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Fri, 06 Nov 2020 10:03:12 -0800 (PST) Date: Fri, 6 Nov 2020 11:03:11 -0700 From: Nathan Chancellor To: Arnd Bergmann Cc: Adrian Ratiu , Linux ARM , Nick Desaulniers , Arnd Bergmann , clang-built-linux , Russell King , "linux-kernel@vger.kernel.org" , Collabora kernel ML Subject: Re: [PATCH 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning Message-ID: <20201106180311.GC2959494@ubuntu-m3-large-x86> References: <20201106051436.2384842-1-adrian.ratiu@collabora.com> <20201106051436.2384842-2-adrian.ratiu@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 06, 2020 at 03:46:36PM +0100, Arnd Bergmann wrote: > On Fri, Nov 6, 2020 at 6:14 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"). > > > > Reported-by: Nick Desaulniers > > Signed-off-by: Nathan Chancellor > > Signed-off-by: Adrian Ratiu > > --- > > 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 > > I think we still need the #else path, otherwise we don't warn about > clang being broken here. > > If it is intentional that we now silently build this code with clang > without it working as intended, that should be mentioned in the > changelog. > > Arnd Maybe patch 2/2 should come before this one? With that patch, we are not even going to build this code so this patch purely becomes a "we do not support this GCC version anymore" cleanup patch. Cheers, Nathan