Subject: Re: [PATCH 2/7] PowerPC: add unlikely() to BUG_ON()

From: Coly Li <[email-masked]>
Date: Fri, 28 Jan 2011 19:02:19 +0800

On 2011年01月28日 18:14, Andreas Schwab Wrote:
> "David Laight"<[email-masked]>  writes:
>
>> Also, as (I think) in some of the generated code quoted,
>> use of __builtin_expect() with a boolean expression can
>> force some versions of gcc to generate the integer
>> value of the expression
>
> That's more likely a side effect of the definition of likely/unlikely:
> they expand to !!(x).
>

It seems whether or not using unlikely() inside arch implemented BUG_ON() is arch dependent. Maybe a reasonable method 
to use BUG_ON() is,
1) do not explicitly use unlikely() when using macro BUG_ON().
2) whether or not using unlikely() inside BUG_ON(), it depends on the implementation of BUG_ON(), including arch 
implementation.

So from current feed back, doing "unlikely() optimization" here doesn't make anything better.

Thanks for all of your feed back :-)

-- 
Coly Li