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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/106950] New: Missed PRE full redundancy
 without post-loop use
Date: Thu, 15 Sep 2022 12:45:11 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 13.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106950

            Bug ID: 106950
           Summary: Missed PRE full redundancy without post-loop use
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

when we have the situation of PR106922, aka g++.dg/tree-ssa/pr106922.C whic=
h is
XFAILed on !lp64 because of this there's

  mem =3D 0;
  do
    {
       if (mem)
         mem =3D 0;
       if (mem) // as 'char' instead of 'bool', maybe relevant
         bar ();
       if (i++ !=3D n)
         break;
    }
  while (1);
  .. =3D mem;

with the use of 'mem' after the loop we get that antic-in in the loop
exit condition block and eventually figure the full redundancy in
the conditional redundant set to zero during PRE insertion.  When that
'mem' after the loop is _not_ there this isn't triggered (possibly
because of the 'char' vs. 'bool' here, but then one can eventually
elide the whole if (mem) bar () code).=