1 //===- BitstreamReader.h - Low-level bitstream reader interface -*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This header defines the BitstreamReader class. This class can be used to
11 // read an arbitrary bitstream, regardless of its contents.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_BITCODE_BITSTREAMREADER_H
16 #define LLVM_BITCODE_BITSTREAMREADER_H
18 #include "llvm/Bitcode/BitCodes.h"
19 #include "llvm/Support/Endian.h"
20 #include "llvm/Support/StreamingMemoryObject.h"
27 /// This class is used to read from an LLVM bitcode stream, maintaining
28 /// information that is global to decoding the entire file. While a file is
29 /// being read, multiple cursors can be independently advanced or skipped around
30 /// within the file. These are represented by the BitstreamCursor class.
31 class BitstreamReader {
33 /// This contains information emitted to BLOCKINFO_BLOCK blocks. These
34 /// describe abbreviations that all blocks of the specified ID inherit.
37 std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> Abbrevs;
40 std::vector<std::pair<unsigned, std::string> > RecordNames;
43 std::unique_ptr<MemoryObject> BitcodeBytes;
45 std::vector<BlockInfo> BlockInfoRecords;
47 /// This is set to true if we don't care about the block/record name
48 /// information in the BlockInfo block. Only llvm-bcanalyzer uses this.
49 bool IgnoreBlockInfoNames;
51 BitstreamReader(const BitstreamReader&) = delete;
52 void operator=(const BitstreamReader&) = delete;
54 BitstreamReader() : IgnoreBlockInfoNames(true) {
57 BitstreamReader(const unsigned char *Start, const unsigned char *End)
58 : IgnoreBlockInfoNames(true) {
62 BitstreamReader(std::unique_ptr<MemoryObject> BitcodeBytes)
63 : BitcodeBytes(std::move(BitcodeBytes)), IgnoreBlockInfoNames(true) {}
65 BitstreamReader(BitstreamReader &&Other) {
66 *this = std::move(Other);
69 BitstreamReader &operator=(BitstreamReader &&Other) {
70 BitcodeBytes = std::move(Other.BitcodeBytes);
71 // Explicitly swap block info, so that nothing gets destroyed twice.
72 std::swap(BlockInfoRecords, Other.BlockInfoRecords);
73 IgnoreBlockInfoNames = Other.IgnoreBlockInfoNames;
77 void init(const unsigned char *Start, const unsigned char *End) {
78 assert(((End-Start) & 3) == 0 &&"Bitcode stream not a multiple of 4 bytes");
79 BitcodeBytes.reset(getNonStreamedMemoryObject(Start, End));
82 MemoryObject &getBitcodeBytes() { return *BitcodeBytes; }
84 /// This is called by clients that want block/record name information.
85 void CollectBlockInfoNames() { IgnoreBlockInfoNames = false; }
86 bool isIgnoringBlockInfoNames() { return IgnoreBlockInfoNames; }
88 //===--------------------------------------------------------------------===//
90 //===--------------------------------------------------------------------===//
92 /// Return true if we've already read and processed the block info block for
93 /// this Bitstream. We only process it for the first cursor that walks over
95 bool hasBlockInfoRecords() const { return !BlockInfoRecords.empty(); }
97 /// If there is block info for the specified ID, return it, otherwise return
99 const BlockInfo *getBlockInfo(unsigned BlockID) const {
100 // Common case, the most recent entry matches BlockID.
101 if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
102 return &BlockInfoRecords.back();
104 for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size());
106 if (BlockInfoRecords[i].BlockID == BlockID)
107 return &BlockInfoRecords[i];
111 BlockInfo &getOrCreateBlockInfo(unsigned BlockID) {
112 if (const BlockInfo *BI = getBlockInfo(BlockID))
113 return *const_cast<BlockInfo*>(BI);
115 // Otherwise, add a new record.
116 BlockInfoRecords.push_back(BlockInfo());
117 BlockInfoRecords.back().BlockID = BlockID;
118 return BlockInfoRecords.back();
121 /// Takes block info from the other bitstream reader.
123 /// This is a "take" operation because BlockInfo records are non-trivial, and
124 /// indeed rather expensive.
125 void takeBlockInfo(BitstreamReader &&Other) {
126 assert(!hasBlockInfoRecords());
127 BlockInfoRecords = std::move(Other.BlockInfoRecords);
131 /// When advancing through a bitstream cursor, each advance can discover a few
132 /// different kinds of entries:
133 struct BitstreamEntry {
135 Error, // Malformed bitcode was found.
136 EndBlock, // We've reached the end of the current block, (or the end of the
137 // file, which is treated like a series of EndBlock records.
138 SubBlock, // This is the start of a new subblock of a specific ID.
139 Record // This is a record with a specific AbbrevID.
144 static BitstreamEntry getError() {
145 BitstreamEntry E; E.Kind = Error; return E;
147 static BitstreamEntry getEndBlock() {
148 BitstreamEntry E; E.Kind = EndBlock; return E;
150 static BitstreamEntry getSubBlock(unsigned ID) {
151 BitstreamEntry E; E.Kind = SubBlock; E.ID = ID; return E;
153 static BitstreamEntry getRecord(unsigned AbbrevID) {
154 BitstreamEntry E; E.Kind = Record; E.ID = AbbrevID; return E;
158 /// This represents a position within a bitcode file. There may be multiple
159 /// independent cursors reading within one bitstream, each maintaining their own
162 /// Unlike iterators, BitstreamCursors are heavy-weight objects that should not
163 /// be passed by value.
