[perl #131805] [REGRESSION] [PERF] .grep-ing with a code block is now almost twice slower ( .grep({/foo/}) )

[Aleks-Daniel Jakimenko-Aleksejev via RT]

Oh! You're totally right!

Then, it's not as bad as it looks.

In fact, this commit actually *improved* the case when it has to match Str-s
(more than 2x speedup).

So perhaps the slowdown is not so critical. After all, how often do people
match thousands of Ints…

On 2017-07-26 23:55:21, elizabeth wrote:
> Looking at the profile of
>
> (^10000).grep({!/1/}).elems.say
>
> the first 5 entries (responsible for 70% of CPU in that example) have
> nothing to do with matching, but everything with trying to find the
> right dispatchee. And it looks like this is basically caused by:
>
> $_ = 1; /1/
>
> Because $_ contains an Int, this becomes a very slow path. Compare
> this with:
>
> (^10000)>>.Str.grep({!/1/}).elems.say
>
> which is 3x faster, even when using a sub-optimal hyper.
>
> Investigating further...
>
> > On 27 Jul 2017, at 04:06, Aleks-Daniel Jakimenko-Aleksejev (via RT)
> > <perl6-bugs-follo...@perl.org> wrote:
> >
> > # New Ticket Created by Aleks-Daniel Jakimenko-Aleksejev
> > # Please include the string: [perl #131805]
> > # in the subject line of all future correspondence about this issue.
> > # <URL: https://rt.perl.org/Ticket/Display.html?id=131805 >
> >
> >
> > See this benchable6 output:
> > https://gist.github.com/Whateverable/6001c5744e3c877d76928d465de31e46
> >
> > If you look closely, benchable has not only built the graph across
> > all releases, but it also bisected the performance drop to the exact
> > commit. Here is that commit:
> >
https://github.com/rakudo/rakudo/commit/b7201a8f22338a906f2d8027a21387e8f5c77f41
> >
> > This was double-checked with committable6:
> > <AlexDaniel> c: b7201a8^,b7201a8 (^99999).grep({!/1/}).elems.say; say
> > now - BEGIN now
> > <committable6> AlexDaniel, ¦b7201a8^: «59048␤5.0481256» ¦b7201a8:
> > «59048␤9.0262629»
> >
> > So it is ≈5 seconds before vs ≈9 seconds after. A significant
> > performance drop even if we assume possible bench noise.
> >
> > This was noticed because of this ticket:
> > https://github.com/perl6/doc/issues/1425
> >
> > See also IRC discussion: https://irclog.perlgeek.de/perl6/2017-07-
> > 27#i_14927626
> >
> > And maybe coverable output on HEAD if it may help you:
> > https://gist.github.com/Whateverable/f3db9e924cebe9b96a71a2b4cd67ae9c
> >
> > Note that whether it's {!/1/} or {/1/} doesn't really matter:
> > https://irclog.perlgeek.de/perl6/2017-07-27#i_14927789