src/llvm/include/llvm/Bitcode/BitstreamReader.h

   1 //===- BitstreamReader.h - Low-level bitstream reader interface -*- 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 header defines the BitstreamReader class.  This class can be used to
  11 // read an arbitrary bitstream, regardless of its contents.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #ifndef LLVM_BITCODE_BITSTREAMREADER_H
  16 #define LLVM_BITCODE_BITSTREAMREADER_H
  17
  18 #include "llvm/Bitcode/BitCodes.h"
  19 #include "llvm/Support/Endian.h"
  20 #include "llvm/Support/StreamingMemoryObject.h"
  21 #include <climits>
  22 #include <string>
  23 #include <vector>
  24
  25 namespace llvm {
  26
  27 class Deserializer;
  28
  29 /// This class is used to read from an LLVM bitcode stream, maintaining
  30 /// information that is global to decoding the entire file. While a file is
  31 /// being read, multiple cursors can be independently advanced or skipped around
  32 /// within the file.  These are represented by the BitstreamCursor class.
  33 class BitstreamReader {
  34 public:
  35   /// This contains information emitted to BLOCKINFO_BLOCK blocks. These
  36   /// describe abbreviations that all blocks of the specified ID inherit.
  37   struct BlockInfo {
  38     unsigned BlockID;
  39     std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> Abbrevs;
  40     std::string Name;
  41
  42     std::vector<std::pair<unsigned, std::string> > RecordNames;
  43   };
  44 private:
  45   std::unique_ptr<MemoryObject> BitcodeBytes;
  46
  47   std::vector<BlockInfo> BlockInfoRecords;
  48
  49   /// This is set to true if we don't care about the block/record name
  50   /// information in the BlockInfo block. Only llvm-bcanalyzer uses this.
  51   bool IgnoreBlockInfoNames;
  52
  53   BitstreamReader(const BitstreamReader&) LLVM_DELETED_FUNCTION;
  54   void operator=(const BitstreamReader&) LLVM_DELETED_FUNCTION;
  55 public:
  56   BitstreamReader() : IgnoreBlockInfoNames(true) {
  57   }
  58
  59   BitstreamReader(const unsigned char *Start, const unsigned char *End)
  60       : IgnoreBlockInfoNames(true) {
  61     init(Start, End);
  62   }
  63
  64   BitstreamReader(std::unique_ptr<MemoryObject> BitcodeBytes)
  65       : BitcodeBytes(std::move(BitcodeBytes)), IgnoreBlockInfoNames(true) {}
  66
  67   BitstreamReader(BitstreamReader &&Other) {
  68     *this = std::move(Other);
  69   }
  70
  71   BitstreamReader &operator=(BitstreamReader &&Other) {
  72     BitcodeBytes = std::move(Other.BitcodeBytes);
  73     // Explicitly swap block info, so that nothing gets destroyed twice.
  74     std::swap(BlockInfoRecords, Other.BlockInfoRecords);
  75     IgnoreBlockInfoNames = Other.IgnoreBlockInfoNames;
  76     return *this;
  77   }
  78
  79   void init(const unsigned char *Start, const unsigned char *End) {
  80     assert(((End-Start) & 3) == 0 &&"Bitcode stream not a multiple of 4 bytes");
  81     BitcodeBytes.reset(getNonStreamedMemoryObject(Start, End));
  82   }
  83
  84   MemoryObject &getBitcodeBytes() { return *BitcodeBytes; }
  85
  86   /// This is called by clients that want block/record name information.
  87   void CollectBlockInfoNames() { IgnoreBlockInfoNames = false; }
  88   bool isIgnoringBlockInfoNames() { return IgnoreBlockInfoNames; }
  89
  90   //===--------------------------------------------------------------------===//
  91   // Block Manipulation
  92   //===--------------------------------------------------------------------===//
  93
  94   /// Return true if we've already read and processed the block info block for
  95   /// this Bitstream. We only process it for the first cursor that walks over
  96   /// it.
