Modestly expanded response: MY66000 predicate shadow

By: Paul A. Clayton (paaronclayton.delete@this.gmail.com), January 7, 2019 10:53 am
Room: Moderated Discussions
Michael S (already5chosen.delete@this.yahoo.com) on January 6, 2019 1:01 am wrote:
> anon (spam.delete.delete.delete@this.this.this.spam.com) on January 5, 2019 5:14 pm wrote:
[snip]
>> Predication was completely dropped for Thumb (unless you count branches) and Thumb2
>> only got the "if-then-else" instruction to predicate the next 1-4 instructions.
>>
>> You could certainly call only "predicating" branches and a single instruction instead of all instructions
>> "less ubiquitous", but on the other hand every instruction can still be predicated indirectly.
>
> Yes, I forgot to take IT into account.
> I wonder if there are uArch tricks that could make implementation of IT cheaper than full predication.

Since Mitch Alsup has described his practical/didactic RISC ISA, MY66000, extensively on comp.arch, you are presumably aware that he chose to define an instruction similar to If-Then (with explicit support for overlays, which (IIRC) are explicitly disallowed with Thumb2). While his argument in support of such on comp.arch has (as I recall) been focused on code density (and he has emphasized the RISC-y composability which facilitates more complex masking), his hardware orientation is obvious so the choice must also have been practical. (One of his recent-ish posts mentioned some hardware implementation details, but I have not given such a thoughtful reading.)

Obviously, earlier knowledge of use may facilitate optimizations (such as early removal of predicated-off operations), but my very minor point was that if a somewhat broadly experienced hardware designer (RISC [M88k], CISC [x86], GPU, possibly others) proposes an ISA feature it is likely to be practical for a variety of implementations. (Mitch Alsup is a strong believer in hardware execution of the long-term stable software distribution format, so he necessarily believes that any proposed ISA feature be friendly to a variety of microarchitectures and implementation technologies.)

(If I could give it the time and thought it deserves, I would already have asked him for his book-in-progress. His comp.arch postings are making it increasingly difficult to resist, but I know it would be a slow and difficult read (especially since I am not a "hardware person") and that I would be tempted to make hasty comments.)
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              Independent micro threadsDavid Hess2019/01/01 10:41 AM
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              Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Domaldel2018/12/31 11:44 PM
                Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Domaldel2018/12/31 11:49 PM
                  Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Domaldel2018/12/31 11:51 PM
              Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Simon Farnsworth2019/01/01 05:05 AM
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                Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Maynard Handley2019/01/01 12:17 PM
                  Taking things to extremes.Domaldel2019/01/01 04:44 PM
                    Yes, I know, the forum is named *Real* World Tech, but I'm thinking that perhapsDomaldel2019/01/01 04:52 PM
                      Yes, I know, the forum is named *Real* World Tech, but I'm thinking that perhapsMontaray Jack2019/01/02 06:26 AM
                        Yes, I know, the forum is named *Real* World Tech, but I'm thinking that perhapsMontaray Jack2019/01/02 07:21 AM
                    Taking things to extremes.Maynard Handley2019/01/01 05:55 PM
                    Taking things to extremes.Kevin G2019/01/04 07:57 AM
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    Independent micro threadsTravis Downs2018/12/30 06:38 PM
    Independent micro threadsBrett2018/12/30 06:41 PM
  Independent micro threadsanon2018/12/30 07:20 PM
    Independent micro threadsBrett2018/12/30 07:51 PM
      Independent micro threadsTravis Downs2018/12/30 08:48 PM
        Mill and Independent micro threadsBrett2019/01/01 06:39 PM
          No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Heikki Kultala2019/01/01 11:29 PM
            No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Brett2019/01/02 12:15 AM
              No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Heikki Kultala2019/01/02 01:22 AM
                No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Brett2019/01/03 12:13 AM
                  "Leaf branch" is not a commonly used termHeikki Kultala2019/01/03 02:48 AM
                    "Leaf branch" is not a commonly used termBrett2019/01/03 03:35 AM
                      You lack parallelism than OoOE givesHeikki Kultala2019/01/03 06:38 AM
                        You lack parallelism than OoOE givesBrett2019/01/04 01:41 AM
                          You lack parallelism than OoOE givesBrett2019/01/04 03:10 PM
