[AMDGPU, NFC] Refactor FP/BP spill index code in emitPrologue/emitEpilogue

[scott.linder]

This LGTM, thank you!

I have a few further suggestions while you are already cleaning things up. If you like them feel free to commit without updating the review.

llvm/lib/Target/AMDGPU/SIFrameLowering.cpp

1125–1128

Can be FI

1153

I'd either change the FI above to FramePointerFI or change this BasePtrFI to FI. I'd lean towards the first choice, as I think the scope for the if gives enough context.

[RamNalamothu]

Address review comments.

[RamNalamothu]

Address feedback as suggested.

[RamNalamothu]

Incorporated the suggestions. Thank you.

llvm/lib/Target/AMDGPU/SIFrameLowering.cpp

static Register buildScratchExecCopy(LivePhysRegs &LiveRegs,
 
   const unsigned OrSaveExec =
       ST.isWave32() ? AMDGPU::S_OR_SAVEEXEC_B32 : AMDGPU::S_OR_SAVEEXEC_B64;
   BuildMI(MBB, MBBI, DL, TII->get(OrSaveExec), ScratchExecCopy).addImm(-1);
 
   return ScratchExecCopy;
 }
 
+// A StackID of SGPRSpill implies that this is a spill from SGPR to VGPR.
+// Otherwise we are spilling to memory.
+static bool spilledToMemory(const MachineFunction &MF, int SaveIndex) {
+  const MachineFrameInfo &MFI = MF.getFrameInfo();
+  return MFI.getStackID(SaveIndex) != TargetStackID::SGPRSpill;
+}
+
 void SIFrameLowering::emitPrologue(MachineFunction &MF,
                                    MachineBasicBlock &MBB) const {
   SIMachineFunctionInfo *FuncInfo = MF.getInfo<SIMachineFunctionInfo>();
   if (FuncInfo->isEntryFunction()) {
     emitEntryFunctionPrologue(MF, MBB);
     return;
   }
 
void SIFrameLowering::emitPrologue(MachineFunction &MF,
   bool HasFP = false;
   bool HasBP = false;
   uint32_t NumBytes = MFI.getStackSize();
   uint32_t RoundedSize = NumBytes;
   // To avoid clobbering VGPRs in lanes that weren't active on function entry,
   // turn on all lanes before doing the spill to memory.
   Register ScratchExecCopy;
 
-  bool HasFPSaveIndex = FuncInfo->FramePointerSaveIndex.hasValue();
-  bool SpillFPToMemory = false;
-  // A StackID of SGPRSpill implies that this is a spill from SGPR to VGPR.
-  // Otherwise we are spilling the FP to memory.
-  if (HasFPSaveIndex) {
-    SpillFPToMemory = MFI.getStackID(*FuncInfo->FramePointerSaveIndex) !=
-                      TargetStackID::SGPRSpill;
-  }
-
-  bool HasBPSaveIndex = FuncInfo->BasePointerSaveIndex.hasValue();
-  bool SpillBPToMemory = false;
-  // A StackID of SGPRSpill implies that this is a spill from SGPR to VGPR.
-  // Otherwise we are spilling the BP to memory.
-  if (HasBPSaveIndex) {
-    SpillBPToMemory = MFI.getStackID(*FuncInfo->BasePointerSaveIndex) !=
-                      TargetStackID::SGPRSpill;
-  }
+  Optional<int> FPSaveIndex = FuncInfo->FramePointerSaveIndex;
+  Optional<int> BPSaveIndex = FuncInfo->BasePointerSaveIndex;
 
   for (const SIMachineFunctionInfo::SGPRSpillVGPRCSR &Reg
          : FuncInfo->getSGPRSpillVGPRs()) {
     if (!Reg.FI.hasValue())
       continue;
 
     if (!ScratchExecCopy)
       ScratchExecCopy = buildScratchExecCopy(LiveRegs, MF, MBB, MBBI, true);
 
     buildPrologSpill(ST, LiveRegs, MBB, MBBI, TII, Reg.VGPR,
                      FuncInfo->getScratchRSrcReg(),
                      StackPtrReg,
                      Reg.FI.getValue());
   }
 
-  if (HasFPSaveIndex && SpillFPToMemory) {
-    assert(!MFI.isDeadObjectIndex(FuncInfo->FramePointerSaveIndex.getValue()));
+  if (FPSaveIndex && spilledToMemory(MF, *FPSaveIndex)) {
+    const int FramePtrFI = *FPSaveIndex;
+    assert(!MFI.isDeadObjectIndex(FramePtrFI));
 
     if (!ScratchExecCopy)
       ScratchExecCopy = buildScratchExecCopy(LiveRegs, MF, MBB, MBBI, true);
 
