The RISC-V bitmanip ISA extension has conditional moves

By: Adrian (a.delete@this.acm.org), November 7, 2019 9:38 am
Room: Moderated Discussions
Ronald Maas (ronaldjmaas.delete@this.gmail.com) on November 6, 2019 11:53 pm wrote:
>
> 5000 year ago we used wheels for transportation. And today we still use wheels
> for transportation. Does not necessarily means every old idea is bad.
>
> Once implementation complexity exceeds a certain level and RISC-V implementations start to
> implement a full spectrum of extensions, caches, branch prediction, etc. the differences between


There is no problem when a base ISA lacks useful instructions, if there are opcode spaces reserved for extensions.


Nevertheless, an extensible ISA should define all the instruction formats, because otherwise it is certain that the extensions will use inefficiently the instruction code space.


If some addressing modes are missing in the base ISA, it would be OK if the format of the load and store instructions would include reserved fields dedicated for specifying extra addressing modes.


If the base ISA lacks the useful addressing modes and, like RISC-V, it was not designed to be extensible for this feature, then, even if it might be possible to add some extra load/store instructions in some extension, it is certain that the instruction encoding will not be so efficient as when the instruction formats would have been designed from the beginning to include all that might be needed, even if only a small subset would be implemented in the cheap implementations.


So no, targeting cheap implementations is not an excuse for RISC-V. They could have easily designed a decent ISA with only a small subset required to be implemented in small chips.

This is a concept well known since the days of IBM System/360, 55 years ago.


RISC-V has always had only one advantage: ignoring the weird SPARC, it was the only royalty-free ISA for which one had a complete set of tools, i.e. compilers, assembler & linker, so that there was no need to develop those.

Now there are other better alternatives, e.g. MIPS & POWER, but, obviously, for whoever has already adopted RISC-V it makes little sense to switch to yet another ISA, so RISC-V will continue to be used in many embedded applications for an indefinite time.


Unlike for ARM, I do not see any chance for RISC-V to be ever useful in a personal computer, unless it would be a variant so extended that it will have little but the name in common with the initial RISC-V specification.









< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
Risc-V getting real?Anon2019/10/31 03:10 PM
  Risc-V getting real?Gabriele Svelto2019/11/01 03:28 AM
    Risc-V getting real?anon2019/11/02 01:46 AM
      Risc-V getting real?lockederboss2019/11/02 01:49 AM
      Risc-V getting real?Gabriele Svelto2019/11/03 02:20 AM
        Risc-V getting real?Michael S2019/11/03 03:03 AM
          Risc-V getting real?Gabriele Svelto2019/11/03 04:45 AM
        Risc-V getting real?anon2019/11/03 08:29 PM
          Risc-V getting real?Gabriele Svelto2019/11/04 06:39 AM
        Risc-V getting real?dmcq2019/11/04 06:41 AM
    Documentation QualityKonrad Schwarz2019/11/04 05:43 AM
      Documentation QualityGabriele Svelto2019/11/04 06:31 AM
        Documentation QualityAnon2019/11/04 12:28 PM
  Trivium: Andy Glew works for SiFivePaul A. Clayton2019/11/01 10:51 AM
    RISC-V - incompetitive instruction set compared to ARMv8Heikki Kultala2019/11/02 02:31 AM
      RISC-V - incompetitive instruction set compared to ARMv8Ronald Maas2019/11/02 10:02 AM
        RISC-V - incompetitive instruction set compared to ARMv8Ronald Maas2019/11/02 10:04 AM
          RISC-V - incompetitive instruction set compared to ARMv8Michael S2019/11/02 03:18 PM
        RISC-V - incompetitive instruction set compared to ARMv8Adrian2019/11/02 10:33 AM
          RISC-V - incompetitive instruction set compared to ARMv8anon2019/11/02 10:49 AM
            RISC-V - incompetitive instruction set compared to ARMv8Wilco2019/11/02 12:20 PM
              RISC-V - incompetitive instruction set compared to ARMv8anon2019/11/02 01:57 PM
              RISC-V - incompetitive instruction set compared to ARMv8Ronald Maas2019/11/03 08:58 AM
                RISC-V - incompetitive instruction set compared to ARMv8anon2019/11/03 10:06 AM
                  RISC-V - incompetitive instruction set compared to ARMv8Gabriele Svelto2019/11/04 06:43 AM
                    RISC-V - incompetitive instruction set compared to ARMv8anon2019/11/04 07:03 AM
                      RISC-V - incompetitive instruction set compared to ARMv8Gabriele Svelto2019/11/04 07:13 AM
                        RISC-V - incompetitive instruction set compared to ARMv8Michael S2019/11/04 09:58 AM
                    RISC-V - incompetitive instruction set compared to ARMv8David Hess2019/11/04 09:57 AM
                      RISC-V - incompetitive instruction set compared to ARMv8rwessel2019/11/04 10:25 AM
                        RISC-V - incompetitive instruction set compared to ARMv8David Hess2019/11/04 10:48 AM
                RISC-V - incompetitive instruction set compared to ARMv8Wilco2019/11/03 12:09 PM
                  RISC-V - incompetitive instruction set compared to ARMv8Ronald Maas2019/11/03 10:44 PM
                    RISC-V - incompetitive instruction set compared to ARMv8Wilco2019/11/04 04:01 PM
                      RISC-V - incompetitive instruction set compared to ARMv8Gabriele Svelto2019/11/04 04:14 PM
                      RISC-V - incompetitive instruction set compared to ARMv8R2019/11/04 11:35 PM
                RISC-V - incompetitive instruction set compared to ARMv8sylt2019/11/03 01:35 PM
                  RISC-V - incompetitive instruction set compared to ARMv8l2019/11/03 08:26 PM
            The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/03 02:25 AM
              The RISC-V bitmanip ISA extension has conditional movesWilco2019/11/03 06:38 AM
                The RISC-V bitmanip ISA extension has conditional movesLinus Torvalds2019/11/03 10:03 AM
                The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/04 06:29 AM
                  The RISC-V bitmanip ISA extension has conditional movesnone2019/11/04 06:38 AM
                    The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/04 06:45 AM
                      The RISC-V bitmanip ISA extension has conditional movesnone2019/11/04 06:55 AM
                        The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/04 07:17 AM
                          The RISC-V bitmanip ISA extension has conditional movesnone2019/11/04 09:36 AM
                            I'm glad you're not that blind :) (NT)none2019/11/04 09:36 AM
                            The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/04 10:23 AM
                          The RISC-V bitmanip ISA extension has conditional movesMaynard Handley2019/11/04 06:16 PM
                            The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/04 11:42 PM
                              The RISC-V bitmanip ISA extension has conditional movesAdrian2019/11/05 06:25 AM
                                The RISC-V bitmanip ISA extension has conditional movesRonald Maas2019/11/05 06:04 PM
                                  The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/06 02:21 AM
