Reword

Author: MacDue

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -2537,7 +2537,7 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
   } else if (SVEStackSize) {
     const AArch64RegisterInfo *RegInfo = Subtarget.getRegisterInfo();
     int64_t SVECalleeSavedSize = AFI->getSVECalleeSavedStackSize();
-    Register BaseForSVERestore = [&]() -> Register {
+    Register BaseForSVEDealloc = [&]() -> Register {
       // With stack realignment we must use the FP to restore SVE CSRs (as both
       // the SP and BP can't be used due to the unknown alignment padding).
       if (AFI->isStackRealigned())
@@ -2548,11 +2548,11 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
       if (MFI.hasVarSizedObjects()) {
         if (DeallocateBefore && !AFI->hasStackHazardSlotIndex()) {
           // If there's SVE locals and no hazard padding we can do:
-          //  ADDVL SP, X29, #(-SVECalleeSavedSize)
+          //  ADDVL SP, FP, #(-SVECalleeSavedSize)
           return AArch64::FP;
         }
         // If there's SVE locals and hazard padding we can choose between:
-        //  SUB TMP, X29, #(-CalleeSaveBaseOffset)
+        //  SUB TMP, FP, #(-CalleeSaveBaseOffset)
         //  ADDVL SP, TMP, #(-SVECalleeSavedSize)
         // OR:
         //  ADD SP, BP, #NumBytes
@@ -2565,8 +2565,13 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
       // In the standard case we use the SP.
       return AArch64::SP;
     }();
-
-    if (SVECalleeSavedSize && BaseForSVERestore == AArch64::FP) {
+    // If we have any SVE callee saves they must be restored now.
+    bool MustRestoreSVECalleSaves = SVECalleeSavedSize != 0;
+    // If the base for deallocation is the SP we must deallocate the SVE area
+    // regardless of if we have SVE callee saves. For any other base the SVE
+    // area will be implicitly deallocated when we set the SP to the FP.
+    bool MustDeallocateSVEArea = BaseForSVEDealloc == AArch64::SP;
+    if (MustRestoreSVECalleSaves && BaseForSVEDealloc == AArch64::FP) {
       Register CalleeSaveBase = AArch64::FP;
       if (int64_t CalleeSaveBaseOffset =
               AFI->getCalleeSaveBaseToFrameRecordOffset()) {
@@ -2588,16 +2593,15 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
       emitFrameOffset(MBB, RestoreBegin, DL, AArch64::SP, CalleeSaveBase,
                       StackOffset::getScalable(-SVECalleeSavedSize), TII,
                       MachineInstr::FrameDestroy);
-    } else if (BaseForSVERestore == AArch64::SP || SVECalleeSavedSize) {
+    } else if (MustRestoreSVECalleSaves || MustDeallocateSVEArea) {
       if (SVECalleeSavedSize) {
         // Deallocate the non-SVE locals first before we can deallocate (and
         // restore callee saves) from the SVE area.
         emitFrameOffset(
-            MBB, RestoreBegin, DL, AArch64::SP, BaseForSVERestore,
+            MBB, RestoreBegin, DL, AArch64::SP, BaseForSVEDealloc,
             StackOffset::getFixed(NumBytes), TII, MachineInstr::FrameDestroy,
             false, NeedsWinCFI, &HasWinCFI, EmitCFI && !hasFP(MF),
             SVEStackSize + StackOffset::getFixed(NumBytes + PrologueSaveSize));
-
         NumBytes = 0;
       }
 
@@ -2607,10 +2611,7 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
                       SVEStackSize +
                           StackOffset::getFixed(NumBytes + PrologueSaveSize));
 
-      if (BaseForSVERestore == AArch64::SP) {
-        // Note: If the base is not SP it is the base pointer, in which case the
-        // SVE CSs will be implicitly deallocated by setting the SP to the FP to
-        // restore the non-SVE CSs.
+      if (MustDeallocateSVEArea) {
         emitFrameOffset(MBB, RestoreEnd, DL, AArch64::SP, AArch64::SP,
                         DeallocateAfter, TII, MachineInstr::FrameDestroy, false,
                         NeedsWinCFI, &HasWinCFI, EmitCFI && !hasFP(MF),