[Vm-dev] String comparison primitive preliminary speed-up result: 20-600x

Denis Kudriashov dionisiydk at gmail.com
Wed Feb 21 12:03:42 UTC 2018

Thank's Clement and others.

Really huge improvement. And we will finally have standard return values
for comparison.

2018-02-21 11:33 GMT+01:00 Clément Bera <bera.clement at gmail.com>:

> Hi all,
> *The short version:*
> After looking into MiscPlugin with Eliot, we decided to work on a numbered
> primitive to speed up String comparison especially String>>#= (which
> matters for parsers that are widely used by our communities) as a long-term
> replacement for compare:with:collated: Misc primitive. Being numbered
> allows the JIT to have an entry for it. We (likely Eliot) will work on
> other Misc primitives to compile them differently in the future (No
> Smalltalk level smart syntax to ease cross language management) but aside
> from String comparison, they will remain in a plugin, since they're not as
> critical.
> The new primitive is as follow (optional last parameter so 2 versions):
> ByteString >> *compareWith:* anotherString
> ByteString >> *compareWith:* anotherString *collated:* order
> "Return a negative Smi, 0 or a positive Smi if self is < = or  > to
> anotherString, with the collating order of characters given optionally by
> the order array."
> Preliminary benchmarks show 20 to 600x speed-up in String comparison (< <=
> = > >= on Strings; 600x on small strings, 20x on large strings). String
> comparison does not use any more the optional last parameter, only other
> APIs do. Sophie in CC did the bulk of the work as part of a 100h student
> project, though various discussion in the mailing list involving many of us
> but especially Levente, Eliot and me helped a lot. There are still some
> tests to write to make sure everything is stable before integration, but my
> understanding is that integration should happen anytime soon. Sophie, could
> you please answer a time frame for integration to this mail?
> *The long version:*
> The blog version includes assembly code, Cog's RTL code & Slang code for
> each version as well as the exact preliminary benchmarks we ran:
> https://clementbera.wordpress.com/2018/02/17/massive-string-
> comparison-performance-boost-up-coming-in-the-cog-vm/
> Levente maybe you want to review the long version in my blog if you have
> comments/advises before integration. I guess you will write accurate
> micro-benchmarks once it's integrated anyway.
> This LLVM/GCC performance difference is very annoying though for correct
> evaluation of speed-ups, I wonder, have any one seen a difference there
> before for other primitives? PrimitiveStringReplace might have similar
> issues. I don't know if we could report those things as bugs to the LLVM
> people somehow.
> Best,
> --
> Clément Béra
> Pharo consortium engineer
> https://clementbera.wordpress.com/
> Bâtiment B 40, avenue Halley 59650 Villeneuve d'Ascq
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