[llvm] [InstSimplify] Treat float binop with identity as refining (PR #120098)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon approved this pull request.

> If x if NaN, then fmul (x, 1) may produce a different NaN value.

s/if/is/.

LGTM, thanks!

https://github.com/llvm/llvm-project/pull/120098