[PATCH] x86_64: Optimize ffsll function code size.

[Richard Henderson]

On 7/26/23 09:05, 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.
> ---
>   sysdeps/x86_64/ffsll.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sysdeps/x86_64/ffsll.c b/sysdeps/x86_64/ffsll.c
> index a1c13d4906..dbded6f0a1 100644
> --- a/sysdeps/x86_64/ffsll.c
> +++ b/sysdeps/x86_64/ffsll.c
> @@ -29,7 +29,7 @@ ffsll (long long int x)
>     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.  */
> +       "cmove %k1,%k0\n"	/* If number was zero, use -1 as result.  */

This no longer produces -1, but 0xffffffff in cnt.  However, since the return type is 
'int', cnt need not be 'long long int' either.  I'm not sure why tmp exists at all, since 
cnt is the only register modified.


r~