linux-kernel - Re: [RFC 06/12] asm-generic: unaligned: remove byteshift helpers

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Message-ID: <CAK8P3a3GP7Wwyes_08nRQ-ESfx2dQr2Ygdz6jpSC1754M2s82A@mail.gmail.com>
Date:   Sat, 8 May 2021 13:38:01 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-arch <linux-arch@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Vineet Gupta <vgupta@...opsys.com>,
        Russell King <linux@...linux.org.uk>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [RFC 06/12] asm-generic: unaligned: remove byteshift helpers

On Sat, May 8, 2021 at 12:11 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> I've included this patch in the series because Linus asked about
> removing the byteshift version, but after trying it out, I'd
> prefer to drop this and use the byteshift version for the
> generic code as well.

Update: I've tried to create a small test case that illustrates the problem
with using the swab() based version, however all cases combinations
I tried showed either both producing identical output, or the shift
version being worse, see https://godbolt.org/z/bTdsjnjfT

I'll rewrite the patch description accordingly and leave this in place.

       Arnd