clang __builtin_addcll

By: Michael S (already5chosen.delete@this.yahoo.com), October 21, 2017 11:05 am
Room: Moderated Discussions
Wilco (Wilco.Dijkstra.delete@this.ntlworld.com) on October 21, 2017 7:16 am wrote:
> Adrian (a.delete@this.acm.org) on October 21, 2017 1:49 am wrote:
> > Maynard Handley (name99.delete@this.name99.org) on October 20, 2017 8:16 pm wrote:
>
> > The low performance for multi-precision operations is not surprising.
> >
> > While this version of Mathematica can probably be improved a lot, it cannot not reach parity
> > with x86, because this (support for multi-precision operations) is exactly the area were the
> > ARMv8 ISA is the most deficient compared with the x86 ISA (especially since Broadwell, but
> > also Intel since Nehalem & the AMD before Bulldozer were far above any competition).
>
> What essential instructions do you think are missing? It's trivial to do fast bignums on AArch64, so
> adding new instructions cannot give much gain, let alone 20x. Most likely the difference is due to using
> a badly written generic C implementation in one case and hand optimized assembly in the other.
>
> Wilco
>
>

clang has primitives for exactly that sort of tasks, but right now they appear to do more harm that good, at least on x86. Generated code is horrible.

https://godbolt.org/g/RT9hNL

So far I didn't figure out how to force clang of goldbolt to generate aarch64 code.

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                  Does this give better formatting?anon2017/10/21 10:01 AM
        Mathematica on iPadAdrian2017/10/21 01:49 AM
          Sorry for the typoAdrian2017/10/21 01:51 AM
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          Mathematica on iPadWilco2017/10/21 07:16 AM
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            clang __builtin_addcllMichael S2017/10/21 11:05 AM
          Mathematica on iPadMaynard Handley2017/10/21 09:55 AM
  Mathematica on iPadAnon2017/10/21 04:20 PM
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      A quick search shows that Mathematica is using Intel MKLGabriele Svelto2017/10/21 11:38 PM
        A quick search shows that Mathematica is using Intel MKLAnon2017/10/22 05:12 PM
          A quick search shows that Mathematica is using Intel MKLMaynard Handley2017/10/22 06:08 PM
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            A quick search shows that Mathematica is using Intel MKLMichael S2017/10/23 05:32 AM
  Mathematica on iPadnone2017/10/22 06:06 AM
    Mathematica on iPaddmcq2017/10/23 03:43 AM
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