BitstreamWriter.h
//===- BitstreamWriter.h - Low-level bitstream writer interface -*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This header defines the BitstreamWriter class. This class can be used to
// write an arbitrary bitstream, regardless of its contents.
//
//===----------------------------------------------------------------------===//
#ifndef BITSTREAM_WRITER_H
#define BITSTREAM_WRITER_H
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Bitcode/BitCodes.h"
#include <vector>
namespace llvm {
class BitstreamWriter {
SmallVectorImpl<char> &Out;
/// CurBit - Always between 0 and 31 inclusive, specifies the next bit to use.
unsigned CurBit;
/// CurValue - The current value. Only bits < CurBit are valid.
uint32_t CurValue;
/// CurCodeSize - This is the declared size of code values used for the
/// current block, in bits.
unsigned CurCodeSize;
/// BlockInfoCurBID - When emitting a BLOCKINFO_BLOCK, this is the currently
/// selected BLOCK ID.
unsigned BlockInfoCurBID;
/// CurAbbrevs - Abbrevs installed at in this block.
std::vector<BitCodeAbbrev*> CurAbbrevs;
struct Block {
unsigned PrevCodeSize;
unsigned StartSizeWord;
std::vector<BitCodeAbbrev*> PrevAbbrevs;
Block(unsigned PCS, unsigned SSW) : PrevCodeSize(PCS), StartSizeWord(SSW) {}
};
/// BlockScope - This tracks the current blocks that we have entered.
std::vector<Block> BlockScope;
/// BlockInfo - This contains information emitted to BLOCKINFO_BLOCK blocks.
/// These describe abbreviations that all blocks of the specified ID inherit.
struct BlockInfo {
unsigned BlockID;
std::vector<BitCodeAbbrev*> Abbrevs;
};
std::vector<BlockInfo> BlockInfoRecords;
// BackpatchWord - Backpatch a 32-bit word in the output with the specified
// value.
void BackpatchWord(unsigned ByteNo, unsigned NewWord) {
Out[ByteNo++] = (unsigned char)(NewWord >> 0);
Out[ByteNo++] = (unsigned char)(NewWord >> 8);
Out[ByteNo++] = (unsigned char)(NewWord >> 16);
Out[ByteNo ] = (unsigned char)(NewWord >> 24);
}
void WriteByte(unsigned char Value) {
Out.push_back(Value);
}
void WriteWord(unsigned Value) {
unsigned char Bytes[4] = {
(unsigned char)(Value >> 0),
(unsigned char)(Value >> 8),
(unsigned char)(Value >> 16),
(unsigned char)(Value >> 24) };
Out.append(&Bytes[0], &Bytes[4]);
}
unsigned GetBufferOffset() const {
return Out.size();
}
unsigned GetWordIndex() const {
unsigned Offset = GetBufferOffset();
assert((Offset & 3) == 0 && "Not 32-bit aligned");
return Offset / 4;
}
public:
explicit BitstreamWriter(SmallVectorImpl<char> &O)
: Out(O), CurBit(0), CurValue(0), CurCodeSize(2) {}
~BitstreamWriter() {
assert(CurBit == 0 && "Unflused data remaining");
assert(BlockScope.empty() && CurAbbrevs.empty() && "Block imbalance");
// Free the BlockInfoRecords.
while (!BlockInfoRecords.empty()) {
BlockInfo &Info = BlockInfoRecords.back();
// Free blockinfo abbrev info.
for (unsigned i = 0, e = static_cast<unsigned>(Info.Abbrevs.size());
i != e; ++i)
Info.Abbrevs[i]->dropRef();
BlockInfoRecords.pop_back();
}
}
/// \brief Retrieve the current position in the stream, in bits.
uint64_t GetCurrentBitNo() const { return GetBufferOffset() * 8 + CurBit; }
//===--------------------------------------------------------------------===//
// Basic Primitives for emitting bits to the stream.