  97   bool hasBlockInfoRecords() const { return !BlockInfoRecords.empty(); }
  98
  99   /// If there is block info for the specified ID, return it, otherwise return
 100   /// null.
 101   const BlockInfo *getBlockInfo(unsigned BlockID) const {
 102     // Common case, the most recent entry matches BlockID.
 103     if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
 104       return &BlockInfoRecords.back();
 105
 106     for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size());
 107          i != e; ++i)
 108       if (BlockInfoRecords[i].BlockID == BlockID)
 109         return &BlockInfoRecords[i];
 110     return nullptr;
 111   }
 112
 113   BlockInfo &getOrCreateBlockInfo(unsigned BlockID) {
 114     if (const BlockInfo *BI = getBlockInfo(BlockID))
 115       return *const_cast<BlockInfo*>(BI);
 116
 117     // Otherwise, add a new record.
 118     BlockInfoRecords.push_back(BlockInfo());
 119     BlockInfoRecords.back().BlockID = BlockID;
 120     return BlockInfoRecords.back();
 121   }
 122
 123   /// Takes block info from the other bitstream reader.
 124   ///
 125   /// This is a "take" operation because BlockInfo records are non-trivial, and
 126   /// indeed rather expensive.
 127   void takeBlockInfo(BitstreamReader &&Other) {
 128     assert(!hasBlockInfoRecords());
 129     BlockInfoRecords = std::move(Other.BlockInfoRecords);
 130   }
 131 };
 132
 133 /// When advancing through a bitstream cursor, each advance can discover a few
 134 /// different kinds of entries:
 135 struct BitstreamEntry {
 136   enum {
 137     Error,    // Malformed bitcode was found.
 138     EndBlock, // We've reached the end of the current block, (or the end of the
 139               // file, which is treated like a series of EndBlock records.
 140     SubBlock, // This is the start of a new subblock of a specific ID.
 141     Record    // This is a record with a specific AbbrevID.
 142   } Kind;
 143
 144   unsigned ID;
 145
 146   static BitstreamEntry getError() {
 147     BitstreamEntry E; E.Kind = Error; return E;
 148   }
 149   static BitstreamEntry getEndBlock() {
 150     BitstreamEntry E; E.Kind = EndBlock; return E;
 151   }
 152   static BitstreamEntry getSubBlock(unsigned ID) {
 153     BitstreamEntry E; E.Kind = SubBlock; E.ID = ID; return E;
 154   }
 155   static BitstreamEntry getRecord(unsigned AbbrevID) {
 156     BitstreamEntry E; E.Kind = Record; E.ID = AbbrevID; return E;
 157   }
 158 };
 159
 160 /// This represents a position within a bitcode file. There may be multiple
 161 /// independent cursors reading within one bitstream, each maintaining their own
 162 /// local state.
 163 ///
 164 /// Unlike iterators, BitstreamCursors are heavy-weight objects that should not
 165 /// be passed by value.
 166 class BitstreamCursor {
 167   friend class Deserializer;
 168   BitstreamReader *BitStream;
 169   size_t NextChar;
 170
 171   // The size of the bicode. 0 if we don't know it yet.
 172   size_t Size;
 173
 174   /// This is the current data we have pulled from the stream but have not
 175   /// returned to the client. This is specifically and intentionally defined to
 176   /// follow the word size of the host machine for efficiency. We use word_t in
 177   /// places that are aware of this to make it perfectly explicit what is going
 178   /// on.
 179   typedef size_t word_t;
 180   word_t CurWord;
 181
 182   /// This is the number of bits in CurWord that are valid. This is always from
 183   /// [0...bits_of(size_t)-1] inclusive.
 184   unsigned BitsInCurWord;
 185
 186   // This is the declared size of code values used for the current block, in
 187   // bits.
 188   unsigned CurCodeSize;
 189
 190   /// Abbrevs installed at in this block.
