llvm-6502/lib/Target/SparcV9/SparcV9InstrSelection.cpp

// $Id$
//***************************************************************************
// File:
//	SparcInstrSelection.cpp
// 
// Purpose:
//      BURS instruction selection for SPARC V9 architecture.      
//	
// History:
//	7/02/01	 -  Vikram Adve  -  Created
//**************************************************************************/

#include "SparcInternals.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/InstrForest.h"
#include "llvm/CodeGen/InstrSelection.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/DerivedTypes.h"
#include "llvm/iTerminators.h"
#include "llvm/iMemory.h"
#include "llvm/iOther.h"
#include "llvm/BasicBlock.h"
#include "llvm/Method.h"
#include "llvm/ConstPoolVals.h"


//******************** Internal Data Declarations ************************/

// to be used later
struct BranchPattern {
  bool          flipCondition; // should the sense of the test be reversed
  BasicBlock*   targetBB;      // which basic block to branch to
  MachineInstr* extraBranch;   // if neither branch is fall-through, then this
                               // BA must be inserted after the cond'l one
};

//************************* Forward Declarations ***************************/


static void SetMemOperands_Internal     (MachineInstr* minstr,
                                         const InstructionNode* vmInstrNode,
                                         Value* ptrVal,
                                         Value* arrayOffsetVal,
                                         const vector<ConstPoolVal*>& idxVec,
                                         const TargetMachine& target);


//************************ Internal Functions ******************************/

// Convenience function to get the value of an integer constant, for an
// appropriate integer or non-integer type that can be held in an integer.
// The type of the argument must be the following:
//      Signed or unsigned integer
//      Boolean
//      Pointer
// 
// isValidConstant is set to true if a valid constant was found.
// 
static int64_t
GetConstantValueAsSignedInt(const Value *V,
                            bool &isValidConstant)
{
  if (!isa<ConstPoolVal>(V))
    {
      isValidConstant = false;
      return 0;
    }
  
  isValidConstant = true;
  
  if (V->getType() == Type::BoolTy)
    return (int64_t) ((ConstPoolBool*)V)->getValue();
  
  if (V->getType()->isIntegral())
    {
      if (V->getType()->isSigned())
        return ((ConstPoolSInt*)V)->getValue();
      
      assert(V->getType()->isUnsigned());
      uint64_t Val = ((ConstPoolUInt*)V)->getValue();
      if (Val < INT64_MAX)     // then safe to cast to signed
        return (int64_t)Val;
    }

  isValidConstant = false;
  return 0;
}



//------------------------------------------------------------------------ 
// External Function: ThisIsAChainRule
//
// Purpose:
//   Check if a given BURG rule is a chain rule.
//------------------------------------------------------------------------ 

extern bool
ThisIsAChainRule(int eruleno)
{
  switch(eruleno)
    {
    case 111:	// stmt:  reg
    case 113:	// stmt:  bool
    case 123:
    case 124:
    case 125:
    case 126:
    case 127:
    case 128:
    case 129:
    case 130:
    case 131:
    case 132:
    case 133:
    case 155:
    case 221:
    case 222:
    case 241:
    case 242:
    case 243:
    case 244:
      return true; break;
      
    default:
      return false; break;
    }
}


static inline MachineOpCode 
ChooseBprInstruction(const InstructionNode* instrNode)
{
  MachineOpCode opCode;
  
  Instruction* setCCInstr =
    ((InstructionNode*) instrNode->leftChild())->getInstruction();
  
  switch(setCCInstr->getOpcode())
    {
    case Instruction::SetEQ: opCode = BRZ;   break;
    case Instruction::SetNE: opCode = BRNZ;  break;
    case Instruction::SetLE: opCode = BRLEZ; break;
    case Instruction::SetGE: opCode = BRGEZ; break;
    case Instruction::SetLT: opCode = BRLZ;  break;
    case Instruction::SetGT: opCode = BRGZ;  break;
    default:
      assert(0 && "Unrecognized VM instruction!");
      opCode = INVALID_OPCODE;
      break; 
    }
  
  return opCode;
}


static inline MachineOpCode 
ChooseBpccInstruction(const InstructionNode* instrNode,
                      const BinaryOperator* setCCInstr)
{
  MachineOpCode opCode = INVALID_OPCODE;
  
  bool isSigned = setCCInstr->getOperand(0)->getType()->isSigned();
  
  if (isSigned)
    {
      switch(setCCInstr->getOpcode())
        {
        case Instruction::SetEQ: opCode = BE;  break;
        case Instruction::SetNE: opCode = BNE; break;
        case Instruction::SetLE: opCode = BLE; break;
        case Instruction::SetGE: opCode = BGE; break;
        case Instruction::SetLT: opCode = BL;  break;
        case Instruction::SetGT: opCode = BG;  break;
        default:
          assert(0 && "Unrecognized VM instruction!");
          break; 
        }
    }
  else
    {
      switch(setCCInstr->getOpcode())
        {
        case Instruction::SetEQ: opCode = BE;   break;
        case Instruction::SetNE: opCode = BNE;  break;
        case Instruction::SetLE: opCode = BLEU; break;
        case Instruction::SetGE: opCode = BCC;  break;
        case Instruction::SetLT: opCode = BCS;  break;
        case Instruction::SetGT: opCode = BGU;  break;
        default:
          assert(0 && "Unrecognized VM instruction!");
          break; 
        }
    }
  
  return opCode;
}

static inline MachineOpCode 
ChooseBFpccInstruction(const InstructionNode* instrNode,
                       const BinaryOperator* setCCInstr)
{
  MachineOpCode opCode = INVALID_OPCODE;
  
  switch(setCCInstr->getOpcode())
    {
    case Instruction::SetEQ: opCode = FBE;  break;
    case Instruction::SetNE: opCode = FBNE; break;
    case Instruction::SetLE: opCode = FBLE; break;
    case Instruction::SetGE: opCode = FBGE; break;
    case Instruction::SetLT: opCode = FBL;  break;
    case Instruction::SetGT: opCode = FBG;  break;
    default:
      assert(0 && "Unrecognized VM instruction!");
      break; 
    }
  
  return opCode;
}


static inline MachineOpCode 
ChooseBccInstruction(const InstructionNode* instrNode,
                     bool& isFPBranch)
{
  InstructionNode* setCCNode = (InstructionNode*) instrNode->leftChild();
  BinaryOperator* setCCInstr = (BinaryOperator*) setCCNode->getInstruction();
  const Type* setCCType = setCCInstr->getOperand(0)->getType();
  
  isFPBranch = (setCCType == Type::FloatTy || setCCType == Type::DoubleTy); 
  
  if (isFPBranch) 
    return ChooseBFpccInstruction(instrNode, setCCInstr);
  else
    return ChooseBpccInstruction(instrNode, setCCInstr);
}


static inline MachineOpCode 
ChooseMovFpccInstruction(const InstructionNode* instrNode)
{
  MachineOpCode opCode = INVALID_OPCODE;
  
  switch(instrNode->getInstruction()->getOpcode())
    {
    case Instruction::SetEQ: opCode = MOVFE;  break;
    case Instruction::SetNE: opCode = MOVFNE; break;
    case Instruction::SetLE: opCode = MOVFLE; break;
    case Instruction::SetGE: opCode = MOVFGE; break;
    case Instruction::SetLT: opCode = MOVFL;  break;
    case Instruction::SetGT: opCode = MOVFG;  break;
    default:
      assert(0 && "Unrecognized VM instruction!");
      break; 
    }
  
  return opCode;
}


// Assumes that SUBcc v1, v2 -> v3 has been executed.
// In most cases, we want to clear v3 and then follow it by instruction
// MOVcc 1 -> v3.
// Set mustClearReg=false if v3 need not be cleared before conditional move.
// Set valueToMove=0 if we want to conditionally move 0 instead of 1
//                      (i.e., we want to test inverse of a condition)
// (The latter two cases do not seem to arise because SetNE needs nothing.)
// 
static MachineOpCode
ChooseMovpccAfterSub(const InstructionNode* instrNode,
                     bool& mustClearReg,
                     int& valueToMove)
{
  MachineOpCode opCode = INVALID_OPCODE;
  mustClearReg = true;
  valueToMove = 1;
  
  switch(instrNode->getInstruction()->getOpcode())
    {
    case Instruction::SetEQ: opCode = MOVE;  break;
    case Instruction::SetLE: opCode = MOVLE; break;
    case Instruction::SetGE: opCode = MOVGE; break;
    case Instruction::SetLT: opCode = MOVL;  break;
    case Instruction::SetGT: opCode = MOVG;  break;
    case Instruction::SetNE: assert(0 && "No move required!"); break;
    default:		     assert(0 && "Unrecognized VM instr!"); break; 
    }
  
  return opCode;
}


static inline MachineOpCode
ChooseConvertToFloatInstr(const InstructionNode* instrNode,
                          const Type* opType)
{
  MachineOpCode opCode = INVALID_OPCODE;
  
  switch(instrNode->getOpLabel())
    {
    case ToFloatTy: 
      if (opType == Type::SByteTy || opType == Type::ShortTy || opType == Type::IntTy)
        opCode = FITOS;
      else if (opType == Type::LongTy)
        opCode = FXTOS;
      else if (opType == Type::DoubleTy)
        opCode = FDTOS;
      else if (opType == Type::FloatTy)
        ;
      else
        assert(0 && "Cannot convert this type to FLOAT on SPARC");
      break;
      
