CGRecordLayoutBuilder.cpp revision 206084
1//===--- CGRecordLayoutBuilder.cpp - CGRecordLayout builder ----*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// Builder implementation for CGRecordLayout objects. 11// 12//===----------------------------------------------------------------------===// 13 14#include "CGRecordLayout.h" 15#include "clang/AST/ASTContext.h" 16#include "clang/AST/Attr.h" 17#include "clang/AST/DeclCXX.h" 18#include "clang/AST/Expr.h" 19#include "clang/AST/RecordLayout.h" 20#include "CodeGenTypes.h" 21#include "llvm/Type.h" 22#include "llvm/DerivedTypes.h" 23#include "llvm/Target/TargetData.h" 24using namespace clang; 25using namespace CodeGen; 26 27namespace clang { 28namespace CodeGen { 29 30class CGRecordLayoutBuilder { 31public: 32 /// FieldTypes - Holds the LLVM types that the struct is created from. 33 std::vector<const llvm::Type *> FieldTypes; 34 35 /// LLVMFieldInfo - Holds a field and its corresponding LLVM field number. 36 typedef std::pair<const FieldDecl *, unsigned> LLVMFieldInfo; 37 llvm::SmallVector<LLVMFieldInfo, 16> LLVMFields; 38 39 /// LLVMBitFieldInfo - Holds location and size information about a bit field. 40 struct LLVMBitFieldInfo { 41 LLVMBitFieldInfo(const FieldDecl *FD, unsigned FieldNo, unsigned Start, 42 unsigned Size) 43 : FD(FD), FieldNo(FieldNo), Start(Start), Size(Size) { } 44 45 const FieldDecl *FD; 46 47 unsigned FieldNo; 48 unsigned Start; 49 unsigned Size; 50 }; 51 llvm::SmallVector<LLVMBitFieldInfo, 16> LLVMBitFields; 52 53 /// ContainsPointerToDataMember - Whether one of the fields in this record 54 /// layout is a pointer to data member, or a struct that contains pointer to 55 /// data member. 56 bool ContainsPointerToDataMember; 57 58 /// Packed - Whether the resulting LLVM struct will be packed or not. 59 bool Packed; 60 61private: 62 CodeGenTypes &Types; 63 64 /// Alignment - Contains the alignment of the RecordDecl. 65 // 66 // FIXME: This is not needed and should be removed. 67 unsigned Alignment; 68 69 /// AlignmentAsLLVMStruct - Will contain the maximum alignment of all the 70 /// LLVM types. 71 unsigned AlignmentAsLLVMStruct; 72 73 /// BitsAvailableInLastField - If a bit field spans only part of a LLVM field, 74 /// this will have the number of bits still available in the field. 75 char BitsAvailableInLastField; 76 77 /// NextFieldOffsetInBytes - Holds the next field offset in bytes. 78 uint64_t NextFieldOffsetInBytes; 79 80 /// LayoutUnion - Will layout a union RecordDecl. 81 void LayoutUnion(const RecordDecl *D); 82 83 /// LayoutField - try to layout all fields in the record decl. 84 /// Returns false if the operation failed because the struct is not packed. 85 bool LayoutFields(const RecordDecl *D); 86 87 /// LayoutBases - layout the bases and vtable pointer of a record decl. 88 void LayoutBases(const CXXRecordDecl *RD, const ASTRecordLayout &Layout); 89 90 /// LayoutField - layout a single field. Returns false if the operation failed 91 /// because the current struct is not packed. 92 bool LayoutField(const FieldDecl *D, uint64_t FieldOffset); 93 94 /// LayoutBitField - layout a single bit field. 