EIC code displayed by LXR master/​include/​llvm/​Bitstream/​BitstreamReader.h	Source navigation Diff markup Identifier search General search
	Version: master test Revert   Change

File indexing completed on 2026-05-10 08:43:22

 //===- BitstreamReader.h - Low-level bitstream reader interface -*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This header defines the BitstreamReader class.  This class can be used to
 // read an arbitrary bitstream, regardless of its contents.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_BITSTREAM_BITSTREAMREADER_H
 #define LLVM_BITSTREAM_BITSTREAMREADER_H
 
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Bitstream/BitCodes.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/MemoryBufferRef.h"
 #include <algorithm>
 #include <cassert>
 #include <climits>
 #include <cstddef>
 #include <cstdint>
 #include <memory>
 #include <optional>
 #include <string>
 #include <utility>
 #include <vector>
 
 namespace llvm {
 
 /// This class maintains the abbreviations read from a block info block.
 class BitstreamBlockInfo {
 public:
   /// This contains information emitted to BLOCKINFO_BLOCK blocks. These
   /// describe abbreviations that all blocks of the specified ID inherit.
   struct BlockInfo {
     unsigned BlockID = 0;
     std::vector<std::shared_ptr<BitCodeAbbrev>> Abbrevs;
     std::string Name;
     std::vector<std::pair<unsigned, std::string>> RecordNames;
   };
 
 private:
   std::vector<BlockInfo> BlockInfoRecords;
 
 public:
   /// If there is block info for the specified ID, return it, otherwise return
   /// null.
   const BlockInfo *getBlockInfo(unsigned BlockID) const {
     // Common case, the most recent entry matches BlockID.
     if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
       return &BlockInfoRecords.back();
 
     for (const BlockInfo &BI : BlockInfoRecords)
       if (BI.BlockID == BlockID)
         return &BI;
     return nullptr;
   }
 
   BlockInfo &getOrCreateBlockInfo(unsigned BlockID) {
     if (const BlockInfo *BI = getBlockInfo(BlockID))
       return *const_cast<BlockInfo*>(BI);
 
     // Otherwise, add a new record.
     BlockInfoRecords.emplace_back();
     BlockInfoRecords.back().BlockID = BlockID;
     return BlockInfoRecords.back();
   }
 };
 
 /// This represents a position within a bitstream. There may be multiple
 /// independent cursors reading within one bitstream, each maintaining their
 /// own local state.
 class SimpleBitstreamCursor {
   ArrayRef<uint8_t> BitcodeBytes;
   size_t NextChar = 0;
 
 public:
   /// This is the current data we have pulled from the stream but have not
   /// returned to the client. This is specifically and intentionally defined to
   /// follow the word size of the host machine for efficiency. We use word_t in
   /// places that are aware of this to make it perfectly explicit what is going
   /// on.
   using word_t = size_t;
 
 private:
   word_t CurWord = 0;
 
   /// This is the number of bits in CurWord that are valid. This is always from
   /// [0...bits_of(size_t)-1] inclusive.
   unsigned BitsInCurWord = 0;
 
 public:
   SimpleBitstreamCursor() = default;
   explicit SimpleBitstreamCursor(ArrayRef<uint8_t> BitcodeBytes)
       : BitcodeBytes(BitcodeBytes) {}
   explicit SimpleBitstreamCursor(StringRef BitcodeBytes)
       : BitcodeBytes(arrayRefFromStringRef(BitcodeBytes)) {}
   explicit SimpleBitstreamCursor(MemoryBufferRef BitcodeBytes)
       : SimpleBitstreamCursor(BitcodeBytes.getBuffer()) {}
 
   bool canSkipToPos(size_t pos) const {
     // pos can be skipped to if it is a valid address or one byte past the end.
     return pos <= BitcodeBytes.size();
   }
 
   bool AtEndOfStream() {
     return BitsInCurWord == 0 && BitcodeBytes.size() <= NextChar;
   }
 
   /// Return the bit # of the bit we are reading.
   uint64_t GetCurrentBitNo() const {
     return uint64_t(NextChar)*CHAR_BIT - BitsInCurWord;
   }
 
   // Return the byte # of the current bit.
   uint64_t getCurrentByteNo() const { return GetCurrentBitNo() / 8; }
 