     MCPhysReg TmpVGPR = findScratchNonCalleeSaveRegister(
         MRI, LiveRegs, AMDGPU::VGPR_32RegClass);
     if (!TmpVGPR)
       report_fatal_error("failed to find free scratch register");
 
     BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::V_MOV_B32_e32), TmpVGPR)
         .addReg(FramePtrReg);
 
     buildPrologSpill(ST, LiveRegs, MBB, MBBI, TII, TmpVGPR,
-                     FuncInfo->getScratchRSrcReg(), StackPtrReg,
-                     FuncInfo->FramePointerSaveIndex.getValue());
+                     FuncInfo->getScratchRSrcReg(), StackPtrReg, FramePtrFI);
   }
 
-  if (HasBPSaveIndex && SpillBPToMemory) {
-    assert(!MFI.isDeadObjectIndex(*FuncInfo->BasePointerSaveIndex));
+  if (BPSaveIndex && spilledToMemory(MF, *BPSaveIndex)) {
+    const int BasePtrFI = *BPSaveIndex;
+    assert(!MFI.isDeadObjectIndex(BasePtrFI));
 
     if (!ScratchExecCopy)
       ScratchExecCopy = buildScratchExecCopy(LiveRegs, MF, MBB, MBBI, true);
 
     MCPhysReg TmpVGPR = findScratchNonCalleeSaveRegister(
         MRI, LiveRegs, AMDGPU::VGPR_32RegClass);
     if (!TmpVGPR)
       report_fatal_error("failed to find free scratch register");
 
     BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::V_MOV_B32_e32), TmpVGPR)
         .addReg(BasePtrReg);
 
     buildPrologSpill(ST, LiveRegs, MBB, MBBI, TII, TmpVGPR,
-                     FuncInfo->getScratchRSrcReg(), StackPtrReg,
-                     *FuncInfo->BasePointerSaveIndex);
+                     FuncInfo->getScratchRSrcReg(), StackPtrReg, BasePtrFI);
   }
 
   if (ScratchExecCopy) {
     // FIXME: Split block and make terminator.
     unsigned ExecMov = ST.isWave32() ? AMDGPU::S_MOV_B32 : AMDGPU::S_MOV_B64;
     MCRegister Exec = ST.isWave32() ? AMDGPU::EXEC_LO : AMDGPU::EXEC;
     BuildMI(MBB, MBBI, DL, TII->get(ExecMov), Exec)
         .addReg(ScratchExecCopy, RegState::Kill);
     LiveRegs.addReg(ScratchExecCopy);
   }
 
   // In this case, spill the FP to a reserved VGPR.
-  if (HasFPSaveIndex && !SpillFPToMemory) {
-    const int FI = FuncInfo->FramePointerSaveIndex.getValue();
-    assert(!MFI.isDeadObjectIndex(FI));
+  if (FPSaveIndex && !spilledToMemory(MF, *FPSaveIndex)) {
+    const int FramePtrFI = *FPSaveIndex;
+    assert(!MFI.isDeadObjectIndex(FramePtrFI));
 
-    assert(MFI.getStackID(FI) == TargetStackID::SGPRSpill);
+    assert(MFI.getStackID(FramePtrFI) == TargetStackID::SGPRSpill);
     ArrayRef<SIMachineFunctionInfo::SpilledReg> Spill =
-        FuncInfo->getSGPRToVGPRSpills(FI);
+        FuncInfo->getSGPRToVGPRSpills(FramePtrFI);
     assert(Spill.size() == 1);
 
     // Save FP before setting it up.
     // FIXME: This should respect spillSGPRToVGPR;
     BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::V_WRITELANE_B32), Spill[0].VGPR)
         .addReg(FramePtrReg)
         .addImm(Spill[0].Lane)
         .addReg(Spill[0].VGPR, RegState::Undef);
   }
 
   // In this case, spill the BP to a reserved VGPR.
-  if (HasBPSaveIndex && !SpillBPToMemory) {
-    const int BasePtrFI = *FuncInfo->BasePointerSaveIndex;
+  if (BPSaveIndex && !spilledToMemory(MF, *BPSaveIndex)) {
+    const int BasePtrFI = *BPSaveIndex;
     assert(!MFI.isDeadObjectIndex(BasePtrFI));
 
     assert(MFI.getStackID(BasePtrFI) == TargetStackID::SGPRSpill);
     ArrayRef<SIMachineFunctionInfo::SpilledReg> Spill =
         FuncInfo->getSGPRToVGPRSpills(BasePtrFI);
     assert(Spill.size() == 1);
 
     // Save BP before setting it up.
void SIFrameLowering::emitEpilogue(MachineFunction &MF,
   uint32_t RoundedSize = FuncInfo->isStackRealigned()
                              ? NumBytes + MFI.getMaxAlign().value()
                              : NumBytes;
   const Register StackPtrReg = FuncInfo->getStackPtrOffsetReg();
   const Register FramePtrReg = FuncInfo->getFrameOffsetReg();
   const Register BasePtrReg =
       TRI.hasBasePointer(MF) ? TRI.getBaseRegister() : Register();
 
