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From: Duncan Sands <baldrick@wanadoo.fr>
To: "Martin J. Bligh" <mbligh@aracnet.com>, Andrew Morton <akpm@digeo.com>
Subject: Re: BUGed to death
Date: Tue, 15 Apr 2003 16:39:25 +0200
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On Tuesday 15 April 2003 16:35, Martin J. Bligh wrote:
> >> Seems all these bug checks are fairly expensive. I can get 1%
> >> back on system time for kernel compiles by changing BUG to
> >> "do {} while (0)" to make them all compile away. Profiles aren't
> >> very revealing though ... seems to be within experimental error ;-(
> >
> > What happens if you just turn BUG_ON into "do {} while (0)"?
>
> I believe I already did that by turning BUG() into a null expression.
>
> #define BUG_ON(condition)
> 	do { if (unlikely((condition)!=0)) BUG(); } while(0)
>
> The compiler should be smart enough to optimise that away, methinks.

No, I meant what happens if BUG() is non-trivial and BUG_ON is a no-op.
I thought it might give an indication of whether time was being lost
evaluating the condition (occurs with BUG and BUG_ON), or mispredicting
the branch (only occurs with BUG).

Duncan.