From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from devianza.investici.org (devianza.investici.org [198.167.222.108]) by sourceware.org (Postfix) with ESMTPS id A76353858C2B for ; Sun, 6 Nov 2022 10:53:20 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org A76353858C2B Authentication-Results: sourceware.org; dmarc=pass (p=reject dis=none) header.from=autistici.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=autistici.org Received: from 1.mail-backend.investici.org (unknown [10.0.0.11]) by devianza.investici.org (Postfix) with ESMTP id 4N4rnB4JGmz6vCr for ; Sun, 6 Nov 2022 10:53:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=autistici.org; s=stigmate; t=1667731998; bh=sFemf8HpE2EjottUYc3ZZiMrbseIDwfO6v9h8xKOBo4=; h=Date:From:To:Subject:From; b=s21AzbvTqV40q7nzaJoe6pDg8++0R45NSaYFuCMDaKL01zWFoEHkZPB8SoNlolQXC f0n8bj0aP94yJn6SAm+SeTNLGxJ//EXo61Ojiu4iGwyW59Bz+CMvJ3vPc4KCcjI3Ro gTdWsP1/DtB3l1PfWh0qq+2DB4VBVrgsv1+pcfok= Received: from 1.webmail.investici.org (localhost [127.0.0.1]) (Authenticated sender: i.nixman@autistici.org) by 1.mail-backend.investici.org (Postfix) with ESMTPA id 4N4rnB3Gp5z5tFZ for ; Sun, 6 Nov 2022 10:53:18 +0000 (UTC) MIME-Version: 1.0 Date: Sun, 06 Nov 2022 10:53:18 +0000 From: i.nixman@autistici.org To: gcc-help@gcc.gnu.org Subject: simd, redundant pcmpeqb and pxor User-Agent: Roundcube Webmail Message-ID: X-Sender: i.nixman@autistici.org Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,SPF_HELO_PASS,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: Hello, look at this example(https://godbolt.org/z/TnGMsfMs6): ``` auto foo(const char *p) { const auto substr = _mm_loadu_si128((const __m128i *)p); return _mm_cmplt_epi8(substr, _mm_set1_epi8('0')); } ``` and to the generated asm: ``` 1: foo(char const*): 2: movdqu xmm0, XMMWORD PTR [rdi] 3: pxor xmm1, xmm1 4: pcmpgtb xmm0, XMMWORD PTR .LC0[rip] 5: pcmpeqb xmm0, xmm1 6: ret ``` look at line 5. is there any reason for `pcmpeqb` instruction? just for info, clang's output(https://godbolt.org/z/MPnvEMdhr): ``` 1: foo(char const*): 2: movdqu xmm1, xmmword ptr [rdi] 3: movdqa xmm0, xmmword ptr [rip + .LCPI0_0] 4: pcmpgtb xmm0, xmm1 5: ret ``` best!