Execution.cpp

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//===-- Execution.cpp - Implement code to simulate the program ------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file contains the actual instruction interpreter.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "interpreter"
#include "Interpreter.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/CodeGen/IntrinsicLowering.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include <algorithm>
#include <cmath>
#include <cstring>
using namespace llvm;

STATISTIC(NumDynamicInsts, "Number of dynamic instructions executed");
static Interpreter *TheEE = 0;

static cl::opt<bool> PrintVolatile("interpreter-print-volatile", cl::Hidden,
          cl::desc("make the interpreter print every volatile load and store"));

//===----------------------------------------------------------------------===//
//                     Various Helper Functions
//===----------------------------------------------------------------------===//

static inline uint64_t doSignExtension(uint64_t Val, const IntegerType* ITy) {
  // Determine if the value is signed or not
  bool isSigned = (Val & (1 << (ITy->getBitWidth()-1))) != 0;
  // If its signed, extend the sign bits
  if (isSigned)
    Val |= ~ITy->getBitMask();
  return Val;
}

static void SetValue(Value *V, GenericValue Val, ExecutionContext &SF) {
  SF.Values[V] = Val;
}

void Interpreter::initializeExecutionEngine() {
  TheEE = this;
}

//===----------------------------------------------------------------------===//
//                    Binary Instruction Implementations
//===----------------------------------------------------------------------===//

#define IMPLEMENT_BINARY_OPERATOR(OP, TY) \
   case Type::TY##TyID: \
     Dest.TY##Val = Src1.TY##Val OP Src2.TY##Val; \
     break

#define IMPLEMENT_INTEGER_BINOP1(OP, TY) \
   case Type::IntegerTyID: { \
     Dest.IntVal = Src1.IntVal OP Src2.IntVal; \
     break; \
   }


static void executeAddInst(GenericValue &Dest, GenericValue Src1, 
                           GenericValue Src2, const Type *Ty) {
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_BINOP1(+, Ty);
    IMPLEMENT_BINARY_OPERATOR(+, Float);
    IMPLEMENT_BINARY_OPERATOR(+, Double);
  default:
    cerr << "Unhandled type for Add instruction: " << *Ty << "\n";
    abort();
  }
}

static void executeSubInst(GenericValue &Dest, GenericValue Src1, 
                           GenericValue Src2, const Type *Ty) {
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_BINOP1(-, Ty);
    IMPLEMENT_BINARY_OPERATOR(-, Float);
    IMPLEMENT_BINARY_OPERATOR(-, Double);
  default:
    cerr << "Unhandled type for Sub instruction: " << *Ty << "\n";
    abort();
  }
}

static void executeMulInst(GenericValue &Dest, GenericValue Src1, 
                           GenericValue Src2, const Type *Ty) {
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_BINOP1(*, Ty);
    IMPLEMENT_BINARY_OPERATOR(*, Float);
    IMPLEMENT_BINARY_OPERATOR(*, Double);
  default:
    cerr << "Unhandled type for Mul instruction: " << *Ty << "\n";
    abort();
  }
}

static void executeFDivInst(GenericValue &Dest, GenericValue Src1, 
                            GenericValue Src2, const Type *Ty) {
  switch (Ty->getTypeID()) {
    IMPLEMENT_BINARY_OPERATOR(/, Float);
    IMPLEMENT_BINARY_OPERATOR(/, Double);
  default:
    cerr << "Unhandled type for FDiv instruction: " << *Ty << "\n";
    abort();
  }
}

static void executeFRemInst(GenericValue &Dest, GenericValue Src1, 
                            GenericValue Src2, const Type *Ty) {
  switch (Ty->getTypeID()) {
  case Type::FloatTyID:
    Dest.FloatVal = fmod(Src1.FloatVal, Src2.FloatVal);
    break;
  case Type::DoubleTyID:
    Dest.DoubleVal = fmod(Src1.DoubleVal, Src2.DoubleVal);
    break;
  default:
    cerr << "Unhandled type for Rem instruction: " << *Ty << "\n";
    abort();
  }
}

