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
So from current feed back, doing "unlikely() optimization" here doesn't make anything better.
Thanks for all of your feed back :-)
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