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BitstreamReader.h
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1 //===- BitstreamReader.h - Low-level bitstream reader 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 BitstreamReader class. This class can be used to
10 // read an arbitrary bitstream, regardless of its contents.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_BITSTREAM_BITSTREAMREADER_H
15 #define LLVM_BITSTREAM_BITSTREAMREADER_H
16 
17 #include "llvm/ADT/ArrayRef.h"
18 #include "llvm/ADT/SmallVector.h"
20 #include "llvm/Support/Endian.h"
24 #include <algorithm>
25 #include <cassert>
26 #include <climits>
27 #include <cstddef>
28 #include <cstdint>
29 #include <memory>
30 #include <string>
31 #include <utility>
32 #include <vector>
33 
34 namespace llvm {
35 
36 /// This class maintains the abbreviations read from a block info block.
38 public:
39  /// This contains information emitted to BLOCKINFO_BLOCK blocks. These
40  /// describe abbreviations that all blocks of the specified ID inherit.
41  struct BlockInfo {
42  unsigned BlockID;
43  std::vector<std::shared_ptr<BitCodeAbbrev>> Abbrevs;
44  std::string Name;
45  std::vector<std::pair<unsigned, std::string>> RecordNames;
46  };
47 
48 private:
49  std::vector<BlockInfo> BlockInfoRecords;
50 
51 public:
52  /// If there is block info for the specified ID, return it, otherwise return
53  /// null.
54  const BlockInfo *getBlockInfo(unsigned BlockID) const {
55  // Common case, the most recent entry matches BlockID.
56  if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
57  return &BlockInfoRecords.back();
58 
59  for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size());
60  i != e; ++i)
61  if (BlockInfoRecords[i].BlockID == BlockID)
62  return &BlockInfoRecords[i];
63  return nullptr;
64  }
65 
67  if (const BlockInfo *BI = getBlockInfo(BlockID))
68  return *const_cast<BlockInfo*>(BI);
69 
70  // Otherwise, add a new record.
71  BlockInfoRecords.emplace_back();
72  BlockInfoRecords.back().BlockID = BlockID;
73  return BlockInfoRecords.back();
74  }
75 };
76 
77 /// This represents a position within a bitstream. There may be multiple
78 /// independent cursors reading within one bitstream, each maintaining their
79 /// own local state.
81  ArrayRef<uint8_t> BitcodeBytes;
82  size_t NextChar = 0;
83 
84 public:
85  /// This is the current data we have pulled from the stream but have not
86  /// returned to the client. This is specifically and intentionally defined to
87  /// follow the word size of the host machine for efficiency. We use word_t in
88  /// places that are aware of this to make it perfectly explicit what is going
89  /// on.
90  using word_t = size_t;
91 
92 private:
93  word_t CurWord = 0;
94 
95  /// This is the number of bits in CurWord that are valid. This is always from
96  /// [0...bits_of(size_t)-1] inclusive.
97  unsigned BitsInCurWord = 0;
98 
99 public:
100  static const constexpr size_t MaxChunkSize = sizeof(word_t) * 8;
101 
102  SimpleBitstreamCursor() = default;
104  : BitcodeBytes(BitcodeBytes) {}
105  explicit SimpleBitstreamCursor(StringRef BitcodeBytes)
106  : BitcodeBytes(arrayRefFromStringRef(BitcodeBytes)) {}
107  explicit SimpleBitstreamCursor(MemoryBufferRef BitcodeBytes)
108  : SimpleBitstreamCursor(BitcodeBytes.getBuffer()) {}
109 
110  bool canSkipToPos(size_t pos) const {
111  // pos can be skipped to if it is a valid address or one byte past the end.
112  return pos <= BitcodeBytes.size();
113  }
114 
115  bool AtEndOfStream() {
116  return BitsInCurWord == 0 && BitcodeBytes.size() <= NextChar;
117  }
118 
119  /// Return the bit # of the bit we are reading.
120  uint64_t GetCurrentBitNo() const {
121  return NextChar*CHAR_BIT - BitsInCurWord;
122  }
123 
124  // Return the byte # of the current bit.
