From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-475308-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 21551 invoked by alias); 28 Jan 2015 20:38:24 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Received: (qmail 15387 invoked by uid 48); 28 Jan 2015 20:38:15 -0000
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/64843] miscompilation of atomic_fetch_add on atomic pointer type
Date: Wed, 28 Jan 2015 20:38:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: 4.9.0
X-Bugzilla-Keywords: documentation, wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: NEW
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 bug_status cf_reconfirmed_on everconfirmed cf_known_to_fail
Message-ID: <bug-64843-4-mIMHmWKJEJ@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-64843-4@http.gcc.gnu.org/bugzilla/>
References: <bug-64843-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2015-01/txt/msg03302.txt.bz2

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64843

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |documentation, wrong-code
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-01-28
     Ever confirmed|0                           |1
      Known to fail|                            |5.0

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
The documentation indeed suggests this:

"These built-in functions perform the operation suggested by the name, and
return the value that had previously been in @code{*@var{ptr}}.  That is,

@smallexample
@{ tmp = *ptr; *ptr @var{op}= val; return tmp; @}
@end smallexample"

thus here

 *(&p) += 1;

Whether the bug is in documentation or code is another question.  Confirmed
that the testcase produces cited assembly on x86_64 and some older trunk.