linux-kernel - Re: [PATCH 08/17] alpha: Implement xor_unlock_is_negative

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Message-ID: <CAHk-=wj+QEzoiUjeUkYqkJe4mcTQCshaAje51PiAuJu+REYxSA@mail.gmail.com>
Date:   Fri, 15 Sep 2023 19:14:52 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, Nicholas Piggin <npiggin@...il.com>
Subject: Re: [PATCH 08/17] alpha: Implement xor_unlock_is_negative_byte

On Fri, 15 Sept 2023 at 19:01, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> No, I think "mov src,dst" is just a pseudo-op for "or src,src,dst",
> there's no actual "mov" instruction, iirc.

Bah. I looked it up. It's actually supposed to be "BIS r31,src,dst".

Where "BIS" is indeed what most sane people call just "or". I think
it's "BIt Set", but the assembler will accept the normal "or" mnemonic
too.

There's BIC ("BIt Clear") too. Also known as "and with complement".

I assume it comes from some VAX background. Or maybe it's just a NIH
thing and alpha wanted to be "special".

              Linus