//===--------------------------------------------------------------------===//
void Emit(uint32_t Val, unsigned NumBits) {
assert(NumBits && NumBits <= 32 && "Invalid value size!");
assert((Val & ~(~0U >> (32-NumBits))) == 0 && "High bits set!");
CurValue |= Val << CurBit;
if (CurBit + NumBits < 32) {
CurBit += NumBits;
return;
}
// Add the current word.
WriteWord(CurValue);
if (CurBit)
CurValue = Val >> (32-CurBit);
else
CurValue = 0;
CurBit = (CurBit+NumBits) & 31;
}
void Emit64(uint64_t Val, unsigned NumBits) {
if (NumBits <= 32)
Emit((uint32_t)Val, NumBits);
else {
Emit((uint32_t)Val, 32);
Emit((uint32_t)(Val >> 32), NumBits-32);
}
}
void FlushToWord() {
if (CurBit) {
WriteWord(CurValue);
CurBit = 0;
CurValue = 0;
}
}
void EmitVBR(uint32_t Val, unsigned NumBits) {
uint32_t Threshold = 1U << (NumBits-1);
// Emit the bits with VBR encoding, NumBits-1 bits at a time.
while (Val >= Threshold) {
Emit((Val & ((1 << (NumBits-1))-1)) | (1 << (NumBits-1)), NumBits);
Val >>= NumBits-1;
}
Emit(Val, NumBits);
}
void EmitVBR64(uint64_t Val, unsigned NumBits) {
if ((uint32_t)Val == Val)
return EmitVBR((uint32_t)Val, NumBits);
uint64_t Threshold = 1U << (NumBits-1);
// Emit the bits with VBR encoding, NumBits-1 bits at a time.
while (Val >= Threshold) {
Emit(((uint32_t)Val & ((1 << (NumBits-1))-1)) |
(1 << (NumBits-1)), NumBits);
Val >>= NumBits-1;
}
Emit((uint32_t)Val, NumBits);
}
/// EmitCode - Emit the specified code.
void EmitCode(unsigned Val) {
Emit(Val, CurCodeSize);
}
//===--------------------------------------------------------------------===//
// Block Manipulation
//===--------------------------------------------------------------------===//
/// getBlockInfo - If there is block info for the specified ID, return it,
/// otherwise return null.
BlockInfo *getBlockInfo(unsigned BlockID) {
// Common case, the most recent entry matches BlockID.
if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
return &BlockInfoRecords.back();
for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size());
i != e; ++i)
if (BlockInfoRecords[i].BlockID == BlockID)
return &BlockInfoRecords[i];
return 0;
}
void EnterSubblock(unsigned BlockID, unsigned CodeLen) {
// Block header:
// [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
EmitCode(bitc::ENTER_SUBBLOCK);
EmitVBR(BlockID, bitc::BlockIDWidth);
EmitVBR(CodeLen, bitc::CodeLenWidth);
FlushToWord();
unsigned BlockSizeWordIndex = GetWordIndex();
unsigned OldCodeSize = CurCodeSize;
// Emit a placeholder, which will be replaced when the block is popped.
Emit(0, bitc::BlockSizeWidth);
CurCodeSize = CodeLen;
// Push the outer block's abbrev set onto the stack, start out with an
// empty abbrev set.
BlockScope.push_back(Block(OldCodeSize, BlockSizeWordIndex));
BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);
// If there is a blockinfo for this BlockID, add all the predefined abbrevs
// to the abbrev list.
if (BlockInfo *Info = getBlockInfo(BlockID)) {
for (unsigned i = 0, e = static_cast<unsigned>(Info->Abbrevs.size());
i != e; ++i) {
CurAbbrevs.push_back(Info->Abbrevs[i]);
Info->Abbrevs[i]->addRef();
}
}
}
void ExitBlock() {
assert(!BlockScope.empty() && "Block scope imbalance!");
// Delete all abbrevs.
for (unsigned i = 0, e = static_cast<unsigned>(CurAbbrevs.size());
i != e; ++i)
CurAbbrevs[i]->dropRef();
const Block &B = BlockScope.back();
// Block tail:
// [END_BLOCK, <align4bytes>]
EmitCode(bitc::END_BLOCK);
FlushToWord();
// Compute the size of the block, in words, not counting the size field.
unsigned SizeInWords = GetWordIndex() - B.StartSizeWord - 1;
unsigned ByteNo = B.StartSizeWord*4;
// Update the block size field in the header of this sub-block.
