From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id 453973858402; Thu, 26 Aug 2021 12:02:06 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 453973858402
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/45178] CDDCE doesn't eliminate conditional
 code in infinite loop
Date: Thu, 26 Aug 2021 12:02:05 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 4.6.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: keywords cf_reconfirmed_on
Message-ID: <bug-45178-4-3S8ZVcMVUJ@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-45178-4@http.gcc.gnu.org/bugzilla/>
References: <bug-45178-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Thu, 26 Aug 2021 12:02:06 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D45178

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|TREE                        |
   Last reconfirmed|2021-07-26 00:00:00         |2021-8-26

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
So no, that's not the problem at all.  The only loop is the infinite while =
(1)
one, the problem is that because we cannot prove finiteness of the loop we'=
re
doing

      for (auto loop : loops_list (cfun, 0))
        if (!finite_loop_p (loop))
          {
            if (dump_file)
              fprintf (dump_file, "cannot prove finiteness of loop %i\n",
loop->num);
            mark_control_dependent_edges_necessary (loop->latch, false);
          }

and that marks a condition that has nothing to do with loop control.  I sup=
pose
we can elide this when the loop has no exit (we are already marking backedg=
es
of irreducible loops).

But I never actually understood this particular part of CD-DCE.

The desired transform is that we end up with just

int main()
{
  while (1)
    ;
}=