From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-return-64548-listarch-gcc=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 18558 invoked by alias); 13 Dec 2002 13:53:31 -0000
Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
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
Received: (qmail 18531 invoked from network); 13 Dec 2002 13:53:30 -0000
Received: from unknown (HELO mail.libertysurf.net) (213.36.80.91)
  by sources.redhat.com with SMTP; 13 Dec 2002 13:53:30 -0000
Received: from localhost.localdomain (213.36.79.115) by mail.libertysurf.net (6.5.026)
        id 3DE39B43002823DD; Fri, 13 Dec 2002 14:50:41 +0100
Content-Type: text/plain;
  charset="iso-8859-1"
From: Eric Botcazou <ebotcazou@libertysurf.fr>
To: "Christian Ehrhardt" <ehrhardt@mathematik.uni-ulm.de>
Subject: Re: optimization/7799: [3.2/3.3 regression] Loop bug with optimization flag -Os in gcc
Date: Fri, 13 Dec 2002 06:13:00 -0000
User-Agent: KMail/1.4.1
References: <20021213133626.29733.qmail@theseus.mathematik.uni-ulm.de>
In-Reply-To: <20021213133626.29733.qmail@theseus.mathematik.uni-ulm.de>
Cc: nejataydin@superonline.com,
 gcc-gnats@gcc.gnu.org,
 gcc@gcc.gnu.org,
 gcc-bugs@gcc.gnu.org,
 nobody@gcc.gnu.org
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Message-Id: <200212131449.01528.ebotcazou@libertysurf.fr>
X-SW-Source: 2002-12/txt/msg00722.txt.bz2

> This transformation is IMHO illegal because there is no way to make the
> comparison in general equivialent to that in the original for loop.
> If p is initially 0x7ffffffc the comparison must be treated as unsigned,
> however, if p is initially 0xfffffffc the comparison must be treated as
> signed.

Well-known deficiency of the strength reduction pass (see the testcase=20
testsuite/gcc.c-torture/execute/loop-2e.c which is XFAILed on x86 at -Os).

--=20
Eric Botcazou