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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Mon, 18 Jan 2021 12:33:29 +0100
Message-ID: <CAK8P3a1wxZH_sX9eeTGecvDYGTcniF7_ZoSj8LSOFhCTo_CB=A@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 12:28 PM Adrian Ratiu
<adrian.ratiu@collabora.com> wrote:
> On Mon, 18 Jan 2021, Arnd Bergmann <arnd@kernel.org> wrote:
> > On Mon, Jan 18, 2021 at 11:56 AM Adrian Ratiu <adrian.ratiu@collabora.com> wrote:
>
> No, clang does not produce vectorized code by default, not even
> with the -ftree-vectorize flag explicitely added like in the next
> patch in this series (that flag is enabled by default in clang
> anyway, so no effect).
>
> Clang needs more investigation and testing because with additional
> code changes it can be "forced" to output vectorized code, but
> that is outside the scope of this series.
>
> If you think it's a good idea I can add a warning only for Clang
> which makes more sense than telling clang users to upgrade their
> GCC, since now Clang is officially supported. What do you think?

Yes, either a warning or a Kconfig check seems better to me than
just trying to build code that ends up not doing what it is meant to.

       Arnd