1 //===- BitstreamWriter.h - Low-level bitstream writer interface -*- 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 // This header defines the BitstreamWriter class. This class can be used to 10 // write an arbitrary bitstream, regardless of its contents. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_BITSTREAM_BITSTREAMWRITER_H 15 #define LLVM_BITSTREAM_BITSTREAMWRITER_H 16 17 #include "llvm/ADT/ArrayRef.h" 18 #include "llvm/ADT/Optional.h" 19 #include "llvm/ADT/SmallVector.h" 20 #include "llvm/ADT/StringRef.h" 21 #include "llvm/Bitstream/BitCodes.h" 22 #include "llvm/Support/Endian.h" 23 #include <vector> 24 25 namespace llvm { 26 27 class BitstreamWriter { 28 SmallVectorImpl<char> &Out; 29 30 /// CurBit - Always between 0 and 31 inclusive, specifies the next bit to use. 31 unsigned CurBit; 32 33 /// CurValue - The current value. Only bits < CurBit are valid. 34 uint32_t CurValue; 35 36 /// CurCodeSize - This is the declared size of code values used for the 37 /// current block, in bits. 38 unsigned CurCodeSize; 39 40 /// BlockInfoCurBID - When emitting a BLOCKINFO_BLOCK, this is the currently 41 /// selected BLOCK ID. 42 unsigned BlockInfoCurBID; 43 44 /// CurAbbrevs - Abbrevs installed at in this block. 45 std::vector<std::shared_ptr<BitCodeAbbrev>> CurAbbrevs; 46 47 struct Block { 48 unsigned PrevCodeSize; 49 size_t StartSizeWord; 50 std::vector<std::shared_ptr<BitCodeAbbrev>> PrevAbbrevs; 51 Block(unsigned PCS, size_t SSW) : PrevCodeSize(PCS), StartSizeWord(SSW) {} 52 }; 53 54 /// BlockScope - This tracks the current blocks that we have entered. 55 std::vector<Block> BlockScope; 56 57 /// BlockInfo - This contains information emitted to BLOCKINFO_BLOCK blocks. 58 /// These describe abbreviations that all blocks of the specified ID inherit. 59 struct BlockInfo { 60 unsigned BlockID; 61 std::vector<std::shared_ptr<BitCodeAbbrev>> Abbrevs; 62 }; 63 std::vector<BlockInfo> BlockInfoRecords; 64 65 void WriteByte(unsigned char Value) { 66 Out.push_back(Value); 67 } 68 69 void WriteWord(unsigned Value) { 70 Value = support::endian::byte_swap<uint32_t, support::little>(Value); 71 Out.append(reinterpret_cast<const char *>(&Value), 72 reinterpret_cast<const char *>(&Value + 1)); 73 } 74 75 size_t GetBufferOffset() const { return Out.size(); } 76 77 size_t GetWordIndex() const { 78 size_t Offset = GetBufferOffset(); 79 assert((Offset & 3) == 0 && "Not 32-bit aligned"); 80 return Offset / 4; 81 } 82 83 public: 84 explicit BitstreamWriter(SmallVectorImpl<char> &O) 85 : Out(O), CurBit(0), CurValue(0), CurCodeSize(2) {} 86 87 ~BitstreamWriter() { 88 assert(CurBit == 0 && "Unflushed data remaining"); 89 assert(BlockScope.empty() && CurAbbrevs.empty() && "Block imbalance"); 90 } 91 92 /// Retrieve the current position in the stream, in bits. 93 uint64_t GetCurrentBitNo() const { return GetBufferOffset() * 8 + CurBit; } 94 95 /// Retrieve the number of bits currently used to encode an abbrev ID. 96 unsigned GetAbbrevIDWidth() const { return CurCodeSize; } 97 98 //===--------------------------------------------------------------------===// 99 // Basic Primitives for emitting bits to the stream. 