From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 121914 invoked by alias); 9 Sep 2015 06:08:14 -0000 Mailing-List: contact gcc-help-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-help-owner@gcc.gnu.org Received: (qmail 121904 invoked by uid 89); 9 Sep 2015 06:08:14 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.5 required=5.0 tests=AWL,BAYES_00,FREEMAIL_FROM,RCVD_IN_DNSWL_LOW,SPF_PASS autolearn=ham version=3.3.2 X-HELO: mail-yk0-f171.google.com Received: from mail-yk0-f171.google.com (HELO mail-yk0-f171.google.com) (209.85.160.171) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-GCM-SHA256 encrypted) ESMTPS; Wed, 09 Sep 2015 06:08:12 +0000 Received: by ykei199 with SMTP id i199so154472727yke.0 for ; Tue, 08 Sep 2015 23:08:09 -0700 (PDT) X-Received: by 10.170.217.68 with SMTP id j65mr35001375ykf.61.1441778889820; Tue, 08 Sep 2015 23:08:09 -0700 (PDT) MIME-Version: 1.0 Received: by 10.37.231.7 with HTTP; Tue, 8 Sep 2015 23:07:50 -0700 (PDT) In-Reply-To: <55EF53AC.9020306@gmail.com> References: <55EF53AC.9020306@gmail.com> From: Mathieu Malaterre Date: Wed, 09 Sep 2015 06:08:00 -0000 Message-ID: Subject: Re: -ffloat-store behavior (Re: Susprising behavior of gcc on x86 (-m32)) To: =?UTF-8?B?TWFudWVsIEzDs3Blei1JYsOhw7Fleg==?= Cc: gcc-help , Andrew Haley , Markus Trippelsdorf Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-IsSubscribed: yes X-SW-Source: 2015-09/txt/msg00039.txt.bz2 Manuel, On Tue, Sep 8, 2015 at 11:31 PM, Manuel L=C3=B3pez-Ib=C3=A1=C3=B1ez wrote: > On 08/09/15 22:05, Mathieu Malaterre wrote: >> >> >> Ok, I think I understand now. -O0 did produce code that is compatible >> with -ffloat-store. However I am still required to use -ffloat-store >> (explicitly) for any other optimization (at least required with -O2 in >> my case). > > > You are not required to use -ffloat-store, neither is -ffloat-store > guaranteed to work. Please read https://gcc.gnu.org/wiki/FAQ#PR323 > > (If there is something that is not explained there, it would be better to > expand the answer rather than reply here with bits of info.) Thanks for the link. However -in my case- the compile option `-fexcess-precision=3Dstandard` does produce the same code as `-ffloat-store`. At least for [...] double div; /* OPJ_FLOAT64 */ div =3D dd / dr; if (div >=3D thresh) [...] Is there a longer description for `-fexcess-precision=3Dstandard` which explains case of failures ? Thanks again,