[PATCH v2] x86: Don't set AVX_U128_DIRTY when all bits are zero

[H.J. Lu]

On Thu, Jul 15, 2021 at 6:36 PM Hongtao Liu <crazylht@gmail.com> wrote:
>
> On Fri, Jul 16, 2021 at 1:30 AM H.J. Lu via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > In a single SET, all bits of the source YMM/ZMM register are zero when
> >
> > 1. The source is contant zero.
> > 2. The source YMM/ZMM operand are defined from contant zero.
> >
> > and we don't set AVX_U128_DIRTY.
> >
> > gcc/
> >
> >         PR target/101456
> >         * config/i386/i386.c (ix86_avx_u128_mode_needed): Don't set
> >         AVX_U128_DIRTY when all bits are zero.
> >
> > gcc/testsuite/
> >
> >         PR target/101456
> >         * gcc.target/i386/pr101456-1.c: New test.
> > ---
> >  gcc/config/i386/i386.c                     | 47 ++++++++++++++++++++++
> >  gcc/testsuite/gcc.target/i386/pr101456-1.c | 28 +++++++++++++
> >  2 files changed, 75 insertions(+)
> >  create mode 100644 gcc/testsuite/gcc.target/i386/pr101456-1.c
> >
> > diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> > index cff26909292..c2b06934053 100644
> > --- a/gcc/config/i386/i386.c
> > +++ b/gcc/config/i386/i386.c
> > @@ -14129,6 +14129,53 @@ ix86_avx_u128_mode_needed (rtx_insn *insn)
> >        return AVX_U128_CLEAN;
> >      }
> >
> > +  rtx set = single_set (insn);
> > +  if (set)
> > +    {
> > +      rtx dest = SET_DEST (set);
> > +      rtx src = SET_SRC (set);
> > +      if (ix86_check_avx_upper_register (dest))
> > +       {
> > +         /* It is not dirty if the source is known zero.  */
> > +         if (standard_sse_constant_p (src, GET_MODE (dest)) == 1)
> > +           return AVX_U128_ANY;
> > +         else
> > +           return AVX_U128_DIRTY;
> > +       }
> > +      else if (ix86_check_avx_upper_register (src))
> > +       {
> > +         /* Check for the source operand with all DEFs from constant
> > +            zero.  */
> > +         df_ref def = DF_REG_DEF_CHAIN (REGNO (src));
> > +         if (!def)
> > +           return AVX_U128_DIRTY;
> > +
> > +         for (; def; def = DF_REF_NEXT_REG (def))
> > +           if (DF_REF_REG_DEF_P (def)
> > +               && !DF_REF_IS_ARTIFICIAL (def))
> > +             {
> > +               rtx_insn *def_insn = DF_REF_INSN (def);
> > +               set = single_set (def_insn);
> > +               if (!set)
> > +                 return AVX_U128_DIRTY;
> > +
> > +               dest = SET_DEST (set);
> > +               if (ix86_check_avx_upper_register (dest))
> > +                 {
> > +                   src = SET_SRC (set);
> > +                   /* It is dirty if the source operand isn't constant
> > +                      zero.  */
> > +                   if (standard_sse_constant_p (src, GET_MODE (dest))
> > +                       != 1)
> > +                     return AVX_U128_DIRTY;
> > +                 }
> > +             }
> > +
> > +         /* It is not dirty only if all sources are known zero.  */
> > +         return AVX_U128_ANY;
> > +       }
> > +    }
> > +
> >    /* Require DIRTY mode if a 256bit or 512bit AVX register is referenced.
> >       Hardware changes state only when a 256bit register is written to,
> >       but we need to prevent the compiler from moving optimal insertion
> > diff --git a/gcc/testsuite/gcc.target/i386/pr101456-1.c b/gcc/testsuite/gcc.target/i386/pr101456-1.c
> > new file mode 100644
> > index 00000000000..6a0f6ccd756
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/i386/pr101456-1.c
> > @@ -0,0 +1,28 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2 -march=skylake" } */
> > +
> > +#include <x86intrin.h>
> > +
> > +extern __m256 x1;
> > +extern __m256d x2;
> > +extern __m256i x3;
> > +
> > +void
> > +foo1 (void)
> > +{
> > +  x1 = _mm256_setzero_ps ();
> > +}
> > +
> > +void
> > +foo2 (void)
> > +{
> > +  x2 = _mm256_setzero_pd ();
> > +}
> > +
> > +void
> > +foo3 (void)
> > +{
> > +  x3 = _mm256_setzero_si256 ();
> > +}
> > +
> > +/* { dg-final { scan-assembler-not "vzeroupper" } } */
> > --
> > 2.31.1
> >
>
> LGTM.
>

Here is the v2 patch to handle calls.

-- 
H.J.
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