95 void LayoutBitField(const FieldDecl *D, uint64_t FieldOffset); 96 97 /// AppendField - Appends a field with the given offset and type. 98 void AppendField(uint64_t FieldOffsetInBytes, const llvm::Type *FieldTy); 99 100 /// AppendPadding - Appends enough padding bytes so that the total struct 101 /// size matches the alignment of the passed in type. 102 void AppendPadding(uint64_t FieldOffsetInBytes, const llvm::Type *FieldTy); 103 104 /// AppendPadding - Appends enough padding bytes so that the total 105 /// struct size is a multiple of the field alignment. 106 void AppendPadding(uint64_t FieldOffsetInBytes, unsigned FieldAlignment); 107 108 /// AppendBytes - Append a given number of bytes to the record. 109 void AppendBytes(uint64_t NumBytes); 110 111 /// AppendTailPadding - Append enough tail padding so that the type will have 112 /// the passed size. 113 void AppendTailPadding(uint64_t RecordSize); 114 115 unsigned getTypeAlignment(const llvm::Type *Ty) const; 116 uint64_t getTypeSizeInBytes(const llvm::Type *Ty) const; 117 118 /// CheckForPointerToDataMember - Check if the given type contains a pointer 119 /// to data member. 120 void CheckForPointerToDataMember(QualType T); 121 122public: 123 CGRecordLayoutBuilder(CodeGenTypes &Types) 124 : ContainsPointerToDataMember(false), Packed(false), Types(Types), 125 Alignment(0), AlignmentAsLLVMStruct(1), 126 BitsAvailableInLastField(0), NextFieldOffsetInBytes(0) { } 127 128 /// Layout - Will layout a RecordDecl. 129 void Layout(const RecordDecl *D); 130}; 131 132} 133} 134 135void CGRecordLayoutBuilder::Layout(const RecordDecl *D) { 136 Alignment = Types.getContext().getASTRecordLayout(D).getAlignment() / 8; 137 Packed = D->hasAttr<PackedAttr>(); 138 139 if (D->isUnion()) { 140 LayoutUnion(D); 141 return; 142 } 143 144 if (LayoutFields(D)) 145 return; 146 147 // We weren't able to layout the struct. Try again with a packed struct 148 Packed = true; 149 AlignmentAsLLVMStruct = 1; 150 NextFieldOffsetInBytes = 0; 151 FieldTypes.clear(); 152 LLVMFields.clear(); 153 LLVMBitFields.clear(); 154 155 LayoutFields(D); 156} 157 158void CGRecordLayoutBuilder::LayoutBitField(const FieldDecl *D, 159 uint64_t FieldOffset) { 160 uint64_t FieldSize = 161 D->getBitWidth()->EvaluateAsInt(Types.getContext()).getZExtValue(); 162 163 if (FieldSize == 0) 164 return; 165 166 uint64_t NextFieldOffset = NextFieldOffsetInBytes * 8; 167 unsigned NumBytesToAppend; 168 169 if (FieldOffset < NextFieldOffset) { 170 assert(BitsAvailableInLastField && "Bitfield size mismatch!"); 171 assert(NextFieldOffsetInBytes && "Must have laid out at least one byte!"); 172 173 // The bitfield begins in the previous bit-field. 174 NumBytesToAppend = 175 llvm::RoundUpToAlignment(FieldSize - BitsAvailableInLastField, 8) / 8; 176 } else { 177 assert(FieldOffset % 8 == 0 && "Field offset not aligned correctly"); 178 179 // Append padding if necessary. 180 AppendBytes((FieldOffset - NextFieldOffset) / 8); 181 182 NumBytesToAppend = 183 llvm::RoundUpToAlignment(FieldSize, 8) / 8; 184 185 assert(NumBytesToAppend && "No bytes to append!"); 186 } 187 188 const llvm::Type *Ty = Types.ConvertTypeForMemRecursive(D->getType()); 189 uint64_t TypeSizeInBits = getTypeSizeInBytes(Ty) * 8; 190 191 LLVMBitFields.push_back(LLVMBitFieldInfo(D, FieldOffset / TypeSizeInBits, 192 FieldOffset % TypeSizeInBits, 193 FieldSize)); 194 195 AppendBytes(NumBytesToAppend); 196 197 BitsAvailableInLastField = 198 NextFieldOffsetInBytes * 8 - (FieldOffset + FieldSize); 199} 200 201bool CGRecordLayoutBuilder::LayoutField(const FieldDecl *D, 202 uint64_t FieldOffset) { 203 // If the field is packed, then we need a packed struct. 