llvm-6502/include/llvm/Bitcode/BitstreamReader.h
Chris Lattner aea2012433 implement reading of abbrevs
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36366 91177308-0d34-0410-b5e6-96231b3b80d8
2007-04-23 18:57:58 +00:00

301 lines
8.7 KiB
C++

//===- BitstreamReader.h - Low-level bitstream reader interface -*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Chris Lattner and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This header defines the BitstreamReader class. This class can be used to
// read an arbitrary bitstream, regardless of its contents.
//
//===----------------------------------------------------------------------===//
#ifndef BITSTREAM_READER_H
#define BITSTREAM_READER_H
#include "llvm/Bitcode/BitCodes.h"
namespace llvm {
class BitstreamReader {
const unsigned char *NextChar;
const unsigned char *LastChar;
/// CurWord - This is the current data we have pulled from the stream but have
/// not returned to the client.
uint32_t CurWord;
/// BitsInCurWord - This is the number of bits in CurWord that are valid. This
/// is always from [0...31] inclusive.
unsigned BitsInCurWord;
// CurCodeSize - This is the declared size of code values used for the current
// block, in bits.
unsigned CurCodeSize;
/// CurAbbrevs - Abbrevs installed at in this block.
std::vector<BitCodeAbbrev*> CurAbbrevs;
struct Block {
unsigned PrevCodeSize;
std::vector<BitCodeAbbrev*> PrevAbbrevs;
explicit Block(unsigned PCS) : PrevCodeSize(PCS) {}
};
/// BlockScope - This tracks the codesize of parent blocks.
SmallVector<Block, 8> BlockScope;
public:
BitstreamReader(const unsigned char *Start, const unsigned char *End)
: NextChar(Start), LastChar(End) {
assert(((End-Start) & 3) == 0 &&"Bitcode stream not a multiple of 4 bytes");
CurWord = 0;
BitsInCurWord = 0;
CurCodeSize = 2;
}
~BitstreamReader() {
// Abbrevs could still exist if the stream was broken. If so, don't leak
// them.
for (unsigned i = 0, e = CurAbbrevs.size(); i != e; ++i)
delete CurAbbrevs[i];
for (unsigned S = 0, e = BlockScope.size(); S != e; ++S) {
std::vector<BitCodeAbbrev*> &Abbrevs = BlockScope[S].PrevAbbrevs;
for (unsigned i = 0, e = Abbrevs.size(); i != e; ++i)
delete Abbrevs[i];
}
}
bool AtEndOfStream() const { return NextChar == LastChar; }
uint32_t Read(unsigned NumBits) {
// If the field is fully contained by CurWord, return it quickly.
if (BitsInCurWord >= NumBits) {
uint32_t R = CurWord & ((1U << NumBits)-1);
CurWord >>= NumBits;
BitsInCurWord -= NumBits;
return R;
}
// If we run out of data, stop at the end of the stream.
if (LastChar == NextChar) {
CurWord = 0;
BitsInCurWord = 0;
return 0;
}
unsigned R = CurWord;
// Read the next word from the stream.
CurWord = (NextChar[0] << 0) | (NextChar[1] << 8) |
(NextChar[2] << 16) | (NextChar[3] << 24);
NextChar += 4;
// Extract NumBits-BitsInCurWord from what we just read.
unsigned BitsLeft = NumBits-BitsInCurWord;
// Be careful here, BitsLeft is in the range [1..32] inclusive.
R |= (CurWord & (~0U >> (32-BitsLeft))) << BitsInCurWord;
// BitsLeft bits have just been used up from CurWord.
if (BitsLeft != 32)
CurWord >>= BitsLeft;
else
CurWord = 0;
BitsInCurWord = 32-BitsLeft;
return R;
}
uint64_t Read64(unsigned NumBits) {
if (NumBits <= 32) return Read(NumBits);
uint64_t V = Read(32);
return V | (uint64_t)Read(NumBits-32) << 32;
}
uint32_t ReadVBR(unsigned NumBits) {
uint32_t Piece = Read(NumBits);
if ((Piece & (1U << (NumBits-1))) == 0)
return Piece;
uint32_t Result = 0;
unsigned NextBit = 0;
while (1) {
Result |= (Piece & ((1U << (NumBits-1))-1)) << NextBit;
if ((Piece & (1U << (NumBits-1))) == 0)
return Result;
NextBit += NumBits-1;
Piece = Read(NumBits);
}
}
uint64_t ReadVBR64(unsigned NumBits) {
uint64_t Piece = Read(NumBits);
if ((Piece & (1U << (NumBits-1))) == 0)
return Piece;
uint64_t Result = 0;
unsigned NextBit = 0;
while (1) {
Result |= (Piece & ((1U << (NumBits-1))-1)) << NextBit;
if ((Piece & (1U << (NumBits-1))) == 0)
return Result;
NextBit += NumBits-1;
Piece = Read(NumBits);
}
}
void SkipToWord() {
BitsInCurWord = 0;
CurWord = 0;
}
unsigned ReadCode() {
return Read(CurCodeSize);
}
//===--------------------------------------------------------------------===//
// Block Manipulation
//===--------------------------------------------------------------------===//
// Block header:
// [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
/// ReadSubBlockID - Having read the ENTER_SUBBLOCK code, read the BlockID for
/// the block.
