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Re: Matmul in VVM

From Stefan Monnier <monnier@iro.umontreal.ca>
Newsgroups comp.arch
Subject Re: Matmul in VVM
Date 2026-05-10 16:15 -0400
Organization A noiseless patient Spider
Message-ID <jwv7bpbxc5l.fsf-monnier+comp.arch@gnu.org> (permalink)
References (7 earlier) <10t4cr0$21gah$1@dont-email.me> <1777747608-5857@newsgrouper.org> <10t6tnl$2o13n$1@dont-email.me> <1777847330-5857@newsgrouper.org> <10tpa5b$6obi$1@dont-email.me>

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Thomas Koenig [2026-05-10 06:55:39] wrote:
> MitchAlsup <user5857@newsgrouper.org.invalid> schrieb:
>> The solution to the excessive a[] traffic would be having the ability
>> to index the register file Ra[#] so the array can be allocated into
>> registers and indexed from the file itself. Most ISAs do not have this
>> ability--although a few GPU ISAs do.
> What are its drawbacks?

I guess the problem is that in an OoO design, this introduces a deeply
problematic dependency between the in-order front-end that renames
logical registers to physical registers and the OoO core.

Usually such dependencies (where the front-end needs info from the
OoO core) are handled via speculation, the classical example being
branches.

> Do register accesses get slower?

In order not to mess the whole pipeline, I think you'd have to predict
the register indexing.

In the mean time you can "simulate" it by replacing the register
indexing by a `switch` table to various copies of the code, each one
using the appropriate register.  Of course, this wouldn't work in vVM
since IIRC vVM doesn't support branches within the loop, and using
predication to simulate the `switch` table would be impractical.