204 if (!Packed && D->hasAttr<PackedAttr>()) 205 return false; 206 207 if (D->isBitField()) { 208 // We must use packed structs for unnamed bit fields since they 209 // don't affect the struct alignment. 210 if (!Packed && !D->getDeclName()) 211 return false; 212 213 LayoutBitField(D, FieldOffset); 214 return true; 215 } 216 217 // Check if we have a pointer to data member in this field. 218 CheckForPointerToDataMember(D->getType()); 219 220 assert(FieldOffset % 8 == 0 && "FieldOffset is not on a byte boundary!"); 221 uint64_t FieldOffsetInBytes = FieldOffset / 8; 222 223 const llvm::Type *Ty = Types.ConvertTypeForMemRecursive(D->getType()); 224 unsigned TypeAlignment = getTypeAlignment(Ty); 225 226 // If the type alignment is larger then the struct alignment, we must use 227 // a packed struct. 228 if (TypeAlignment > Alignment) { 229 assert(!Packed && "Alignment is wrong even with packed struct!"); 230 return false; 231 } 232 233 if (const RecordType *RT = D->getType()->getAs<RecordType>()) { 234 const RecordDecl *RD = cast<RecordDecl>(RT->getDecl()); 235 if (const PragmaPackAttr *PPA = RD->getAttr<PragmaPackAttr>()) { 236 if (PPA->getAlignment() != TypeAlignment * 8 && !Packed) 237 return false; 238 } 239 } 240 241 // Round up the field offset to the alignment of the field type. 242 uint64_t AlignedNextFieldOffsetInBytes = 243 llvm::RoundUpToAlignment(NextFieldOffsetInBytes, TypeAlignment); 244 245 if (FieldOffsetInBytes < AlignedNextFieldOffsetInBytes) { 246 assert(!Packed && "Could not place field even with packed struct!"); 247 return false; 248 } 249 250 if (AlignedNextFieldOffsetInBytes < FieldOffsetInBytes) { 251 // Even with alignment, the field offset is not at the right place, 252 // insert padding. 253 uint64_t PaddingInBytes = FieldOffsetInBytes - NextFieldOffsetInBytes; 254 255 AppendBytes(PaddingInBytes); 256 } 257 258 // Now append the field. 259 LLVMFields.push_back(LLVMFieldInfo(D, FieldTypes.size())); 260 AppendField(FieldOffsetInBytes, Ty); 261 262 return true; 263} 264 265void CGRecordLayoutBuilder::LayoutUnion(const RecordDecl *D) { 266 assert(D->isUnion() && "Can't call LayoutUnion on a non-union record!"); 267 268 const ASTRecordLayout &Layout = Types.getContext().getASTRecordLayout(D); 269 270 const llvm::Type *Ty = 0; 271 uint64_t Size = 0; 272 unsigned Align = 0; 273 274 bool HasOnlyZeroSizedBitFields = true; 275 276 unsigned FieldNo = 0; 277 for (RecordDecl::field_iterator Field = D->field_begin(), 278 FieldEnd = D->field_end(); Field != FieldEnd; ++Field, ++FieldNo) { 279 assert(Layout.getFieldOffset(FieldNo) == 0 && 280 "Union field offset did not start at the beginning of record!"); 281 282 if (Field->isBitField()) { 283 uint64_t FieldSize = 284 Field->getBitWidth()->EvaluateAsInt(Types.getContext()).getZExtValue(); 285 286 // Ignore zero sized bit fields. 287 if (FieldSize == 0) 288 continue; 289 290 // Add the bit field info. 291 LLVMBitFields.push_back(LLVMBitFieldInfo(*Field, 0, 0, FieldSize)); 292 } else { 293 LLVMFields.push_back(LLVMFieldInfo(*Field, 0)); 294 } 295 296 HasOnlyZeroSizedBitFields = false; 297 298 const llvm::Type *FieldTy = 299 Types.ConvertTypeForMemRecursive(Field->getType()); 300 unsigned FieldAlign = Types.getTargetData().getABITypeAlignment(FieldTy); 301 uint64_t FieldSize = Types.getTargetData().getTypeAllocSize(FieldTy); 302 303 if (FieldAlign < Align) 304 continue; 305 306 if (FieldAlign > Align || FieldSize > Size) { 307 Ty = FieldTy; 308 Align = FieldAlign; 309 Size = FieldSize; 310 } 311 } 312 313 // Now add our field. 