Adding ChangeToTargetIndex function to MachineOperand

[kariddi]

Summary

MachineOperand is missing a ChangeToTargetIndex method that could be useful to be used by backends (we found it useful for our backend, there are hacks to workaround it in order to call "removeRegsFromUses", but are not nice).

[qcolombet]

LGTM

llvm/trunk/include/llvm/CodeGen/MachineOperand.h

public:
   void ChangeToES(const char *SymName, unsigned char TargetFlags = 0);
 
   /// ChangeToMCSymbol - Replace this operand with a new MC symbol operand.
   void ChangeToMCSymbol(MCSymbol *Sym);
 
   /// Replace this operand with a frame index.
   void ChangeToFrameIndex(int Idx);
 
+  /// Replace this operand with a target index.
+  void ChangeToTargetIndex(unsigned Idx, int64_t Offset,
+                           unsigned char TargetFlags = 0);
+
   /// ChangeToRegister - Replace this operand with a new register operand of
   /// the specified value.  If an operand is known to be an register already,
   /// the setReg method should be used.
   void ChangeToRegister(unsigned Reg, bool isDef, bool isImp = false,
                         bool isKill = false, bool isDead = false,
                         bool isUndef = false, bool isDebug = false);
 
   //===--------------------------------------------------------------------===//

llvm/trunk/lib/CodeGen/MachineInstr.cpp

assert((!isReg() || !isTied()) &&
          "Cannot change a tied operand into a FrameIndex");
 
   removeRegFromUses();
 
   OpKind = MO_FrameIndex;
   setIndex(Idx);
 }
 
+void MachineOperand::ChangeToTargetIndex(unsigned Idx, int64_t Offset,
+                                         unsigned char TargetFlags) {
+  assert((!isReg() || !isTied()) &&
+         "Cannot change a tied operand into a FrameIndex");
+
+  removeRegFromUses();
+
+  OpKind = MO_TargetIndex;
+  setIndex(Idx);
+  setOffset(Offset);
+  setTargetFlags(TargetFlags);
+}
+
 /// ChangeToRegister - Replace this operand with a new register operand of
 /// the specified value.  If an operand is known to be an register already,
 /// the setReg method should be used.
 void MachineOperand::ChangeToRegister(unsigned Reg, bool isDef, bool isImp,
                                       bool isKill, bool isDead, bool isUndef,
                                       bool isDebug) {
   MachineRegisterInfo *RegInfo = nullptr;
   if (MachineInstr *MI = getParent())