Re: [PATCH 2/2] Make option mvzeroupper independent of optimization level.

[Uros Bizjak <ubizjak@gmail.com>]

On Tue, Jun 27, 2023 at 8:09 AM Hongtao Liu <crazylht@gmail.com> wrote:
>
> On Tue, Jun 27, 2023 at 2:05 PM Uros Bizjak <ubizjak@gmail.com> wrote:
> >
> > On Tue, Jun 27, 2023 at 7:55 AM liuhongt <hongtao.liu@intel.com> wrote:
> > >
> > > pass_insert_vzeroupper is under condition
> > >
> > > TARGET_AVX && TARGET_VZEROUPPER
> > > && flag_expensive_optimizations && !optimize_size
> > >
> > > But the document of mvzeroupper doesn't mention the insertion
> > > required -O2 and above, it may confuse users when they explicitly
> > > use -Os -mvzeroupper.
> > >
> > > ------------
> > > mvzeroupper
> > > Target Mask(VZEROUPPER) Save
> > > Generate vzeroupper instruction before a transfer of control flow out of
> > > the function.
> > > ------------
> > >
> > > The patch moves flag_expensive_optimizations && !optimize_size to
> > > ix86_option_override_internal. It makes -mvzeroupper independent of
> > > optimization level, but still keeps the behavior of architecture
> > > tuning(emit_vzeroupper) unchanged.
> > >
> > > Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> > > Ok for trunk?
> > >
> > > gcc/ChangeLog:
> > >
> > >         * config/i386/i386-features.cc (pass_insert_vzeroupper:gate):
> > >         Move flag_expensive_optimizations && !optimize_size to ..
> > >         * config/i386/i386-options.cc (ix86_option_override_internal):
> > >         .. this, it makes -mvzeroupper independent of optimization
> > >         level, but still keeps the behavior of architecture
> > >         tuning(emit_vzeroupper) unchanged.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > >         * gcc.target/i386/avx-vzeroupper-29.c: New testcase.
> >
> > OK.
> I'd like to backport this patch to GCC10/GCC11/GCC12/GCC13.

Also OK.

Thanks,
Uros.

> >
> > Thanks,
> > Uros.
> >
> > > ---
> > >  gcc/config/i386/i386-features.cc                  |  3 +--
> > >  gcc/config/i386/i386-options.cc                   |  4 +++-
> > >  gcc/testsuite/gcc.target/i386/avx-vzeroupper-29.c | 14 ++++++++++++++
> > >  3 files changed, 18 insertions(+), 3 deletions(-)
> > >  create mode 100644 gcc/testsuite/gcc.target/i386/avx-vzeroupper-29.c
> > >
> > > diff --git a/gcc/config/i386/i386-features.cc b/gcc/config/i386/i386-features.cc
> > > index 4a3b07ae045..92ae08d442e 100644
> > > --- a/gcc/config/i386/i386-features.cc
> > > +++ b/gcc/config/i386/i386-features.cc
> > > @@ -2489,8 +2489,7 @@ public:
> > >    /* opt_pass methods: */
> > >    bool gate (function *) final override
> > >      {
> > > -      return TARGET_AVX && TARGET_VZEROUPPER
> > > -       && flag_expensive_optimizations && !optimize_size;
> > > +      return TARGET_AVX && TARGET_VZEROUPPER;
> > >      }
> > >
> > >    unsigned int execute (function *) final override
> > > diff --git a/gcc/config/i386/i386-options.cc b/gcc/config/i386/i386-options.cc
> > > index 2cb0bddcd35..f76e7c5947b 100644
> > > --- a/gcc/config/i386/i386-options.cc
> > > +++ b/gcc/config/i386/i386-options.cc
> > > @@ -2727,7 +2727,9 @@ ix86_option_override_internal (bool main_args_p,
> > >      sorry ("%<-mcall-ms2sysv-xlogues%> isn%'t currently supported with SEH");
> > >
> > >    if (!(opts_set->x_target_flags & MASK_VZEROUPPER)
> > > -      && TARGET_EMIT_VZEROUPPER)
> > > +      && TARGET_EMIT_VZEROUPPER
> > > +      && flag_expensive_optimizations
> > > +      && !optimize_size)
> > >      opts->x_target_flags |= MASK_VZEROUPPER;
> > >    if (!(opts_set->x_target_flags & MASK_STV))
> > >      opts->x_target_flags |= MASK_STV;
> > > diff --git a/gcc/testsuite/gcc.target/i386/avx-vzeroupper-29.c b/gcc/testsuite/gcc.target/i386/avx-vzeroupper-29.c
> > > new file mode 100644
> > > index 00000000000..4af637757f7
> > > --- /dev/null
> > > +++ b/gcc/testsuite/gcc.target/i386/avx-vzeroupper-29.c
> > > @@ -0,0 +1,14 @@
> > > +/* { dg-do compile } */
> > > +/* { dg-options "-O0 -mavx -mtune=generic -mvzeroupper -dp" } */
> > > +
> > > +#include <immintrin.h>
> > > +
> > > +extern __m256 x, y;
> > > +
> > > +void
> > > +foo ()
> > > +{
> > > +  x = y;
> > > +}
> > > +
> > > +/* { dg-final { scan-assembler-times "avx_vzeroupper" 1 } } */
> > > --
> > > 2.39.1.388.g2fc9e9ca3c
> > >
>
>
>
> --
> BR,
> Hongtao