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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/103393] [12 Regression] Generating 256bit register usage
 with -mprefer-avx128 -mprefer-vector-width=128
Date: Thu, 25 Nov 2021 01:25:53 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103393

--- Comment #6 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Hongtao.liu from comment #5)
> (In reply to Richard Biener from comment #3)
> > (In reply to H.J. Lu from comment #2)
> > > (In reply to Richard Biener from comment #1)
> > > > It isn't the vectorizer but memmove inline expansion.  I'm not sure=
 it's
> > > > really a bug, but there isn't a way to disable %ymm use besides dis=
abling
> > > > AVX entirely.
> > > > HJ?
> > >=20
> > > YMM move is generated by loop distribution which doesn't check
> > > TARGET_PREFER_AVX128.
> >=20
> > I think it's generated by gimple_fold_builtin_memory_op which since Ric=
hards
> > changes accepts bigger now, up to MOVE_MAX * MOVE_RATIO and that ends up
> > picking an integer mode via
> >=20
> >               scalar_int_mode mode;
> >               if (int_mode_for_size (ilen * 8, 0).exists (&mode)
> >                   && GET_MODE_SIZE (mode) * BITS_PER_UNIT =3D=3D ilen *=
 8
> >                   && have_insn_for (SET, mode)
> >                   /* If the destination pointer is not aligned we must =
be
> > able
> >                      to emit an unaligned store.  */
> >                   && (dest_align >=3D GET_MODE_ALIGNMENT (mode)
> >                       || !targetm.slow_unaligned_access (mode, dest_ali=
gn)
> >                       || (optab_handler (movmisalign_optab, mode)
> >                           !=3D CODE_FOR_nothing)))
> >=20
> > not sure if there's another way to validate things.
>=20
> For one single set operation, shouldn't the total size be less than MOVE_=
MAX
> instead of MOVE_MAX * MOVE_RATIO?

r12-3482 change MOVE_MAX to MOVE_MAX * MOVE_RATIO=