[PATCH] D23134: Make cltz and cttz zero undef when the operand cannot be zero in InstCombine

[Amaury SECHET via llvm-commits]

deadalnix added a comment.

@spatel , the undef version lead to much better codegen on X86 at least, because bsf/bsr instruction are undefined when the operand is 0.


https://reviews.llvm.org/D23134