CGRecordLayoutBuilder.cpp revision d0eb3b93e89f0ab83a2305eb0ec42076f8d46142
1//===--- CGRecordLayoutBuilder.cpp - Record builder helper ------*- 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// This is a helper class used to build CGRecordLayout objects and LLVM types. 11// 12//===----------------------------------------------------------------------===// 13 14#include "CGRecordLayoutBuilder.h" 15 16#include "clang/AST/ASTContext.h" 17#include "clang/AST/Attr.h" 18#include "clang/AST/DeclCXX.h" 19#include "clang/AST/Expr.h" 20#include "clang/AST/RecordLayout.h" 21#include "CodeGenTypes.h" 22#include "llvm/DerivedTypes.h" 23#include "llvm/Target/TargetData.h" 24 25 26using namespace clang; 27using namespace CodeGen; 28 29void CGRecordLayoutBuilder::Layout(const RecordDecl *D) { 30 Alignment = Types.getContext().getASTRecordLayout(D).getAlignment() / 8; 31 Packed = D->hasAttr<PackedAttr>(); 32 33 if (D->isUnion()) { 34 LayoutUnion(D); 35 return; 36 } 37 38 if (LayoutFields(D)) 39 return; 40 41 // We weren't able to layout the struct. Try again with a packed struct 42 Packed = true; 43 AlignmentAsLLVMStruct = 1; 44 NextFieldOffsetInBytes = 0; 45 FieldTypes.clear(); 46 LLVMFields.clear(); 47 LLVMBitFields.clear(); 48 49 LayoutFields(D); 50} 51 52void CGRecordLayoutBuilder::LayoutBitField(const FieldDecl *D, 53 uint64_t FieldOffset) { 54 uint64_t FieldSize = 55 D->getBitWidth()->EvaluateAsInt(Types.getContext()).getZExtValue(); 56 57 if (FieldSize == 0) 58 return; 59 60 uint64_t NextFieldOffset = NextFieldOffsetInBytes * 8; 61 unsigned NumBytesToAppend; 62 63 if (FieldOffset < NextFieldOffset) { 64 assert(BitsAvailableInLastField && "Bitfield size mismatch!"); 65 assert(NextFieldOffsetInBytes && "Must have laid out at least one byte!"); 66 67 // The bitfield begins in the previous bit-field. 68 NumBytesToAppend = 69 llvm::RoundUpToAlignment(FieldSize - BitsAvailableInLastField, 8) / 8; 70 } else { 71 assert(FieldOffset % 8 == 0 && "Field offset not aligned correctly"); 72 73 // Append padding if necessary. 74 AppendBytes((FieldOffset - NextFieldOffset) / 8); 75 76 NumBytesToAppend = 77 llvm::RoundUpToAlignment(FieldSize, 8) / 8; 78 79 assert(NumBytesToAppend && "No bytes to append!"); 80 } 81 82 const llvm::Type *Ty = Types.ConvertTypeForMemRecursive(D->getType()); 83 uint64_t TypeSizeInBits = getTypeSizeInBytes(Ty) * 8; 84 85 LLVMBitFields.push_back(LLVMBitFieldInfo(D, FieldOffset / TypeSizeInBits, 86 FieldOffset % TypeSizeInBits, 87 FieldSize)); 88 89 AppendBytes(NumBytesToAppend); 90 91 AlignmentAsLLVMStruct = std::max(AlignmentAsLLVMStruct, getTypeAlignment(Ty)); 92 93 BitsAvailableInLastField = 94 NextFieldOffsetInBytes * 8 - (FieldOffset + FieldSize); 95} 96 97bool CGRecordLayoutBuilder::LayoutField(const FieldDecl *D, 98 uint64_t FieldOffset) { 99 // If the field is packed, then we need a packed struct. 100 if (!Packed && D->hasAttr<PackedAttr>()) 101 return false; 102 103 if (D->isBitField()) { 104 // We must use packed structs for unnamed bit fields since they 105 // don't affect the struct alignment. 106 if (!Packed && !D->getDeclName()) 107 return false; 108 109 LayoutBitField(D, FieldOffset); 110 return true; 111 } 112 113 assert(FieldOffset % 8 == 0 && "FieldOffset is not on a byte boundary!"); 114 uint64_t FieldOffsetInBytes = FieldOffset / 8; 115 116 const llvm::Type *Ty = Types.ConvertTypeForMemRecursive(D->getType()); 117 unsigned TypeAlignment = getTypeAlignment(Ty); 118 119 // If the type alignment is larger then the struct alignment, we must use 120 // a packed struct. 