include/llvm/Bitstream/BitstreamWriter.h

   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