X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;ds=sidebyside;f=include%2Fllvm%2FBitcode%2FBitstreamReader.h;h=c0cf6cde887f12d032256a9ffb4472e8bd0dbfc0;hb=1f05ba2fcb8063468aabfc81c9a82b8da211bb6c;hp=e55910b27ae4a31b8dfaca18327cd5c659f48d94;hpb=ffa1ff16d77f76ef86b696eeec383b3f7c380397;p=oota-llvm.git

diff --git a/include/llvm/Bitcode/BitstreamReader.h b/include/llvm/Bitcode/BitstreamReader.h
index e55910b27ae..c0cf6cde887 100644
--- a/include/llvm/Bitcode/BitstreamReader.h
+++ b/include/llvm/Bitcode/BitstreamReader.h
@@ -12,54 +12,66 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef BITSTREAM_READER_H
-#define BITSTREAM_READER_H
+#ifndef LLVM_BITCODE_BITSTREAMREADER_H
+#define LLVM_BITCODE_BITSTREAMREADER_H
 
-#include "llvm/ADT/OwningPtr.h"
 #include "llvm/Bitcode/BitCodes.h"
-#include "llvm/Support/StreamableMemoryObject.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/StreamingMemoryObject.h"
 #include <climits>
 #include <string>
 #include <vector>
 
 namespace llvm {
 
-  class Deserializer;
-
+/// This class is used to read from an LLVM bitcode stream, maintaining
+/// information that is global to decoding the entire file. While a file is
+/// being read, multiple cursors can be independently advanced or skipped around
+/// within the file.  These are represented by the BitstreamCursor class.
 class BitstreamReader {
 public:
-  /// BlockInfo - This contains information emitted to BLOCKINFO_BLOCK blocks.
-  /// These describe abbreviations that all blocks of the specified ID inherit.
+  /// 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<IntrusiveRefCntPtr<BitCodeAbbrev>> Abbrevs;
     std::string Name;
-    
+
     std::vector<std::pair<unsigned, std::string> > RecordNames;
   };
 private:
-  OwningPtr<StreamableMemoryObject> BitcodeBytes;
-  
+  std::unique_ptr<MemoryObject> BitcodeBytes;
+
   std::vector<BlockInfo> BlockInfoRecords;
 
-  /// IgnoreBlockInfoNames - This is set to true if we don't care about the
-  /// block/record name information in the BlockInfo block. Only llvm-bcanalyzer
-  /// uses this.
+  /// This is set to true if we don't care about the block/record name
+  /// information in the BlockInfo block. Only llvm-bcanalyzer uses this.
   bool IgnoreBlockInfoNames;
-  
-  BitstreamReader(const BitstreamReader&);  // DO NOT IMPLEMENT
-  void operator=(const BitstreamReader&);  // DO NOT IMPLEMENT
+
+  BitstreamReader(const BitstreamReader&) = delete;
+  void operator=(const BitstreamReader&) = delete;
 public:
   BitstreamReader() : IgnoreBlockInfoNames(true) {
   }
 
-  BitstreamReader(const unsigned char *Start, const unsigned char *End) {
-    IgnoreBlockInfoNames = true;
+  BitstreamReader(const unsigned char *Start, const unsigned char *End)
+      : IgnoreBlockInfoNames(true) {
     init(Start, End);
   }
 
-  BitstreamReader(StreamableMemoryObject *bytes) {
-    BitcodeBytes.reset(bytes);
+  BitstreamReader(std::unique_ptr<MemoryObject> BitcodeBytes)
+      : BitcodeBytes(std::move(BitcodeBytes)), IgnoreBlockInfoNames(true) {}
+
+  BitstreamReader(BitstreamReader &&Other) {
+    *this = std::move(Other);
+  }
+
+  BitstreamReader &operator=(BitstreamReader &&Other) {
+    BitcodeBytes = std::move(Other.BitcodeBytes);
+    // Explicitly swap block info, so that nothing gets destroyed twice.
+    std::swap(BlockInfoRecords, Other.BlockInfoRecords);
+    IgnoreBlockInfoNames = Other.IgnoreBlockInfoNames;
+    return *this;
   }
 
   void init(const unsigned char *Start, const unsigned char *End) {
@@ -67,36 +79,23 @@ public:
     BitcodeBytes.reset(getNonStreamedMemoryObject(Start, End));
   }
 
