On Tue, Aug 23, 2005 at 07:03:41AM -0400, Michael wrote:
> Hello,
> 
> > hmmm, VIS.  does netbsd/sparc64 actually save VIS registers in the
> > context or what?  they need to be "owned" like the FPU don't they?
> 
> Doesn't VIS just (ab)use the FPU registers?

You know, I thought the answer was that it used a different set of
registers, but it actually does overlay the VIS registers on the
FPU registers in the processor.

http://www.sun.com/processors/whitepapers/vis_wp_external.pdf

	While targeted at integer data types, the VIS instruction
	set was incorporated into the UltraSPARC processor's Floating
	Point Unit (FPU). The decision to segregate the integer
	and integer SIMD units has a couple of important performance
	benefits.  Firstly, by integrating the VIS instruction set
	into a different set of pipelines, both the VIS instruction
	set and the integer units can be utilized in parallel,
	maximizing instruction level parallelism. Secondly, this
	segregation has the additional benefit of maximizing the
	number of usable registers, with the VIS instruction set
	utilizing a different register set to the standard integer
	units.

So, there it is, straight from the horse's mouth.

-Kurt