lib/Bytecode/Reader/Reader.cpp

//===- Reader.cpp - Code to read bytecode files ---------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This library implements the functionality defined in llvm/Bytecode/Reader.h
//
// Note that this library should be as fast as possible, reentrant, and
// threadsafe!!
//
// TODO: Allow passing in an option to ignore the symbol table
//
//===----------------------------------------------------------------------===//

#include "Reader.h"
#include "llvm/Assembly/AutoUpgrade.h"
#include "llvm/Bytecode/BytecodeHandler.h"
#include "llvm/BasicBlock.h"
#include "llvm/CallingConv.h"
#include "llvm/Constants.h"
#include "llvm/InlineAsm.h"
#include "llvm/Instructions.h"
#include "llvm/SymbolTable.h"
#include "llvm/Bytecode/Format.h"
#include "llvm/Config/alloca.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/Compressor.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/ADT/StringExtras.h"
#include <sstream>
#include <algorithm>
using namespace llvm;

namespace {
  /// @brief A class for maintaining the slot number definition
  /// as a placeholder for the actual definition for forward constants defs.
  class ConstantPlaceHolder : public ConstantExpr {
    ConstantPlaceHolder();                       // DO NOT IMPLEMENT
    void operator=(const ConstantPlaceHolder &); // DO NOT IMPLEMENT
  public:
    Use Op;
    ConstantPlaceHolder(const Type *Ty)
      : ConstantExpr(Ty, Instruction::UserOp1, &Op, 1),
        Op(UndefValue::get(Type::IntTy), this) {
    }
  };
}

// Provide some details on error
inline void BytecodeReader::error(const std::string& err) {
  ErrorMsg = err + " (Vers=" + itostr(RevisionNum) + ", Pos=" 
    + itostr(At-MemStart) + ")";
  longjmp(context,1);
}

//===----------------------------------------------------------------------===//
// Bytecode Reading Methods
//===----------------------------------------------------------------------===//

/// Determine if the current block being read contains any more data.
inline bool BytecodeReader::moreInBlock() {
  return At < BlockEnd;
}

/// Throw an error if we've read past the end of the current block
inline void BytecodeReader::checkPastBlockEnd(const char * block_name) {
  if (At > BlockEnd)
    error(std::string("Attempt to read past the end of ") + block_name +
          " block.");
}

/// Align the buffer position to a 32 bit boundary
inline void BytecodeReader::align32() {
  if (hasAlignment) {
    BufPtr Save = At;
    At = (const unsigned char *)((intptr_t)(At+3) & (~3UL));
    if (At > Save)
      if (Handler) Handler->handleAlignment(At - Save);
    if (At > BlockEnd)
      error("Ran out of data while aligning!");
  }
}

/// Read a whole unsigned integer
inline unsigned BytecodeReader::read_uint() {
  if (At+4 > BlockEnd)
    error("Ran out of data reading uint!");
  At += 4;
  return At[-4] | (At[-3] << 8) | (At[-2] << 16) | (At[-1] << 24);
}

/// Read a variable-bit-rate encoded unsigned integer
inline unsigned BytecodeReader::read_vbr_uint() {
  unsigned Shift = 0;
  unsigned Result = 0;
  BufPtr Save = At;

  do {
    if (At == BlockEnd)
      error("Ran out of data reading vbr_uint!");
    Result |= (unsigned)((*At++) & 0x7F) << Shift;
    Shift += 7;
  } while (At[-1] & 0x80);
  if (Handler) Handler->handleVBR32(At-Save);
  return Result;
}

/// Read a variable-bit-rate encoded unsigned 64-bit integer.
inline uint64_t BytecodeReader::read_vbr_uint64() {
  unsigned Shift = 0;
  uint64_t Result = 0;
  BufPtr Save = At;

  do {
    if (At == BlockEnd)
      error("Ran out of data reading vbr_uint64!");
    Result |= (uint64_t)((*At++) & 0x7F) << Shift;
    Shift += 7;
  } while (At[-1] & 0x80);
  if (Handler) Handler->handleVBR64(At-Save);
  return Result;
}

/// Read a variable-bit-rate encoded signed 64-bit integer.
inline int64_t BytecodeReader::read_vbr_int64() {
  uint64_t R = read_vbr_uint64();
  if (R & 1) {
    if (R != 1)
      return -(int64_t)(R >> 1);
    else   // There is no such thing as -0 with integers.  "-0" really means
           // 0x8000000000000000.
      return 1LL << 63;
  } else
    return  (int64_t)(R >> 1);
}

/// Read a pascal-style string (length followed by text)
inline std::string BytecodeReader::read_str() {
  unsigned Size = read_vbr_uint();
  const unsigned char *OldAt = At;
  At += Size;
  if (At > BlockEnd)             // Size invalid?
    error("Ran out of data reading a string!");
  return std::string((char*)OldAt, Size);
}

/// Read an arbitrary block of data
inline void BytecodeReader::read_data(void *Ptr, void *End) {
  unsigned char *Start = (unsigned char *)Ptr;
  unsigned Amount = (unsigned char *)End - Start;
  if (At+Amount > BlockEnd)
    error("Ran out of data!");
  std::copy(At, At+Amount, Start);
  At += Amount;
}

/// Read a float value in little-endian order
inline void BytecodeReader::read_float(float& FloatVal) {
  /// FIXME: This isn't optimal, it has size problems on some platforms
  /// where FP is not IEEE.
  FloatVal = BitsToFloat(At[0] | (At[1] << 8) | (At[2] << 16) | (At[3] << 24));
  At+=sizeof(uint32_t);
}

/// Read a double value in little-endian order
inline void BytecodeReader::read_double(double& DoubleVal) {
  /// FIXME: This isn't optimal, it has size problems on some platforms
  /// where FP is not IEEE.
  DoubleVal = BitsToDouble((uint64_t(At[0]) <<  0) | (uint64_t(At[1]) << 8) |
                           (uint64_t(At[2]) << 16) | (uint64_t(At[3]) << 24) |
                           (uint64_t(At[4]) << 32) | (uint64_t(At[5]) << 40) |
                           (uint64_t(At[6]) << 48) | (uint64_t(At[7]) << 56));
  At+=sizeof(uint64_t);
}

/// Read a block header and obtain its type and size
inline void BytecodeReader::read_block(unsigned &Type, unsigned &Size) {
  if ( hasLongBlockHeaders ) {
    Type = read_uint();
    Size = read_uint();
    switch (Type) {
    case BytecodeFormat::Reserved_DoNotUse :
      error("Reserved_DoNotUse used as Module Type?");
      Type = BytecodeFormat::ModuleBlockID; break;
    case BytecodeFormat::Module:
      Type = BytecodeFormat::ModuleBlockID; break;
    case BytecodeFormat::Function:
      Type = BytecodeFormat::FunctionBlockID; break;
    case BytecodeFormat::ConstantPool:
      Type = BytecodeFormat::ConstantPoolBlockID; break;
    case BytecodeFormat::SymbolTable:
      Type = BytecodeFormat::SymbolTableBlockID; break;
    case BytecodeFormat::ModuleGlobalInfo:
      Type = BytecodeFormat::ModuleGlobalInfoBlockID; break;
    case BytecodeFormat::GlobalTypePlane:
      Type = BytecodeFormat::GlobalTypePlaneBlockID; break;
    case BytecodeFormat::InstructionList:
      Type = BytecodeFormat::InstructionListBlockID; break;
    case BytecodeFormat::CompactionTable:
      Type = BytecodeFormat::CompactionTableBlockID; break;
    case BytecodeFormat::BasicBlock:
      /// This block type isn't used after version 1.1. However, we have to
      /// still allow the value in case this is an old bc format file.
      /// We just let its value creep thru.
      break;
    default:
      error("Invalid block id found: " + utostr(Type));
      break;
    }
  } else {
    Size = read_uint();
    Type = Size & 0x1F; // mask low order five bits
    Size >>= 5; // get rid of five low order bits, leaving high 27
  }
  BlockStart = At;
  if (At + Size > BlockEnd)
    error("Attempt to size a block past end of memory");
  BlockEnd = At + Size;
  if (Handler) Handler->handleBlock(Type, BlockStart, Size);
}


/// In LLVM 1.2 and before, Types were derived from Value and so they were
/// written as part of the type planes along with any other Value. In LLVM
/// 1.3 this changed so that Type does not derive from Value. Consequently,
/// the BytecodeReader's containers for Values can't contain Types because
/// there's no inheritance relationship. This means that the "Type Type"
/// plane is defunct along with the Type::TypeTyID TypeID. In LLVM 1.3
/// whenever a bytecode construct must have both types and values together,
/// the types are always read/written first and then the Values. Furthermore
/// since Type::TypeTyID no longer exists, its value (12) now corresponds to
/// Type::LabelTyID. In order to overcome this we must "sanitize" all the
/// type TypeIDs we encounter. For LLVM 1.3 bytecode files, there's no change.
/// For LLVM 1.2 and before, this function will decrement the type id by
/// one to account for the missing Type::TypeTyID enumerator if the value is
/// larger than 12 (Type::LabelTyID). If the value is exactly 12, then this
/// function returns true, otherwise false. This helps detect situations
/// where the pre 1.3 bytecode is indicating that what follows is a type.
/// @returns true iff type id corresponds to pre 1.3 "type type"
inline bool BytecodeReader::sanitizeTypeId(unsigned &TypeId) {
  if (hasTypeDerivedFromValue) { /// do nothing if 1.3 or later
    if (TypeId == Type::LabelTyID) {
      TypeId = Type::VoidTyID; // sanitize it
      return true; // indicate we got TypeTyID in pre 1.3 bytecode
    } else if (TypeId > Type::LabelTyID)
      --TypeId; // shift all planes down because type type plane is missing
  }
  return false;
}

/// Reads a vbr uint to read in a type id and does the necessary
/// conversion on it by calling sanitizeTypeId.
/// @returns true iff \p TypeId read corresponds to a pre 1.3 "type type"
/// @see sanitizeTypeId
inline bool BytecodeReader::read_typeid(unsigned &TypeId) {
  TypeId = read_vbr_uint();
  if ( !has32BitTypes )
    if ( TypeId == 0x00FFFFFF )
      TypeId = read_vbr_uint();
  return sanitizeTypeId(TypeId);
}

//===----------------------------------------------------------------------===//
// IR Lookup Methods
//===----------------------------------------------------------------------===//

/// Determine if a type id has an implicit null value
inline bool BytecodeReader::hasImplicitNull(unsigned TyID) {
  if (!hasExplicitPrimitiveZeros)
    return TyID != Type::LabelTyID && TyID != Type::VoidTyID;
  return TyID >= Type::FirstDerivedTyID;
}

/// Obtain a type given a typeid and account for things like compaction tables,
/// function level vs module level, and the offsetting for the primitive types.
const Type *BytecodeReader::getType(unsigned ID) {
  if (ID < Type::FirstDerivedTyID)
    if (const Type *T = Type::getPrimitiveType((Type::TypeID)ID))
      return T;   // Asked for a primitive type...

  // Otherwise, derived types need offset...
  ID -= Type::FirstDerivedTyID;

  if (!CompactionTypes.empty()) {
    if (ID >= CompactionTypes.size())
      error("Type ID out of range for compaction table!");
    return CompactionTypes[ID].first;
  }

  // Is it a module-level type?
  if (ID < ModuleTypes.size())
    return ModuleTypes[ID].get();

  // Nope, is it a function-level type?
  ID -= ModuleTypes.size();
  if (ID < FunctionTypes.size())
    return FunctionTypes[ID].get();

  error("Illegal type reference!");
  return Type::VoidTy;
}

/// Get a sanitized type id. This just makes sure that the \p ID
/// is both sanitized and not the "type type" of pre-1.3 bytecode.
/// @see sanitizeTypeId
inline const Type* BytecodeReader::getSanitizedType(unsigned& ID) {
  if (sanitizeTypeId(ID))
    error("Invalid type id encountered");
  return getType(ID);
}

/// This method just saves some coding. It uses read_typeid to read
/// in a sanitized type id, errors that its not the type type, and
/// then calls getType to return the type value.
inline const Type* BytecodeReader::readSanitizedType() {
  unsigned ID;
  if (read_typeid(ID))
    error("Invalid type id encountered");
  return getType(ID);
}

/// Get the slot number associated with a type accounting for primitive
/// types, compaction tables, and function level vs module level.
unsigned BytecodeReader::getTypeSlot(const Type *Ty) {
  if (Ty->isPrimitiveType())
    return Ty->getTypeID();

  // Scan the compaction table for the type if needed.
  if (!CompactionTypes.empty()) {
    for (unsigned i = 0, e = CompactionTypes.size(); i != e; ++i)
      if (CompactionTypes[i].first == Ty)
        return Type::FirstDerivedTyID + i;

    error("Couldn't find type specified in compaction table!");
  }

  // Check the function level types first...
  TypeListTy::iterator I = std::find(FunctionTypes.begin(),
                                     FunctionTypes.end(), Ty);

  if (I != FunctionTypes.end())
    return Type::FirstDerivedTyID + ModuleTypes.size() +
           (&*I - &FunctionTypes[0]);

