From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-x22c.google.com (mail-lj1-x22c.google.com [IPv6:2a00:1450:4864:20::22c]) by sourceware.org (Postfix) with ESMTPS id B973F385B51B for ; Wed, 22 Mar 2023 13:58:23 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org B973F385B51B Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-lj1-x22c.google.com with SMTP id h9so19096711ljq.2 for ; Wed, 22 Mar 2023 06:58:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1679493502; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=fqj69cQuijaE5atQcoEIpFtON1tQwjNrpOWnWZfqlzo=; b=de9HIpB9ALdzyPC0539B/xBmzdiepvCS3hpHt0dF266s0zkP1+YefwvOOqpGofVDpf inHz8ojr0/NTnjXbjC6RseLdeZsWDniJ8bXqo7Jt919jswuPpwfEXzqJpR3u2/gw08Cj dzU4HBe3xEjIcdzxGqM7i4f0SjIE5WwcQNp3mXIABKSRzFxZyk/18z+PTDLErGZ1rCvJ 2YLAsA0vXZ73DdewlqgCD8b6kvxwa2bLH37Oc26w6C4kkYfAwH46yNwUyMxbxYIl9UjA iSDRUTDaKSYIWvpsgjjBRI9UyRYrk7HCacGEK8g2xft/OQo+8PnZVsJKEFsWutAZAZgE eWSw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1679493502; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=fqj69cQuijaE5atQcoEIpFtON1tQwjNrpOWnWZfqlzo=; b=Fv6C9b5x9RQ0AI420UgLjarsanEegmVqnaEa9NVQSR88JLPS04uDtWHZHSeuO/ISdm UXDMyYuTbf+NLdLOU7XycCgCcTHdr7cOroam1Eqb8+bYdT2RUxxikadYJKF+llAeLrtk FqYrYllkrn3LSk9tjbrRvK7ukkVhoPrYI64AXpXMrm3ygmLbT5j3tiAKxxjryp8/5wDS IPwx0x/srrBRzQwdpnAsPvPK2wfTVGww/u7rNbtbranLC/YzPxAkh5eWqWDxF52tfYRM KYfxLD68xHxm37zkBCOEtUNst4KxMR0+A4lc88HuypZdduiI2ymtHzsSkmWFeI+9OgJC etnA== X-Gm-Message-State: AO0yUKUwTKmyUspaDXsJAf65b0tLKX/DeNSoJ6w47YxsKiyKyLixWEk3 M9rl7vKp1GIn+2jHDFEXVJQGFC4jqDygFQ/Uxk4= X-Google-Smtp-Source: AK7set+CTp4NGy+8KbWBRdnHC72nM7KvrRIkfrqJR4MWpO7+BZ+XXTsh2vdjQgPmd2jOLyt8+3SDVPDF/nskjk6lFOs= X-Received: by 2002:a2e:901a:0:b0:299:aa7a:94c8 with SMTP id h26-20020a2e901a000000b00299aa7a94c8mr2014760ljg.10.1679493502064; Wed, 22 Mar 2023 06:58:22 -0700 (PDT) MIME-Version: 1.0 References: <6659A77B-DA2F-40A6-BDBD-E8B29B9E901D@oracle.com> <87384938-FDB1-487B-8B03-7787996435B2@comcast.net> <7C6B7ED7-7AA4-47EF-8E44-E3AD81BF3E29@oracle.com> <4a670847-9728-e0cb-46f3-d476839f7cd4@gmail.com> <435162cb-99b5-1204-d723-ec3800e78997@ispras.ru> In-Reply-To: <435162cb-99b5-1204-d723-ec3800e78997@ispras.ru> From: Richard Biener Date: Wed, 22 Mar 2023 14:57:49 +0100 Message-ID: Subject: Re: Should -ffp-contract=off the default on GCC? To: Alexander Monakov Cc: Jeff Law , gcc-patches@gcc.gnu.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-1.2 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Wed, Mar 22, 2023 at 1:26=E2=80=AFPM Alexander Monakov wrote: > > > On Wed, 22 Mar 2023, Richard Biener wrote: > > > I think it's even less realistic to expect users to know the details of > > floating-point math. So I doubt any such sentence will be helpful > > besides spreading some FUD? > > I think it's closer to "fundamental notions" rather than "details". For > users who bother to read the GCC manual there's a decent chance it wouldn= 't > be for naught. > > For documentation, I was thinking > > Together with -fexcess-precision=3Dstandard, -ffp-contract=3Doff > is necessary to ensure that rounding of intermediate results to precisi= on > implied by the source code and the FLT_EVAL_METHOD macro is not > omitted by the compiler. that sounds good to me > Alexander