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=-18.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,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 E42F9C4332B for ; Wed, 20 Jan 2021 13:26:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ADB9A233FA for ; Wed, 20 Jan 2021 13:26:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389849AbhATN0N (ORCPT ); Wed, 20 Jan 2021 08:26:13 -0500 Received: from bhuna.collabora.co.uk ([46.235.227.227]:48526 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389027AbhATNTD (ORCPT ); Wed, 20 Jan 2021 08:19:03 -0500 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: aratiu) with ESMTPSA id 0296C1F455A1 From: Adrian Ratiu To: Nathan Chancellor , Adrian Ratiu Cc: linux-arm-kernel@lists.infradead.org, Nick Desaulniers , Arnd Bergmann , Russell King , Ard Biesheuvel , Arvind Sankar , clang-built-linux , kernel@collabora.com, Linux Kernel Mailing List Subject: Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning In-Reply-To: <20210119215435.GA1727211@ubuntu-m3-large-x86> References: <20210119131724.308884-1-adrian.ratiu@collabora.com> <20210119131724.308884-2-adrian.ratiu@collabora.com> <20210119215435.GA1727211@ubuntu-m3-large-x86> Date: Wed, 20 Jan 2021 15:18:17 +0200 Message-ID: <87lfcng31i.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 Tue, 19 Jan 2021, Nathan Chancellor wrote: > On Tue, Jan 19, 2021 at 03:17:23PM +0200, 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 >> Signed-off-by: Nathan Chancellor >> Signed-off-by: Adrian Ratiu > > The commit message looks like it is written by me but I never > added a Clang specific warning. I appreciate wanting to give me > credit but when you change things about my original commit > message, please make it clear that you did the edits, something > like: > > Signed-off-by: Nathan Chancellor > [adrian: Add clang specific warning] Signed-off-by: Adrian Ratiu > > Thanks for the suggestion. Makes sense. I contemplated adding another patch by me on top but thought it was too much churn. Sorry if my edits were unclear. >> --- >> 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 > > I really do not like this. With the GCC specific warning, the > user could just upgrade their GCC. With this warning, it is > basically telling them don't use clang, in which case, it would > just be better to disable this code altogether. I would rather > see: > > 1. Just don't build this file with clang altogether, which I > believe was > v1's 2/2 patch. > > OR > > 2. Use the pragma: > > #pragma clang loop vectorize(enable) > > as Nick suggests in v1's 2/2 patch. > > Alternatively, __restrict__ sounds like it might be beneficial > for both GCC and clang: > > https://lore.kernel.org/lkml/20201112215033.GA438824@rani.riverdale.lan/ > Option 1 from v1 got clearly NACKed by Nick a while back so the only option gonig forward is to also fix clang vectorization together with these changes so the warning becomes unnecessary. >> /* >> * 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 >>