linux-kernel - Re: [PATCH v3 RESEND 1/2] arm: lib: xor-neon: remove unnecessary GCC

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Date:   Mon, 18 Jan 2021 12:06:59 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Adrian Ratiu <adrian.ratiu@...labora.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Collabora kernel ML <kernel@...labora.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 RESEND 1/2] arm: lib: xor-neon: remove unnecessary GCC
 < 4.6 warning

On Mon, Jan 18, 2021 at 11:56 AM 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")
> 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@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> Signed-off-by: Adrian Ratiu <adrian.ratiu@...labora.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