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516 lines
16 KiB
C++
516 lines
16 KiB
C++
//===- BitstreamReader.h - Low-level bitstream reader interface -*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This header defines the BitstreamReader class. This class can be used to
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// read an arbitrary bitstream, regardless of its contents.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_BITCODE_BITSTREAMREADER_H
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#define LLVM_BITCODE_BITSTREAMREADER_H
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#include "llvm/Bitcode/BitCodes.h"
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#include "llvm/Support/Endian.h"
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#include "llvm/Support/StreamingMemoryObject.h"
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#include <climits>
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#include <string>
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#include <vector>
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namespace llvm {
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/// This class is used to read from an LLVM bitcode stream, maintaining
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/// information that is global to decoding the entire file. While a file is
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/// being read, multiple cursors can be independently advanced or skipped around
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/// within the file. These are represented by the BitstreamCursor class.
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class BitstreamReader {
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public:
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/// This contains information emitted to BLOCKINFO_BLOCK blocks. These
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/// describe abbreviations that all blocks of the specified ID inherit.
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struct BlockInfo {
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unsigned BlockID;
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std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> Abbrevs;
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std::string Name;
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std::vector<std::pair<unsigned, std::string> > RecordNames;
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};
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private:
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std::unique_ptr<MemoryObject> BitcodeBytes;
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std::vector<BlockInfo> BlockInfoRecords;
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/// This is set to true if we don't care about the block/record name
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/// information in the BlockInfo block. Only llvm-bcanalyzer uses this.
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bool IgnoreBlockInfoNames;
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BitstreamReader(const BitstreamReader&) = delete;
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void operator=(const BitstreamReader&) = delete;
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public:
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BitstreamReader() : IgnoreBlockInfoNames(true) {
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}
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BitstreamReader(const unsigned char *Start, const unsigned char *End)
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: IgnoreBlockInfoNames(true) {
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init(Start, End);
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}
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BitstreamReader(std::unique_ptr<MemoryObject> BitcodeBytes)
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: BitcodeBytes(std::move(BitcodeBytes)), IgnoreBlockInfoNames(true) {}
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BitstreamReader(BitstreamReader &&Other) {
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*this = std::move(Other);
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}
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BitstreamReader &operator=(BitstreamReader &&Other) {
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BitcodeBytes = std::move(Other.BitcodeBytes);
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// Explicitly swap block info, so that nothing gets destroyed twice.
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std::swap(BlockInfoRecords, Other.BlockInfoRecords);
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IgnoreBlockInfoNames = Other.IgnoreBlockInfoNames;
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return *this;
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}
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void init(const unsigned char *Start, const unsigned char *End) {
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assert(((End-Start) & 3) == 0 &&"Bitcode stream not a multiple of 4 bytes");
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BitcodeBytes.reset(getNonStreamedMemoryObject(Start, End));
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}
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MemoryObject &getBitcodeBytes() { return *BitcodeBytes; }
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/// This is called by clients that want block/record name information.
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void CollectBlockInfoNames() { IgnoreBlockInfoNames = false; }
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bool isIgnoringBlockInfoNames() { return IgnoreBlockInfoNames; }
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//===--------------------------------------------------------------------===//
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// Block Manipulation
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//===--------------------------------------------------------------------===//
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/// Return true if we've already read and processed the block info block for
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/// this Bitstream. We only process it for the first cursor that walks over
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/// it.
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bool hasBlockInfoRecords() const { return !BlockInfoRecords.empty(); }
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/// If there is block info for the specified ID, return it, otherwise return
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/// null.
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const BlockInfo *getBlockInfo(unsigned BlockID) const {
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// Common case, the most recent entry matches BlockID.
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if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
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return &BlockInfoRecords.back();
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for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size());
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i != e; ++i)
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if (BlockInfoRecords[i].BlockID == BlockID)
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return &BlockInfoRecords[i];
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return nullptr;
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}
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BlockInfo &getOrCreateBlockInfo(unsigned BlockID) {
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if (const BlockInfo *BI = getBlockInfo(BlockID))
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return *const_cast<BlockInfo*>(BI);
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// Otherwise, add a new record.
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BlockInfoRecords.push_back(BlockInfo());
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BlockInfoRecords.back().BlockID = BlockID;
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return BlockInfoRecords.back();
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}
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/// Takes block info from the other bitstream reader.