 191   std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> CurAbbrevs;
 192
 193   struct Block {
 194     unsigned PrevCodeSize;
 195     std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> PrevAbbrevs;
 196     explicit Block(unsigned PCS) : PrevCodeSize(PCS) {}
 197   };
 198
 199   /// This tracks the codesize of parent blocks.
 200   SmallVector<Block, 8> BlockScope;
 201
 202
 203 public:
 204   BitstreamCursor() { init(nullptr); }
 205
 206   explicit BitstreamCursor(BitstreamReader &R) { init(&R); }
 207
 208   void init(BitstreamReader *R) {
 209     freeState();
 210
 211     BitStream = R;
 212     NextChar = 0;
 213     Size = 0;
 214     BitsInCurWord = 0;
 215     CurCodeSize = 2;
 216   }
 217
 218   void freeState();
 219
 220   bool canSkipToPos(size_t pos) const {
 221     // pos can be skipped to if it is a valid address or one byte past the end.
 222     return pos == 0 || BitStream->getBitcodeBytes().isValidAddress(
 223         static_cast<uint64_t>(pos - 1));
 224   }
 225
 226   bool AtEndOfStream() {
 227     if (BitsInCurWord != 0)
 228       return false;
 229     if (Size != 0)
 230       return Size == NextChar;
 231     fillCurWord();
 232     return BitsInCurWord == 0;
 233   }
 234
 235   /// Return the number of bits used to encode an abbrev #.
 236   unsigned getAbbrevIDWidth() const { return CurCodeSize; }
 237
 238   /// Return the bit # of the bit we are reading.
 239   uint64_t GetCurrentBitNo() const {
 240     return NextChar*CHAR_BIT - BitsInCurWord;
 241   }
 242
 243   BitstreamReader *getBitStreamReader() {
 244     return BitStream;
 245   }
 246   const BitstreamReader *getBitStreamReader() const {
 247     return BitStream;
 248   }
 249
 250   /// Flags that modify the behavior of advance().
 251   enum {
 252     /// If this flag is used, the advance() method does not automatically pop
 253     /// the block scope when the end of a block is reached.
 254     AF_DontPopBlockAtEnd = 1,
 255
 256     /// If this flag is used, abbrev entries are returned just like normal
 257     /// records.
 258     AF_DontAutoprocessAbbrevs = 2
 259   };
 260
 261       /// Advance the current bitstream, returning the next entry in the stream.
 262       BitstreamEntry advance(unsigned Flags = 0) {
 263     while (1) {
 264       unsigned Code = ReadCode();
 265       if (Code == bitc::END_BLOCK) {
 266         // Pop the end of the block unless Flags tells us not to.
 267         if (!(Flags & AF_DontPopBlockAtEnd) && ReadBlockEnd())
 268           return BitstreamEntry::getError();
 269         return BitstreamEntry::getEndBlock();
 270       }
 271
 272       if (Code == bitc::ENTER_SUBBLOCK)
 273         return BitstreamEntry::getSubBlock(ReadSubBlockID());
 274
 275       if (Code == bitc::DEFINE_ABBREV &&
 276           !(Flags & AF_DontAutoprocessAbbrevs)) {
 277         // We read and accumulate abbrev's, the client can't do anything with
 278         // them anyway.
 279         ReadAbbrevRecord();
 280         continue;
 281       }
 282
 283       return BitstreamEntry::getRecord(Code);
 284     }
 285   }
 286
 287   /// This is a convenience function for clients that don't expect any
 288   /// subblocks. This just skips over them automatically.
 289   BitstreamEntry advanceSkippingSubblocks(unsigned Flags = 0) {
 290     while (1) {
 291       // If we found a normal entry, return it.
 292       BitstreamEntry Entry = advance(Flags);
 293       if (Entry.Kind != BitstreamEntry::SubBlock)
 294         return Entry;
 295
 296       // If we found a sub-block, just skip over it and check the next entry.
 297       if (SkipBlock())
 298         return BitstreamEntry::getError();
 299     }
 300   }
 301
 302   /// Reset the stream to the specified bit number.
