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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/93264] [10 Regression] ICE in
 cfg_layout_redirect_edge_and_branch_force, at cfgrtl.c:4522
Date: Thu, 02 Apr 2020 11:44:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D93264

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
So let's try to address this in cfgloop.c - we're likely facing the situati=
on
of

 header:
...
  if (...) goto latch1;

 latch2:
   goto header;

 latch1: // in cold section
   goto header;

where latch disambiguation via merge_latch_egdes tries to build

  header:
...
  if (...) goto latch1;

 latch2:
   goto latch3;

 latch1: // in cold section
   goto latch3;

 latch3: // somewhere
   goto header;

but somehow we end up redirecting a jump that was formerly crossing
to non-crossing.  Looking at the backtrace it must be entry edges
that are being redirected but the whole setup should be so that
the crossing state of a branch is never changed.

Unfortunately I can't reproduce on todays trunk, will try rewiding backwards
to the reporting time to have a closer look.=