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///
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/// This is a "take" operation because BlockInfo records are non-trivial, and
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/// indeed rather expensive.
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void takeBlockInfo(BitstreamReader &&Other) {
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assert(!hasBlockInfoRecords());
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BlockInfoRecords = std::move(Other.BlockInfoRecords);
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}
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};
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/// When advancing through a bitstream cursor, each advance can discover a few
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/// different kinds of entries:
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struct BitstreamEntry {
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enum {
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Error, // Malformed bitcode was found.
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EndBlock, // We've reached the end of the current block, (or the end of the
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// file, which is treated like a series of EndBlock records.
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SubBlock, // This is the start of a new subblock of a specific ID.
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Record // This is a record with a specific AbbrevID.
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} Kind;
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unsigned ID;
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static BitstreamEntry getError() {
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BitstreamEntry E; E.Kind = Error; return E;
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}
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static BitstreamEntry getEndBlock() {
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BitstreamEntry E; E.Kind = EndBlock; return E;
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}
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static BitstreamEntry getSubBlock(unsigned ID) {
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BitstreamEntry E; E.Kind = SubBlock; E.ID = ID; return E;
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}
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static BitstreamEntry getRecord(unsigned AbbrevID) {
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BitstreamEntry E; E.Kind = Record; E.ID = AbbrevID; return E;
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}
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};
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/// This represents a position within a bitcode file. There may be multiple
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/// independent cursors reading within one bitstream, each maintaining their own
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/// local state.
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///
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/// Unlike iterators, BitstreamCursors are heavy-weight objects that should not
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/// be passed by value.
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class BitstreamCursor {
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BitstreamReader *BitStream;
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size_t NextChar;
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// The size of the bicode. 0 if we don't know it yet.
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size_t Size;
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/// This is the current data we have pulled from the stream but have not
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/// returned to the client. This is specifically and intentionally defined to
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/// follow the word size of the host machine for efficiency. We use word_t in
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/// places that are aware of this to make it perfectly explicit what is going
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/// on.
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typedef size_t word_t;
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word_t CurWord;
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/// This is the number of bits in CurWord that are valid. This is always from
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/// [0...bits_of(size_t)-1] inclusive.
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unsigned BitsInCurWord;
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// This is the declared size of code values used for the current block, in
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// bits.
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unsigned CurCodeSize;
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/// Abbrevs installed at in this block.
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std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> CurAbbrevs;
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struct Block {
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unsigned PrevCodeSize;
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std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> PrevAbbrevs;
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explicit Block(unsigned PCS) : PrevCodeSize(PCS) {}
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};
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/// This tracks the codesize of parent blocks.
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SmallVector<Block, 8> BlockScope;
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public:
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BitstreamCursor() { init(nullptr); }
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explicit BitstreamCursor(BitstreamReader &R) { init(&R); }
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void init(BitstreamReader *R) {
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freeState();
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BitStream = R;
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NextChar = 0;
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Size = 0;
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BitsInCurWord = 0;
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CurCodeSize = 2;
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}
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void freeState();
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bool canSkipToPos(size_t pos) const {
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// pos can be skipped to if it is a valid address or one byte past the end.
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return pos == 0 || BitStream->getBitcodeBytes().isValidAddress(
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static_cast<uint64_t>(pos - 1));
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}
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bool AtEndOfStream() {
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if (BitsInCurWord != 0)
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return false;
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if (Size != 0)
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return Size == NextChar;
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fillCurWord();
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return BitsInCurWord == 0;
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}
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/// Return the number of bits used to encode an abbrev #.
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unsigned getAbbrevIDWidth() const { return CurCodeSize; }
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/// Return the bit # of the bit we are reading.
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uint64_t GetCurrentBitNo() const {
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return NextChar*CHAR_BIT - BitsInCurWord;
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}
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BitstreamReader *getBitStreamReader() {
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return BitStream;
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}
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const BitstreamReader *getBitStreamReader() const {
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return BitStream;
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}
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/// Flags that modify the behavior of advance().
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enum {
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/// If this flag is used, the advance() method does not automatically pop
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/// the block scope when the end of a block is reached.
