From: Ard Biesheuvel <ardb@kernel.org> To: Adrian Ratiu <adrian.ratiu@collabora.com> Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>, Nathan Chancellor <natechancellor@gmail.com>, Nick Desaulniers <ndesaulniers@google.com>, Arnd Bergmann <arnd@arndb.de>, Russell King <linux@armlinux.org.uk>, Arvind Sankar <nivedita@alum.mit.edu>, Collabora Kernel ML <kernel@collabora.com>, clang-built-linux <clang-built-linux@googlegroups.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org> Subject: Re: [PATCH v2 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning Date: Fri, 13 Nov 2020 12:41:04 +0100 [thread overview] Message-ID: <CAMj1kXHQ94ZzoSUg6U70FnRtFs0KeVXT=Zg6ri2+OU_TKQcGfg@mail.gmail.com> (raw) In-Reply-To: <87mtzljz12.fsf@iwork.i-did-not-set--mail-host-address--so-tickle-me> On Fri, 13 Nov 2020 at 12:05, Adrian Ratiu <adrian.ratiu@collabora.com> wrote: > > Hi Ard, > > On Fri, 13 Nov 2020, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Thu, 12 Nov 2020 at 22:23, Adrian Ratiu > > <adrian.ratiu@collabora.com> wrote: > >> > >> From: Nathan Chancellor <natechancellor@gmail.com> > >> > >> Drop warning because kernel now requires GCC >= v4.9 after > >> commit 6ec4476ac825 ("Raise gcc version requirement to 4.9"). > >> > >> Reported-by: Nick Desaulniers <ndesaulniers@google.com> > >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > >> Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com> > > > > 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? > > > > 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 > >>
WARNING: multiple messages have this Message-ID (diff)
From: Ard Biesheuvel <ardb@kernel.org> To: Adrian Ratiu <adrian.ratiu@collabora.com> Cc: Arnd Bergmann <arnd@arndb.de>, Nick Desaulniers <ndesaulniers@google.com>, Russell King <linux@armlinux.org.uk>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, clang-built-linux <clang-built-linux@googlegroups.com>, Arvind Sankar <nivedita@alum.mit.edu>, Nathan Chancellor <natechancellor@gmail.com>, Collabora Kernel ML <kernel@collabora.com>, Linux ARM <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH v2 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning Date: Fri, 13 Nov 2020 12:41:04 +0100 [thread overview] Message-ID: <CAMj1kXHQ94ZzoSUg6U70FnRtFs0KeVXT=Zg6ri2+OU_TKQcGfg@mail.gmail.com> (raw) In-Reply-To: <87mtzljz12.fsf@iwork.i-did-not-set--mail-host-address--so-tickle-me> On Fri, 13 Nov 2020 at 12:05, Adrian Ratiu <adrian.ratiu@collabora.com> wrote: > > Hi Ard, > > On Fri, 13 Nov 2020, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Thu, 12 Nov 2020 at 22:23, Adrian Ratiu > > <adrian.ratiu@collabora.com> wrote: > >> > >> From: Nathan Chancellor <natechancellor@gmail.com> > >> > >> Drop warning because kernel now requires GCC >= v4.9 after > >> commit 6ec4476ac825 ("Raise gcc version requirement to 4.9"). > >> > >> Reported-by: Nick Desaulniers <ndesaulniers@google.com> > >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > >> Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com> > > > > 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? > > > > 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 > >> _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-11-13 11:44 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-11-12 21:24 [PATCH v2 0/2] xor-neon: Remove GCC warn & pragmas Adrian Ratiu 2020-11-12 21:24 ` Adrian Ratiu 2020-11-12 21:24 ` [PATCH v2 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning Adrian Ratiu 2020-11-12 21:24 ` Adrian Ratiu 2020-11-12 21:38 ` Nick Desaulniers 2020-11-12 21:38 ` Nick Desaulniers 2020-11-13 7:49 ` Ard Biesheuvel 2020-11-13 7:49 ` Ard Biesheuvel 2020-11-13 11:07 ` Adrian Ratiu 2020-11-13 11:07 ` Adrian Ratiu 2020-11-13 11:41 ` Ard Biesheuvel [this message] 2020-11-13 11:41 ` Ard Biesheuvel 2020-11-13 11:59 ` Adrian Ratiu 2020-11-13 11:59 ` Adrian Ratiu 2020-11-12 21:24 ` [PATCH v2 2/2] arm: lib: xor-neon: move pragma options to makefile Adrian Ratiu 2020-11-12 21:24 ` Adrian Ratiu 2020-11-12 21:40 ` Nick Desaulniers 2020-11-12 21:40 ` Nick Desaulniers 2020-11-12 21:50 ` Nathan Chancellor 2020-11-12 21:50 ` Nathan Chancellor 2020-11-13 7:50 ` Ard Biesheuvel 2020-11-13 7:50 ` Ard Biesheuvel 2020-11-13 11:17 ` Adrian Ratiu 2020-11-13 11:17 ` Adrian Ratiu
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