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BitstreamReader.h
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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/ADT/ArrayRef.h"
19 #include "llvm/ADT/SmallVector.h"
20 #include "llvm/Bitcode/BitCodes.h"
21 #include "llvm/Support/Endian.h"
25 #include <algorithm>
26 #include <cassert>
27 #include <climits>
28 #include <cstddef>
29 #include <cstdint>
30 #include <memory>
31 #include <string>
32 #include <utility>
33 #include <vector>
34 
35 namespace llvm {
36 
37 /// This class maintains the abbreviations read from a block info block.
39 public:
40  /// This contains information emitted to BLOCKINFO_BLOCK blocks. These
41  /// describe abbreviations that all blocks of the specified ID inherit.
42  struct BlockInfo {
43  unsigned BlockID;
44  std::vector<std::shared_ptr<BitCodeAbbrev>> Abbrevs;
45  std::string Name;
46  std::vector<std::pair<unsigned, std::string>> RecordNames;
47  };
48 
49 private:
50  std::vector<BlockInfo> BlockInfoRecords;
51 
52 public:
53  /// If there is block info for the specified ID, return it, otherwise return
54  /// null.
55  const BlockInfo *getBlockInfo(unsigned BlockID) const {
56  // Common case, the most recent entry matches BlockID.
57  if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
58  return &BlockInfoRecords.back();
59 
60  for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size());
61  i != e; ++i)
62  if (BlockInfoRecords[i].BlockID == BlockID)
63  return &BlockInfoRecords[i];
64  return nullptr;
65  }
66 
68  if (const BlockInfo *BI = getBlockInfo(BlockID))
69  return *const_cast<BlockInfo*>(BI);
70 
71  // Otherwise, add a new record.
72  BlockInfoRecords.emplace_back();
73  BlockInfoRecords.back().BlockID = BlockID;
74  return BlockInfoRecords.back();
75  }
76 };
77 
78 /// This represents a position within a bitstream. There may be multiple
79 /// independent cursors reading within one bitstream, each maintaining their
80 /// own local state.
82  ArrayRef<uint8_t> BitcodeBytes;
83  size_t NextChar = 0;
84 
85 public:
86  /// This is the current data we have pulled from the stream but have not
87  /// returned to the client. This is specifically and intentionally defined to
88  /// follow the word size of the host machine for efficiency. We use word_t in
89  /// places that are aware of this to make it perfectly explicit what is going
90  /// on.
91  using word_t = size_t;
92 
93 private:
94  word_t CurWord = 0;
95 
96  /// This is the number of bits in CurWord that are valid. This is always from
97  /// [0...bits_of(size_t)-1] inclusive.
98  unsigned BitsInCurWord = 0;
99 
100 public:
101  static const size_t MaxChunkSize = sizeof(word_t) * 8;
102 
103  SimpleBitstreamCursor() = default;
105  : BitcodeBytes(BitcodeBytes) {}
106  explicit SimpleBitstreamCursor(StringRef BitcodeBytes)
107  : BitcodeBytes(reinterpret_cast<const uint8_t *>(BitcodeBytes.data()),
108  BitcodeBytes.size()) {}
109  explicit SimpleBitstreamCursor(MemoryBufferRef BitcodeBytes)
110  : SimpleBitstreamCursor(BitcodeBytes.getBuffer()) {}
111 
112  bool canSkipToPos(size_t pos) const {
113  // pos can be skipped to if it is a valid address or one byte past the end.
114  return pos <= BitcodeBytes.size();
115  }
116 
117  bool AtEndOfStream() {
118  return BitsInCurWord == 0 && BitcodeBytes.size() <= NextChar;
119  }
120 
121  /// Return the bit # of the bit we are reading.
122  uint64_t GetCurrentBitNo() const {
123  return NextChar*CHAR_BIT - BitsInCurWord;
124  }
125 
126  // Return the byte # of the current bit.
