[llvm] [InstCombine] Fold more 'fcmp' 'select' instrs idioms into 'fabs' (PR #83381)

[Andy Kaylor via llvm-commits]

andykaylor wrote:

> I'm leaving this pull request open for now while simultaneously looking if I can set FMF in SROA, will return back with whatever I find.

This is obviously a contrived example, but here is a case that will not be optimized if you rely on the function attributes but could be optimized if the flags were propagated by SROA.

https://godbolt.org/z/senb3bEbn

https://github.com/llvm/llvm-project/pull/83381