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 014783858D33; Wed, 15 Mar 2023 09:40:00 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 014783858D33
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1678873200;
	bh=LJSDjKpDd/q8B3vcwNQZCvkfoqcSykX6RcPBTbR2tp8=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=Dxg2TfkiGV6t35zAqFuWxA7RZmeurthxFsT9sH0tbAWslEk3E6pGbJoC3dXQIQT5K
	 9+0XnpAwwDWL8+bC0t5fGYnpFrisUJ1pgx0KcjovUCwuRFEZsobP1g/nw7oBlPzxVi
	 8f/naodI5PkyYbH46nzE3x9pmvX5fiEEEWvR/EU0=
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109138] [10/11/12/13 Regression] wrong code
 at -O1 and above on x86_64-linux-gnu
Date: Wed, 15 Mar 2023 09:39:59 +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: 13.0
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub at gcc dot gnu.org
X-Bugzilla-Status: RESOLVED
X-Bugzilla-Resolution: INVALID
X-Bugzilla-Priority: P2
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 10.5
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: resolution bug_status
Message-ID: <bug-109138-4-LDxAqS2yZ3@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-109138-4@http.gcc.gnu.org/bugzilla/>
References: <bug-109138-4@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
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109138

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|NEW                         |RESOLVED

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I don't think this has anything to do with reassoc though.
The testcase looks incorrect to me.
Because d is defined in the scope of the outer loop's body, for b =3D=3D 0 =
a is -1U
and
so the inner loop does nothing, d is set to 1, a is set to 0 and then d goes
out of scope.
Then for b =3D 1, a scope with d variable is entered but the variable is ag=
ain
uninitialized, a <=3D 0 is true, and we use the uninitialized variable.
fixup_cfg1 dump shows this nicely with the clobber in there:

  <bb 2> :
  b =3D 0;
  goto <bb 6>; [INV]

  <bb 3> :
  d.0_1 =3D d;
  if (d.0_1 !=3D 0)
    goto <bb 5>; [INV]
  else
    goto <bb 4>; [INV]

  <bb 4> :
L:
  a.1_2 =3D a;
  if (a.1_2 =3D=3D 0)
    goto <bb 3>; [INV]
  else
    goto <bb 5>; [INV]

  <bb 5> :
  d =3D 1;
  a.2_3 =3D a;
  _4 =3D a.2_3 + 1;
  a =3D _4;
  d =3D {CLOBBER(eol)};
  b =3D b + 1;

  <bb 6> :
  if (b <=3D 1)
    goto <bb 4>; [INV]
  else
    goto <bb 7>; [INV]

  <bb 7> :
  D.2753 =3D 0;
  return D.2753;=