linux-kernel - Re: [PATCH v2 1/2] arm: lib: xor-neon: remove unnecessary GCC

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Date:   Thu, 12 Nov 2020 13:38:56 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Adrian Ratiu <adrian.ratiu@...labora.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Collabora Kernel ML <kernel@...labora.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning

On Thu, Nov 12, 2020 at 1:23 PM Adrian Ratiu <adrian.ratiu@...labora.com> wrote:
>
> From: Nathan Chancellor <natechancellor@...il.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@...gle.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> Signed-off-by: Adrian Ratiu <adrian.ratiu@...labora.com>

Link: https://github.com/ClangBuiltLinux/linux/issues/496
Link: https://github.com/ClangBuiltLinux/linux/issues/503
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  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
>


-- 
Thanks,
~Nick Desaulniers