                                    The RISC-V bitmanip ISA extension has conditional movesdmcq2019/11/06 03:31 AM
                                    The RISC-V bitmanip ISA extension has conditional movesKonrad Schwarz2019/11/06 07:03 AM
                                      The RISC-V bitmanip ISA extension has conditional movesnone2019/11/06 07:57 AM
                                        The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/06 08:55 AM
                      The RISC-V bitmanip ISA extension has conditional movesanon2019/11/04 07:24 AM
                        The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/04 04:07 PM
                          The RISC-V bitmanip ISA extension has conditional movesanon2019/11/04 05:02 PM
                            The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/04 11:39 PM
                              The RISC-V bitmanip ISA extension has conditional movesnone2019/11/05 12:45 AM
                                RISC-V - incompetitive instruction set compared to ARMv8Ronald Maas2019/11/05 05:41 PM
                                  RISC-V - incompetitive instruction set compared to ARMv8anonymou52019/11/06 12:24 AM
                                    The RISC-V bitmanip ISA extension has conditional movesRonald Maas2019/11/06 12:41 AM
                                      The RISC-V bitmanip ISA extension has conditional movesnone2019/11/06 01:12 AM
                                        The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/06 02:22 AM
                                      The RISC-V bitmanip ISA extension has conditional movesAdrian2019/11/06 02:44 AM
                                        The RISC-V bitmanip ISA extension has conditional movesAdrian2019/11/06 02:50 AM
                                        The RISC-V bitmanip ISA extension has conditional movesnone2019/11/06 03:08 AM
                                          The RISC-V bitmanip ISA extension has conditional movesAdrian2019/11/06 07:24 AM
                                      The RISC-V bitmanip ISA extension has conditional movesdmcq2019/11/06 05:53 AM
                                      The RISC-V bitmanip ISA extension has conditional movesnoko2019/11/06 11:07 AM
                                        The RISC-V bitmanip ISA extension has conditional movesRonald Maas2019/11/07 09:35 AM
                              The RISC-V bitmanip ISA extension has conditional movesj2019/11/05 01:43 AM
                          The RISC-V bitmanip ISA extension has conditional movesdmcq2019/11/04 05:39 PM
                          The RISC-V bitmanip ISA extension has conditional movesMaynard Handley2019/11/04 06:25 PM
                      The RISC-V bitmanip ISA extension has conditional movesAnon2019/11/04 08:31 AM
                        RISC-V - incompetitive instruction set compared to ARMv8Ronal2019/11/04 08:59 AM
          RISC-V - incompetitive instruction set compared to ARMv8dmcq2019/11/02 03:00 PM
          RISC-V - incompetitive instruction set compared to ARMv8lockederboss2019/11/03 09:37 AM
          RISC-V - incompetitive instruction set compared to ARMv8j2019/11/03 03:29 PM
            RISC-V - incompetitive instruction set compared to ARMv8anon2019/11/03 10:00 PM
              RISC-V - incompetitive instruction set compared to ARMv8j2019/11/04 12:30 AM
                RISC-V - incompetitive instruction set compared to ARMv8Michael S2019/11/04 02:45 AM
                  RISC-V - incompetitive instruction set compared to ARMv8none2019/11/04 03:59 AM
                    RISC-V - incompetitive instruction set compared to ARMv8anon2019/11/04 05:22 AM
                      RISC-V - incompetitive instruction set compared to ARMv8Adrian2019/11/04 06:10 AM
                      RISC-V - incompetitive instruction set compared to ARMv8Michael S2019/11/04 11:03 AM
                        RISC-V - incompetitive instruction set compared to ARMv8Linus Torvalds2019/11/04 11:27 AM
                          RISC-V - incompetitive instruction set compared to ARMv8David Hess2019/11/04 12:07 PM
                          RISC-V - incompetitive instruction set compared to ARMv8Michael S2019/11/04 01:22 PM
                            RISC-V - incompetitive instruction set compared to ARMv8Linus Torvalds2019/11/04 03:08 PM
                Flags RegisterDavid Hess2019/11/04 11:05 AM
                  Flags RegisterWilco2019/11/04 02:49 PM
                    Flags RegisterMaynard Handley2019/11/04 07:17 PM
                    Flags RegisterDavid Hess2019/11/05 04:35 PM
                      Flags RegisterWilco2019/11/05 05:54 PM
                        Flags RegisterMegol2019/11/06 06:11 AM
