[Beowulf] [rjdyer at vcu.edu: Re: Intel?]

Greg Lindahl lindahl at pathscale.com
Wed Jun 8 10:58:57 PDT 2005

On Wed, Jun 08, 2005 at 11:21:34AM -0400, Mark Hahn wrote:

> for instance, altivec has 32x128 and x86-64 has "only" 16x128.
> but how relevant is this?  studies of conventional reg-set usage
> show diminishing returns after about 16 regs.

These studies are always contaminated by compiler quality. If you look
back you can find papers where the authors used a horrible compiler
and "proved" that you didn't need more than 4 registers. Even with a
really aggressive compiler, you can find many example apps that run
out of registers with only 16. Then the question becomes: How many
customers are hurt by this?

-- greg

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