100 //===--------------------------------------------------------------------===// 101 102 /// Backpatch a 32-bit word in the output at the given bit offset 103 /// with the specified value. 104 void BackpatchWord(uint64_t BitNo, unsigned NewWord) { 105 using namespace llvm::support; 106 unsigned ByteNo = BitNo / 8; 107 assert((!endian::readAtBitAlignment<uint32_t, little, unaligned>( 108 &Out[ByteNo], BitNo & 7)) && 109 "Expected to be patching over 0-value placeholders"); 110 endian::writeAtBitAlignment<uint32_t, little, unaligned>( 111 &Out[ByteNo], NewWord, BitNo & 7); 112 } 113 114 void BackpatchWord64(uint64_t BitNo, uint64_t Val) { 115 BackpatchWord(BitNo, (uint32_t)Val); 116 BackpatchWord(BitNo + 32, (uint32_t)(Val >> 32)); 117 } 118 119 void Emit(uint32_t Val, unsigned NumBits) { 120 assert(NumBits && NumBits <= 32 && "Invalid value size!"); 121 assert((Val & ~(~0U >> (32-NumBits))) == 0 && "High bits set!"); 122 CurValue |= Val << CurBit; 123 if (CurBit + NumBits < 32) { 124 CurBit += NumBits; 125 return; 126 } 127 128 // Add the current word. 129 WriteWord(CurValue); 130 131 if (CurBit) 132 CurValue = Val >> (32-CurBit); 133 else 134 CurValue = 0; 135 CurBit = (CurBit+NumBits) & 31; 136 } 137 138 void FlushToWord() { 139 if (CurBit) { 140 WriteWord(CurValue); 141 CurBit = 0; 142 CurValue = 0; 143 } 144 } 145 146 void EmitVBR(uint32_t Val, unsigned NumBits) { 147 assert(NumBits <= 32 && "Too many bits to emit!"); 148 uint32_t Threshold = 1U << (NumBits-1); 149 150 // Emit the bits with VBR encoding, NumBits-1 bits at a time. 151 while (Val >= Threshold) { 152 Emit((Val & ((1 << (NumBits-1))-1)) | (1 << (NumBits-1)), NumBits); 153 Val >>= NumBits-1; 154 } 155 156 Emit(Val, NumBits); 157 } 158 159 void EmitVBR64(uint64_t Val, unsigned NumBits) { 160 assert(NumBits <= 32 && "Too many bits to emit!"); 161 if ((uint32_t)Val == Val) 162 return EmitVBR((uint32_t)Val, NumBits); 163 164 uint32_t Threshold = 1U << (NumBits-1); 165 166 // Emit the bits with VBR encoding, NumBits-1 bits at a time. 167 while (Val >= Threshold) { 168 Emit(((uint32_t)Val & ((1 << (NumBits-1))-1)) | 169 (1 << (NumBits-1)), NumBits); 170 Val >>= NumBits-1; 171 } 172 173 Emit((uint32_t)Val, NumBits); 174 } 175 176 /// EmitCode - Emit the specified code. 177 void EmitCode(unsigned Val) { 178 Emit(Val, CurCodeSize); 179 } 180 181 //===--------------------------------------------------------------------===// 182 // Block Manipulation 183 //===--------------------------------------------------------------------===// 184 185 /// getBlockInfo - If there is block info for the specified ID, return it, 186 /// otherwise return null. 187 BlockInfo *getBlockInfo(unsigned BlockID) { 188 // Common case, the most recent entry matches BlockID. 189 if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID) 190 return &BlockInfoRecords.back(); 191 192 for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size()); 193 i != e; ++i) 194 if (BlockInfoRecords[i].BlockID == BlockID) 195 return &BlockInfoRecords[i]; 196 return nullptr; 197 } 198 199 void EnterSubblock(unsigned BlockID, unsigned CodeLen) { 200 // Block header: 201 // [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen] 202 EmitCode(bitc::ENTER_SUBBLOCK); 203 EmitVBR(BlockID, bitc::BlockIDWidth); 204 EmitVBR(CodeLen, bitc::CodeLenWidth); 205 FlushToWord(); 206 207 size_t BlockSizeWordIndex = GetWordIndex(); 208 unsigned OldCodeSize = CurCodeSize; 209 210 // Emit a placeholder, which will be replaced when the block is popped. 