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

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

[markus at trippelsdorf dot de]

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

            Bug ID: 58250
           Summary: -fprofile-use causes: "warning: -fprefetch-loop-arrays
                    is not supported with -Os"
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: gcov-profile
          Assignee: unassigned at gcc dot gnu.org
          Reporter: markus at trippelsdorf dot de

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;

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

[rguenth at gcc dot 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?

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

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Prefetching generally increases code size, so I think we shouldn't do it, at
least not by default.  So I'd say for !optimize_size -fprofile-use should just
not add -fprefetch-loop-arrays.

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

[hubicka at ucw dot cz]

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

--- Comment #3 from Jan Hubicka <hubicka at ucw dot cz> ---
> Prefetching generally increases code size, so I think we shouldn't do it, at
> least not by default.  So I'd say for !optimize_size -fprofile-use should just
> not add -fprefetch-loop-arrays.

Yep, I think -fprofile-use code should not enable code expanding optimizations
when
optimize_size.   I will look into that.

Honza
> 
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