linux-kernel - Re: pud_bad vs pud

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Message-ID: <20090205193121.GA31839@elte.hu>
Date:	Thu, 5 Feb 2009 20:31:21 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	William Lee Irwin III <wli@...omorphy.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: pud_bad vs pud_bad


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Ingo Molnar wrote:
>> But the 32-bit check does the exact same thing but via a single binary  
>> operation: it checks whether any bits outside of those bits are zero - 
>> just via a simpler test that compiles to more compact code.
>>
>> So i'd go with the 32-bit version. (unless there are some 
>> sign-extension complications i'm missing - but i think we got rid of 
>> those already.)
>
> OK, fair enough.  I wouldn't be surprised if gcc does that transform 
> anyway, but we may as well be consistent about it.

i checked and it doesnt - at least 4.3.2 inserts an extra AND instruction. 
So the 32-bit version is really better. (beyond being more readable)

	Ingo
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