[clang] [llvm] InstCombine: Use SimplifyDemandedFPClass on fmul (PR #177490)

[Yingwei Zheng via cfe-commits]

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

LGTM.

> I was wondering if this should go into InstCombineAggressive, but that
apparently does not make use of InstCombineInternal's worklist.

I hope we can move all SimplifyDemanded* optimizations out of InstCombinePass.


https://github.com/llvm/llvm-project/pull/177490