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?