   ArrayRef<uint8_t> getBitcodeBytes() const { return BitcodeBytes; }
 
   /// Reset the stream to the specified bit number.
   Error JumpToBit(uint64_t BitNo) {
     size_t ByteNo = size_t(BitNo/8) & ~(sizeof(word_t)-1);
     unsigned WordBitNo = unsigned(BitNo & (sizeof(word_t)*8-1));
     assert(canSkipToPos(ByteNo) && "Invalid location");
 
     // Move the cursor to the right word.
     NextChar = ByteNo;
     BitsInCurWord = 0;
 
     // Skip over any bits that are already consumed.
     if (WordBitNo) {
       if (Expected<word_t> Res = Read(WordBitNo))
         return Error::success();
       else
         return Res.takeError();
     }
 
     return Error::success();
   }
 
   /// Get a pointer into the bitstream at the specified byte offset.
   const uint8_t *getPointerToByte(uint64_t ByteNo, uint64_t NumBytes) {
     return BitcodeBytes.data() + ByteNo;
   }
 
   /// Get a pointer into the bitstream at the specified bit offset.
   ///
   /// The bit offset must be on a byte boundary.
   const uint8_t *getPointerToBit(uint64_t BitNo, uint64_t NumBytes) {
     assert(!(BitNo % 8) && "Expected bit on byte boundary");
     return getPointerToByte(BitNo / 8, NumBytes);
   }
 
   Error fillCurWord() {
     if (NextChar >= BitcodeBytes.size())
       return createStringError(std::errc::io_error,
                                "Unexpected end of file reading %u of %u bytes",
                                NextChar, BitcodeBytes.size());
 
     // Read the next word from the stream.
     const uint8_t *NextCharPtr = BitcodeBytes.data() + NextChar;
     unsigned BytesRead;
     if (BitcodeBytes.size() >= NextChar + sizeof(word_t)) {
       BytesRead = sizeof(word_t);
       CurWord =
           support::endian::read<word_t, llvm::endianness::little>(NextCharPtr);
     } else {
       // Short read.
       BytesRead = BitcodeBytes.size() - NextChar;
       CurWord = 0;
       for (unsigned B = 0; B != BytesRead; ++B)
         CurWord |= uint64_t(NextCharPtr[B]) << (B * 8);
     }
     NextChar += BytesRead;
     BitsInCurWord = BytesRead * 8;
     return Error::success();
   }
 
   Expected<word_t> Read(unsigned NumBits) {
     static const unsigned BitsInWord = sizeof(word_t) * 8;
 
     assert(NumBits && NumBits <= BitsInWord &&
            "Cannot return zero or more than BitsInWord bits!");
 
     static const unsigned Mask = sizeof(word_t) > 4 ? 0x3f : 0x1f;
 
     // If the field is fully contained by CurWord, return it quickly.
     if (BitsInCurWord >= NumBits) {
       word_t R = CurWord & (~word_t(0) >> (BitsInWord - NumBits));
 
       // Use a mask to avoid undefined behavior.
       CurWord >>= (NumBits & Mask);
 
       BitsInCurWord -= NumBits;
       return R;
     }
 
     word_t R = BitsInCurWord ? CurWord : 0;
     unsigned BitsLeft = NumBits - BitsInCurWord;
 
     if (Error fillResult = fillCurWord())
       return std::move(fillResult);
 
     // If we run out of data, abort.
     if (BitsLeft > BitsInCurWord)
       return createStringError(std::errc::io_error,
                                "Unexpected end of file reading %u of %u bits",
                                BitsInCurWord, BitsLeft);
 
     word_t R2 = CurWord & (~word_t(0) >> (BitsInWord - BitsLeft));
 
     // Use a mask to avoid undefined behavior.
     CurWord >>= (BitsLeft & Mask);
 
     BitsInCurWord -= BitsLeft;
 
     R |= R2 << (NumBits - BitsLeft);
 
     return R;
   }
 
   Expected<uint32_t> ReadVBR(const unsigned NumBits) {
     Expected<unsigned> MaybeRead = Read(NumBits);
     if (!MaybeRead)
       return MaybeRead;
     uint32_t Piece = MaybeRead.get();
 
     assert(NumBits <= 32 && NumBits >= 1 && "Invalid NumBits value");
     const uint32_t MaskBitOrder = (NumBits - 1);
     const uint32_t Mask = 1UL << MaskBitOrder;
 
     if ((Piece & Mask) == 0)
       return Piece;
 
     uint32_t Result = 0;
     unsigned NextBit = 0;
     while (true) {
       Result |= (Piece & (Mask - 1)) << NextBit;
 
       if ((Piece & Mask) == 0)
         return Result;
 