211 Emit(0, bitc::BlockSizeWidth); 212 213 CurCodeSize = CodeLen; 214 215 // Push the outer block's abbrev set onto the stack, start out with an 216 // empty abbrev set. 217 BlockScope.emplace_back(OldCodeSize, BlockSizeWordIndex); 218 BlockScope.back().PrevAbbrevs.swap(CurAbbrevs); 219 220 // If there is a blockinfo for this BlockID, add all the predefined abbrevs 221 // to the abbrev list. 222 if (BlockInfo *Info = getBlockInfo(BlockID)) { 223 CurAbbrevs.insert(CurAbbrevs.end(), Info->Abbrevs.begin(), 224 Info->Abbrevs.end()); 225 } 226 } 227 228 void ExitBlock() { 229 assert(!BlockScope.empty() && "Block scope imbalance!"); 230 const Block &B = BlockScope.back(); 231 232 // Block tail: 233 // [END_BLOCK, <align4bytes>] 234 EmitCode(bitc::END_BLOCK); 235 FlushToWord(); 236 237 // Compute the size of the block, in words, not counting the size field. 238 size_t SizeInWords = GetWordIndex() - B.StartSizeWord - 1; 239 uint64_t BitNo = uint64_t(B.StartSizeWord) * 32; 240 241 // Update the block size field in the header of this sub-block. 242 BackpatchWord(BitNo, SizeInWords); 243 244 // Restore the inner block's code size and abbrev table. 245 CurCodeSize = B.PrevCodeSize; 246 CurAbbrevs = std::move(B.PrevAbbrevs); 247 BlockScope.pop_back(); 248 } 249 250 //===--------------------------------------------------------------------===// 251 // Record Emission 252 //===--------------------------------------------------------------------===// 253 254 private: 255 /// EmitAbbreviatedLiteral - Emit a literal value according to its abbrev 256 /// record. This is a no-op, since the abbrev specifies the literal to use. 257 template<typename uintty> 258 void EmitAbbreviatedLiteral(const BitCodeAbbrevOp &Op, uintty V) { 259 assert(Op.isLiteral() && "Not a literal"); 260 // If the abbrev specifies the literal value to use, don't emit 261 // anything. 262 assert(V == Op.getLiteralValue() && 263 "Invalid abbrev for record!"); 264 } 265 266 /// EmitAbbreviatedField - Emit a single scalar field value with the specified 267 /// encoding. 268 template<typename uintty> 269 void EmitAbbreviatedField(const BitCodeAbbrevOp &Op, uintty V) { 270 assert(!Op.isLiteral() && "Literals should use EmitAbbreviatedLiteral!"); 271 272 // Encode the value as we are commanded. 273 switch (Op.getEncoding()) { 274 default: llvm_unreachable("Unknown encoding!"); 275 case BitCodeAbbrevOp::Fixed: 276 if (Op.getEncodingData()) 277 Emit((unsigned)V, (unsigned)Op.getEncodingData()); 278 break; 279 case BitCodeAbbrevOp::VBR: 280 if (Op.getEncodingData()) 281 EmitVBR64(V, (unsigned)Op.getEncodingData()); 282 break; 283 case BitCodeAbbrevOp::Char6: 284 Emit(BitCodeAbbrevOp::EncodeChar6((char)V), 6); 285 break; 286 } 287 } 288 289 /// EmitRecordWithAbbrevImpl - This is the core implementation of the record 