[AMDGPU] allSGPRSpillsAreDead() should use actual FP/BP frame indices

[RamNalamothu]

Summary

The SGPR spills happen in SILowerSGPRSpills() and allSGPRSpillsAreDead()
make sure there are no SGPR spills pending during PEI. But the FP/BP
spills happen during PEI and are exceptions.

Use actual frame indices of FP/BP in allSGPRSpillsAreDead() to
accommodate the exceptions.

llvm/lib/Target/AMDGPU/SIFrameLowering.cpp

for (int I = MFI.getObjectIndexBegin(), E = MFI.getObjectIndexEnd();
     if (!MFI.isDeadObjectIndex(I))
       return false;
   }
 
   return true;
 }
 
 #ifndef NDEBUG
-static bool allSGPRSpillsAreDead(const MachineFrameInfo &MFI,
-                                 Optional<int> FramePointerSaveIndex,
-                                 Optional<int> BasePointerSaveIndex) {
+static bool allSGPRSpillsAreDead(const MachineFunction &MF) {
+  const MachineFrameInfo &MFI = MF.getFrameInfo();
+  const SIMachineFunctionInfo *FuncInfo = MF.getInfo<SIMachineFunctionInfo>();
   for (int I = MFI.getObjectIndexBegin(), E = MFI.getObjectIndexEnd();
        I != E; ++I) {
     if (!MFI.isDeadObjectIndex(I) &&
         MFI.getStackID(I) == TargetStackID::SGPRSpill &&
-        ((FramePointerSaveIndex && I != FramePointerSaveIndex) ||
-         (BasePointerSaveIndex && I != BasePointerSaveIndex))) {
+        (I != FuncInfo->FramePointerSaveIndex &&
+         I != FuncInfo->BasePointerSaveIndex)) {
       return false;
     }
   }
 
   return true;
 }
 #endif
 
void SIFrameLowering::processFunctionBeforeFrameFinalized(
   RegScavenger *RS) const {
   MachineFrameInfo &MFI = MF.getFrameInfo();
 
   const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
   const SIRegisterInfo *TRI = ST.getRegisterInfo();
   SIMachineFunctionInfo *FuncInfo = MF.getInfo<SIMachineFunctionInfo>();
 
   FuncInfo->removeDeadFrameIndices(MFI);
-  assert(allSGPRSpillsAreDead(MFI, None, None) &&
+  assert(allSGPRSpillsAreDead(MF) &&
          "SGPR spill should have been removed in SILowerSGPRSpills");
 
   // FIXME: The other checks should be redundant with allStackObjectsAreDead,
   // but currently hasNonSpillStackObjects is set only from source
   // allocas. Stack temps produced from legalization are not counted currently.
   if (!allStackObjectsAreDead(MFI)) {
     assert(RS && "RegScavenger required if spilling");