    case ToDoubleTy: 
      if (opType == Type::SByteTy || opType == Type::ShortTy || opType == Type::IntTy)
        opCode = FITOD;
      else if (opType == Type::LongTy)
        opCode = FXTOD;
      else if (opType == Type::FloatTy)
        opCode = FSTOD;
      else if (opType == Type::DoubleTy)
        ;
      else
        assert(0 && "Cannot convert this type to DOUBLE on SPARC");
      break;
      
    default:
      break;
    }
  
  return opCode;
}

static inline MachineOpCode 
ChooseConvertToIntInstr(const InstructionNode* instrNode,
                        const Type* opType)
{
  MachineOpCode opCode = INVALID_OPCODE;;
  
  int instrType = (int) instrNode->getOpLabel();
  
  if (instrType == ToSByteTy || instrType == ToShortTy || instrType == ToIntTy)
    {
      switch (opType->getPrimitiveID())
        {
        case Type::FloatTyID:   opCode = FSTOI; break;
        case Type::DoubleTyID:  opCode = FDTOI; break;
        default:
          assert(0 && "Non-numeric non-bool type cannot be converted to Int");
          break;
        }
    }
  else if (instrType == ToLongTy)
    {
      switch (opType->getPrimitiveID())
        {
        case Type::FloatTyID:   opCode = FSTOX; break;
        case Type::DoubleTyID:  opCode = FDTOX; break;
        default:
          assert(0 && "Non-numeric non-bool type cannot be converted to Long");
          break;
        }
    }
  else
      assert(0 && "Should not get here, Mo!");
  
  return opCode;
}


static inline MachineOpCode 
ChooseAddInstructionByType(const Type* resultType)
{
  MachineOpCode opCode = INVALID_OPCODE;
  
  if (resultType->isIntegral() ||
      isa<PointerType>(resultType) ||
      isa<MethodType>(resultType) ||
      resultType->isLabelType() ||
      resultType == Type::BoolTy)
    {
      opCode = ADD;
    }
  else
    switch(resultType->getPrimitiveID())
      {
      case Type::FloatTyID:  opCode = FADDS; break;
      case Type::DoubleTyID: opCode = FADDD; break;
      default: assert(0 && "Invalid type for ADD instruction"); break; 
      }
  
  return opCode;
}


static inline MachineOpCode 
ChooseAddInstruction(const InstructionNode* instrNode)
{
  return ChooseAddInstructionByType(instrNode->getInstruction()->getType());
}


static inline MachineInstr* 
CreateMovFloatInstruction(const InstructionNode* instrNode,
                          const Type* resultType)
{
  MachineInstr* minstr = new MachineInstr((resultType == Type::FloatTy)
                                          ? FMOVS : FMOVD);
  minstr->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                            instrNode->leftChild()->getValue());
  minstr->SetMachineOperand(1, MachineOperand::MO_VirtualRegister,
                            instrNode->getValue());
  return minstr;
}

static inline MachineInstr* 
CreateAddConstInstruction(const InstructionNode* instrNode)
{
  MachineInstr* minstr = NULL;
  
  Value* constOp = ((InstrTreeNode*) instrNode->rightChild())->getValue();
  assert(isa<ConstPoolVal>(constOp));
  
  // Cases worth optimizing are:
  // (1) Add with 0 for float or double: use an FMOV of appropriate type,
  //	 instead of an FADD (1 vs 3 cycles).  There is no integer MOV.
  // 
  const Type* resultType = instrNode->getInstruction()->getType();
  
  if (resultType == Type::FloatTy ||
      resultType == Type::DoubleTy)
    {
      double dval = ((ConstPoolFP*) constOp)->getValue();
      if (dval == 0.0)
        minstr = CreateMovFloatInstruction(instrNode, resultType);
    }
  
  return minstr;
}


static inline MachineOpCode 
ChooseSubInstruction(const InstructionNode* instrNode)
{
  MachineOpCode opCode = INVALID_OPCODE;
  
  const Type* resultType = instrNode->getInstruction()->getType();
  
  if (resultType->isIntegral() ||
      resultType->isPointerType())
    {
      opCode = SUB;
    }
  else
    switch(resultType->getPrimitiveID())
      {
      case Type::FloatTyID:  opCode = FSUBS; break;
      case Type::DoubleTyID: opCode = FSUBD; break;
      default: assert(0 && "Invalid type for SUB instruction"); break; 
      }
  
  return opCode;
}


static inline MachineInstr* 
CreateSubConstInstruction(const InstructionNode* instrNode)
{
  MachineInstr* minstr = NULL;
  
  Value* constOp = ((InstrTreeNode*) instrNode->rightChild())->getValue();
  assert(isa<ConstPoolVal>(constOp));
  
  // Cases worth optimizing are:
  // (1) Sub with 0 for float or double: use an FMOV of appropriate type,
  //	 instead of an FSUB (1 vs 3 cycles).  There is no integer MOV.
  // 
  const Type* resultType = instrNode->getInstruction()->getType();
  
  if (resultType == Type::FloatTy ||
      resultType == Type::DoubleTy)
    {
      double dval = ((ConstPoolFP*) constOp)->getValue();
      if (dval == 0.0)
        minstr = CreateMovFloatInstruction(instrNode, resultType);
    }
  
  return minstr;
}


static inline MachineOpCode 
ChooseFcmpInstruction(const InstructionNode* instrNode)
{
  MachineOpCode opCode = INVALID_OPCODE;
  
  Value* operand = ((InstrTreeNode*) instrNode->leftChild())->getValue();
  switch(operand->getType()->getPrimitiveID()) {
  case Type::FloatTyID:  opCode = FCMPS; break;
  case Type::DoubleTyID: opCode = FCMPD; break;
  default: assert(0 && "Invalid type for FCMP instruction"); break; 
  }
  
  return opCode;
}


// Assumes that leftArg and rightArg are both cast instructions.
//
static inline bool
BothFloatToDouble(const InstructionNode* instrNode)
{
  InstrTreeNode* leftArg = instrNode->leftChild();
  InstrTreeNode* rightArg = instrNode->rightChild();
  InstrTreeNode* leftArgArg = leftArg->leftChild();
  InstrTreeNode* rightArgArg = rightArg->leftChild();
  assert(leftArg->getValue()->getType() == rightArg->getValue()->getType());
  
  // Check if both arguments are floats cast to double
  return (leftArg->getValue()->getType() == Type::DoubleTy &&
          leftArgArg->getValue()->getType() == Type::FloatTy &&
          rightArgArg->getValue()->getType() == Type::FloatTy);
}


static inline MachineOpCode 
ChooseMulInstruction(const InstructionNode* instrNode,
                     bool checkCasts)
{
  MachineOpCode opCode = INVALID_OPCODE;
  
  if (checkCasts && BothFloatToDouble(instrNode))
    {
      return opCode = FSMULD;
    }
  // else fall through and use the regular multiply instructions
  
  const Type* resultType = instrNode->getInstruction()->getType();
  
  if (resultType->isIntegral())
    {
      opCode = MULX;
    }
  else
    switch(resultType->getPrimitiveID())
      {
      case Type::FloatTyID:  opCode = FMULS; break;
      case Type::DoubleTyID: opCode = FMULD; break;
      default: assert(0 && "Invalid type for MUL instruction"); break; 
      }
  
  return opCode;
}


static inline MachineInstr*
CreateIntNegInstruction(TargetMachine& target,
                        Value* vreg)
{
  MachineInstr* minstr = new MachineInstr(SUB);
  minstr->SetMachineOperand(0, target.getRegInfo().getZeroRegNum());
  minstr->SetMachineOperand(1, MachineOperand::MO_VirtualRegister, vreg);
  minstr->SetMachineOperand(2, MachineOperand::MO_VirtualRegister, vreg);
  return minstr;
}


static inline MachineInstr* 
CreateMulConstInstruction(TargetMachine &target,
                          const InstructionNode* instrNode,
                          MachineInstr*& getMinstr2)
{
  MachineInstr* minstr = NULL;
  getMinstr2 = NULL;
  bool needNeg = false;

  Value* constOp = ((InstrTreeNode*) instrNode->rightChild())->getValue();
  assert(isa<ConstPoolVal>(constOp));
  
  // Cases worth optimizing are:
  // (1) Multiply by 0 or 1 for any type: replace with copy (ADD or FMOV)
  // (2) Multiply by 2^x for integer types: replace with Shift
  // 
  const Type* resultType = instrNode->getInstruction()->getType();
  
  if (resultType->isIntegral() || resultType->isPointerType())
    {
      unsigned pow;
      bool isValidConst;
      int64_t C = GetConstantValueAsSignedInt(constOp, isValidConst);
      if (isValidConst)
        {
          bool needNeg = false;
          if (C < 0)
            {
              needNeg = true;
              C = -C;
            }
          
          if (C == 0 || C == 1)
            {
              minstr = new MachineInstr(ADD);
              
              if (C == 0)
                minstr->SetMachineOperand(0,
                                          target.getRegInfo().getZeroRegNum());
              else
                minstr->SetMachineOperand(0,MachineOperand::MO_VirtualRegister,
                                          instrNode->leftChild()->getValue());
              minstr->SetMachineOperand(1,target.getRegInfo().getZeroRegNum());
            }
          else if (IsPowerOf2(C, pow))
            {
              minstr = new MachineInstr((resultType == Type::LongTy)
                                        ? SLLX : SLL);
              minstr->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                           instrNode->leftChild()->getValue());
              minstr->SetMachineOperand(1, MachineOperand::MO_UnextendedImmed,
                                           pow);
            }
          
          if (minstr && needNeg)
            { // insert <reg = SUB 0, reg> after the instr to flip the sign
              getMinstr2 = CreateIntNegInstruction(target,
                                                   instrNode->getValue());
            }
        }
    }
  else
    {
      if (resultType == Type::FloatTy ||
          resultType == Type::DoubleTy)
        {
          bool isValidConst;
          double dval = ((ConstPoolFP*) constOp)->getValue();
          
          if (isValidConst)
            {
              if (dval == 0)
                {
                  minstr = new MachineInstr((resultType == Type::FloatTy)
                                            ? FITOS : FITOD);
                  minstr->SetMachineOperand(0,
                                        target.getRegInfo().getZeroRegNum());
                }
              else if (fabs(dval) == 1)
                {
                  bool needNeg = (dval < 0);
                  
