linux-kernel - Re: [PATCH] x86/entry/64: Use TEST %reg,%reg instead of CMP $0,%reg

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Message-ID: <CALCETrU_zdfTwOyymq+N9t99BJJyQJaUtCJ4wPxxvBC53zBabQ@mail.gmail.com>
Date:   Thu, 29 Oct 2020 07:41:55 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/entry/64: Use TEST %reg,%reg instead of CMP $0,%reg

On Thu, Oct 29, 2020 at 7:29 AM Uros Bizjak <ubizjak@...il.com> wrote:
>
> Use TEST %reg,%reg which sets the zero flag in the same way
> as CMP $0,%reg, but the encoding uses one byte less.

This will make a Linux distro fit on an embedded device that
previously had four bytes too little flash :)

Reviewed-by: Andy Lutomirski <luto@...nel.org>