[llvm] [AArch64] Unfold adds when eliminating frame index with scalable offset (PR #158597)

[Sander de Smalen via llvm-commits]

================
@@ -0,0 +1,103 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
----------------
sdesmalen-arm wrote:

The test can be simplified further to:
```
# RUN: llc -mtriple=aarch64-none-linux-gnu -run-pass prologepilog -frame-pointer=none -o - %s | FileCheck %s
---
name: test_addsxri_scalable_offset
stack:
  - { id: 0, type: default, size: 4, alignment: 4, stack-id: default }
  - { id: 1, type: default, size: 16, alignment: 16, stack-id: scalable-vector }
body: |
  bb.0:
    $x8 = ADDSXri %stack.0, 0, 0, implicit-def $nzcv
    RET_ReallyLR implicit $x8
... 
```

https://github.com/llvm/llvm-project/pull/158597