//===-- llvm/CodeGen/MachineInstr.h - MachineInstr class ---------*- C++ -*--=//
//
// This file contains the declaration of the MachineInstr class, which is the
// basic representation for all target dependant machine instructions used by
// the back end.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_MACHINEINSTR_H
#define LLVM_CODEGEN_MACHINEINSTR_H

#include "llvm/Target/MRegisterInfo.h"
#include "Support/Annotation.h"
#include "Support/iterator"
#include <set>

class Value;
class Function;
class MachineBasicBlock;
class TargetMachine;
class GlobalValue;

typedef int MachineOpCode;

//===----------------------------------------------------------------------===//
/// Special flags on instructions that modify the opcode.
/// These flags are unused for now, but having them enforces that some
/// changes will be needed if they are used.
///
enum MachineOpCodeFlags {
  AnnulFlag,         /// 1 if annul bit is set on a branch
  PredTakenFlag,     /// 1 if branch should be predicted taken
  PredNotTakenFlag   /// 1 if branch should be predicted not taken
};

//===----------------------------------------------------------------------===//
/// MOTy - MachineOperandType - This namespace contains an enum that describes
/// how the machine operand is used by the instruction: is it read, defined, or
/// both?  Note that the MachineInstr/Operator class currently uses bool
/// arguments to represent this information instead of an enum.  Eventually this
/// should change over to use this _easier to read_ representation instead.
///
namespace MOTy {
  enum UseType {
    Use,             /// This machine operand is only read by the instruction
    Def,             /// This machine operand is only written by the instruction
    UseAndDef        /// This machine operand is read AND written
  };
}

//===----------------------------------------------------------------------===//
// class MachineOperand 
// 
// Purpose:
//   Representation of each machine instruction operand.
//   This class is designed so that you can allocate a vector of operands
//   first and initialize each one later.
//
//   E.g, for this VM instruction:
//		ptr = alloca type, numElements
//   we generate 2 machine instructions on the SPARC:
// 
//		mul Constant, Numelements -> Reg
//		add %sp, Reg -> Ptr
// 
//   Each instruction has 3 operands, listed above.  Of those:
//   -	Reg, NumElements, and Ptr are of operand type MO_Register.
//   -	Constant is of operand type MO_SignExtendedImmed on the SPARC.
//	
//   For the register operands, the virtual register type is as follows:
//	
//   -  Reg will be of virtual register type MO_MInstrVirtualReg.  The field
//	MachineInstr* minstr will point to the instruction that computes reg.
// 
//   -	%sp will be of virtual register type MO_MachineReg.
//	The field regNum identifies the machine register.
// 
//   -	NumElements will be of virtual register type MO_VirtualReg.
//	The field Value* value identifies the value.
// 
//   -	Ptr will also be of virtual register type MO_VirtualReg.
//	Again, the field Value* value identifies the value.
// 
//===----------------------------------------------------------------------===//

struct MachineOperand {
  enum MachineOperandType {
    MO_VirtualRegister,		// virtual register for *value
    MO_MachineRegister,		// pre-assigned machine register `regNum'
    MO_CCRegister,
    MO_SignExtendedImmed,
    MO_UnextendedImmed,
    MO_PCRelativeDisp,
    MO_MachineBasicBlock,       // MachineBasicBlock reference
    MO_FrameIndex,              // Abstract Stack Frame Index
    MO_ConstantPoolIndex,       // Address of indexed Constant in Constant Pool
    MO_ExternalSymbol,          // Name of external global symbol
    MO_GlobalAddress,           // Address of a global value
  };
  
private:
  // Bit fields of the flags variable used for different operand properties
  enum {
    DEFONLYFLAG = 0x01,       // this is a def but not a use of the operand
    DEFUSEFLAG  = 0x02,       // this is both a def and a use
    HIFLAG32    = 0x04,       // operand is %hi32(value_or_immedVal)
    LOFLAG32    = 0x08,       // operand is %lo32(value_or_immedVal)
    HIFLAG64    = 0x10,       // operand is %hi64(value_or_immedVal)
    LOFLAG64    = 0x20,       // operand is %lo64(value_or_immedVal)
    PCRELATIVE  = 0x40,       // Operand is relative to PC, not a global address
  