                  MachineOpCode opCode = needNeg
                    ? (resultType == Type::FloatTy? FNEGS : FNEGD)
                    : (resultType == Type::FloatTy? FMOVS : FMOVD);
                  
                  minstr = new MachineInstr(opCode);
                  minstr->SetMachineOperand(0,
                                           MachineOperand::MO_VirtualRegister,
                                           instrNode->leftChild()->getValue());
                } 
            }
        }
    }
  
  if (minstr != NULL)
    minstr->SetMachineOperand(2, MachineOperand::MO_VirtualRegister,
                              instrNode->getValue());   
  
  return minstr;
}


static inline MachineOpCode 
ChooseDivInstruction(TargetMachine &target,
                     const InstructionNode* instrNode)
{
  MachineOpCode opCode = INVALID_OPCODE;
  
  const Type* resultType = instrNode->getInstruction()->getType();
  
  if (resultType->isIntegral())
    opCode = resultType->isSigned()? SDIVX : UDIVX;
  else
    switch(resultType->getPrimitiveID())
      {
      case Type::FloatTyID:  opCode = FDIVS; break;
      case Type::DoubleTyID: opCode = FDIVD; break;
      default: assert(0 && "Invalid type for DIV instruction"); break; 
      }
  
  return opCode;
}


static inline MachineInstr* 
CreateDivConstInstruction(TargetMachine &target,
                          const InstructionNode* instrNode,
                          MachineInstr*& getMinstr2)
{
  MachineInstr* minstr = NULL;
  getMinstr2 = NULL;
  
  Value* constOp = ((InstrTreeNode*) instrNode->rightChild())->getValue();
  assert(isa<ConstPoolVal>(constOp));
  
  // Cases worth optimizing are:
  // (1) Divide by 1 for any type: replace with copy (ADD or FMOV)
  // (2) Divide by 2^x for integer types: replace with SR[L or A]{X}
  // 
  const Type* resultType = instrNode->getInstruction()->getType();
  
  if (resultType->isIntegral())
    {
      unsigned pow;
      bool isValidConst;
      int64_t C = GetConstantValueAsSignedInt(constOp, isValidConst);
      if (isValidConst)
        {
          bool needNeg = false;
          if (C < 0)
            {
              needNeg = true;
              C = -C;
            }
          
          if (C == 1)
            {
              minstr = new MachineInstr(ADD);
              minstr->SetMachineOperand(0,MachineOperand::MO_VirtualRegister,
                                          instrNode->leftChild()->getValue());
              minstr->SetMachineOperand(1,target.getRegInfo().getZeroRegNum());
            }
          else if (IsPowerOf2(C, pow))
            {
              MachineOpCode opCode= ((resultType->isSigned())
                                     ? (resultType==Type::LongTy)? SRAX : SRA
                                     : (resultType==Type::LongTy)? SRLX : SRL);
              minstr = new MachineInstr(opCode);
              minstr->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                           instrNode->leftChild()->getValue());
              minstr->SetMachineOperand(1, MachineOperand::MO_UnextendedImmed,
                                           pow);
            }
          
          if (minstr && needNeg)
            { // insert <reg = SUB 0, reg> after the instr to flip the sign
              getMinstr2 = CreateIntNegInstruction(target,
                                                   instrNode->getValue());
            }
        }
    }
  else
    {
      if (resultType == Type::FloatTy ||
          resultType == Type::DoubleTy)
        {
          bool isValidConst;
          double dval = ((ConstPoolFP*) constOp)->getValue();
          
          if (isValidConst && fabs(dval) == 1)
            {
              bool needNeg = (dval < 0);
              
              MachineOpCode opCode = needNeg
                ? (resultType == Type::FloatTy? FNEGS : FNEGD)
                : (resultType == Type::FloatTy? FMOVS : FMOVD);
              
              minstr = new MachineInstr(opCode);
              minstr->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                           instrNode->leftChild()->getValue());
            } 
        }
    }
  
  if (minstr != NULL)
    minstr->SetMachineOperand(2, MachineOperand::MO_VirtualRegister,
                              instrNode->getValue());   
  
  return minstr;
}


static inline MachineOpCode
ChooseLoadInstruction(const Type *DestTy)
{
  switch (DestTy->getPrimitiveID()) {
  case Type::BoolTyID:
  case Type::UByteTyID:   return LDUB;
  case Type::SByteTyID:   return LDSB;
  case Type::UShortTyID:  return LDUH;
  case Type::ShortTyID:   return LDSH;
  case Type::UIntTyID:    return LDUW;
  case Type::IntTyID:     return LDSW;
  case Type::PointerTyID:
  case Type::ULongTyID:
  case Type::LongTyID:    return LDX;
  case Type::FloatTyID:   return LD;
  case Type::DoubleTyID:  return LDD;
  default: assert(0 && "Invalid type for Load instruction");
  }
  
  return 0;
}


static inline MachineOpCode
ChooseStoreInstruction(const Type *DestTy)
{
  switch (DestTy->getPrimitiveID()) {
  case Type::BoolTyID:
  case Type::UByteTyID:
  case Type::SByteTyID:   return STB;
  case Type::UShortTyID:
  case Type::ShortTyID:   return STH;
  case Type::UIntTyID:
  case Type::IntTyID:     return STW;
  case Type::PointerTyID:
  case Type::ULongTyID:
  case Type::LongTyID:    return STX;
  case Type::FloatTyID:   return ST;
  case Type::DoubleTyID:  return STD;
  default: assert(0 && "Invalid type for Store instruction");
  }
  
  return 0;
}


//------------------------------------------------------------------------ 
// Function SetOperandsForMemInstr
//
// Choose addressing mode for the given load or store instruction.
// Use [reg+reg] if it is an indexed reference, and the index offset is
//		 not a constant or if it cannot fit in the offset field.
// Use [reg+offset] in all other cases.
// 
// This assumes that all array refs are "lowered" to one of these forms:
//	%x = load (subarray*) ptr, constant	; single constant offset
//	%x = load (subarray*) ptr, offsetVal	; single non-constant offset
// Generally, this should happen via strength reduction + LICM.
// Also, strength reduction should take care of using the same register for
// the loop index variable and an array index, when that is profitable.
//------------------------------------------------------------------------ 

static void
SetOperandsForMemInstr(MachineInstr* minstr,
                       const InstructionNode* vmInstrNode,
                       const TargetMachine& target)
{
  MemAccessInst* memInst = (MemAccessInst*) vmInstrNode->getInstruction();
  
  // Variables to hold the index vector, ptr value, and offset value.
  // The major work here is to extract these for all 3 instruction types
  // and then call the common function SetMemOperands_Internal().
  // 
  const vector<ConstPoolVal*>* idxVec = & memInst->getIndexVec();
  vector<ConstPoolVal*>* newIdxVec = NULL;
  Value* ptrVal;
  Value* arrayOffsetVal = NULL;
  
  // Test if a GetElemPtr instruction is being folded into this mem instrn.
  // If so, it will be in the left child for Load and GetElemPtr,
  // and in the right child for Store instructions.
  // 
  InstrTreeNode* ptrChild = (vmInstrNode->getOpLabel() == Instruction::Store
                             ? vmInstrNode->rightChild()
                             : vmInstrNode->leftChild()); 
  
  if (ptrChild->getOpLabel() == Instruction::GetElementPtr ||
      ptrChild->getOpLabel() == GetElemPtrIdx)
    {
      // There is a GetElemPtr instruction and there may be a chain of
      // more than one.  Use the pointer value of the last one in the chain.
      // Fold the index vectors from the entire chain and from the mem
      // instruction into one single index vector.
      // Finally, we never fold for an array instruction so make that NULL.
      
      newIdxVec = new vector<ConstPoolVal*>;
      ptrVal = FoldGetElemChain((InstructionNode*) ptrChild, *newIdxVec);
      
      newIdxVec->insert(newIdxVec->end(), idxVec->begin(), idxVec->end());
      idxVec = newIdxVec;
      
      assert(! ((PointerType*)ptrVal->getType())->getValueType()->isArrayType()
             && "GetElemPtr cannot be folded into array refs in selection");
    }
  else
    {
      // There is no GetElemPtr instruction.
      // Use the pointer value and the index vector from the Mem instruction.
      // If it is an array reference, get the array offset value.
      // 
      ptrVal = memInst->getPtrOperand();

      const Type* opType =
        ((const PointerType*) ptrVal->getType())->getValueType();
      if (opType->isArrayType())
        {
          assert((memInst->getNumOperands()
                  == (unsigned) 1 + memInst->getFirstOffsetIdx())
                 && "Array refs must be lowered before Instruction Selection");
          
          arrayOffsetVal = memInst->getOperand(memInst->getFirstOffsetIdx());
        }
    }
  
