[llvm] [NVPTX] Add support for nvvm.flo.[us] intrinsics (PR #114489)

[Artem Belevich via llvm-commits]

Artem-B wrote:

These intrinsics look like a solution in search of a problem. The instruction has been present in PTX ~ forever, but I've only learned about it today and I can't think of a single case where I would wish for something like `llvm.nvvm.flo`, nor did any LLVM/NVPTX users ever asked me for them.

So, my first question is -- do we really need them? If so, why?

If we do need them, is there any benefit in using the instructions? In case where there's no direct h/w support for the functionality, it may be better to expand to LLVM IR and let LLVM optimize that. To me it looks like a combination of logical ops and `llvm.ctlz` might just do the job.

https://github.com/llvm/llvm-project/pull/114489