base subobject type.
1085 llvm::StructType *BaseTy = nullptr;
1086 if (isa<CXXRecordDecl>(Val: D)) {
1087 BaseTy = Ty;
1088 if (Builder.Layout.getNonVirtualSize() != Builder.Layout.getSize()) {
1089 CGRecordLowering BaseBuilder(*this, D, /*Packed=*/Builder.Packed);
1090 BaseBuilder.lower(/*NonVirtualBaseType=*/NVBaseType: true);
1091 BaseTy = llvm::StructType::create(
1092 Context&: getLLVMContext(), Elements: BaseBuilder.FieldTypes, Name: "", isPacked: BaseBuilder.Packed);
1093 addRecordTypeName(RD: D, Ty: BaseTy, suffix: ".base");
1094 // BaseTy and Ty must agree on their packedness for getLLVMFieldNo to work
1095 // on both of them with the same index.
1096 assert(Builder.Packed == BaseBuilder.Packed &&
1097 "Non-virtual and complete types must agree on packedness");
1098 }
1099 }
1100
1101 // Fill in the struct *after* computing the base type. Filling in the body
1102 // signifies that the type is no longer opaque and record layout is complete,
1103 // but we may need to recursively layout D while laying D out as a base type.
1104 Ty->setBody(Elements: Builder.FieldTypes, isPacked: Builder.Packed);
1105
1106 auto RL = std::make_unique<CGRecordLayout>(
1107 args&: Ty, args&: BaseTy, args: (bool)Builder.IsZeroInitializable,
1108 args: (bool)Builder.IsZeroInitializableAsBase);
1109
1110 RL->NonVirtualBases.swap(RHS&: Builder.NonVirtualBases);
1111 RL->CompleteObjectVirtualBases.swap(RHS&: Builder.VirtualBases);
1112
1113 // Add all the field numbers.
1114 RL->FieldInfo.swap(RHS&: Builder.Fields);
1115
1116 // Add bitfield info.
1117 RL->BitFields.swap(RHS&: Builder.BitFields);
1118
1119 // Dump the layout, if requested.
1120 if (getContext().getLangOpts().DumpRecordLayouts) {
1121 llvm::outs() << "\n*** Dumping IRgen Record Layout\n";
1122 llvm::outs() << "Record: ";
1123 D->dump(Out&: llvm::outs());
1124 llvm::outs() << "\nLayout: ";
1125 RL->print(OS&: llvm::outs());
1126 }
1127
1128#ifndef NDEBUG
1129 // Verify that the computed LLVM struct size matches the AST layout size.
1130 const ASTRecordLayout &Layout = getContext().getASTRecordLayout(D);
1131
1132 uint64_t TypeSizeInBits = getContext().toBits(Layout.getSize());
1133 assert(TypeSizeInBits == getDataLayout().getTypeAllocSizeInBits(Ty) &&
1134 "Type size mismatch!");
1135
1136 if (BaseTy) {
1137 CharUnits NonVirtualSize = Layout.getNonVirtualSize();
1138
1139 uint64_t AlignedNonVirtualTypeSizeInBits =
1140 getContext().toBits(NonVirtualSize);
1141
1142 assert(AlignedNonVirtualTypeSizeInBits ==
1143 getDataLayout().getTypeAllocSizeInBits(BaseTy) &&
1144 "Type size mismatch!");
1145 }
1146
1147 // Verify that the LLVM and AST field offsets agree.
1148 llvm::StructType *ST = RL->getLLVMType();
1149 const llvm::StructLayout *SL = getDataLayout().getStructLayout(ST);
1150
1151 const ASTRecordLayout &AST_RL = getContext().getASTRecordLayout(D);
1152 RecordDecl::field_iterator it = D->field_begin();
1153 for (unsigned i = 0, e = AST_RL.getFieldCount(); i != e; ++i, ++it) {
1154 const FieldDecl *FD = *it;
1155
1156 // Ignore zero-sized fields.
1157 if (isEmptyFieldForLayout(getContext(), FD))
1158 continue;
1159
1160 // For non-bit-fields, just check that the LLVM struct offset matches the
1161 // AST offset.