unsigned ReadSubBlockID() {
return ReadVBR(bitc::BlockIDWidth);
}
/// SkipBlock - Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip
/// over the body of this block. If the block record is malformed, return
/// true.
bool SkipBlock() {
// Read and ignore the codelen value. Since we are skipping this block, we
// don't care what code widths are used inside of it.
ReadVBR(bitc::CodeLenWidth);
SkipToWord();
unsigned NumWords = Read(bitc::BlockSizeWidth);
// Check that the block wasn't partially defined, and that the offset isn't
// bogus.
if (AtEndOfStream() || NextChar+NumWords*4 > LastChar)
return true;
NextChar += NumWords*4;
return false;
}
/// EnterSubBlock - Having read the ENTER_SUBBLOCK abbrevid, read and enter
/// the block, returning the BlockID of the block we just entered.
bool EnterSubBlock() {
BlockScope.push_back(Block(CurCodeSize));
BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);
// Get the codesize of this block.
CurCodeSize = ReadVBR(bitc::CodeLenWidth);
SkipToWord();
unsigned NumWords = Read(bitc::BlockSizeWidth);
// Validate that this block is sane.
if (CurCodeSize == 0 || AtEndOfStream() || NextChar+NumWords*4 > LastChar)
return true;
return false;
}
bool ReadBlockEnd() {
if (BlockScope.empty()) return true;
// Block tail:
// [END_BLOCK, <align4bytes>]
SkipToWord();
CurCodeSize = BlockScope.back().PrevCodeSize;
// Delete abbrevs from popped scope.
for (unsigned i = 0, e = CurAbbrevs.size(); i != e; ++i)
delete CurAbbrevs[i];
BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);
BlockScope.pop_back();
return false;
}
//===--------------------------------------------------------------------===//
// Record Processing
//===--------------------------------------------------------------------===//
unsigned ReadRecord(unsigned AbbrevID, SmallVectorImpl<uint64_t> &Vals) {
if (AbbrevID == bitc::UNABBREV_RECORD) {
unsigned Code = ReadVBR(6);
unsigned NumElts = ReadVBR(6);
for (unsigned i = 0; i != NumElts; ++i)
Vals.push_back(ReadVBR64(6));
return Code;
}
unsigned AbbrevNo = AbbrevID-bitc::FIRST_ABBREV;
assert(AbbrevNo < CurAbbrevs.size() && "Invalid abbrev #!");
BitCodeAbbrev *Abbv = CurAbbrevs[AbbrevNo];
for (unsigned i = 0, e = Abbv->getNumOperandInfos(); i != e; ++i) {
const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
if (Op.isLiteral()) {
// If the abbrev specifies the literal value to use, use it.
Vals.push_back(Op.getLiteralValue());
} else {
// Decode the value as we are commanded.
switch (Op.getEncoding()) {
default: assert(0 && "Unknown encoding!");
case BitCodeAbbrevOp::FixedWidth:
Vals.push_back(Read(Op.getEncodingData()));
break;
case BitCodeAbbrevOp::VBR:
Vals.push_back(ReadVBR64(Op.getEncodingData()));
break;
}
}
}
unsigned Code = Vals[0];
Vals.erase(Vals.begin());
return Code;
}
//===--------------------------------------------------------------------===//
// Abbrev Processing
//===--------------------------------------------------------------------===//
void ReadAbbrevRecord() {
BitCodeAbbrev *Abbv = new BitCodeAbbrev();
unsigned NumOpInfo = ReadVBR(5);
for (unsigned i = 0; i != NumOpInfo; ++i) {
bool IsLiteral = Read(1);
if (IsLiteral) {
Abbv->Add(BitCodeAbbrevOp(ReadVBR64(8)));
continue;
}
BitCodeAbbrevOp::Encoding E = (BitCodeAbbrevOp::Encoding)Read(3);
if (BitCodeAbbrevOp::hasEncodingData(E)) {
Abbv->Add(BitCodeAbbrevOp(E, ReadVBR64(5)));
} else {
assert(0 && "unimp");
}
}
CurAbbrevs.push_back(Abbv);
}
};
} // End llvm namespace
#endif