From owner-freebsd-fs@FreeBSD.ORG  Sun Apr 10 12:04:48 2005
Return-Path: <owner-freebsd-fs@FreeBSD.ORG>
Delivered-To: freebsd-fs@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id 654A116A4CE; Sun, 10 Apr 2005 12:04:48 +0000 (GMT)
Received: from tensor.xs4all.nl (tensor.xs4all.nl [194.109.160.97])
	by mx1.FreeBSD.org (Postfix) with ESMTP
	id B785643D2F; Sun, 10 Apr 2005 12:04:47 +0000 (GMT)
	(envelope-from dimitry@andric.com)
Received: from kilgore.dim (kilgore.dim [192.168.0.3])
	(using TLSv1 with cipher AES256-SHA (256/256 bits))
	(No client certificate requested)
	by tensor.xs4all.nl (Postfix) with ESMTP id 0474622867;
	Sun, 10 Apr 2005 14:04:44 +0200 (CEST)
Date: Sun, 10 Apr 2005 14:04:23 +0200
From: Dimitry Andric <dimitry@andric.com>
X-Priority: 3 (Normal)
Message-ID: <1892195662.20050410140423@andric.com>
To: Daniel Ellard <ellard@eecs.harvard.edu>
In-Reply-To: <20050410074009.N66651@bowser.eecs.harvard.edu>
References: <200504100251.j3A2pLEH055107@sana.init-main.com>
 <20050410092417.GA774@galgenberg.net>
 <20050410074009.N66651@bowser.eecs.harvard.edu>
MIME-Version: 1.0
Content-Type: multipart/signed; protocol="application/pgp-signature";
	micalg="pgp-sha1";  boundary="----------1291C69219E9F339"
cc: freebsd-fs@freebsd.org
cc: bp@freebsd.org
cc: Ulrich Spoerlein <q@uni.de>
cc: freebsd-current@freebsd.org
Subject: Re: smbfs bug introduced at smbfs_vnops.c:1.58
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
	<mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
	<mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 10 Apr 2005 12:04:48 -0000

------------1291C69219E9F339
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

On 2005-04-10 at 13:45:50 Daniel Ellard wrote:

>> int main(void) {
>>   int a;
>>   a+=1;
>>   return (0);
>> }
[snip]
> If you change the -O to -g, then the code for "a" is not
> removed -- but there's still no warning.  I think this is
> a bug, because if the expression wasn't an innocuous a+=1
> it could be a real problem if the variable wasn't removed.

The idea here is that gcc sees that the value of a is never used, and
therefore it doesn't have to warn.  (Whether you agree with this, or
not, is more of a political or philosophical question. ;)  But as soon
as you actually *do* something with a's value afterwards, it will
start to complain.  IOW, if you change main into:

    int main(void)
    {
        int a;
        a += 1;
        a++;
        //...bunch of other operations on a...
        ++a;
        a *= 3;
        return 0;
    }

and gcc will still issue no warning.  However, add one actual *use*
of a:

    extern void f(int i);

    int main(void)
    {
        int a;
        a += 1;
        f(a);
        return 0;
    }

and you'll get the warning you want... :)

------------1291C69219E9F339
Content-Type: application/pgp-signature

-----BEGIN PGP MESSAGE-----
Version: GnuPG v1.4.0 (MingW32)

iD8DBQFCWRZHsF6jCi4glqMRAlQwAKCcHtIlJkcR3rdp2N99qz6JimAGLwCcDisx
Xiqm/Q0yy9TeULi2QHQnwts=
=hO98
-----END PGP MESSAGE-----

------------1291C69219E9F339--