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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Mon, 18 Jan 2021 12:06:59 +0100
Message-ID: <CAK8P3a3dDgbppAB3Bm2iJA7LOqRvHZew1_e-yE1R=9mS4W4xjQ@mail.gmail.com>
Subject: Re: [PATCH v3 RESEND 1/2] arm: lib: xor-neon: remove unnecessary GCC
 < 4.6 warning
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>,
        Ard Biesheuvel <ardb@kernel.org>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Collabora kernel ML <kernel@collabora.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Jan 18, 2021 at 11:56 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 risks misleading users.
>
> As a side-note remark, -fttree-vectorize is on by default in
> Clang, but it currently does not work (see linked issues).
>
> 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>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>

Shouldn't there be a check for whatever minimum version of clang
produces optimized code now? As I understand it, the warning
was originally meant to complain about both old gcc and any
version of clang, while waiting for a new version of clang to
produce vectorized code.

Has that happened now?

       Arnd