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