From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 7209 invoked by alias); 27 Feb 2013 16:34:46 -0000 Received: (qmail 7061 invoked by uid 22791); 27 Feb 2013 16:34:44 -0000 X-SWARE-Spam-Status: No, hits=-5.2 required=5.0 tests=AWL,BAYES_00,DKIM_SIGNED,DKIM_VALID,FREEMAIL_ENVFROM_END_DIGIT,FREEMAIL_FROM,KHOP_RCVD_TRUST,KHOP_SPAMHAUS_DROP,KHOP_THREADED,RCVD_IN_DNSWL_LOW,RCVD_IN_HOSTKARMA_YE,TW_CL X-Spam-Check-By: sourceware.org Received: from mail-vc0-f181.google.com (HELO mail-vc0-f181.google.com) (209.85.220.181) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 27 Feb 2013 16:34:39 +0000 Received: by mail-vc0-f181.google.com with SMTP id f13so503119vcb.26 for ; Wed, 27 Feb 2013 08:34:38 -0800 (PST) X-Received: by 10.220.119.147 with SMTP id z19mr1080803vcq.69.1361982878512; Wed, 27 Feb 2013 08:34:38 -0800 (PST) Received: from anchor.twiddle.net (50-194-63-110-static.hfc.comcastbusiness.net. [50.194.63.110]) by mx.google.com with ESMTPS id qj8sm1183118veb.2.2013.02.27.08.34.35 (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 27 Feb 2013 08:34:37 -0800 (PST) Message-ID: <512E3599.5000504@twiddle.net> Date: Wed, 27 Feb 2013 16:34:00 -0000 From: Richard Henderson User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130219 Thunderbird/17.0.3 MIME-Version: 1.0 To: =?ISO-8859-1?Q?M=E5ns_Rullg=E5rd?= CC: libc-ports@sourceware.org, Joseph Myers Subject: Re: [PATCH 19/26] arm: Add optimized ffs for armv6t2 References: <1361934986-17018-1-git-send-email-rth@twiddle.net> <1361934986-17018-20-git-send-email-rth@twiddle.net> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-IsSubscribed: yes Mailing-List: contact libc-ports-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: libc-ports-owner@sourceware.org X-SW-Source: 2013-02/txt/msg00101.txt.bz2 On 02/27/2013 07:51 AM, Måns Rullgård wrote: > Richard Henderson writes: > >> +ENTRY(__ffs) >> + cmp r0, #0 >> + ittt ne >> + rbitne r0, r0 >> + clzne r0, r0 >> + addne r0, r0, #1 >> + bx lr >> +END(__ffs) > > Making the RBIT unconditional (bit-reverse of zero is still zero) is > better since it reduces dependencies between instructions. Depending on > microarchitecture details, this might save a cycle. > Fair enough. Consider this change made for any next round. r~