                            You lack parallelism than OoOE givesBrett2019/01/05 07:29 PM
                              Mill speculates, more parallelism than OoOE givesBrett2019/01/05 07:31 PM
                                Mill *is* a speculationEric Bron2019/01/06 04:04 AM
                                  Mill *is* a speculationMichael S2019/01/06 04:53 AM
                                    Mill *is* a speculationBrett2019/01/06 08:03 PM
                                  Mill *is* a speculationjuanrga2019/01/06 05:10 AM
                                    probably ~2 (NT)Michael S2019/01/06 05:51 AM
                                  Mill *is* a speculationBrett2019/01/06 12:18 PM
                                    Mill *is* a speculationEric Bron2019/01/06 02:36 PM
                                      Mill *is* a speculationBrett2019/01/06 07:47 PM
                                        Mill *is* a speculationJacob Marley2019/01/06 09:29 PM
                                          Mill *is* a speculationBrett2019/01/07 03:24 AM
                                            Mill *is* a speculationMichael S2019/01/07 04:23 AM
                                            Mill *is* a speculationEric Bron2019/01/07 04:36 AM
                                              Mill *is* a speculationBrett2019/01/07 02:40 PM
                                                Mill *is* a speculationEric Bron2019/01/07 04:32 PM
                                            Mill is something you don't understandHeikki Kultala2019/01/08 03:19 AM
                                              Mill is something you don't understandMichael S2019/01/08 06:44 AM
                                                Itanium and static vs dynamicHeikki Kultala2019/01/09 02:14 AM
                                                  Itanium and static vs dynamicPaul A. Clayton2019/01/09 07:51 AM
                                        Mill *is* a speculationEric Bron2019/01/07 04:27 AM
                                          Mill *is* a speculationEric Bron2019/01/07 05:23 AM
                                      Mill *is* a speculationanon2019/01/07 05:24 AM
                                        Mill *is* a speculationEric Bron2019/01/07 05:52 AM
                                          Mill *is* a speculationanon2019/01/07 07:36 AM
                                            Mill *is* a speculationEric Bron2019/01/07 08:20 AM
                                        Mill *is* a speculationjuanrga2019/01/07 09:22 AM
                                          Mill *is* a speculationanon2019/01/07 12:16 PM
                                        Mill *is* a speculationanon2019/01/07 08:46 PM
                                          Mill *is* a speculationanon2019/01/08 12:56 AM
                                            Mill *is* a speculationanon2019/01/08 02:39 AM
                                              Mill *is* a speculationMichael S2019/01/08 02:52 AM
                                                Mill *is* a speculationanon2019/01/08 09:10 PM
                                                  Wasted width not wasted work.Brett2019/01/09 10:44 AM
                                                    No such thing was declared. (NT)anon2019/01/09 02:41 PM
                                                    Very simple test for new uarch ideassomeone2019/01/10 06:03 AM
                                                      Very simple test for new uarch ideasdmcq2019/01/10 06:21 AM
                                                        Very simple test for new uarch ideasDoug S2019/01/10 09:01 AM
                                                          Very simple test for new uarch ideasDan Fay2019/01/10 12:13 PM
                                                      Very simple test for new uarch ideasanonymous22019/01/10 10:03 AM
                                                        Very simple test for new uarch ideasAlberto2019/01/10 10:32 AM
                                                      Very simple test for new uarch ideasEtienne2019/01/11 02:03 AM
                                                        Very simple test for new uarch ideasFoo_2019/01/11 03:31 AM
                                                          Very simple test for new uarch ideasEtienne2019/01/11 04:51 AM
                                                            Very simple test for new uarch ideasFoo_2019/01/11 04:53 AM
                                                              Very simple test for new uarch ideasdmcq2019/01/11 05:08 AM
                                                              Very simple test for new uarch ideasEtienne2019/01/11 05:13 AM
                                                                Very simple test for new uarch ideasFoo_2019/01/11 05:54 AM
                                                                  Very simple test for new uarch ideasEtienne2019/01/11 06:32 AM
                                                                    Very simple test for new uarch ideasBrett2019/01/11 09:25 AM
