x86 MUL 64x64

By: Eric Fink (eric.delete@this.anon.com), July 26, 2022 1:06 am
Room: Moderated Discussions
none (none.delete@this.none.com) on July 25, 2022 11:35 pm wrote:
> Bill G (bill.delete@this.g.com) on July 25, 2022 10:06 pm wrote:
> > Adrian (a.delete@this.acm.org) on July 16, 2022 11:19 pm wrote:
> > > for the computations dominated by the use of floating-point numbers or big integer numbers,
> > > the AMD and Intel CPUs remain without competition (except from GPUs).
> >
> > What is it about AMD and Intel CPUs that make them good for computations on big integers? ARM
> > has add, subtract with carry flag instructions (ADC, SBC) and multiply, multiply-accumulate producing
> > the full width product (MULL, MLAL). x86 has similar instructions (ADCX, ADOX, MULX).
> I'm not sure what Adrian claim is, but Apple M1 likely is the fastest per clock CPU for GMP.
> See https://gmplib.org/gmpbench
> What matters (beyond what you wrote) is the number of integer multiplications you can issue
> per clock. For AArch64, you don't have 64x64->128 bit multiply instructions, so you have to
> use more 64x64->64 bit ones (AArch64 has 64x64->64 low and high, so you need 2 such
> instructions; a possibility, not implemented as far as I know, would be to fuse two such
> multiplies).

Isn't it also the case that the x86 64x64 MUL has some significant restrictions for the location of the operands? If I remember correctly, one of them has to be in EAX and the result is placed in EAX + EDX or something like that. Depending on your problem, this might require additional scaffolding to get things into place, making the advantage over ARM's two instruction approach less obvious.