290 /// emission code. If BlobData is non-null, then it specifies an array of 291 /// data that should be emitted as part of the Blob or Array operand that is 292 /// known to exist at the end of the record. If Code is specified, then 293 /// it is the record code to emit before the Vals, which must not contain 294 /// the code. 295 template <typename uintty> 296 void EmitRecordWithAbbrevImpl(unsigned Abbrev, ArrayRef<uintty> Vals, 297 StringRef Blob, Optional<unsigned> Code) { 298 const char *BlobData = Blob.data(); 299 unsigned BlobLen = (unsigned) Blob.size(); 300 unsigned AbbrevNo = Abbrev-bitc::FIRST_APPLICATION_ABBREV; 301 assert(AbbrevNo < CurAbbrevs.size() && "Invalid abbrev #!"); 302 const BitCodeAbbrev *Abbv = CurAbbrevs[AbbrevNo].get(); 303 304 EmitCode(Abbrev); 305 306 unsigned i = 0, e = static_cast<unsigned>(Abbv->getNumOperandInfos()); 307 if (Code) { 308 assert(e && "Expected non-empty abbreviation"); 309 const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i++); 310 311 if (Op.isLiteral()) 312 EmitAbbreviatedLiteral(Op, Code.getValue()); 313 else { 314 assert(Op.getEncoding() != BitCodeAbbrevOp::Array && 315 Op.getEncoding() != BitCodeAbbrevOp::Blob && 316 "Expected literal or scalar"); 317 EmitAbbreviatedField(Op, Code.getValue()); 318 } 319 } 320 321 unsigned RecordIdx = 0; 322 for (; i != e; ++i) { 323 const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i); 324 if (Op.isLiteral()) { 325 assert(RecordIdx < Vals.size() && "Invalid abbrev/record"); 326 EmitAbbreviatedLiteral(Op, Vals[RecordIdx]); 327 ++RecordIdx; 328 } else if (Op.getEncoding() == BitCodeAbbrevOp::Array) { 329 // Array case. 330 assert(i + 2 == e && "array op not second to last?"); 331 const BitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i); 332 333 // If this record has blob data, emit it, otherwise we must have record 334 // entries to encode this way. 335 if (BlobData) { 336 assert(RecordIdx == Vals.size() && 337 "Blob data and record entries specified for array!"); 338 // Emit a vbr6 to indicate the number of elements present. 339 EmitVBR(static_cast<uint32_t>(BlobLen), 6); 340 341 // Emit each field. 342 for (unsigned i = 0; i != BlobLen; ++i) 343 EmitAbbreviatedField(EltEnc, (unsigned char)BlobData[i]); 344 345 // Know that blob data is consumed for assertion below. 346 BlobData = nullptr; 347 } else { 348 // Emit a vbr6 to indicate the number of elements present. 349 EmitVBR(static_cast<uint32_t>(Vals.size()-RecordIdx), 6); 350 351 // Emit each field. 352 for (unsigned e = Vals.size(); RecordIdx != e; ++RecordIdx) 353 EmitAbbreviatedField(EltEnc, Vals[RecordIdx]); 354 } 355 } else if (Op.getEncoding() == BitCodeAbbrevOp::Blob) { 356 // If this record has blob data, emit it, otherwise we must have record 357 // entries to encode this way. 358 359 if (BlobData) { 360 assert(RecordIdx == Vals.size() && 361 "Blob data and record entries specified for blob operand!"); 362 363 assert(Blob.data() == BlobData && "BlobData got moved"); 364 assert(Blob.size() == BlobLen && "BlobLen got changed"); 365 emitBlob(Blob); 366 BlobData = nullptr; 367 } else { 368 emitBlob(Vals.slice(RecordIdx)); 369 } 370 } else { // Single scalar field. 