125  uint64_t getCurrentByteNo() const { return GetCurrentBitNo() / 8; }
126 
127  ArrayRef<uint8_t> getBitcodeBytes() const { return BitcodeBytes; }
128 
129  /// Reset the stream to the specified bit number.
130  Error JumpToBit(uint64_t BitNo) {
131  size_t ByteNo = size_t(BitNo/8) & ~(sizeof(word_t)-1);
132  unsigned WordBitNo = unsigned(BitNo & (sizeof(word_t)*8-1));
133  assert(canSkipToPos(ByteNo) && "Invalid location");
134 
135  // Move the cursor to the right word.
136  NextChar = ByteNo;
137  BitsInCurWord = 0;
138 
139  // Skip over any bits that are already consumed.
140  if (WordBitNo) {
141  if (Expected<word_t> Res = Read(WordBitNo))
142  return Error::success();
143  else
144  return Res.takeError();
145  }
146 
147  return Error::success();
148  }
149 
150  /// Get a pointer into the bitstream at the specified byte offset.
151  const uint8_t *getPointerToByte(uint64_t ByteNo, uint64_t NumBytes) {
152  return BitcodeBytes.data() + ByteNo;
153  }
154 
155  /// Get a pointer into the bitstream at the specified bit offset.
156  ///
157  /// The bit offset must be on a byte boundary.
158  const uint8_t *getPointerToBit(uint64_t BitNo, uint64_t NumBytes) {
159  assert(!(BitNo % 8) && "Expected bit on byte boundary");
160  return getPointerToByte(BitNo / 8, NumBytes);
161  }
162 
164  if (NextChar >= BitcodeBytes.size())
165  return createStringError(std::errc::io_error,
166  "Unexpected end of file reading %u of %u bytes",
167  NextChar, BitcodeBytes.size());
168 
169  // Read the next word from the stream.
170  const uint8_t *NextCharPtr = BitcodeBytes.data() + NextChar;
171  unsigned BytesRead;
172  if (BitcodeBytes.size() >= NextChar + sizeof(word_t)) {
173  BytesRead = sizeof(word_t);
174  CurWord =
175  support::endian::read<word_t, support::little, support::unaligned>(
176  NextCharPtr);
177  } else {
178  // Short read.
179  BytesRead = BitcodeBytes.size() - NextChar;
180  CurWord = 0;
181  for (unsigned B = 0; B != BytesRead; ++B)
182  CurWord |= uint64_t(NextCharPtr[B]) << (B * 8);
183  }
184  NextChar += BytesRead;
185  BitsInCurWord = BytesRead * 8;
186  return Error::success();
187  }
188 
189  Expected<word_t> Read(unsigned NumBits) {
190  static const unsigned BitsInWord = MaxChunkSize;
191 
192  assert(NumBits && NumBits <= BitsInWord &&
193  "Cannot return zero or more than BitsInWord bits!");
194 
195  static const unsigned Mask = sizeof(word_t) > 4 ? 0x3f : 0x1f;
196 
197  // If the field is fully contained by CurWord, return it quickly.
198  if (BitsInCurWord >= NumBits) {
199  word_t R = CurWord & (~word_t(0) >> (BitsInWord - NumBits));
200 
201  // Use a mask to avoid undefined behavior.
202  CurWord >>= (NumBits & Mask);
203 
204  BitsInCurWord -= NumBits;
205  return R;
206  }
207 
208  word_t R = BitsInCurWord ? CurWord : 0;
209  unsigned BitsLeft = NumBits - BitsInCurWord;
210 
211  if (Error fillResult = fillCurWord())
212  return std::move(fillResult);
213 
214  // If we run out of data, abort.
215  if (BitsLeft > BitsInCurWord)
216  return createStringError(std::errc::io_error,
217  "Unexpected end of file reading %u of %u bits",
218  BitsInCurWord, BitsLeft);
219 
220  word_t R2 = CurWord & (~word_t(0) >> (BitsInWord - BitsLeft));
221 
222  // Use a mask to avoid undefined behavior.