                                                                      Very simple test for new uarch ideasMegol2019/01/12 05:29 AM
                                                                        Very simple test for new uarch ideasMichael S2019/01/12 08:21 AM
                                                                          Word salad AI fundamentaliy brokenBrett2019/01/12 12:59 PM
                                                                          Very simple test for new uarch ideasMegol2019/01/13 10:51 AM
                                              Mill *is* a speculationanon2019/01/08 07:50 AM
                                                Mill *is* a speculationEric Bron2019/01/08 08:03 AM
                                                  Mill *is* a speculationanon2019/01/08 08:21 AM
                      "Leaf branch" is not a commonly used termMichael S2019/01/03 06:57 AM
                        "Leaf branch" is not a commonly used termBrett2019/01/04 02:29 AM
                  Calls are not needed for speculation for mill if there are no side effect,and dont help if there areHeikki Kultala2019/01/08 03:28 AM
              No. Mill does not get the hit because it does not get the benefit even when correctly predicted.anon2019/01/02 02:05 AM
              No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Doug S2019/01/02 10:38 AM
                No. Mill does not get the hit because it does not get the benefit even when correctly predicted.rwessel2019/01/02 04:53 PM
                  No. Mill does not get the hit because it does not get the benefit even when correctly predicted.anon2019/01/02 07:56 PM
                    itanicBrett2019/01/02 11:41 PM
                      itanicanon2019/01/03 02:12 AM
                      itanicDavid Hess2019/01/03 07:06 AM
                    No. Mill does not get the hit because it does not get the benefit even when correctly predicted.rwessel2019/01/03 08:18 AM
                      No. Mill does not get the hit because it does not get the benefit even when correctly predicted.anon2019/01/04 04:25 AM
                    Itanium could have been RISC or CISC - same outcomesomeone2019/01/04 06:45 AM
                      Itanium could have been RISC or CISC - same outcomeDoug S2019/01/04 11:39 AM
                        Itanium could have been RISC or CISC - same outcomeJan Olšan2019/01/04 12:58 PM
                          "fluffyRISC" has a namevvid2019/01/04 02:48 PM
                        Itanium could have been RISC or CISC - same outcomeBrett2019/01/04 02:43 PM
                      Itanium could have been RISC or CISC - same outcomeanonymou52019/01/04 11:41 AM
                  No. Mill does not get the hit because it does not get the benefit even when correctly predicted.David Hess2019/01/03 07:15 AM
                No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Maynard Handley2019/01/03 11:24 AM
                  No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Maynard Handley2019/01/03 11:27 AM
                    No. Mill does not get the hit because it does not get the benefit even when correctly predicted.dmcq2019/01/04 12:59 AM
                  EPIC target marketsFoo_2019/01/04 05:29 AM
                    EPIC target marketsDoug S2019/01/04 11:42 AM
                      Lack of future visionDoug S2019/01/04 11:57 AM
                        Lack of future visionBrett2019/01/04 01:59 PM
                          Lack of future visionDoug S2019/01/04 03:25 PM
                            Lack of future visionBrett2019/01/04 04:18 PM
                              Lack of future visionDoug S2019/01/04 11:47 PM
                                Lack of future visionBrett2019/01/05 01:06 PM
                                  Lack of future visiondmcq2019/01/05 01:22 PM
                                  Lack of future visionanon2019/01/05 02:01 PM
                                    Lack of future visionMichael S2019/01/05 03:18 PM
                                      Lack of future visionanon2019/01/05 05:14 PM
                                        Lack of future visionMichael S2019/01/06 01:01 AM
                                          Lack of future visionanon2019/01/06 02:23 AM
                                          Mitch Alsup's MY66000 uses IF-like predication (I think) (NT)Paul A. Clayton2019/01/06 03:54 PM
                                            ??? (NT)Michael S2019/01/07 04:25 AM
                                            88K ? (NT)anonymous22019/01/07 03:20 PM
                                          Modestly expanded response: MY66000 predicate shadowPaul A. Clayton2019/01/07 10:53 AM
                      Thanks for the correction (NT)Foo_2019/01/04 03:31 PM
              No. Mill does not get the hit because it does not get the benefit even when correctly predicted.sdrc2019/01/04 06:36 AM
          Mill and Independent micro threadsMichael S2019/01/02 01:32 AM
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