       NextBit += NumBits-1;
       if (NextBit >= 32)
         return createStringError(std::errc::illegal_byte_sequence,
                                  "Unterminated VBR");
 
       MaybeRead = Read(NumBits);
       if (!MaybeRead)
         return MaybeRead;
       Piece = MaybeRead.get();
     }
   }
 
   // Read a VBR that may have a value up to 64-bits in size. The chunk size of
   // the VBR must still be <= 32 bits though.
   Expected<uint64_t> ReadVBR64(const unsigned NumBits) {
     Expected<uint64_t> MaybeRead = Read(NumBits);
     if (!MaybeRead)
       return MaybeRead;
     uint32_t Piece = MaybeRead.get();
     assert(NumBits <= 32 && NumBits >= 1 && "Invalid NumBits value");
     const uint32_t MaskBitOrder = (NumBits - 1);
     const uint32_t Mask = 1UL << MaskBitOrder;
 
     if ((Piece & Mask) == 0)
       return uint64_t(Piece);
 
     uint64_t Result = 0;
     unsigned NextBit = 0;
     while (true) {
       Result |= uint64_t(Piece & (Mask - 1)) << NextBit;
 
       if ((Piece & Mask) == 0)
         return Result;
 
       NextBit += NumBits-1;
       if (NextBit >= 64)
         return createStringError(std::errc::illegal_byte_sequence,
                                  "Unterminated VBR");
 
       MaybeRead = Read(NumBits);
       if (!MaybeRead)
         return MaybeRead;
       Piece = MaybeRead.get();
     }
   }
 
   void SkipToFourByteBoundary() {
     // If word_t is 64-bits and if we've read less than 32 bits, just dump
     // the bits we have up to the next 32-bit boundary.
     if (sizeof(word_t) > 4 &&
         BitsInCurWord >= 32) {
       CurWord >>= BitsInCurWord-32;
       BitsInCurWord = 32;
       return;
     }
 
     BitsInCurWord = 0;
   }
 
   /// Return the size of the stream in bytes.
   size_t SizeInBytes() const { return BitcodeBytes.size(); }
 
   /// Skip to the end of the file.
   void skipToEnd() { NextChar = BitcodeBytes.size(); }
 
   /// Check whether a reservation of Size elements is plausible.
   bool isSizePlausible(size_t Size) const {
     // Don't allow reserving more elements than the number of bits, assuming
     // at least one bit is needed to encode an element.
     return Size < BitcodeBytes.size() * 8;
   }
 };
 
 /// When advancing through a bitstream cursor, each advance can discover a few
 /// different kinds of entries:
 struct BitstreamEntry {
   enum {
     Error,    // Malformed bitcode was found.
     EndBlock, // We've reached the end of the current block, (or the end of the
               // file, which is treated like a series of EndBlock records.
     SubBlock, // This is the start of a new subblock of a specific ID.
     Record    // This is a record with a specific AbbrevID.
   } Kind;
 
   unsigned ID;
 
   static BitstreamEntry getError() {
     BitstreamEntry E; E.Kind = Error; return E;
   }
 
   static BitstreamEntry getEndBlock() {
     BitstreamEntry E; E.Kind = EndBlock; return E;
   }
 
   static BitstreamEntry getSubBlock(unsigned ID) {
     BitstreamEntry E; E.Kind = SubBlock; E.ID = ID; return E;
   }
 
   static BitstreamEntry getRecord(unsigned AbbrevID) {
     BitstreamEntry E; E.Kind = Record; E.ID = AbbrevID; return E;
   }
 };
 
 /// This represents a position within a bitcode file, implemented on top of a
 /// SimpleBitstreamCursor.
 ///
 /// Unlike iterators, BitstreamCursors are heavy-weight objects that should not
 /// be passed by value.
 class BitstreamCursor : SimpleBitstreamCursor {
   // This is the declared size of code values used for the current block, in
   // bits.
   unsigned CurCodeSize = 2;
 