-  StreamableMemoryObject &getBitcodeBytes() { return *BitcodeBytes; }
-
-  ~BitstreamReader() {
-    // 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();
-    }
-  }
+  MemoryObject &getBitcodeBytes() { return *BitcodeBytes; }
 
-  /// CollectBlockInfoNames - This is called by clients that want block/record
-  /// name information.
+  /// This is called by clients that want block/record name information.
   void CollectBlockInfoNames() { IgnoreBlockInfoNames = false; }
   bool isIgnoringBlockInfoNames() { return IgnoreBlockInfoNames; }
-  
+
   //===--------------------------------------------------------------------===//
   // Block Manipulation
   //===--------------------------------------------------------------------===//
 
-  /// hasBlockInfoRecords - Return true if we've already read and processed the
-  /// block info block for this Bitstream.  We only process it for the first
-  /// cursor that walks over it.
+  /// Return true if we've already read and processed the block info block for
+  /// this Bitstream. We only process it for the first cursor that walks over
+  /// it.
   bool hasBlockInfoRecords() const { return !BlockInfoRecords.empty(); }
-  
-  /// getBlockInfo - If there is block info for the specified ID, return it,
-  /// otherwise return null.
+
+  /// If there is block info for the specified ID, return it, otherwise return
+  /// null.
   const BlockInfo *getBlockInfo(unsigned BlockID) const {
     // Common case, the most recent entry matches BlockID.
     if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
@@ -106,7 +105,7 @@ public:
          i != e; ++i)
       if (BlockInfoRecords[i].BlockID == BlockID)
         return &BlockInfoRecords[i];
-    return 0;
+    return nullptr;
   }
 
   BlockInfo &getOrCreateBlockInfo(unsigned BlockID) {
@@ -114,120 +113,108 @@ public:
       return *const_cast<BlockInfo*>(BI);
 
     // Otherwise, add a new record.
-    BlockInfoRecords.push_back(BlockInfo());
+    BlockInfoRecords.emplace_back();
     BlockInfoRecords.back().BlockID = BlockID;
     return BlockInfoRecords.back();
   }
 
+  /// Takes block info from the other bitstream reader.
+  ///
+  /// This is a "take" operation because BlockInfo records are non-trivial, and
+  /// indeed rather expensive.
+  void takeBlockInfo(BitstreamReader &&Other) {
+    assert(!hasBlockInfoRecords());
+    BlockInfoRecords = std::move(Other.BlockInfoRecords);
+  }
+};
+
+/// When advancing through a bitstream cursor, each advance can discover a few
+/// different kinds of entries:
+struct BitstreamEntry {
+  enum {
+    Error,    // Malformed bitcode was found.
+    EndBlock, // We've reached the end of the current block, (or the end of the
+              // file, which is treated like a series of EndBlock records.
+    SubBlock, // This is the start of a new subblock of a specific ID.
+    Record    // This is a record with a specific AbbrevID.
+  } Kind;
+
+  unsigned ID;
+
+  static BitstreamEntry getError() {
+    BitstreamEntry E; E.Kind = Error; return E;
+  }
+  static BitstreamEntry getEndBlock() {
+    BitstreamEntry E; E.Kind = EndBlock; return E;
+  }
+  static BitstreamEntry getSubBlock(unsigned ID) {
+    BitstreamEntry E; E.Kind = SubBlock; E.ID = ID; return E;
+  }
+  static BitstreamEntry getRecord(unsigned AbbrevID) {
+    BitstreamEntry E; E.Kind = Record; E.ID = AbbrevID; return E;
+  }
 };
 
