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

[Yashwant Singh via llvm-commits]

yashssh wrote:

> > I'm wondering whether we should be propagating the function-level attributes to instruction flags _somewhere_ so that this is handled generically, rather than in individual folds?
> 
> TBH I think fast-math flags should only be function-level attributes :(

Will that be more efficient? What about function inlining when we end up losing these attributes?

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