164 class BitstreamCursor {
165 BitstreamReader *BitStream;
168 // The size of the bicode. 0 if we don't know it yet.
171 /// This is the current data we have pulled from the stream but have not
172 /// returned to the client. This is specifically and intentionally defined to
173 /// follow the word size of the host machine for efficiency. We use word_t in
174 /// places that are aware of this to make it perfectly explicit what is going
176 typedef size_t word_t;
179 /// This is the number of bits in CurWord that are valid. This is always from
180 /// [0...bits_of(size_t)-1] inclusive.
181 unsigned BitsInCurWord;
183 // This is the declared size of code values used for the current block, in
185 unsigned CurCodeSize;
187 /// Abbrevs installed at in this block.
188 std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> CurAbbrevs;
191 unsigned PrevCodeSize;
192 std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> PrevAbbrevs;
193 explicit Block(unsigned PCS) : PrevCodeSize(PCS) {}
196 /// This tracks the codesize of parent blocks.
197 SmallVector<Block, 8> BlockScope;
201 BitstreamCursor() { init(nullptr); }
203 explicit BitstreamCursor(BitstreamReader &R) { init(&R); }
205 void init(BitstreamReader *R) {
217 bool canSkipToPos(size_t pos) const {
218 // pos can be skipped to if it is a valid address or one byte past the end.
219 return pos == 0 || BitStream->getBitcodeBytes().isValidAddress(
220 static_cast<uint64_t>(pos - 1));
223 bool AtEndOfStream() {
224 if (BitsInCurWord != 0)
227 return Size == NextChar;
229 return BitsInCurWord == 0;
232 /// Return the number of bits used to encode an abbrev #.
233 unsigned getAbbrevIDWidth() const { return CurCodeSize; }
235 /// Return the bit # of the bit we are reading.
236 uint64_t GetCurrentBitNo() const {
237 return NextChar*CHAR_BIT - BitsInCurWord;
240 BitstreamReader *getBitStreamReader() {
243 const BitstreamReader *getBitStreamReader() const {
247 /// Flags that modify the behavior of advance().
249 /// If this flag is used, the advance() method does not automatically pop
250 /// the block scope when the end of a block is reached.
251 AF_DontPopBlockAtEnd = 1,
253 /// If this flag is used, abbrev entries are returned just like normal
255 AF_DontAutoprocessAbbrevs = 2
258 /// Advance the current bitstream, returning the next entry in the stream.
259 BitstreamEntry advance(unsigned Flags = 0) {
261 unsigned Code = ReadCode();
262 if (Code == bitc::END_BLOCK) {
263 // Pop the end of the block unless Flags tells us not to.
264 if (!(Flags & AF_DontPopBlockAtEnd) && ReadBlockEnd())
265 return BitstreamEntry::getError();
266 return BitstreamEntry::getEndBlock();
269 if (Code == bitc::ENTER_SUBBLOCK)
270 return BitstreamEntry::getSubBlock(ReadSubBlockID());
272 if (Code == bitc::DEFINE_ABBREV &&
273 !(Flags & AF_DontAutoprocessAbbrevs)) {
274 // We read and accumulate abbrev's, the client can't do anything with
280 return BitstreamEntry::getRecord(Code);
284 /// This is a convenience function for clients that don't expect any
285 /// subblocks. This just skips over them automatically.
286 BitstreamEntry advanceSkippingSubblocks(unsigned Flags = 0) {
288 // If we found a normal entry, return it.
289 BitstreamEntry Entry = advance(Flags);
290 if (Entry.Kind != BitstreamEntry::SubBlock)
293 // If we found a sub-block, just skip over it and check the next entry.
295 return BitstreamEntry::getError();
299 /// Reset the stream to the specified bit number.
300 void JumpToBit(uint64_t BitNo) {
301 size_t ByteNo = size_t(BitNo/8) & ~(sizeof(word_t)-1);
302 unsigned WordBitNo = unsigned(BitNo & (sizeof(word_t)*8-1));
303 assert(canSkipToPos(ByteNo) && "Invalid location");
305 // Move the cursor to the right word.
309 // Skip over any bits that are already consumed.
315 if (Size != 0 && NextChar >= Size)
316 report_fatal_error("Unexpected end of file");
318 // Read the next word from the stream.
319 uint8_t Array[sizeof(word_t)] = {0};
322 BitStream->getBitcodeBytes().readBytes(Array, sizeof(Array), NextChar);
324 // If we run out of data, stop at the end of the stream.
