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 35EF93857C60; Thu, 25 Mar 2021 11:46:27 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 35EF93857C60
From: "acoplan at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/99768] New: [11 Regression] Bogus -Wuninitialized diagnostic
 with type punning
Date: Thu, 25 Mar 2021 11:46:27 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: 11.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: acoplan at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
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: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-99768-4@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, 25 Mar 2021 11:46:27 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99768

            Bug ID: 99768
           Summary: [11 Regression] Bogus -Wuninitialized diagnostic with
                    type punning
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: acoplan at gcc dot gnu.org
  Target Milestone: ---

For the following code (which has a strict aliasing violation):

float foo(unsigned v)
{
    unsigned tmp =3D v;
    float *f =3D (float *)(&tmp);
    return *f;
}

at -O2 -Wall we warn that tmp is used uninitialized:

test.c: In function =E2=80=98foo=E2=80=99:
test.c:5:12: warning: =E2=80=98tmp=E2=80=99 is used uninitialized [-Wuninit=
ialized]
    5 |     return *f;
      |            ^~
test.c:3:14: note: =E2=80=98tmp=E2=80=99 declared here
    3 |     unsigned tmp =3D v;
      |              ^~~

but this is clearly bogus. Not sure if this is strictly considered a bug gi=
ven
the strict aliasing problem, but thought it might be worth checking in any
case.=