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 583FA386F02B; Tue, 21 Apr 2020 07:58:54 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 583FA386F02B
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
 s=default; t=1587455934;
 bh=ULsTuC/TlI7WZ6EzKyEKl7cTbQfRdq/HF2LGPjayFM4=;
 h=From:To:Subject:Date:In-Reply-To:References:From;
 b=pYrTLquC1rBUmagSF+B7BNhre/CY+mIXR0R6OTRJOccsVBSP98srMFaHR1H+ux+aV
 2L/5zK7j4MGPL1a66HSrP1avfR1LahbPKHI89L4q6W3VSDwuar9wmbnWOOuRwcO1x6
 kD/nEraVMOownapwIyIgdR3oEGkEoVcbqo79wR0A=
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/94675] [9/10 regression] -Warray-bounds false
 positive with -O2
Date: Tue, 21 Apr 2020 07:58:54 +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: 9.3.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
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: 9.4
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: cf_known_to_fail short_desc cf_known_to_work
Message-ID: <bug-94675-4-mW9C3T4dbV@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-94675-4@http.gcc.gnu.org/bugzilla/>
References: <bug-94675-4@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: <http://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: <http://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Tue, 21 Apr 2020 07:58:54 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94675

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |10.0, 9.3.0
            Summary|[9 regression]              |[9/10 regression]
                   |-Warray-bounds false        |-Warray-bounds false
                   |positive with -O2           |positive with -O2
      Known to work|                            |8.4.0

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
In the original testcase I clearly see some missed optimizations, notably
the failure to "thread"

  if (_12 > 6)
    goto <bb 4>; [50.00%]
  else
    goto <bb 3>; [50.00%]

  <bb 3> [local count: 536870913]:

  <bb 4> [local count: 1073741824]:
  # iftmp.2_13 =3D PHI <0(3), 1(2)>
  _14 =3D (_Bool) iftmp.2_13;
  if (_14 !=3D 0)
    goto <bb 5>; [90.00%]
  else
    goto <bb 6>; [10.00%]

and as you say simplification of a pointer comparison

  _6 =3D &c + _2;
  _11 =3D _6 - &c;
  _12 =3D (long unsigned int) _11;
  if (_12 > 6)

we're doing the simplification only late because forwprop depends on FRE
and FRE doesn't apply match.pd rules unrestricted like forwprop does.
Not doing any DCE before VRP probably doesn't help either (DCE
would have removed the offending statement).=