    USEDEFMASK = 0x03,
  };

private:
  union {
    Value*	value;		// BasicBlockVal for a label operand.
				// ConstantVal for a non-address immediate.
				// Virtual register for an SSA operand,
				//   including hidden operands required for
				//   the generated machine code.     
                                // LLVM global for MO_GlobalAddress.

    int64_t immedVal;		// Constant value for an explicit constant

    MachineBasicBlock *MBB;     // For MO_MachineBasicBlock type
    std::string *SymbolName;    // For MO_ExternalSymbol type
  };

  char flags;                   // see bit field definitions above
  MachineOperandType opType:8;  // Pack into 8 bits efficiently after flags.
  int regNum;	                // register number for an explicit register
                                // will be set for a value after reg allocation
private:
  MachineOperand()
    : immedVal(0),
      flags(0),
      opType(MO_VirtualRegister),
      regNum(-1) {}

  MachineOperand(int64_t ImmVal, MachineOperandType OpTy)
    : immedVal(ImmVal),
      flags(0),
      opType(OpTy),
      regNum(-1) {}

  MachineOperand(int Reg, MachineOperandType OpTy, MOTy::UseType UseTy)
    : immedVal(0),
      opType(OpTy),
      regNum(Reg) {
    switch (UseTy) {
    case MOTy::Use:       flags = 0; break;
    case MOTy::Def:       flags = DEFONLYFLAG; break;
    case MOTy::UseAndDef: flags = DEFUSEFLAG; break;
    default: assert(0 && "Invalid value for UseTy!");
    }
  }

  MachineOperand(Value *V, MachineOperandType OpTy, MOTy::UseType UseTy,
		 bool isPCRelative = false)
    : value(V), opType(OpTy), regNum(-1) {
    switch (UseTy) {
    case MOTy::Use:       flags = 0; break;
    case MOTy::Def:       flags = DEFONLYFLAG; break;
    case MOTy::UseAndDef: flags = DEFUSEFLAG; break;
    default: assert(0 && "Invalid value for UseTy!");
    }
    if (isPCRelative) flags |= PCRELATIVE;
  }

  MachineOperand(MachineBasicBlock *mbb)
    : MBB(mbb), flags(0), opType(MO_MachineBasicBlock), regNum(-1) {}

  MachineOperand(const std::string &SymName, bool isPCRelative)
    : SymbolName(new std::string(SymName)), flags(isPCRelative ? PCRELATIVE :0),
      opType(MO_ExternalSymbol), regNum(-1) {}

public:
  MachineOperand(const MachineOperand &M) : immedVal(M.immedVal),
					    flags(M.flags),
					    opType(M.opType),
					    regNum(M.regNum) {
    if (isExternalSymbol())
      SymbolName = new std::string(M.getSymbolName());
  }

  ~MachineOperand() {
    if (isExternalSymbol())
      delete SymbolName;
  }
  
  const MachineOperand &operator=(const MachineOperand &MO) {
    if (isExternalSymbol())             // if old operand had a symbol name,
      delete SymbolName;                // release old memory
    immedVal = MO.immedVal;
    flags    = MO.flags;
    opType   = MO.opType;
    regNum   = MO.regNum;
    if (isExternalSymbol())
      SymbolName = new std::string(MO.getSymbolName());
    return *this;
  }

  // Accessor methods.  Caller is responsible for checking the
  // operand type before invoking the corresponding accessor.
  // 
  MachineOperandType getType() const { return opType; }

  /// isPCRelative - This returns the value of the PCRELATIVE flag, which
  /// indicates whether this operand should be emitted as a PC relative value
  /// instead of a global address.  This is used for operands of the forms:
  /// MachineBasicBlock, GlobalAddress, ExternalSymbol
  ///
  bool isPCRelative() const { return (flags & PCRELATIVE) != 0; }