#define IMPLEMENT_INTEGER_ICMP(OP, TY) \
   case Type::IntegerTyID:  \
      Dest.IntVal = APInt(1,Src1.IntVal.OP(Src2.IntVal)); \
      break;

// Handle pointers specially because they must be compared with only as much
// width as the host has.  We _do not_ want to be comparing 64 bit values when
// running on a 32-bit target, otherwise the upper 32 bits might mess up
// comparisons if they contain garbage.
#define IMPLEMENT_POINTER_ICMP(OP) \
   case Type::PointerTyID: \
      Dest.IntVal = APInt(1,(void*)(intptr_t)Src1.PointerVal OP \
                            (void*)(intptr_t)Src2.PointerVal); \
      break;

static GenericValue executeICMP_EQ(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_ICMP(eq,Ty);
    IMPLEMENT_POINTER_ICMP(==);
  default:
    cerr << "Unhandled type for ICMP_EQ predicate: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeICMP_NE(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_ICMP(ne,Ty);
    IMPLEMENT_POINTER_ICMP(!=);
  default:
    cerr << "Unhandled type for ICMP_NE predicate: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeICMP_ULT(GenericValue Src1, GenericValue Src2,
                                    const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_ICMP(ult,Ty);
    IMPLEMENT_POINTER_ICMP(<);
  default:
    cerr << "Unhandled type for ICMP_ULT predicate: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeICMP_SLT(GenericValue Src1, GenericValue Src2,
                                    const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_ICMP(slt,Ty);
    IMPLEMENT_POINTER_ICMP(<);
  default:
    cerr << "Unhandled type for ICMP_SLT predicate: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeICMP_UGT(GenericValue Src1, GenericValue Src2,
                                    const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_ICMP(ugt,Ty);
    IMPLEMENT_POINTER_ICMP(>);
  default:
    cerr << "Unhandled type for ICMP_UGT predicate: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeICMP_SGT(GenericValue Src1, GenericValue Src2,
                                    const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_ICMP(sgt,Ty);
    IMPLEMENT_POINTER_ICMP(>);
  default:
    cerr << "Unhandled type for ICMP_SGT predicate: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeICMP_ULE(GenericValue Src1, GenericValue Src2,
                                    const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_ICMP(ule,Ty);
    IMPLEMENT_POINTER_ICMP(<=);
  default:
    cerr << "Unhandled type for ICMP_ULE predicate: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeICMP_SLE(GenericValue Src1, GenericValue Src2,
                                    const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_ICMP(sle,Ty);
    IMPLEMENT_POINTER_ICMP(<=);
  default:
    cerr << "Unhandled type for ICMP_SLE predicate: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeICMP_UGE(GenericValue Src1, GenericValue Src2,
                                    const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_ICMP(uge,Ty);
    IMPLEMENT_POINTER_ICMP(>=);
  default:
    cerr << "Unhandled type for ICMP_UGE predicate: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeICMP_SGE(GenericValue Src1, GenericValue Src2,
                                    const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_INTEGER_ICMP(sge,Ty);
    IMPLEMENT_POINTER_ICMP(>=);
  default:
    cerr << "Unhandled type for ICMP_SGE predicate: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

void Interpreter::visitICmpInst(ICmpInst &I) {
  ExecutionContext &SF = ECStack.back();
  const Type *Ty    = I.getOperand(0)->getType();
  GenericValue Src1 = getOperandValue(I.getOperand(0), SF);
  GenericValue Src2 = getOperandValue(I.getOperand(1), SF);
  GenericValue R;   // Result
  
