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Re: Register file splits, a new look.

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On Saturday, February 11, 2012 7:25:41 AM UTC-6, Brett Davis wrote:
> In article 
> <8314925.1151.1328905578623.JavaMail.geo-discussion-forums@vbbgq7>,
>  MitchAlsup  wrote:
> > No, the conclusion is that addresses, ints, and FP are close enough in desired data path requirements that placing them in a sufficiently large file is the better of several less tham optimal choices.
> > 
> > In addition, there is a different kind of data (short vector) that IS enough different to warrent a different kind of file in which to manage data over short periods of time.
> 
> MIPS puts 128 bit integer vectors in the integer register file.
> My assumption was that you had separate register select lines for the high half, and high 64 bit half, to save power. 

If you want to go this far, then you can make ANY register wide enough for ANY kind of data the processor can process. ANd the single unified file works just fine.

Splitting files vertically for power makes sense because in modern processes, the select lines are buffered down to the bit cells anyways, and changing a buffer (double inverter) into a gated inverter is "brain dead easy".

> (MIPS has 32 bit adds, as well as 64 bit.)

I don't know that I would have gone that far. I WOULD, however, like to have been a fly on the wall listening to the discussion where this issue was resolved.

> Am I wrong, and you need separate vector registers?

I support separate registers for short vectors because they are usefully different in size. If you want to or can make the register as tall as you like, the argument for separation is ameliorated.

I did an x86 design where the file contained 84-bit values and could deal with x86-64, x87, and 1/2 and SSE in any register. The interger data path and the FP data path were abuted, and there were 2 forwarding networks. Presto, unified physical register file even though the architecture specifies 3 completely different logical register files. We did this to save register file area and to have one unified MAP to make branch recovery a lot easier.

Mitch

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Register file splits, a new look. Brett Davis <ggtgp@yahoo.com> - 2012-02-06 06:33 -0600
  Re: Register file splits, a new look. MitchAlsup <MitchAlsup@aol.com> - 2012-02-06 09:29 -0800
    Re: Register file splits, a new look. Brett Davis <ggtgp@yahoo.com> - 2012-02-07 07:08 -0600
  Re: Register file splits, a new look. torbenm@diku.dk (Torben Ægidius Mogensen) - 2012-02-09 11:19 +0100
    Re: Register file splits, a new look. MitchAlsup <MitchAlsup@aol.com> - 2012-02-09 12:12 -0800
      Re: Register file splits, a new look. "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-02-09 15:27 -0800
        Re: Register file splits, a new look. MitchAlsup <MitchAlsup@aol.com> - 2012-02-09 15:52 -0800
      Re: Register file splits, a new look. nmm1@cam.ac.uk - 2012-02-10 08:07 +0000
        Re: Register file splits, a new look. "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-02-10 06:37 -0800
      Re: Register file splits, a new look. Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-02-10 09:36 +0100
      Re: Register file splits, a new look. Brett Davis <ggtgp@yahoo.com> - 2012-02-10 12:22 -0600
        Re: Register file splits, a new look. MitchAlsup <MitchAlsup@aol.com> - 2012-02-10 12:26 -0800
          Re: Register file splits, a new look. Brett Davis <ggtgp@yahoo.com> - 2012-02-11 07:25 -0600
            Re: Register file splits, a new look. Brett Davis <ggtgp@yahoo.com> - 2012-02-16 17:17 -0600
            Re: Register file splits, a new look. MitchAlsup <MitchAlsup@aol.com> - 2012-02-16 16:25 -0800
              Re: Register file splits, a new look. Brett Davis <ggtgp@yahoo.com> - 2012-02-17 14:08 -0600
                Re: Register file splits, a new look. MitchAlsup <MitchAlsup@aol.com> - 2012-02-28 08:54 -0800
                Re: Register file splits, a new look. Brett Davis <ggtgp@yahoo.com> - 2012-02-28 19:33 -0600

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