  // If we don't have our cache yet, build it now.
  if (ModuleTypeIDCache.empty()) {
    unsigned N = 0;
    ModuleTypeIDCache.reserve(ModuleTypes.size());
    for (TypeListTy::iterator I = ModuleTypes.begin(), E = ModuleTypes.end();
         I != E; ++I, ++N)
      ModuleTypeIDCache.push_back(std::make_pair(*I, N));
    
    std::sort(ModuleTypeIDCache.begin(), ModuleTypeIDCache.end());
  }
  
  // Binary search the cache for the entry.
  std::vector<std::pair<const Type*, unsigned> >::iterator IT =
    std::lower_bound(ModuleTypeIDCache.begin(), ModuleTypeIDCache.end(),
                     std::make_pair(Ty, 0U));
  if (IT == ModuleTypeIDCache.end() || IT->first != Ty)
    error("Didn't find type in ModuleTypes.");
    
  return Type::FirstDerivedTyID + IT->second;
}

/// This is just like getType, but when a compaction table is in use, it is
/// ignored.  It also ignores function level types.
/// @see getType
const Type *BytecodeReader::getGlobalTableType(unsigned Slot) {
  if (Slot < Type::FirstDerivedTyID) {
    const Type *Ty = Type::getPrimitiveType((Type::TypeID)Slot);
    if (!Ty)
      error("Not a primitive type ID?");
    return Ty;
  }
  Slot -= Type::FirstDerivedTyID;
  if (Slot >= ModuleTypes.size())
    error("Illegal compaction table type reference!");
  return ModuleTypes[Slot];
}

/// This is just like getTypeSlot, but when a compaction table is in use, it
/// is ignored. It also ignores function level types.
unsigned BytecodeReader::getGlobalTableTypeSlot(const Type *Ty) {
  if (Ty->isPrimitiveType())
    return Ty->getTypeID();
  
  // If we don't have our cache yet, build it now.
  if (ModuleTypeIDCache.empty()) {
    unsigned N = 0;
    ModuleTypeIDCache.reserve(ModuleTypes.size());
    for (TypeListTy::iterator I = ModuleTypes.begin(), E = ModuleTypes.end();
         I != E; ++I, ++N)
      ModuleTypeIDCache.push_back(std::make_pair(*I, N));
    
    std::sort(ModuleTypeIDCache.begin(), ModuleTypeIDCache.end());
  }
  
  // Binary search the cache for the entry.
  std::vector<std::pair<const Type*, unsigned> >::iterator IT =
    std::lower_bound(ModuleTypeIDCache.begin(), ModuleTypeIDCache.end(),
                     std::make_pair(Ty, 0U));
  if (IT == ModuleTypeIDCache.end() || IT->first != Ty)
    error("Didn't find type in ModuleTypes.");
  
  return Type::FirstDerivedTyID + IT->second;
}

/// Retrieve a value of a given type and slot number, possibly creating
/// it if it doesn't already exist.
Value * BytecodeReader::getValue(unsigned type, unsigned oNum, bool Create) {
  assert(type != Type::LabelTyID && "getValue() cannot get blocks!");
  unsigned Num = oNum;

  // If there is a compaction table active, it defines the low-level numbers.
  // If not, the module values define the low-level numbers.
  if (CompactionValues.size() > type && !CompactionValues[type].empty()) {
    if (Num < CompactionValues[type].size())
      return CompactionValues[type][Num];
    Num -= CompactionValues[type].size();
  } else {
    // By default, the global type id is the type id passed in
    unsigned GlobalTyID = type;

    // If the type plane was compactified, figure out the global type ID by
    // adding the derived type ids and the distance.
    if (!CompactionTypes.empty() && type >= Type::FirstDerivedTyID)
      GlobalTyID = CompactionTypes[type-Type::FirstDerivedTyID].second;

    if (hasImplicitNull(GlobalTyID)) {
      const Type *Ty = getType(type);
      if (!isa<OpaqueType>(Ty)) {
        if (Num == 0)
          return Constant::getNullValue(Ty);
        --Num;
      }
    }

    if (GlobalTyID < ModuleValues.size() && ModuleValues[GlobalTyID]) {
      if (Num < ModuleValues[GlobalTyID]->size())
        return ModuleValues[GlobalTyID]->getOperand(Num);
      Num -= ModuleValues[GlobalTyID]->size();
    }
  }

  if (FunctionValues.size() > type &&
      FunctionValues[type] &&
      Num < FunctionValues[type]->size())
    return FunctionValues[type]->getOperand(Num);

  if (!Create) return 0;  // Do not create a placeholder?

  // Did we already create a place holder?
  std::pair<unsigned,unsigned> KeyValue(type, oNum);
  ForwardReferenceMap::iterator I = ForwardReferences.lower_bound(KeyValue);
  if (I != ForwardReferences.end() && I->first == KeyValue)
    return I->second;   // We have already created this placeholder

  // If the type exists (it should)
  if (const Type* Ty = getType(type)) {
    // Create the place holder
    Value *Val = new Argument(Ty);
    ForwardReferences.insert(I, std::make_pair(KeyValue, Val));
    return Val;
  }
  error("Can't create placeholder for value of type slot #" + utostr(type));
  return 0; // just silence warning, error calls longjmp
}

/// This is just like getValue, but when a compaction table is in use, it
/// is ignored.  Also, no forward references or other fancy features are
/// supported.
Value* BytecodeReader::getGlobalTableValue(unsigned TyID, unsigned SlotNo) {
  if (SlotNo == 0)
    return Constant::getNullValue(getType(TyID));

  if (!CompactionTypes.empty() && TyID >= Type::FirstDerivedTyID) {
    TyID -= Type::FirstDerivedTyID;
    if (TyID >= CompactionTypes.size())
      error("Type ID out of range for compaction table!");
    TyID = CompactionTypes[TyID].second;
  }

  --SlotNo;

  if (TyID >= ModuleValues.size() || ModuleValues[TyID] == 0 ||
      SlotNo >= ModuleValues[TyID]->size()) {
    if (TyID >= ModuleValues.size() || ModuleValues[TyID] == 0)
      error("Corrupt compaction table entry!"
            + utostr(TyID) + ", " + utostr(SlotNo) + ": "
            + utostr(ModuleValues.size()));
    else
      error("Corrupt compaction table entry!"
            + utostr(TyID) + ", " + utostr(SlotNo) + ": "
            + utostr(ModuleValues.size()) + ", "
            + utohexstr(reinterpret_cast<uint64_t>(((void*)ModuleValues[TyID])))
            + ", "
            + utostr(ModuleValues[TyID]->size()));
  }
  return ModuleValues[TyID]->getOperand(SlotNo);
}

/// Just like getValue, except that it returns a null pointer
/// only on error.  It always returns a constant (meaning that if the value is
/// defined, but is not a constant, that is an error).  If the specified
/// constant hasn't been parsed yet, a placeholder is defined and used.
/// Later, after the real value is parsed, the placeholder is eliminated.
Constant* BytecodeReader::getConstantValue(unsigned TypeSlot, unsigned Slot) {
  if (Value *V = getValue(TypeSlot, Slot, false))
    if (Constant *C = dyn_cast<Constant>(V))
      return C;   // If we already have the value parsed, just return it
    else
      error("Value for slot " + utostr(Slot) +
            " is expected to be a constant!");

  std::pair<unsigned, unsigned> Key(TypeSlot, Slot);
  ConstantRefsType::iterator I = ConstantFwdRefs.lower_bound(Key);

  if (I != ConstantFwdRefs.end() && I->first == Key) {
    return I->second;
  } else {
    // Create a placeholder for the constant reference and
    // keep track of the fact that we have a forward ref to recycle it
    Constant *C = new ConstantPlaceHolder(getType(TypeSlot));

    // Keep track of the fact that we have a forward ref to recycle it
    ConstantFwdRefs.insert(I, std::make_pair(Key, C));
    return C;
  }
}

//===----------------------------------------------------------------------===//
// IR Construction Methods
//===----------------------------------------------------------------------===//

/// As values are created, they are inserted into the appropriate place
/// with this method. The ValueTable argument must be one of ModuleValues
/// or FunctionValues data members of this class.
unsigned BytecodeReader::insertValue(Value *Val, unsigned type,
                                      ValueTable &ValueTab) {
  if (ValueTab.size() <= type)
    ValueTab.resize(type+1);

  if (!ValueTab[type]) ValueTab[type] = new ValueList();

  ValueTab[type]->push_back(Val);

  bool HasOffset = hasImplicitNull(type) && !isa<OpaqueType>(Val->getType());
  return ValueTab[type]->size()-1 + HasOffset;
}

/// Insert the arguments of a function as new values in the reader.
void BytecodeReader::insertArguments(Function* F) {
  const FunctionType *FT = F->getFunctionType();
  Function::arg_iterator AI = F->arg_begin();
  for (FunctionType::param_iterator It = FT->param_begin();
       It != FT->param_end(); ++It, ++AI)
    insertValue(AI, getTypeSlot(AI->getType()), FunctionValues);
}

// Convert previous opcode values into the current value and/or construct
// the instruction. This function handles all *abnormal* cases for instruction
// generation based on obsolete opcode values. The normal cases are handled
// in ParseInstruction below.  Generally this function just produces a new
// Opcode value (first argument). In a few cases (VAArg, VANext) the upgrade
// path requies that the instruction (sequence) be generated differently from
// the normal case in order to preserve the original semantics. In these 
// cases the result of the function will be a non-zero Instruction pointer. In
// all other cases, zero will be returned indicating that the *normal*
// instruction generation should be used, but with the new Opcode value.
// 
Instruction*
BytecodeReader::handleObsoleteOpcodes(
  unsigned &Opcode,   ///< The old opcode, possibly updated by this function
  std::vector<unsigned> &Oprnds, ///< The operands to the instruction
  unsigned &iType,    ///< The type code from the bytecode file
  const Type* InstTy, ///< The type of the instruction
  BasicBlock* BB      ///< The basic block to insert into, if we need to
) {

  // First, short circuit this if no conversion is required. When signless
  // instructions were implemented the entire opcode sequence was revised so
  // we key on this first which means that the opcode value read is the one
  // we should use.
  if (!hasSignlessInstructions)
    return 0; // The opcode is fine the way it is.

  // Declare the resulting instruction we might build. In general we just 
  // change the Opcode argument but in a few cases we need to generate the 
  // Instruction here because the upgrade case is significantly different from 
  // the normal case.
  Instruction *Result = 0;

  // If this is a bytecode format that did not include the unreachable
  // instruction, bump up the opcode number to adjust it.
  if (hasNoUnreachableInst)
    if (Opcode >= Instruction::Unreachable && Opcode < 62)
      ++Opcode;

  // We're dealing with an upgrade situation. For each of the opcode values,
  // perform the necessary conversion.
  switch (Opcode) {
    default: // Error
      // This switch statement provides cases for all known opcodes prior to
      // version 6 bytecode format. We know we're in an upgrade situation so
      // if there isn't a match in this switch, then something is horribly
      // wrong.
      error("Unknown obsolete opcode encountered.");
      break;
    case 1: // Ret
      Opcode = Instruction::Ret;
      break;
    case 2: // Br
      Opcode = Instruction::Br;
      break;
    case 3: // Switch
      Opcode = Instruction::Switch;
      break;
    case 4: // Invoke
      Opcode = Instruction::Invoke;
      break;
    case 5: // Unwind
      Opcode = Instruction::Unwind;
      break;
    case 6: // Unreachable
      Opcode = Instruction::Unreachable;
      break;
    case 7: // Add
      Opcode = Instruction::Add;
      break;
    case 8: // Sub
      Opcode = Instruction::Sub;
      break;
    case 9: // Mul
      Opcode = Instruction::Mul;
      break;
    case 10: // Div 
      // The type of the instruction is based on the operands. We need to select
      // fdiv, udiv or sdiv based on that type. The iType values are hardcoded
      // to the values used in bytecode version 5 (and prior) because it is
      // likely these codes will change in future versions of LLVM.
      if (iType == 10 || iType == 11 )
        Opcode = Instruction::FDiv;
      else if (iType >= 2 && iType <= 9 && iType % 2 != 0)
        Opcode = Instruction::SDiv;
      else
        Opcode = Instruction::UDiv;
      break;

    case 11: // Rem
      // As with "Div", make the signed/unsigned or floating point Rem 
      // instruction choice based on the type of the operands.
      if (iType == 10 || iType == 11)
        Opcode = Instruction::FRem;
      else if (iType >= 2 && iType <= 9 && iType % 2 != 0)
        Opcode = Instruction::SRem;
      else
        Opcode = Instruction::URem;
      break;
    case 12: // And
      Opcode = Instruction::And;
      break;
    case 13: // Or
      Opcode = Instruction::Or;
      break;
    case 14: // Xor
      Opcode = Instruction::Xor;
      break;
    case 15: // SetEQ
      Opcode = Instruction::SetEQ;
      break;
    case 16: // SetNE
      Opcode = Instruction::SetNE;
      break;
    case 17: // SetLE
      Opcode = Instruction::SetLE;
      break;
    case 18: // SetGE
      Opcode = Instruction::SetGE;
      break;
    case 19: // SetLT
      Opcode = Instruction::SetLT;
      break;
    case 20: // SetGT
      Opcode = Instruction::SetGT;
      break;
    case 21: // Malloc
      Opcode = Instruction::Malloc;
      break;
    case 22: // Free
      Opcode = Instruction::Free;
      break;
    case 23: // Alloca
      Opcode = Instruction::Alloca;
      break;
    case 24: // Load
      Opcode = Instruction::Load;
      break;
    case 25: // Store
      Opcode = Instruction::Store;
      break;
    case 26: // GetElementPtr
      Opcode = Instruction::GetElementPtr;
      break;
    case 27: // PHI
      Opcode = Instruction::PHI;
      break;
    case 28: // Cast
      Opcode = Instruction::Cast;
      break;
    case 29: // Call
      Opcode = Instruction::Call;
      break;
    case 30: // Shl
      Opcode = Instruction::Shl;
      break;
    case 31: // Shr
      Opcode = Instruction::Shr;
      break;
    case 32: { //VANext_old ( <= llvm 1.5 )
      const Type* ArgTy = getValue(iType, Oprnds[0])->getType();
      Function* NF = TheModule->getOrInsertFunction(
        "llvm.va_copy", ArgTy, ArgTy, (Type *)0);