  switch (I.getPredicate()) {
  case ICmpInst::ICMP_EQ:  R = executeICMP_EQ(Src1,  Src2, Ty); break;
  case ICmpInst::ICMP_NE:  R = executeICMP_NE(Src1,  Src2, Ty); break;
  case ICmpInst::ICMP_ULT: R = executeICMP_ULT(Src1, Src2, Ty); break;
  case ICmpInst::ICMP_SLT: R = executeICMP_SLT(Src1, Src2, Ty); break;
  case ICmpInst::ICMP_UGT: R = executeICMP_UGT(Src1, Src2, Ty); break;
  case ICmpInst::ICMP_SGT: R = executeICMP_SGT(Src1, Src2, Ty); break;
  case ICmpInst::ICMP_ULE: R = executeICMP_ULE(Src1, Src2, Ty); break;
  case ICmpInst::ICMP_SLE: R = executeICMP_SLE(Src1, Src2, Ty); break;
  case ICmpInst::ICMP_UGE: R = executeICMP_UGE(Src1, Src2, Ty); break;
  case ICmpInst::ICMP_SGE: R = executeICMP_SGE(Src1, Src2, Ty); break;
  default:
    cerr << "Don't know how to handle this ICmp predicate!\n-->" << I;
    abort();
  }
 
  SetValue(&I, R, SF);
}

#define IMPLEMENT_FCMP(OP, TY) \
   case Type::TY##TyID: \
     Dest.IntVal = APInt(1,Src1.TY##Val OP Src2.TY##Val); \
     break

static GenericValue executeFCMP_OEQ(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_FCMP(==, Float);
    IMPLEMENT_FCMP(==, Double);
  default:
    cerr << "Unhandled type for FCmp EQ instruction: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeFCMP_ONE(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_FCMP(!=, Float);
    IMPLEMENT_FCMP(!=, Double);

  default:
    cerr << "Unhandled type for FCmp NE instruction: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeFCMP_OLE(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_FCMP(<=, Float);
    IMPLEMENT_FCMP(<=, Double);
  default:
    cerr << "Unhandled type for FCmp LE instruction: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeFCMP_OGE(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_FCMP(>=, Float);
    IMPLEMENT_FCMP(>=, Double);
  default:
    cerr << "Unhandled type for FCmp GE instruction: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeFCMP_OLT(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_FCMP(<, Float);
    IMPLEMENT_FCMP(<, Double);
  default:
    cerr << "Unhandled type for FCmp LT instruction: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

static GenericValue executeFCMP_OGT(GenericValue Src1, GenericValue Src2,
                                     const Type *Ty) {
  GenericValue Dest;
  switch (Ty->getTypeID()) {
    IMPLEMENT_FCMP(>, Float);
    IMPLEMENT_FCMP(>, Double);
  default:
    cerr << "Unhandled type for FCmp GT instruction: " << *Ty << "\n";
    abort();
  }
  return Dest;
}

#define IMPLEMENT_UNORDERED(TY, X,Y)                                     \
  if (TY == Type::FloatTy) {                                             \
    if (X.FloatVal != X.FloatVal || Y.FloatVal != Y.FloatVal) {          \
      Dest.IntVal = APInt(1,true);                                       \
      return Dest;                                                       \
    }                                                                    \
  } else if (X.DoubleVal != X.DoubleVal || Y.DoubleVal != Y.DoubleVal) { \
    Dest.IntVal = APInt(1,true);                                         \
    return Dest;                                                         \
  }


static GenericValue executeFCMP_UEQ(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  IMPLEMENT_UNORDERED(Ty, Src1, Src2)
  return executeFCMP_OEQ(Src1, Src2, Ty);
}

static GenericValue executeFCMP_UNE(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  IMPLEMENT_UNORDERED(Ty, Src1, Src2)
  return executeFCMP_ONE(Src1, Src2, Ty);
}

static GenericValue executeFCMP_ULE(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  IMPLEMENT_UNORDERED(Ty, Src1, Src2)
  return executeFCMP_OLE(Src1, Src2, Ty);
}

static GenericValue executeFCMP_UGE(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  IMPLEMENT_UNORDERED(Ty, Src1, Src2)
  return executeFCMP_OGE(Src1, Src2, Ty);
}

