[TargetInstrInfo][PowerPC] Remove virtual function that is only called from PPC specific code.

[craig.topper]

Summary

There are two signatures of setSpecialOperandAttr in TargetInstrInfo.
One of them is only called from PPC's implementation of the other
signature and PPC has an override for it.

Remove it from TargetInstrInfo and make it a non-virtual method in
PPCInstrInfo.

[RKSimon]

LGTM with one minor

llvm/lib/Target/PowerPC/PPCInstrInfo.h

396–398

Add a comment saying this is a PowerPC custom wrapper?

llvm/include/llvm/CodeGen/TargetInstrInfo.h

public:
   virtual int getExtendResourceLenLimit() const { return 0; }
 
   /// This is an architecture-specific helper function of reassociateOps.
   /// Set special operand attributes for new instructions after reassociation.
   virtual void setSpecialOperandAttr(MachineInstr &OldMI1, MachineInstr &OldMI2,
                                      MachineInstr &NewMI1,
                                      MachineInstr &NewMI2) const {}
 
-  virtual void setSpecialOperandAttr(MachineInstr &MI, uint16_t Flags) const {}
-
   /// Return true when a target supports MachineCombiner.
   virtual bool useMachineCombiner() const { return false; }
 
   /// Return true if the given SDNode can be copied during scheduling
   /// even if it has glue.
   virtual bool canCopyGluedNodeDuringSchedule(SDNode *N) const { return false; }
 
 protected:

llvm/lib/Target/PowerPC/PPCInstrInfo.h

public:
   /// We need to execlude the 1 bigger case even the resource length is not
   /// perserved for more FMA chain reassociations on PowerPC.
   int getExtendResourceLenLimit() const override { return 1; }
 
   void setSpecialOperandAttr(MachineInstr &OldMI1, MachineInstr &OldMI2,
                              MachineInstr &NewMI1,
                              MachineInstr &NewMI2) const override;
 
-  void setSpecialOperandAttr(MachineInstr &MI, uint16_t Flags) const override;
+  // PowerPC specific version of setSpecialOperandAttr that copies Flags to MI
+  // and clears nuw, nsw, and exact flags.
+  void setSpecialOperandAttr(MachineInstr &MI, uint16_t Flags) const;
 
   bool isCoalescableExtInstr(const MachineInstr &MI,
                              Register &SrcReg, Register &DstReg,
                              unsigned &SubIdx) const override;
   unsigned isLoadFromStackSlot(const MachineInstr &MI,
                                int &FrameIndex) const override;
   bool isReallyTriviallyReMaterializable(const MachineInstr &MI,
                                          AAResults *AA) const override;