On Thu 02 Aug 2007 18:22, Thiago Macieira wrote:
> The instructions marked (p1) are executed only if p1=1 -- that is, if the
> cmp.eq operation succeeded. Same for (p2) and in this case p1 = !p2, so
> only one of the last two instructions are executed.

Yes, I really meant predication. Thanks Thiago!

IA-64 is notable because all instructions are predicated. For instructions 
that really should be executed all the time, there's a predicate register 
hardwired to 1. There's also a high number of predicate register (64 IIRC).
Wikipedia has a page on predication [1], but Thiago's explanation is better 
IMO.

I agree it's no free lunch, as the instructions still have to be in the 
pipeline anyway. But for some code paths the difference can be really 
large.

[1] http://en.wikipedia.org/wiki/Branch_predication

-- 
	Henrique Pinto
	henrique.pinto@kdemail.net
 
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