static GenericValue executeFCMP_ULT(GenericValue Src1, GenericValue Src2,
                                   const Type *Ty) {
  GenericValue Dest;
  IMPLEMENT_UNORDERED(Ty, Src1, Src2)
  return executeFCMP_OLT(Src1, Src2, Ty);
}

static GenericValue executeFCMP_UGT(GenericValue Src1, GenericValue Src2,
                                     const Type *Ty) {
  GenericValue Dest;
  IMPLEMENT_UNORDERED(Ty, Src1, Src2)
  return executeFCMP_OGT(Src1, Src2, Ty);
}

static GenericValue executeFCMP_ORD(GenericValue Src1, GenericValue Src2,
                                     const Type *Ty) {
  GenericValue Dest;
  if (Ty == Type::FloatTy)
    Dest.IntVal = APInt(1,(Src1.FloatVal == Src1.FloatVal && 
                           Src2.FloatVal == Src2.FloatVal));
  else
    Dest.IntVal = APInt(1,(Src1.DoubleVal == Src1.DoubleVal && 
                           Src2.DoubleVal == Src2.DoubleVal));
  return Dest;
}

static GenericValue executeFCMP_UNO(GenericValue Src1, GenericValue Src2,
                                     const Type *Ty) {
  GenericValue Dest;
  if (Ty == Type::FloatTy)
    Dest.IntVal = APInt(1,(Src1.FloatVal != Src1.FloatVal || 
                           Src2.FloatVal != Src2.FloatVal));
  else
    Dest.IntVal = APInt(1,(Src1.DoubleVal != Src1.DoubleVal || 
                           Src2.DoubleVal != Src2.DoubleVal));
  return Dest;
}

void Interpreter::visitFCmpInst(FCmpInst &I) {
  ExecutionContext &SF = ECStack.back();
  const Type *Ty    = I.getOperand(0)->getType();
  GenericValue Src1 = getOperandValue(I.getOperand(0), SF);
  GenericValue Src2 = getOperandValue(I.getOperand(1), SF);
  GenericValue R;   // Result
  
  switch (I.getPredicate()) {
  case FCmpInst::FCMP_FALSE: R.IntVal = APInt(1,false); break;
  case FCmpInst::FCMP_TRUE:  R.IntVal = APInt(1,true); break;
  case FCmpInst::FCMP_ORD:   R = executeFCMP_ORD(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_UNO:   R = executeFCMP_UNO(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_UEQ:   R = executeFCMP_UEQ(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_OEQ:   R = executeFCMP_OEQ(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_UNE:   R = executeFCMP_UNE(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_ONE:   R = executeFCMP_ONE(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_ULT:   R = executeFCMP_ULT(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_OLT:   R = executeFCMP_OLT(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_UGT:   R = executeFCMP_UGT(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_OGT:   R = executeFCMP_OGT(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_ULE:   R = executeFCMP_ULE(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_OLE:   R = executeFCMP_OLE(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_UGE:   R = executeFCMP_UGE(Src1, Src2, Ty); break;
  case FCmpInst::FCMP_OGE:   R = executeFCMP_OGE(Src1, Src2, Ty); break;
  default:
    cerr << "Don't know how to handle this FCmp predicate!\n-->" << I;
    abort();
  }
 
