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From: "crazylht at gmail dot com" <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 07:29:31 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108601

--- 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)
> >     ;
> > }

Normally when vf is not constant, it will be prevented by
vectorizable_nonlinear_inductions, but for this case, it failed going
into

    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);

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.=