223  CurWord >>= (BitsLeft & Mask);
224 
225  BitsInCurWord -= BitsLeft;
226 
227  R |= R2 << (NumBits - BitsLeft);
228 
229  return R;
230  }
231 
232  Expected<uint32_t> ReadVBR(unsigned NumBits) {
233  Expected<unsigned> MaybeRead = Read(NumBits);
234  if (!MaybeRead)
235  return MaybeRead;
236  uint32_t Piece = MaybeRead.get();
237 
238  if ((Piece & (1U << (NumBits-1))) == 0)
239  return Piece;
240 
241  uint32_t Result = 0;
242  unsigned NextBit = 0;
243  while (true) {
244  Result |= (Piece & ((1U << (NumBits-1))-1)) << NextBit;
245 
246  if ((Piece & (1U << (NumBits-1))) == 0)
247  return Result;
248 
249  NextBit += NumBits-1;
250  MaybeRead = Read(NumBits);
251  if (!MaybeRead)
252  return MaybeRead;
253  Piece = MaybeRead.get();
254  }
255  }
256 
257  // Read a VBR that may have a value up to 64-bits in size. The chunk size of
258  // the VBR must still be <= 32 bits though.
259  Expected<uint64_t> ReadVBR64(unsigned NumBits) {
260  Expected<uint64_t> MaybeRead = Read(NumBits);
261  if (!MaybeRead)
262  return MaybeRead;
263  uint32_t Piece = MaybeRead.get();
264 
265  if ((Piece & (1U << (NumBits-1))) == 0)
266  return uint64_t(Piece);
267 
268  uint64_t Result = 0;
269  unsigned NextBit = 0;
270  while (true) {
271  Result |= uint64_t(Piece & ((1U << (NumBits-1))-1)) << NextBit;
272 
273  if ((Piece & (1U << (NumBits-1))) == 0)
274  return Result;
275 
276  NextBit += NumBits-1;
277  MaybeRead = Read(NumBits);
278  if (!MaybeRead)
279  return MaybeRead;
280  Piece = MaybeRead.get();
281  }
282  }
283 
285  // If word_t is 64-bits and if we've read less than 32 bits, just dump
286  // the bits we have up to the next 32-bit boundary.
287  if (sizeof(word_t) > 4 &&
288  BitsInCurWord >= 32) {
289  CurWord >>= BitsInCurWord-32;
290  BitsInCurWord = 32;
291  return;
292  }
293 
294  BitsInCurWord = 0;
295  }
296 
297  /// Return the size of the stream in bytes.
298  size_t SizeInBytes() const { return BitcodeBytes.size(); }
299 
300  /// Skip to the end of the file.
301  void skipToEnd() { NextChar = BitcodeBytes.size(); }
302 };
303 
304 /// When advancing through a bitstream cursor, each advance can discover a few
305 /// different kinds of entries:
307  enum {
308  Error, // Malformed bitcode was found.
309  EndBlock, // We've reached the end of the current block, (or the end of the
310  // file, which is treated like a series of EndBlock records.
311  SubBlock, // This is the start of a new subblock of a specific ID.
312  Record // This is a record with a specific AbbrevID.
313  } Kind;
314 
315  unsigned ID;
316 
318  BitstreamEntry E; E.Kind = Error; return E;
319  }
320 
322  BitstreamEntry E; E.Kind = EndBlock; return E;
323  }
324 
325  static BitstreamEntry getSubBlock(unsigned ID) {
326  BitstreamEntry E; E.Kind = SubBlock; E.ID = ID; return E;
327  }
328 
329  static BitstreamEntry getRecord(unsigned AbbrevID) {
330  BitstreamEntry E; E.Kind = Record; E.ID = AbbrevID; return E;
331  }
332 };
333 
334 /// This represents a position within a bitcode file, implemented on top of a
335 /// SimpleBitstreamCursor.
336 ///
337 /// Unlike iterators, BitstreamCursors are heavy-weight objects that should not
338 /// be passed by value.
340  // This is the declared size of code values used for the current block, in
341  // bits.
342  unsigned CurCodeSize = 2;
343 
344  /// Abbrevs installed at in this block.