+/// This represents a position within a bitcode file. There may be multiple
+/// independent cursors reading within one bitstream, each maintaining their own
+/// local state.
+///
+/// Unlike iterators, BitstreamCursors are heavy-weight objects that should not
+/// be passed by value.
 class BitstreamCursor {
-  friend class Deserializer;
   BitstreamReader *BitStream;
   size_t NextChar;
-  
-  /// 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.
+
+  // The size of the bicode. 0 if we don't know it yet.
+  size_t Size;
+
+  /// This is the current data we have pulled from the stream but have not
+  /// returned to the client. This is specifically and intentionally defined to
+  /// follow the word size of the host machine for efficiency. We use word_t in
+  /// places that are aware of this to make it perfectly explicit what is going
+  /// on.
+  typedef size_t word_t;
+  word_t CurWord;
+
+  /// This is the number of bits in CurWord that are valid. This is always from
+  /// [0...bits_of(size_t)-1] inclusive.
   unsigned BitsInCurWord;
-  
-  // CurCodeSize - This is the declared size of code values used for the current
-  // block, in bits.
+
+  // 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;
-  
+
+  /// Abbrevs installed at in this block.
+  std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> CurAbbrevs;
+
   struct Block {
     unsigned PrevCodeSize;
-    std::vector<BitCodeAbbrev*> PrevAbbrevs;
+    std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> PrevAbbrevs;
     explicit Block(unsigned PCS) : PrevCodeSize(PCS) {}
   };
-  
-  /// BlockScope - This tracks the codesize of parent blocks.
+
+  /// This tracks the codesize of parent blocks.
   SmallVector<Block, 8> BlockScope;
-  
+
+
 public:
-  BitstreamCursor() : BitStream(0), NextChar(0) {
-  }
-  BitstreamCursor(const BitstreamCursor &RHS) : BitStream(0), NextChar(0) {
-    operator=(RHS);
-  }
-  
-  explicit BitstreamCursor(BitstreamReader &R) : BitStream(&R) {
-    NextChar = 0;
-    CurWord = 0;
-    BitsInCurWord = 0;
-    CurCodeSize = 2;
-  }
-  
-  void init(BitstreamReader &R) {
+  static const size_t MaxChunkSize = sizeof(word_t) * 8;
+
+  BitstreamCursor() { init(nullptr); }
+
+  explicit BitstreamCursor(BitstreamReader &R) { init(&R); }
+
+  void init(BitstreamReader *R) {
     freeState();
-    
-    BitStream = &R;
+
+    BitStream = R;
     NextChar = 0;
-    CurWord = 0;
+    Size = 0;
     BitsInCurWord = 0;
     CurCodeSize = 2;
   }
-  
-  ~BitstreamCursor() {
-    freeState();
-  }
-  
-  void operator=(const BitstreamCursor &RHS) {
-    freeState();
-    
-    BitStream = RHS.BitStream;
-    NextChar = RHS.NextChar;
-    CurWord = RHS.CurWord;
-    BitsInCurWord = RHS.BitsInCurWord;
-    CurCodeSize = RHS.CurCodeSize;
-    
-    // Copy abbreviations, and bump ref counts.
-    CurAbbrevs = RHS.CurAbbrevs;
-    for (unsigned i = 0, e = static_cast<unsigned>(CurAbbrevs.size());
-         i != e; ++i)
-      CurAbbrevs[i]->addRef();
-    
-    // Copy block scope and bump ref counts.
-    BlockScope = RHS.BlockScope;
-    for (unsigned S = 0, e = static_cast<unsigned>(BlockScope.size());
-         S != e; ++S) {
-      std::vector<BitCodeAbbrev*> &Abbrevs = BlockScope[S].PrevAbbrevs;
-      for (unsigned i = 0, e = static_cast<unsigned>(Abbrevs.size());
-           i != e; ++i)
-        Abbrevs[i]->addRef();
-    }
-  }
-  
-  void freeState() {
-    // Free all the Abbrevs.
-    for (unsigned i = 0, e = static_cast<unsigned>(CurAbbrevs.size());
-         i != e; ++i)
-      CurAbbrevs[i]->dropRef();
-    CurAbbrevs.clear();
-    
-    // Free all the Abbrevs in the block scope.
-    for (unsigned S = 0, e = static_cast<unsigned>(BlockScope.size());
-         S != e; ++S) {
-      std::vector<BitCodeAbbrev*> &Abbrevs = BlockScope[S].PrevAbbrevs;
-      for (unsigned i = 0, e = static_cast<unsigned>(Abbrevs.size());
-           i != e; ++i)
-        Abbrevs[i]->dropRef();
-    }
-    BlockScope.clear();
-  }
-  
-  /// GetAbbrevIDWidth - Return the number of bits used to encode an abbrev #.
-  unsigned GetAbbrevIDWidth() const { return CurCodeSize; }
-  
-  bool isEndPos(size_t pos) {
-    return BitStream->getBitcodeBytes().isObjectEnd(static_cast<uint64_t>(pos));
-  }
+
+  void freeState();
 