  SetMemOperands_Internal(minstr, vmInstrNode, ptrVal, arrayOffsetVal,
                          *idxVec, target);
  
  if (newIdxVec != NULL)
    delete newIdxVec;
}


static void
SetMemOperands_Internal(MachineInstr* minstr,
                        const InstructionNode* vmInstrNode,
                        Value* ptrVal,
                        Value* arrayOffsetVal,
                        const vector<ConstPoolVal*>& idxVec,
                        const TargetMachine& target)
{
  MemAccessInst* memInst = (MemAccessInst*) vmInstrNode->getInstruction();
  
  // Initialize so we default to storing the offset in a register.
  int64_t smallConstOffset;
  Value* valueForRegOffset = NULL;
  MachineOperand::MachineOperandType offsetOpType =MachineOperand::MO_VirtualRegister;

  // Check if there is an index vector and if so, if it translates to
  // a small enough constant to fit in the immediate-offset field.
  // 
  if (idxVec.size() > 0)
    {
      bool isConstantOffset = false;
      unsigned offset;
      
      const PointerType* ptrType = (PointerType*) ptrVal->getType();
      
      if (ptrType->getValueType()->isStructType())
        {
          // the offset is always constant for structs
          isConstantOffset = true;
          
          // Compute the offset value using the index vector
          offset = target.DataLayout.getIndexedOffset(ptrType, idxVec);
        }
      else
        {
          // It must be an array ref.  Check if the offset is a constant,
          // and that the indexing has been lowered to a single offset.
          // 
          assert(ptrType->getValueType()->isArrayType());
          assert(arrayOffsetVal != NULL
                 && "Expect to be given Value* for array offsets");
          
          if (ConstPoolVal *CPV = dyn_cast<ConstPoolVal>(arrayOffsetVal))
            {
              isConstantOffset = true;  // always constant for structs
              assert(arrayOffsetVal->getType()->isIntegral());
              offset = (CPV->getType()->isSigned()
                        ? ((ConstPoolSInt*)CPV)->getValue()
                        : (int64_t) ((ConstPoolUInt*)CPV)->getValue());
            }
          else
            {
              valueForRegOffset = arrayOffsetVal;
            }
        }
      
      if (isConstantOffset)
        {
          // create a virtual register for the constant
          valueForRegOffset = ConstPoolSInt::get(Type::IntTy, offset);
        }
    }
  else
    {
      offsetOpType = MachineOperand::MO_SignExtendedImmed;
      smallConstOffset = 0;
    }
  
  // Operand 0 is value for STORE, ptr for LOAD or GET_ELEMENT_PTR
  // It is the left child in the instruction tree in all cases.
  Value* leftVal = vmInstrNode->leftChild()->getValue();
  minstr->SetMachineOperand(0, MachineOperand::MO_VirtualRegister, leftVal);
  
  // Operand 1 is ptr for STORE, offset for LOAD or GET_ELEMENT_PTR
  // Operand 2 is offset for STORE, result reg for LOAD or GET_ELEMENT_PTR
  //
  unsigned offsetOpNum = (memInst->getOpcode() == Instruction::Store)? 2 : 1;
  if (offsetOpType == MachineOperand::MO_VirtualRegister)
    {
      assert(valueForRegOffset != NULL);
      minstr->SetMachineOperand(offsetOpNum, offsetOpType, valueForRegOffset); 
    }
  else
    minstr->SetMachineOperand(offsetOpNum, offsetOpType, smallConstOffset);
  
  if (memInst->getOpcode() == Instruction::Store)
    minstr->SetMachineOperand(1, MachineOperand::MO_VirtualRegister, ptrVal);
  else
    minstr->SetMachineOperand(2, MachineOperand::MO_VirtualRegister,
                                 vmInstrNode->getValue());
}


static inline MachineInstr*
CreateIntSetInstruction(int64_t C, bool isSigned, Value* dest)
{
  MachineInstr* minstr;
  if (isSigned)
    {
      minstr = new MachineInstr(SETSW);
      minstr->SetMachineOperand(0, MachineOperand::MO_SignExtendedImmed, C);
    }
  else
    {
      minstr = new MachineInstr(SETUW);
      minstr->SetMachineOperand(0, MachineOperand::MO_UnextendedImmed, C);
    }
  
  minstr->SetMachineOperand(1, MachineOperand::MO_VirtualRegister, dest);
  
  return minstr;
}


// Create an instruction sequence to load a constant into a register.
// This always creates either one or two instructions.
// If two instructions are created, the second one is returned in getMinstr2
// The implicit virtual register used to hold the constant is returned in
// tmpReg.
// 
static MachineInstr*
CreateLoadConstInstr(const TargetMachine &target,
                     Instruction* vmInstr,
                     Value* val,
                     Instruction* dest,
                     MachineInstr*& getMinstr2)
{
  assert(isa<ConstPoolVal>(val));
  
  MachineInstr* minstr1 = NULL;
  
  getMinstr2 = NULL;
  
  // Use a "set" instruction for known constants that can go in an integer reg.
  // Use a "set" instruction followed by a int-to-float conversion for known
  // constants that must go in a floating point reg but have an integer value.
  // Use a "load" instruction for all other constants, in particular,
  // floating point constants.
  // 
  const Type* valType = val->getType();
  
  if (valType->isIntegral() || valType == Type::BoolTy)
    {
      bool isValidConstant;
      int64_t C = GetConstantValueAsSignedInt(val, isValidConstant);
      assert(isValidConstant && "Unrecognized constant");
      minstr1 = CreateIntSetInstruction(C, valType->isSigned(), dest);
    }
  else
    {
      
#undef MOVE_INT_TO_FP_REG_AVAILABLE
#ifdef MOVE_INT_TO_FP_REG_AVAILABLE
      //
      // This code was written to generate the following sequence:
      //        SET[SU]W <int-const> <int-reg>
      //        FITO[SD] <int-reg>   <fp-reg>
      // (it really should have moved the int-reg to an fp-reg and then FITOS).
      // But for now the only way to move a value from an int-reg to an fp-reg
      // is via memory.  Leave this code here but unused.
      // 
      assert(valType == Type::FloatTy || valType == Type::DoubleTy);
      double dval = ((ConstPoolFP*) val)->getValue();
      if (dval == (int64_t) dval)
        {
          // The constant actually has an integer value, so use a
          // [set; int-to-float] sequence instead of a load instruction.
          // 
          TmpInstruction* tmpReg2 = NULL;
          if (dval != 0.0)
            { // First, create an integer constant of the same value as dval
              ConstPoolSInt* ival = ConstPoolSInt::get(Type::IntTy,
                                                       (int64_t) dval);
              // Create another TmpInstruction for the hidden integer register
              tmpReg2 = new TmpInstruction(Instruction::UserOp1, ival, NULL);
              vmInstr->getMachineInstrVec().addTempValue(tmpReg2);
              
              // Create the `SET' instruction
              minstr1 = CreateIntSetInstruction((int64_t)dval, true, tmpReg2);
              tmpReg2->addMachineInstruction(minstr1);
            }
          
          // In which variable do we put the second instruction?
          MachineInstr*& instr2 = (minstr1)? getMinstr2 : minstr1;
          
          // Create the int-to-float instruction
          instr2 = new MachineInstr(valType == Type::FloatTy? FITOS : FITOD);
          
          if (dval == 0.0)
            instr2->SetMachineOperand(0, target.getRegInfo().getZeroRegNum());
          else
            instr2->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                         tmpReg2);
          
          instr2->SetMachineOperand(1, MachineOperand::MO_VirtualRegister,
                                         dest);
        }
      else
#endif MOVE_INT_TO_FP_REG_AVAILABLE
        
        {
          // Make an instruction sequence to load the constant, viz:
          //            SETSW <addr-of-constant>, tmpReg2
          //            LOAD  /*addr*/ tmpReg2, /*offset*/ 0, dest
          // set the offset field to 0.
          // 
          int64_t zeroOffset = 0; // to avoid ambiguity with (Value*) 0

          // Create another TmpInstruction for the hidden integer register
          TmpInstruction* tmpReg2 =
            new TmpInstruction(Instruction::UserOp1, val, NULL);
          vmInstr->getMachineInstrVec().addTempValue(tmpReg2);
          
          minstr1 = new MachineInstr(SETUW);
          minstr1->SetMachineOperand(0, MachineOperand::MO_PCRelativeDisp,val);
          minstr1->SetMachineOperand(1, MachineOperand::MO_VirtualRegister,
                                        tmpReg2);
          tmpReg2->addMachineInstruction(minstr1);
          
          getMinstr2 = new MachineInstr(ChooseLoadInstruction(val->getType()));
          getMinstr2->SetMachineOperand(0,MachineOperand::MO_VirtualRegister,
                                          tmpReg2);
          getMinstr2->SetMachineOperand(1,MachineOperand::MO_SignExtendedImmed,
                                          zeroOffset);
          getMinstr2->SetMachineOperand(2,MachineOperand::MO_VirtualRegister,
                                          dest);
        }
    }
  
  assert(minstr1);
  return minstr1;
}

// Special handling for constant operands:
// -- if the constant is 0, use the hardwired 0 register, if any;
// -- if the constant is of float or double type but has an integer value,
//    use int-to-float conversion instruction instead of generating a load;
// -- if the constant fits in the IMMEDIATE field, use that field;
// -- else insert instructions to put the constant into a register, either
//    directly or by loading explicitly from the constant pool.
// 
static unsigned
FixConstantOperands(const InstructionNode* vmInstrNode,
                    MachineInstr** mvec,
                    unsigned numInstr,
                    TargetMachine& target)
{
  static MachineInstr* loadConstVec[MAX_INSTR_PER_VMINSTR];

  unsigned numNew = 0;
  Instruction* vmInstr = vmInstrNode->getInstruction();
  
  for (unsigned i=0; i < numInstr; i++)
    {
      MachineInstr* minstr = mvec[i];
      const MachineInstrDescriptor& instrDesc =
        target.getInstrInfo().getDescriptor(minstr->getOpCode());
      
      for (unsigned op=0; op < minstr->getNumOperands(); op++)
        {
          const MachineOperand& mop = minstr->getOperand(op);
          
