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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/102997] [12 Regression] 45% 454.calculix regression
 with LTO+PGO -march=native -Ofast on Zen since
 r12-4526-gd8edfadfc7a9795b65177a50ce44fd348858e844
Date: Mon, 08 Nov 2021 14:10:15 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102997

--- Comment #25 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to rguenther@suse.de from comment #24)
> On Mon, 8 Nov 2021, hubicka at kam dot mff.cuni.cz wrote:
>=20
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102997
> >=20
> > --- Comment #23 from hubicka at kam dot mff.cuni.cz ---
> > > We verify that by simply looking at the loop depth relation of
> > > the entry and exit of the path.
> >=20
> > Which seem wrong for the path leaving loop and entering another...
>=20
> True I guess.  The path should end it the same loop as it starts
> or end in a loop containing the start loop.  Would have to double
> check this.

Yep, done:

  // The path should either start and end in the same loop or exit the
  // loop it starts in but never enter a loop.  This also catches
  // creating irreducible loops, not only rotation.
  if (entry->src->loop_father !=3D exit->dest->loop_father
      && !flow_loop_nested_p (exit->src->loop_father,
                              entry->dest->loop_father))
    {
      cancel_thread (&path, "Path rotates loop");
      return true;
    }=