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

[Jeffrey Byrnes via llvm-commits]

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+# 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
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jrbyrnes wrote:

Do we have tests for combining on dst?

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