          // skip the result position (for efficiency below) and any other
          // positions already marked as not a virtual register
          if (instrDesc.resultPos == (int) op || 
              mop.getOperandType() != MachineOperand::MO_VirtualRegister ||
              mop.getVRegValue() == NULL)
            {
              continue;
            }
          
          Value* opValue = mop.getVRegValue();
          
          if (isa<ConstPoolVal>(opValue))
            {
              unsigned int machineRegNum;
              int64_t immedValue;
              MachineOperand::MachineOperandType opType =
                ChooseRegOrImmed(opValue, minstr->getOpCode(), target,
                                 /*canUseImmed*/ (op == 1),
                                 machineRegNum, immedValue);
              
              if (opType == MachineOperand::MO_MachineRegister)
                minstr->SetMachineOperand(op, machineRegNum);
              else if (opType == MachineOperand::MO_VirtualRegister)
                {
                  // value is constant and must be loaded into a register.
                  // First, create a tmp virtual register (TmpInstruction)
                  // to hold the constant.
                  // This will replace the constant operand in `minstr'.
                  TmpInstruction* tmpReg =
                    new TmpInstruction(Instruction::UserOp1, opValue, NULL);
                  vmInstr->getMachineInstrVec().addTempValue(tmpReg);
                  minstr->SetMachineOperand(op, opType, tmpReg);
                  
                  MachineInstr *minstr1, *minstr2;
                  minstr1 = CreateLoadConstInstr(target, vmInstr,
                                                 opValue, tmpReg, minstr2);
                  tmpReg->addMachineInstruction(minstr1);
                  
                  loadConstVec[numNew++] = minstr1;
                  if (minstr2 != NULL)
                    loadConstVec[numNew++] = minstr2;
                }
              else
                minstr->SetMachineOperand(op, opType, immedValue);
            }
        }
    }
  
  if (numNew > 0)
    {
      // Insert the new instructions *before* the old ones by moving
      // the old ones over `numNew' positions (last-to-first, of course!).
      // We do check *after* returning that we did not exceed the vector mvec.
      for (int i=numInstr-1; i >= 0; i--)
        mvec[i+numNew] = mvec[i];
      
      for (unsigned i=0; i < numNew; i++)
        mvec[i] = loadConstVec[i];
    }
  
  return (numInstr + numNew);
}


// 
// Substitute operand `operandNum' of the instruction in node `treeNode'
// in place the use(s) of that instruction in node `parent'.
// 
static void
ForwardOperand(InstructionNode* treeNode,
               InstrTreeNode*   parent,
               int operandNum)
{
  assert(treeNode && parent && "Invalid invocation of ForwardOperand");
  
  Instruction* unusedOp = treeNode->getInstruction();
  Value* fwdOp = unusedOp->getOperand(operandNum);

  // The parent itself may be a list node, so find the real parent instruction
  while (parent->getNodeType() != InstrTreeNode::NTInstructionNode)
    {
      parent = parent->parent();
      assert(parent && "ERROR: Non-instruction node has no parent in tree.");
    }
  InstructionNode* parentInstrNode = (InstructionNode*) parent;
  
  Instruction* userInstr = parentInstrNode->getInstruction();
  MachineCodeForVMInstr& mvec = userInstr->getMachineInstrVec();
  for (unsigned i=0, N=mvec.size(); i < N; i++)
    {
      MachineInstr* minstr = mvec[i];
      for (unsigned i=0, numOps=minstr->getNumOperands(); i < numOps; i++)
        {
          const MachineOperand& mop = minstr->getOperand(i);
          if (mop.getOperandType() == MachineOperand::MO_VirtualRegister &&
              mop.getVRegValue() == unusedOp)
            {
              minstr->SetMachineOperand(i, MachineOperand::MO_VirtualRegister,
                                           fwdOp);
            }
        }
    }
}


MachineInstr*
CreateCopyInstructionsByType(const TargetMachine& target,
                             Value* src,
                             Instruction* dest,
                             MachineInstr*& getMinstr2)
{
  getMinstr2 = NULL;                    // initialize second return value
  
  MachineInstr* minstr1 = NULL;
  
  const Type* resultType = dest->getType();
  
  MachineOpCode opCode = ChooseAddInstructionByType(resultType);
  if (opCode == INVALID_OPCODE)
    {
      assert(0 && "Unsupported result type in CreateCopyInstructionsByType()");
      return NULL;
    }
  
  // if `src' is a constant that doesn't fit in the immed field, generate
  // a load instruction instead of an add
  if (isa<ConstPoolVal>(src))
    {
      unsigned int machineRegNum;
      int64_t immedValue;
      MachineOperand::MachineOperandType opType =
        ChooseRegOrImmed(src, opCode, target, /*canUseImmed*/ true,
                         machineRegNum, immedValue);
      
      if (opType == MachineOperand::MO_VirtualRegister)
        { // value is constant and cannot fit in immed field for the ADD
          minstr1 = CreateLoadConstInstr(target, dest, src, dest, getMinstr2);
        }
    }
  
  if (minstr1 == NULL)
    { // Create the appropriate add instruction.
      // Make `src' the second operand, in case it is a constant
      // Use (unsigned long) 0 for a NULL pointer value.
      // 
      const Type* nullValueType =
        (resultType->getPrimitiveID() == Type::PointerTyID)? Type::ULongTy
                                                           : resultType;
      minstr1 = new MachineInstr(opCode);
      minstr1->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                 ConstPoolVal::getNullConstant(nullValueType));
      minstr1->SetMachineOperand(1, MachineOperand::MO_VirtualRegister, src);
      minstr1->SetMachineOperand(2, MachineOperand::MO_VirtualRegister, dest);
    }
  
  return minstr1;
}


// This function is currently unused and incomplete but will be 
// used if we have a linear layout of basic blocks in LLVM code.
// It decides which branch should fall-through, and whether an
// extra unconditional branch is needed (when neither falls through).
// 
void
ChooseBranchPattern(Instruction* vmInstr, BranchPattern& brPattern)
{
  BranchInst* brInstr = (BranchInst*) vmInstr;
  
  brPattern.flipCondition = false;
  brPattern.targetBB      = brInstr->getSuccessor(0);
  brPattern.extraBranch   = NULL;
  
  assert(brInstr->getNumSuccessors() > 1 &&
         "Unnecessary analysis for unconditional branch");
  
  assert(0 && "Fold branches in peephole optimization");
}


//******************* Externally Visible Functions *************************/


//------------------------------------------------------------------------ 
// External Function: GetInstructionsByRule
//
// Purpose:
//   Choose machine instructions for the SPARC according to the
//   patterns chosen by the BURG-generated parser.
//------------------------------------------------------------------------ 

unsigned
GetInstructionsByRule(InstructionNode* subtreeRoot,
                      int ruleForNode,
                      short* nts,
                      TargetMachine &target,
                      MachineInstr** mvec)
{
  int numInstr = 1;			// initialize for common case
  bool checkCast = false;		// initialize here to use fall-through
  Value *leftVal, *rightVal;
  const Type* opType;
  int nextRule;
  int forwardOperandNum = -1;
  int64_t s0 = 0;			// variables holding zero to avoid
  uint64_t u0 = 0;			// overloading ambiguities below
  
  mvec[0] = mvec[1] = mvec[2] = mvec[3] = NULL;	// just for safety
  
  // 
  // Let's check for chain rules outside the switch so that we don't have
  // to duplicate the list of chain rule production numbers here again
  // 
  if (ThisIsAChainRule(ruleForNode))
    {
      // Chain rules have a single nonterminal on the RHS.
      // Get the rule that matches the RHS non-terminal and use that instead.
      // 
      assert(nts[0] && ! nts[1]
             && "A chain rule should have only one RHS non-terminal!");
      nextRule = burm_rule(subtreeRoot->state, nts[0]);
      nts = burm_nts[nextRule];
      numInstr = GetInstructionsByRule(subtreeRoot, nextRule, nts,target,mvec);
    }
  else
    {
      switch(ruleForNode) {
      case 1:	// stmt:   Ret
      case 2:	// stmt:   RetValue(reg)
                // NOTE: Prepass of register allocation is responsible
                //	 for moving return value to appropriate register.
                // Mark the return-address register as a hidden virtual reg.
                // Mark the return value   register as an implicit use.
        {		
        ReturnInst* returnInstr = (ReturnInst*) subtreeRoot->getInstruction();
        assert(returnInstr->getOpcode() == Instruction::Ret);
        
