[llvm] [CodeGen] [AMDGPU] Adds pre-commit test for fmul-select combine (PR #111107)

[Matt Arsenault via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+;RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 < %s | FileCheck -check-prefix=GFX9 %s
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arsenm wrote:

Test gfx700 

https://github.com/llvm/llvm-project/pull/111107