From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-425996-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 10333 invoked by alias); 9 Jul 2013 08:48:22 -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 10279 invoked by uid 48); 9 Jul 2013 08:48:17 -0000
From: "francesco.zappa.nardelli at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/47409] volatile struct member bug
Date: Tue, 09 Jul 2013 08:48:00 -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: 4.6.0
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: francesco.zappa.nardelli at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
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: cc
Message-ID: <bug-47409-4-X5FwJK4N1J@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-47409-4@http.gcc.gnu.org/bugzilla/>
References: <bug-47409-4@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: 2013-07/txt/msg00503.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47409

Francesco Zappa Nardelli <francesco.zappa.nardelli at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |francesco.zappa.nardelli@gm
                   |                            |ail.com

--- Comment #16 from Francesco Zappa Nardelli <francesco.zappa.nardelli at gmail dot com> ---
Dear all

a possibly related issue.  Consider

struct S1 {
  long f;
};
volatile struct S1 g;

struct S1 func_1 () {
  return g;
}

void main () {
  func_1 ();
}

This program, if compiled with a recent gcc svn:

$ gcc -v
Target: x86_64-unknown-linux-gnu
gcc version 4.9.0 20130625 (experimental) (GCC) 

correctly loads the long at g.f at -O0.  However the assembly generated at -O2:

func_1:
      movq    g(%rip), %rax
      ret
main:
      rep; ret 

does not perform the volatile load access, which, as far as I understand, is
incorrect.

-francesco