  // This is to finally stop caring whether we have a virtual or machine
  // register -- an easier interface is to simply call both virtual and machine
  // registers essentially the same, yet be able to distinguish when
  // necessary. Thus the instruction selector can just add registers without
  // abandon, and the register allocator won't be confused.
  bool isVirtualRegister() const {
    return (opType == MO_VirtualRegister || opType == MO_MachineRegister) 
      && regNum >= MRegisterInfo::FirstVirtualRegister;
  }
  bool isPhysicalRegister() const {
    return (opType == MO_VirtualRegister || opType == MO_MachineRegister) 
      && (unsigned)regNum < MRegisterInfo::FirstVirtualRegister;
  }
  bool isRegister() const { return isVirtualRegister() || isPhysicalRegister();}
  bool isMachineRegister() const { return !isVirtualRegister(); }
  bool isMachineBasicBlock() const { return opType == MO_MachineBasicBlock; }
  bool isPCRelativeDisp() const { return opType == MO_PCRelativeDisp; }
  bool isImmediate() const {
    return opType == MO_SignExtendedImmed || opType == MO_UnextendedImmed;
  }
  bool isFrameIndex() const { return opType == MO_FrameIndex; }
  bool isConstantPoolIndex() const { return opType == MO_ConstantPoolIndex; }
  bool isGlobalAddress() const { return opType == MO_GlobalAddress; }
  bool isExternalSymbol() const { return opType == MO_ExternalSymbol; }

  Value* getVRegValue() const {
    assert(opType == MO_VirtualRegister || opType == MO_CCRegister || 
	   isPCRelativeDisp());
    return value;
  }
  Value* getVRegValueOrNull() const {
    return (opType == MO_VirtualRegister || opType == MO_CCRegister || 
            isPCRelativeDisp()) ? value : NULL;
  }
  int getMachineRegNum() const {
    assert(opType == MO_MachineRegister);
    return regNum;
  }
  int64_t getImmedValue() const { assert(isImmediate()); return immedVal; }
  MachineBasicBlock *getMachineBasicBlock() const {
    assert(isMachineBasicBlock() && "Can't get MBB in non-MBB operand!");
    return MBB;
  }
  int getFrameIndex() const { assert(isFrameIndex()); return immedVal; }
  unsigned getConstantPoolIndex() const {
    assert(isConstantPoolIndex());
    return immedVal;
  }

  GlobalValue *getGlobal() const {
    assert(isGlobalAddress());
    return (GlobalValue*)value;
  }

  const std::string &getSymbolName() const {
    assert(isExternalSymbol());
    return *SymbolName;
  }

  bool          opIsUse         () const { return (flags & USEDEFMASK) == 0; }
  bool		opIsDefOnly     () const { return flags & DEFONLYFLAG; }
  bool		opIsDefAndUse	() const { return flags & DEFUSEFLAG; }
  bool          opHiBits32      () const { return flags & HIFLAG32; }
  bool          opLoBits32      () const { return flags & LOFLAG32; }
  bool          opHiBits64      () const { return flags & HIFLAG64; }
  bool          opLoBits64      () const { return flags & LOFLAG64; }

  // used to check if a machine register has been allocated to this operand
  bool hasAllocatedReg() const {
    return (regNum >= 0 &&
            (opType == MO_VirtualRegister || opType == MO_CCRegister || 
             opType == MO_MachineRegister));
  }

  // used to get the reg number if when one is allocated
  int getAllocatedRegNum() const {
    assert(hasAllocatedReg());
    return regNum;
  }

  // ********** TODO: get rid of this duplicate code! ***********
  unsigned getReg() const {
    return getAllocatedRegNum();
  }    

  friend std::ostream& operator<<(std::ostream& os, const MachineOperand& mop);

private:

  // Construction methods needed for fine-grain control.
  // These must be accessed via coresponding methods in MachineInstr.
  void markHi32()      { flags |= HIFLAG32; }
  void markLo32()      { flags |= LOFLAG32; }
  void markHi64()      { flags |= HIFLAG64; }
  void markLo64()      { flags |= LOFLAG64; }
  
  // Replaces the Value with its corresponding physical register after
  // register allocation is complete
  void setRegForValue(int reg) {
    assert(opType == MO_VirtualRegister || opType == MO_CCRegister || 
	   opType == MO_MachineRegister);
    regNum = reg;
  }
  
  friend class MachineInstr;
};


//===----------------------------------------------------------------------===//
// class MachineInstr 
// 
// Purpose:
//   Representation of each machine instruction.
// 
//   MachineOpCode must be an enum, defined separately for each target.
//   E.g., It is defined in SparcInstructionSelection.h for the SPARC.
// 
//  There are 2 kinds of operands:
// 
//  (1) Explicit operands of the machine instruction in vector operands[] 
// 
//  (2) "Implicit operands" are values implicitly used or defined by the
//      machine instruction, such as arguments to a CALL, return value of
//      a CALL (if any), and return value of a RETURN.
//===----------------------------------------------------------------------===//

class MachineInstr {
  int              opCode;              // the opcode
  unsigned         opCodeFlags;         // flags modifying instrn behavior
  std::vector<MachineOperand> operands; // the operands
  unsigned numImplicitRefs;             // number of implicit operands