127  uint64_t getCurrentByteNo() const { return GetCurrentBitNo() / 8; }
128 
129  ArrayRef<uint8_t> getBitcodeBytes() const { return BitcodeBytes; }
130 
131  /// Reset the stream to the specified bit number.
132  void JumpToBit(uint64_t BitNo) {
133  size_t ByteNo = size_t(BitNo/8) & ~(sizeof(word_t)-1);
134  unsigned WordBitNo = unsigned(BitNo & (sizeof(word_t)*8-1));
135  assert(canSkipToPos(ByteNo) && "Invalid location");
136 
137  // Move the cursor to the right word.
138  NextChar = ByteNo;
139  BitsInCurWord = 0;
140 
141  // Skip over any bits that are already consumed.
142  if (WordBitNo)
143  Read(WordBitNo);
144  }
145 
146  /// Get a pointer into the bitstream at the specified byte offset.
147  const uint8_t *getPointerToByte(uint64_t ByteNo, uint64_t NumBytes) {
148  return BitcodeBytes.data() + ByteNo;
149  }
150 
151  /// Get a pointer into the bitstream at the specified bit offset.
152  ///
153  /// The bit offset must be on a byte boundary.
154  const uint8_t *getPointerToBit(uint64_t BitNo, uint64_t NumBytes) {
155  assert(!(BitNo % 8) && "Expected bit on byte boundary");
156  return getPointerToByte(BitNo / 8, NumBytes);
157  }
158 
159  void fillCurWord() {
160  if (NextChar >= BitcodeBytes.size())
161  report_fatal_error("Unexpected end of file");
162 
163  // Read the next word from the stream.
164  const uint8_t *NextCharPtr = BitcodeBytes.data() + NextChar;
165  unsigned BytesRead;
166  if (BitcodeBytes.size() >= NextChar + sizeof(word_t)) {
167  BytesRead = sizeof(word_t);
168  CurWord =
169  support::endian::read<word_t, support::little, support::unaligned>(
170  NextCharPtr);
171  } else {
172  // Short read.
173  BytesRead = BitcodeBytes.size() - NextChar;
174  CurWord = 0;
175  for (unsigned B = 0; B != BytesRead; ++B)
176  CurWord |= uint64_t(NextCharPtr[B]) << (B * 8);
177  }
178  NextChar += BytesRead;
179  BitsInCurWord = BytesRead * 8;
180  }
181 
182  word_t Read(unsigned NumBits) {
183  static const unsigned BitsInWord = MaxChunkSize;
184 
185  assert(NumBits && NumBits <= BitsInWord &&
186  "Cannot return zero or more than BitsInWord bits!");
187 
188  static const unsigned Mask = sizeof(word_t) > 4 ? 0x3f : 0x1f;
189 
190  // If the field is fully contained by CurWord, return it quickly.
191  if (BitsInCurWord >= NumBits) {
192  word_t R = CurWord & (~word_t(0) >> (BitsInWord - NumBits));
193 
194  // Use a mask to avoid undefined behavior.
195  CurWord >>= (NumBits & Mask);
196 
197  BitsInCurWord -= NumBits;
198  return R;
199  }
200 
201  word_t R = BitsInCurWord ? CurWord : 0;
202  unsigned BitsLeft = NumBits - BitsInCurWord;
203 
204  fillCurWord();
205 
206  // If we run out of data, abort.
207  if (BitsLeft > BitsInCurWord)
208  report_fatal_error("Unexpected end of file");
209 
210  word_t R2 = CurWord & (~word_t(0) >> (BitsInWord - BitsLeft));
211 
212  // Use a mask to avoid undefined behavior.
213  CurWord >>= (BitsLeft & Mask);
214 
215  BitsInCurWord -= BitsLeft;
216 
217  R |= R2 << (NumBits - BitsLeft);
218 
219  return R;
220  }
221 
222  uint32_t ReadVBR(unsigned NumBits) {
223  uint32_t Piece = Read(NumBits);
224  if ((Piece & (1U << (NumBits-1))) == 0)
225  return Piece;
226 
227  uint32_t Result = 0;
228  unsigned NextBit = 0;
229  while (true) {
230  Result |= (Piece & ((1U << (NumBits-1))-1)) << NextBit;
231 
232  if ((Piece & (1U << (NumBits-1))) == 0)
233  return Result;
234 
235  NextBit += NumBits-1;
236  Piece = Read(NumBits);
237  }
238  }
239 
240  // Read a VBR that may have a value up to 64-bits in size. The chunk size of
241  // the VBR must still be <= 32 bits though.