        Instruction* returnReg = new TmpInstruction(Instruction::UserOp1,
                                                    returnInstr, NULL);
        returnInstr->getMachineInstrVec().addTempValue(returnReg);

        if (returnInstr->getReturnValue() != NULL)
          returnInstr->getMachineInstrVec().addImplicitUse(
                                             returnInstr->getReturnValue());
        
        mvec[0] = new MachineInstr(RETURN);
        mvec[0]->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                      returnReg);
        mvec[0]->SetMachineOperand(1, MachineOperand::MO_SignExtendedImmed,s0);
        
        returnReg->addMachineInstruction(mvec[0]);
        
        mvec[numInstr++] = new MachineInstr(NOP); // delay slot
        break;
        }  
        
      case 3:	// stmt:   Store(reg,reg)
      case 4:	// stmt:   Store(reg,ptrreg)
        mvec[0] = new MachineInstr(
                       ChooseStoreInstruction(
                            subtreeRoot->leftChild()->getValue()->getType()));
        SetOperandsForMemInstr(mvec[0], subtreeRoot, target);
        break;

      case 5:	// stmt:   BrUncond
        mvec[0] = new MachineInstr(BA);
        mvec[0]->SetMachineOperand(0, MachineOperand::MO_CCRegister,
                                      (Value*)NULL);
        mvec[0]->SetMachineOperand(1, MachineOperand::MO_PCRelativeDisp,
              ((BranchInst*) subtreeRoot->getInstruction())->getSuccessor(0));
        
        // delay slot
        mvec[numInstr++] = new MachineInstr(NOP);
        break;

      case 206:	// stmt:   BrCond(setCCconst)
        // setCCconst => boolean was computed with `%b = setCC type reg1 const'
        // If the constant is ZERO, we can use the branch-on-integer-register
        // instructions and avoid the SUBcc instruction entirely.
        // Otherwise this is just the same as case 5, so just fall through.
        {
        InstrTreeNode* constNode = subtreeRoot->leftChild()->rightChild();
        assert(constNode &&
               constNode->getNodeType() ==InstrTreeNode::NTConstNode);
        ConstPoolVal* constVal = (ConstPoolVal*) constNode->getValue();
        bool isValidConst;

        if ((constVal->getType()->isIntegral()
             || constVal->getType()->isPointerType())
            && GetConstantValueAsSignedInt(constVal, isValidConst) == 0
            && isValidConst)
          {
            // That constant is a zero after all...
            // Use the left child of setCC as the first argument!
            mvec[0] = new MachineInstr(ChooseBprInstruction(subtreeRoot));
            mvec[0]->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                          subtreeRoot->leftChild()->leftChild()->getValue());
            mvec[0]->SetMachineOperand(1, MachineOperand::MO_PCRelativeDisp,
              ((BranchInst*) subtreeRoot->getInstruction())->getSuccessor(0));

            // delay slot
            mvec[numInstr++] = new MachineInstr(NOP);

            // false branch
            int n = numInstr++; 
            mvec[n] = new MachineInstr(BA);
            mvec[n]->SetMachineOperand(0, MachineOperand::MO_CCRegister,
                                          (Value*) NULL);
            mvec[n]->SetMachineOperand(1, MachineOperand::MO_PCRelativeDisp,
               ((BranchInst*) subtreeRoot->getInstruction())->getSuccessor(1));
            
            // delay slot
            mvec[numInstr++] = new MachineInstr(NOP);
            
            break;
          }
        // ELSE FALL THROUGH
        }

      case 6:	// stmt:   BrCond(bool)
        // bool => boolean was computed with some boolean operator
        // (SetCC, Not, ...).  We need to check whether the type was a FP,
        // signed int or unsigned int, and check the branching condition in
        // order to choose the branch to use.
        // 
        {
        bool isFPBranch;
        mvec[0] = new MachineInstr(ChooseBccInstruction(subtreeRoot,
                                                        isFPBranch));
        mvec[0]->SetMachineOperand(0, MachineOperand::MO_CCRegister,
                                      subtreeRoot->leftChild()->getValue());
        mvec[0]->SetMachineOperand(1, MachineOperand::MO_PCRelativeDisp,
              ((BranchInst*) subtreeRoot->getInstruction())->getSuccessor(0));

        // delay slot
        mvec[numInstr++] = new MachineInstr(NOP);

        // false branch
        int n = numInstr++;
        mvec[n] = new MachineInstr(BA);
        mvec[n]->SetMachineOperand(0, MachineOperand::MO_CCRegister,
                                      (Value*) NULL);
        mvec[n]->SetMachineOperand(1, MachineOperand::MO_PCRelativeDisp,
              ((BranchInst*) subtreeRoot->getInstruction())->getSuccessor(1));
        
        // delay slot
        mvec[numInstr++] = new MachineInstr(NOP);
        break;
        }
        
      case 208:	// stmt:   BrCond(boolconst)
        {
        // boolconst => boolean is a constant; use BA to first or second label
        ConstPoolVal* constVal = 
          cast<ConstPoolVal>(subtreeRoot->leftChild()->getValue());
        unsigned dest = ((ConstPoolBool*) constVal)->getValue()? 0 : 1;
        
        mvec[0] = new MachineInstr(BA);
        mvec[0]->SetMachineOperand(0, MachineOperand::MO_CCRegister,
                                      (Value*) NULL);
        mvec[0]->SetMachineOperand(1, MachineOperand::MO_PCRelativeDisp,
          ((BranchInst*) subtreeRoot->getInstruction())->getSuccessor(dest));
        
        // delay slot
        mvec[numInstr++] = new MachineInstr(NOP);
        break;
        }
        
      case   8:	// stmt:   BrCond(boolreg)
        // boolreg   => boolean is stored in an existing register.
        // Just use the branch-on-integer-register instruction!
        // 
        {
        mvec[0] = new MachineInstr(BRNZ);
        mvec[0]->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                      subtreeRoot->leftChild()->getValue());
        mvec[0]->SetMachineOperand(1, MachineOperand::MO_PCRelativeDisp,
              ((BranchInst*) subtreeRoot->getInstruction())->getSuccessor(0));

        // delay slot
        mvec[numInstr++] = new MachineInstr(NOP); // delay slot

        // false branch
        int n = numInstr++;
        mvec[n] = new MachineInstr(BA);
        mvec[n]->SetMachineOperand(0, MachineOperand::MO_CCRegister,
                                      (Value*) NULL);
        mvec[n]->SetMachineOperand(1, MachineOperand::MO_PCRelativeDisp,
              ((BranchInst*) subtreeRoot->getInstruction())->getSuccessor(1));
        
        // delay slot
        mvec[numInstr++] = new MachineInstr(NOP);
        break;
        }  
      
      case 9:	// stmt:   Switch(reg)
        assert(0 && "*** SWITCH instruction is not implemented yet.");
        numInstr = 0;
        break;

      case 10:	// reg:   VRegList(reg, reg)
        assert(0 && "VRegList should never be the topmost non-chain rule");
        break;

      case 21:	// reg:   Not(reg):	Implemented as reg = reg XOR-NOT 0
        mvec[0] = new MachineInstr(XNOR);
        mvec[0]->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                      subtreeRoot->leftChild()->getValue());
        mvec[0]->SetMachineOperand(1, target.getRegInfo().getZeroRegNum());
        mvec[0]->SetMachineOperand(2, MachineOperand::MO_VirtualRegister,
                                     subtreeRoot->getValue());
        break;

      case 322:	// reg:   ToBoolTy(bool):
      case 22:	// reg:   ToBoolTy(reg):
        opType = subtreeRoot->leftChild()->getValue()->getType();
        assert(opType->isIntegral() || opType == Type::BoolTy);
        numInstr = 0;
        forwardOperandNum = 0;
        break;

      case 23:	// reg:   ToUByteTy(reg)
      case 25:	// reg:   ToUShortTy(reg)
      case 27:	// reg:   ToUIntTy(reg)
      case 29:	// reg:   ToULongTy(reg)
        opType = subtreeRoot->leftChild()->getValue()->getType();
        assert(opType->isIntegral() ||
               opType->isPointerType() ||
               opType == Type::BoolTy && "Cast is illegal for other types");
        numInstr = 0;
        forwardOperandNum = 0;
        break;
        
      case 24:	// reg:   ToSByteTy(reg)
      case 26:	// reg:   ToShortTy(reg)
      case 28:	// reg:   ToIntTy(reg)
      case 30:	// reg:   ToLongTy(reg)
        opType = subtreeRoot->leftChild()->getValue()->getType();
        if (opType->isIntegral() || opType == Type::BoolTy)
          {
            numInstr = 0;
            forwardOperandNum = 0;
          }
        else
          {
            mvec[0] = new MachineInstr(ChooseConvertToIntInstr(subtreeRoot,
                                                              opType));
            Set2OperandsFromInstr(mvec[0], subtreeRoot, target);
          }
        break;
        
      case  31:	// reg:   ToFloatTy(reg):
      case  32:	// reg:   ToDoubleTy(reg):
      case 232:	// reg:   ToDoubleTy(Constant):
        
