[PATCH v1 1/2] x86: Add comment explaining no Slow_SSE4_2 check in ifunc-sse4_2

[H.J. Lu]

On Tue, Jun 28, 2022 at 8:27 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> Just for clarities sake and so that if a future implementation is
> added we remember to add the check.
> ---
>  sysdeps/x86_64/multiarch/ifunc-sse4_2.h | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/sysdeps/x86_64/multiarch/ifunc-sse4_2.h b/sysdeps/x86_64/multiarch/ifunc-sse4_2.h
> index ee36525bcf..204c4b5406 100644
> --- a/sysdeps/x86_64/multiarch/ifunc-sse4_2.h
> +++ b/sysdeps/x86_64/multiarch/ifunc-sse4_2.h
> @@ -27,7 +27,11 @@ IFUNC_SELECTOR (void)
>  {
>    const struct cpu_features* cpu_features = __get_cpu_features ();
>
> -  if (CPU_FEATURE_USABLE_P (cpu_features, SSE4_2))
> +  /* This function uses slow sse4.2 instructions (pcmpstri) but since
> +     there is no other optimized implementation keep using.  If an
> +     optimized fallback is added add a X86_ISA_CPU_FEATURE_USABLE_P
> +     (cpu_features, SSE4_2) check.  */

Did you mean Slow_SSE4_2?

> +  if (ISA_CPU_FEATURE_USABLE_P (cpu_features, SSE4_2))
>      return OPTIMIZE (sse42);
>
>    return OPTIMIZE (generic);
> --
> 2.34.1
>


-- 
H.J.