BackpatchWord(ByteNo, SizeInWords);
// Restore the inner block's code size and abbrev table.
CurCodeSize = B.PrevCodeSize;
BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);
BlockScope.pop_back();
}
//===--------------------------------------------------------------------===//
// Record Emission
//===--------------------------------------------------------------------===//
private:
/// EmitAbbreviatedLiteral - Emit a literal value according to its abbrev
/// record. This is a no-op, since the abbrev specifies the literal to use.
template<typename uintty>
void EmitAbbreviatedLiteral(const BitCodeAbbrevOp &Op, uintty V) {
assert(Op.isLiteral() && "Not a literal");
// If the abbrev specifies the literal value to use, don't emit
// anything.
assert(V == Op.getLiteralValue() &&
"Invalid abbrev for record!");
}
/// EmitAbbreviatedField - Emit a single scalar field value with the specified
/// encoding.
template<typename uintty>
void EmitAbbreviatedField(const BitCodeAbbrevOp &Op, uintty V) {
assert(!Op.isLiteral() && "Literals should use EmitAbbreviatedLiteral!");
// Encode the value as we are commanded.
switch (Op.getEncoding()) {
default: llvm_unreachable("Unknown encoding!");
case BitCodeAbbrevOp::Fixed:
if (Op.getEncodingData())
Emit((unsigned)V, (unsigned)Op.getEncodingData());
break;
case BitCodeAbbrevOp::VBR:
if (Op.getEncodingData())
EmitVBR64(V, (unsigned)Op.getEncodingData());
break;
case BitCodeAbbrevOp::Char6:
Emit(BitCodeAbbrevOp::EncodeChar6((char)V), 6);
break;
}
}
/// EmitRecordWithAbbrevImpl - This is the core implementation of the record
/// emission code. If BlobData is non-null, then it specifies an array of
/// data that should be emitted as part of the Blob or Array operand that is
/// known to exist at the end of the record.
template<typename uintty>
void EmitRecordWithAbbrevImpl(unsigned Abbrev, SmallVectorImpl<uintty> &Vals,
StringRef Blob) {
const char *BlobData = Blob.data();
unsigned BlobLen = (unsigned) Blob.size();
unsigned AbbrevNo = Abbrev-bitc::FIRST_APPLICATION_ABBREV;
assert(AbbrevNo < CurAbbrevs.size() && "Invalid abbrev #!");
BitCodeAbbrev *Abbv = CurAbbrevs[AbbrevNo];
EmitCode(Abbrev);
unsigned RecordIdx = 0;
for (unsigned i = 0, e = static_cast<unsigned>(Abbv->getNumOperandInfos());
i != e; ++i) {
const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
if (Op.isLiteral()) {
assert(RecordIdx < Vals.size() && "Invalid abbrev/record");
EmitAbbreviatedLiteral(Op, Vals[RecordIdx]);
++RecordIdx;
} else if (Op.getEncoding() == BitCodeAbbrevOp::Array) {
// Array case.
assert(i+2 == e && "array op not second to last?");
const BitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i);
// If this record has blob data, emit it, otherwise we must have record
// entries to encode this way.
if (BlobData) {
assert(RecordIdx == Vals.size() &&
"Blob data and record entries specified for array!");
// Emit a vbr6 to indicate the number of elements present.
EmitVBR(static_cast<uint32_t>(BlobLen), 6);
// Emit each field.
for (unsigned i = 0; i != BlobLen; ++i)
EmitAbbreviatedField(EltEnc, (unsigned char)BlobData[i]);
// Know that blob data is consumed for assertion below.
