[AArch64] NFC: Rename LastPopI in emitEpilogue (#156884)

LastPopI suggests it is an iterator to the last stack pop instruction,
which is not what it actually points to. Instead, in one instance it
points to the homogenous epilogue instruction, in the other it points to
the first GPR reload.

Author: sdesmalen-arm

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -2548,15 +2548,15 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
     AFI->setLocalStackSize(NumBytes - PrologueSaveSize);
   if (homogeneousPrologEpilog(MF, &MBB)) {
     assert(!NeedsWinCFI);
-    auto LastPopI = MBB.getFirstTerminator();
-    if (LastPopI != MBB.begin()) {
-      auto HomogeneousEpilog = std::prev(LastPopI);
+    auto FirstHomogenousEpilogI = MBB.getFirstTerminator();
+    if (FirstHomogenousEpilogI != MBB.begin()) {
+      auto HomogeneousEpilog = std::prev(FirstHomogenousEpilogI);
       if (HomogeneousEpilog->getOpcode() == AArch64::HOM_Epilog)
-        LastPopI = HomogeneousEpilog;
+        FirstHomogenousEpilogI = HomogeneousEpilog;
     }
 
     // Adjust local stack
-    emitFrameOffset(MBB, LastPopI, DL, AArch64::SP, AArch64::SP,
+    emitFrameOffset(MBB, FirstHomogenousEpilogI, DL, AArch64::SP, AArch64::SP,
                     StackOffset::getFixed(AFI->getLocalStackSize()), TII,
                     MachineInstr::FrameDestroy, false, NeedsWinCFI, &HasWinCFI);
 
@@ -2602,17 +2602,17 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
   // Move past the restores of the callee-saved registers.
   // If we plan on combining the sp bump of the local stack size and the callee
   // save stack size, we might need to adjust the CSR save and restore offsets.
-  MachineBasicBlock::iterator LastPopI = MBB.getFirstTerminator();
+  MachineBasicBlock::iterator FirstGPRRestoreI = MBB.getFirstTerminator();
   MachineBasicBlock::iterator Begin = MBB.begin();
-  while (LastPopI != Begin) {
-    --LastPopI;
-    if (!LastPopI->getFlag(MachineInstr::FrameDestroy) ||
-        (!FPAfterSVECalleeSaves && IsSVECalleeSave(LastPopI))) {
-      ++LastPopI;
+  while (FirstGPRRestoreI != Begin) {
+    --FirstGPRRestoreI;
+    if (!FirstGPRRestoreI->getFlag(MachineInstr::FrameDestroy) ||
+        (!FPAfterSVECalleeSaves && IsSVECalleeSave(FirstGPRRestoreI))) {
+      ++FirstGPRRestoreI;
       break;
     } else if (CombineSPBump)
-      fixupCalleeSaveRestoreStackOffset(*LastPopI, AFI->getLocalStackSize(),
-                                        NeedsWinCFI, &HasWinCFI);
+      fixupCalleeSaveRestoreStackOffset(
+          *FirstGPRRestoreI, AFI->getLocalStackSize(), NeedsWinCFI, &HasWinCFI);
   }
 
   if (NeedsWinCFI) {
@@ -2622,9 +2622,9 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
     // arguments. Insert the SEH_EpilogStart and remove it later if it
     // we didn't emit any SEH opcodes to avoid generating WinCFI for
     // functions that don't need it.
-    BuildMI(MBB, LastPopI, DL, TII->get(AArch64::SEH_EpilogStart))
+    BuildMI(MBB, FirstGPRRestoreI, DL, TII->get(AArch64::SEH_EpilogStart))
         .setMIFlag(MachineInstr::FrameDestroy);
-    EpilogStartI = LastPopI;
+    EpilogStartI = FirstGPRRestoreI;
     --EpilogStartI;
   }
 
@@ -2665,7 +2665,7 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
 
     // When we are about to restore the CSRs, the CFA register is SP again.
     if (EmitCFI && hasFP(MF))
-      CFIInstBuilder(MBB, LastPopI, MachineInstr::FrameDestroy)
+      CFIInstBuilder(MBB, FirstGPRRestoreI, MachineInstr::FrameDestroy)
           .buildDefCFA(AArch64::SP, NumBytes);
 
     emitFrameOffset(MBB, MBB.getFirstTerminator(), DL, AArch64::SP, AArch64::SP,
@@ -2681,7 +2681,8 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
   // Process the SVE callee-saves to determine what space needs to be
   // deallocated.
   StackOffset DeallocateBefore = {}, DeallocateAfter = SVEStackSize;
-  MachineBasicBlock::iterator RestoreBegin = LastPopI, RestoreEnd = LastPopI;
+  MachineBasicBlock::iterator RestoreBegin = FirstGPRRestoreI,
+                              RestoreEnd = FirstGPRRestoreI;
   if (int64_t CalleeSavedSize = AFI->getSVECalleeSavedStackSize()) {
     if (FPAfterSVECalleeSaves)
       RestoreEnd = MBB.getFirstTerminator();
@@ -2706,7 +2707,7 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
     // deallocates non-callee-save SVE allocations.  Otherwise, deallocate
     // them explicitly.
     if (!AFI->isStackRealigned() && !MFI.hasVarSizedObjects()) {
-      emitFrameOffset(MBB, LastPopI, DL, AArch64::SP, AArch64::SP,
+      emitFrameOffset(MBB, FirstGPRRestoreI, DL, AArch64::SP, AArch64::SP,
                       DeallocateBefore, TII, MachineInstr::FrameDestroy, false,
                       NeedsWinCFI, &HasWinCFI);
     }
@@ -2796,7 +2797,7 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
       StackRestoreBytes += AfterCSRPopSize;
 
     emitFrameOffset(
-        MBB, LastPopI, DL, AArch64::SP, AArch64::SP,
+        MBB, FirstGPRRestoreI, DL, AArch64::SP, AArch64::SP,
         StackOffset::getFixed(StackRestoreBytes), TII,
         MachineInstr::FrameDestroy, false, NeedsWinCFI, &HasWinCFI, EmitCFI,
         StackOffset::getFixed((RedZone ? 0 : NumBytes) + PrologueSaveSize));
@@ -2816,17 +2817,17 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
   // be able to save any instructions.
   if (!IsFunclet && (MFI.hasVarSizedObjects() || AFI->isStackRealigned())) {
     emitFrameOffset(
-        MBB, LastPopI, DL, AArch64::SP, AArch64::FP,
+        MBB, FirstGPRRestoreI, DL, AArch64::SP, AArch64::FP,
         StackOffset::getFixed(-AFI->getCalleeSaveBaseToFrameRecordOffset()),
         TII, MachineInstr::FrameDestroy, false, NeedsWinCFI, &HasWinCFI);
   } else if (NumBytes)
-    emitFrameOffset(MBB, LastPopI, DL, AArch64::SP, AArch64::SP,
+    emitFrameOffset(MBB, FirstGPRRestoreI, DL, AArch64::SP, AArch64::SP,
                     StackOffset::getFixed(NumBytes), TII,
                     MachineInstr::FrameDestroy, false, NeedsWinCFI, &HasWinCFI);
 
   // When we are about to restore the CSRs, the CFA register is SP again.
   if (EmitCFI && hasFP(MF))
-    CFIInstBuilder(MBB, LastPopI, MachineInstr::FrameDestroy)
+    CFIInstBuilder(MBB, FirstGPRRestoreI, MachineInstr::FrameDestroy)
         .buildDefCFA(AArch64::SP, PrologueSaveSize);
 
   // This must be placed after the callee-save restore code because that code