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 C9A483858415; Wed,  9 Mar 2022 13:07:19 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org C9A483858415
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/104492] [12 Regression] Bogus dangling pointer
 warning at -O3
Date: Wed, 09 Mar 2022 13:07:19 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: diagnostic
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: 12.0
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-104492-4-R8ux2qePyY@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-104492-4@http.gcc.gnu.org/bugzilla/>
References: <bug-104492-4@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: Wed, 09 Mar 2022 13:07:19 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104492

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #5)
> Setting aside the question of warning about inequality expressions involv=
ing
> invalid pointers, it seems that if the annotation 'candidates =3D{v}
> {CLOBBER(eol)};' is to be interpreted as one would intuitively expect -- =
as
> ending the variable's lifetime -- then GCC moving its use past that point
> should be considered a bug in that transformation.

The lifetime of the object ends but this is just a value and GCC cannot
distinguish for example between (uintptr_t)&candidates and &candidates
(where "leaking" the former is obviously OK).  It's similar to the
issue with __builtin_object_size and &a.b[0] vs. &a - it's nothing we can
fix.  So diagnosing uses of the _address_ (rather than the pointed to
storage) is going to have GCC generated false positives.=