      // In llvm 1.6 the VANext instruction was dropped because it was only 
      // necessary to have a VAArg instruction. The code below transforms an
      // old vanext instruction into the equivalent code given only the 
      // availability of the new vaarg instruction. Essentially, the transform
      // is as follows:
      //    b = vanext a, t ->
      //    foo = alloca 1 of t
      //    bar = vacopy a
      //    store bar -> foo
      //    tmp = vaarg foo, t
      //    b = load foo
      AllocaInst* foo = new AllocaInst(ArgTy, 0, "vanext.fix");
      BB->getInstList().push_back(foo);
      CallInst* bar = new CallInst(NF, getValue(iType, Oprnds[0]));
      BB->getInstList().push_back(bar);
      BB->getInstList().push_back(new StoreInst(bar, foo));
      Instruction* tmp = new VAArgInst(foo, getSanitizedType(Oprnds[1]));
      BB->getInstList().push_back(tmp);
      Result = new LoadInst(foo);
      break;
    }
    case 33: { //VAArg_old
      const Type* ArgTy = getValue(iType, Oprnds[0])->getType();
      Function* NF = TheModule->getOrInsertFunction(
        "llvm.va_copy", ArgTy, ArgTy, (Type *)0);

      // In llvm 1.6 the VAArg's instruction semantics were changed.  The code 
      // below transforms an old vaarg instruction into the equivalent code 
      // given only the availability of the new vaarg instruction. Essentially,
      // the transform is as follows:
      //    b = vaarg a, t ->
      //    foo = alloca 1 of t
      //    bar = vacopy a
      //    store bar -> foo
      //    b = vaarg foo, t
      AllocaInst* foo = new AllocaInst(ArgTy, 0, "vaarg.fix");
      BB->getInstList().push_back(foo);
      CallInst* bar = new CallInst(NF, getValue(iType, Oprnds[0]));
      BB->getInstList().push_back(bar);
      BB->getInstList().push_back(new StoreInst(bar, foo));
      Result = new VAArgInst(foo, getSanitizedType(Oprnds[1]));
      break;
    }
    case 34: // Select
      Opcode = Instruction::Select;
      break;
    case 35: // UserOp1
      Opcode = Instruction::UserOp1;
      break;
    case 36: // UserOp2
      Opcode = Instruction::UserOp2;
      break;
    case 37: // VAArg
      Opcode = Instruction::VAArg;
      break;
    case 38: // ExtractElement
      Opcode = Instruction::ExtractElement;
      break;
    case 39: // InsertElement
      Opcode = Instruction::InsertElement;
      break;
    case 40: // ShuffleVector
      Opcode = Instruction::ShuffleVector;
      break;
    case 56: // Invoke with encoded CC
    case 57: // Invoke Fast CC
    case 58: // Call with extra operand for calling conv
    case 59: // tail call, Fast CC
    case 60: // normal call, Fast CC
    case 61: // tail call, C Calling Conv
    case 62: // volatile load
    case 63: // volatile store
      // In all these cases, we pass the opcode through. The new version uses
      // the same code (for now, this might change in 2.0). These are listed
      // here to document the opcodes in use in vers 5 bytecode and to make it
      // easier to migrate these opcodes in the future.
      break;
  }
  return Result;
}

//===----------------------------------------------------------------------===//
// Bytecode Parsing Methods
//===----------------------------------------------------------------------===//

/// This method parses a single instruction. The instruction is
/// inserted at the end of the \p BB provided. The arguments of
/// the instruction are provided in the \p Oprnds vector.
void BytecodeReader::ParseInstruction(std::vector<unsigned> &Oprnds,
                                      BasicBlock* BB) {
  BufPtr SaveAt = At;

  // Clear instruction data
  Oprnds.clear();
  unsigned iType = 0;
  unsigned Opcode = 0;
  unsigned Op = read_uint();

  // bits   Instruction format:        Common to all formats
  // --------------------------
  // 01-00: Opcode type, fixed to 1.
  // 07-02: Opcode
  Opcode    = (Op >> 2) & 63;
  Oprnds.resize((Op >> 0) & 03);

  // Extract the operands
  switch (Oprnds.size()) {
  case 1:
    // bits   Instruction format:
    // --------------------------
    // 19-08: Resulting type plane
    // 31-20: Operand #1 (if set to (2^12-1), then zero operands)
    //
    iType   = (Op >>  8) & 4095;
    Oprnds[0] = (Op >> 20) & 4095;
    if (Oprnds[0] == 4095)    // Handle special encoding for 0 operands...
      Oprnds.resize(0);
    break;
  case 2:
    // bits   Instruction format:
    // --------------------------
    // 15-08: Resulting type plane
    // 23-16: Operand #1
    // 31-24: Operand #2
    //
    iType   = (Op >>  8) & 255;
    Oprnds[0] = (Op >> 16) & 255;
    Oprnds[1] = (Op >> 24) & 255;
    break;
  case 3:
    // bits   Instruction format:
    // --------------------------
    // 13-08: Resulting type plane
    // 19-14: Operand #1
    // 25-20: Operand #2
    // 31-26: Operand #3
    //
    iType   = (Op >>  8) & 63;
    Oprnds[0] = (Op >> 14) & 63;
    Oprnds[1] = (Op >> 20) & 63;
    Oprnds[2] = (Op >> 26) & 63;
    break;
  case 0:
    At -= 4;  // Hrm, try this again...
    Opcode = read_vbr_uint();
    Opcode >>= 2;
    iType = read_vbr_uint();

    unsigned NumOprnds = read_vbr_uint();
    Oprnds.resize(NumOprnds);

    if (NumOprnds == 0)
      error("Zero-argument instruction found; this is invalid.");

    for (unsigned i = 0; i != NumOprnds; ++i)
      Oprnds[i] = read_vbr_uint();
    align32();
    break;
  }

  const Type *InstTy = getSanitizedType(iType);

  // Make the necessary adjustments for dealing with backwards compatibility
  // of opcodes.
  Instruction* Result = 
    handleObsoleteOpcodes(Opcode, Oprnds, iType, InstTy, BB);

  // We have enough info to inform the handler now.
  if (Handler) 
    Handler->handleInstruction(Opcode, InstTy, Oprnds, At-SaveAt);

  // If the backwards compatibility code didn't produce an instruction then
  // we do the *normal* thing ..
  if (!Result) {
    // First, handle the easy binary operators case
    if (Opcode >= Instruction::BinaryOpsBegin &&
        Opcode <  Instruction::BinaryOpsEnd  && Oprnds.size() == 2)
      Result = BinaryOperator::create(Instruction::BinaryOps(Opcode),
                                      getValue(iType, Oprnds[0]),
                                      getValue(iType, Oprnds[1]));

    // Indicate that we don't think this is a call instruction (yet).
    // Process based on the Opcode read
    switch (Opcode) {
    default: // There was an error, this shouldn't happen.
      if (Result == 0)
        error("Illegal instruction read!");
      break;
    case Instruction::VAArg:
      if (Oprnds.size() != 2)
        error("Invalid VAArg instruction!");
      Result = new VAArgInst(getValue(iType, Oprnds[0]),
                             getSanitizedType(Oprnds[1]));
      break;
    case Instruction::ExtractElement: {
      if (Oprnds.size() != 2)
        error("Invalid extractelement instruction!");
      Value *V1 = getValue(iType, Oprnds[0]);
      Value *V2 = getValue(Type::UIntTyID, Oprnds[1]);
      
      if (!ExtractElementInst::isValidOperands(V1, V2))
        error("Invalid extractelement instruction!");

      Result = new ExtractElementInst(V1, V2);
      break;
    }
    case Instruction::InsertElement: {
      const PackedType *PackedTy = dyn_cast<PackedType>(InstTy);
      if (!PackedTy || Oprnds.size() != 3)
        error("Invalid insertelement instruction!");
      
      Value *V1 = getValue(iType, Oprnds[0]);
      Value *V2 = getValue(getTypeSlot(PackedTy->getElementType()),Oprnds[1]);
      Value *V3 = getValue(Type::UIntTyID, Oprnds[2]);
        
      if (!InsertElementInst::isValidOperands(V1, V2, V3))
        error("Invalid insertelement instruction!");
      Result = new InsertElementInst(V1, V2, V3);
      break;
    }
    case Instruction::ShuffleVector: {
      const PackedType *PackedTy = dyn_cast<PackedType>(InstTy);
      if (!PackedTy || Oprnds.size() != 3)
        error("Invalid shufflevector instruction!");
      Value *V1 = getValue(iType, Oprnds[0]);
      Value *V2 = getValue(iType, Oprnds[1]);
      const PackedType *EltTy = 
        PackedType::get(Type::UIntTy, PackedTy->getNumElements());
      Value *V3 = getValue(getTypeSlot(EltTy), Oprnds[2]);
      if (!ShuffleVectorInst::isValidOperands(V1, V2, V3))
        error("Invalid shufflevector instruction!");
      Result = new ShuffleVectorInst(V1, V2, V3);
      break;
    }
    case Instruction::Cast:
      if (Oprnds.size() != 2)
        error("Invalid Cast instruction!");
      Result = new CastInst(getValue(iType, Oprnds[0]),
                            getSanitizedType(Oprnds[1]));
      break;
    case Instruction::Select:
      if (Oprnds.size() != 3)
        error("Invalid Select instruction!");
      Result = new SelectInst(getValue(Type::BoolTyID, Oprnds[0]),
                              getValue(iType, Oprnds[1]),
                              getValue(iType, Oprnds[2]));
      break;
    case Instruction::PHI: {
      if (Oprnds.size() == 0 || (Oprnds.size() & 1))
        error("Invalid phi node encountered!");

      PHINode *PN = new PHINode(InstTy);
      PN->reserveOperandSpace(Oprnds.size());
      for (unsigned i = 0, e = Oprnds.size(); i != e; i += 2)
        PN->addIncoming(
          getValue(iType, Oprnds[i]), getBasicBlock(Oprnds[i+1]));
      Result = PN;
      break;
    }

    case Instruction::Shl:
    case Instruction::Shr:
      Result = new ShiftInst(Instruction::OtherOps(Opcode),
                             getValue(iType, Oprnds[0]),
                             getValue(Type::UByteTyID, Oprnds[1]));
      break;
    case Instruction::Ret:
      if (Oprnds.size() == 0)
        Result = new ReturnInst();
      else if (Oprnds.size() == 1)
        Result = new ReturnInst(getValue(iType, Oprnds[0]));
      else
        error("Unrecognized instruction!");
      break;

    case Instruction::Br:
      if (Oprnds.size() == 1)
        Result = new BranchInst(getBasicBlock(Oprnds[0]));
      else if (Oprnds.size() == 3)
        Result = new BranchInst(getBasicBlock(Oprnds[0]),
            getBasicBlock(Oprnds[1]), getValue(Type::BoolTyID , Oprnds[2]));
      else
        error("Invalid number of operands for a 'br' instruction!");
      break;
    case Instruction::Switch: {
      if (Oprnds.size() & 1)
        error("Switch statement with odd number of arguments!");

      SwitchInst *I = new SwitchInst(getValue(iType, Oprnds[0]),
                                     getBasicBlock(Oprnds[1]),
                                     Oprnds.size()/2-1);
      for (unsigned i = 2, e = Oprnds.size(); i != e; i += 2)
        I->addCase(cast<ConstantInt>(getValue(iType, Oprnds[i])),
                   getBasicBlock(Oprnds[i+1]));
      Result = I;
      break;
    }
    case 58:                   // Call with extra operand for calling conv
    case 59:                   // tail call, Fast CC
    case 60:                   // normal call, Fast CC
    case 61:                   // tail call, C Calling Conv
    case Instruction::Call: {  // Normal Call, C Calling Convention
      if (Oprnds.size() == 0)
        error("Invalid call instruction encountered!");

      Value *F = getValue(iType, Oprnds[0]);

      unsigned CallingConv = CallingConv::C;
      bool isTailCall = false;

      if (Opcode == 61 || Opcode == 59)
        isTailCall = true;
      
      if (Opcode == 58) {
        isTailCall = Oprnds.back() & 1;
        CallingConv = Oprnds.back() >> 1;
        Oprnds.pop_back();
      } else if (Opcode == 59 || Opcode == 60) {
        CallingConv = CallingConv::Fast;
      }
      