325 if (BytesRead == 0) {
331 support::endian::read<word_t, support::little, support::unaligned>(
333 NextChar += BytesRead;
334 BitsInCurWord = BytesRead * 8;
337 word_t Read(unsigned NumBits) {
338 static const unsigned BitsInWord = sizeof(word_t) * 8;
340 assert(NumBits && NumBits <= BitsInWord &&
341 "Cannot return zero or more than BitsInWord bits!");
343 static const unsigned Mask = sizeof(word_t) > 4 ? 0x3f : 0x1f;
345 // If the field is fully contained by CurWord, return it quickly.
346 if (BitsInCurWord >= NumBits) {
347 word_t R = CurWord & (~word_t(0) >> (BitsInWord - NumBits));
349 // Use a mask to avoid undefined behavior.
350 CurWord >>= (NumBits & Mask);
352 BitsInCurWord -= NumBits;
356 word_t R = BitsInCurWord ? CurWord : 0;
357 unsigned BitsLeft = NumBits - BitsInCurWord;
361 // If we run out of data, stop at the end of the stream.
362 if (BitsLeft > BitsInCurWord)
365 word_t R2 = CurWord & (~word_t(0) >> (BitsInWord - BitsLeft));
367 // Use a mask to avoid undefined behavior.
368 CurWord >>= (BitsLeft & Mask);
370 BitsInCurWord -= BitsLeft;
372 R |= R2 << (NumBits - BitsLeft);
377 uint32_t ReadVBR(unsigned NumBits) {
378 uint32_t Piece = Read(NumBits);
379 if ((Piece & (1U << (NumBits-1))) == 0)
383 unsigned NextBit = 0;
385 Result |= (Piece & ((1U << (NumBits-1))-1)) << NextBit;
387 if ((Piece & (1U << (NumBits-1))) == 0)
390 NextBit += NumBits-1;
391 Piece = Read(NumBits);
395 // Read a VBR that may have a value up to 64-bits in size. The chunk size of
396 // the VBR must still be <= 32 bits though.
397 uint64_t ReadVBR64(unsigned NumBits) {
398 uint32_t Piece = Read(NumBits);
399 if ((Piece & (1U << (NumBits-1))) == 0)
400 return uint64_t(Piece);
403 unsigned NextBit = 0;
405 Result |= uint64_t(Piece & ((1U << (NumBits-1))-1)) << NextBit;
407 if ((Piece & (1U << (NumBits-1))) == 0)
410 NextBit += NumBits-1;
411 Piece = Read(NumBits);
416 void SkipToFourByteBoundary() {
417 // If word_t is 64-bits and if we've read less than 32 bits, just dump
418 // the bits we have up to the next 32-bit boundary.
419 if (sizeof(word_t) > 4 &&
420 BitsInCurWord >= 32) {
421 CurWord >>= BitsInCurWord-32;
430 unsigned ReadCode() {
431 return Read(CurCodeSize);
436 // [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
438 /// Having read the ENTER_SUBBLOCK code, read the BlockID for the block.
439 unsigned ReadSubBlockID() {
440 return ReadVBR(bitc::BlockIDWidth);
443 /// Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip over the body
444 /// of this block. If the block record is malformed, return true.
446 // Read and ignore the codelen value. Since we are skipping this block, we
447 // don't care what code widths are used inside of it.
448 ReadVBR(bitc::CodeLenWidth);
449 SkipToFourByteBoundary();
450 unsigned NumFourBytes = Read(bitc::BlockSizeWidth);
452 // Check that the block wasn't partially defined, and that the offset isn't
454 size_t SkipTo = GetCurrentBitNo() + NumFourBytes*4*8;
455 if (AtEndOfStream() || !canSkipToPos(SkipTo/8))
462 /// Having read the ENTER_SUBBLOCK abbrevid, enter the block, and return true
463 /// if the block has an error.
464 bool EnterSubBlock(unsigned BlockID, unsigned *NumWordsP = nullptr);
466 bool ReadBlockEnd() {
467 if (BlockScope.empty()) return true;
470 // [END_BLOCK, <align4bytes>]
471 SkipToFourByteBoundary();
479 void popBlockScope() {
480 CurCodeSize = BlockScope.back().PrevCodeSize;
482 CurAbbrevs = std::move(BlockScope.back().PrevAbbrevs);
483 BlockScope.pop_back();
486 //===--------------------------------------------------------------------===//
488 //===--------------------------------------------------------------------===//
491 /// Return the abbreviation for the specified AbbrevId.
492 const BitCodeAbbrev *getAbbrev(unsigned AbbrevID) {
493 unsigned AbbrevNo = AbbrevID - bitc::FIRST_APPLICATION_ABBREV;
494 if (AbbrevNo >= CurAbbrevs.size())
495 report_fatal_error("Invalid abbrev number");
496 return CurAbbrevs[AbbrevNo].get();
499 /// Read the current record and discard it.
500 void skipRecord(unsigned AbbrevID);
502 unsigned readRecord(unsigned AbbrevID, SmallVectorImpl<uint64_t> &Vals,
503 StringRef *Blob = nullptr);
505 //===--------------------------------------------------------------------===//
507 //===--------------------------------------------------------------------===//
508 void ReadAbbrevRecord();
510 bool ReadBlockInfoBlock();
513 } // End llvm namespace