  // regsUsed - all machine registers used for this instruction, including regs
  // used to save values across the instruction.  This is a bitset of registers.
  std::set<int>    regsUsed;

  // OperandComplete - Return true if it's illegal to add a new operand
  bool OperandsComplete() const;

  MachineInstr(const MachineInstr &);  // DO NOT IMPLEMENT
  void operator=(const MachineInstr&); // DO NOT IMPLEMENT
public:
  MachineInstr(int Opcode, unsigned numOperands);

  /// MachineInstr ctor - This constructor only does a _reserve_ of the
  /// operands, not a resize for them.  It is expected that if you use this that
  /// you call add* methods below to fill up the operands, instead of the Set
  /// methods.  Eventually, the "resizing" ctors will be phased out.
  ///
  MachineInstr(int Opcode, unsigned numOperands, bool XX, bool YY);

  /// MachineInstr ctor - Work exactly the same as the ctor above, except that
  /// the MachineInstr is created and added to the end of the specified basic
  /// block.
  ///
  MachineInstr(MachineBasicBlock *MBB, int Opcode, unsigned numOps);
  

  // The opcode.
  // 
  const int getOpcode() const { return opCode; }
  const int getOpCode() const { return opCode; }

  // Opcode flags.
  // 
  unsigned       getOpCodeFlags() const { return opCodeFlags; }

  //
  // Access to explicit operands of the instruction
  // 
  unsigned getNumOperands() const { return operands.size() - numImplicitRefs; }
  
  const MachineOperand& getOperand(unsigned i) const {
    assert(i < getNumOperands() && "getOperand() out of range!");
    return operands[i];
  }
  MachineOperand& getOperand(unsigned i) {
    assert(i < getNumOperands() && "getOperand() out of range!");
    return operands[i];
  }

  //
  // Access to explicit or implicit operands of the instruction
  // This returns the i'th entry in the operand vector.
  // That represents the i'th explicit operand or the (i-N)'th implicit operand,
  // depending on whether i < N or i >= N.
  // 
  const MachineOperand& getExplOrImplOperand(unsigned i) const {
    assert(i < operands.size() && "getExplOrImplOperand() out of range!");
    return (i < getNumOperands()? getOperand(i)
                                : getImplicitOp(i - getNumOperands()));
  }

  //
  // Access to implicit operands of the instruction
  // 
  unsigned getNumImplicitRefs() const{ return numImplicitRefs; }
  
  MachineOperand& getImplicitOp(unsigned i) {
    assert(i < numImplicitRefs && "implicit ref# out of range!");
    return operands[i + operands.size() - numImplicitRefs];
  }
  const MachineOperand& getImplicitOp(unsigned i) const {
    assert(i < numImplicitRefs && "implicit ref# out of range!");
    return operands[i + operands.size() - numImplicitRefs];
  }

  Value* getImplicitRef(unsigned i) {
    return getImplicitOp(i).getVRegValue();
  }
  const Value* getImplicitRef(unsigned i) const {
    return getImplicitOp(i).getVRegValue();
  }

  void addImplicitRef(Value* V, bool isDef = false, bool isDefAndUse = false) {
    ++numImplicitRefs;
    addRegOperand(V, isDef, isDefAndUse);
  }
  void setImplicitRef(unsigned i, Value* V, bool isDef=false,
                      bool isDefAndUse=false) {
    assert(i < getNumImplicitRefs() && "setImplicitRef() out of range!");
    SetMachineOperandVal(i + getNumOperands(),
                         MachineOperand::MO_VirtualRegister,
                         V, isDef, isDefAndUse);
  }

  //
  // Information about registers used in this instruction.
  // 
  const std::set<int> &getRegsUsed() const {
    return regsUsed;
  }
  bool isRegUsed(int regNum) const {
    return regsUsed.find(regNum) != regsUsed.end();
  }
  void insertUsedReg(unsigned Reg) {
    assert(((int) Reg) >= 0 && "Invalid register being marked as used");
    regsUsed.insert((int) Reg);
  }

  //
  // Debugging support
  //
  void print(std::ostream &OS, const TargetMachine &TM) const;
  void dump() const;
  friend std::ostream& operator<<(std::ostream& os, const MachineInstr& minstr);

