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

[Nikita Popov via cfe-commits]

nikic wrote:

Are there plans to extend this to other instructions? The overhead here looks problematic if it's going to be similar for other roots.

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