[Bug tree-optimization/108601] [13 Regression] vector peeling ICEs with VLA in gcc_r in SPEC2017 since g:c13223b790bbc5e4a3f5605e057eac59b61b2c85

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108601

--- 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=108601
> 
> --- Comment #10 from Hongtao.liu <crazylht at gmail dot com> ---
> (In reply to Hongtao.liu from comment #9)
> > > ----
> > > 
> > > decode_options() {
> > >   int flag = 1;
> > >   for (; flag <= 1 << 21; flag <<= 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 = true;
>         if (STMT_VINFO_DEF_TYPE (stmt_info) == vect_induction_def
>             && ! PURE_SLP_STMT (stmt_info))
>           ok = 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.

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