  //
  // Define iterators to access the Value operands of the Machine Instruction.
  // Note that these iterators only enumerate the explicit operands.
  // begin() and end() are defined to produce these iterators...
  //
  template<class _MI, class _V> class ValOpIterator;
  typedef ValOpIterator<const MachineInstr*,const Value*> const_val_op_iterator;
  typedef ValOpIterator<      MachineInstr*,      Value*> val_op_iterator;


  //===--------------------------------------------------------------------===//
  // Accessors to add operands when building up machine instructions
  //

  /// addRegOperand - Add a MO_VirtualRegister operand to the end of the
  /// operands list...
  ///
  void addRegOperand(Value *V, bool isDef, bool isDefAndUse=false) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(V, MachineOperand::MO_VirtualRegister,
             !isDef ? MOTy::Use : (isDefAndUse ? MOTy::UseAndDef : MOTy::Def)));
  }

  void addRegOperand(Value *V, MOTy::UseType UTy = MOTy::Use,
		     bool isPCRelative = false) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(V, MachineOperand::MO_VirtualRegister,
                                      UTy, isPCRelative));
  }

  void addCCRegOperand(Value *V, MOTy::UseType UTy = MOTy::Use) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(V, MachineOperand::MO_CCRegister, UTy,
                                      false));
  }


  /// addRegOperand - Add a symbolic virtual register reference...
  ///
  void addRegOperand(int reg, bool isDef) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(reg, MachineOperand::MO_VirtualRegister,
                                      isDef ? MOTy::Def : MOTy::Use));
  }

  /// addRegOperand - Add a symbolic virtual register reference...
  ///
  void addRegOperand(int reg, MOTy::UseType UTy = MOTy::Use) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(reg, MachineOperand::MO_VirtualRegister,
                                      UTy));
  }

  /// addPCDispOperand - Add a PC relative displacement operand to the MI
  ///
  void addPCDispOperand(Value *V) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(V, MachineOperand::MO_PCRelativeDisp,
                                      MOTy::Use));
  }

  /// addMachineRegOperand - Add a virtual register operand to this MachineInstr
  ///
  void addMachineRegOperand(int reg, bool isDef) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(reg, MachineOperand::MO_MachineRegister,
                                      isDef ? MOTy::Def : MOTy::Use));
    insertUsedReg(reg);
  }

  /// addMachineRegOperand - Add a virtual register operand to this MachineInstr
  ///
  void addMachineRegOperand(int reg, MOTy::UseType UTy = MOTy::Use) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(reg, MachineOperand::MO_MachineRegister,
                                      UTy));
    insertUsedReg(reg);
  }

  /// addZeroExtImmOperand - Add a zero extended constant argument to the
  /// machine instruction.
  ///
  void addZeroExtImmOperand(int64_t intValue) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(intValue,
                                      MachineOperand::MO_UnextendedImmed));
  }

  /// addSignExtImmOperand - Add a zero extended constant argument to the
  /// machine instruction.
  ///
  void addSignExtImmOperand(int64_t intValue) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(intValue,
                                      MachineOperand::MO_SignExtendedImmed));
  }

  void addMachineBasicBlockOperand(MachineBasicBlock *MBB) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(MBB));
  }

  /// addFrameIndexOperand - Add an abstract frame index to the instruction
  ///
  void addFrameIndexOperand(unsigned Idx) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(Idx, MachineOperand::MO_FrameIndex));
  }

  /// addConstantPoolndexOperand - Add a constant pool object index to the
  /// instruction.
  ///
  void addConstantPoolIndexOperand(unsigned I) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand(I, MachineOperand::MO_ConstantPoolIndex));
  }

  void addGlobalAddressOperand(GlobalValue *GV, bool isPCRelative) {
    assert(!OperandsComplete() &&
           "Trying to add an operand to a machine instr that is already done!");
    operands.push_back(MachineOperand((Value*)GV,
				      MachineOperand::MO_GlobalAddress,
                                      MOTy::Use, isPCRelative));
  }

  /// addExternalSymbolOperand - Add an external symbol operand to this instr
  ///
  void addExternalSymbolOperand(const std::string &SymName, bool isPCRelative) {
    operands.push_back(MachineOperand(SymName, isPCRelative));
  }

  //===--------------------------------------------------------------------===//
  // Accessors used to modify instructions in place.
  //
  // FIXME: Move this stuff to MachineOperand itself!