1162 if (!FD->isBitField()) {
1163 unsigned FieldNo = RL->getLLVMFieldNo(FD);
1164 assert(AST_RL.getFieldOffset(i) == SL->getElementOffsetInBits(FieldNo) &&
1165 "Invalid field offset!");
1166 continue;
1167 }
1168
1169 // Ignore unnamed bit-fields.
1170 if (!FD->getDeclName())
1171 continue;
1172
1173 const CGBitFieldInfo &Info = RL->getBitFieldInfo(FD);
1174 llvm::Type *ElementTy = ST->getTypeAtIndex(RL->getLLVMFieldNo(FD));
1175
1176 // Unions have overlapping elements dictating their layout, but for
1177 // non-unions we can verify that this section of the layout is the exact
1178 // expected size.
1179 if (D->isUnion()) {
1180 // For unions we verify that the start is zero and the size
1181 // is in-bounds. However, on BE systems, the offset may be non-zero, but
1182 // the size + offset should match the storage size in that case as it
1183 // "starts" at the back.
1184 if (getDataLayout().isBigEndian())
1185 assert(static_cast<unsigned>(Info.Offset + Info.Size) ==
1186 Info.StorageSize &&
1187 "Big endian union bitfield does not end at the back");
1188 else
1189 assert(Info.Offset == 0 &&
1190 "Little endian union bitfield with a non-zero offset");
1191 assert(Info.StorageSize <= SL->getSizeInBits() &&
1192 "Union not large enough for bitfield storage");
1193 } else {
1194 assert((Info.StorageSize ==
1195 getDataLayout().getTypeAllocSizeInBits(ElementTy) ||
1196 Info.VolatileStorageSize ==
1197 getDataLayout().getTypeAllocSizeInBits(ElementTy)) &&
1198 "Storage size does not match the element type size");
1199 }
1200 assert(Info.Size > 0 && "Empty bitfield!");
1201 assert(static_cast<unsigned>(Info.Offset) + Info.Size <= Info.StorageSize &&
1202 "Bitfield outside of its allocated storage");
1203 }
1204#endif
1205
1206 return RL;
1207}
1208
1209void CGRecordLayout::print(raw_ostream &OS) const {
1210 OS << "<CGRecordLayout\n";
1211 OS << " LLVMType:" << *CompleteObjectType << "\n";
1212 if (BaseSubobjectType)
1213 OS << " NonVirtualBaseLLVMType:" << *BaseSubobjectType << "\n";
1214 OS << " IsZeroInitializable:" << IsZeroInitializable << "\n";
1215 OS << " BitFields:[\n";
1216
1217 // Print bit-field infos in declaration order.
1218 std::vector<std::pair<unsigned, const CGBitFieldInfo*> > BFIs;
1219 for (const auto &BitField : BitFields) {
1220 const RecordDecl *RD = BitField.first->getParent();
1221 unsigned Index = 0;
1222 for (RecordDecl::field_iterator it2 = RD->field_begin();
1223 *it2 != BitField.first; ++it2)
1224 ++Index;
1225 BFIs.push_back(x: std::make_pair(x&: Index, y: &BitField.second));
1226 }
1227 llvm::array_pod_sort(Start: BFIs.begin(), End: BFIs.end());
1228 for (auto &BFI : BFIs) {
1229 OS.indent(NumSpaces: 4);
1230 BFI.second->print(OS);
1231 OS << "\n";
1232 }
1233
1234 OS << "]>\n";
1235}
1236
1237LLVM_DUMP_METHOD void CGRecordLayout::dump() const {
1238 print(OS&: llvm::errs());
1239}
1240
1241void CGBitFieldInfo::print(raw_ostream &OS) const {
1242 OS << "<CGBitFieldInfo"
1243 << " Offset:" << Offset << " Size:" << Size << " IsSigned:" << IsSigned
1244 << " StorageSize:" << StorageSize
1245 << " StorageOffset:" << StorageOffset.getQuantity()
1246 << " VolatileOffset:" << VolatileOffset
1247 << " VolatileStorageSize:" << VolatileStorageSize
1248 << " VolatileStorageOffset:" << VolatileStorageOffset.getQuantity() << ">";
1249}
1250
1251LLVM_DUMP_METHOD void CGBitFieldInfo::dump() const {
1252 print(OS&: llvm::errs());
1253}
1254