      // Check to make sure we have a pointer to function type
      const PointerType *PTy = dyn_cast<PointerType>(F->getType());
      if (PTy == 0) error("Call to non function pointer value!");
      const FunctionType *FTy = dyn_cast<FunctionType>(PTy->getElementType());
      if (FTy == 0) error("Call to non function pointer value!");

      std::vector<Value *> Params;
      if (!FTy->isVarArg()) {
        FunctionType::param_iterator It = FTy->param_begin();

        for (unsigned i = 1, e = Oprnds.size(); i != e; ++i) {
          if (It == FTy->param_end())
            error("Invalid call instruction!");
          Params.push_back(getValue(getTypeSlot(*It++), Oprnds[i]));
        }
        if (It != FTy->param_end())
          error("Invalid call instruction!");
      } else {
        Oprnds.erase(Oprnds.begin(), Oprnds.begin()+1);

        unsigned FirstVariableOperand;
        if (Oprnds.size() < FTy->getNumParams())
          error("Call instruction missing operands!");

        // Read all of the fixed arguments
        for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
          Params.push_back(
            getValue(getTypeSlot(FTy->getParamType(i)),Oprnds[i]));

        FirstVariableOperand = FTy->getNumParams();

        if ((Oprnds.size()-FirstVariableOperand) & 1)
          error("Invalid call instruction!");   // Must be pairs of type/value

        for (unsigned i = FirstVariableOperand, e = Oprnds.size();
             i != e; i += 2)
          Params.push_back(getValue(Oprnds[i], Oprnds[i+1]));
      }

      Result = new CallInst(F, Params);
      if (isTailCall) cast<CallInst>(Result)->setTailCall();
      if (CallingConv) cast<CallInst>(Result)->setCallingConv(CallingConv);
      break;
    }
    case 56:                     // Invoke with encoded CC
    case 57:                     // Invoke Fast CC
    case Instruction::Invoke: {  // Invoke C CC
      if (Oprnds.size() < 3)
        error("Invalid invoke instruction!");
      Value *F = getValue(iType, Oprnds[0]);

      // Check to make sure we have a pointer to function type
      const PointerType *PTy = dyn_cast<PointerType>(F->getType());
      if (PTy == 0)
        error("Invoke to non function pointer value!");
      const FunctionType *FTy = dyn_cast<FunctionType>(PTy->getElementType());
      if (FTy == 0)
        error("Invoke to non function pointer value!");

      std::vector<Value *> Params;
      BasicBlock *Normal, *Except;
      unsigned CallingConv = CallingConv::C;

      if (Opcode == 57)
        CallingConv = CallingConv::Fast;
      else if (Opcode == 56) {
        CallingConv = Oprnds.back();
        Oprnds.pop_back();
      }

      if (!FTy->isVarArg()) {
        Normal = getBasicBlock(Oprnds[1]);
        Except = getBasicBlock(Oprnds[2]);

        FunctionType::param_iterator It = FTy->param_begin();
        for (unsigned i = 3, e = Oprnds.size(); i != e; ++i) {
          if (It == FTy->param_end())
            error("Invalid invoke instruction!");
          Params.push_back(getValue(getTypeSlot(*It++), Oprnds[i]));
        }
        if (It != FTy->param_end())
          error("Invalid invoke instruction!");
      } else {
        Oprnds.erase(Oprnds.begin(), Oprnds.begin()+1);

        Normal = getBasicBlock(Oprnds[0]);
        Except = getBasicBlock(Oprnds[1]);

        unsigned FirstVariableArgument = FTy->getNumParams()+2;
        for (unsigned i = 2; i != FirstVariableArgument; ++i)
          Params.push_back(getValue(getTypeSlot(FTy->getParamType(i-2)),
                                    Oprnds[i]));

        // Must be type/value pairs. If not, error out.
        if (Oprnds.size()-FirstVariableArgument & 1) 
          error("Invalid invoke instruction!");

        for (unsigned i = FirstVariableArgument; i < Oprnds.size(); i += 2)
          Params.push_back(getValue(Oprnds[i], Oprnds[i+1]));
      }

      Result = new InvokeInst(F, Normal, Except, Params);
      if (CallingConv) cast<InvokeInst>(Result)->setCallingConv(CallingConv);
      break;
    }
    case Instruction::Malloc: {
      unsigned Align = 0;
      if (Oprnds.size() == 2)
        Align = (1 << Oprnds[1]) >> 1;
      else if (Oprnds.size() > 2)
        error("Invalid malloc instruction!");
      if (!isa<PointerType>(InstTy))
        error("Invalid malloc instruction!");

      Result = new MallocInst(cast<PointerType>(InstTy)->getElementType(),
                              getValue(Type::UIntTyID, Oprnds[0]), Align);
      break;
    }
    case Instruction::Alloca: {
      unsigned Align = 0;
      if (Oprnds.size() == 2)
        Align = (1 << Oprnds[1]) >> 1;
      else if (Oprnds.size() > 2)
        error("Invalid alloca instruction!");
      if (!isa<PointerType>(InstTy))
        error("Invalid alloca instruction!");

      Result = new AllocaInst(cast<PointerType>(InstTy)->getElementType(),
                              getValue(Type::UIntTyID, Oprnds[0]), Align);
      break;
    }
    case Instruction::Free:
      if (!isa<PointerType>(InstTy))
        error("Invalid free instruction!");
      Result = new FreeInst(getValue(iType, Oprnds[0]));
      break;
    case Instruction::GetElementPtr: {
      if (Oprnds.size() == 0 || !isa<PointerType>(InstTy))
        error("Invalid getelementptr instruction!");

      std::vector<Value*> Idx;

      const Type *NextTy = InstTy;
      for (unsigned i = 1, e = Oprnds.size(); i != e; ++i) {
        const CompositeType *TopTy = dyn_cast_or_null<CompositeType>(NextTy);
        if (!TopTy)
          error("Invalid getelementptr instruction!");

        unsigned ValIdx = Oprnds[i];
        unsigned IdxTy = 0;
        if (!hasRestrictedGEPTypes) {
          // Struct indices are always uints, sequential type indices can be 
          // any of the 32 or 64-bit integer types.  The actual choice of 
          // type is encoded in the low two bits of the slot number.
          if (isa<StructType>(TopTy))
            IdxTy = Type::UIntTyID;
          else {
            switch (ValIdx & 3) {
            default:
            case 0: IdxTy = Type::UIntTyID; break;
            case 1: IdxTy = Type::IntTyID; break;
            case 2: IdxTy = Type::ULongTyID; break;
            case 3: IdxTy = Type::LongTyID; break;
            }
            ValIdx >>= 2;
          }
        } else {
          IdxTy = isa<StructType>(TopTy) ? Type::UByteTyID : Type::LongTyID;
        }

        Idx.push_back(getValue(IdxTy, ValIdx));

        // Convert ubyte struct indices into uint struct indices.
        if (isa<StructType>(TopTy) && hasRestrictedGEPTypes)
          if (ConstantInt *C = dyn_cast<ConstantInt>(Idx.back()))
            if (C->getType() == Type::UByteTy)
              Idx[Idx.size()-1] = ConstantExpr::getCast(C, Type::UIntTy);

        NextTy = GetElementPtrInst::getIndexedType(InstTy, Idx, true);
      }

      Result = new GetElementPtrInst(getValue(iType, Oprnds[0]), Idx);
      break;
    }
    case 62:   // volatile load
    case Instruction::Load:
      if (Oprnds.size() != 1 || !isa<PointerType>(InstTy))
        error("Invalid load instruction!");
      Result = new LoadInst(getValue(iType, Oprnds[0]), "", Opcode == 62);
      break;
    case 63:   // volatile store
    case Instruction::Store: {
      if (!isa<PointerType>(InstTy) || Oprnds.size() != 2)
        error("Invalid store instruction!");

      Value *Ptr = getValue(iType, Oprnds[1]);
      const Type *ValTy = cast<PointerType>(Ptr->getType())->getElementType();
      Result = new StoreInst(getValue(getTypeSlot(ValTy), Oprnds[0]), Ptr,
                             Opcode == 63);
      break;
    }
    case Instruction::Unwind:
      if (Oprnds.size() != 0) error("Invalid unwind instruction!");
      Result = new UnwindInst();
      break;
    case Instruction::Unreachable:
      if (Oprnds.size() != 0) error("Invalid unreachable instruction!");
      Result = new UnreachableInst();
      break;
    }  // end switch(Opcode)
  } // end if *normal*

  BB->getInstList().push_back(Result);

  unsigned TypeSlot;
  if (Result->getType() == InstTy)
    TypeSlot = iType;
  else
    TypeSlot = getTypeSlot(Result->getType());

  insertValue(Result, TypeSlot, FunctionValues);
}

/// Get a particular numbered basic block, which might be a forward reference.
/// This works together with ParseBasicBlock to handle these forward references
/// in a clean manner.  This function is used when constructing phi, br, switch,
/// and other instructions that reference basic blocks. Blocks are numbered
/// sequentially as they appear in the function.
BasicBlock *BytecodeReader::getBasicBlock(unsigned ID) {
  // Make sure there is room in the table...
  if (ParsedBasicBlocks.size() <= ID) ParsedBasicBlocks.resize(ID+1);

  // First check to see if this is a backwards reference, i.e., ParseBasicBlock
  // has already created this block, or if the forward reference has already
  // been created.
  if (ParsedBasicBlocks[ID])
    return ParsedBasicBlocks[ID];

  // Otherwise, the basic block has not yet been created.  Do so and add it to
  // the ParsedBasicBlocks list.
  return ParsedBasicBlocks[ID] = new BasicBlock();
}

/// In LLVM 1.0 bytecode files, we used to output one basicblock at a time.
/// This method reads in one of the basicblock packets. This method is not used
/// for bytecode files after LLVM 1.0
/// @returns The basic block constructed.
BasicBlock *BytecodeReader::ParseBasicBlock(unsigned BlockNo) {
  if (Handler) Handler->handleBasicBlockBegin(BlockNo);

  BasicBlock *BB = 0;

  if (ParsedBasicBlocks.size() == BlockNo)
    ParsedBasicBlocks.push_back(BB = new BasicBlock());
  else if (ParsedBasicBlocks[BlockNo] == 0)
    BB = ParsedBasicBlocks[BlockNo] = new BasicBlock();
  else
    BB = ParsedBasicBlocks[BlockNo];

  std::vector<unsigned> Operands;
  while (moreInBlock())
    ParseInstruction(Operands, BB);

  if (Handler) Handler->handleBasicBlockEnd(BlockNo);
  return BB;
}

/// Parse all of the BasicBlock's & Instruction's in the body of a function.
/// In post 1.0 bytecode files, we no longer emit basic block individually,
/// in order to avoid per-basic-block overhead.
/// @returns Rhe number of basic blocks encountered.
unsigned BytecodeReader::ParseInstructionList(Function* F) {
  unsigned BlockNo = 0;
  std::vector<unsigned> Args;

  while (moreInBlock()) {
    if (Handler) Handler->handleBasicBlockBegin(BlockNo);
    BasicBlock *BB;
    if (ParsedBasicBlocks.size() == BlockNo)
      ParsedBasicBlocks.push_back(BB = new BasicBlock());
    else if (ParsedBasicBlocks[BlockNo] == 0)
      BB = ParsedBasicBlocks[BlockNo] = new BasicBlock();
    else
      BB = ParsedBasicBlocks[BlockNo];
    ++BlockNo;
    F->getBasicBlockList().push_back(BB);

    // Read instructions into this basic block until we get to a terminator
    while (moreInBlock() && !BB->getTerminator())
      ParseInstruction(Args, BB);

    if (!BB->getTerminator())
      error("Non-terminated basic block found!");

    if (Handler) Handler->handleBasicBlockEnd(BlockNo-1);
  }

  return BlockNo;
}

/// Parse a symbol table. This works for both module level and function
/// level symbol tables.  For function level symbol tables, the CurrentFunction
/// parameter must be non-zero and the ST parameter must correspond to
/// CurrentFunction's symbol table. For Module level symbol tables, the
/// CurrentFunction argument must be zero.
void BytecodeReader::ParseSymbolTable(Function *CurrentFunction,
                                      SymbolTable *ST) {
  if (Handler) Handler->handleSymbolTableBegin(CurrentFunction,ST);

  // Allow efficient basic block lookup by number.
  std::vector<BasicBlock*> BBMap;
  if (CurrentFunction)
    for (Function::iterator I = CurrentFunction->begin(),
           E = CurrentFunction->end(); I != E; ++I)
      BBMap.push_back(I);

  /// In LLVM 1.3 we write types separately from values so
  /// The types are always first in the symbol table. This is
  /// because Type no longer derives from Value.
  if (!hasTypeDerivedFromValue) {
    // Symtab block header: [num entries]
    unsigned NumEntries = read_vbr_uint();
    for (unsigned i = 0; i < NumEntries; ++i) {
      // Symtab entry: [def slot #][name]
      unsigned slot = read_vbr_uint();
      std::string Name = read_str();
      const Type* T = getType(slot);
      ST->insert(Name, T);
    }
  }

  while (moreInBlock()) {
    // Symtab block header: [num entries][type id number]
    unsigned NumEntries = read_vbr_uint();
    unsigned Typ = 0;
    bool isTypeType = read_typeid(Typ);

    for (unsigned i = 0; i != NumEntries; ++i) {
      // Symtab entry: [def slot #][name]
      unsigned slot = read_vbr_uint();
      std::string Name = read_str();