=== Stefan

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Thread

Sane(r) SIMD Thomas Koenig <tkoenig@netcologne.de> - 2026-04-26 10:26 +0000
  Re: Sane(r) SIMD BGB <cr88192@gmail.com> - 2026-04-26 12:27 -0500
    Re: Sane(r) SIMD Thomas Koenig <tkoenig@netcologne.de> - 2026-04-26 19:07 +0000
    Re: Sane(r) SIMD Stefan Monnier <monnier@iro.umontreal.ca> - 2026-04-26 18:30 -0400
      Re: Sane(r) SIMD BGB <cr88192@gmail.com> - 2026-04-27 13:58 -0500
      Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-04-27 19:42 +0000
        Re: Sane(r) SIMD BGB <cr88192@gmail.com> - 2026-04-27 16:42 -0500
      Re: Sane(r) SIMD Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-04-28 05:46 +0000
  Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-04-26 18:25 +0000
    Re: Sane(r) SIMD Thomas Koenig <tkoenig@netcologne.de> - 2026-04-26 19:38 +0000
      Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-04-26 21:27 +0000
        Re: Sane(r) SIMD Thomas Koenig <tkoenig@netcologne.de> - 2026-04-27 05:42 +0000
          Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-04-27 19:22 +0000
            Re: Sane(r) SIMD Thomas Koenig <tkoenig@netcologne.de> - 2026-04-27 20:22 +0000
              Re: Sane(r) SIMD BGB <cr88192@gmail.com> - 2026-04-27 17:39 -0500
              Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-04-28 00:03 +0000
    Re: Sane(r) SIMD anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-27 06:56 +0000
      Re: Sane(r) SIMD Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-04-27 08:48 +0000
        Re: Sane(r) SIMD Michael S <already5chosen@yahoo.com> - 2026-04-27 12:23 +0300
          Re: Sane(r) SIMD Michael S <already5chosen@yahoo.com> - 2026-04-27 17:11 +0300
          Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-04-27 19:32 +0000
            Re: Sane(r) SIMD Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-04-27 21:54 +0000
              Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-04-28 00:11 +0000
                Re: Sane(r) SIMD Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-04-28 01:17 +0000
                Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-04-28 18:03 +0000
            Re: Sane(r) SIMD Michael S <already5chosen@yahoo.com> - 2026-04-28 14:36 +0300
              Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-04-28 17:45 +0000
                Re: Sane(r) SIMD Terje Mathisen <terje.mathisen@tmsw.no> - 2026-04-30 10:02 +0200
          Re: Sane(r) SIMD BGB <cr88192@gmail.com> - 2026-04-27 15:55 -0500
      Re: Sane(r) SIMD BGB <cr88192@gmail.com> - 2026-04-27 15:27 -0500
  Re: Sane(r) SIMD Terje Mathisen <terje.mathisen@tmsw.no> - 2026-04-27 18:47 +0200
    Re: Sane(r) SIMD Thomas Koenig <tkoenig@netcologne.de> - 2026-04-27 20:02 +0000
      Re: Sane(r) SIMD Terje Mathisen <terje.mathisen@tmsw.no> - 2026-04-30 14:36 +0200
        Re: Sane(r) SIMD Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-04-30 10:35 -0700
          Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-04-30 17:51 +0000
            Re: Sane(r) SIMD scott@slp53.sl.home (Scott Lurndal) - 2026-04-30 18:16 +0000
              Re: Sane(r) SIMD MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-01 00:28 +0000
              Re: Sane(r) SIMD anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-01 07:48 +0000
                Re: Sane(r) SIMD Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-05-01 08:14 +0000
                Re: Sane(r) SIMD George Neuner <gneuner2@comcast.net> - 2026-05-02 00:59 -0400
        Matmul in VVM (was: Sane(r) SIMD) Thomas Koenig <tkoenig@netcologne.de> - 2026-05-01 10:21 +0000
          Re: Matmul in VVM (was: Sane(r) SIMD) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-01 21:48 +0000
            Re: Matmul in VVM (was: Sane(r) SIMD) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-02 02:10 +0000
              Re: Matmul in VVM (was: Sane(r) SIMD) Thomas Koenig <tkoenig@netcologne.de> - 2026-05-02 08:32 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-02 18:46 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) Thomas Koenig <tkoenig@netcologne.de> - 2026-05-03 07:33 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) Michael S <already5chosen@yahoo.com> - 2026-05-03 11:13 +0300
                Re: Matmul in VVM (was: Sane(r) SIMD) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-03 22:28 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) Thomas Koenig <tkoenig@netcologne.de> - 2026-05-10 06:55 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-10 17:28 +0000
                Re: Matmul in VVM Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-10 16:15 -0400
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-10 08:58 -0700
                Re: Matmul in VVM Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-05-12 02:17 +0000
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-11 20:11 -0700
                Re: Matmul in VVM anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-12 05:14 +0000
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-11 23:11 -0700
                Re: Matmul in VVM anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-12 07:23 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-12 18:16 +0000
                Re: Matmul in VVM anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-14 08:05 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-14 18:20 +0000
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-13 09:09 -0700
                Re: Matmul in VVM anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-13 17:55 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-13 20:46 +0000
                Re: Matmul in VVM scott@slp53.sl.home (Scott Lurndal) - 2026-05-12 14:33 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-12 18:23 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-12 18:12 +0000
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-12 17:08 -0700
