On Mon, Jul 31, 2023 at 1:12 PM Adhemerval Zanella Netto <
adhemerval.zanella@linaro.org> wrote:

>
>
> On 31/07/23 15:35, Sunil K Pandey via Libc-alpha wrote:
> > Ffsll function size is 17 byte, this patch optimizes size to 16 byte.
> > Currently ffsll function randomly regress by ~20%, depending on how
> > code get aligned.
> >
> > This patch fixes ffsll function random performance regression.
> >
> > Changes from v1:
> > - Further reduce size ffsll function size to 12 bytes.
> > ---
> >  sysdeps/x86_64/ffsll.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/sysdeps/x86_64/ffsll.c b/sysdeps/x86_64/ffsll.c
> > index a1c13d4906..6a5803c7c1 100644
> > --- a/sysdeps/x86_64/ffsll.c
> > +++ b/sysdeps/x86_64/ffsll.c
> > @@ -26,13 +26,13 @@ int
> >  ffsll (long long int x)
> >  {
> >    long long int cnt;
> > -  long long int tmp;
> >
> > -  asm ("bsfq %2,%0\n"                /* Count low bits in X and store
> in %1.  */
> > -       "cmoveq %1,%0\n"              /* If number was zero, use -1 as
> result.  */
> > -       : "=&r" (cnt), "=r" (tmp) : "rm" (x), "1" (-1));
> > +  asm ("mov $-1,%k0\n"       /* Intialize CNT to -1.  */
> > +       "bsf %1,%0\n" /* Count low bits in X and store in CNT.  */
> > +       "inc %k0\n"   /* Increment CNT by 1.  */
> > +       : "=&r" (cnt) : "r" (x));
> >
> > -  return cnt + 1;
> > +  return cnt;
> >  }
> >
> >  #ifndef __ILP32__
>
>
>
> I still prefer if we can just remove this arch-optimized function in favor
> in compiler builtins.
>

Sure, compiler builtin should replace it in the long run.
In the meantime, can it get fixed?