From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 9759 invoked by alias); 30 Oct 2015 10:24:15 -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 9749 invoked by uid 89); 30 Oct 2015 10:24:14 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.4 required=5.0 tests=AWL,BAYES_00,FREEMAIL_FROM,RCVD_IN_DNSWL_LOW,SPF_PASS autolearn=ham version=3.3.2 X-HELO: mail-lb0-f177.google.com Received: from mail-lb0-f177.google.com (HELO mail-lb0-f177.google.com) (209.85.217.177) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-GCM-SHA256 encrypted) ESMTPS; Fri, 30 Oct 2015 10:24:13 +0000 Received: by lbbes7 with SMTP id es7so47154673lbb.2 for ; Fri, 30 Oct 2015 03:24:10 -0700 (PDT) MIME-Version: 1.0 X-Received: by 10.112.119.133 with SMTP id ku5mr3515496lbb.1.1446200650217; Fri, 30 Oct 2015 03:24:10 -0700 (PDT) Received: by 10.25.135.138 with HTTP; Fri, 30 Oct 2015 03:24:10 -0700 (PDT) In-Reply-To: <56257F53.2000905@samsung.com> References: <56257F53.2000905@samsung.com> Date: Fri, 30 Oct 2015 10:26:00 -0000 Message-ID: Subject: Re: [PATCH][AArch64] Replace insn to zero up DF register From: Marcus Shawcroft To: Evandro Menezes Cc: "gcc-patches@gcc.gnu.org" , Marcus Shawcroft , Kyrill Tkachov Content-Type: text/plain; charset=UTF-8 X-IsSubscribed: yes X-SW-Source: 2015-10/txt/msg03347.txt.bz2 On 20 October 2015 at 00:40, Evandro Menezes wrote: > In the existing targets, it seems that it's always faster to zero up a DF > register with "movi %d0, #0" instead of "fmov %d0, xzr". > > This patch modifies the respective pattern. Hi Evandro, This patch changes the generic, u architecture independent instruction selection. The ARM ARM (C3.5.3) makes a specific recommendation about the choice of instruction in this situation and the current implementation in GCC follows that recommendation. Wilco has also picked up on this issue he has the same patch internal to ARM along with an ongoing discussion with ARM architecture folk regarding this recommendation. I'm reluctant to take this patch right now on the basis that it runs contrary to ARM ARM recommendation pending the conclusion of Wilco's discussion with ARM architecture folk. Cheers /Marcus