  /// replace - Support to rewrite a machine instruction in place: for now,
  /// simply replace() and then set new operands with Set.*Operand methods
  /// below.
  /// 
  void replace(int Opcode, unsigned numOperands);

  /// setOpcode - Replace the opcode of the current instruction with a new one.
  ///
  void setOpcode(unsigned Op) { opCode = Op; }

  /// RemoveOperand - Erase an operand  from an instruction, leaving it with one
  /// fewer operand than it started with.
  ///
  void RemoveOperand(unsigned i) {
    operands.erase(operands.begin()+i);
  }

  // Access to set the operands when building the machine instruction
  // 
  void SetMachineOperandVal     (unsigned i,
                                 MachineOperand::MachineOperandType operandType,
                                 Value* V,
                                 bool isDef=false,
                                 bool isDefAndUse=false);

  void SetMachineOperandConst   (unsigned i,
                                 MachineOperand::MachineOperandType operandType,
                                 int64_t intValue);

  void SetMachineOperandReg     (unsigned i,
                                 int regNum,
                                 bool isDef=false);


  unsigned substituteValue(const Value* oldVal, Value* newVal,
                           bool defsOnly, bool notDefsAndUses,
                           bool& someArgsWereIgnored);

  void setOperandHi32(unsigned i) { operands[i].markHi32(); }
  void setOperandLo32(unsigned i) { operands[i].markLo32(); }
  void setOperandHi64(unsigned i) { operands[i].markHi64(); }
  void setOperandLo64(unsigned i) { operands[i].markLo64(); }
  
  
  // SetRegForOperand -
  // SetRegForImplicitRef -
  // Mark an explicit or implicit operand with its allocated physical register.
  // 
  void SetRegForOperand(unsigned i, int regNum);
  void SetRegForImplicitRef(unsigned i, int regNum);

  //
  // Iterator to enumerate machine operands.
  // 
  template<class MITy, class VTy>
  class ValOpIterator : public forward_iterator<VTy, ptrdiff_t> {
    unsigned i;
    MITy MI;
    
    void skipToNextVal() {
      while (i < MI->getNumOperands() &&
             !( (MI->getOperand(i).getType() == MachineOperand::MO_VirtualRegister ||
                 MI->getOperand(i).getType() == MachineOperand::MO_CCRegister)
                && MI->getOperand(i).getVRegValue() != 0))
        ++i;
    }
  
    inline ValOpIterator(MITy mi, unsigned I) : i(I), MI(mi) {
      skipToNextVal();
    }
  
  public:
    typedef ValOpIterator<MITy, VTy> _Self;
    
    inline VTy operator*() const {
      return MI->getOperand(i).getVRegValue();
    }

    const MachineOperand &getMachineOperand() const { return MI->getOperand(i);}
          MachineOperand &getMachineOperand()       { return MI->getOperand(i);}

    inline VTy operator->() const { return operator*(); }

    inline bool isUseOnly()   const { return MI->getOperand(i).opIsUse(); } 
    inline bool isDefOnly()   const { return MI->getOperand(i).opIsDefOnly(); } 
    inline bool isDefAndUse() const { return MI->getOperand(i).opIsDefAndUse();}

    inline _Self& operator++() { i++; skipToNextVal(); return *this; }
    inline _Self  operator++(int) { _Self tmp = *this; ++*this; return tmp; }

    inline bool operator==(const _Self &y) const { 
      return i == y.i;
    }
    inline bool operator!=(const _Self &y) const { 
      return !operator==(y);
    }

    static _Self begin(MITy MI) {
      return _Self(MI, 0);
    }
    static _Self end(MITy MI) {
      return _Self(MI, MI->getNumOperands());
    }
  };

  // define begin() and end()
  val_op_iterator begin() { return val_op_iterator::begin(this); }
  val_op_iterator end()   { return val_op_iterator::end(this); }

  const_val_op_iterator begin() const {
    return const_val_op_iterator::begin(this);
  }
  const_val_op_iterator end() const {
    return const_val_op_iterator::end(this);
  }
};


//===----------------------------------------------------------------------===//
// Debugging Support

std::ostream& operator<<(std::ostream &OS, const MachineInstr &MI);
std::ostream& operator<<(std::ostream &OS, const MachineOperand &MO);
void PrintMachineInstructions(const Function *F);

#endif