   /// Abbrevs installed at in this block.
   std::vector<std::shared_ptr<BitCodeAbbrev>> CurAbbrevs;
 
   struct Block {
     unsigned PrevCodeSize;
     std::vector<std::shared_ptr<BitCodeAbbrev>> PrevAbbrevs;
 
     explicit Block(unsigned PCS) : PrevCodeSize(PCS) {}
   };
 
   /// This tracks the codesize of parent blocks.
   SmallVector<Block, 8> BlockScope;
 
   BitstreamBlockInfo *BlockInfo = nullptr;
 
 public:
   static const size_t MaxChunkSize = 32;
 
   BitstreamCursor() = default;
   explicit BitstreamCursor(ArrayRef<uint8_t> BitcodeBytes)
       : SimpleBitstreamCursor(BitcodeBytes) {}
   explicit BitstreamCursor(StringRef BitcodeBytes)
       : SimpleBitstreamCursor(BitcodeBytes) {}
   explicit BitstreamCursor(MemoryBufferRef BitcodeBytes)
       : SimpleBitstreamCursor(BitcodeBytes) {}
 
   using SimpleBitstreamCursor::AtEndOfStream;
   using SimpleBitstreamCursor::canSkipToPos;
   using SimpleBitstreamCursor::fillCurWord;
   using SimpleBitstreamCursor::getBitcodeBytes;
   using SimpleBitstreamCursor::GetCurrentBitNo;
   using SimpleBitstreamCursor::getCurrentByteNo;
   using SimpleBitstreamCursor::getPointerToByte;
   using SimpleBitstreamCursor::JumpToBit;
   using SimpleBitstreamCursor::Read;
   using SimpleBitstreamCursor::ReadVBR;
   using SimpleBitstreamCursor::ReadVBR64;
   using SimpleBitstreamCursor::SizeInBytes;
   using SimpleBitstreamCursor::skipToEnd;
 
   /// Return the number of bits used to encode an abbrev #.
   unsigned getAbbrevIDWidth() const { return CurCodeSize; }
 
   /// Flags that modify the behavior of advance().
   enum {
     /// If this flag is used, the advance() method does not automatically pop
     /// the block scope when the end of a block is reached.
     AF_DontPopBlockAtEnd = 1,
 
     /// If this flag is used, abbrev entries are returned just like normal
     /// records.
     AF_DontAutoprocessAbbrevs = 2
   };
 
   /// Advance the current bitstream, returning the next entry in the stream.
   Expected<BitstreamEntry> advance(unsigned Flags = 0) {
     while (true) {
       if (AtEndOfStream())
         return BitstreamEntry::getError();
 
       Expected<unsigned> MaybeCode = ReadCode();
       if (!MaybeCode)
         return MaybeCode.takeError();
       unsigned Code = MaybeCode.get();
 
       if (Code == bitc::END_BLOCK) {
         // Pop the end of the block unless Flags tells us not to.
         if (!(Flags & AF_DontPopBlockAtEnd) && ReadBlockEnd())
           return BitstreamEntry::getError();
         return BitstreamEntry::getEndBlock();
       }
 
       if (Code == bitc::ENTER_SUBBLOCK) {
         if (Expected<unsigned> MaybeSubBlock = ReadSubBlockID())
           return BitstreamEntry::getSubBlock(MaybeSubBlock.get());
         else
           return MaybeSubBlock.takeError();
       }
 
       if (Code == bitc::DEFINE_ABBREV &&
           !(Flags & AF_DontAutoprocessAbbrevs)) {
         // We read and accumulate abbrev's, the client can't do anything with
         // them anyway.
         if (Error Err = ReadAbbrevRecord())
           return std::move(Err);
         continue;
       }
 
       return BitstreamEntry::getRecord(Code);
     }
   }
 
   /// This is a convenience function for clients that don't expect any
   /// subblocks. This just skips over them automatically.
   Expected<BitstreamEntry> advanceSkippingSubblocks(unsigned Flags = 0) {
     while (true) {
       // If we found a normal entry, return it.
       Expected<BitstreamEntry> MaybeEntry = advance(Flags);
       if (!MaybeEntry)
         return MaybeEntry;
       BitstreamEntry Entry = MaybeEntry.get();
 
       if (Entry.Kind != BitstreamEntry::SubBlock)
         return Entry;
 
