[llvm] [NVPTX] Add IR pass for FMA transformation in the llc pipeline (PR #154735)

[Artem Belevich via llvm-commits]

https://github.com/Artem-B approved this pull request.

In general, I agree with @AlexMaclean that the usefulness of the change is yet to be determined. If it remains a NVPTX-specific pass, I'm OK with landing it so we can see how it fares in practice. If it proves to be useful, for NVPTX or in general, we can consider promoting it to a generic IR pass. If it does not pan out, this specific optimization should be easy to remove.

https://github.com/llvm/llvm-project/pull/154735