From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 28921 invoked by alias); 6 Aug 2019 12:30:58 -0000 Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Received: (qmail 28623 invoked by uid 89); 6 Aug 2019 12:30:41 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-0.5 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_NONE,RCVD_IN_SEMBLACK,SPF_FAIL,SPF_HELO_PASS autolearn=no version=3.3.1 spammy=__m128d, HContent-Transfer-Encoding:8bit X-HELO: gateway30.websitewelcome.com Received: from gateway30.websitewelcome.com (HELO gateway30.websitewelcome.com) (192.185.197.25) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 06 Aug 2019 12:30:39 +0000 Received: from cm17.websitewelcome.com (cm17.websitewelcome.com [100.42.49.20]) by gateway30.websitewelcome.com (Postfix) with ESMTP id CB53021146 for ; Tue, 6 Aug 2019 07:30:36 -0500 (CDT) Received: from gator4009.hostgator.com ([192.185.4.20]) by cmsmtp with SMTP id uybsh2zZ890onuybsht6aF; Tue, 06 Aug 2019 07:30:36 -0500 Received: from 0190101441.0.fullrate.ninja ([2.110.93.203]:57951 helo=[192.168.1.49]) by gator4009.hostgator.com with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.92) (envelope-from ) id 1huybs-000Kgb-DJ for cygwin@cygwin.com; Tue, 06 Aug 2019 07:30:36 -0500 To: "cygwin@cygwin.com" From: Agner Fog Subject: Inefficient use of 64-bit addresses in Clang Message-ID: <578eb489-9391-9009-82ad-676eeb4c1c92@agner.org> Date: Tue, 06 Aug 2019 12:30:00 -0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-IsSubscribed: yes X-SW-Source: 2019-08/txt/msg00071.txt.bz2 Clang is using 64-bit absolute addresses when accessing static data in 64-bit mode. This is inefficient because it requires an extra 10-bytes long instruction for loading an address into a register every time it needs to access static data. All other compilers use relative addresses. Example: > #include > > __m128d test (__m128d a) { >     __m128d b = _mm_add_pd(a, _mm_set1_pd(1.5)); >     __m128d c = _mm_mul_pd(b, _mm_set1_pd(2.5)); >     return c; > } Assembly output: > .LCPI0_0: >     .quad    4609434218613702656     # double 1.5 >     .quad    4609434218613702656     # double 1.5 > .LCPI0_1: >     .quad    4612811918334230528     # double 2.5 >     .quad    4612811918334230528     # double 2.5 >     .text >     .globl    _Z4testDv2_d >     .p2align    4, 0x90 > _Z4testDv2_d:                           # @_Z4testDv2_d > # BB#0: >     vmovapd    (%rcx), %xmm0 >     movabsq    $.LCPI0_0, %rax >     vaddpd    (%rax), %xmm0, %xmm0 >     movabsq    $.LCPI0_1, %rax >     vmulpd    (%rax), %xmm0, %xmm0 >     retq Linux Clang uses 32-bit relative addresses: >     vaddpd    .LCPI0_0(%rip), %xmm0, %xmm0 >     vmulpd    .LCPI0_1(%rip), %xmm0, %xmm0 >     retq -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple