[Bug gcov-profile/58250] -fprofile-use causes: "warning: -fprefetch-loop-arrays is not supported with -Os"

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58250

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Markus Trippelsdorf from comment #0)
> Just noticed this issue during a PGO/LTO Firefox build.
> During the -fprofile-use phase I always get the following warning:
>  warning: -fprefetch-loop-arrays is not supported with -Os [enabled by
> default]
> 
> This is caused by rev.193135:
>    /* Enable sw prefetching at -O3 for CPUS that prefetching is helpful.  */
>    if (flag_prefetch_loop_arrays < 0
>        && HAVE_prefetch
> -      && optimize >= 3
> +      && (optimize >= 3 || flag_profile_use)
>        && TARGET_SOFTWARE_PREFETCHING_BENEFICIAL)
>      flag_prefetch_loop_arrays = 1;
> 
> 
> Does the following patch look OK?
> 
> diff --git a/gcc/toplev.c b/gcc/toplev.c
> index 53f53fd..9955ed4 100644
> --- a/gcc/toplev.c
> +++ b/gcc/toplev.c
> @@ -1506,7 +1506,7 @@ process_options (void)
>  
>    /* This combination of options isn't handled for i386 targets and doesn't
>       make much sense anyway, so don't allow it.  */
> -  if (flag_prefetch_loop_arrays > 0 && optimize_size)
> +  if (flag_prefetch_loop_arrays > 0 && optimize_size && !flag_profile_use)
>      {
>        warning (0, "-fprefetch-loop-arrays is not supported with -Os");
>        flag_prefetch_loop_arrays = 0;

Hmm, I rather question this hunk - where does it come from?  Why is
prefetching "unsupported" at -Os?