[llvm] [X86] Allow speculative BSR/BSF instructions on targets with CMOV (PR #102885)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Thanks @comex - I'm investigating this on #122004 (for both BSR + BSF) - my old draft patch was intending to perform this for all x86 CPUs, but now its likely that I will limit this to just x64, which will require a rewrite.

https://github.com/llvm/llvm-project/pull/102885