121 if (TypeAlignment > Alignment) { 122 assert(!Packed && "Alignment is wrong even with packed struct!"); 123 return false; 124 } 125 126 if (const RecordType *RT = D->getType()->getAs<RecordType>()) { 127 const RecordDecl *RD = cast<RecordDecl>(RT->getDecl()); 128 if (const PragmaPackAttr *PPA = RD->getAttr<PragmaPackAttr>()) { 129 if (PPA->getAlignment() != TypeAlignment * 8 && !Packed) 130 return false; 131 } 132 } 133 134 // Round up the field offset to the alignment of the field type. 135 uint64_t AlignedNextFieldOffsetInBytes = 136 llvm::RoundUpToAlignment(NextFieldOffsetInBytes, TypeAlignment); 137 138 if (FieldOffsetInBytes < AlignedNextFieldOffsetInBytes) { 139 assert(!Packed && "Could not place field even with packed struct!"); 140 return false; 141 } 142 143 if (AlignedNextFieldOffsetInBytes < FieldOffsetInBytes) { 144 // Even with alignment, the field offset is not at the right place, 145 // insert padding. 146 uint64_t PaddingInBytes = FieldOffsetInBytes - NextFieldOffsetInBytes; 147 148 AppendBytes(PaddingInBytes); 149 } 150 151 // Now append the field. 152 LLVMFields.push_back(LLVMFieldInfo(D, FieldTypes.size())); 153 AppendField(FieldOffsetInBytes, Ty); 154 155 return true; 156} 157 158void CGRecordLayoutBuilder::LayoutUnion(const RecordDecl *D) { 159 assert(D->isUnion() && "Can't call LayoutUnion on a non-union record!"); 160 161 const ASTRecordLayout &Layout = Types.getContext().getASTRecordLayout(D); 162 163 const llvm::Type *Ty = 0; 164 uint64_t Size = 0; 165 unsigned Align = 0; 166 167 unsigned FieldNo = 0; 168 for (RecordDecl::field_iterator Field = D->field_begin(), 169 FieldEnd = D->field_end(); Field != FieldEnd; ++Field, ++FieldNo) { 170 assert(Layout.getFieldOffset(FieldNo) == 0 && 171 "Union field offset did not start at the beginning of record!"); 172 173 if (Field->isBitField()) { 174 uint64_t FieldSize = 175 Field->getBitWidth()->EvaluateAsInt(Types.getContext()).getZExtValue(); 176 177 // Ignore zero sized bit fields. 178 if (FieldSize == 0) 179 continue; 180 181 // Add the bit field info. 182 Types.addBitFieldInfo(*Field, 0, 0, FieldSize); 183 } else 184 Types.addFieldInfo(*Field, 0); 185 186 const llvm::Type *FieldTy = 187 Types.ConvertTypeForMemRecursive(Field->getType()); 188 unsigned FieldAlign = Types.getTargetData().getABITypeAlignment(FieldTy); 189 uint64_t FieldSize = Types.getTargetData().getTypeAllocSize(FieldTy); 190 191 if (FieldAlign < Align) 192 continue; 193 194 if (FieldAlign > Align || FieldSize > Size) { 195 Ty = FieldTy; 196 Align = FieldAlign; 197 Size = FieldSize; 198 } 199 } 200 201 // Now add our field. 202 if (Ty) 203 AppendField(0, Ty); 204 205 // Append tail padding. 206 if (Layout.getSize() / 8 > Size) 207 AppendPadding(Layout.getSize() / 8, Align); 208} 209 210bool CGRecordLayoutBuilder::LayoutFields(const RecordDecl *D) { 211 assert(!D->isUnion() && "Can't call LayoutFields on a union!"); 212 assert(Alignment && "Did not set alignment!"); 213 214 const ASTRecordLayout &Layout = Types.getContext().getASTRecordLayout(D); 215 216 unsigned FieldNo = 0; 217 218 for (RecordDecl::field_iterator Field = D->field_begin(), 219 FieldEnd = D->field_end(); Field != FieldEnd; ++Field, ++FieldNo) { 220 if (!LayoutField(*Field, Layout.getFieldOffset(FieldNo))) { 221 assert(!Packed && 222 "Could not layout fields even with a packed LLVM struct!"); 223 return false; 224 } 225 } 226 227 // Append tail padding if necessary. 