[Bug middle-end/102997] [12 Regression] 45% 454.calculix regression with LTO+PGO -march=native -Ofast on Zen since r12-4526-gd8edfadfc7a9795b65177a50ce44fd348858e844

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102997

--- Comment #25 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to rguent...@suse.de from comment #24)
> On Mon, 8 Nov 2021, hubicka at kam dot mff.cuni.cz wrote:
> 
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102997
> > 
> > --- 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.
> > 
> > Which seem wrong for the path leaving loop and entering another...
> 
> 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 != exit->dest->loop_father
      && !flow_loop_nested_p (exit->src->loop_father,
                              entry->dest->loop_father))
    {
      cancel_thread (&path, "Path rotates loop");
      return true;
    }