   bool canSkipToPos(size_t pos) const {
     // pos can be skipped to if it is a valid address or one byte past the end.
@@ -235,100 +222,162 @@ public:
         static_cast<uint64_t>(pos - 1));
   }
 
-  unsigned char getByte(size_t pos) {
-    uint8_t byte = -1;
-    BitStream->getBitcodeBytes().readByte(pos, &byte);
-    return byte;
+  bool AtEndOfStream() {
+    if (BitsInCurWord != 0)
+      return false;
+    if (Size != 0)
+      return Size == NextChar;
+    fillCurWord();
+    return BitsInCurWord == 0;
   }
 
-  uint32_t getWord(size_t pos) {
-    uint32_t word = -1;
-    BitStream->getBitcodeBytes().readBytes(pos,
-                                           sizeof(word),
-                                           reinterpret_cast<uint8_t *>(&word),
-                                           NULL);
-    return word;
-  }
+  /// Return the number of bits used to encode an abbrev #.
+  unsigned getAbbrevIDWidth() const { return CurCodeSize; }
 
-  bool AtEndOfStream() {
-    return isEndPos(NextChar) && BitsInCurWord == 0;
-  }
-  
-  /// GetCurrentBitNo - Return the bit # of the bit we are reading.
+  /// Return the bit # of the bit we are reading.
   uint64_t GetCurrentBitNo() const {
     return NextChar*CHAR_BIT - BitsInCurWord;
   }
-  
+
   BitstreamReader *getBitStreamReader() {
     return BitStream;
   }
   const BitstreamReader *getBitStreamReader() const {
     return BitStream;
   }
-  
-  
-  /// JumpToBit - Reset the stream to the specified bit number.
+
+  /// Flags that modify the behavior of advance().
+  enum {
+    /// If this flag is used, the advance() method does not automatically pop
+    /// the block scope when the end of a block is reached.
+    AF_DontPopBlockAtEnd = 1,
+
+    /// If this flag is used, abbrev entries are returned just like normal
+    /// records.
+    AF_DontAutoprocessAbbrevs = 2
+  };
+
+  /// Advance the current bitstream, returning the next entry in the stream.
+  BitstreamEntry advance(unsigned Flags = 0) {
+    while (1) {
+      unsigned Code = ReadCode();
+      if (Code == bitc::END_BLOCK) {
+        // Pop the end of the block unless Flags tells us not to.
+        if (!(Flags & AF_DontPopBlockAtEnd) && ReadBlockEnd())
+          return BitstreamEntry::getError();
+        return BitstreamEntry::getEndBlock();
+      }
+
+      if (Code == bitc::ENTER_SUBBLOCK)
+        return BitstreamEntry::getSubBlock(ReadSubBlockID());
+
+      if (Code == bitc::DEFINE_ABBREV &&
+          !(Flags & AF_DontAutoprocessAbbrevs)) {
+        // We read and accumulate abbrev's, the client can't do anything with
+        // them anyway.
+        ReadAbbrevRecord();
+        continue;
+      }
+
+      return BitstreamEntry::getRecord(Code);
+    }
+  }
+
+  /// This is a convenience function for clients that don't expect any
+  /// subblocks. This just skips over them automatically.
+  BitstreamEntry advanceSkippingSubblocks(unsigned Flags = 0) {
+    while (1) {
+      // If we found a normal entry, return it.
+      BitstreamEntry Entry = advance(Flags);
+      if (Entry.Kind != BitstreamEntry::SubBlock)
+        return Entry;
+
+      // If we found a sub-block, just skip over it and check the next entry.
+      if (SkipBlock())
+        return BitstreamEntry::getError();
+    }
+  }
+
+  /// Reset the stream to the specified bit number.
   void JumpToBit(uint64_t BitNo) {
-    uintptr_t ByteNo = uintptr_t(BitNo/8) & ~3;
-    uintptr_t WordBitNo = uintptr_t(BitNo) & 31;
+    size_t ByteNo = size_t(BitNo/8) & ~(sizeof(word_t)-1);
+    unsigned WordBitNo = unsigned(BitNo & (sizeof(word_t)*8-1));
     assert(canSkipToPos(ByteNo) && "Invalid location");
-    
+
     // Move the cursor to the right word.
     NextChar = ByteNo;
     BitsInCurWord = 0;
-    CurWord = 0;
-    
+
     // Skip over any bits that are already consumed.
     if (WordBitNo)
-      Read(static_cast<unsigned>(WordBitNo));
+      Read(WordBitNo);
   }
-  
-  
-  uint32_t Read(unsigned NumBits) {
-    assert(NumBits <= 32 && "Cannot return more than 32 bits!");
+
+  void fillCurWord() {
+    if (Size != 0 && NextChar >= Size)
+      report_fatal_error("Unexpected end of file");
+
+    // Read the next word from the stream.
+    uint8_t Array[sizeof(word_t)] = {0};
+
+    uint64_t BytesRead =
+        BitStream->getBitcodeBytes().readBytes(Array, sizeof(Array), NextChar);
+
+    // If we run out of data, stop at the end of the stream.
+    if (BytesRead == 0) {
+      CurWord = 0;
+      BitsInCurWord = 0;
+      Size = NextChar;
+      return;
+    }
+
+    CurWord =
+        support::endian::read<word_t, support::little, support::unaligned>(
+            Array);
+    NextChar += BytesRead;
+    BitsInCurWord = BytesRead * 8;
+  }
+
+  word_t Read(unsigned NumBits) {
+    static const unsigned BitsInWord = MaxChunkSize;
+
+    assert(NumBits && NumBits <= BitsInWord &&
+           "Cannot return zero or more than BitsInWord bits!");
+
+    static const unsigned Mask = sizeof(word_t) > 4 ? 0x3f : 0x1f;
+
     // If the field is fully contained by CurWord, return it quickly.
     if (BitsInCurWord >= NumBits) {
-      uint32_t R = CurWord & ((1U << NumBits)-1);
-      CurWord >>= NumBits;
+      word_t R = CurWord & (~word_t(0) >> (BitsInWord - NumBits));
+
+      // Use a mask to avoid undefined behavior.
+      CurWord >>= (NumBits & Mask);
+
       BitsInCurWord -= NumBits;
       return R;
     }
 