 303   void JumpToBit(uint64_t BitNo) {
 304     uintptr_t ByteNo = uintptr_t(BitNo/8) & ~(sizeof(word_t)-1);
 305     unsigned WordBitNo = unsigned(BitNo & (sizeof(word_t)*8-1));
 306     assert(canSkipToPos(ByteNo) && "Invalid location");
 307
 308     // Move the cursor to the right word.
 309     NextChar = ByteNo;
 310     BitsInCurWord = 0;
 311
 312     // Skip over any bits that are already consumed.
 313     if (WordBitNo)
 314       Read(WordBitNo);
 315   }
 316
 317   void fillCurWord() {
 318     assert(Size == 0 || NextChar < (unsigned)Size);
 319
 320     // Read the next word from the stream.
 321     uint8_t Array[sizeof(word_t)] = {0};
 322
 323     uint64_t BytesRead =
 324         BitStream->getBitcodeBytes().readBytes(Array, sizeof(Array), NextChar);
 325
 326     // If we run out of data, stop at the end of the stream.
 327     if (BytesRead == 0) {
 328       Size = NextChar;
 329       return;
 330     }
 331
 332     CurWord =
 333         support::endian::read<word_t, support::little, support::unaligned>(
 334             Array);
 335     NextChar += BytesRead;
 336     BitsInCurWord = BytesRead * 8;
 337   }
 338
 339   word_t Read(unsigned NumBits) {
 340     static const unsigned BitsInWord = sizeof(word_t) * 8;
 341
 342     assert(NumBits && NumBits <= BitsInWord &&
 343            "Cannot return zero or more than BitsInWord bits!");
 344
 345     static const unsigned Mask = sizeof(word_t) > 4 ? 0x3f : 0x1f;
 346
 347     // If the field is fully contained by CurWord, return it quickly.
 348     if (BitsInCurWord >= NumBits) {
 349       word_t R = CurWord & (~word_t(0) >> (BitsInWord - NumBits));
 350
 351       // Use a mask to avoid undefined behavior.
 352       CurWord >>= (NumBits & Mask);
 353
 354       BitsInCurWord -= NumBits;
 355       return R;
 356     }
 357
 358     word_t R = BitsInCurWord ? CurWord : 0;
 359     unsigned BitsLeft = NumBits - BitsInCurWord;
 360
 361     fillCurWord();
 362
 363     // If we run out of data, stop at the end of the stream.
 364     if (BitsLeft > BitsInCurWord)
 365       return 0;
 366
 367     word_t R2 = CurWord & (~word_t(0) >> (BitsInWord - BitsLeft));
 368
 369     // Use a mask to avoid undefined behavior.
 370     CurWord >>= (BitsLeft & Mask);
 371
 372     BitsInCurWord -= BitsLeft;
 373
 374     R |= R2 << (NumBits - BitsLeft);
 375
 376     return R;
 377   }
 378
 379   uint32_t ReadVBR(unsigned NumBits) {
 380     uint32_t Piece = Read(NumBits);
 381     if ((Piece & (1U << (NumBits-1))) == 0)
 382       return Piece;
 383
 384     uint32_t Result = 0;
 385     unsigned NextBit = 0;
 386     while (1) {
 387       Result |= (Piece & ((1U << (NumBits-1))-1)) << NextBit;
 388
 389       if ((Piece & (1U << (NumBits-1))) == 0)
 390         return Result;
 391
 392       NextBit += NumBits-1;
 393       Piece = Read(NumBits);
 394     }
 395   }
 396
 397   // Read a VBR that may have a value up to 64-bits in size. The chunk size of
 398   // the VBR must still be <= 32 bits though.
