From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 115824 invoked by alias); 25 Oct 2017 20:01:05 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Received: (qmail 115815 invoked by uid 89); 25 Oct 2017 20:01:05 -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=reduces, Hx-languages-length:1437, H*c:HHHHH 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; Wed, 25 Oct 2017 20:01:04 +0000 Received: from nat-ies.mentorg.com ([192.94.31.2] helo=SVR-IES-MBX-03.mgc.mentorg.com) by relay1.mentorg.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-SHA384:256) id 1e7RrK-0000zT-Om from joseph_myers@mentor.com ; Wed, 25 Oct 2017 13:01:02 -0700 Received: from digraph.polyomino.org.uk (137.202.0.87) by SVR-IES-MBX-03.mgc.mentorg.com (139.181.222.3) with Microsoft SMTP Server (TLS) id 15.0.1320.4; Wed, 25 Oct 2017 21:00:59 +0100 Received: from jsm28 (helo=localhost) by digraph.polyomino.org.uk with local-esmtp (Exim 4.86_2) (envelope-from ) id 1e7RrE-00056A-1T; Wed, 25 Oct 2017 20:00:56 +0000 Date: Wed, 25 Oct 2017 20:04:00 -0000 From: Joseph Myers To: CC: Subject: Re: [PATCH] PR libgcc/59714 complex division is surprising on aarch64 In-Reply-To: Message-ID: References: <1508952211-12992-1-git-send-email-vladimir.mezentsev@oracle.com> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="-1152306461-1424691898-1508961656=:18935" X-ClientProxiedBy: svr-ies-mbx-01.mgc.mentorg.com (139.181.222.1) To SVR-IES-MBX-03.mgc.mentorg.com (139.181.222.3) X-SW-Source: 2017-10/txt/msg01842.txt.bz2 ---1152306461-1424691898-1508961656=:18935 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8BIT Content-length: 1379 On Wed, 25 Oct 2017, vladimir.mezentsev@oracle.com wrote: > On 10/25/2017 10:28 AM, Joseph Myers wrote: > > On Wed, 25 Oct 2017, vladimir.mezentsev@oracle.com wrote: > > > >> +# Disable FMA (floating-point multiply-add) instructions for complex division. > >> +# These instructions can produce different result if two operations executed separately. > >> +LIBGCC2_FFP_CONTRAST_CFLAGS = -ffp-contract=off > >> +LIB2_DIV3_FUNCS = _divdc3 _divhc3 _divsc3 > > Without regard to whether the change is appropriate in the first place, > > I'm doubtful of the logic for selecting floating-point modes. I'd expect > > something that applies to all floating-point modes. Even if nothing has > > fused XFmode operations, some architectures (e.g. s390, powerpc) have > > fused operations on TFmode / KFmode. > >    Hello Joseph and GCC-team, > Different people are giving me different directions. > I am glad to change my fix but please provide clear directions on how > you want to see it. I am unconvinced of the need for a change that reduces accuracy in some cases to make things less surprising in other cases. I am clear that if there is to be such a change, it should be made consistently for all affected floating-point modes, including TFmode / KFmode where available, since those have fused operations on some platforms. -- Joseph S. Myers joseph@codesourcery.com ---1152306461-1424691898-1508961656=:18935--