      // if we're reading a pre 1.3 bytecode file and the type plane
      // is the "type type", handle it here
      if (isTypeType) {
        const Type* T = getType(slot);
        if (T == 0)
          error("Failed type look-up for name '" + Name + "'");
        ST->insert(Name, T);
        continue; // code below must be short circuited
      } else {
        Value *V = 0;
        if (Typ == Type::LabelTyID) {
          if (slot < BBMap.size())
            V = BBMap[slot];
        } else {
          V = getValue(Typ, slot, false); // Find mapping...
        }
        if (V == 0)
          error("Failed value look-up for name '" + Name + "'");
        V->setName(Name);
      }
    }
  }
  checkPastBlockEnd("Symbol Table");
  if (Handler) Handler->handleSymbolTableEnd();
}

/// Read in the types portion of a compaction table.
void BytecodeReader::ParseCompactionTypes(unsigned NumEntries) {
  for (unsigned i = 0; i != NumEntries; ++i) {
    unsigned TypeSlot = 0;
    if (read_typeid(TypeSlot))
      error("Invalid type in compaction table: type type");
    const Type *Typ = getGlobalTableType(TypeSlot);
    CompactionTypes.push_back(std::make_pair(Typ, TypeSlot));
    if (Handler) Handler->handleCompactionTableType(i, TypeSlot, Typ);
  }
}

/// Parse a compaction table.
void BytecodeReader::ParseCompactionTable() {

  // Notify handler that we're beginning a compaction table.
  if (Handler) Handler->handleCompactionTableBegin();

  // In LLVM 1.3 Type no longer derives from Value. So,
  // we always write them first in the compaction table
  // because they can't occupy a "type plane" where the
  // Values reside.
  if (! hasTypeDerivedFromValue) {
    unsigned NumEntries = read_vbr_uint();
    ParseCompactionTypes(NumEntries);
  }

  // Compaction tables live in separate blocks so we have to loop
  // until we've read the whole thing.
  while (moreInBlock()) {
    // Read the number of Value* entries in the compaction table
    unsigned NumEntries = read_vbr_uint();
    unsigned Ty = 0;
    unsigned isTypeType = false;

    // Decode the type from value read in. Most compaction table
    // planes will have one or two entries in them. If that's the
    // case then the length is encoded in the bottom two bits and
    // the higher bits encode the type. This saves another VBR value.
    if ((NumEntries & 3) == 3) {
      // In this case, both low-order bits are set (value 3). This
      // is a signal that the typeid follows.
      NumEntries >>= 2;
      isTypeType = read_typeid(Ty);
    } else {
      // In this case, the low-order bits specify the number of entries
      // and the high order bits specify the type.
      Ty = NumEntries >> 2;
      isTypeType = sanitizeTypeId(Ty);
      NumEntries &= 3;
    }

    // if we're reading a pre 1.3 bytecode file and the type plane
    // is the "type type", handle it here
    if (isTypeType) {
      ParseCompactionTypes(NumEntries);
    } else {
      // Make sure we have enough room for the plane.
      if (Ty >= CompactionValues.size())
        CompactionValues.resize(Ty+1);

      // Make sure the plane is empty or we have some kind of error.
      if (!CompactionValues[Ty].empty())
        error("Compaction table plane contains multiple entries!");

      // Notify handler about the plane.
      if (Handler) Handler->handleCompactionTablePlane(Ty, NumEntries);

      // Push the implicit zero.
      CompactionValues[Ty].push_back(Constant::getNullValue(getType(Ty)));

      // Read in each of the entries, put them in the compaction table
      // and notify the handler that we have a new compaction table value.
      for (unsigned i = 0; i != NumEntries; ++i) {
        unsigned ValSlot = read_vbr_uint();
        Value *V = getGlobalTableValue(Ty, ValSlot);
        CompactionValues[Ty].push_back(V);
        if (Handler) Handler->handleCompactionTableValue(i, Ty, ValSlot);
      }
    }
  }
  // Notify handler that the compaction table is done.
  if (Handler) Handler->handleCompactionTableEnd();
}

// Parse a single type. The typeid is read in first. If its a primitive type
// then nothing else needs to be read, we know how to instantiate it. If its
// a derived type, then additional data is read to fill out the type
// definition.
const Type *BytecodeReader::ParseType() {
  unsigned PrimType = 0;
  if (read_typeid(PrimType))
    error("Invalid type (type type) in type constants!");

  const Type *Result = 0;
  if ((Result = Type::getPrimitiveType((Type::TypeID)PrimType)))
    return Result;

  switch (PrimType) {
  case Type::FunctionTyID: {
    const Type *RetType = readSanitizedType();

    unsigned NumParams = read_vbr_uint();

    std::vector<const Type*> Params;
    while (NumParams--)
      Params.push_back(readSanitizedType());

    bool isVarArg = Params.size() && Params.back() == Type::VoidTy;
    if (isVarArg) Params.pop_back();

    Result = FunctionType::get(RetType, Params, isVarArg);
    break;
  }
  case Type::ArrayTyID: {
    const Type *ElementType = readSanitizedType();
    unsigned NumElements = read_vbr_uint();
    Result =  ArrayType::get(ElementType, NumElements);
    break;
  }
  case Type::PackedTyID: {
    const Type *ElementType = readSanitizedType();
    unsigned NumElements = read_vbr_uint();
    Result =  PackedType::get(ElementType, NumElements);
    break;
  }
  case Type::StructTyID: {
    std::vector<const Type*> Elements;
    unsigned Typ = 0;
    if (read_typeid(Typ))
      error("Invalid element type (type type) for structure!");

    while (Typ) {         // List is terminated by void/0 typeid
      Elements.push_back(getType(Typ));
      if (read_typeid(Typ))
        error("Invalid element type (type type) for structure!");
    }

    Result = StructType::get(Elements);
    break;
  }
  case Type::PointerTyID: {
    Result = PointerType::get(readSanitizedType());
    break;
  }

  case Type::OpaqueTyID: {
    Result = OpaqueType::get();
    break;
  }

  default:
    error("Don't know how to deserialize primitive type " + utostr(PrimType));
    break;
  }
  if (Handler) Handler->handleType(Result);
  return Result;
}

// ParseTypes - We have to use this weird code to handle recursive
// types.  We know that recursive types will only reference the current slab of
// values in the type plane, but they can forward reference types before they
// have been read.  For example, Type #0 might be '{ Ty#1 }' and Type #1 might
// be 'Ty#0*'.  When reading Type #0, type number one doesn't exist.  To fix
// this ugly problem, we pessimistically insert an opaque type for each type we
// are about to read.  This means that forward references will resolve to
// something and when we reread the type later, we can replace the opaque type
// with a new resolved concrete type.
//
void BytecodeReader::ParseTypes(TypeListTy &Tab, unsigned NumEntries){
  assert(Tab.size() == 0 && "should not have read type constants in before!");

  // Insert a bunch of opaque types to be resolved later...
  Tab.reserve(NumEntries);
  for (unsigned i = 0; i != NumEntries; ++i)
    Tab.push_back(OpaqueType::get());

  if (Handler)
    Handler->handleTypeList(NumEntries);

  // If we are about to resolve types, make sure the type cache is clear.
  if (NumEntries)
    ModuleTypeIDCache.clear();
  
  // Loop through reading all of the types.  Forward types will make use of the
  // opaque types just inserted.
  //
  for (unsigned i = 0; i != NumEntries; ++i) {
    const Type* NewTy = ParseType();
    const Type* OldTy = Tab[i].get();
    if (NewTy == 0)
      error("Couldn't parse type!");

    // Don't directly push the new type on the Tab. Instead we want to replace
    // the opaque type we previously inserted with the new concrete value. This
    // approach helps with forward references to types. The refinement from the
    // abstract (opaque) type to the new type causes all uses of the abstract
    // type to use the concrete type (NewTy). This will also cause the opaque
    // type to be deleted.
    cast<DerivedType>(const_cast<Type*>(OldTy))->refineAbstractTypeTo(NewTy);

    // This should have replaced the old opaque type with the new type in the
    // value table... or with a preexisting type that was already in the system.
    // Let's just make sure it did.
    assert(Tab[i] != OldTy && "refineAbstractType didn't work!");
  }
}

// Upgrade obsolete constant expression opcodes (ver. 5 and prior) to the new 
// values used after ver 6. bytecode format. The operands are provided to the
// function so that decisions based on the operand type can be made when 
// auto-upgrading obsolete opcodes to the new ones.
// NOTE: This code needs to be kept synchronized with handleObsoleteOpcodes. 
// We can't use that function because of that functions argument requirements.
// This function only deals with the subset of opcodes that are applicable to
// constant expressions and is therefore simpler than handleObsoleteOpcodes.
inline unsigned fixCEOpcodes(
  unsigned Opcode, const std::vector<Constant*> &ArgVec
) {
  switch (Opcode) {
    default: // Pass Through
      // If we don't match any of the cases here then the opcode is fine the
      // way it is.
      break;
    case 7: // Add
      Opcode = Instruction::Add;
      break;
    case 8: // Sub
      Opcode = Instruction::Sub;
      break;
    case 9: // Mul
      Opcode = Instruction::Mul;
      break;
    case 10: // Div 
      // The type of the instruction is based on the operands. We need to select
      // either udiv or sdiv based on that type. This expression selects the
      // cases where the type is floating point or signed in which case we
      // generated an sdiv instruction.
      if (ArgVec[0]->getType()->isFloatingPoint())
        Opcode = Instruction::FDiv;
      else if (ArgVec[0]->getType()->isSigned())
        Opcode = Instruction::SDiv;
      else
        Opcode = Instruction::UDiv;
      break;
    case 11: // Rem
      // As with "Div", make the signed/unsigned or floating point Rem 
      // instruction choice based on the type of the operands.
      if (ArgVec[0]->getType()->isFloatingPoint())
        Opcode = Instruction::FRem;
      else if (ArgVec[0]->getType()->isSigned())
        Opcode = Instruction::SRem;
      else
        Opcode = Instruction::URem;
      break;
    case 12: // And
      Opcode = Instruction::And;
      break;
    case 13: // Or
      Opcode = Instruction::Or;
      break;
    case 14: // Xor
      Opcode = Instruction::Xor;
      break;
    case 15: // SetEQ
      Opcode = Instruction::SetEQ;
      break;
    case 16: // SetNE
      Opcode = Instruction::SetNE;
      break;
    case 17: // SetLE
      Opcode = Instruction::SetLE;
      break;
    case 18: // SetGE
      Opcode = Instruction::SetGE;
      break;
    case 19: // SetLT
      Opcode = Instruction::SetLT;
      break;
    case 20: // SetGT
      Opcode = Instruction::SetGT;
      break;
    case 26: // GetElementPtr
      Opcode = Instruction::GetElementPtr;
      break;
    case 28: // Cast
      Opcode = Instruction::Cast;
      break;
    case 30: // Shl
      Opcode = Instruction::Shl;
      break;
    case 31: // Shr
      Opcode = Instruction::Shr;
      break;
    case 34: // Select
      Opcode = Instruction::Select;
      break;
    case 38: // ExtractElement
      Opcode = Instruction::ExtractElement;
      break;
    case 39: // InsertElement
      Opcode = Instruction::InsertElement;
      break;
    case 40: // ShuffleVector
      Opcode = Instruction::ShuffleVector;
      break;
  }
  return Opcode;
}

/// Parse a single constant value
Value *BytecodeReader::ParseConstantPoolValue(unsigned TypeID) {
  // We must check for a ConstantExpr before switching by type because
  // a ConstantExpr can be of any type, and has no explicit value.
  //
  // 0 if not expr; numArgs if is expr
  unsigned isExprNumArgs = read_vbr_uint();

  if (isExprNumArgs) {
    if (!hasNoUndefValue) {
      // 'undef' is encoded with 'exprnumargs' == 1.
      if (isExprNumArgs == 1)
        return UndefValue::get(getType(TypeID));

      // Inline asm is encoded with exprnumargs == ~0U.
      if (isExprNumArgs == ~0U) {
        std::string AsmStr = read_str();
        std::string ConstraintStr = read_str();
        unsigned Flags = read_vbr_uint();
        
        const PointerType *PTy = dyn_cast<PointerType>(getType(TypeID));
        const FunctionType *FTy = 
          PTy ? dyn_cast<FunctionType>(PTy->getElementType()) : 0;

        if (!FTy || !InlineAsm::Verify(FTy, ConstraintStr))
          error("Invalid constraints for inline asm");
        if (Flags & ~1U)
          error("Invalid flags for inline asm");
        bool HasSideEffects = Flags & 1;
        return InlineAsm::get(FTy, AsmStr, ConstraintStr, HasSideEffects);
      }
      
      --isExprNumArgs;
    }

    // FIXME: Encoding of constant exprs could be much more compact!
    std::vector<Constant*> ArgVec;
    ArgVec.reserve(isExprNumArgs);
    unsigned Opcode = read_vbr_uint();

    // Bytecode files before LLVM 1.4 need have a missing terminator inst.
    if (hasNoUnreachableInst) Opcode++;

    // Read the slot number and types of each of the arguments
    for (unsigned i = 0; i != isExprNumArgs; ++i) {
      unsigned ArgValSlot = read_vbr_uint();
      unsigned ArgTypeSlot = 0;
      if (read_typeid(ArgTypeSlot))
        error("Invalid argument type (type type) for constant value");

      // Get the arg value from its slot if it exists, otherwise a placeholder
      ArgVec.push_back(getConstantValue(ArgTypeSlot, ArgValSlot));
    }

    // Handle backwards compatibility for the opcode numbers
    if (hasSignlessInstructions)
      Opcode = fixCEOpcodes(Opcode, ArgVec);

