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

From: Coly Li
Date: Fri Jan 28 2011 - 05:36:34 EST

On 2011å01æ28æ 18:14, Andreas Schwab Wrote:
"David Laight"<David.Laight@xxxxxxxxxx> 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
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