[llvm] [AMDGPU] Account for existing SDWA selections (PR #123221)

[Matt Arsenault via llvm-commits]

================
@@ -0,0 +1,796 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=amdgcn -mcpu=gfx1030 -simplify-mir -run-pass=si-peephole-sdwa -o - %s | FileCheck %s
+
+# Test the combination of SDWA selections in si-peephole-sdwa. In each
----------------
arsenm wrote:

The destination case is significantly more likely to break, so should also cover those 

https://github.com/llvm/llvm-project/pull/123221