345  std::vector<std::shared_ptr<BitCodeAbbrev>> CurAbbrevs;
346 
347  struct Block {
348  unsigned PrevCodeSize;
349  std::vector<std::shared_ptr<BitCodeAbbrev>> PrevAbbrevs;
350 
351  explicit Block(unsigned PCS) : PrevCodeSize(PCS) {}
352  };
353 
354  /// This tracks the codesize of parent blocks.
355  SmallVector<Block, 8> BlockScope;
356 
357  BitstreamBlockInfo *BlockInfo = nullptr;
358 
359 public:
360  static const size_t MaxChunkSize = sizeof(word_t) * 8;
361 
362  BitstreamCursor() = default;
363  explicit BitstreamCursor(ArrayRef<uint8_t> BitcodeBytes)
364  : SimpleBitstreamCursor(BitcodeBytes) {}
365  explicit BitstreamCursor(StringRef BitcodeBytes)
366  : SimpleBitstreamCursor(BitcodeBytes) {}
367  explicit BitstreamCursor(MemoryBufferRef BitcodeBytes)
368  : SimpleBitstreamCursor(BitcodeBytes) {}
369 
383 
384  /// Return the number of bits used to encode an abbrev #.
385  unsigned getAbbrevIDWidth() const { return CurCodeSize; }
386 
387  /// Flags that modify the behavior of advance().
388  enum {
389  /// If this flag is used, the advance() method does not automatically pop
390  /// the block scope when the end of a block is reached.
391  AF_DontPopBlockAtEnd = 1,
392 
393  /// If this flag is used, abbrev entries are returned just like normal
394  /// records.
395  AF_DontAutoprocessAbbrevs = 2
396  };
397 
398  /// Advance the current bitstream, returning the next entry in the stream.
399  Expected<BitstreamEntry> advance(unsigned Flags = 0) {
400  while (true) {
401  if (AtEndOfStream())
402  return BitstreamEntry::getError();
403 
404  Expected<unsigned> MaybeCode = ReadCode();
405  if (!MaybeCode)
406  return MaybeCode.takeError();
407  unsigned Code = MaybeCode.get();
408 
409  if (Code == bitc::END_BLOCK) {
410  // Pop the end of the block unless Flags tells us not to.
411  if (!(Flags & AF_DontPopBlockAtEnd) && ReadBlockEnd())
412  return BitstreamEntry::getError();
414  }
415 
416  if (Code == bitc::ENTER_SUBBLOCK) {
417  if (Expected<unsigned> MaybeSubBlock = ReadSubBlockID())
418  return BitstreamEntry::getSubBlock(MaybeSubBlock.get());
419  else
420  return MaybeSubBlock.takeError();
421  }
422 
423  if (Code == bitc::DEFINE_ABBREV &&
424  !(Flags & AF_DontAutoprocessAbbrevs)) {
425  // We read and accumulate abbrev's, the client can't do anything with
426  // them anyway.
427  if (Error Err = ReadAbbrevRecord())
428  return std::move(Err);
429  continue;
430  }
431 
432  return BitstreamEntry::getRecord(Code);
433  }
434  }
435 
436  /// This is a convenience function for clients that don't expect any
437  /// subblocks. This just skips over them automatically.
439  while (true) {
440  // If we found a normal entry, return it.
441  Expected<BitstreamEntry> MaybeEntry = advance(Flags);
442  if (!MaybeEntry)
443  return MaybeEntry;
444  BitstreamEntry Entry = MaybeEntry.get();
445 
446  if (Entry.Kind != BitstreamEntry::SubBlock)
447  return Entry;
448 
449  // If we found a sub-block, just skip over it and check the next entry.
450  if (Error Err = SkipBlock())
451  return std::move(Err);
452  }
453  }
454 
455  Expected<unsigned> ReadCode() { return Read(CurCodeSize); }
456 
457  // Block header:
458  // [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
459 
460  /// Having read the ENTER_SUBBLOCK code, read the BlockID for the block.
462 
463  /// Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip over the body
464  /// of this block.
466  // Read and ignore the codelen value.
467  if (Expected<uint32_t> Res = ReadVBR(bitc::CodeLenWidth))
468  ; // Since we are skipping this block, we don't care what code widths are
469  // used inside of it.
