From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yb1-xb2c.google.com (mail-yb1-xb2c.google.com [IPv6:2607:f8b0:4864:20::b2c]) by sourceware.org (Postfix) with ESMTPS id 720013858C1F for ; Mon, 7 Nov 2022 06:29:47 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 720013858C1F Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-yb1-xb2c.google.com with SMTP id j130so12430415ybj.9 for ; Sun, 06 Nov 2022 22:29:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=VXzUzOPZGY0w7SFN55jJgIcxIVzGw3+AaTIGuqdaIhw=; b=DYE0nm6sfFw4q0zry7NinG5aD/M8KVZONOthA14yMsr8AqMewCcEEyrhxOTSokcELD +DUKKZY38YCuWhjLZ16QJv6mMush9PffPiiILqkuTmGwe/mqWwM8J9WRid3uihhXEghc D1nJ7DzcHu/Iukw7rlXu14/QpQ3YIXPgrb+rMvLOb8ZgSihlUEyWn1pKmLD8Y9eHHKcN ZHYA55ZnVCDfPnXgGKdes6pdkiGsCKpisFyovQrTevA/V80M5kkoq16nefxMLwVoge2g 5Ql91Isfb0TJfLefpQK7BiqrO2zaPjZved8PiGA6Vf1ixgqy7NM4MdLGbiYElEGa/B8R WlQg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=VXzUzOPZGY0w7SFN55jJgIcxIVzGw3+AaTIGuqdaIhw=; b=6JVpgNkFykoG5AYeR0k+6sWwdAMGdi+2VXscipEjHPcJLopGfDjPUFr5Eb6p4PVx4S N9pZXikeka/W+hlHMkT5eshYAX/xHKs9Pb5yqNHfeoJALlI3GreACUYsK7xZBW9Xq7Zm 2f1CKMn6D3hC2udXyDT2/vw5bN/pTYtnBhCVeqxszhYBr6oqMA+irPp3Yp08bVKGqIwv VBr63EJruqfSUy/EO4/Qr8S2O6WGonxel3HqtzfGxsnpjPJdb9iaNm81QJzEr89Lfbzq HrIiQ9l9/FvKMfoQ+34NKUOWAJGYsYiSvRfiw/YuXvWW/xkvMwgAZGBvwjazzVbjX+Y1 558g== X-Gm-Message-State: ANoB5pn/0ZSG1QD19AqUILfVXjkywJfdJ5qteqk/RybULkm/J0K1Xbd9 i/iL538oj+4VBLfdLeJLOYAqS4MPj43lk+joTDI= X-Google-Smtp-Source: AA0mqf6PRaDeqHvktztpRJGsOXY3+yUoR7EiZG4OIRhFA3G+PoeEb9SXyOADOwyR5w9fjLzuX47CZdpQW0ZOngAutn8= X-Received: by 2002:a25:4c6:0:b0:6d6:fb7a:a4d7 with SMTP id 189-20020a2504c6000000b006d6fb7aa4d7mr126483ybe.601.1667802586897; Sun, 06 Nov 2022 22:29:46 -0800 (PST) MIME-Version: 1.0 References: <71218c0c63bfa161f9f828cbf312debe@autistici.org> In-Reply-To: <71218c0c63bfa161f9f828cbf312debe@autistici.org> From: Hongtao Liu Date: Mon, 7 Nov 2022 14:32:55 +0800 Message-ID: Subject: Re: simd, redundant pcmpeqb and pxor To: i.nixman@autistici.org Cc: gcc-help@gcc.gnu.org Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,KAM_SHORT,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,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: On Mon, Nov 7, 2022 at 2:26 PM wrote: > > On 2022-11-07 03:32, Hongtao Liu wrote: > > On Sun, Nov 6, 2022 at 6:54 PM i.nixman--- via Gcc-help > > wrote: > >> > >> > >> 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? > > hi, > > > Looks like a mis optimization from > > > > _4 = VIEW_CONVERT_EXPR<__v16qs>(_7); > > _3 = _4 <= { 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, > > 47, 47 }; > > _5 = VIEW_CONVERT_EXPR(_3); --- this? > > > > Could you open a bugzilla for it > > https://gcc.gnu.org/bugzilla/ > > sure, but for which component? Let's put it as rtl-optimization first. > > > > >> > >> 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! -- BR, Hongtao