BlobData = 0;
} else {
// Emit a vbr6 to indicate the number of elements present.
EmitVBR(static_cast<uint32_t>(Vals.size()-RecordIdx), 6);
// Emit each field.
for (unsigned e = Vals.size(); RecordIdx != e; ++RecordIdx)
EmitAbbreviatedField(EltEnc, Vals[RecordIdx]);
}
} else if (Op.getEncoding() == BitCodeAbbrevOp::Blob) {
// If this record has blob data, emit it, otherwise we must have record
// entries to encode this way.
// Emit a vbr6 to indicate the number of elements present.
if (BlobData) {
EmitVBR(static_cast<uint32_t>(BlobLen), 6);
assert(RecordIdx == Vals.size() &&
"Blob data and record entries specified for blob operand!");
} else {
EmitVBR(static_cast<uint32_t>(Vals.size()-RecordIdx), 6);
}
// Flush to a 32-bit alignment boundary.
FlushToWord();
// Emit each field as a literal byte.
if (BlobData) {
for (unsigned i = 0; i != BlobLen; ++i)
WriteByte((unsigned char)BlobData[i]);
// Know that blob data is consumed for assertion below.
BlobData = 0;
} else {
for (unsigned e = Vals.size(); RecordIdx != e; ++RecordIdx) {
assert(Vals[RecordIdx] < 256 && "Value too large to emit as blob");
WriteByte((unsigned char)Vals[RecordIdx]);
}
}
// Align end to 32-bits.
while (GetBufferOffset() & 3)
WriteByte(0);
} else { // Single scalar field.
assert(RecordIdx < Vals.size() && "Invalid abbrev/record");
EmitAbbreviatedField(Op, Vals[RecordIdx]);
++RecordIdx;
}
}
assert(RecordIdx == Vals.size() && "Not all record operands emitted!");
assert(BlobData == 0 &&
"Blob data specified for record that doesn't use it!");
}
public:
/// EmitRecord - Emit the specified record to the stream, using an abbrev if
/// we have one to compress the output.
template<typename uintty>
void EmitRecord(unsigned Code, SmallVectorImpl<uintty> &Vals,
unsigned Abbrev = 0) {
if (!Abbrev) {
// If we don't have an abbrev to use, emit this in its fully unabbreviated
// form.
EmitCode(bitc::UNABBREV_RECORD);
EmitVBR(Code, 6);
EmitVBR(static_cast<uint32_t>(Vals.size()), 6);
for (unsigned i = 0, e = static_cast<unsigned>(Vals.size()); i != e; ++i)
EmitVBR64(Vals[i], 6);
return;
}
// Insert the code into Vals to treat it uniformly.
Vals.insert(Vals.begin(), Code);
EmitRecordWithAbbrev(Abbrev, Vals);
}
/// EmitRecordWithAbbrev - Emit a record with the specified abbreviation.
/// Unlike EmitRecord, the code for the record should be included in Vals as
/// the first entry.
template<typename uintty>
void EmitRecordWithAbbrev(unsigned Abbrev, SmallVectorImpl<uintty> &Vals) {
EmitRecordWithAbbrevImpl(Abbrev, Vals, StringRef());
}
/// EmitRecordWithBlob - Emit the specified record to the stream, using an
/// abbrev that includes a blob at the end. The blob data to emit is
/// specified by the pointer and length specified at the end. In contrast to
/// EmitRecord, this routine expects that the first entry in Vals is the code
/// of the record.
template<typename uintty>
void EmitRecordWithBlob(unsigned Abbrev, SmallVectorImpl<uintty> &Vals,
StringRef Blob) {
EmitRecordWithAbbrevImpl(Abbrev, Vals, Blob);
}
template<typename uintty>
void EmitRecordWithBlob(unsigned Abbrev, SmallVectorImpl<uintty> &Vals,
const char *BlobData, unsigned BlobLen) {
return EmitRecordWithAbbrevImpl(Abbrev, Vals, StringRef(BlobData, BlobLen));
}
/// EmitRecordWithArray - Just like EmitRecordWithBlob, works with records
/// that end with an array.
