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List: kde-devel
Subject: Re: The no goto religion
From: Henrique Pinto <henrique.pinto () kdemail ! net>
Date: 2007-08-02 22:16:40
Message-ID: 200708021916.40407.henrique.pinto () kdemail ! net
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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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