314 if (Ty) { 315 AppendField(0, Ty); 316 317 if (getTypeAlignment(Ty) > Layout.getAlignment() / 8) { 318 // We need a packed struct. 319 Packed = true; 320 Align = 1; 321 } 322 } 323 if (!Align) { 324 assert(HasOnlyZeroSizedBitFields && 325 "0-align record did not have all zero-sized bit-fields!"); 326 Align = 1; 327 } 328 329 // Append tail padding. 330 if (Layout.getSize() / 8 > Size) 331 AppendPadding(Layout.getSize() / 8, Align); 332} 333 334void CGRecordLayoutBuilder::LayoutBases(const CXXRecordDecl *RD, 335 const ASTRecordLayout &Layout) { 336 // Check if we need to add a vtable pointer. 337 if (RD->isDynamicClass() && !Layout.getPrimaryBase()) { 338 const llvm::Type *Int8PtrTy = 339 llvm::Type::getInt8PtrTy(Types.getLLVMContext()); 340 341 assert(NextFieldOffsetInBytes == 0 && 342 "Vtable pointer must come first!"); 343 AppendField(NextFieldOffsetInBytes, Int8PtrTy->getPointerTo()); 344 } 345} 346 347bool CGRecordLayoutBuilder::LayoutFields(const RecordDecl *D) { 348 assert(!D->isUnion() && "Can't call LayoutFields on a union!"); 349 assert(Alignment && "Did not set alignment!"); 350 351 const ASTRecordLayout &Layout = Types.getContext().getASTRecordLayout(D); 352 353 if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D)) 354 LayoutBases(RD, Layout); 355 356 unsigned FieldNo = 0; 357 358 for (RecordDecl::field_iterator Field = D->field_begin(), 359 FieldEnd = D->field_end(); Field != FieldEnd; ++Field, ++FieldNo) { 360 if (!LayoutField(*Field, Layout.getFieldOffset(FieldNo))) { 361 assert(!Packed && 362 "Could not layout fields even with a packed LLVM struct!"); 363 return false; 364 } 365 } 366 367 // Append tail padding if necessary. 368 AppendTailPadding(Layout.getSize()); 369 370 return true; 371} 372 373void CGRecordLayoutBuilder::AppendTailPadding(uint64_t RecordSize) { 374 assert(RecordSize % 8 == 0 && "Invalid record size!"); 375 376 uint64_t RecordSizeInBytes = RecordSize / 8; 377 assert(NextFieldOffsetInBytes <= RecordSizeInBytes && "Size mismatch!"); 378 379 uint64_t AlignedNextFieldOffset = 380 llvm::RoundUpToAlignment(NextFieldOffsetInBytes, AlignmentAsLLVMStruct); 381 382 if (AlignedNextFieldOffset == RecordSizeInBytes) { 383 // We don't need any padding. 384 return; 385 } 386 387 unsigned NumPadBytes = RecordSizeInBytes - NextFieldOffsetInBytes; 388 AppendBytes(NumPadBytes); 389} 390 391void CGRecordLayoutBuilder::AppendField(uint64_t FieldOffsetInBytes, 392 const llvm::Type *FieldTy) { 393 AlignmentAsLLVMStruct = std::max(AlignmentAsLLVMStruct, 394 getTypeAlignment(FieldTy)); 395 396 uint64_t FieldSizeInBytes = getTypeSizeInBytes(FieldTy); 397 398 FieldTypes.push_back(FieldTy); 399 400 NextFieldOffsetInBytes = FieldOffsetInBytes + FieldSizeInBytes; 401 BitsAvailableInLastField = 0; 402} 403 404void 405CGRecordLayoutBuilder::AppendPadding(uint64_t FieldOffsetInBytes, 406 const llvm::Type *FieldTy) { 407 AppendPadding(FieldOffsetInBytes, getTypeAlignment(FieldTy)); 408} 409 410void CGRecordLayoutBuilder::AppendPadding(uint64_t FieldOffsetInBytes, 411 unsigned FieldAlignment) { 412 assert(NextFieldOffsetInBytes <= FieldOffsetInBytes && 413 "Incorrect field layout!"); 414 415 // Round up the field offset to the alignment of the field type. 416 uint64_t AlignedNextFieldOffsetInBytes = 417 llvm::RoundUpToAlignment(NextFieldOffsetInBytes, FieldAlignment); 418 419 if (AlignedNextFieldOffsetInBytes < FieldOffsetInBytes) { 420 // Even with alignment, the field offset is not at the right place, 421 // insert padding. 