+    word_t R = BitsInCurWord ? CurWord : 0;
+    unsigned BitsLeft = NumBits - BitsInCurWord;
+
+    fillCurWord();
+
     // If we run out of data, stop at the end of the stream.
-    if (isEndPos(NextChar)) {
-      CurWord = 0;
-      BitsInCurWord = 0;
+    if (BitsLeft > BitsInCurWord)
       return 0;
-    }
 
-    unsigned R = CurWord;
+    word_t R2 = CurWord & (~word_t(0) >> (BitsInWord - BitsLeft));
 
-    // Read the next word from the stream.
-    CurWord = getWord(NextChar);
-    NextChar += 4;
+    // Use a mask to avoid undefined behavior.
+    CurWord >>= (BitsLeft & Mask);
 
-    // Extract NumBits-BitsInCurWord from what we just read.
-    unsigned BitsLeft = NumBits-BitsInCurWord;
+    BitsInCurWord -= BitsLeft;
 
-    // Be careful here, BitsLeft is in the range [1..32] inclusive.
-    R |= (CurWord & (~0U >> (32-BitsLeft))) << BitsInCurWord;
+    R |= R2 << (NumBits - BitsLeft);
 
-    // 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)
@@ -347,8 +396,8 @@ public:
     }
   }
 
-  // ReadVBR64 - Read a VBR that may have a value up to 64-bits in size.  The
-  // chunk size of the VBR must still be <= 32 bits though.
+  // Read a VBR that may have a value up to 64-bits in size. The chunk size of
+  // the VBR must still be <= 32 bits though.
   uint64_t ReadVBR64(unsigned NumBits) {
     uint32_t Piece = Read(NumBits);
     if ((Piece & (1U << (NumBits-1))) == 0)
@@ -367,10 +416,20 @@ public:
     }
   }
 
