[mips] Remove MipsCC::getRegVT(). NFC

[dsanders]

Summary

It's no longer used.

[dsanders]

Added David as reviewer

[theraven]

Looks fine in isolation - I don't think removing dead code needs a review...

[dsanders]

Thanks. I posted this one because some of the other patches in the series don't apply cleanly without it.

lib/Target/Mips/MipsISelLowering.h

public:
       /// reservedArgArea - The size of the area the caller reserves for
       /// register arguments. This is 16-byte if ABI is O32.
       unsigned reservedArgArea() const;
 
       /// Return pointer to array of integer argument registers.
       const ArrayRef<MCPhysReg> intArgRegs() const;
 
     private:
-      /// Return the type of the register which is used to pass an argument or
-      /// return a value. This function returns f64 if the argument is an i64
-      /// value which has been generated as a result of softening an f128 value.
-      /// Otherwise, it just returns VT.
-      MVT getRegVT(MVT VT, const Type *OrigTy, const SDNode *CallNode,
-                   bool IsSoftFloat) const;
-
       CallingConv::ID CallConv;
       const MipsSubtarget &Subtarget;
     };
   protected:
     SDValue lowerLOAD(SDValue Op, SelectionDAG &DAG) const;
     SDValue lowerSTORE(SDValue Op, SelectionDAG &DAG) const;
 
     // Subtarget Info

lib/Target/Mips/MipsISelLowering.cpp

 }
 
 const ArrayRef<MCPhysReg> MipsTargetLowering::MipsCC::intArgRegs() const {
   if (Subtarget.isABI_O32())
     return makeArrayRef(O32IntRegs);
   return makeArrayRef(Mips64IntRegs);
 }
 
-MVT MipsTargetLowering::MipsCC::getRegVT(MVT VT, const Type *OrigTy,
-                                         const SDNode *CallNode,
-                                         bool IsSoftFloat) const {
-  if (IsSoftFloat || Subtarget.isABI_O32())
-    return VT;
-
-  // Check if the original type was fp128.
-  if (originalTypeIsF128(OrigTy, CallNode)) {
-    assert(VT == MVT::i64);
-    return MVT::f64;
-  }
-
-  return VT;
-}
-
 void MipsTargetLowering::copyByValRegs(
     SDValue Chain, SDLoc DL, std::vector<SDValue> &OutChains, SelectionDAG &DAG,
     const ISD::ArgFlagsTy &Flags, SmallVectorImpl<SDValue> &InVals,
     const Argument *FuncArg, const MipsCC &CC, unsigned FirstReg,
     unsigned LastReg, const CCValAssign &VA) const {
   MachineFunction &MF = DAG.getMachineFunction();
   MachineFrameInfo *MFI = MF.getFrameInfo();
   unsigned GPRSizeInBytes = Subtarget.getGPRSizeInBytes();