                Re: Matmul in VVM scott@slp53.sl.home (Scott Lurndal) - 2026-05-13 14:12 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-13 17:36 +0000
                Re: Matmul in VVM Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-05-13 02:57 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-13 17:32 +0000
                Re: Matmul in VVM Terje Mathisen <terje.mathisen@tmsw.no> - 2026-05-14 09:39 +0200
                Re: Matmul in VVM Bernd Linsel <bl1-thispartdoesnotbelonghere@gmx.com> - 2026-05-13 14:02 +0200
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-13 09:14 -0700
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-13 17:40 +0000
                Re: Matmul in VVM Bernd Linsel <bl1-thispartdoesnotbelonghere@gmx.com> - 2026-05-13 21:35 +0200
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-13 20:52 +0000
                Re: Matmul in VVM Bernd Linsel <bl1-thispartdoesnotbelonghere@gmx.com> - 2026-05-15 00:03 +0200
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-14 16:35 -0700
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-15 00:17 +0000
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-18 14:22 -0700
                Re: Matmul in VVM Bernd Linsel <bl1-thispartdoesnotbelonghere@gmx.com> - 2026-05-20 10:06 +0200
                Re: Matmul in VVM Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-14 12:19 -0400
                Re: Matmul in VVM anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-15 06:29 +0000
                Re: Matmul in VVM EricP <ThatWouldBeTelling@thevillage.com> - 2026-05-15 09:19 -0400
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-18 14:18 -0700
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-12 18:06 +0000
                Re: Matmul in VVM Thomas Koenig <tkoenig@netcologne.de> - 2026-05-12 09:48 +0000
                Re: Matmul in VVM David Brown <david.brown@hesbynett.no> - 2026-05-12 12:59 +0200
                Re: Matmul in VVM Thomas Koenig <tkoenig@netcologne.de> - 2026-05-15 16:59 +0000
                Re: Matmul in VVM scott@slp53.sl.home (Scott Lurndal) - 2026-05-15 22:30 +0000
                Re: Matmul in VVM Thomas Koenig <tkoenig@netcologne.de> - 2026-05-16 10:22 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-16 18:09 +0000
                Re: Matmul in VVM Thomas Koenig <tkoenig@netcologne.de> - 2026-05-16 18:11 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-16 22:59 +0000
                Re: Matmul in VVM Thomas Koenig <tkoenig@netcologne.de> - 2026-05-17 07:51 +0000
                Re: Matmul in VVM scott@slp53.sl.home (Scott Lurndal) - 2026-05-17 18:51 +0000
                Re: Matmul in VVM Thomas Koenig <tkoenig@netcologne.de> - 2026-05-18 09:56 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-18 17:50 +0000
                Re: Matmul in VVM scott@slp53.sl.home (Scott Lurndal) - 2026-05-12 14:29 +0000
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-25 12:00 -0700
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-25 19:36 +0000
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-25 17:52 -0700
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-26 17:48 +0000
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-26 11:55 -0700
                Re: Matmul in VVM Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-27 10:57 -0400
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-27 11:13 -0700
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-28 07:43 -0700
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-28 07:53 -0700
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-28 18:08 +0000
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-29 08:50 -0700
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-29 16:58 +0000
                Re: Matmul in VVM Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-28 19:29 -0400
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-29 09:03 -0700
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-29 17:04 +0000
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-29 16:55 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-08 18:15 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) Thomas Koenig <tkoenig@netcologne.de> - 2026-05-10 07:14 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-05-11 05:36 +0000
                Re: Matmul in VVM Stephen Fuld <sfuld@alumni.cmu.edu.invalid> - 2026-05-18 11:02 -0700
                Re: Matmul in VVM MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-18 20:20 +0000
              Re: Matmul in VVM (was: Sane(r) SIMD) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-02 16:29 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) Michael S <already5chosen@yahoo.com> - 2026-05-03 11:29 +0300
                Re: Matmul in VVM (was: Sane(r) SIMD) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-03 11:22 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) Michael S <already5chosen@yahoo.com> - 2026-05-03 16:53 +0300
                Re: Matmul in VVM (was: Sane(r) SIMD) Thomas Koenig <tkoenig@netcologne.de> - 2026-05-03 14:46 +0000
                Re: Matmul in VVM (was: Sane(r) SIMD) Michael S <already5chosen@yahoo.com> - 2026-05-03 19:07 +0300
                Re: Matmul in VVM (was: Sane(r) SIMD) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-03 14:39 +0000
                More real world matmul kernel Was: Matmul in VVM (was: Sane(r) SIMD) Michael S <already5chosen@yahoo.com> - 2026-05-03 18:30 +0300
          Re: Matmul in VVM (was: Sane(r) SIMD) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-01 22:21 +0000
            Re: Matmul in VVM (was: Sane(r) SIMD) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-02 06:02 +0000
              Re: Matmul in VVM (was: Sane(r) SIMD) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-05-02 18:33 +0000
            Re: Matmul in VVM (was: Sane(r) SIMD) Thomas Koenig <tkoenig@netcologne.de> - 2026-05-02 06:54 +0000
              Re: Matmul in VVM (was: Sane(r) SIMD) Thomas Koenig <tkoenig@netcologne.de> - 2026-05-02 15:26 +0000

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