       // If we found a sub-block, just skip over it and check the next entry.
       if (Error Err = SkipBlock())
         return std::move(Err);
     }
   }
 
   Expected<unsigned> ReadCode() { return Read(CurCodeSize); }
 
   // Block header:
   //    [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
 
   /// Having read the ENTER_SUBBLOCK code, read the BlockID for the block.
   Expected<unsigned> ReadSubBlockID() { return ReadVBR(bitc::BlockIDWidth); }
 
   /// Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip over the body
   /// of this block.
   Error SkipBlock() {
     // Read and ignore the codelen value.
     if (Expected<uint32_t> Res = ReadVBR(bitc::CodeLenWidth))
       ; // Since we are skipping this block, we don't care what code widths are
         // used inside of it.
     else
       return Res.takeError();
 
     SkipToFourByteBoundary();
     Expected<unsigned> MaybeNum = Read(bitc::BlockSizeWidth);
     if (!MaybeNum)
       return MaybeNum.takeError();
     size_t NumFourBytes = MaybeNum.get();
 
     // Check that the block wasn't partially defined, and that the offset isn't
     // bogus.
     size_t SkipTo = GetCurrentBitNo() + NumFourBytes * 4 * 8;
     if (AtEndOfStream())
       return createStringError(std::errc::illegal_byte_sequence,
                                "can't skip block: already at end of stream");
     if (!canSkipToPos(SkipTo / 8))
       return createStringError(std::errc::illegal_byte_sequence,
                                "can't skip to bit %zu from %" PRIu64, SkipTo,
                                GetCurrentBitNo());
 
     if (Error Res = JumpToBit(SkipTo))
       return Res;
 
     return Error::success();
   }
 
   /// Having read the ENTER_SUBBLOCK abbrevid, and enter the block.
   Error EnterSubBlock(unsigned BlockID, unsigned *NumWordsP = nullptr);
 
   bool ReadBlockEnd() {
     if (BlockScope.empty()) return true;
 
     // Block tail:
     //    [END_BLOCK, <align4bytes>]
     SkipToFourByteBoundary();
 
     popBlockScope();
     return false;
   }
 
 private:
   void popBlockScope() {
     CurCodeSize = BlockScope.back().PrevCodeSize;
 
     CurAbbrevs = std::move(BlockScope.back().PrevAbbrevs);
     BlockScope.pop_back();
   }
 
   //===--------------------------------------------------------------------===//
   // Record Processing
   //===--------------------------------------------------------------------===//
 
 public:
   /// Return the abbreviation for the specified AbbrevId.
   Expected<const BitCodeAbbrev *> getAbbrev(unsigned AbbrevID) {
     unsigned AbbrevNo = AbbrevID - bitc::FIRST_APPLICATION_ABBREV;
     if (AbbrevNo >= CurAbbrevs.size())
       return createStringError(
           std::errc::illegal_byte_sequence, "Invalid abbrev number");
     return CurAbbrevs[AbbrevNo].get();
   }
 
   /// Read the current record and discard it, returning the code for the record.
   Expected<unsigned> skipRecord(unsigned AbbrevID);
 
   Expected<unsigned> readRecord(unsigned AbbrevID,
                                 SmallVectorImpl<uint64_t> &Vals,
                                 StringRef *Blob = nullptr);
 
   //===--------------------------------------------------------------------===//
   // Abbrev Processing
   //===--------------------------------------------------------------------===//
   Error ReadAbbrevRecord();
 
   /// Read and return a block info block from the bitstream. If an error was
   /// encountered, return std::nullopt.
   ///
   /// \param ReadBlockInfoNames Whether to read block/record name information in
   /// the BlockInfo block. Only llvm-bcanalyzer uses this.
   Expected<std::optional<BitstreamBlockInfo>>
   ReadBlockInfoBlock(bool ReadBlockInfoNames = false);
 
   /// Set the block info to be used by this BitstreamCursor to interpret
   /// abbreviated records.
   void setBlockInfo(BitstreamBlockInfo *BI) { BlockInfo = BI; }
 };
 
 } // end llvm namespace
 
 #endif // LLVM_BITSTREAM_BITSTREAMREADER_H

This page was automatically generated by the 2.3.7 LXR engine. The LXR team