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Re: i486 base architecture



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 comcast net>


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