From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-return-169833-listarch-gcc=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 1055 invoked by alias); 12 Aug 2011 07:32:26 -0000
Received: (qmail 1046 invoked by uid 22791); 12 Aug 2011 07:32:25 -0000
X-SWARE-Spam-Status: No, hits=-2.2 required=5.0	tests=AWL,BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,RCVD_IN_DNSWL_LOW,TW_LV
X-Spam-Check-By: sourceware.org
Received: from mail-yw0-f47.google.com (HELO mail-yw0-f47.google.com) (209.85.213.47)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 12 Aug 2011 07:32:12 +0000
Received: by ywe9 with SMTP id 9so1888616ywe.20        for <gcc@gcc.gnu.org>; Fri, 12 Aug 2011 00:32:11 -0700 (PDT)
MIME-Version: 1.0
Received: by 10.150.243.5 with SMTP id q5mr505629ybh.421.1313134331537; Fri, 12 Aug 2011 00:32:11 -0700 (PDT)
Received: by 10.150.219.17 with HTTP; Fri, 12 Aug 2011 00:32:11 -0700 (PDT)
In-Reply-To: <59662D5BB74CD84D9FA8E6491ADB51A7DEAE4D29@US01WXMBX1.internal.synopsys.com>
References: <201108111715.14240.florian.merz@kit.edu>	<CAFiYyc1aCzF1nC=SG6p_U0ssTQswz4bpPFMUHDNe9JAnB4cy9g@mail.gmail.com>	<201108111805.19582.florian.merz@kit.edu>	<CAFiYyc329Ci7VA=TnK0YD-jCsY=ReLk4LOE8a4wR_XEN990Z6w@mail.gmail.com>	<Pine.LNX.4.64.1108111851570.20653@digraph.polyomino.org.uk>	<CAAiZkiDYmRk8G6C1gGECOnx1meEZbKDQdPjZgqjwPmoevitcaw@mail.gmail.com>	<59662D5BB74CD84D9FA8E6491ADB51A7DEAE4D29@US01WXMBX1.internal.synopsys.com>
Date: Fri, 12 Aug 2011 07:32:00 -0000
Message-ID: <CAFiYyc0d11GpqHMvVX=mxg-1bRT-Vpvh283wcpO_zh4Qr9c7qA@mail.gmail.com>
Subject: Re: [LLVMdev] Handling of pointer difference in llvm-gcc and clang
From: Richard Guenther <richard.guenther@gmail.com>
To: Joe Buck <Joe.Buck@synopsys.com>
Cc: Gabriel Dos Reis <gdr@integrable-solutions.net>, 	"Joseph S. Myers" <joseph@codesourcery.com>, "florian.merz@kit.edu" <florian.merz@kit.edu>, 	"gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
X-IsSubscribed: yes
Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc/>
List-Post: <mailto:gcc@gcc.gnu.org>
List-Help: <http://gcc.gnu.org/ml/>
Sender: gcc-owner@gcc.gnu.org
X-SW-Source: 2011-08/txt/msg00240.txt.bz2

On Thu, Aug 11, 2011 at 10:36 PM, Joe Buck <Joe.Buck@synopsys.com> wrote:
> On Thu, Aug 11, 2011 at 1:58 PM, Joseph S. Myers
> <joseph@codesourcery.com> wrote:
>> =A0-ftrapv and -fwrapv should have no effect on pointer subtraction.
>
> Gaby writes:
>
>> Yes!
>
> Wouldn't it suffice to convert the pointers to unsigned, do an unsigned s=
ubtraction, and then convert the result to signed? This would then guarante=
e that gcc uses two's complement semantics, independent of -ftrapv.

Of course, I think that is what is being proposed.

Richard.