    // Construct a ConstantExpr of the appropriate kind
    if (isExprNumArgs == 1) {           // All one-operand expressions
      if (Opcode != Instruction::Cast)
        error("Only cast instruction has one argument for ConstantExpr");

      Constant* Result = ConstantExpr::getCast(ArgVec[0], getType(TypeID));
      if (Handler) Handler->handleConstantExpression(Opcode, ArgVec, Result);
      return Result;
    } else if (Opcode == Instruction::GetElementPtr) { // GetElementPtr
      std::vector<Constant*> IdxList(ArgVec.begin()+1, ArgVec.end());

      if (hasRestrictedGEPTypes) {
        const Type *BaseTy = ArgVec[0]->getType();
        generic_gep_type_iterator<std::vector<Constant*>::iterator>
          GTI = gep_type_begin(BaseTy, IdxList.begin(), IdxList.end()),
          E = gep_type_end(BaseTy, IdxList.begin(), IdxList.end());
        for (unsigned i = 0; GTI != E; ++GTI, ++i)
          if (isa<StructType>(*GTI)) {
            if (IdxList[i]->getType() != Type::UByteTy)
              error("Invalid index for getelementptr!");
            IdxList[i] = ConstantExpr::getCast(IdxList[i], Type::UIntTy);
          }
      }

      Constant* Result = ConstantExpr::getGetElementPtr(ArgVec[0], IdxList);
      if (Handler) Handler->handleConstantExpression(Opcode, ArgVec, Result);
      return Result;
    } else if (Opcode == Instruction::Select) {
      if (ArgVec.size() != 3)
        error("Select instruction must have three arguments.");
      Constant* Result = ConstantExpr::getSelect(ArgVec[0], ArgVec[1],
                                                 ArgVec[2]);
      if (Handler) Handler->handleConstantExpression(Opcode, ArgVec, Result);
      return Result;
    } else if (Opcode == Instruction::ExtractElement) {
      if (ArgVec.size() != 2 ||
          !ExtractElementInst::isValidOperands(ArgVec[0], ArgVec[1]))
        error("Invalid extractelement constand expr arguments");
      Constant* Result = ConstantExpr::getExtractElement(ArgVec[0], ArgVec[1]);
      if (Handler) Handler->handleConstantExpression(Opcode, ArgVec, Result);
      return Result;
    } else if (Opcode == Instruction::InsertElement) {
      if (ArgVec.size() != 3 ||
          !InsertElementInst::isValidOperands(ArgVec[0], ArgVec[1], ArgVec[2]))
        error("Invalid insertelement constand expr arguments");
        
      Constant *Result = 
        ConstantExpr::getInsertElement(ArgVec[0], ArgVec[1], ArgVec[2]);
      if (Handler) Handler->handleConstantExpression(Opcode, ArgVec, Result);
      return Result;
    } else if (Opcode == Instruction::ShuffleVector) {
      if (ArgVec.size() != 3 ||
          !ShuffleVectorInst::isValidOperands(ArgVec[0], ArgVec[1], ArgVec[2]))
        error("Invalid shufflevector constant expr arguments.");
      Constant *Result = 
        ConstantExpr::getShuffleVector(ArgVec[0], ArgVec[1], ArgVec[2]);
      if (Handler) Handler->handleConstantExpression(Opcode, ArgVec, Result);
      return Result;
    } else {                            // All other 2-operand expressions
      Constant* Result = ConstantExpr::get(Opcode, ArgVec[0], ArgVec[1]);
      if (Handler) Handler->handleConstantExpression(Opcode, ArgVec, Result);
      return Result;
    }
  }

  // Ok, not an ConstantExpr.  We now know how to read the given type...
  const Type *Ty = getType(TypeID);
  Constant *Result = 0;
  switch (Ty->getTypeID()) {
  case Type::BoolTyID: {
    unsigned Val = read_vbr_uint();
    if (Val != 0 && Val != 1)
      error("Invalid boolean value read.");
    Result = ConstantBool::get(Val == 1);
    if (Handler) Handler->handleConstantValue(Result);
    break;
  }

  case Type::UByteTyID:   // Unsigned integer types...
  case Type::UShortTyID:
  case Type::UIntTyID: {
    unsigned Val = read_vbr_uint();
    if (!ConstantInt::isValueValidForType(Ty, uint64_t(Val)))
      error("Invalid unsigned byte/short/int read.");
    Result = ConstantInt::get(Ty, Val);
    if (Handler) Handler->handleConstantValue(Result);
    break;
  }

  case Type::ULongTyID:
    Result = ConstantInt::get(Ty, read_vbr_uint64());
    if (Handler) Handler->handleConstantValue(Result);
    break;
    
  case Type::SByteTyID:   // Signed integer types...
  case Type::ShortTyID:
  case Type::IntTyID:
  case Type::LongTyID: {
    int64_t Val = read_vbr_int64();
    if (!ConstantInt::isValueValidForType(Ty, Val))
      error("Invalid signed byte/short/int/long read.");
    Result = ConstantInt::get(Ty, Val);
    if (Handler) Handler->handleConstantValue(Result);
    break;
  }

  case Type::FloatTyID: {
    float Val;
    read_float(Val);
    Result = ConstantFP::get(Ty, Val);
    if (Handler) Handler->handleConstantValue(Result);
    break;
  }

  case Type::DoubleTyID: {
    double Val;
    read_double(Val);
    Result = ConstantFP::get(Ty, Val);
    if (Handler) Handler->handleConstantValue(Result);
    break;
  }

  case Type::ArrayTyID: {
    const ArrayType *AT = cast<ArrayType>(Ty);
    unsigned NumElements = AT->getNumElements();
    unsigned TypeSlot = getTypeSlot(AT->getElementType());
    std::vector<Constant*> Elements;
    Elements.reserve(NumElements);
    while (NumElements--)     // Read all of the elements of the constant.
      Elements.push_back(getConstantValue(TypeSlot,
                                          read_vbr_uint()));
    Result = ConstantArray::get(AT, Elements);
    if (Handler) Handler->handleConstantArray(AT, Elements, TypeSlot, Result);
    break;
  }

  case Type::StructTyID: {
    const StructType *ST = cast<StructType>(Ty);

    std::vector<Constant *> Elements;
    Elements.reserve(ST->getNumElements());
    for (unsigned i = 0; i != ST->getNumElements(); ++i)
      Elements.push_back(getConstantValue(ST->getElementType(i),
                                          read_vbr_uint()));

    Result = ConstantStruct::get(ST, Elements);
    if (Handler) Handler->handleConstantStruct(ST, Elements, Result);
    break;
  }

  case Type::PackedTyID: {
    const PackedType *PT = cast<PackedType>(Ty);
    unsigned NumElements = PT->getNumElements();
    unsigned TypeSlot = getTypeSlot(PT->getElementType());
    std::vector<Constant*> Elements;
    Elements.reserve(NumElements);
    while (NumElements--)     // Read all of the elements of the constant.
      Elements.push_back(getConstantValue(TypeSlot,
                                          read_vbr_uint()));
    Result = ConstantPacked::get(PT, Elements);
    if (Handler) Handler->handleConstantPacked(PT, Elements, TypeSlot, Result);
    break;
  }

  case Type::PointerTyID: {  // ConstantPointerRef value (backwards compat).
    const PointerType *PT = cast<PointerType>(Ty);
    unsigned Slot = read_vbr_uint();

    // Check to see if we have already read this global variable...
    Value *Val = getValue(TypeID, Slot, false);
    if (Val) {
      GlobalValue *GV = dyn_cast<GlobalValue>(Val);
      if (!GV) error("GlobalValue not in ValueTable!");
      if (Handler) Handler->handleConstantPointer(PT, Slot, GV);
      return GV;
    } else {
      error("Forward references are not allowed here.");
    }
  }

  default:
    error("Don't know how to deserialize constant value of type '" +
                      Ty->getDescription());
    break;
  }
  
  // Check that we didn't read a null constant if they are implicit for this
  // type plane.  Do not do this check for constantexprs, as they may be folded
  // to a null value in a way that isn't predicted when a .bc file is initially
  // produced.
  assert((!isa<Constant>(Result) || !cast<Constant>(Result)->isNullValue()) ||
         !hasImplicitNull(TypeID) &&
         "Cannot read null values from bytecode!");
  return Result;
}

/// Resolve references for constants. This function resolves the forward
/// referenced constants in the ConstantFwdRefs map. It uses the
/// replaceAllUsesWith method of Value class to substitute the placeholder
/// instance with the actual instance.
void BytecodeReader::ResolveReferencesToConstant(Constant *NewV, unsigned Typ,
                                                 unsigned Slot) {
  ConstantRefsType::iterator I =
    ConstantFwdRefs.find(std::make_pair(Typ, Slot));
  if (I == ConstantFwdRefs.end()) return;   // Never forward referenced?

  Value *PH = I->second;   // Get the placeholder...
  PH->replaceAllUsesWith(NewV);
  delete PH;                               // Delete the old placeholder
  ConstantFwdRefs.erase(I);                // Remove the map entry for it
}

/// Parse the constant strings section.
void BytecodeReader::ParseStringConstants(unsigned NumEntries, ValueTable &Tab){
  for (; NumEntries; --NumEntries) {
    unsigned Typ = 0;
    if (read_typeid(Typ))
      error("Invalid type (type type) for string constant");
    const Type *Ty = getType(Typ);
    if (!isa<ArrayType>(Ty))
      error("String constant data invalid!");

    const ArrayType *ATy = cast<ArrayType>(Ty);
    if (ATy->getElementType() != Type::SByteTy &&
        ATy->getElementType() != Type::UByteTy)
      error("String constant data invalid!");

    // Read character data.  The type tells us how long the string is.
    char *Data = reinterpret_cast<char *>(alloca(ATy->getNumElements()));
    read_data(Data, Data+ATy->getNumElements());

    std::vector<Constant*> Elements(ATy->getNumElements());
    const Type* ElemType = ATy->getElementType();
    for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i)
      Elements[i] = ConstantInt::get(ElemType, (unsigned char)Data[i]);

    // Create the constant, inserting it as needed.
    Constant *C = ConstantArray::get(ATy, Elements);
    unsigned Slot = insertValue(C, Typ, Tab);
    ResolveReferencesToConstant(C, Typ, Slot);
    if (Handler) Handler->handleConstantString(cast<ConstantArray>(C));
  }
}

/// Parse the constant pool.
void BytecodeReader::ParseConstantPool(ValueTable &Tab,
                                       TypeListTy &TypeTab,
                                       bool isFunction) {
  if (Handler) Handler->handleGlobalConstantsBegin();

  /// In LLVM 1.3 Type does not derive from Value so the types
  /// do not occupy a plane. Consequently, we read the types
  /// first in the constant pool.
  if (isFunction && !hasTypeDerivedFromValue) {
    unsigned NumEntries = read_vbr_uint();
    ParseTypes(TypeTab, NumEntries);
  }

  while (moreInBlock()) {
    unsigned NumEntries = read_vbr_uint();
    unsigned Typ = 0;
    bool isTypeType = read_typeid(Typ);

    /// In LLVM 1.2 and before, Types were written to the
    /// bytecode file in the "Type Type" plane (#12).
    /// In 1.3 plane 12 is now the label plane.  Handle this here.
    if (isTypeType) {
      ParseTypes(TypeTab, NumEntries);
    } else if (Typ == Type::VoidTyID) {
      /// Use of Type::VoidTyID is a misnomer. It actually means
      /// that the following plane is constant strings
      assert(&Tab == &ModuleValues && "Cannot read strings in functions!");
      ParseStringConstants(NumEntries, Tab);
    } else {
      for (unsigned i = 0; i < NumEntries; ++i) {
        Value *V = ParseConstantPoolValue(Typ);
        assert(V && "ParseConstantPoolValue returned NULL!");
        unsigned Slot = insertValue(V, Typ, Tab);

        // If we are reading a function constant table, make sure that we adjust
        // the slot number to be the real global constant number.
        //
        if (&Tab != &ModuleValues && Typ < ModuleValues.size() &&
            ModuleValues[Typ])
          Slot += ModuleValues[Typ]->size();
        if (Constant *C = dyn_cast<Constant>(V))
          ResolveReferencesToConstant(C, Typ, Slot);
      }
    }
  }

  // After we have finished parsing the constant pool, we had better not have
  // any dangling references left.
  if (!ConstantFwdRefs.empty()) {
    ConstantRefsType::const_iterator I = ConstantFwdRefs.begin();
    Constant* missingConst = I->second;
    error(utostr(ConstantFwdRefs.size()) +
          " unresolved constant reference exist. First one is '" +
          missingConst->getName() + "' of type '" +
          missingConst->getType()->getDescription() + "'.");
  }

  checkPastBlockEnd("Constant Pool");
  if (Handler) Handler->handleGlobalConstantsEnd();
}

/// Parse the contents of a function. Note that this function can be
/// called lazily by materializeFunction
/// @see materializeFunction
void BytecodeReader::ParseFunctionBody(Function* F) {

  unsigned FuncSize = BlockEnd - At;
  GlobalValue::LinkageTypes Linkage = GlobalValue::ExternalLinkage;

  unsigned LinkageType = read_vbr_uint();
  switch (LinkageType) {
  case 0: Linkage = GlobalValue::ExternalLinkage; break;
  case 1: Linkage = GlobalValue::WeakLinkage; break;
  case 2: Linkage = GlobalValue::AppendingLinkage; break;
  case 3: Linkage = GlobalValue::InternalLinkage; break;
  case 4: Linkage = GlobalValue::LinkOnceLinkage; break;
  case 5: Linkage = GlobalValue::DLLImportLinkage; break;
  case 6: Linkage = GlobalValue::DLLExportLinkage; break;
  case 7: Linkage = GlobalValue::ExternalWeakLinkage; break;
  default:
    error("Invalid linkage type for Function.");
    Linkage = GlobalValue::InternalLinkage;
    break;
  }

