From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail3-relais-sop.national.inria.fr (mail3-relais-sop.national.inria.fr [192.134.164.104]) by sourceware.org (Postfix) with ESMTPS id D08293858D3C for ; Thu, 5 May 2022 17:50:03 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org D08293858D3C Received-SPF: SoftFail (mail3-relais-sop.national.inria.fr: domain of Paul.Zimmermann@inria.fr is inclined to not designate 152.81.10.51 as permitted sender) identity=mailfrom; client-ip=152.81.10.51; receiver=mail3-relais-sop.national.inria.fr; envelope-from="Paul.Zimmermann@inria.fr"; x-sender="Paul.Zimmermann@inria.fr"; x-conformance=spf_only; x-record-type="v=spf1"; x-record-text="v=spf1 ip4:192.134.164.0/24 mx ~all" Received-SPF: None (mail3-relais-sop.national.inria.fr: no sender authenticity information available from domain of postmaster@tomate) identity=helo; client-ip=152.81.10.51; receiver=mail3-relais-sop.national.inria.fr; envelope-from="Paul.Zimmermann@inria.fr"; x-sender="postmaster@tomate"; x-conformance=spf_only X-IronPort-AV: E=Sophos;i="5.91,201,1647298800"; d="scan'208";a="13313753" Received: from tomate.loria.fr (HELO tomate) ([152.81.10.51]) by mail3-relais-sop.national.inria.fr with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 May 2022 19:50:02 +0200 Date: Thu, 05 May 2022 19:50:01 +0200 Message-Id: From: Paul Zimmermann To: gcc-help@gcc.gnu.org Cc: stephane.glondu@inria.fr, amonakov@ispras.ru, gcc-help@gcc.gnu.org, sibid@uvic.ca In-Reply-To: <4d36d96-2de9-f8ac-2d52-ea32b1cc6d9@grove.saclay.inria.fr> (message from Marc Glisse on Thu, 5 May 2022 16:41:28 +0200 (CEST)) Subject: Re: slowdown with -std=gnu18 with respect to -std=c99 References: <9f7e3aa9-8d46-1fbb-75b-1c8ad9a667f@ispras.ru> <4d36d96-2de9-f8ac-2d52-ea32b1cc6d9@grove.saclay.inria.fr> MIME-version: 1.0 Content-type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-3.0 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, KAM_NUMSUBJECT, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gcc-help@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-help mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 05 May 2022 17:50:05 -0000 > Date: Thu, 5 May 2022 16:41:28 +0200 (CEST) > From: Marc Glisse > > On Thu, 5 May 2022, Stéphane Glondu via Gcc-help wrote: > > > As additional data points, the performance with several versions of gcc > > (as packaged in Debian testing/unstable): > > > > | gcc-9 | gcc-10 | gcc-11 | gcc-12 | > > ------------|-------|--------|--------|--------| > > -std=c99 | 24 | 23.5 | 23 | 23 | > > -std=gnu18 | 43 | 16.8 | 38 | 38 | > > > > One can see that the performance stays relatively constant with > > -std=c99, but varies significantly with -std=gnu18. > > Could you compare with c18 or gnu99, to determine if the issue is with c > vs gnu (most likely since fma seems important) or 99 vs 18? yes it is easy. On another i5: | gcc-9 | gcc-10 | gcc-11 | ------------|-------|--------|--------| -std=c99 | 24.3 | 23.8 | 23.8 | -std=c18 | 24.4 | 23.8 | 23.9 | -std=gnu99 | 42.9 | 19.2 | 35.0 | -std=gnu18 | 42.9 | 19.2 | 35.0 | Thus the issue is definitely c vs gnu. Paul