[llvm] [AArch64] Initial compiler support for SVE unwind on Windows. (PR #138609)

[Benjamin Maxwell via llvm-commits]

================
@@ -2587,7 +2684,12 @@ AArch64FrameLowering::getFrameIndexReferenceFromSP(const MachineFunction &MF,
     return StackOffset::getFixed(ObjectOffset - getOffsetOfLocalArea());
 
   const auto *AFI = MF.getInfo<AArch64FunctionInfo>();
+  bool FPAfterSVECalleeSaves =
+      isTargetWindows(MF) && AFI->getSVECalleeSavedStackSize();
   if (MFI.getStackID(FI) == TargetStackID::ScalableVector) {
+    if (FPAfterSVECalleeSaves &&
+        -ObjectOffset <= (int64_t)AFI->getSVECalleeSavedStackSize())
+      return StackOffset::get(0, ObjectOffset);
----------------
MacDue wrote:

nit:
```suggestion
      return StackOffset::getScalable(ObjectOffset);
```

https://github.com/llvm/llvm-project/pull/138609