Define the content-independent interfaces to read/write bitcode files and

the high-level interface to read/write LLVM IR bitcode files.

This is a work in progress.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36329 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Bitcode/BitstreamReader.h

@@ -0,0 +1,220 @@
+//===- 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"
+#include "llvm/ADT/SmallVector.h"
+#include <cassert>
+
+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;
+  
+  /// BlockScope - This tracks the codesize of parent blocks.
+  SmallVector<unsigned, 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;
+  }
+  
+  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;
+  }
+  
+  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(CurCodeSize);
+    
+    // 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();
+    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;
+    }
+    
+    assert(0 && "Reading with abbrevs not implemented!");
+  }
+  
+};
+
+} // End llvm namespace
+
+#endif
+
+