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Re: [PATCH] x86: emit tzcnt unconditionally


On Fri, Apr 27, 2012 at 3:30 PM, Paolo Bonzini <bonzini@gnu.org> wrote:
> tzcnt is encoded as "rep;bsf" and unlike lzcnt is a drop-in replacement
> if we don't care about the flags (it has the same semantics for non-zero
> values).
>
> Since bsf is usually slower, just emit tzcnt unconditionally. ?However,
> write it as rep;bsf unless -mbmi is in use, to cater for old assemblers.

Please emit "rep;bsf" when optimize_insn_for_speed_p () is true.

> Bootstrapped on a non-BMI x86_64-linux host, regtest in progress.
> Ok for mainline?

OK with the optimize_insn_for_speed_p conditional.

Thanks,
Uros.


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