i486 base architecture
Nicholas Miell
nmiell at comcast.net
Mon Nov 29 09:30:11 UTC 2004
On Mon, 2004-11-29 at 10:16 +0100, Arjan van de Ven wrote:
> On Mon, Nov 29, 2004 at 01:02:46AM -0800, Nicholas Miell wrote:
> > CMOVcc will use less space in the instruction cache than the Jcc/MOV
> > pair, though.
>
> only sometimes.... since cmov doens't work on all register/memory
> combinations extra code might be needed to glue that together...
>
>
> .... and we're suddenly talking about 0.01% performance ;)
Well, yeah. :)
There's also branch prediction and decode bandwidth issues that I didn't
bother to mention.
But, if you're going to optimize for i686 or better for other reasons,
there's no reason not to use CMOVcc instead of Jcc/MOV, where possible.
Not that you'll ever notice the difference...
--
Nicholas Miell <nmiell at comcast.net>
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