  SetValue(&I, R, SF);
}

static GenericValue executeCmpInst(unsigned predicate, GenericValue Src1, 
                                   GenericValue Src2, const Type *Ty) {
  GenericValue Result;
  switch (predicate) {
  case ICmpInst::ICMP_EQ:    return executeICMP_EQ(Src1, Src2, Ty);
  case ICmpInst::ICMP_NE:    return executeICMP_NE(Src1, Src2, Ty);
  case ICmpInst::ICMP_UGT:   return executeICMP_UGT(Src1, Src2, Ty);
  case ICmpInst::ICMP_SGT:   return executeICMP_SGT(Src1, Src2, Ty);
  case ICmpInst::ICMP_ULT:   return executeICMP_ULT(Src1, Src2, Ty);
  case ICmpInst::ICMP_SLT:   return executeICMP_SLT(Src1, Src2, Ty);
  case ICmpInst::ICMP_UGE:   return executeICMP_UGE(Src1, Src2, Ty);
  case ICmpInst::ICMP_SGE:   return executeICMP_SGE(Src1, Src2, Ty);
  case ICmpInst::ICMP_ULE:   return executeICMP_ULE(Src1, Src2, Ty);
  case ICmpInst::ICMP_SLE:   return executeICMP_SLE(Src1, Src2, Ty);
  case FCmpInst::FCMP_ORD:   return executeFCMP_ORD(Src1, Src2, Ty);
  case FCmpInst::FCMP_UNO:   return executeFCMP_UNO(Src1, Src2, Ty);
  case FCmpInst::FCMP_OEQ:   return executeFCMP_OEQ(Src1, Src2, Ty);
  case FCmpInst::FCMP_UEQ:   return executeFCMP_UEQ(Src1, Src2, Ty);
  case FCmpInst::FCMP_ONE:   return executeFCMP_ONE(Src1, Src2, Ty);
  case FCmpInst::FCMP_UNE:   return executeFCMP_UNE(Src1, Src2, Ty);
  case FCmpInst::FCMP_OLT:   return executeFCMP_OLT(Src1, Src2, Ty);
  case FCmpInst::FCMP_ULT:   return executeFCMP_ULT(Src1, Src2, Ty);
  case FCmpInst::FCMP_OGT:   return executeFCMP_OGT(Src1, Src2, Ty);
  case FCmpInst::FCMP_UGT:   return executeFCMP_UGT(Src1, Src2, Ty);
  case FCmpInst::FCMP_OLE:   return executeFCMP_OLE(Src1, Src2, Ty);
  case FCmpInst::FCMP_ULE:   return executeFCMP_ULE(Src1, Src2, Ty);
  case FCmpInst::FCMP_OGE:   return executeFCMP_OGE(Src1, Src2, Ty);
  case FCmpInst::FCMP_UGE:   return executeFCMP_UGE(Src1, Src2, Ty);
  case FCmpInst::FCMP_FALSE: { 
    GenericValue Result;
    Result.IntVal = APInt(1, false);
    return Result;
  }
  case FCmpInst::FCMP_TRUE: {
    GenericValue Result;
    Result.IntVal = APInt(1, true);
    return Result;
  }
  default:
    cerr << "Unhandled Cmp predicate\n";
    abort();
  }
}

void Interpreter::visitBinaryOperator(BinaryOperator &I) {
  ExecutionContext &SF = ECStack.back();
  const Type *Ty    = I.getOperand(0)->getType();
  GenericValue Src1 = getOperandValue(I.getOperand(0), SF);
  GenericValue Src2 = getOperandValue(I.getOperand(1), SF);
  GenericValue R;   // Result

  switch (I.getOpcode()) {
  case Instruction::Add:   executeAddInst  (R, Src1, Src2, Ty); break;
  case Instruction::Sub:   executeSubInst  (R, Src1, Src2, Ty); break;
  case Instruction::Mul:   executeMulInst  (R, Src1, Src2, Ty); break;
  case Instruction::FDiv:  executeFDivInst (R, Src1, Src2, Ty); break;
  case Instruction::FRem:  executeFRemInst (R, Src1, Src2, Ty); break;
  case Instruction::UDiv:  R.IntVal = Src1.IntVal.udiv(Src2.IntVal); break;
  case Instruction::SDiv:  R.IntVal = Src1.IntVal.sdiv(Src2.IntVal); break;
  case Instruction::URem:  R.IntVal = Src1.IntVal.urem(Src2.IntVal); break;
  case Instruction::SRem:  R.IntVal = Src1.IntVal.srem(Src2.IntVal); break;
  case Instruction::And:   R.IntVal = Src1.IntVal & Src2.IntVal; break;
  case Instruction::Or:    R.IntVal = Src1.IntVal | Src2.IntVal; break;
  case Instruction::Xor:   R.IntVal = Src1.IntVal ^ Src2.IntVal; break;
  default:
    cerr << "Don't know how to handle this binary operator!\n-->" << I;
    abort();
  }