470  else
471  return Res.takeError();
472 
473  SkipToFourByteBoundary();
474  Expected<unsigned> MaybeNum = Read(bitc::BlockSizeWidth);
475  if (!MaybeNum)
476  return MaybeNum.takeError();
477  size_t NumFourBytes = MaybeNum.get();
478 
479  // Check that the block wasn't partially defined, and that the offset isn't
480  // bogus.
481  size_t SkipTo = GetCurrentBitNo() + NumFourBytes * 4 * 8;
482  if (AtEndOfStream())
483  return createStringError(std::errc::illegal_byte_sequence,
484  "can't skip block: already at end of stream");
485  if (!canSkipToPos(SkipTo / 8))
486  return createStringError(std::errc::illegal_byte_sequence,
487  "can't skip to bit %zu from %" PRIu64, SkipTo,
488  GetCurrentBitNo());
489 
490  if (Error Res = JumpToBit(SkipTo))
491  return Res;
492 
493  return Error::success();
494  }
495 
496  /// Having read the ENTER_SUBBLOCK abbrevid, and enter the block.
497  Error EnterSubBlock(unsigned BlockID, unsigned *NumWordsP = nullptr);
498 
499  bool ReadBlockEnd() {
500  if (BlockScope.empty()) return true;
501 
502  // Block tail:
503  // [END_BLOCK, <align4bytes>]
504  SkipToFourByteBoundary();
505 
506  popBlockScope();
507  return false;
508  }
509 
510 private:
511  void popBlockScope() {
512  CurCodeSize = BlockScope.back().PrevCodeSize;
513 
514  CurAbbrevs = std::move(BlockScope.back().PrevAbbrevs);
515  BlockScope.pop_back();
516  }
517 
518  //===--------------------------------------------------------------------===//
519  // Record Processing
520  //===--------------------------------------------------------------------===//
521 
522 public:
523  /// Return the abbreviation for the specified AbbrevId.
524  const BitCodeAbbrev *getAbbrev(unsigned AbbrevID) {
525  unsigned AbbrevNo = AbbrevID - bitc::FIRST_APPLICATION_ABBREV;
526  if (AbbrevNo >= CurAbbrevs.size())
527  report_fatal_error("Invalid abbrev number");
528  return CurAbbrevs[AbbrevNo].get();
529  }
530 
531  /// Read the current record and discard it, returning the code for the record.
532  Expected<unsigned> skipRecord(unsigned AbbrevID);
533 
534  Expected<unsigned> readRecord(unsigned AbbrevID,
536  StringRef *Blob = nullptr);
537 
538  //===--------------------------------------------------------------------===//
539  // Abbrev Processing
540  //===--------------------------------------------------------------------===//
541  Error ReadAbbrevRecord();
542 
543  /// Read and return a block info block from the bitstream. If an error was
544  /// encountered, return None.
545  ///
546  /// \param ReadBlockInfoNames Whether to read block/record name information in
547  /// the BlockInfo block. Only llvm-bcanalyzer uses this.
549  ReadBlockInfoBlock(bool ReadBlockInfoNames = false);
550 
551  /// Set the block info to be used by this BitstreamCursor to interpret
552  /// abbreviated records.
553  void setBlockInfo(BitstreamBlockInfo *BI) { BlockInfo = BI; }
554 };
555 
556 } // end llvm namespace
557 
558 #endif // LLVM_BITSTREAM_BITSTREAMREADER_H
This contains information emitted to BLOCKINFO_BLOCK blocks.
const BitCodeAbbrev * getAbbrev(unsigned AbbrevID)
Return the abbreviation for the specified AbbrevId.
BlockInfo & getOrCreateBlockInfo(unsigned BlockID)
LLVM_ATTRIBUTE_NORETURN void report_fatal_error(Error Err, bool gen_crash_diag=true)
Report a serious error, calling any installed error handler.
Definition: Error.cpp:139
This class represents lattice values for constants.