242  uint64_t ReadVBR64(unsigned NumBits) {
243  uint32_t Piece = Read(NumBits);
244  if ((Piece & (1U << (NumBits-1))) == 0)
245  return uint64_t(Piece);
246 
247  uint64_t Result = 0;
248  unsigned NextBit = 0;
249  while (true) {
250  Result |= uint64_t(Piece & ((1U << (NumBits-1))-1)) << NextBit;
251 
252  if ((Piece & (1U << (NumBits-1))) == 0)
253  return Result;
254 
255  NextBit += NumBits-1;
256  Piece = Read(NumBits);
257  }
258  }
259 
261  // If word_t is 64-bits and if we've read less than 32 bits, just dump
262  // the bits we have up to the next 32-bit boundary.
263  if (sizeof(word_t) > 4 &&
264  BitsInCurWord >= 32) {
265  CurWord >>= BitsInCurWord-32;
266  BitsInCurWord = 32;
267  return;
268  }
269 
270  BitsInCurWord = 0;
271  }
272 
273  /// Skip to the end of the file.
274  void skipToEnd() { NextChar = BitcodeBytes.size(); }
275 };
276 
277 /// When advancing through a bitstream cursor, each advance can discover a few
278 /// different kinds of entries:
280  enum {
281  Error, // Malformed bitcode was found.
282  EndBlock, // We've reached the end of the current block, (or the end of the
283  // file, which is treated like a series of EndBlock records.
284  SubBlock, // This is the start of a new subblock of a specific ID.
285  Record // This is a record with a specific AbbrevID.
286  } Kind;
287 
288  unsigned ID;
289 
291  BitstreamEntry E; E.Kind = Error; return E;
292  }
293 
295  BitstreamEntry E; E.Kind = EndBlock; return E;
296  }
297 
298  static BitstreamEntry getSubBlock(unsigned ID) {
299  BitstreamEntry E; E.Kind = SubBlock; E.ID = ID; return E;
300  }
301 
302  static BitstreamEntry getRecord(unsigned AbbrevID) {
303  BitstreamEntry E; E.Kind = Record; E.ID = AbbrevID; return E;
304  }
305 };
306 
307 /// This represents a position within a bitcode file, implemented on top of a
308 /// SimpleBitstreamCursor.
309 ///
310 /// Unlike iterators, BitstreamCursors are heavy-weight objects that should not
311 /// be passed by value.
313  // This is the declared size of code values used for the current block, in
314  // bits.
315  unsigned CurCodeSize = 2;
316 
317  /// Abbrevs installed at in this block.
318  std::vector<std::shared_ptr<BitCodeAbbrev>> CurAbbrevs;
319 
320  struct Block {
321  unsigned PrevCodeSize;
322  std::vector<std::shared_ptr<BitCodeAbbrev>> PrevAbbrevs;
323 
324  explicit Block(unsigned PCS) : PrevCodeSize(PCS) {}
325  };
326 
327  /// This tracks the codesize of parent blocks.
328  SmallVector<Block, 8> BlockScope;
329 
330  BitstreamBlockInfo *BlockInfo = nullptr;
331 
332 public:
333  static const size_t MaxChunkSize = sizeof(word_t) * 8;
334 
335  BitstreamCursor() = default;
336  explicit BitstreamCursor(ArrayRef<uint8_t> BitcodeBytes)
337  : SimpleBitstreamCursor(BitcodeBytes) {}
338  explicit BitstreamCursor(StringRef BitcodeBytes)
339  : SimpleBitstreamCursor(BitcodeBytes) {}
340  explicit BitstreamCursor(MemoryBufferRef BitcodeBytes)
341  : SimpleBitstreamCursor(BitcodeBytes) {}
342 
354 
355  /// Return the number of bits used to encode an abbrev #.