-  bool HasFPSaveIndex = FuncInfo->FramePointerSaveIndex.hasValue();
-  bool SpillFPToMemory = false;
-  if (HasFPSaveIndex) {
-    SpillFPToMemory = MFI.getStackID(*FuncInfo->FramePointerSaveIndex) !=
-                      TargetStackID::SGPRSpill;
-  }
-
-  bool HasBPSaveIndex = FuncInfo->BasePointerSaveIndex.hasValue();
-  bool SpillBPToMemory = false;
-  if (HasBPSaveIndex) {
-    SpillBPToMemory = MFI.getStackID(*FuncInfo->BasePointerSaveIndex) !=
-                      TargetStackID::SGPRSpill;
-  }
+  Optional<int> FPSaveIndex = FuncInfo->FramePointerSaveIndex;
+  Optional<int> BPSaveIndex = FuncInfo->BasePointerSaveIndex;
 
   if (RoundedSize != 0 && hasFP(MF)) {
     BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::S_SUB_U32), StackPtrReg)
       .addReg(StackPtrReg)
       .addImm(RoundedSize * getScratchScaleFactor(ST))
       .setMIFlag(MachineInstr::FrameDestroy);
   }
 
   if (FuncInfo->SGPRForFPSaveRestoreCopy) {
     BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::COPY), FramePtrReg)
         .addReg(FuncInfo->SGPRForFPSaveRestoreCopy)
         .setMIFlag(MachineInstr::FrameDestroy);
   }
 
   if (FuncInfo->SGPRForBPSaveRestoreCopy) {
     BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::COPY), BasePtrReg)
         .addReg(FuncInfo->SGPRForBPSaveRestoreCopy)
         .setMIFlag(MachineInstr::FrameDestroy);
   }
 
   Register ScratchExecCopy;
-  if (HasFPSaveIndex) {
-    const int FI = FuncInfo->FramePointerSaveIndex.getValue();
-    assert(!MFI.isDeadObjectIndex(FI));
-    if (SpillFPToMemory) {
+  if (FPSaveIndex) {
+    const int FramePtrFI = *FPSaveIndex;
+    assert(!MFI.isDeadObjectIndex(FramePtrFI));
+    if (spilledToMemory(MF, FramePtrFI)) {
       if (!ScratchExecCopy)
         ScratchExecCopy = buildScratchExecCopy(LiveRegs, MF, MBB, MBBI, false);
 
       MCPhysReg TempVGPR = findScratchNonCalleeSaveRegister(
           MRI, LiveRegs, AMDGPU::VGPR_32RegClass);
       if (!TempVGPR)
         report_fatal_error("failed to find free scratch register");
       buildEpilogReload(ST, LiveRegs, MBB, MBBI, TII, TempVGPR,
-                        FuncInfo->getScratchRSrcReg(), StackPtrReg, FI);
+                        FuncInfo->getScratchRSrcReg(), StackPtrReg, FramePtrFI);
       BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::V_READFIRSTLANE_B32), FramePtrReg)
           .addReg(TempVGPR, RegState::Kill);
     } else {
       // Reload from VGPR spill.
-      assert(MFI.getStackID(FI) == TargetStackID::SGPRSpill);
+      assert(MFI.getStackID(FramePtrFI) == TargetStackID::SGPRSpill);
       ArrayRef<SIMachineFunctionInfo::SpilledReg> Spill =
-          FuncInfo->getSGPRToVGPRSpills(FI);
+          FuncInfo->getSGPRToVGPRSpills(FramePtrFI);
       assert(Spill.size() == 1);
       BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::V_READLANE_B32), FramePtrReg)
           .addReg(Spill[0].VGPR)
           .addImm(Spill[0].Lane);
     }
   }
 
-  if (HasBPSaveIndex) {
-    const int BasePtrFI = *FuncInfo->BasePointerSaveIndex;
+  if (BPSaveIndex) {
+    const int BasePtrFI = *BPSaveIndex;
     assert(!MFI.isDeadObjectIndex(BasePtrFI));
-    if (SpillBPToMemory) {
+    if (spilledToMemory(MF, BasePtrFI)) {
       if (!ScratchExecCopy)
         ScratchExecCopy = buildScratchExecCopy(LiveRegs, MF, MBB, MBBI, false);
 
       MCPhysReg TempVGPR = findScratchNonCalleeSaveRegister(
           MRI, LiveRegs, AMDGPU::VGPR_32RegClass);
       if (!TempVGPR)
         report_fatal_error("failed to find free scratch register");
       buildEpilogReload(ST, LiveRegs, MBB, MBBI, TII, TempVGPR,