Definition: AllocatorList.h:23
uint64_t GetCurrentBitNo() const
Return the bit # of the bit we are reading.
const uint8_t * getPointerToByte(uint64_t ByteNo, uint64_t NumBytes)
Get a pointer into the bitstream at the specified byte offset.
BitCodeAbbrev - This class represents an abbreviation record.
Definition: BitCodes.h:167
const uint8_t * getPointerToBit(uint64_t BitNo, uint64_t NumBytes)
Get a pointer into the bitstream at the specified bit offset.
Expected< uint32_t > ReadVBR(unsigned NumBits)
ArrayRef< uint8_t > arrayRefFromStringRef(StringRef Input)
Construct a string ref from an array ref of unsigned chars.
Definition: StringExtras.h:60
BitstreamCursor(MemoryBufferRef BitcodeBytes)
#define R2(n)
Error takeError()
Take ownership of the stored error.
Definition: Error.h:552
SimpleBitstreamCursor(ArrayRef< uint8_t > BitcodeBytes)
std::vector< std::pair< unsigned, std::string > > RecordNames
void setBlockInfo(BitstreamBlockInfo *BI)
Set the block info to be used by this BitstreamCursor to interpret abbreviated records.
bool canSkipToPos(size_t pos) const
Expected< BitstreamEntry > advance(unsigned Flags=0)
Advance the current bitstream, returning the next entry in the stream.
Error SkipBlock()
Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip over the body of this block...
Tagged union holding either a T or a Error.
Definition: yaml2obj.h:21
void skipToEnd()
Skip to the end of the file.
Expected< unsigned > ReadCode()
static BitstreamEntry getSubBlock(unsigned ID)
ArrayRef< uint8_t > getBitcodeBytes() const
size_t SizeInBytes() const
Return the size of the stream in bytes.
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
uint64_t getCurrentByteNo() const
size_t size() const
size - Get the array size.
Definition: ArrayRef.h:148
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This represents a position within a bitcode file, implemented on top of a SimpleBitstreamCursor.
Expected< uint64_t > ReadVBR64(unsigned NumBits)
constexpr double e
Definition: MathExtras.h:57
const BlockInfo * getBlockInfo(unsigned BlockID) const
If there is block info for the specified ID, return it, otherwise return null.
unsigned getAbbrevIDWidth() const
Return the number of bits used to encode an abbrev #.
Expected< unsigned > ReadSubBlockID()
Having read the ENTER_SUBBLOCK code, read the BlockID for the block.
const T * data() const
Definition: ArrayRef.h:145
std::vector< std::shared_ptr< BitCodeAbbrev > > Abbrevs
Error JumpToBit(uint64_t BitNo)
Reset the stream to the specified bit number.
SimpleBitstreamCursor(MemoryBufferRef BitcodeBytes)
static ErrorSuccess success()
Create a success value.
Definition: Error.h:326
When advancing through a bitstream cursor, each advance can discover a few different kinds of entries...
BitstreamCursor(ArrayRef< uint8_t > BitcodeBytes)
This class maintains the abbreviations read from a block info block.
reference get()
Returns a reference to the stored T value.
Definition: Error.h:532
DEFINE_ABBREV - Defines an abbrev for the current block.
Definition: BitCodes.h:54
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:55
static BitstreamEntry getEndBlock()
static BitstreamEntry getRecord(unsigned AbbrevID)
Expected< BitstreamEntry > advanceSkippingSubblocks(unsigned Flags=0)
This is a convenience function for clients that don&#39;t expect any subblocks.
SimpleBitstreamCursor(StringRef BitcodeBytes)
static BitstreamEntry getError()
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
Lightweight error class with error context and mandatory checking.
Definition: Error.h:157
std::underlying_type< E >::type Mask()
Get a bitmask with 1s in all places up to the high-order bit of E&#39;s largest value.
Definition: BitmaskEnum.h:80
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48
enum llvm::BitstreamEntry::@159 Kind
This represents a position within a bitstream.
Expected< word_t > Read(unsigned NumBits)
Error createStringError(std::error_code EC, char const *Fmt, const Ts &... Vals)
Create formatted StringError object.
Definition: Error.h:1197
BitstreamCursor(StringRef BitcodeBytes)