356  unsigned getAbbrevIDWidth() const { return CurCodeSize; }
357 
358  /// Flags that modify the behavior of advance().
359  enum {
360  /// If this flag is used, the advance() method does not automatically pop
361  /// the block scope when the end of a block is reached.
362  AF_DontPopBlockAtEnd = 1,
363 
364  /// If this flag is used, abbrev entries are returned just like normal
365  /// records.
366  AF_DontAutoprocessAbbrevs = 2
367  };
368 
369  /// Advance the current bitstream, returning the next entry in the stream.
370  BitstreamEntry advance(unsigned Flags = 0) {
371  while (true) {
372  if (AtEndOfStream())
373  return BitstreamEntry::getError();
374 
375  unsigned Code = ReadCode();
376  if (Code == bitc::END_BLOCK) {
377  // Pop the end of the block unless Flags tells us not to.
378  if (!(Flags & AF_DontPopBlockAtEnd) && ReadBlockEnd())
379  return BitstreamEntry::getError();
381  }
382 
383  if (Code == bitc::ENTER_SUBBLOCK)
384  return BitstreamEntry::getSubBlock(ReadSubBlockID());
385 
386  if (Code == bitc::DEFINE_ABBREV &&
387  !(Flags & AF_DontAutoprocessAbbrevs)) {
388  // We read and accumulate abbrev's, the client can't do anything with
389  // them anyway.
390  ReadAbbrevRecord();
391  continue;
392  }
393 
394  return BitstreamEntry::getRecord(Code);
395  }
396  }
397 
398  /// This is a convenience function for clients that don't expect any
399  /// subblocks. This just skips over them automatically.
401  while (true) {
402  // If we found a normal entry, return it.
403  BitstreamEntry Entry = advance(Flags);
404  if (Entry.Kind != BitstreamEntry::SubBlock)
405  return Entry;
406 
407  // If we found a sub-block, just skip over it and check the next entry.
408  if (SkipBlock())
409  return BitstreamEntry::getError();
410  }
411  }
412 
413  unsigned ReadCode() {
414  return Read(CurCodeSize);
415  }
416 
417  // Block header:
418  // [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
419 
420  /// Having read the ENTER_SUBBLOCK code, read the BlockID for the block.
421  unsigned ReadSubBlockID() {
422  return ReadVBR(bitc::BlockIDWidth);
423  }
424 
425  /// Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip over the body
426  /// of this block. If the block record is malformed, return true.
427  bool SkipBlock() {
428  // Read and ignore the codelen value. Since we are skipping this block, we
429  // don't care what code widths are used inside of it.
430  ReadVBR(bitc::CodeLenWidth);
431  SkipToFourByteBoundary();
432  unsigned NumFourBytes = Read(bitc::BlockSizeWidth);
433 
434  // Check that the block wasn't partially defined, and that the offset isn't
435  // bogus.
436  size_t SkipTo = GetCurrentBitNo() + NumFourBytes*4*8;
437  if (AtEndOfStream() || !canSkipToPos(SkipTo/8))
438  return true;
439 
440  JumpToBit(SkipTo);
441  return false;
442  }
443 
444  /// Having read the ENTER_SUBBLOCK abbrevid, enter the block, and return true
445  /// if the block has an error.
446  bool EnterSubBlock(unsigned BlockID, unsigned *NumWordsP = nullptr);
447 
448  bool ReadBlockEnd() {
449  if (BlockScope.empty()) return true;
450 
451  // Block tail:
452  // [END_BLOCK, <align4bytes>]
453  SkipToFourByteBoundary();
454 
455  popBlockScope();
456  return false;
457  }
458 
459 private:
460  void popBlockScope() {
461  CurCodeSize = BlockScope.back().PrevCodeSize;
462 
463  CurAbbrevs = std::move(BlockScope.back().PrevAbbrevs);
464  BlockScope.pop_back();
465  }
466 
467  //===--------------------------------------------------------------------===//
468  // Record Processing
469  //===--------------------------------------------------------------------===//
470 
471 public:
472  /// Return the abbreviation for the specified AbbrevId.