        // If this instruction has a parent (a user) in the tree 
        // and the user is translated as an FsMULd instruction,
        // then the cast is unnecessary.  So check that first.
        // In the future, we'll want to do the same for the FdMULq instruction,
        // so do the check here instead of only for ToFloatTy(reg).
        // 
        if (subtreeRoot->parent() != NULL &&
            ((InstructionNode*) subtreeRoot->parent())->getInstruction()->getMachineInstrVec()[0]->getOpCode() == FSMULD)
          {
            numInstr = 0;
            forwardOperandNum = 0;
          }
        else
          {
            opType = subtreeRoot->leftChild()->getValue()->getType();
            MachineOpCode opCode=ChooseConvertToFloatInstr(subtreeRoot,opType);
            if (opCode == INVALID_OPCODE)	// no conversion needed
              {
                numInstr = 0;
                forwardOperandNum = 0;
              }
            else
              {
                mvec[0] = new MachineInstr(opCode);
                Set2OperandsFromInstr(mvec[0], subtreeRoot, target);
              }
          }
        break;

      case 19:	// reg:   ToArrayTy(reg):
      case 20:	// reg:   ToPointerTy(reg):
        numInstr = 0;
        forwardOperandNum = 0;
        break;

      case 233:	// reg:   Add(reg, Constant)
        mvec[0] = CreateAddConstInstruction(subtreeRoot);
        if (mvec[0] != NULL)
          break;
        // ELSE FALL THROUGH

      case 33:	// reg:   Add(reg, reg)
        mvec[0] = new MachineInstr(ChooseAddInstruction(subtreeRoot));
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case 234:	// reg:   Sub(reg, Constant)
        mvec[0] = CreateSubConstInstruction(subtreeRoot);
        if (mvec[0] != NULL)
          break;
        // ELSE FALL THROUGH

      case 34:	// reg:   Sub(reg, reg)
        mvec[0] = new MachineInstr(ChooseSubInstruction(subtreeRoot));
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case 135:	// reg:   Mul(todouble, todouble)
        checkCast = true;
        // FALL THROUGH 

      case 35:	// reg:   Mul(reg, reg)
        mvec[0] =new MachineInstr(ChooseMulInstruction(subtreeRoot,checkCast));
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case 335:	// reg:   Mul(todouble, todoubleConst)
        checkCast = true;
        // FALL THROUGH 

      case 235:	// reg:   Mul(reg, Constant)
        mvec[0] = CreateMulConstInstruction(target, subtreeRoot, mvec[1]);
        if (mvec[0] == NULL)
          {
            mvec[0] = new MachineInstr(ChooseMulInstruction(subtreeRoot,
                                                            checkCast));
            Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
          }
        else
          if (mvec[1] != NULL)
            ++numInstr;
        break;

      case 236:	// reg:   Div(reg, Constant)
        mvec[0] = CreateDivConstInstruction(target, subtreeRoot, mvec[1]);
        if (mvec[0] != NULL)
          {
            if (mvec[1] != NULL)
              ++numInstr;
          }
        else
        // ELSE FALL THROUGH

      case 36:	// reg:   Div(reg, reg)
        mvec[0] = new MachineInstr(ChooseDivInstruction(target, subtreeRoot));
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case  37:	// reg:   Rem(reg, reg)
      case 237:	// reg:   Rem(reg, Constant)
        assert(0 && "REM instruction unimplemented for the SPARC.");
        break;

      case  38:	// reg:   And(reg, reg)
      case 238:	// reg:   And(reg, Constant)
        mvec[0] = new MachineInstr(AND);
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case 138:	// reg:   And(reg, not)
        mvec[0] = new MachineInstr(ANDN);
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case  39:	// reg:   Or(reg, reg)
      case 239:	// reg:   Or(reg, Constant)
        mvec[0] = new MachineInstr(ORN);
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case 139:	// reg:   Or(reg, not)
        mvec[0] = new MachineInstr(ORN);
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case  40:	// reg:   Xor(reg, reg)
      case 240:	// reg:   Xor(reg, Constant)
        mvec[0] = new MachineInstr(XOR);
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case 140:	// reg:   Xor(reg, not)
        mvec[0] = new MachineInstr(XNOR);
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case 41:	// boolconst:   SetCC(reg, Constant)
        // Check if this is an integer comparison, and
        // there is a parent, and the parent decided to use
        // a branch-on-integer-register instead of branch-on-condition-code.
        // If so, the SUBcc instruction is not required.
        // (However, we must still check for constants to be loaded from
        // the constant pool so that such a load can be associated with
        // this instruction.)
        // 
        // Otherwise this is just the same as case 42, so just fall through.
        // 
        if (subtreeRoot->leftChild()->getValue()->getType()->isIntegral() &&
            subtreeRoot->parent() != NULL)
          {
            InstructionNode* parent = (InstructionNode*) subtreeRoot->parent();
            assert(parent->getNodeType() == InstrTreeNode::NTInstructionNode);
            const vector<MachineInstr*>&
              minstrVec = parent->getInstruction()->getMachineInstrVec();
            MachineOpCode parentOpCode;
            if (parent->getInstruction()->getOpcode() == Instruction::Br &&
                (parentOpCode = minstrVec[0]->getOpCode()) >= BRZ &&
                parentOpCode <= BRGEZ)
              {
                numInstr = 0;		// don't forward the operand!
                break;
              }
          }
        // ELSE FALL THROUGH

      case 42:	// bool:   SetCC(reg, reg):
      {
        // If result of the SetCC is only used for a single branch, we can
        // discard the result.  Otherwise, the boolean value must go into
        // an integer register.
        // 
        bool keepBoolVal = (subtreeRoot->parent() == NULL ||
                            ((InstructionNode*) subtreeRoot->parent())
                            ->getInstruction()->getOpcode() !=Instruction::Br);
        bool subValIsBoolVal =
          subtreeRoot->getInstruction()->getOpcode() == Instruction::SetNE;
        bool keepSubVal = keepBoolVal && subValIsBoolVal;
        bool computeBoolVal = keepBoolVal && ! subValIsBoolVal;
        
        bool mustClearReg;
        int valueToMove;
        MachineOpCode movOpCode;
        
        if (subtreeRoot->leftChild()->getValue()->getType()->isIntegral() ||
            subtreeRoot->leftChild()->getValue()->getType()->isPointerType())
          {
            // Integer condition: dest. should be %g0 or an integer register.
            // If result must be saved but condition is not SetEQ then we need
            // a separate instruction to compute the bool result, so discard
            // result of SUBcc instruction anyway.
            // 
            mvec[0] = new MachineInstr(SUBcc);
            Set3OperandsFromInstr(mvec[0], subtreeRoot, target, ! keepSubVal);
            
            // mark the 4th operand as being a CC register, and a "result"
            mvec[0]->SetMachineOperand(3, MachineOperand::MO_CCRegister,
                                          subtreeRoot->getValue(),/*def*/true);
            
            if (computeBoolVal)
              { // recompute bool using the integer condition codes
                movOpCode =
                  ChooseMovpccAfterSub(subtreeRoot,mustClearReg,valueToMove);
              }
          }
        else
          {
            // FP condition: dest of FCMP should be some FCCn register
            mvec[0] = new MachineInstr(ChooseFcmpInstruction(subtreeRoot));
            mvec[0]->SetMachineOperand(0,MachineOperand::MO_CCRegister,
                                         subtreeRoot->getValue());
            mvec[0]->SetMachineOperand(1,MachineOperand::MO_VirtualRegister,
                                         subtreeRoot->leftChild()->getValue());
            mvec[0]->SetMachineOperand(2,MachineOperand::MO_VirtualRegister,
                                        subtreeRoot->rightChild()->getValue());
            
            if (computeBoolVal)
              {// recompute bool using the FP condition codes
                mustClearReg = true;
                valueToMove = 1;
                movOpCode = ChooseMovFpccInstruction(subtreeRoot);
              }
          }
        
        if (computeBoolVal)
          {
            if (mustClearReg)
              {// Unconditionally set register to 0
               int n = numInstr++;
               mvec[n] = new MachineInstr(SETHI);
               mvec[n]->SetMachineOperand(0,MachineOperand::MO_UnextendedImmed,
                                            s0);
               mvec[n]->SetMachineOperand(1,MachineOperand::MO_VirtualRegister,
                                            subtreeRoot->getValue());
              }
            
            // Now conditionally move `valueToMove' (0 or 1) into the register
            int n = numInstr++;
            mvec[n] = new MachineInstr(movOpCode);
            mvec[n]->SetMachineOperand(0, MachineOperand::MO_CCRegister,
                                          subtreeRoot->getValue());
            mvec[n]->SetMachineOperand(1, MachineOperand::MO_UnextendedImmed,
                                          valueToMove);
            mvec[n]->SetMachineOperand(2, MachineOperand::MO_VirtualRegister,
                                          subtreeRoot->getValue());
          }
        break;
      }    

      case 43:	// boolreg: VReg
      case 44:	// boolreg: Constant
        numInstr = 0;
        break;

      case 51:	// reg:   Load(reg)
      case 52:	// reg:   Load(ptrreg)
      case 53:	// reg:   LoadIdx(reg,reg)
      case 54:	// reg:   LoadIdx(ptrreg,reg)
        mvec[0] = new MachineInstr(ChooseLoadInstruction(
                                     subtreeRoot->getValue()->getType()));
        SetOperandsForMemInstr(mvec[0], subtreeRoot, target);
        break;

      case 55:	// reg:   GetElemPtr(reg)
      case 56:	// reg:   GetElemPtrIdx(reg,reg)
        if (subtreeRoot->parent() != NULL)
          {
            // Check if the parent was an array access.
            // If so, we still need to generate this instruction.
            MemAccessInst* memInst = (MemAccessInst*)
              subtreeRoot->getInstruction();
            const PointerType* ptrType =
              (const PointerType*) memInst->getPtrOperand()->getType();
            if (! ptrType->getValueType()->isArrayType())
              {// we don't need a separate instr
                numInstr = 0;		// don't forward operand!
                break;
              }
          }
        // else in all other cases we need to a separate ADD instruction
        mvec[0] = new MachineInstr(ADD);
        SetOperandsForMemInstr(mvec[0], subtreeRoot, target);
        break;

      case 57:	// reg:   Alloca: Implement as 2 instructions:
                    //	sub %sp, tmp -> %sp
        {		//	add %sp, 0   -> result
        Instruction* instr = subtreeRoot->getInstruction();
        const PointerType* instrType = (const PointerType*) instr->getType();
        assert(instrType->isPointerType());
        int tsize = (int)
          target.findOptimalStorageSize(instrType->getValueType());
        assert(tsize != 0 && "Just to check when this can happen");
        