228 AppendTailPadding(Layout.getSize()); 229 230 return true; 231} 232 233void CGRecordLayoutBuilder::AppendTailPadding(uint64_t RecordSize) { 234 assert(RecordSize % 8 == 0 && "Invalid record size!"); 235 236 uint64_t RecordSizeInBytes = RecordSize / 8; 237 assert(NextFieldOffsetInBytes <= RecordSizeInBytes && "Size mismatch!"); 238 239 unsigned NumPadBytes = RecordSizeInBytes - NextFieldOffsetInBytes; 240 AppendBytes(NumPadBytes); 241} 242 243void CGRecordLayoutBuilder::AppendField(uint64_t FieldOffsetInBytes, 244 const llvm::Type *FieldTy) { 245 AlignmentAsLLVMStruct = std::max(AlignmentAsLLVMStruct, 246 getTypeAlignment(FieldTy)); 247 248 uint64_t FieldSizeInBytes = getTypeSizeInBytes(FieldTy); 249 250 FieldTypes.push_back(FieldTy); 251 252 NextFieldOffsetInBytes = FieldOffsetInBytes + FieldSizeInBytes; 253 BitsAvailableInLastField = 0; 254} 255 256void 257CGRecordLayoutBuilder::AppendPadding(uint64_t FieldOffsetInBytes, 258 const llvm::Type *FieldTy) { 259 AppendPadding(FieldOffsetInBytes, getTypeAlignment(FieldTy)); 260} 261 262void CGRecordLayoutBuilder::AppendPadding(uint64_t FieldOffsetInBytes, 263 unsigned FieldAlignment) { 264 assert(NextFieldOffsetInBytes <= FieldOffsetInBytes && 265 "Incorrect field layout!"); 266 267 // Round up the field offset to the alignment of the field type. 268 uint64_t AlignedNextFieldOffsetInBytes = 269 llvm::RoundUpToAlignment(NextFieldOffsetInBytes, FieldAlignment); 270 271 if (AlignedNextFieldOffsetInBytes < FieldOffsetInBytes) { 272 // Even with alignment, the field offset is not at the right place, 273 // insert padding. 274 uint64_t PaddingInBytes = FieldOffsetInBytes - NextFieldOffsetInBytes; 275 276 AppendBytes(PaddingInBytes); 277 } 278} 279 280void CGRecordLayoutBuilder::AppendBytes(uint64_t NumBytes) { 281 if (NumBytes == 0) 282 return; 283 284 const llvm::Type *Ty = llvm::Type::getInt8Ty(Types.getLLVMContext()); 285 if (NumBytes > 1) 286 Ty = llvm::ArrayType::get(Ty, NumBytes); 287 288 // Append the padding field 289 AppendField(NextFieldOffsetInBytes, Ty); 290} 291 292unsigned CGRecordLayoutBuilder::getTypeAlignment(const llvm::Type *Ty) const { 293 if (Packed) 294 return 1; 295 296 return Types.getTargetData().getABITypeAlignment(Ty); 297} 298 299uint64_t CGRecordLayoutBuilder::getTypeSizeInBytes(const llvm::Type *Ty) const { 300 return Types.getTargetData().getTypeAllocSize(Ty); 301} 302 303void CGRecordLayoutBuilder::CheckForMemberPointer(const FieldDecl *FD) { 304 // This record already contains a member pointer. 305 if (ContainsMemberPointer) 306 return; 307 308 // Can only have member pointers if we're compiling C++. 309 if (!Types.getContext().getLangOptions().CPlusPlus) 310 return; 311 312 QualType Ty = FD->getType(); 313 314 if (Ty->isMemberPointerType()) { 315 // We have a member pointer! 316 ContainsMemberPointer = true; 317 return; 318 } 319 320} 321 322CGRecordLayout * 323CGRecordLayoutBuilder::ComputeLayout(CodeGenTypes &Types, 324 const RecordDecl *D) { 325 CGRecordLayoutBuilder Builder(Types); 326 327 Builder.Layout(D); 328 329 const llvm::Type *Ty = llvm::StructType::get(Types.getLLVMContext(), 330 Builder.FieldTypes, 331 Builder.Packed); 332 assert(Types.getContext().getASTRecordLayout(D).getSize() / 8 == 333 Types.getTargetData().getTypeAllocSize(Ty) && 334 "Type size mismatch!"); 335 336 // Add all the field numbers. 337 for (unsigned i = 0, e = Builder.LLVMFields.size(); i != e; ++i) { 338 const FieldDecl *FD = Builder.LLVMFields[i].first; 339 unsigned FieldNo = Builder.LLVMFields[i].second; 340 341 Types.addFieldInfo(FD, FieldNo); 342 } 343 344 // Add bitfield info. 345 for (unsigned i = 0, e = Builder.LLVMBitFields.size(); i != e; ++i) { 346 const LLVMBitFieldInfo &Info = Builder.LLVMBitFields[i]; 347 348 Types.addBitFieldInfo(Info.FD, Info.FieldNo, Info.Start, Info.Size); 349 } 350 351 return new CGRecordLayout(Ty, Builder.ContainsMemberPointer); 352} 353