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AF_DontPopBlockAtEnd = 1,
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/// If this flag is used, abbrev entries are returned just like normal
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/// records.
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AF_DontAutoprocessAbbrevs = 2
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};
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/// Advance the current bitstream, returning the next entry in the stream.
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BitstreamEntry advance(unsigned Flags = 0) {
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while (1) {
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unsigned Code = ReadCode();
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if (Code == bitc::END_BLOCK) {
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// Pop the end of the block unless Flags tells us not to.
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if (!(Flags & AF_DontPopBlockAtEnd) && ReadBlockEnd())
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return BitstreamEntry::getError();
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return BitstreamEntry::getEndBlock();
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}
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if (Code == bitc::ENTER_SUBBLOCK)
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return BitstreamEntry::getSubBlock(ReadSubBlockID());
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if (Code == bitc::DEFINE_ABBREV &&
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!(Flags & AF_DontAutoprocessAbbrevs)) {
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// We read and accumulate abbrev's, the client can't do anything with
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// them anyway.
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ReadAbbrevRecord();
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continue;
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}
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return BitstreamEntry::getRecord(Code);
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}
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}
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/// This is a convenience function for clients that don't expect any
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/// subblocks. This just skips over them automatically.
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BitstreamEntry advanceSkippingSubblocks(unsigned Flags = 0) {
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while (1) {
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// If we found a normal entry, return it.
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BitstreamEntry Entry = advance(Flags);
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if (Entry.Kind != BitstreamEntry::SubBlock)
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return Entry;
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// If we found a sub-block, just skip over it and check the next entry.
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if (SkipBlock())
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return BitstreamEntry::getError();
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}
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}
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/// Reset the stream to the specified bit number.
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void JumpToBit(uint64_t BitNo) {
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size_t ByteNo = size_t(BitNo/8) & ~(sizeof(word_t)-1);
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unsigned WordBitNo = unsigned(BitNo & (sizeof(word_t)*8-1));
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assert(canSkipToPos(ByteNo) && "Invalid location");
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// Move the cursor to the right word.
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NextChar = ByteNo;
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BitsInCurWord = 0;
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// Skip over any bits that are already consumed.
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if (WordBitNo)
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Read(WordBitNo);
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}
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void fillCurWord() {
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if (Size != 0 && NextChar >= Size)
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report_fatal_error("Unexpected end of file");
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// Read the next word from the stream.
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uint8_t Array[sizeof(word_t)] = {0};
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uint64_t BytesRead =
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BitStream->getBitcodeBytes().readBytes(Array, sizeof(Array), NextChar);
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// If we run out of data, stop at the end of the stream.
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if (BytesRead == 0) {
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Size = NextChar;
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return;
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}
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CurWord =
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support::endian::read<word_t, support::little, support::unaligned>(
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Array);
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NextChar += BytesRead;
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BitsInCurWord = BytesRead * 8;
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}
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word_t Read(unsigned NumBits) {
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static const unsigned BitsInWord = sizeof(word_t) * 8;
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assert(NumBits && NumBits <= BitsInWord &&
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"Cannot return zero or more than BitsInWord bits!");
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static const unsigned Mask = sizeof(word_t) > 4 ? 0x3f : 0x1f;
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// If the field is fully contained by CurWord, return it quickly.
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if (BitsInCurWord >= NumBits) {
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word_t R = CurWord & (~word_t(0) >> (BitsInWord - NumBits));
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// Use a mask to avoid undefined behavior.
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CurWord >>= (NumBits & Mask);
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BitsInCurWord -= NumBits;
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return R;
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}
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word_t R = BitsInCurWord ? CurWord : 0;
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unsigned BitsLeft = NumBits - BitsInCurWord;
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fillCurWord();
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// If we run out of data, stop at the end of the stream.
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if (BitsLeft > BitsInCurWord)
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return 0;
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word_t R2 = CurWord & (~word_t(0) >> (BitsInWord - BitsLeft));
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// Use a mask to avoid undefined behavior.