-  void SkipToWord() {
+private:
+  void SkipToFourByteBoundary() {
+    // If word_t is 64-bits and if we've read less than 32 bits, just dump
+    // the bits we have up to the next 32-bit boundary.
+    if (sizeof(word_t) > 4 &&
+        BitsInCurWord >= 32) {
+      CurWord >>= BitsInCurWord-32;
+      BitsInCurWord = 32;
+      return;
+    }
+
     BitsInCurWord = 0;
-    CurWord = 0;
   }
+public:
 
   unsigned ReadCode() {
     return Read(CurCodeSize);
@@ -380,287 +439,81 @@ public:
   // Block header:
   //    [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
 
-  /// ReadSubBlockID - Having read the ENTER_SUBBLOCK code, read the BlockID for
-  /// the block.
+  /// 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.
+  /// 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);
+    SkipToFourByteBoundary();
+    unsigned NumFourBytes = Read(bitc::BlockSizeWidth);
 
     // Check that the block wasn't partially defined, and that the offset isn't
     // bogus.
-    size_t SkipTo = NextChar + NumWords*4;
-    if (AtEndOfStream() || !canSkipToPos(SkipTo))
+    size_t SkipTo = GetCurrentBitNo() + NumFourBytes*4*8;
+    if (AtEndOfStream() || !canSkipToPos(SkipTo/8))
       return true;
 
-    NextChar = SkipTo;
+    JumpToBit(SkipTo);
     return false;
   }
 
-  /// EnterSubBlock - Having read the ENTER_SUBBLOCK abbrevid, enter
-  /// the block, and return true if the block is valid.
-  bool EnterSubBlock(unsigned BlockID, unsigned *NumWordsP = 0) {
-    // Save the current block's state on BlockScope.
-    BlockScope.push_back(Block(CurCodeSize));
-    BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);
-
-    // Add the abbrevs specific to this block to the CurAbbrevs list.
-    if (const BitstreamReader::BlockInfo *Info =
-          BitStream->getBlockInfo(BlockID)) {
-      for (unsigned i = 0, e = static_cast<unsigned>(Info->Abbrevs.size());
-           i != e; ++i) {
-        CurAbbrevs.push_back(Info->Abbrevs[i]);
-        CurAbbrevs.back()->addRef();
-      }
-    }
-
-    // Get the codesize of this block.
-    CurCodeSize = ReadVBR(bitc::CodeLenWidth);
-    SkipToWord();
-    unsigned NumWords = Read(bitc::BlockSizeWidth);
-    if (NumWordsP) *NumWordsP = NumWords;
-
-    // Validate that this block is sane.
-    if (CurCodeSize == 0 || AtEndOfStream())
-      return true;
-
-    return false;
-  }
+  /// Having read the ENTER_SUBBLOCK abbrevid, enter the block, and return true
+  /// if the block has an error.
+  bool EnterSubBlock(unsigned BlockID, unsigned *NumWordsP = nullptr);
 
   bool ReadBlockEnd() {
     if (BlockScope.empty()) return true;
 
     // Block tail:
     //    [END_BLOCK, <align4bytes>]
-    SkipToWord();
+    SkipToFourByteBoundary();
 
-    PopBlockScope();
+    popBlockScope();
     return false;
   }
 
 private:
-  void PopBlockScope() {
-    CurCodeSize = BlockScope.back().PrevCodeSize;
 
-    // Delete abbrevs from popped scope.
-    for (unsigned i = 0, e = static_cast<unsigned>(CurAbbrevs.size());
-         i != e; ++i)
-      CurAbbrevs[i]->dropRef();
+  void popBlockScope() {
+    CurCodeSize = BlockScope.back().PrevCodeSize;
 
-    BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);
+    CurAbbrevs = std::move(BlockScope.back().PrevAbbrevs);
     BlockScope.pop_back();
   }
 
- //===--------------------------------------------------------------------===//
+  //===--------------------------------------------------------------------===//
   // Record Processing
   //===--------------------------------------------------------------------===//
 