371 assert(RecordIdx < Vals.size() && "Invalid abbrev/record"); 372 EmitAbbreviatedField(Op, Vals[RecordIdx]); 373 ++RecordIdx; 374 } 375 } 376 assert(RecordIdx == Vals.size() && "Not all record operands emitted!"); 377 assert(BlobData == nullptr && 378 "Blob data specified for record that doesn't use it!"); 379 } 380 381 public: 382 /// Emit a blob, including flushing before and tail-padding. 383 template <class UIntTy> 384 void emitBlob(ArrayRef<UIntTy> Bytes, bool ShouldEmitSize = true) { 385 // Emit a vbr6 to indicate the number of elements present. 386 if (ShouldEmitSize) 387 EmitVBR(static_cast<uint32_t>(Bytes.size()), 6); 388 389 // Flush to a 32-bit alignment boundary. 390 FlushToWord(); 391 392 // Emit literal bytes. 393 for (const auto &B : Bytes) { 394 assert(isUInt<8>(B) && "Value too large to emit as byte"); 395 WriteByte((unsigned char)B); 396 } 397 398 // Align end to 32-bits. 399 while (GetBufferOffset() & 3) 400 WriteByte(0); 401 } 402 void emitBlob(StringRef Bytes, bool ShouldEmitSize = true) { 403 emitBlob(makeArrayRef((const uint8_t *)Bytes.data(), Bytes.size()), 404 ShouldEmitSize); 405 } 406 407 /// EmitRecord - Emit the specified record to the stream, using an abbrev if 408 /// we have one to compress the output. 409 template <typename Container> 410 void EmitRecord(unsigned Code, const Container &Vals, unsigned Abbrev = 0) { 411 if (!Abbrev) { 412 // If we don't have an abbrev to use, emit this in its fully unabbreviated 413 // form. 414 auto Count = static_cast<uint32_t>(makeArrayRef(Vals).size()); 415 EmitCode(bitc::UNABBREV_RECORD); 416 EmitVBR(Code, 6); 417 EmitVBR(Count, 6); 418 for (unsigned i = 0, e = Count; i != e; ++i) 419 EmitVBR64(Vals[i], 6); 420 return; 421 } 422 423 EmitRecordWithAbbrevImpl(Abbrev, makeArrayRef(Vals), StringRef(), Code); 424 } 425 426 /// EmitRecordWithAbbrev - Emit a record with the specified abbreviation. 427 /// Unlike EmitRecord, the code for the record should be included in Vals as 428 /// the first entry. 429 template <typename Container> 430 void EmitRecordWithAbbrev(unsigned Abbrev, const Container &Vals) { 431 EmitRecordWithAbbrevImpl(Abbrev, makeArrayRef(Vals), StringRef(), None); 432 } 433 434 /// EmitRecordWithBlob - Emit the specified record to the stream, using an 435 /// abbrev that includes a blob at the end. The blob data to emit is 436 /// specified by the pointer and length specified at the end. In contrast to 437 /// EmitRecord, this routine expects that the first entry in Vals is the code 438 /// of the record. 439 template <typename Container> 440 void EmitRecordWithBlob(unsigned Abbrev, const Container &Vals, 441 StringRef Blob) { 442 EmitRecordWithAbbrevImpl(Abbrev, makeArrayRef(Vals), Blob, None); 443 } 444 template <typename Container> 445 void EmitRecordWithBlob(unsigned Abbrev, const Container &Vals, 446 const char *BlobData, unsigned BlobLen) { 447 return EmitRecordWithAbbrevImpl(Abbrev, makeArrayRef(Vals), 448 StringRef(BlobData, BlobLen), None); 449 } 450 451 /// EmitRecordWithArray - Just like EmitRecordWithBlob, works with records 452 /// that end with an array. 