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

["crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

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.