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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108601] [13 Regression] vector peeling ICEs
 with VLA in gcc_r in SPEC2017 since
 g:c13223b790bbc5e4a3f5605e057eac59b61b2c85
Date: Wed, 01 Feb 2023 07:32:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108601

--- Comment #11 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 1 Feb 2023, crazylht at gmail dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108601
>=20
> --- Comment #10 from Hongtao.liu <crazylht at gmail dot com> ---
> (In reply to Hongtao.liu from comment #9)
> > > ----
> > >=20
> > > decode_options() {
> > >   int flag =3D 1;
> > >   for (; flag <=3D 1 << 21; flag <<=3D 1)
> > >     ;
> > > }
>=20
> Normally when vf is not constant, it will be prevented by
> vectorizable_nonlinear_inductions, but for this case, it failed going
> into
>=20
>     if (STMT_VINFO_RELEVANT_P (stmt_info))
>       {
>         need_to_vectorize =3D true;
>         if (STMT_VINFO_DEF_TYPE (stmt_info) =3D=3D vect_induction_def
>             && ! PURE_SLP_STMT (stmt_info))
>           ok =3D vectorizable_induction (loop_vinfo,
>                                        stmt_info, NULL, NULL,
>                                        &cost_vec);
>=20
> since the iv is never used outside of the loop, and will be dce later, so
> vectorizer doesn't bother checking if it's vectorizable. It's
> true but hit gcc_assert in vect_peel_nonlinear_iv_init when vf is not
> constant. One solution is ignoring the nonlinear iv peeling if it's
> !STMT_VINFO_RELEVANT_P (stmt_info) just like the upper code, the other
> solution is returning false earlier in the
> vect_can_peel_nonlinear_iv_p when vf is not known.

When the VF is not known we usually do not require an epilogue?  If
we don't require one we should avoid creating one.=