473  const BitCodeAbbrev *getAbbrev(unsigned AbbrevID) {
474  unsigned AbbrevNo = AbbrevID - bitc::FIRST_APPLICATION_ABBREV;
475  if (AbbrevNo >= CurAbbrevs.size())
476  report_fatal_error("Invalid abbrev number");
477  return CurAbbrevs[AbbrevNo].get();
478  }
479 
480  /// Read the current record and discard it, returning the code for the record.
481  unsigned skipRecord(unsigned AbbrevID);
482 
483  unsigned readRecord(unsigned AbbrevID, SmallVectorImpl<uint64_t> &Vals,
484  StringRef *Blob = nullptr);
485 
486  //===--------------------------------------------------------------------===//
487  // Abbrev Processing
488  //===--------------------------------------------------------------------===//
489  void ReadAbbrevRecord();
490 
491  /// Read and return a block info block from the bitstream. If an error was
492  /// encountered, return None.
493  ///
494  /// \param ReadBlockInfoNames Whether to read block/record name information in
495  /// the BlockInfo block. Only llvm-bcanalyzer uses this.
497  ReadBlockInfoBlock(bool ReadBlockInfoNames = false);
498 
499  /// Set the block info to be used by this BitstreamCursor to interpret
500  /// abbreviated records.
501  void setBlockInfo(BitstreamBlockInfo *BI) { BlockInfo = BI; }
502 };
503 
504 } // end llvm namespace
505 
506 #endif // LLVM_BITCODE_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:115
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
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:168
const uint8_t * getPointerToBit(uint64_t BitNo, uint64_t NumBytes)
Get a pointer into the bitstream at the specified bit offset.
BitstreamCursor(MemoryBufferRef BitcodeBytes)
#define R2(n)
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.
word_t Read(unsigned NumBits)
bool canSkipToPos(size_t pos) const
uint64_t ReadVBR64(unsigned NumBits)
void skipToEnd()
Skip to the end of the file.
uint32_t ReadVBR(unsigned NumBits)
static BitstreamEntry getSubBlock(unsigned ID)
ArrayRef< uint8_t > getBitcodeBytes() const
BitstreamEntry advanceSkippingSubblocks(unsigned Flags=0)
This is a convenience function for clients that don&#39;t expect any subblocks.
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:149
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This represents a position within a bitcode file, implemented on top of a SimpleBitstreamCursor.
const BlockInfo * getBlockInfo(unsigned BlockID) const
If there is block info for the specified ID, return it, otherwise return null.
void JumpToBit(uint64_t BitNo)
Reset the stream to the specified bit number.
unsigned getAbbrevIDWidth() const
Return the number of bits used to encode an abbrev #.
bool SkipBlock()
Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip over the body of this block...
const T * data() const
Definition: ArrayRef.h:146
std::vector< std::shared_ptr< BitCodeAbbrev > > Abbrevs
SimpleBitstreamCursor(MemoryBufferRef BitcodeBytes)
unsigned ReadSubBlockID()
Having read the ENTER_SUBBLOCK code, read the BlockID for the block.
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.
DEFINE_ABBREV - Defines an abbrev for the current block.
Definition: BitCodes.h:53
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:61
static BitstreamEntry getEndBlock()
static BitstreamEntry getRecord(unsigned AbbrevID)
SimpleBitstreamCursor(StringRef BitcodeBytes)
const unsigned Kind
static BitstreamEntry getError()
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
aarch64 promote const
enum llvm::BitstreamEntry::@134 Kind
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:81
BitstreamEntry advance(unsigned Flags=0)
Advance the current bitstream, returning the next entry in the stream.
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:49
This represents a position within a bitstream.
BitstreamCursor(StringRef BitcodeBytes)