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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Mon, 11 Mar 2019 17:21:56 +0100
Message-ID: <CAK8P3a05QL855mx21R-Pr6c2WjhSoopdFk9z4HvKoeM19A5aSQ@mail.gmail.com>
Subject: Re: [PATCH] ARM: Ensure that NEON code always compiles with Clang
To:     Nathan Chancellor <natechancellor@gmail.com>
Cc:     Russell King <linux@armlinux.org.uk>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Tri Vo <trong@android.com>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
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On Sat, Dec 15, 2018 at 10:24 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>  endif
> diff --git a/arch/arm/lib/xor-neon.c b/arch/arm/lib/xor-neon.c
> index a6741a895189..4600b62d845f 100644
> --- a/arch/arm/lib/xor-neon.c
> +++ b/arch/arm/lib/xor-neon.c
> @@ -14,7 +14,7 @@
>  MODULE_LICENSE("GPL");
>
>  #ifndef __ARM_NEON__
> -#error You should compile this file with '-mfloat-abi=softfp -mfpu=neon'
> +#error You should compile this file with '-march=armv7-a -mfloat-abi=softfp -mfpu=neon'
>  #endif
>

I see this patch has made it in now, but I also see two other problems with the
same file that prevent it from working right with clang:

- it triggers #warning This code requires at least version 4.6 of GCC
- As I reported in https://bugs.llvm.org/show_bug.cgi?id=40976, even
  when it builds cleanly, it does not get vectorized.

Has anyone actually managed to get this to do the right thing?

       Arnd