422 uint64_t PaddingInBytes = FieldOffsetInBytes - NextFieldOffsetInBytes; 423 424 AppendBytes(PaddingInBytes); 425 } 426} 427 428void CGRecordLayoutBuilder::AppendBytes(uint64_t NumBytes) { 429 if (NumBytes == 0) 430 return; 431 432 const llvm::Type *Ty = llvm::Type::getInt8Ty(Types.getLLVMContext()); 433 if (NumBytes > 1) 434 Ty = llvm::ArrayType::get(Ty, NumBytes); 435 436 // Append the padding field 437 AppendField(NextFieldOffsetInBytes, Ty); 438} 439 440unsigned CGRecordLayoutBuilder::getTypeAlignment(const llvm::Type *Ty) const { 441 if (Packed) 442 return 1; 443 444 return Types.getTargetData().getABITypeAlignment(Ty); 445} 446 447uint64_t CGRecordLayoutBuilder::getTypeSizeInBytes(const llvm::Type *Ty) const { 448 return Types.getTargetData().getTypeAllocSize(Ty); 449} 450 451void CGRecordLayoutBuilder::CheckForPointerToDataMember(QualType T) { 452 // This record already contains a member pointer. 453 if (ContainsPointerToDataMember) 454 return; 455 456 // Can only have member pointers if we're compiling C++. 457 if (!Types.getContext().getLangOptions().CPlusPlus) 458 return; 459 460 T = Types.getContext().getBaseElementType(T); 461 462 if (const MemberPointerType *MPT = T->getAs<MemberPointerType>()) { 463 if (!MPT->getPointeeType()->isFunctionType()) { 464 // We have a pointer to data member. 465 ContainsPointerToDataMember = true; 466 } 467 } else if (const RecordType *RT = T->getAs<RecordType>()) { 468 const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl()); 469 470 // FIXME: It would be better if there was a way to explicitly compute the 471 // record layout instead of converting to a type. 472 Types.ConvertTagDeclType(RD); 473 474 const CGRecordLayout &Layout = Types.getCGRecordLayout(RD); 475 476 if (Layout.containsPointerToDataMember()) 477 ContainsPointerToDataMember = true; 478 } 479} 480 481CGRecordLayout *CodeGenTypes::ComputeRecordLayout(const RecordDecl *D) { 482 CGRecordLayoutBuilder Builder(*this); 483 484 Builder.Layout(D); 485 486 const llvm::Type *Ty = llvm::StructType::get(getLLVMContext(), 487 Builder.FieldTypes, 488 Builder.Packed); 489 assert(getContext().getASTRecordLayout(D).getSize() / 8 == 490 getTargetData().getTypeAllocSize(Ty) && 491 "Type size mismatch!"); 492 493 CGRecordLayout *RL = 494 new CGRecordLayout(Ty, Builder.ContainsPointerToDataMember); 495 496 // Add all the field numbers. 497 for (unsigned i = 0, e = Builder.LLVMFields.size(); i != e; ++i) { 498 const FieldDecl *FD = Builder.LLVMFields[i].first; 499 unsigned FieldNo = Builder.LLVMFields[i].second; 500 501 RL->FieldInfo.insert(std::make_pair(FD, FieldNo)); 502 } 503 504 // Add bitfield info. 505 for (unsigned i = 0, e = Builder.LLVMBitFields.size(); i != e; ++i) { 506 const CGRecordLayoutBuilder::LLVMBitFieldInfo &Info = 507 Builder.LLVMBitFields[i]; 508 509 CGRecordLayout::BitFieldInfo BFI(Info.FieldNo, Info.Start, Info.Size); 510 RL->BitFields.insert(std::make_pair(Info.FD, BFI)); 511 } 512 513 return RL; 514} 515