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Date: Fri, 03 Feb 2012 22:54:50 -0800
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Subject: Re: Are rotating register files still a bad idea?
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On 2/2/2012 12:16 AM, Brett Davis wrote:
> Are rotating register files still a bad idea?
>
> Rotating register files used to mean slow clock speeds.
> SPARC has had competitive clocks for the past decade,
> largely because everyone hit a thermal brick wall...
>
> I assume that if that brink wall breaks, rotating register files
> are back to being doomed, but that looks unlikely.
>
> Does rotating register files buy you anything net after costs,
> or is it just a fiasco in the age of modern OoO pipelines?



When I first saw your post, I thought that you were talking about the 
rotating register file that Cydrome and Itanium had, that could be made 
to rotate on every loop iteration, and not SPARC-style overlapping 
register windows (which Itanium also had).

I actually think that Cydrome state rotating register files may be a 
good idea, albeit neglected.  They allow software pipelining to be done 
without requiring reg-reg moves and give many of the benefits of loop 
unrolling without increasing code size.

Overlapping register windows for function calls I am not so sure about.

One thing the think about:  GPU style multiple threads in the same 
register file.

a) COULD work with rotating register windows for loops

b) would be much harder to make work with overlapping register windows 
for function calls.