  SetValue(&I, R, SF);
}

static GenericValue executeSelectInst(GenericValue Src1, GenericValue Src2,
                                      GenericValue Src3) {
  return Src1.IntVal == 0 ? Src3 : Src2;
}

void Interpreter::visitSelectInst(SelectInst &I) {
  ExecutionContext &SF = ECStack.back();
  GenericValue Src1 = getOperandValue(I.getOperand(0), SF);
  GenericValue Src2 = getOperandValue(I.getOperand(1), SF);
  GenericValue Src3 = getOperandValue(I.getOperand(2), SF);
  GenericValue R = executeSelectInst(Src1, Src2, Src3);
  SetValue(&I, R, SF);
}


//===----------------------------------------------------------------------===//
//                     Terminator Instruction Implementations
//===----------------------------------------------------------------------===//

void Interpreter::exitCalled(GenericValue GV) {
  // runAtExitHandlers() assumes there are no stack frames, but
  // if exit() was called, then it had a stack frame. Blow away
  // the stack before interpreting atexit handlers.
  ECStack.clear ();
  runAtExitHandlers ();
  exit (GV.IntVal.zextOrTrunc(32).getZExtValue());
}

/// Pop the last stack frame off of ECStack and then copy the result
/// back into the result variable if we are not returning void. The
/// result variable may be the ExitValue, or the Value of the calling
/// CallInst if there was a previous stack frame. This method may
/// invalidate any ECStack iterators you have. This method also takes
/// care of switching to the normal destination BB, if we are returning
/// from an invoke.
///
void Interpreter::popStackAndReturnValueToCaller (const Type *RetTy,
                                                  GenericValue Result) {
  // Pop the current stack frame.
  ECStack.pop_back();

  if (ECStack.empty()) {  // Finished main.  Put result into exit code...
    if (RetTy && RetTy->isInteger()) {          // Nonvoid return type?
      ExitValue = Result;   // Capture the exit value of the program
    } else {
      memset(&ExitValue.Untyped, 0, sizeof(ExitValue.Untyped));
    }
  } else {
    // If we have a previous stack frame, and we have a previous call,
    // fill in the return value...
    ExecutionContext &CallingSF = ECStack.back();
    if (Instruction *I = CallingSF.Caller.getInstruction()) {
      if (CallingSF.Caller.getType() != Type::VoidTy)      // Save result...
        SetValue(I, Result, CallingSF);
      if (InvokeInst *II = dyn_cast<InvokeInst> (I))
        SwitchToNewBasicBlock (II->getNormalDest (), CallingSF);
      CallingSF.Caller = CallSite();          // We returned from the call...
    }
  }
}

void Interpreter::visitReturnInst(ReturnInst &I) {
  ExecutionContext &SF = ECStack.back();
  const Type *RetTy = Type::VoidTy;
  GenericValue Result;

  // Save away the return value... (if we are not 'ret void')
  if (I.getNumOperands()) {
    RetTy  = I.getReturnValue()->getType();
    Result = getOperandValue(I.getReturnValue(), SF);
  }

  popStackAndReturnValueToCaller(RetTy, Result);
}

void Interpreter::visitUnwindInst(UnwindInst &I) {
  // Unwind stack
  Instruction *Inst;
  do {
    ECStack.pop_back ();
    if (ECStack.empty ())
      abort ();
    Inst = ECStack.back ().Caller.getInstruction ();
  } while (!(Inst && isa<InvokeInst> (Inst)));

  // Return from invoke
  ExecutionContext &InvokingSF = ECStack.back ();
  InvokingSF.Caller = CallSite ();