Besides, are modern x86 implementations doing this operation with the same latency/throughtput as the truncated multiplication? I wouldn't be surprised if the full multiplication required more u-ops and were slower. Something like M1 that has more integer multiply ports can probably easily catch up even if the multiplication is split at the ISA level.
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Yitian 710 anonymous22021/10/20 08:57 PM
  Yitian 710 Adrian2021/10/21 12:20 AM
  Yitian 710 Wilco2021/10/21 03:47 AM
    Yitian 710 Rayla2021/10/21 05:52 AM
      Yitian 710 Wilco2021/10/21 11:59 AM
        Yitian 710 anon22021/10/21 05:16 PM
        Yitian 710 Wilco2022/07/16 12:21 PM
          Yitian 710 Anon2022/07/16 08:22 PM
            Yitian 710 Rayla2022/07/17 09:10 AM
              Yitian 710 Anon2022/07/17 12:04 PM
                Yitian 710 Rayla2022/07/17 12:08 PM
                  Yitian 710 Wilco2022/07/17 01:16 PM
                    Yitian 710 Anon2022/07/17 01:32 PM
                      Yitian 710 Wilco2022/07/17 02:22 PM
                        Yitian 710 Anon2022/07/17 02:47 PM
                          Yitian 710 Wilco2022/07/17 03:50 PM
                            Yitian 710 Anon2022/07/17 08:46 PM
                              Yitian 710 Wilco2022/07/18 03:01 AM
                                Yitian 710 Anon2022/07/19 11:21 AM
                                  Yitian 710 Wilco2022/07/19 06:15 PM
                                    Yitian 710 Anon2022/07/21 01:25 AM
                                      Yitian 710 none2022/07/21 01:49 AM
                                        Yitian 710 Anon2022/07/21 03:03 AM
                                          Yitian 710 none2022/07/21 04:34 AM
                                      Yitian 710 James2022/07/21 02:29 AM
                                        Yitian 710 Anon2022/07/21 03:05 AM
                                      Yitian 710 Wilco2022/07/21 04:31 AM
                                        Yitian 710 Anon2022/07/21 05:17 AM
                                          Yitian 710 Wilco2022/07/21 05:33 AM
                                            Yitian 710 Anon2022/07/21 05:50 AM
                                              Yitian 710 Wilco2022/07/21 06:07 AM
                                                Yitian 710 Anon2022/07/21 06:20 AM
                                                  Yitian 710 Wilco2022/07/21 10:02 AM
                                                    Yitian 710 Anon2022/07/21 10:22 AM
                    Yitian 710 Adrian2022/07/17 11:09 PM
                      Yitian 710 Wilco2022/07/18 01:15 AM
                        Yitian 710 Adrian2022/07/18 02:35 AM
          Yitian 710 Adrian2022/07/16 11:19 PM
            Computations on Big IntegersBill G2022/07/25 10:06 PM
              Computations on Big Integersnone2022/07/25 11:35 PM
                x86 MUL 64x64 Eric Fink2022/07/26 01:06 AM
                  x86 MUL 64x64 Adrian2022/07/26 02:27 AM
                  x86 MUL 64x64 none2022/07/26 02:38 AM
                    x86 MUL 64x64 Jörn Engel2022/07/26 10:17 AM
                      x86 MUL 64x64 Linus Torvalds2022/07/27 10:13 AM
                        x86 MUL 64x64 2022/07/28 09:40 AM
                        x86 MUL 64x64 Jörn Engel2022/07/28 10:18 AM
                          More than 3 registers per instruction-.-2022/07/28 07:01 PM
                            More than 3 registers per instructionAnon2022/07/28 10:39 PM
                            More than 3 registers per instructionJörn Engel2022/07/28 10:42 PM
                              More than 3 registers per instruction-.-2022/07/29 04:31 AM
                Computations on Big IntegersBill G2022/07/26 01:40 AM
                  Computations on Big Integersnone2022/07/26 02:17 AM
                    Computations on Big IntegersBill G2022/07/26 03:52 AM
                    Computations on Big Integers---2022/07/26 09:57 AM
                  Computations on Big IntegersAdrian2022/07/26 02:53 AM
                    Computations on Big IntegersBill G2022/07/26 03:39 AM
                      Computations on Big IntegersAdrian2022/07/26 04:21 AM
                    Computations on Big Integers in Apple AMX UnitsBill G2022/07/26 04:28 AM
                      Computations on Big Integers in Apple AMX UnitsAdrian2022/07/26 05:13 AM
                        TypoAdrian2022/07/26 05:20 AM
                          IEEE binary64 is 53 bits rather than 52. (NT)Michael S2022/07/26 05:34 AM
                            IEEE binary64 is 53 bits rather than 52.Adrian2022/07/26 07:32 AM
                              IEEE binary64 is 53 bits rather than 52.Michael S2022/07/26 10:02 AM
                                IEEE binary64 is 53 bits rather than 52.Adrian2022/07/27 06:58 AM
                                  IEEE binary64 is 53 bits rather than 52.none2022/07/27 07:14 AM
                                    IEEE binary64 is 53 bits rather than 52.Adrian2022/07/27 07:55 AM
                                      Thanks a lot for the link to the article! (NT)none2022/07/27 08:09 AM
                          TypozArchJon2022/07/26 09:51 AM
                            TypoMichael S2022/07/26 10:25 AM
                              TypozArchJon2022/07/26 11:52 AM
                                TypoMichael S2022/07/26 01:02 PM
                    Computations on Big IntegersMichael S2022/07/26 05:55 AM
                      Computations on Big IntegersAdrian2022/07/26 07:59 AM
                        IFMA and DivisionBill G2022/07/26 04:25 PM
                          IFMA and Divisionrwessel2022/07/26 08:16 PM
                          IFMA and DivisionAdrian2022/07/27 07:25 AM
                      Computations on Big Integersnone2022/07/27 01:22 AM
                    Big integer multiplication with vector IFMABill G2022/07/29 01:06 AM
                      Big integer multiplication with vector IFMAAdrian2022/07/29 01:35 AM
                        Big integer multiplication with vector IFMA-.-2022/07/29 04:32 AM
                          Big integer multiplication with vector IFMAAdrian2022/07/29 09:47 PM
                            Big integer multiplication with vector IFMAAnon2022/07/30 08:12 AM
                              Big integer multiplication with vector IFMAAdrian2022/07/30 09:27 AM
                                AVX-512 unfriendly to heter-performance coresPaul A. Clayton2022/07/31 03:20 PM
                                  AVX-512 unfriendly to heter-performance coresAnon2022/07/31 03:33 PM
                                    AVX-512 unfriendly to heter-performance coresanonymou52022/07/31 05:03 PM
                                  AVX-512 unfriendly to heter-performance coresBrett2022/07/31 07:26 PM
                                  AVX-512 unfriendly to heter-performance coresAdrian2022/08/01 01:45 AM
                                    Why can't E-cores have narrow/slow AVX-512? (NT)anonymous22022/08/01 03:37 PM
                                      Why can't E-cores have narrow/slow AVX-512?Ivan2022/08/02 12:09 AM
                                        Why can't E-cores have narrow/slow AVX-512?anonymou52022/08/02 10:13 AM
                                        Why can't E-cores have narrow/slow AVX-512?Dummond D. Slow2022/08/02 03:02 PM
                                    AVX-512 unfriendly to heter-performance coresPaul A. Clayton2022/08/02 01:19 PM
                                      AVX-512 unfriendly to heter-performance coresAnon2022/08/02 09:09 PM
                                      AVX-512 unfriendly to heter-performance coresAdrian2022/08/03 12:50 AM
                                        AVX-512 unfriendly to heter-performance coresAnon2022/08/03 09:15 AM
                                          AVX-512 unfriendly to heter-performance cores-.-2022/08/03 08:17 PM
                                            AVX-512 unfriendly to heter-performance coresAnon2022/08/03 09:02 PM
                        IFMA: empty promises from Intel as usualKent R2022/07/29 07:15 PM
                          No hype lasts foreverAnon2022/07/30 08:06 AM
                        Big integer multiplication with vector IFMAme2022/07/30 09:15 AM
                Computations on Big Integers---2022/07/26 09:48 AM
                  Computations on Big Integersnone2022/07/27 01:10 AM
                    Computations on Big Integers---2022/07/28 11:43 AM
                      Computations on Big Integers---2022/07/28 06:44 PM
              Computations on Big Integersdmcq2022/07/26 02:27 PM
                Computations on Big IntegersAdrian2022/07/27 08:15 AM
                  Computations on Big IntegersBrett2022/07/27 11:07 AM
      Yitian 710 Wes Felter2021/10/21 12:51 PM
        Yitian 710 Adrian2021/10/21 01:25 PM
    Yitian 710 Anon2021/10/21 06:08 AM
      Strange definition of the word single. (NT)anon22021/10/21 05:00 PM
        AMD Epyc uses chiplets. This is why "strange"?Mark Roulo2021/10/21 05:08 PM
          AMD Epyc uses chiplets. This is why "strange"?anon22021/10/21 05:34 PM
            Yeah. Blame spec.org, too, though!Mark Roulo2021/10/21 05:58 PM
              Yeah. Blame spec.org, too, though!anon22021/10/21 08:07 PM
                Yeah. Blame spec.org, too, though!Björn Ragnar Björnsson2022/07/17 06:23 AM
              Yeah. Blame spec.org, too, though!Rayla2022/07/17 09:13 AM
                Yeah. Blame spec.org, too, though!Anon2022/07/17 12:01 PM
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