        // Create a temporary Value to hold the constant type-size
        ConstPoolSInt* valueForTSize = ConstPoolSInt::get(Type::IntTy, tsize);

        // Instruction 1: sub %sp, tsize -> %sp
        // tsize is always constant, but it may have to be put into a
        // register if it doesn't fit in the immediate field.
        // 
        mvec[0] = new MachineInstr(SUB);
        mvec[0]->SetMachineOperand(0, /*regNum %sp=o6=r[14]*/(unsigned int)14);
        mvec[0]->SetMachineOperand(1, MachineOperand::MO_VirtualRegister,
                                      valueForTSize);
        mvec[0]->SetMachineOperand(2, /*regNum %sp=o6=r[14]*/(unsigned int)14);

        // Instruction 2: add %sp, 0 -> result
        numInstr++;
        mvec[1] = new MachineInstr(ADD);
        mvec[1]->SetMachineOperand(0, /*regNum %sp=o6=r[14]*/(unsigned int)14);
        mvec[1]->SetMachineOperand(1, target.getRegInfo().getZeroRegNum());
        mvec[1]->SetMachineOperand(2, MachineOperand::MO_VirtualRegister,
                                      instr);
        break;
        }
        
      case 58:	// reg:   Alloca(reg): Implement as 3 instructions:
                //	mul num, typeSz -> tmp
                //	sub %sp, tmp    -> %sp
        {	//	add %sp, 0      -> result
        Instruction* instr = subtreeRoot->getInstruction();
        const PointerType* instrType = (const PointerType*) instr->getType();
        assert(instrType->isPointerType() &&
               instrType->getValueType()->isArrayType());
        const Type* eltType =
          ((ArrayType*) instrType->getValueType())->getElementType();
        int tsize = (int) target.findOptimalStorageSize(eltType);

        assert(tsize != 0 && "Just to check when this can happen");
        // if (tsize == 0)
          // {
            // numInstr = 0;
            // break;
          // }
        //else go on to create the instructions needed...

        // Create a temporary Value to hold the constant type-size
        ConstPoolSInt* valueForTSize = ConstPoolSInt::get(Type::IntTy, tsize);

        // Create a temporary value to hold `tmp'
        Instruction* tmpInstr = new TmpInstruction(Instruction::UserOp1,
                                          subtreeRoot->leftChild()->getValue(),
                                          NULL /*could insert tsize here*/);
        subtreeRoot->getInstruction()->getMachineInstrVec().addTempValue(tmpInstr);
        
        // Instruction 1: mul numElements, typeSize -> tmp
        mvec[0] = new MachineInstr(MULX);
        mvec[0]->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                    subtreeRoot->leftChild()->getValue());
        mvec[0]->SetMachineOperand(1, MachineOperand::MO_VirtualRegister,
                                      valueForTSize);
        mvec[0]->SetMachineOperand(2, MachineOperand::MO_VirtualRegister,
                                      tmpInstr);

        tmpInstr->addMachineInstruction(mvec[0]);

        // Instruction 2: sub %sp, tmp -> %sp
        numInstr++;
        mvec[1] = new MachineInstr(SUB);
        mvec[1]->SetMachineOperand(0, /*regNum %sp=o6=r[14]*/(unsigned int)14);
        mvec[1]->SetMachineOperand(1, MachineOperand::MO_VirtualRegister,
                                      tmpInstr);
        mvec[1]->SetMachineOperand(2, /*regNum %sp=o6=r[14]*/(unsigned int)14);
        
        // Instruction 3: add %sp, 0 -> result
        numInstr++;
        mvec[2] = new MachineInstr(ADD);
        mvec[2]->SetMachineOperand(0, /*regNum %sp=o6=r[14]*/(unsigned int)14);
        mvec[2]->SetMachineOperand(1, target.getRegInfo().getZeroRegNum());
        mvec[2]->SetMachineOperand(2, MachineOperand::MO_VirtualRegister,
                                      instr);
        break;
        }

      case 61:	// reg:   Call
                // Generate a call-indirect (i.e., JMPL) for now to expose
                // the potential need for registers.  If an absolute address
                // is available, replace this with a CALL instruction.
                // Mark both the indirection register and the return-address
        	// register as hidden virtual registers.
                // Also, mark the operands of the Call as implicit operands
                // of the machine instruction.
        {
        CallInst* callInstr = (CallInst*) subtreeRoot->getInstruction();
        Method* callee = callInstr->getCalledMethod();
        assert(callInstr->getOpcode() == Instruction::Call); 
        
        Instruction* jmpAddrReg = new TmpInstruction(Instruction::UserOp1,
                                                     callee, NULL);
        Instruction* retAddrReg = new TmpInstruction(Instruction::UserOp1,
                                                     callInstr, NULL);

        // Note temporary values and implicit uses in mvec
        callInstr->getMachineInstrVec().addTempValue(jmpAddrReg);
        callInstr->getMachineInstrVec().addTempValue(retAddrReg);
        for (unsigned i=0, N=callInstr->getNumOperands(); i < N; ++i)
          if (callInstr->getOperand(i) != callee)
            callInstr->getMachineInstrVec().addImplicitUse(
                                                   callInstr->getOperand(i));
        
        // Generate the machine instruction and its operands
        mvec[0] = new MachineInstr(JMPL);
        mvec[0]->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                      jmpAddrReg);
        mvec[0]->SetMachineOperand(1, MachineOperand::MO_SignExtendedImmed,
                                      (int64_t) 0);
        mvec[0]->SetMachineOperand(2, MachineOperand::MO_VirtualRegister,
                                      retAddrReg);
        
        // NOTE: jmpAddrReg will be loaded by a different instruction generated
        //   by the final code generator, so we just mark the CALL instruction
        //   as computing that value.
        //   The retAddrReg is actually computed by the CALL instruction.
        //
        jmpAddrReg->addMachineInstruction(mvec[0]);
        retAddrReg->addMachineInstruction(mvec[0]);
        
        mvec[numInstr++] = new MachineInstr(NOP); // delay slot
        break;
        }

      case 62:	// reg:   Shl(reg, reg)
        opType = subtreeRoot->leftChild()->getValue()->getType();
        assert(opType->isIntegral()
               || opType == Type::BoolTy
               || opType->isPointerType()&& "Shl unsupported for other types");
        mvec[0] = new MachineInstr((opType == Type::LongTy)? SLLX : SLL);
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case 63:	// reg:   Shr(reg, reg)
        opType = subtreeRoot->leftChild()->getValue()->getType();
        assert(opType->isIntegral()
               || opType == Type::BoolTy
               || opType->isPointerType() &&"Shr unsupported for other types");
        mvec[0] = new MachineInstr((opType->isSigned()
                                    ? ((opType == Type::LongTy)? SRAX : SRA)
                                    : ((opType == Type::LongTy)? SRLX : SRL)));
        Set3OperandsFromInstr(mvec[0], subtreeRoot, target);
        break;

      case 64:	// reg:   Phi(reg,reg)
      {		// This instruction has variable #operands, so resultPos is 0.
        Instruction* phi = subtreeRoot->getInstruction();
        mvec[0] = new MachineInstr(PHI, 1 + phi->getNumOperands());
        mvec[0]->SetMachineOperand(0, MachineOperand::MO_VirtualRegister,
                                      subtreeRoot->getValue());
        for (unsigned i=0, N=phi->getNumOperands(); i < N; i++)
          mvec[0]->SetMachineOperand(i+1, MachineOperand::MO_VirtualRegister,
                                          phi->getOperand(i));
        break;
      }  
      case 71:	// reg:     VReg
      case 72:	// reg:     Constant
        numInstr = 0;			// don't forward the value
        break;

      default:
        assert(0 && "Unrecognized BURG rule");
        numInstr = 0;
        break;
      }
    }
  
  if (forwardOperandNum >= 0)
    { // We did not generate a machine instruction but need to use operand.
      // If user is in the same tree, replace Value in its machine operand.
      // If not, insert a copy instruction which should get coalesced away
      // by register allocation.
      if (subtreeRoot->parent() != NULL)
        ForwardOperand(subtreeRoot, subtreeRoot->parent(), forwardOperandNum);
      else
        {
          MachineInstr *minstr1 = NULL, *minstr2 = NULL;
          minstr1 = CreateCopyInstructionsByType(target,
                subtreeRoot->getInstruction()->getOperand(forwardOperandNum),
                subtreeRoot->getInstruction(), minstr2);
          assert(minstr1);
          mvec[numInstr++] = minstr1;
          if (minstr2 != NULL)
            mvec[numInstr++] = minstr2;
        }
    }
  
  if (! ThisIsAChainRule(ruleForNode))
    numInstr = FixConstantOperands(subtreeRoot, mvec, numInstr, target);
  
  return numInstr;
}