  // Go to exceptional destination BB of invoke instruction
  SwitchToNewBasicBlock(cast<InvokeInst>(Inst)->getUnwindDest(), InvokingSF);
}

void Interpreter::visitUnreachableInst(UnreachableInst &I) {
  cerr << "ERROR: Program executed an 'unreachable' instruction!\n";
  abort();
}

void Interpreter::visitBranchInst(BranchInst &I) {
  ExecutionContext &SF = ECStack.back();
  BasicBlock *Dest;

  Dest = I.getSuccessor(0);          // Uncond branches have a fixed dest...
  if (!I.isUnconditional()) {
    Value *Cond = I.getCondition();
    if (getOperandValue(Cond, SF).IntVal == 0) // If false cond...
      Dest = I.getSuccessor(1);
  }
  SwitchToNewBasicBlock(Dest, SF);
}

void Interpreter::visitSwitchInst(SwitchInst &I) {
  ExecutionContext &SF = ECStack.back();
  GenericValue CondVal = getOperandValue(I.getOperand(0), SF);
  const Type *ElTy = I.getOperand(0)->getType();

  // Check to see if any of the cases match...
  BasicBlock *Dest = 0;
  for (unsigned i = 2, e = I.getNumOperands(); i != e; i += 2)
    if (executeICMP_EQ(CondVal, getOperandValue(I.getOperand(i), SF), ElTy)
        .IntVal != 0) {
      Dest = cast<BasicBlock>(I.getOperand(i+1));
      break;
    }

  if (!Dest) Dest = I.getDefaultDest();   // No cases matched: use default
  SwitchToNewBasicBlock(Dest, SF);
}

// SwitchToNewBasicBlock - This method is used to jump to a new basic block.
// This function handles the actual updating of block and instruction iterators
// as well as execution of all of the PHI nodes in the destination block.
//
// This method does this because all of the PHI nodes must be executed
// atomically, reading their inputs before any of the results are updated.  Not
// doing this can cause problems if the PHI nodes depend on other PHI nodes for
// their inputs.  If the input PHI node is updated before it is read, incorrect
// results can happen.  Thus we use a two phase approach.
//
void Interpreter::SwitchToNewBasicBlock(BasicBlock *Dest, ExecutionContext &SF){
  BasicBlock *PrevBB = SF.CurBB;      // Remember where we came from...
  SF.CurBB   = Dest;                  // Update CurBB to branch destination
  SF.CurInst = SF.CurBB->begin();     // Update new instruction ptr...

  if (!isa<PHINode>(SF.CurInst)) return;  // Nothing fancy to do

  // Loop over all of the PHI nodes in the current block, reading their inputs.
  std::vector<GenericValue> ResultValues;

  for (; PHINode *PN = dyn_cast<PHINode>(SF.CurInst); ++SF.CurInst) {
    // Search for the value corresponding to this previous bb...
    int i = PN->getBasicBlockIndex(PrevBB);
    assert(i != -1 && "PHINode doesn't contain entry for predecessor??");
    Value *IncomingValue = PN->getIncomingValue(i);

    // Save the incoming value for this PHI node...
    ResultValues.push_back(getOperandValue(IncomingValue, SF));
  }

  // Now loop over all of the PHI nodes setting their values...
  SF.CurInst = SF.CurBB->begin();
  for (unsigned i = 0; isa<PHINode>(SF.CurInst); ++SF.CurInst, ++i) {
    PHINode *PN = cast<PHINode>(SF.CurInst);
    SetValue(PN, ResultValues[i], SF);
  }
}

//===----------------------------------------------------------------------===//
//                     Memory Instruction Implementations
//===----------------------------------------------------------------------===//

void Interpreter::visitAllocationInst(AllocationInst &I) {
  ExecutionContext &SF = ECStack.back();

  const Type *Ty = I.getType()->getElementType();  // Type to be allocated

  // Get the number of elements being allocated by the array...
  unsigned NumElements = 
    getOperandValue(I.getOperand(0), SF).IntVal.getZExtValue();

  unsigned TypeSize = (size_t)TD.getABITypeSize(Ty);

  // Avoid malloc-ing zero bytes, use max()...
  unsigned MemToAlloc = std::max(1