[llvm] [AArch64][SME] Fix restoring callee-saves from FP with hazard padding (PR #143371)

[Benjamin Maxwell via llvm-commits]

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@@ -2539,13 +2554,35 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
     // restore the stack pointer from the frame pointer prior to SVE CSR
     // restoration.
     if (AFI->isStackRealigned() || MFI.hasVarSizedObjects()) {
-      if (int64_t CalleeSavedSize = AFI->getSVECalleeSavedStackSize()) {
+      if (int64_t SVECalleeSavedSize = AFI->getSVECalleeSavedStackSize()) {
         // Set SP to start of SVE callee-save area from which they can
-        // be reloaded. The code below will deallocate the stack space
-        // space by moving FP -> SP.
-        emitFrameOffset(MBB, RestoreBegin, DL, AArch64::SP, AArch64::FP,
-                        StackOffset::getScalable(-CalleeSavedSize), TII,
-                        MachineInstr::FrameDestroy);
+        // be reloaded.
+        const AArch64RegisterInfo *RegInfo = Subtarget.getRegisterInfo();
+        if (!AFI->isStackRealigned() && RegInfo->hasBasePointer(MF)) {
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MacDue wrote:

I've reworked this so the selection of the base pointer is a seperate step, which I think makes things a little easier to follow. This also made me realize I'd missed the case there there's SVE locals and we're restoring from the BP (which is now fixed). 

https://github.com/llvm/llvm-project/pull/143371