 399   uint64_t ReadVBR64(unsigned NumBits) {
 400     uint32_t Piece = Read(NumBits);
 401     if ((Piece & (1U << (NumBits-1))) == 0)
 402       return uint64_t(Piece);
 403
 404     uint64_t Result = 0;
 405     unsigned NextBit = 0;
 406     while (1) {
 407       Result |= uint64_t(Piece & ((1U << (NumBits-1))-1)) << NextBit;
 408
 409       if ((Piece & (1U << (NumBits-1))) == 0)
 410         return Result;
 411
 412       NextBit += NumBits-1;
 413       Piece = Read(NumBits);
 414     }
 415   }
 416
 417 private:
 418   void SkipToFourByteBoundary() {
 419     // If word_t is 64-bits and if we've read less than 32 bits, just dump
 420     // the bits we have up to the next 32-bit boundary.
 421     if (sizeof(word_t) > 4 &&
 422         BitsInCurWord >= 32) {
 423       CurWord >>= BitsInCurWord-32;
 424       BitsInCurWord = 32;
 425       return;
 426     }
 427
 428     BitsInCurWord = 0;
 429   }
 430 public:
 431
 432   unsigned ReadCode() {
 433     return Read(CurCodeSize);
 434   }
 435
 436
 437   // Block header:
 438   //    [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
 439
 440   /// Having read the ENTER_SUBBLOCK code, read the BlockID for the block.
 441   unsigned ReadSubBlockID() {
 442     return ReadVBR(bitc::BlockIDWidth);
 443   }
 444
 445   /// Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip over the body
 446   /// of this block. If the block record is malformed, return true.
 447   bool SkipBlock() {
 448     // Read and ignore the codelen value.  Since we are skipping this block, we
 449     // don't care what code widths are used inside of it.
 450     ReadVBR(bitc::CodeLenWidth);
 451     SkipToFourByteBoundary();
 452     unsigned NumFourBytes = Read(bitc::BlockSizeWidth);
 453
 454     // Check that the block wasn't partially defined, and that the offset isn't
 455     // bogus.
 456     size_t SkipTo = GetCurrentBitNo() + NumFourBytes*4*8;
 457     if (AtEndOfStream() || !canSkipToPos(SkipTo/8))
 458       return true;
 459
 460     JumpToBit(SkipTo);
 461     return false;
 462   }
 463
 464   /// Having read the ENTER_SUBBLOCK abbrevid, enter the block, and return true
 465   /// if the block has an error.
 466   bool EnterSubBlock(unsigned BlockID, unsigned *NumWordsP = nullptr);
 467
 468   bool ReadBlockEnd() {
 469     if (BlockScope.empty()) return true;
 470
 471     // Block tail:
 472     //    [END_BLOCK, <align4bytes>]
 473     SkipToFourByteBoundary();
 474
 475     popBlockScope();
 476     return false;
 477   }
 478
 479 private:
 480
 481   void popBlockScope() {
 482     CurCodeSize = BlockScope.back().PrevCodeSize;
 483
 484     CurAbbrevs = std::move(BlockScope.back().PrevAbbrevs);
 485     BlockScope.pop_back();
 486   }
 487
 488   //===--------------------------------------------------------------------===//
 489   // Record Processing
 490   //===--------------------------------------------------------------------===//
 491
 492 public:
 493
 494   /// Return the abbreviation for the specified AbbrevId.
 495   const BitCodeAbbrev *getAbbrev(unsigned AbbrevID) {
 496     unsigned AbbrevNo = AbbrevID-bitc::FIRST_APPLICATION_ABBREV;
 497     assert(AbbrevNo < CurAbbrevs.size() && "Invalid abbrev #!");
 498     return CurAbbrevs[AbbrevNo].get();
 499   }
 500
 501   /// Read the current record and discard it.
 502   void skipRecord(unsigned AbbrevID);
 503
 504   unsigned readRecord(unsigned AbbrevID, SmallVectorImpl<uint64_t> &Vals,
 505                       StringRef *Blob = nullptr);
 506
 507   //===--------------------------------------------------------------------===//
 508   // Abbrev Processing
 509   //===--------------------------------------------------------------------===//
 510   void ReadAbbrevRecord();
 511
 512   bool ReadBlockInfoBlock();
 513 };
 514
 515 } // End llvm namespace
 516
 517 #endif