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CurWord >>= (BitsLeft & Mask);
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BitsInCurWord -= BitsLeft;
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R |= R2 << (NumBits - BitsLeft);
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return R;
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}
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uint32_t ReadVBR(unsigned NumBits) {
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uint32_t Piece = Read(NumBits);
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if ((Piece & (1U << (NumBits-1))) == 0)
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return Piece;
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uint32_t Result = 0;
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unsigned NextBit = 0;
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while (1) {
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Result |= (Piece & ((1U << (NumBits-1))-1)) << NextBit;
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if ((Piece & (1U << (NumBits-1))) == 0)
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return Result;
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NextBit += NumBits-1;
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Piece = Read(NumBits);
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}
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}
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// Read a VBR that may have a value up to 64-bits in size. The chunk size of
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// the VBR must still be <= 32 bits though.
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uint64_t ReadVBR64(unsigned NumBits) {
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uint32_t Piece = Read(NumBits);
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if ((Piece & (1U << (NumBits-1))) == 0)
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return uint64_t(Piece);
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uint64_t Result = 0;
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unsigned NextBit = 0;
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while (1) {
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Result |= uint64_t(Piece & ((1U << (NumBits-1))-1)) << NextBit;
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if ((Piece & (1U << (NumBits-1))) == 0)
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return Result;
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NextBit += NumBits-1;
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Piece = Read(NumBits);
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}
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}
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private:
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void SkipToFourByteBoundary() {
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// If word_t is 64-bits and if we've read less than 32 bits, just dump
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// the bits we have up to the next 32-bit boundary.
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if (sizeof(word_t) > 4 &&
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BitsInCurWord >= 32) {
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CurWord >>= BitsInCurWord-32;
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BitsInCurWord = 32;
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return;
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}
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BitsInCurWord = 0;
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}
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public:
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unsigned ReadCode() {
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return Read(CurCodeSize);
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}
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// Block header:
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// [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
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/// Having read the ENTER_SUBBLOCK code, read the BlockID for the block.
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unsigned ReadSubBlockID() {
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return ReadVBR(bitc::BlockIDWidth);
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}
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/// Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip over the body
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/// of this block. If the block record is malformed, return true.
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bool SkipBlock() {
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// Read and ignore the codelen value. Since we are skipping this block, we
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// don't care what code widths are used inside of it.
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ReadVBR(bitc::CodeLenWidth);
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SkipToFourByteBoundary();
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unsigned NumFourBytes = Read(bitc::BlockSizeWidth);
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// Check that the block wasn't partially defined, and that the offset isn't
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// bogus.
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size_t SkipTo = GetCurrentBitNo() + NumFourBytes*4*8;
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if (AtEndOfStream() || !canSkipToPos(SkipTo/8))
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return true;
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JumpToBit(SkipTo);
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return false;
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}
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/// Having read the ENTER_SUBBLOCK abbrevid, enter the block, and return true
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/// if the block has an error.
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bool EnterSubBlock(unsigned BlockID, unsigned *NumWordsP = nullptr);
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bool ReadBlockEnd() {
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if (BlockScope.empty()) return true;
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// Block tail:
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// [END_BLOCK, <align4bytes>]
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SkipToFourByteBoundary();
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popBlockScope();
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return false;
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}
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private:
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void popBlockScope() {
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CurCodeSize = BlockScope.back().PrevCodeSize;
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CurAbbrevs = std::move(BlockScope.back().PrevAbbrevs);
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BlockScope.pop_back();
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}
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//===--------------------------------------------------------------------===//
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// Record Processing
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//===--------------------------------------------------------------------===//
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public:
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/// Return the abbreviation for the specified AbbrevId.
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const BitCodeAbbrev *getAbbrev(unsigned AbbrevID) {
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unsigned AbbrevNo = AbbrevID - bitc::FIRST_APPLICATION_ABBREV;
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if (AbbrevNo >= CurAbbrevs.size())
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report_fatal_error("Invalid abbrev number");
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return CurAbbrevs[AbbrevNo].get();
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}
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/// Read the current record and discard it.
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void skipRecord(unsigned AbbrevID);
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unsigned readRecord(unsigned AbbrevID, SmallVectorImpl<uint64_t> &Vals,
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StringRef *Blob = nullptr);
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//===--------------------------------------------------------------------===//
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// Abbrev Processing
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//===--------------------------------------------------------------------===//
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void ReadAbbrevRecord();
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bool ReadBlockInfoBlock();
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};
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} // End llvm namespace
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#endif
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