-private:
-  void ReadAbbreviatedLiteral(const BitCodeAbbrevOp &Op,
-                              SmallVectorImpl<uint64_t> &Vals) {
-    assert(Op.isLiteral() && "Not a literal");
-    // If the abbrev specifies the literal value to use, use it.
-    Vals.push_back(Op.getLiteralValue());
-  }
-  
-  void ReadAbbreviatedField(const BitCodeAbbrevOp &Op,
-                            SmallVectorImpl<uint64_t> &Vals) {
-    assert(!Op.isLiteral() && "Use ReadAbbreviatedLiteral for literals!");
-
-    // Decode the value as we are commanded.
-    switch (Op.getEncoding()) {
-    default: llvm_unreachable("Unknown encoding!");
-    case BitCodeAbbrevOp::Fixed:
-      Vals.push_back(Read((unsigned)Op.getEncodingData()));
-      break;
-    case BitCodeAbbrevOp::VBR:
-      Vals.push_back(ReadVBR64((unsigned)Op.getEncodingData()));
-      break;
-    case BitCodeAbbrevOp::Char6:
-      Vals.push_back(BitCodeAbbrevOp::DecodeChar6(Read(6)));
-      break;
-    }
-  }
 public:
-
-  /// getAbbrev - Return the abbreviation for the specified AbbrevId. 
+  /// Return the abbreviation for the specified AbbrevId.
   const BitCodeAbbrev *getAbbrev(unsigned AbbrevID) {
-    unsigned AbbrevNo = AbbrevID-bitc::FIRST_APPLICATION_ABBREV;
-    assert(AbbrevNo < CurAbbrevs.size() && "Invalid abbrev #!");
-    return CurAbbrevs[AbbrevNo];
-  }
-  
-  unsigned ReadRecord(unsigned AbbrevID, SmallVectorImpl<uint64_t> &Vals,
-                      const char **BlobStart = 0, unsigned *BlobLen = 0) {
-    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;
-    }
-
-    const BitCodeAbbrev *Abbv = getAbbrev(AbbrevID);
-
-    for (unsigned i = 0, e = Abbv->getNumOperandInfos(); i != e; ++i) {
-      const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
-      if (Op.isLiteral()) {
-        ReadAbbreviatedLiteral(Op, Vals); 
-      } else if (Op.getEncoding() == BitCodeAbbrevOp::Array) {
-        // Array case.  Read the number of elements as a vbr6.
-        unsigned NumElts = ReadVBR(6);
-
-        // Get the element encoding.
-        assert(i+2 == e && "array op not second to last?");
-        const BitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i);
-
-        // Read all the elements.
-        for (; NumElts; --NumElts)
-          ReadAbbreviatedField(EltEnc, Vals);
-      } else if (Op.getEncoding() == BitCodeAbbrevOp::Blob) {
-        // Blob case.  Read the number of bytes as a vbr6.
-        unsigned NumElts = ReadVBR(6);
-        SkipToWord();  // 32-bit alignment
-
-        // Figure out where the end of this blob will be including tail padding.
-        size_t NewEnd = NextChar+((NumElts+3)&~3);
-        
-        // If this would read off the end of the bitcode file, just set the
-        // record to empty and return.
-        if (!canSkipToPos(NewEnd)) {
-          Vals.append(NumElts, 0);
-          NextChar = BitStream->getBitcodeBytes().getExtent();
-          break;
-        }
-        
-        // Otherwise, read the number of bytes.  If we can return a reference to
-        // the data, do so to avoid copying it.
-        if (BlobStart) {
-          *BlobStart = (const char*)BitStream->getBitcodeBytes().getPointer(
-              NextChar, NumElts);
-          *BlobLen = NumElts;
-        } else {
-          for (; NumElts; ++NextChar, --NumElts)
-            Vals.push_back(getByte(NextChar));
-        }
-        // Skip over tail padding.
-        NextChar = NewEnd;
-      } else {
-        ReadAbbreviatedField(Op, Vals);
-      }
-    }
-
-    unsigned Code = (unsigned)Vals[0];
-    Vals.erase(Vals.begin());
-    return Code;
+    unsigned AbbrevNo = AbbrevID - bitc::FIRST_APPLICATION_ABBREV;
+    if (AbbrevNo >= CurAbbrevs.size())
+      report_fatal_error("Invalid abbrev number");
+    return CurAbbrevs[AbbrevNo].get();
   }
 
