[Bug tree-optimization/108601] [13 Regression] vector peeling ICEs with PGO + LTO + IPA inlining in gcc_r in SPEC2017

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

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

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
So for the trivial

void
__attribute__((noipa))
foo_mul (int* a, int b, int n)
{
  for (int i = 0; i != N; i++)
    {
      a[i] = b;
      b *= 3;
    }
}


I get

t.c:5:21: note:   examining phi: b_17 = PHI <b_12(6), b_7(D)(5)>
t.c:5:21: missed:   Peeling for epilogue is not supported for nonlinear
induction except neg when iteration count is unknown.
t.c:3:1: missed:   not vectorized: relevant phi not supported: b_17 = PHI
<b_12(6), b_7(D)(5)>
t.c:5:21: missed:  bad operation or unsupported loop bound.

so for some reason this check doesn't trigger for the case in SPEC?  The
check seems to be

vect_can_peel_nonlinear_iv_p (loop_vec_info loop_vinfo,
                              enum vect_induction_op_type induction_type)
{
  tree niters_skip;
  /* Init_expr will be update by vect_update_ivs_after_vectorizer,
     if niters is unkown:
     For shift, when shift mount >= precision, there would be UD.
     For mult, don't known how to generate
     init_expr * pow (step, niters) for variable niters.
     For neg, it should be ok, since niters of vectorized main loop
     will always be multiple of 2.  */
  if (!LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
      && induction_type != vect_step_op_neg)
    {
      if (dump_enabled_p ())
        dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
                         "Peeling for epilogue is not supported"
                         " for nonlinear induction except neg"
                         " when iteration count is unknown.\n");
      return false;
    }

that might not be entirely sufficient to detect all epilogue peeling cases.