453 template <typename Container> 454 void EmitRecordWithArray(unsigned Abbrev, const Container &Vals, 455 StringRef Array) { 456 EmitRecordWithAbbrevImpl(Abbrev, makeArrayRef(Vals), Array, None); 457 } 458 template <typename Container> 459 void EmitRecordWithArray(unsigned Abbrev, const Container &Vals, 460 const char *ArrayData, unsigned ArrayLen) { 461 return EmitRecordWithAbbrevImpl(Abbrev, makeArrayRef(Vals), 462 StringRef(ArrayData, ArrayLen), None); 463 } 464 465 //===--------------------------------------------------------------------===// 466 // Abbrev Emission 467 //===--------------------------------------------------------------------===// 468 469 private: 470 // Emit the abbreviation as a DEFINE_ABBREV record. 471 void EncodeAbbrev(const BitCodeAbbrev &Abbv) { 472 EmitCode(bitc::DEFINE_ABBREV); 473 EmitVBR(Abbv.getNumOperandInfos(), 5); 474 for (unsigned i = 0, e = static_cast<unsigned>(Abbv.getNumOperandInfos()); 475 i != e; ++i) { 476 const BitCodeAbbrevOp &Op = Abbv.getOperandInfo(i); 477 Emit(Op.isLiteral(), 1); 478 if (Op.isLiteral()) { 479 EmitVBR64(Op.getLiteralValue(), 8); 480 } else { 481 Emit(Op.getEncoding(), 3); 482 if (Op.hasEncodingData()) 483 EmitVBR64(Op.getEncodingData(), 5); 484 } 485 } 486 } 487 public: 488 489 /// Emits the abbreviation \p Abbv to the stream. 490 unsigned EmitAbbrev(std::shared_ptr<BitCodeAbbrev> Abbv) { 491 EncodeAbbrev(*Abbv); 492 CurAbbrevs.push_back(std::move(Abbv)); 493 return static_cast<unsigned>(CurAbbrevs.size())-1 + 494 bitc::FIRST_APPLICATION_ABBREV; 495 } 496 497 //===--------------------------------------------------------------------===// 498 // BlockInfo Block Emission 499 //===--------------------------------------------------------------------===// 500 501 /// EnterBlockInfoBlock - Start emitting the BLOCKINFO_BLOCK. 502 void EnterBlockInfoBlock() { 503 EnterSubblock(bitc::BLOCKINFO_BLOCK_ID, 2); 504 BlockInfoCurBID = ~0U; 505 BlockInfoRecords.clear(); 506 } 507 private: 508 /// SwitchToBlockID - If we aren't already talking about the specified block 509 /// ID, emit a BLOCKINFO_CODE_SETBID record. 510 void SwitchToBlockID(unsigned BlockID) { 511 if (BlockInfoCurBID == BlockID) return; 512 SmallVector<unsigned, 2> V; 513 V.push_back(BlockID); 514 EmitRecord(bitc::BLOCKINFO_CODE_SETBID, V); 515 BlockInfoCurBID = BlockID; 516 } 517 518 BlockInfo &getOrCreateBlockInfo(unsigned BlockID) { 519 if (BlockInfo *BI = getBlockInfo(BlockID)) 520 return *BI; 521 522 // Otherwise, add a new record. 523 BlockInfoRecords.emplace_back(); 524 BlockInfoRecords.back().BlockID = BlockID; 525 return BlockInfoRecords.back(); 526 } 527 528 public: 529 530 /// EmitBlockInfoAbbrev - Emit a DEFINE_ABBREV record for the specified 531 /// BlockID. 532 unsigned EmitBlockInfoAbbrev(unsigned BlockID, std::shared_ptr<BitCodeAbbrev> Abbv) { 533 SwitchToBlockID(BlockID); 534 EncodeAbbrev(*Abbv); 535 536 // Add the abbrev to the specified block record. 537 BlockInfo &Info = getOrCreateBlockInfo(BlockID); 538 Info.Abbrevs.push_back(std::move(Abbv)); 539 540 return Info.Abbrevs.size()-1+bitc::FIRST_APPLICATION_ABBREV; 541 } 542 }; 543 544 545 } // End llvm namespace 546 547 #endif 548