linux-kernel - Re: [RFC][PATCH 2/3] math128: Introduce {mult,add,cmp}

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Date:	Tue, 24 Apr 2012 17:09:41 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Juri Lelli <juri.lelli@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH 2/3] math128: Introduce {mult,add,cmp}_u128

On 04/24/2012 02:54 PM, Peter Zijlstra wrote:
> -       andl    $4294967295, %edx
>         shrq    $32, %rcx
> -       andl    $4294967295, %esi
> +       mov     %esi, %esi

If you can *ever* get gcc to generate those andl instructions on x86,
then please file a gcc bug report: the constant is 0xffffffff and those
are plain zero-extension instructions which is much better done with mov.

	-hpa

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