Messages in this thread | | | From | Nick Desaulniers <> | Date | Tue, 19 Jan 2021 13:18:15 -0800 | Subject | Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning |
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On Tue, Jan 19, 2021 at 5:17 AM 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") > 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 <ndesaulniers@google.com> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
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 <ndesaulniers@google.com>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com> > --- > 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
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