-  unsigned ReadRecord(unsigned AbbrevID, SmallVectorImpl<uint64_t> &Vals,
-                      const char *&BlobStart, unsigned &BlobLen) {
-    return ReadRecord(AbbrevID, Vals, &BlobStart, &BlobLen);
-  }
+  /// Read the current record and discard it.
+  void skipRecord(unsigned AbbrevID);
+
+  unsigned readRecord(unsigned AbbrevID, SmallVectorImpl<uint64_t> &Vals,
+                      StringRef *Blob = nullptr);
 
-  
   //===--------------------------------------------------------------------===//
   // Abbrev Processing
   //===--------------------------------------------------------------------===//
+  void ReadAbbrevRecord();
 
-  void ReadAbbrevRecord() {
-    BitCodeAbbrev *Abbv = new BitCodeAbbrev();
-    unsigned NumOpInfo = ReadVBR(5);
-    for (unsigned i = 0; i != NumOpInfo; ++i) {
-      bool IsLiteral = Read(1) ? true : false;
-      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
-        Abbv->Add(BitCodeAbbrevOp(E));
-    }
-    CurAbbrevs.push_back(Abbv);
-  }
-  
-public:
-
-  bool ReadBlockInfoBlock() {
-    // If this is the second stream to get to the block info block, skip it.
-    if (BitStream->hasBlockInfoRecords())
-      return SkipBlock();
-    
-    if (EnterSubBlock(bitc::BLOCKINFO_BLOCK_ID)) return true;
-
-    SmallVector<uint64_t, 64> Record;
-    BitstreamReader::BlockInfo *CurBlockInfo = 0;
-
-    // Read all the records for this module.
-    while (1) {
-      unsigned Code = ReadCode();
-      if (Code == bitc::END_BLOCK)
-        return ReadBlockEnd();
-      if (Code == bitc::ENTER_SUBBLOCK) {
-        ReadSubBlockID();
-        if (SkipBlock()) return true;
-        continue;
-      }
-
-      // Read abbrev records, associate them with CurBID.
-      if (Code == bitc::DEFINE_ABBREV) {
-        if (!CurBlockInfo) return true;
-        ReadAbbrevRecord();
-
-        // ReadAbbrevRecord installs the abbrev in CurAbbrevs.  Move it to the
-        // appropriate BlockInfo.
-        BitCodeAbbrev *Abbv = CurAbbrevs.back();
-        CurAbbrevs.pop_back();
-        CurBlockInfo->Abbrevs.push_back(Abbv);
-        continue;
-      }
-
-      // Read a record.
-      Record.clear();
-      switch (ReadRecord(Code, Record)) {
-      default: break;  // Default behavior, ignore unknown content.
-      case bitc::BLOCKINFO_CODE_SETBID:
-        if (Record.size() < 1) return true;
-        CurBlockInfo = &BitStream->getOrCreateBlockInfo((unsigned)Record[0]);
-        break;
-      case bitc::BLOCKINFO_CODE_BLOCKNAME: {
-        if (!CurBlockInfo) return true;
-        if (BitStream->isIgnoringBlockInfoNames()) break;  // Ignore name.
-        std::string Name;
-        for (unsigned i = 0, e = Record.size(); i != e; ++i)
-          Name += (char)Record[i];
-        CurBlockInfo->Name = Name;
-        break;
-      }
-      case bitc::BLOCKINFO_CODE_SETRECORDNAME: {
-        if (!CurBlockInfo) return true;
-        if (BitStream->isIgnoringBlockInfoNames()) break;  // Ignore name.
-        std::string Name;
-        for (unsigned i = 1, e = Record.size(); i != e; ++i)
-          Name += (char)Record[i];
-        CurBlockInfo->RecordNames.push_back(std::make_pair((unsigned)Record[0],
-                                                           Name));
-        break;
-      }
-      }
-    }
-  }
+  bool ReadBlockInfoBlock();
 };
-  
+
 } // End llvm namespace
 
 #endif