                          Flags RegisterMaynard Handley2019/11/07 02:42 PM
          RISC-V - instruction fusionAnon2019/11/06 06:40 PM
      RISC-V - incompetitive instruction set compared to ARMv8David Hess2019/11/04 10:38 AM
        RISC-V - incompetitive instruction set compared to ARMv8Michael S2019/11/04 10:59 AM
          RISC-V - incompetitive instruction set compared to ARMv8David Hess2019/11/04 11:11 AM
            RISC-V - incompetitive instruction set compared to ARMv8Michael S2019/11/04 11:17 AM
              RISC-V - incompetitive instruction set compared to ARMv8David Hess2019/11/04 11:54 AM
                RISC-V - incompetitive instruction set compared to ARMv8anon.12019/11/05 07:17 AM
                  RISC-V - incompetitive instruction set compared to ARMv8Linus Torvalds2019/11/05 12:39 PM
                    RISC-V - incompetitive instruction set compared to ARMv8anon.12019/11/06 12:19 PM
                      RISC-V - incompetitive instruction set compared to ARMv8Doug S2019/11/06 12:47 PM
                        RISC-V - incompetitive instruction set compared to ARMv8David Hess2019/11/06 07:36 PM
                          RISC-V - incompetitive instruction set compared to ARMv8Maynard Handley2019/11/06 08:32 PM
                            RISC-V - incompetitive instruction set compared to ARMv8j2019/11/07 04:33 AM
                          RISC-V - incompetitive instruction set compared to ARMv8TREZA2019/11/07 01:31 PM
                            RISC-V - incompetitive instruction set compared to ARMv8David Hess2019/11/08 08:15 PM
                              RISC-V - incompetitive instruction set compared to ARMv8Maynard Handley2019/11/08 09:40 PM
                                RISC-V - incompetitive instruction set compared to ARMv8none2019/11/09 02:02 AM
                        RISC-V - incompetitive instruction set compared to ARMv8anon.12019/11/06 10:36 PM
                          The RISC-V bitmanip ISA extension has conditional movesRonald Maas2019/11/07 12:53 AM
                            Both are excellent ISAs ?Michael S2019/11/07 01:58 AM
                            The RISC-V bitmanip ISA extension has conditional movesdmcq2019/11/07 05:33 AM
                              The RISC-V bitmanip ISA extension has conditional movesRonald Maas2019/11/07 08:31 AM
                            The RISC-V bitmanip ISA extension has conditional movesAdrian2019/11/07 09:38 AM
                              The RISC-V bitmanip ISA extension has conditional movesGabriele Svelto2019/11/08 02:32 AM
                            The RISC-V bitmanip ISA extension has conditional movesanon.12019/11/07 06:39 PM
                              The RISC-V bitmanip ISA extension has conditional movesBrett2019/11/07 07:50 PM
                                The RISC-V bitmanip ISA extension has conditional movesanon.12019/11/07 10:47 PM
                                  The RISC-V bitmanip ISA extension has conditional movesBrett2019/11/08 03:00 PM
                                    The RISC-V bitmanip ISA extension has conditional movesMaynard Handley2019/11/08 06:00 PM
                                    The RISC-V bitmanip ISA extension has conditional movesDavid Hess2019/11/08 08:28 PM
                                      The RISC-V bitmanip ISA extension has conditional movesanon.12019/11/08 09:14 PM
                      RISC-V - incompetitive instruction set compared to ARMv8G. Boniface2019/11/07 06:59 AM
                        Op fusion and superscalar execution do NOT share same hardwareHeikki Kultala2019/11/07 08:39 AM
                          Op fusion and superscalar execution do NOT share same hardwareRonald Maas2019/11/07 09:29 AM
                            Op fusion and superscalar execution do NOT share same hardwareanon2019/11/07 09:37 AM
                            Op fusion and superscalar execution do NOT share same hardwareWilco2019/11/07 12:41 PM
                            Op fusion and superscalar execution do NOT share same hardwareFoo_2019/11/07 12:42 PM
                              Op fusion and superscalar execution do NOT share same hardwareanon.12019/11/07 11:00 PM
                    RISC-V - incompetitive instruction set compared to ARMv8wumpus2019/11/06 05:19 PM
              RISC-V - conditional branches are problematic tooWilco2019/11/04 02:31 PM
                reg-reg branchesMichael S2019/11/06 02:37 AM
                  reg-reg branchesWilco2019/11/07 05:55 PM
      RISC-V - incompetitive instruction set compared to ARMv8Montaray Jack2019/11/08 02:38 AM
        RISC-V - incompetitive instruction set compared to ARMv8Gabriele Svelto2019/11/08 07:03 AM
  Risc-V getting real?Konrad Schwarz2019/11/20 08:12 AM
Reply to this Topic
Name:
Email:
Topic:
Body: No Text
How do you spell avocado?