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Re: Anyone take a serious look at partitioned register sets?

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  Re: Anyone take a serious look at partitioned register sets? "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-05-12 08:26 -0700
    Re: Anyone take a serious look at partitioned register sets? "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-12 19:26 -0700

#1496 — Re: Anyone take a serious look at partitioned register sets?

On Thursday, May 12, 2011 3:43:34 AM UTC-4, Michael S wrote:
[snip] 
> Sounds like you are talking about different things. Or, may be, you
> and Paul are talking about the same thing, but Brett was talking about
> something else.
> Duplicated integer register file in Ev6/Ev7 is just an implementation
> detail. Brett, on the other hand, was arguing in favor of software-
> visible partitioning, similar to TI C6000 family, but more far-
> fetched.

I think Brett is looking at microarchitecture splitting as 
an indication of the appropriateness of Architectural 
splitting.  I.e., if EV6-style clustering is so useful, 
why not Architect the split and avoid some of the 
overhead.

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#1515

On 5/12/2011 8:26 AM, Paul A. Clayton wrote:
> On Thursday, May 12, 2011 3:43:34 AM UTC-4, Michael S wrote:
> [snip]
>> Sounds like you are talking about different things. Or, may be, you
>> and Paul are talking about the same thing, but Brett was talking about
>> something else.
>> Duplicated integer register file in Ev6/Ev7 is just an implementation
>> detail. Brett, on the other hand, was arguing in favor of software-
>> visible partitioning, similar to TI C6000 family, but more far-
>> fetched.
>
> I think Brett is looking at microarchitecture splitting as
> an indication of the appropriateness of Architectural
> splitting.  I.e., if EV6-style clustering is so useful,
> why not Architect the split and avoid some of the
> overhead.

The answer is: compatibility. Lifetime of the architecture.

If your architecture is going to last many years, it may be built on 
many different microarchitectures.  Some of which have split RF, some 
which don't.

If your architecture is likely to only ever be used in 
microarchitectures that benefit from split RF, expose it.

By the way, the TI DSP architecture has lasted a long time.  For many 
years the DSP architectures were characterized by split X/Y registers.

(By the way, I think the meaningful split noawadays is not integer 
versus FP, but scalar (64b) versus SIMD packed vector (128-256-512 bit).)

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