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From:   Eric Dumazet <edumazet@google.com>
Date:   Wed, 24 Nov 2021 22:45:47 -0800
Message-ID: <CANn89iJsFZrm5qzAUJDgYczQiBFa6pmvPDrA_yqkGFhfm-6AnQ@mail.gmail.com>
Subject: Re: [tip:x86/core 1/1] arch/x86/um/../lib/csum-partial_64.c:98:12:
 error: implicit declaration of function 'load_unaligned_zeropad'
To:     Noah Goldstein <goldstein.w.n@gmail.com>
Cc:     Johannes Berg <johannes@sipsolutions.net>, alexanderduyck@fb.com,
        kbuild-all@lists.01.org, open list <linux-kernel@vger.kernel.org>,
        linux-um@lists.infradead.org, lkp@intel.com, peterz@infradead.org,
        X86 ML <x86@kernel.org>
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On Wed, Nov 24, 2021 at 10:32 PM Eric Dumazet <edumazet@google.com> wrote:

> -       }
> +       if (unlikely(odd))
> +               result = ror32(result, 8);
>         return (__force __wsum)result;

Oh well, gcc at least removes the conditional and generates a ror and a cmov

        mov    %edx,%eax
        ror    $0x8,%eax
        test   %r8,%r8
        cmove  %edx,%eax
        ret

clang keeps the cond jmp
         test   $0x1,%dil
         je     93
         rol    $0x18,%eax
93:    ret