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=-9.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED 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 1E5A3C56202 for ; Fri, 13 Nov 2020 12:06:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C6D2822240 for ; Fri, 13 Nov 2020 12:06:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726591AbgKMMGt (ORCPT ); Fri, 13 Nov 2020 07:06:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36170 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726336AbgKMMGs (ORCPT ); Fri, 13 Nov 2020 07:06:48 -0500 Received: from bhuna.collabora.co.uk (bhuna.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e3e3]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4B923C0617A6 for ; Fri, 13 Nov 2020 03:59:13 -0800 (PST) Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: aratiu) with ESMTPSA id D046D1F4693B From: Adrian Ratiu To: Ard Biesheuvel Cc: Linux ARM , Nathan Chancellor , Nick Desaulniers , Arnd Bergmann , Russell King , Arvind Sankar , Collabora Kernel ML , clang-built-linux , Linux Kernel Mailing List Subject: Re: [PATCH v2 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning In-Reply-To: References: <20201112212457.2042105-1-adrian.ratiu@collabora.com> <20201112212457.2042105-2-adrian.ratiu@collabora.com> <87mtzljz12.fsf@iwork.i-did-not-set--mail-host-address--so-tickle-me> Date: Fri, 13 Nov 2020 13:59:48 +0200 Message-ID: <87h7ptjwln.fsf@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; format=flowed Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 13 Nov 2020, Ard Biesheuvel wrote: > On Fri, 13 Nov 2020 at 12:05, Adrian Ratiu > wrote: >> >> Hi Ard, >> >> On Fri, 13 Nov 2020, Ard Biesheuvel wrote: >> > On Thu, 12 Nov 2020 at 22:23, 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"). >> >> >> >> Reported-by: Nick Desaulniers >> >> Signed-off-by: Nathan Chancellor >> >> Signed-off-by: Adrian Ratiu >> > >> > Again, this does not do what it says on the tin. >> > >> > If you want to disable the pragma for Clang, call that out in >> > the commit log, and don't hide it under a GCC version change. >> >> I am not doing anything for Clang in this series. >> >> The option to auto-vectorize in Clang is enabled by default but >> doesn't work for some reason (likely to do with how it computes >> the cost model, so maybe not even a bug at all) and if we >> enable it explicitely (eg via a Clang specific pragma) we get >> some warnings we currently do not understand, so I am not >> changing the Clang behaviour at the recommendation of Nick. >> >> So this is only for GCC as the "tin" says :) We can fix clang >> separately as the Clang bug has always been present and is >> unrelated. >> > > But you are adding the IS_GCC check here, no? Is that > equivalent? IOW, does Clang today identify as GCC <= 4.6? > I see what you mean now. Thanks. Clang identifies as GCC <= 4.6 yes, so the code is not strictly speaking equivalent. The warning to upgrade GCC doesn't make sense for Clang but I should mention removing it in the commit message as well. >> > >> > Without the pragma, the generated code is the same as the >> > generic code, so it makes no sense to build xor-neon.ko at all, >> > right? >> > >> >> Yes that is correct and that is the reason why in v1 I opted to >> not build xor-neon.ko for Clang anymore, but that got NACKed, so >> here I'm fixing the low hanging fruit: the very obvious & clear >> GCC problems. >> >> > > Fair enough. > >> >> --- >> >> arch/arm/lib/xor-neon.c | 9 +-------- >> >> 1 file changed, 1 insertion(+), 8 deletions(-) >> >> >> >> diff --git a/arch/arm/lib/xor-neon.c b/arch/arm/lib/xor-neon.c >> >> index b99dd8e1c93f..e1e76186ec23 100644 >> >> --- a/arch/arm/lib/xor-neon.c >> >> +++ b/arch/arm/lib/xor-neon.c >> >> @@ -19,15 +19,8 @@ MODULE_LICENSE("GPL"); >> >> * -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" >> >> -- >> >> 2.29.2 >> >>