Messages in this thread | | | From | Ard Biesheuvel <> | Date | Fri, 13 Nov 2020 12:41:04 +0100 | Subject | Re: [PATCH v2 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning |
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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 > >>
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