[llvm] [AMDGPU] Implement IR variant of isFMAFasterThanFMulAndFAdd (PR #121465)

[Matt Arsenault via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=simplifycfg -verify-machineinstrs -hoist-common-insts=true -mtriple=amdgcn-- --fp-contract=fast -mcpu=gfx1030 < %s | FileCheck -check-prefix=GFX -check-prefix=FP-CONTRACT-FAST %s
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arsenm wrote:

-verify-machineinstrs does nothing with opt. Is hoist-common-insts available as a pass parameter instead of a cl::opt? 

Also can you pre-commit the test 

https://github.com/llvm/llvm-project/pull/121465