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Regex optimizer on \s+$ is "dumb as bricks" #5470

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p6rt opened this issue Jul 21, 2016 · 2 comments
Open

Regex optimizer on \s+$ is "dumb as bricks" #5470

p6rt opened this issue Jul 21, 2016 · 2 comments
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@p6rt
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@p6rt p6rt commented Jul 21, 2016

Migrated from rt.perl.org#128693 (status was 'new')

Searchable as RT128693$

@p6rt
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@p6rt p6rt commented Jul 21, 2016

From @ajs

When given a pathological input that will always fail, /\s+$/ seems to take
the longest way home. Example in the IRC excerpt, below.

From the IRC discussion​:

[14​:11] <timotimo> m​: use nqp; ((" " x 10000) ~ "end") ~~ / \s+$ /; say now
- INIT now
[14​:11] <+camelia> rakudo-moar 68afa3​: OUTPUT«10.1804368␤»
[14​:11] <timotimo> ah. no. it's definitely the regex :)
[14​:11] <harmil> nice test case, though!
[14​:11] <harmil> I'll submit this. At least it will be useful as a note for
the future.
[14​:11] <timotimo> our regex optimizer is dumb as bricks ;)

--
Aaron Sherman, M.​:
P​: 617-440-4332 Google Talk, Email and Google Plus​: ajs@​ajs.com
Toolsmith, developer, gamer and life-long student.

@p6rt
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@p6rt p6rt commented Jul 21, 2016

From @ajs

Oddly, this also takes a very long time, so I'm no longer certain what the slowdown is​:

time perl6 -e 'my $c = (" " x 10000) ~ "end"; $c ~~ /" " ** 10000..10000 $/ and die'

real 0m15.403s
user 0m15.329s
sys 0m0.046s

@p6rt p6rt added the perf label Jan 5, 2020
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