AMDGPU: Record SGPR spills when restoring too

[arsenm]

Summary

It's possible in some cases to have a restore present without a corresponding spill. Due to an apparent bug in D54366, only the restore for a register was emitted. It's probably always a bug for this to happen, but due to how SGPR spilling is implemented, this makes the issues appear worse than it is.

[rampitec]

LGTM

[arsenm]

r347595

lib/Target/AMDGPU/SIInstrInfo.cpp

 }
 
 void SIInstrInfo::loadRegFromStackSlot(MachineBasicBlock &MBB,
                                        MachineBasicBlock::iterator MI,
                                        unsigned DestReg, int FrameIndex,
                                        const TargetRegisterClass *RC,
                                        const TargetRegisterInfo *TRI) const {
   MachineFunction *MF = MBB.getParent();
-  const SIMachineFunctionInfo *MFI = MF->getInfo<SIMachineFunctionInfo>();
+  SIMachineFunctionInfo *MFI = MF->getInfo<SIMachineFunctionInfo>();
   MachineFrameInfo &FrameInfo = MF->getFrameInfo();
   DebugLoc DL = MBB.findDebugLoc(MI);
   unsigned Align = FrameInfo.getObjectAlignment(FrameIndex);
   unsigned Size = FrameInfo.getObjectSize(FrameIndex);
   unsigned SpillSize = TRI->getSpillSize(*RC);
 
   MachinePointerInfo PtrInfo
     = MachinePointerInfo::getFixedStack(*MF, FrameIndex);
+  MFI->setHasSpilledSGPRs();
 
   MachineMemOperand *MMO = MF->getMachineMemOperand(
     PtrInfo, MachineMemOperand::MOLoad, Size, Align);
 
   if (RI.isSGPRClass(RC)) {
     // FIXME: Maybe this should not include a memoperand because it will be
     // lowered to non-memory instructions.
     const MCInstrDesc &OpDesc = get(getSGPRSpillRestoreOpcode(SpillSize));