template<typename uintty>
void EmitRecordWithArray(unsigned Abbrev, SmallVectorImpl<uintty> &Vals,
StringRef Array) {
EmitRecordWithAbbrevImpl(Abbrev, Vals, Array);
}
template<typename uintty>
void EmitRecordWithArray(unsigned Abbrev, SmallVectorImpl<uintty> &Vals,
const char *ArrayData, unsigned ArrayLen) {
return EmitRecordWithAbbrevImpl(Abbrev, Vals, StringRef(ArrayData,
ArrayLen));
}
//===--------------------------------------------------------------------===//
// Abbrev Emission
//===--------------------------------------------------------------------===//
private:
// Emit the abbreviation as a DEFINE_ABBREV record.
void EncodeAbbrev(BitCodeAbbrev *Abbv) {
EmitCode(bitc::DEFINE_ABBREV);
EmitVBR(Abbv->getNumOperandInfos(), 5);
for (unsigned i = 0, e = static_cast<unsigned>(Abbv->getNumOperandInfos());
i != e; ++i) {
const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
Emit(Op.isLiteral(), 1);
if (Op.isLiteral()) {
EmitVBR64(Op.getLiteralValue(), 8);
} else {
Emit(Op.getEncoding(), 3);
if (Op.hasEncodingData())
EmitVBR64(Op.getEncodingData(), 5);
}
}
}
public:
/// EmitAbbrev - This emits an abbreviation to the stream. Note that this
/// method takes ownership of the specified abbrev.
unsigned EmitAbbrev(BitCodeAbbrev *Abbv) {
// Emit the abbreviation as a record.
EncodeAbbrev(Abbv);
CurAbbrevs.push_back(Abbv);
return static_cast<unsigned>(CurAbbrevs.size())-1 +
bitc::FIRST_APPLICATION_ABBREV;
}
//===--------------------------------------------------------------------===//
// BlockInfo Block Emission
//===--------------------------------------------------------------------===//
/// EnterBlockInfoBlock - Start emitting the BLOCKINFO_BLOCK.
void EnterBlockInfoBlock(unsigned CodeWidth) {
EnterSubblock(bitc::BLOCKINFO_BLOCK_ID, CodeWidth);
BlockInfoCurBID = ~0U;
}
private:
/// SwitchToBlockID - If we aren't already talking about the specified block
/// ID, emit a BLOCKINFO_CODE_SETBID record.
void SwitchToBlockID(unsigned BlockID) {
if (BlockInfoCurBID == BlockID) return;
SmallVector<unsigned, 2> V;
V.push_back(BlockID);
EmitRecord(bitc::BLOCKINFO_CODE_SETBID, V);
BlockInfoCurBID = BlockID;
}
BlockInfo &getOrCreateBlockInfo(unsigned BlockID) {
if (BlockInfo *BI = getBlockInfo(BlockID))
return *BI;
// Otherwise, add a new record.
BlockInfoRecords.push_back(BlockInfo());
BlockInfoRecords.back().BlockID = BlockID;
return BlockInfoRecords.back();
}
public:
/// EmitBlockInfoAbbrev - Emit a DEFINE_ABBREV record for the specified
/// BlockID.
unsigned EmitBlockInfoAbbrev(unsigned BlockID, BitCodeAbbrev *Abbv) {
SwitchToBlockID(BlockID);
EncodeAbbrev(Abbv);
// Add the abbrev to the specified block record.
BlockInfo &Info = getOrCreateBlockInfo(BlockID);
Info.Abbrevs.push_back(Abbv);
return Info.Abbrevs.size()-1+bitc::FIRST_APPLICATION_ABBREV;
}
};
} // End llvm namespace
#endif
