From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-23.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7C598C433DB for ; Tue, 19 Jan 2021 23:14:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4F80222CAD for ; Tue, 19 Jan 2021 23:14:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726212AbhASXMd (ORCPT ); Tue, 19 Jan 2021 18:12:33 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52676 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726828AbhASXLQ (ORCPT ); Tue, 19 Jan 2021 18:11:16 -0500 Received: from mail-pf1-x42d.google.com (mail-pf1-x42d.google.com [IPv6:2607:f8b0:4864:20::42d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3E4F0C061757 for ; Tue, 19 Jan 2021 15:10:36 -0800 (PST) Received: by mail-pf1-x42d.google.com with SMTP id q20so13276593pfu.8 for ; Tue, 19 Jan 2021 15:10:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=yc+iZPAoEfYuwC32vfILEtYohiPDc+ecLJoHB/5av04=; b=LhWvTljfReic7CKreAe27m2eXjgN5quQoLpBNkyfD6kyC7fvFN67x3WzgydizQeZpX QHUr8pyMOWWgsWTCI9EZEPR4VVdIR53EqFLrzymt0haqh8jqXbt2liRnn9LA9h23/si5 zs5hHFg+YXCudqbmyHMoAeHTK2FqjihtHpq0AiB2nDC2ON/dAUKfYDX5MQjOurHEJAuC CF/jFlZLN6cnymBnAA8zs27FN2pIz9LWC82+EZh7BGBKqTOhBN0tjr7NGAWXihIjdaPc QvioPD7khw5WFKknTbTOJAjI5NeqT+uWoRDfKpKO9hkmHBnoBWXYgjlgTKT/X5/VmKl9 ruAA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=yc+iZPAoEfYuwC32vfILEtYohiPDc+ecLJoHB/5av04=; b=MPcqoLQJH0d/n31hqXg7EP6j8S0scMFNHUXG+AKoW4fu2CgNRy/Q3RPzknsQfmL8GM QMdlmDcVrMMX0q928eenzawZr07x64674nsJxa0R4BCEXEICYCLif73/tJDP/sbXGPjw M/ff0X7fI0mAmAa5iB+fYWdzRqBVraKVjmMyL7c/CF0RO6BPeq1910tRycwbM6VFKIcK xO0q6MacExdtIdGBqgf/PaPMM+GDJ2j1kJiQ/QCiPNe5aChEFtjmRiTq1nAw6h6/cdc+ 3HvLavxAQH911lbDuk8PBdhOnQI8yHPG70ttgiS6UignPDuNIC2Ue7vIZaLbeAM0KLN1 9HXA== X-Gm-Message-State: AOAM5306MKKAuiDOjWlReC0jsQ/w8l16pfBteCzXlbKqS3Ikx7sXDbh0 8PcUmRqCwoqTVQpQmzgs7R3XPoRdUifWf6URwu6bzQ== X-Google-Smtp-Source: ABdhPJytR/pnMLVH5rNG9YFjjCcNPc3W4wII4uEWPMjecfYVxyH642jAvxQIwOyx25SMyyFNuCCgogtDVv2Ga93zryk= X-Received: by 2002:a63:5701:: with SMTP id l1mr6516095pgb.381.1611097835433; Tue, 19 Jan 2021 15:10:35 -0800 (PST) MIME-Version: 1.0 References: <20210119131724.308884-1-adrian.ratiu@collabora.com> <20210119131724.308884-2-adrian.ratiu@collabora.com> In-Reply-To: From: Nick Desaulniers Date: Tue, 19 Jan 2021 15:10:24 -0800 Message-ID: Subject: Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning To: Arnd Bergmann Cc: Adrian Ratiu , Arnd Bergmann , Linux ARM , Nathan Chancellor , Russell King , Ard Biesheuvel , Arvind Sankar , clang-built-linux , Collabora Kernel ML , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 19, 2021 at 2:04 PM Nick Desaulniers wrote: > > On Tue, Jan 19, 2021 at 1:35 PM Arnd Bergmann wrote: > > > > On Tue, Jan 19, 2021 at 10:18 PM 'Nick Desaulniers' via Clang Built > > Linux wrote: > > > > > > On Tue, Jan 19, 2021 at 5:17 AM Adrian Ratiu wrote: > > > > diff --git a/arch/arm/lib/xor-neon.c b/arch/arm/lib/xor-neon.c > > > > index b99dd8e1c93f..f9f3601cc2d1 100644 > > > > --- a/arch/arm/lib/xor-neon.c > > > > +++ b/arch/arm/lib/xor-neon.c > > > > @@ -14,20 +14,22 @@ MODULE_LICENSE("GPL"); > > > > #error You should compile this file with '-march=armv7-a -mfloat-abi=softfp -mfpu=neon' > > > > #endif > > > > > > > > +/* > > > > + * TODO: Even though -ftree-vectorize is enabled by default in Clang, the > > > > + * compiler does not produce vectorized code due to its cost model. > > > > + * See: https://github.com/ClangBuiltLinux/linux/issues/503 > > > > + */ > > > > +#ifdef CONFIG_CC_IS_CLANG > > > > +#warning Clang does not vectorize code in this file. > > > > +#endif > > > > > > Arnd, remind me again why it's a bug that the compiler's cost model > > > says it's faster to not produce a vectorized version of these loops? > > > I stand by my previous comment: https://bugs.llvm.org/show_bug.cgi?id=40976#c8 > > > > The point is that without vectorizing the code, there is no point in building > > both the default xor code and a "neon" version that has to save/restore > > the neon registers but doesn't actually use them. > > > > Arnd > > Thoughts? Also, Nathan brings up my previous point about restrict. > This would benefit both GCC and Clang as they would not produce 2 > "versions" of the loop; one vectorized if the std::distance between x > & y >= 8, one scalar otherwise. But the callers would have to ensure > no overlap otherwise UB. > > diff --git a/include/asm-generic/xor.h b/include/asm-generic/xor.h > index b62a2a56a4d4..7db16adc7d89 100644 > --- a/include/asm-generic/xor.h > +++ b/include/asm-generic/xor.h > @@ -7,12 +7,21 @@ > > #include > > +/* Overrule LLVM's cost model in order to always produce a vectorized loop > + * version. > + */ > +#if defined(__clang__) && defined(CONFIG_ARM) > +#define FORCE_VECTORIZE _Pragma("clang loop vectorize(enable)") > +#else > +#define CLANG_FORCE_VECTORIZE ^ err, I had renamed it, but missed this. Should have been `FORCE_VECTORIZE` but you catch the drift. > +#endif > + > static void > xor_8regs_2(unsigned long bytes, unsigned long *p1, unsigned long *p2) > { > long lines = bytes / (sizeof (long)) / 8; > > - do { > + FORCE_VECTORIZE do { > p1[0] ^= p2[0]; > p1[1] ^= p2[1]; > p1[2] ^= p2[2]; > @@ -32,7 +41,7 @@ xor_8regs_3(unsigned long bytes, unsigned long *p1, > unsigned long *p2, > { > long lines = bytes / (sizeof (long)) / 8; > > - do { > + FORCE_VECTORIZE do { > p1[0] ^= p2[0] ^ p3[0]; > p1[1] ^= p2[1] ^ p3[1]; > p1[2] ^= p2[2] ^ p3[2]; > @@ -53,7 +62,7 @@ xor_8regs_4(unsigned long bytes, unsigned long *p1, > unsigned long *p2, > { > long lines = bytes / (sizeof (long)) / 8; > > - do { > + FORCE_VECTORIZE do { > p1[0] ^= p2[0] ^ p3[0] ^ p4[0]; > p1[1] ^= p2[1] ^ p3[1] ^ p4[1]; > p1[2] ^= p2[2] ^ p3[2] ^ p4[2]; > @@ -75,7 +84,7 @@ xor_8regs_5(unsigned long bytes, unsigned long *p1, > unsigned long *p2, > { > long lines = bytes / (sizeof (long)) / 8; > > - do { > + FORCE_VECTORIZE do { > p1[0] ^= p2[0] ^ p3[0] ^ p4[0] ^ p5[0]; > p1[1] ^= p2[1] ^ p3[1] ^ p4[1] ^ p5[1]; > p1[2] ^= p2[2] ^ p3[2] ^ p4[2] ^ p5[2]; > -- > Thanks, > ~Nick Desaulniers -- Thanks, ~Nick Desaulniers