  F->setLinkage(Linkage);
  if (Handler) Handler->handleFunctionBegin(F,FuncSize);

  // Keep track of how many basic blocks we have read in...
  unsigned BlockNum = 0;
  bool InsertedArguments = false;

  BufPtr MyEnd = BlockEnd;
  while (At < MyEnd) {
    unsigned Type, Size;
    BufPtr OldAt = At;
    read_block(Type, Size);

    switch (Type) {
    case BytecodeFormat::ConstantPoolBlockID:
      if (!InsertedArguments) {
        // Insert arguments into the value table before we parse the first basic
        // block in the function, but after we potentially read in the
        // compaction table.
        insertArguments(F);
        InsertedArguments = true;
      }

      ParseConstantPool(FunctionValues, FunctionTypes, true);
      break;

    case BytecodeFormat::CompactionTableBlockID:
      ParseCompactionTable();
      break;

    case BytecodeFormat::BasicBlock: {
      if (!InsertedArguments) {
        // Insert arguments into the value table before we parse the first basic
        // block in the function, but after we potentially read in the
        // compaction table.
        insertArguments(F);
        InsertedArguments = true;
      }

      BasicBlock *BB = ParseBasicBlock(BlockNum++);
      F->getBasicBlockList().push_back(BB);
      break;
    }

    case BytecodeFormat::InstructionListBlockID: {
      // Insert arguments into the value table before we parse the instruction
      // list for the function, but after we potentially read in the compaction
      // table.
      if (!InsertedArguments) {
        insertArguments(F);
        InsertedArguments = true;
      }

      if (BlockNum)
        error("Already parsed basic blocks!");
      BlockNum = ParseInstructionList(F);
      break;
    }

    case BytecodeFormat::SymbolTableBlockID:
      ParseSymbolTable(F, &F->getSymbolTable());
      break;

    default:
      At += Size;
      if (OldAt > At)
        error("Wrapped around reading bytecode.");
      break;
    }
    BlockEnd = MyEnd;

    // Malformed bc file if read past end of block.
    align32();
  }

  // Make sure there were no references to non-existant basic blocks.
  if (BlockNum != ParsedBasicBlocks.size())
    error("Illegal basic block operand reference");

  ParsedBasicBlocks.clear();

  // Resolve forward references.  Replace any uses of a forward reference value
  // with the real value.
  while (!ForwardReferences.empty()) {
    std::map<std::pair<unsigned,unsigned>, Value*>::iterator
      I = ForwardReferences.begin();
    Value *V = getValue(I->first.first, I->first.second, false);
    Value *PlaceHolder = I->second;
    PlaceHolder->replaceAllUsesWith(V);
    ForwardReferences.erase(I);
    delete PlaceHolder;
  }

  // If upgraded intrinsic functions were detected during reading of the 
  // module information, then we need to look for instructions that need to
  // be upgraded. This can't be done while the instructions are read in because
  // additional instructions inserted mess up the slot numbering.
  if (!upgradedFunctions.empty()) {
    for (Function::iterator BI = F->begin(), BE = F->end(); BI != BE; ++BI) 
      for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); 
           II != IE;)
        if (CallInst* CI = dyn_cast<CallInst>(II++)) {
          std::map<Function*,Function*>::iterator FI = 
            upgradedFunctions.find(CI->getCalledFunction());
          if (FI != upgradedFunctions.end())
            UpgradeIntrinsicCall(CI, FI->second);
        }
  }

  // Clear out function-level types...
  FunctionTypes.clear();
  CompactionTypes.clear();
  CompactionValues.clear();
  freeTable(FunctionValues);

  if (Handler) Handler->handleFunctionEnd(F);
}

/// This function parses LLVM functions lazily. It obtains the type of the
/// function and records where the body of the function is in the bytecode
/// buffer. The caller can then use the ParseNextFunction and
/// ParseAllFunctionBodies to get handler events for the functions.
void BytecodeReader::ParseFunctionLazily() {
  if (FunctionSignatureList.empty())
    error("FunctionSignatureList empty!");

  Function *Func = FunctionSignatureList.back();
  FunctionSignatureList.pop_back();

  // Save the information for future reading of the function
  LazyFunctionLoadMap[Func] = LazyFunctionInfo(BlockStart, BlockEnd);

  // This function has a body but it's not loaded so it appears `External'.
  // Mark it as a `Ghost' instead to notify the users that it has a body.
  Func->setLinkage(GlobalValue::GhostLinkage);

  // Pretend we've `parsed' this function
  At = BlockEnd;
}

/// The ParserFunction method lazily parses one function. Use this method to
/// casue the parser to parse a specific function in the module. Note that
/// this will remove the function from what is to be included by
/// ParseAllFunctionBodies.
/// @see ParseAllFunctionBodies
/// @see ParseBytecode
bool BytecodeReader::ParseFunction(Function* Func, std::string* ErrMsg) {

  if (setjmp(context))
    return true;

  // Find {start, end} pointers and slot in the map. If not there, we're done.
  LazyFunctionMap::iterator Fi = LazyFunctionLoadMap.find(Func);

  // Make sure we found it
  if (Fi == LazyFunctionLoadMap.end()) {
    error("Unrecognized function of type " + Func->getType()->getDescription());
    return true;
  }

  BlockStart = At = Fi->second.Buf;
  BlockEnd = Fi->second.EndBuf;
  assert(Fi->first == Func && "Found wrong function?");

  LazyFunctionLoadMap.erase(Fi);

  this->ParseFunctionBody(Func);
  return false;
}

/// The ParseAllFunctionBodies method parses through all the previously
/// unparsed functions in the bytecode file. If you want to completely parse
/// a bytecode file, this method should be called after Parsebytecode because
/// Parsebytecode only records the locations in the bytecode file of where
/// the function definitions are located. This function uses that information
/// to materialize the functions.
/// @see ParseBytecode
bool BytecodeReader::ParseAllFunctionBodies(std::string* ErrMsg) {
  if (setjmp(context))
    return true;

  LazyFunctionMap::iterator Fi = LazyFunctionLoadMap.begin();
  LazyFunctionMap::iterator Fe = LazyFunctionLoadMap.end();

  while (Fi != Fe) {
    Function* Func = Fi->first;
    BlockStart = At = Fi->second.Buf;
    BlockEnd = Fi->second.EndBuf;
    ParseFunctionBody(Func);
    ++Fi;
  }
  LazyFunctionLoadMap.clear();
  return false;
}

/// Parse the global type list
void BytecodeReader::ParseGlobalTypes() {
  // Read the number of types
  unsigned NumEntries = read_vbr_uint();

  // Ignore the type plane identifier for types if the bc file is pre 1.3
  if (hasTypeDerivedFromValue)
    read_vbr_uint();

  ParseTypes(ModuleTypes, NumEntries);
}

/// Parse the Global info (types, global vars, constants)
void BytecodeReader::ParseModuleGlobalInfo() {

  if (Handler) Handler->handleModuleGlobalsBegin();

  // SectionID - If a global has an explicit section specified, this map
  // remembers the ID until we can translate it into a string.
  std::map<GlobalValue*, unsigned> SectionID;
  
  // Read global variables...
  unsigned VarType = read_vbr_uint();
  while (VarType != Type::VoidTyID) { // List is terminated by Void
    // VarType Fields: bit0 = isConstant, bit1 = hasInitializer, bit2,3,4 =
    // Linkage, bit4+ = slot#
    unsigned SlotNo = VarType >> 5;
    if (sanitizeTypeId(SlotNo))
      error("Invalid type (type type) for global var!");
    unsigned LinkageID = (VarType >> 2) & 7;
    bool isConstant = VarType & 1;
    bool hasInitializer = (VarType & 2) != 0;
    unsigned Alignment = 0;
    unsigned GlobalSectionID = 0;
    
    // An extension word is present when linkage = 3 (internal) and hasinit = 0.
    if (LinkageID == 3 && !hasInitializer) {
      unsigned ExtWord = read_vbr_uint();
      // The extension word has this format: bit 0 = has initializer, bit 1-3 =
      // linkage, bit 4-8 = alignment (log2), bits 10+ = future use.
      hasInitializer = ExtWord & 1;
      LinkageID = (ExtWord >> 1) & 7;
      Alignment = (1 << ((ExtWord >> 4) & 31)) >> 1;
      
      if (ExtWord & (1 << 9))  // Has a section ID.
        GlobalSectionID = read_vbr_uint();
    }

    GlobalValue::LinkageTypes Linkage;
    switch (LinkageID) {
    case 0: Linkage = GlobalValue::ExternalLinkage;  break;
    case 1: Linkage = GlobalValue::WeakLinkage;      break;
    case 2: Linkage = GlobalValue::AppendingLinkage; break;
    case 3: Linkage = GlobalValue::InternalLinkage;  break;
    case 4: Linkage = GlobalValue::LinkOnceLinkage;  break;
    case 5: Linkage = GlobalValue::DLLImportLinkage;  break;
    case 6: Linkage = GlobalValue::DLLExportLinkage;  break;
    case 7: Linkage = GlobalValue::ExternalWeakLinkage;  break;
    default:
      error("Unknown linkage type: " + utostr(LinkageID));
      Linkage = GlobalValue::InternalLinkage;
      break;
    }

    const Type *Ty = getType(SlotNo);
    if (!Ty)
      error("Global has no type! SlotNo=" + utostr(SlotNo));

    if (!isa<PointerType>(Ty))
      error("Global not a pointer type! Ty= " + Ty->getDescription());

    const Type *ElTy = cast<PointerType>(Ty)->getElementType();

    // Create the global variable...
    GlobalVariable *GV = new GlobalVariable(ElTy, isConstant, Linkage,
                                            0, "", TheModule);
    GV->setAlignment(Alignment);
    insertValue(GV, SlotNo, ModuleValues);

    if (GlobalSectionID != 0)
      SectionID[GV] = GlobalSectionID;

    unsigned initSlot = 0;
    if (hasInitializer) {
      initSlot = read_vbr_uint();
      GlobalInits.push_back(std::make_pair(GV, initSlot));
    }

    // Notify handler about the global value.
    if (Handler)
      Handler->handleGlobalVariable(ElTy, isConstant, Linkage, SlotNo,initSlot);

    // Get next item
    VarType = read_vbr_uint();
  }

  // Read the function objects for all of the functions that are coming
  unsigned FnSignature = read_vbr_uint();

  if (hasNoFlagsForFunctions)
    FnSignature = (FnSignature << 5) + 1;

  // List is terminated by VoidTy.
  while (((FnSignature & (~0U >> 1)) >> 5) != Type::VoidTyID) {
    const Type *Ty = getType((FnSignature & (~0U >> 1)) >> 5);
    if (!isa<PointerType>(Ty) ||
        !isa<FunctionType>(cast<PointerType>(Ty)->getElementType())) {
      error("Function not a pointer to function type! Ty = " +
            Ty->getDescription());
    }

    // We create functions by passing the underlying FunctionType to create...
    const FunctionType* FTy =
      cast<FunctionType>(cast<PointerType>(Ty)->getElementType());

    // Insert the place holder.
    Function *Func = new Function(FTy, GlobalValue::ExternalLinkage,
                                  "", TheModule);

    insertValue(Func, (FnSignature & (~0U >> 1)) >> 5, ModuleValues);

    // Flags are not used yet.
    unsigned Flags = FnSignature & 31;

    // Save this for later so we know type of lazily instantiated functions.
    // Note that known-external functions do not have FunctionInfo blocks, so we
    // do not add them to the FunctionSignatureList.
    if ((Flags & (1 << 4)) == 0)
      FunctionSignatureList.push_back(Func);

    // Get the calling convention from the low bits.
    unsigned CC = Flags & 15;
    unsigned Alignment = 0;
    if (FnSignature & (1 << 31)) {  // Has extension word?
      unsigned ExtWord = read_vbr_uint();
      Alignment = (1 << (ExtWord & 31)) >> 1;
      CC |= ((ExtWord >> 5) & 15) << 4;
      
      if (ExtWord & (1 << 10))  // Has a section ID.
        SectionID[Func] = read_vbr_uint();

      // Parse external declaration linkage
      switch ((ExtWord >> 11) & 3) {
       case 0: break;
       case 1: Func->setLinkage(Function::DLLImportLinkage); break;
       case 2: Func->setLinkage(Function::ExternalWeakLinkage); break;        
       default: assert(0 && "Unsupported external linkage");        
      }      
    }
    
    Func->setCallingConv(CC-1);
    Func->setAlignment(Alignment);

    if (Handler) Handler->handleFunctionDeclaration(Func);

    // Get the next function signature.
    FnSignature = read_vbr_uint();
    if (hasNoFlagsForFunctions)
      FnSignature = (FnSignature << 5) + 1;
  }

  // Now that the function signature list is set up, reverse it so that we can
  // remove elements efficiently from the back of the vector.
  std::reverse(FunctionSignatureList.begin(), FunctionSignatureList.end());

