From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 97872 invoked by alias); 6 Feb 2018 17:34:30 -0000 Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org Received: (qmail 97860 invoked by uid 89); 6 Feb 2018 17:34:30 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.0 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_NONE,SPF_PASS,URIBL_RED autolearn=ham version=3.3.2 spammy= X-HELO: relay1.mentorg.com Received: from relay1.mentorg.com (HELO relay1.mentorg.com) (192.94.38.131) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 06 Feb 2018 17:34:29 +0000 Received: from nat-ies.mentorg.com ([192.94.31.2] helo=svr-ies-mbx-01.mgc.mentorg.com) by relay1.mentorg.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-SHA384:256) id 1ej78V-0001MX-JN from joseph_myers@mentor.com ; Tue, 06 Feb 2018 09:34:27 -0800 Received: from digraph.polyomino.org.uk (137.202.0.87) by svr-ies-mbx-01.mgc.mentorg.com (139.181.222.1) with Microsoft SMTP Server (TLS) id 15.0.1320.4; Tue, 6 Feb 2018 17:34:24 +0000 Received: from jsm28 (helo=localhost) by digraph.polyomino.org.uk with local-esmtp (Exim 4.86_2) (envelope-from ) id 1ej78R-0005IU-Mr; Tue, 06 Feb 2018 17:34:23 +0000 Date: Tue, 06 Feb 2018 17:34:00 -0000 From: Joseph Myers To: Vincent Lefevre CC: Subject: Re: GCC 8.0.0 Status Report (2018-01-15), Trunk in Regression and Documentation fixes only mode In-Reply-To: <20180206162831.GB10578@zira.vinc17.org> Message-ID: References: <962d449e-3ab8-f9ad-7a2d-8793ae0188d6@sky.com> <8441a3a4-de80-cf19-f9fe-2251fb9064e2@ubuntu.com> <20180206161438.GA10578@zira.vinc17.org> <20180206162831.GB10578@zira.vinc17.org> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-ClientProxiedBy: svr-ies-mbx-01.mgc.mentorg.com (139.181.222.1) To svr-ies-mbx-01.mgc.mentorg.com (139.181.222.1) X-SW-Source: 2018-02/txt/msg00050.txt.bz2 On Tue, 6 Feb 2018, Vincent Lefevre wrote: > Well, if I add -std=c99 or -std=c11, the failure disappears. The > reason is that GCC generates a FMA (indeed, this new machine has > a FMA), but this occurs across different C statements. So, maybe > not a bug, but a bad feature, IMHO. Use -ffp-contract=off to disable all contraction, or -ffp-contract=on to disable it between statements (which currently actually disables all contraction, as the FMA generation doesn't know what was originally a single source expression). The default in the absence of such -std options is -ffp-contract=fast (allowing contraction including between different statements). -- Joseph S. Myers joseph@codesourcery.com