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=-28.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=ham 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 5D4DDC433DB for ; Tue, 19 Jan 2021 21:20:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1854E22D08 for ; Tue, 19 Jan 2021 21:20:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729168AbhASVUJ (ORCPT ); Tue, 19 Jan 2021 16:20:09 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56560 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728221AbhASVTJ (ORCPT ); Tue, 19 Jan 2021 16:19:09 -0500 Received: from mail-pg1-x52c.google.com (mail-pg1-x52c.google.com [IPv6:2607:f8b0:4864:20::52c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C03FFC0613C1 for ; Tue, 19 Jan 2021 13:18:27 -0800 (PST) Received: by mail-pg1-x52c.google.com with SMTP id 15so13767793pgx.7 for ; Tue, 19 Jan 2021 13:18:27 -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=GUbLbmtARwLrukRtqOIAYNu5h84qqes4aFplAP4XxME=; b=pFWSQ7PxnGjqvOIOSz+b9o3QjhNS22c/IpR/WKX1WRJJBSHSEZkpqQH4d3jeXFqwx5 BS53/1afs51JkhbIeGi0M+480mh3kMCnV37bss+xeHpq9KMPSHd7UgqKFZQQPQTkmXyP g9+F/QKE77NR/v2JbDmTc/jQYq/768UxCvPb/kOmAS4bPwSy96usDuqZEFS6gUJ+/Yeh TMSJxfmnWqFUu6qP6ko4NZXcjsT0TcQqfGOgw0dSVIquT3bqftGPMbb7HBuMCwmAvKzm H1RSIFpx/xuH5ujg9yd0XOSeE2/pwaXax8Odq+hLb0q2eldi2JMrmoKYKeq2/CYgJr+s RBrQ== 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=GUbLbmtARwLrukRtqOIAYNu5h84qqes4aFplAP4XxME=; b=p+ELSb5AnpLKzgazP13B/ZNMux4AebcxbzAcruoe0fQ7BDom7vCOfT/8nBginUh9Zn 7bf8MMl8o3ByfKJ39Cfmrktm+UTgGtveASjpSx1MmP6vaeAT1dis/34Chc042IqQBCS6 XQYhhmF5LevyYt5f4BlT4ztt2X/rR0wENyv4l1zKfb/f9yoPBEWaMAZJrhSy29N+aLRB cTIJ+KnRzqpjn89lB+D/OaLF23jVMr9fqzBnDrtdteeNXk+HSw+rm8gEC/ro9NvdQSWv cXZ+xw7xrgU1ak8clIH8WVLUYag1C1a0pxA34pIzR+Rx5unsrLsfuqKyzTdV2tr+HisL oVmw== X-Gm-Message-State: AOAM532V93jTTKNvtNhH9kWAi213y1Ol1oGpOnCQYh7BYO+AWMNCwzff /Mniwl4meAOY6Dg7gtI411yU4mOTgT2F2AtEQVcr0w== X-Google-Smtp-Source: ABdhPJw8pKTzHIo3RJ5xY5RlGpjCInElwVgnKjp2tnXoGZvmUnZPXMzM1QJsasme15Kzt4eqJVuhKaLV93GRhvN1sHA= X-Received: by 2002:a63:5701:: with SMTP id l1mr6165248pgb.381.1611091107085; Tue, 19 Jan 2021 13:18:27 -0800 (PST) MIME-Version: 1.0 References: <20210119131724.308884-1-adrian.ratiu@collabora.com> <20210119131724.308884-2-adrian.ratiu@collabora.com> In-Reply-To: <20210119131724.308884-2-adrian.ratiu@collabora.com> From: Nick Desaulniers Date: Tue, 19 Jan 2021 13:18:15 -0800 Message-ID: Subject: Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning To: Adrian Ratiu , Arnd Bergmann Cc: 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 5:17 AM Adrian Ratiu wrote: > > From: Nathan Chancellor > > Drop warning because kernel now requires GCC >= v4.9 after > commit 6ec4476ac825 ("Raise gcc version requirement to 4.9") > and clarify that -ftree-vectorize now always needs enabling > for GCC by directly testing the presence of CONFIG_CC_IS_GCC. > > Another reason to remove the warning is that Clang exposes > itself as GCC < 4.6 so it triggers the warning about GCC > which doesn't make much sense and misleads Clang users by > telling them to update GCC. > > Because Clang is now supported by the kernel print a clear > Clang-specific warning. > > Link: https://github.com/ClangBuiltLinux/linux/issues/496 > Link: https://github.com/ClangBuiltLinux/linux/issues/503 > Reported-by: Nick Desaulniers > Reviewed-by: Nick Desaulniers This is not the version of the patch I had reviewed; please drop my reviewed-by tag when you change a patch significantly, as otherwise it looks like I approved this patch. Nacked-by: Nick Desaulniers > Signed-off-by: Nathan Chancellor > Signed-off-by: Adrian Ratiu > --- > arch/arm/lib/xor-neon.c | 18 ++++++++++-------- > 1 file changed, 10 insertions(+), 8 deletions(-) > > 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 > + > /* > * Pull in the reference implementations while instructing GCC (through > * -ftree-vectorize) to attempt to exploit implicit parallelism and emit > * NEON instructions. > */ > -#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6) > +#ifdef CONFIG_CC_IS_GCC > #pragma GCC optimize "tree-vectorize" > -#else > -/* > - * While older versions of GCC do not generate incorrect code, they fail to > - * recognize the parallel nature of these functions, and emit plain ARM code, > - * which is known to be slower than the optimized ARM code in asm-arm/xor.h. > - */ > -#warning This code requires at least version 4.6 of GCC > #endif > > #pragma GCC diagnostic ignored "-Wunused-variable" > -- > 2.30.0 > -- Thanks, ~Nick Desaulniers