[llvm] [InstCombine] Ensure Safe Handling of Flags in foldFNegIntoConstant (PR #94148)

[Yingwei Zheng via llvm-commits]

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

LGTM. Thank you!
However, this PR only fixes FMF propagation for `fneg + fmul`. The remaining part of the original issue (`fsub + fmul` and `fneg + fdiv`) is still outstanding: https://alive2.llvm.org/ce/z/Jt3n6P



https://github.com/llvm/llvm-project/pull/94148