  /// SectionNames - This contains the list of section names encoded in the
  /// moduleinfoblock.  Functions and globals with an explicit section index
  /// into this to get their section name.
  std::vector<std::string> SectionNames;
  
  if (hasInconsistentModuleGlobalInfo) {
    align32();
  } else if (!hasNoDependentLibraries) {
    // If this bytecode format has dependent library information in it, read in
    // the number of dependent library items that follow.
    unsigned num_dep_libs = read_vbr_uint();
    std::string dep_lib;
    while (num_dep_libs--) {
      dep_lib = read_str();
      TheModule->addLibrary(dep_lib);
      if (Handler)
        Handler->handleDependentLibrary(dep_lib);
    }

    // Read target triple and place into the module.
    std::string triple = read_str();
    TheModule->setTargetTriple(triple);
    if (Handler)
      Handler->handleTargetTriple(triple);
    
    if (!hasAlignment && At != BlockEnd) {
      // If the file has section info in it, read the section names now.
      unsigned NumSections = read_vbr_uint();
      while (NumSections--)
        SectionNames.push_back(read_str());
    }
    
    // If the file has module-level inline asm, read it now.
    if (!hasAlignment && At != BlockEnd)
      TheModule->setModuleInlineAsm(read_str());
  }

  // If any globals are in specified sections, assign them now.
  for (std::map<GlobalValue*, unsigned>::iterator I = SectionID.begin(), E =
       SectionID.end(); I != E; ++I)
    if (I->second) {
      if (I->second > SectionID.size())
        error("SectionID out of range for global!");
      I->first->setSection(SectionNames[I->second-1]);
    }

  // This is for future proofing... in the future extra fields may be added that
  // we don't understand, so we transparently ignore them.
  //
  At = BlockEnd;

  if (Handler) Handler->handleModuleGlobalsEnd();
}

/// Parse the version information and decode it by setting flags on the
/// Reader that enable backward compatibility of the reader.
void BytecodeReader::ParseVersionInfo() {
  unsigned Version = read_vbr_uint();

  // Unpack version number: low four bits are for flags, top bits = version
  Module::Endianness  Endianness;
  Module::PointerSize PointerSize;
  Endianness  = (Version & 1) ? Module::BigEndian : Module::LittleEndian;
  PointerSize = (Version & 2) ? Module::Pointer64 : Module::Pointer32;

  bool hasNoEndianness = Version & 4;
  bool hasNoPointerSize = Version & 8;

  RevisionNum = Version >> 4;

  // Default values for the current bytecode version
  hasInconsistentModuleGlobalInfo = false;
  hasExplicitPrimitiveZeros = false;
  hasRestrictedGEPTypes = false;
  hasTypeDerivedFromValue = false;
  hasLongBlockHeaders = false;
  has32BitTypes = false;
  hasNoDependentLibraries = false;
  hasAlignment = false;
  hasNoUndefValue = false;
  hasNoFlagsForFunctions = false;
  hasNoUnreachableInst = false;
  hasSignlessInstructions = false;

  // Determine which backwards compatibility flags to set based on the
  // bytecode file's version number
  switch (RevisionNum) {
  case 0:               //  LLVM 1.0, 1.1 (Released)
    // Base LLVM 1.0 bytecode format.
    hasInconsistentModuleGlobalInfo = true;
    hasExplicitPrimitiveZeros = true;

    // FALL THROUGH

  case 1:               // LLVM 1.2 (Released)
    // LLVM 1.2 added explicit support for emitting strings efficiently.

    // Also, it fixed the problem where the size of the ModuleGlobalInfo block
    // included the size for the alignment at the end, where the rest of the
    // blocks did not.

    // LLVM 1.2 and before required that GEP indices be ubyte constants for
    // structures and longs for sequential types.
    hasRestrictedGEPTypes = true;

    // LLVM 1.2 and before had the Type class derive from Value class. This
    // changed in release 1.3 and consequently LLVM 1.3 bytecode files are
    // written differently because Types can no longer be part of the
    // type planes for Values.
    hasTypeDerivedFromValue = true;

    // FALL THROUGH

  case 2:                // 1.2.5 (Not Released)

    // LLVM 1.2 and earlier had two-word block headers. This is a bit wasteful,
    // especially for small files where the 8 bytes per block is a large
    // fraction of the total block size. In LLVM 1.3, the block type and length
    // are compressed into a single 32-bit unsigned integer. 27 bits for length,
    // 5 bits for block type.
    hasLongBlockHeaders = true;

    // LLVM 1.2 and earlier wrote type slot numbers as vbr_uint32. In LLVM 1.3
    // this has been reduced to vbr_uint24. It shouldn't make much difference
    // since we haven't run into a module with > 24 million types, but for
    // safety the 24-bit restriction has been enforced in 1.3 to free some bits
    // in various places and to ensure consistency.
    has32BitTypes = true;

    // LLVM 1.2 and earlier did not provide a target triple nor a list of
    // libraries on which the bytecode is dependent. LLVM 1.3 provides these
    // features, for use in future versions of LLVM.
    hasNoDependentLibraries = true;

    // FALL THROUGH

  case 3:               // LLVM 1.3 (Released)
    // LLVM 1.3 and earlier caused alignment bytes to be written on some block
    // boundaries and at the end of some strings. In extreme cases (e.g. lots
    // of GEP references to a constant array), this can increase the file size
    // by 30% or more. In version 1.4 alignment is done away with completely.
    hasAlignment = true;

    // FALL THROUGH

  case 4:               // 1.3.1 (Not Released)
    // In version 4, we did not support the 'undef' constant.
    hasNoUndefValue = true;

    // In version 4 and above, we did not include space for flags for functions
    // in the module info block.
    hasNoFlagsForFunctions = true;

    // In version 4 and above, we did not include the 'unreachable' instruction
    // in the opcode numbering in the bytecode file.
    hasNoUnreachableInst = true;

    // FALL THROUGH

  case 5:               // 1.4 (Released)
    // In version 5 and prior, instructions were signless while integer types
    // were signed. In version 6, instructions became signed and types became
    // signless. For example in version 5 we have the DIV instruction but in
    // version 6 we have FDIV, SDIV and UDIV to replace it. This caused a 
    // renumbering of the instruction codes in version 6 that must be dealt with
    // when reading old bytecode files.
    hasSignlessInstructions = true;

    // FALL THROUGH
    
  case 6:               // SignlessTypes Implementation (1.9 release)
    break;

  default:
    error("Unknown bytecode version number: " + itostr(RevisionNum));
  }

  if (hasNoEndianness) Endianness  = Module::AnyEndianness;
  if (hasNoPointerSize) PointerSize = Module::AnyPointerSize;

  TheModule->setEndianness(Endianness);
  TheModule->setPointerSize(PointerSize);

  if (Handler) Handler->handleVersionInfo(RevisionNum, Endianness, PointerSize);
}

/// Parse a whole module.
void BytecodeReader::ParseModule() {
  unsigned Type, Size;

  FunctionSignatureList.clear(); // Just in case...

  // Read into instance variables...
  ParseVersionInfo();
  align32();

  bool SeenModuleGlobalInfo = false;
  bool SeenGlobalTypePlane = false;
  BufPtr MyEnd = BlockEnd;
  while (At < MyEnd) {
    BufPtr OldAt = At;
    read_block(Type, Size);

    switch (Type) {

    case BytecodeFormat::GlobalTypePlaneBlockID:
      if (SeenGlobalTypePlane)
        error("Two GlobalTypePlane Blocks Encountered!");

      if (Size > 0)
        ParseGlobalTypes();
      SeenGlobalTypePlane = true;
      break;

    case BytecodeFormat::ModuleGlobalInfoBlockID:
      if (SeenModuleGlobalInfo)
        error("Two ModuleGlobalInfo Blocks Encountered!");
      ParseModuleGlobalInfo();
      SeenModuleGlobalInfo = true;
      break;

    case BytecodeFormat::ConstantPoolBlockID:
      ParseConstantPool(ModuleValues, ModuleTypes,false);
      break;

    case BytecodeFormat::FunctionBlockID:
      ParseFunctionLazily();
      break;

    case BytecodeFormat::SymbolTableBlockID:
      ParseSymbolTable(0, &TheModule->getSymbolTable());
      break;

    default:
      At += Size;
      if (OldAt > At) {
        error("Unexpected Block of Type #" + utostr(Type) + " encountered!");
      }
      break;
    }
    BlockEnd = MyEnd;
    align32();
  }

  // After the module constant pool has been read, we can safely initialize
  // global variables...
  while (!GlobalInits.empty()) {
    GlobalVariable *GV = GlobalInits.back().first;
    unsigned Slot = GlobalInits.back().second;
    GlobalInits.pop_back();

    // Look up the initializer value...
    // FIXME: Preserve this type ID!

    const llvm::PointerType* GVType = GV->getType();
    unsigned TypeSlot = getTypeSlot(GVType->getElementType());
    if (Constant *CV = getConstantValue(TypeSlot, Slot)) {
      if (GV->hasInitializer())
        error("Global *already* has an initializer?!");
      if (Handler) Handler->handleGlobalInitializer(GV,CV);
      GV->setInitializer(CV);
    } else
      error("Cannot find initializer value.");
  }

  if (!ConstantFwdRefs.empty())
    error("Use of undefined constants in a module");

  /// Make sure we pulled them all out. If we didn't then there's a declaration
  /// but a missing body. That's not allowed.
  if (!FunctionSignatureList.empty())
    error("Function declared, but bytecode stream ended before definition");
}

/// This function completely parses a bytecode buffer given by the \p Buf
/// and \p Length parameters.
bool BytecodeReader::ParseBytecode(volatile BufPtr Buf, unsigned Length,
                                   const std::string &ModuleID,
                                   std::string* ErrMsg) {

  /// We handle errors by
  if (setjmp(context)) {
    // Cleanup after error
    if (Handler) Handler->handleError(ErrorMsg);
    freeState();
    delete TheModule;
    TheModule = 0;
    if (decompressedBlock != 0 ) {
      ::free(decompressedBlock);
      decompressedBlock = 0;
    }
    // Set caller's error message, if requested
    if (ErrMsg)
      *ErrMsg = ErrorMsg;
    // Indicate an error occurred
    return true;
  }

  RevisionNum = 0;
  At = MemStart = BlockStart = Buf;
  MemEnd = BlockEnd = Buf + Length;

  // Create the module
  TheModule = new Module(ModuleID);

  if (Handler) Handler->handleStart(TheModule, Length);

  // Read the four bytes of the signature.
  unsigned Sig = read_uint();

  // If this is a compressed file
  if (Sig == ('l' | ('l' << 8) | ('v' << 16) | ('c' << 24))) {

    // Invoke the decompression of the bytecode. Note that we have to skip the
    // file's magic number which is not part of the compressed block. Hence,
    // the Buf+4 and Length-4. The result goes into decompressedBlock, a data
    // member for retention until BytecodeReader is destructed.
    unsigned decompressedLength = Compressor::decompressToNewBuffer(
        (char*)Buf+4,Length-4,decompressedBlock);

    // We must adjust the buffer pointers used by the bytecode reader to point
    // into the new decompressed block. After decompression, the
    // decompressedBlock will point to a contiguous memory area that has
    // the decompressed data.
    At = MemStart = BlockStart = Buf = (BufPtr) decompressedBlock;
    MemEnd = BlockEnd = Buf + decompressedLength;

  // else if this isn't a regular (uncompressed) bytecode file, then its
  // and error, generate that now.
  } else if (Sig != ('l' | ('l' << 8) | ('v' << 16) | ('m' << 24))) {
    error("Invalid bytecode signature: " + utohexstr(Sig));
  }

  // Tell the handler we're starting a module
  if (Handler) Handler->handleModuleBegin(ModuleID);

  // Get the module block and size and verify. This is handled specially
  // because the module block/size is always written in long format. Other
  // blocks are written in short format so the read_block method is used.
  unsigned Type, Size;
  Type = read_uint();
  Size = read_uint();
  if (Type != BytecodeFormat::ModuleBlockID) {
    error("Expected Module Block! Type:" + utostr(Type) + ", Size:"
          + utostr(Size));
  }

  // It looks like the darwin ranlib program is broken, and adds trailing
  // garbage to the end of some bytecode files.  This hack allows the bc
  // reader to ignore trailing garbage on bytecode files.
  if (At + Size < MemEnd)
    MemEnd = BlockEnd = At+Size;

  if (At + Size != MemEnd)
    error("Invalid Top Level Block Length! Type:" + utostr(Type)
          + ", Size:" + utostr(Size));

  // Parse the module contents
  this->ParseModule();

  // Check for missing functions
  if (hasFunctions())
    error("Function expected, but bytecode stream ended!");

  // Look for intrinsic functions to upgrade, upgrade them, and save the
  // mapping from old function to new for use later when instructions are
  // converted.
  for (Module::iterator FI = TheModule->begin(), FE = TheModule->end();
       FI != FE; ++FI)
    if (Function* newF = UpgradeIntrinsicFunction(FI)) {
      upgradedFunctions.insert(std::make_pair(FI, newF));
      FI->setName("");
    }

  // Tell the handler we're done with the module
  if (Handler)
    Handler->handleModuleEnd(ModuleID);

  // Tell the handler we're finished the parse
  if (Handler) Handler->handleFinish();

  return false;

}

//===----------------------------------------------------------------------===//
//=== Default Implementations of Handler Methods
//===----------------------------------------------------------------------===//

BytecodeHandler::~BytecodeHandler() {}