Re: Matmul in VVM

From	Stefan Monnier <monnier@iro.umontreal.ca>
Newsgroups	comp.arch
Subject	Re: Matmul in VVM
Date	2026-05-14 12:19 -0400
Organization	A noiseless patient Spider
Message-ID	<jwvzf229dw4.fsf-monnier+comp.arch@gnu.org> (permalink)
References	(11 earlier) <10tq9vc$g5um$1@dont-email.me> <10tu2kd$1jtti$2@dont-email.me> <10tu5pf$1ko8o$1@dont-email.me> <2026May12.071448@mips.complang.tuwien.ac.at> <10tug9t$1nr8q$1@dont-email.me>

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Stephen Fuld [2026-05-11 23:11:07] wrote:
> Let me give one possible implementation.  There are certainly others. Say
> you have 32 registers.  They are "memory mapped" into the first 32 addresses
> of memory.  So programs would have to start not at zero, but at 32 (I know
> this can cause other problems - I clearly have not thought through all of
> the details.)  So now when the CPU encounters a load (or store) instruction
> where the virtual address is less  than 32, it is resolved not by the memory
> system, but by the appropriate register. i.e. if the virtual address was say
> 4, the load would be from register R4, not memory location 4.    Yes, the
> virtual addressing mechanism would have to be sensitive to whether the
> address was below 32 or not, but that is simple within the CPU.  Note that
> the load instruction in this case would not touch the memory system at all,
> so no cache lookups, no TLB lookups, etc.

That solves the problem of encoding an indirect register access as
a LD/ST instruction, but I highly doubt that's the main problem
introduced by indirect register access.

It'd actually be easier to just add a new instruction for indirect
register access (no need to burden the load/store unit, no need to worry
about access size and alignment, memory remapping, and whatnot).

The implementation problem, AFAIK comes in with OoO: by the time your
instruction (whether a load or a dedicated instruction) gets to know
which register it needs to read, we're in the middle of the OoO engine,
and the first thing it needs to do is to figure out which physical
register corresponds to this logical register (and it needs to find out
also if that physical register's value has already been delivered).
The needed information is definitely out there somewhere in the CPU,
but I'm not sure it can be made available cheaply at that time&place.

Some GPUs offer such indirect register addressing, but they have a very
different microarchitecture, much more like a barrel processor, with no
OoO execution in sight.

=== Stefan

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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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