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 D62ECC43217 for ; Wed, 20 Jan 2021 14:14:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8BABB23380 for ; Wed, 20 Jan 2021 14:14:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390370AbhATOM4 (ORCPT ); Wed, 20 Jan 2021 09:12:56 -0500 Received: from bhuna.collabora.co.uk ([46.235.227.227]:48428 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389152AbhATNMN (ORCPT ); Wed, 20 Jan 2021 08:12:13 -0500 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: aratiu) with ESMTPSA id 971571F454EF From: Adrian Ratiu To: Nick Desaulniers , 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 Subject: Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning In-Reply-To: References: <20210119131724.308884-1-adrian.ratiu@collabora.com> <20210119131724.308884-2-adrian.ratiu@collabora.com> Date: Wed, 20 Jan 2021 15:11:27 +0200 Message-ID: <87o8hjg3cw.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, Nick Desaulniers wrote: > 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 > Sorry for not removing the reviewed-by tags from the previous versions in this v4. I guess the only way forward with this is to actually make clang vectorization work. Also thanks for the patch suggestion in the other e-mail! >> 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