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After a long long time using a fairly ancient Perl, I'm now able to use a more modern build. But I'm running into a fairly severe regex performance regression, and not sure where to start looking...

I've reduced it to this small testcase, where he sub below is called with a large input file (118Mb) that's been slurped into a string:

sub parse_foo { my ($text) = @_; my $name; { last if $text =~ /\G \s* \Z/gcmsx; if ($text =~ /\G \s* ^ \s* begfoo \s+ (\S+?) \s* \( \s* (. +*?) \s* \) \s* ;/gcmsx) { $name = $1 } elsif ($text =~ /\G \s* ^ \s* endfoo /gcmsx) { } elsif ($text =~ /\G \s* ^ \s* \S+ \s+ .*? \s* ;/gcmsx) { } else { die "ERROR: unknown syntax\n" } redo; } print "LAST FOO: $name\n"; }

Using 5.8.8, it runs in about 5 seconds. Using 5.30.0, it takes about 105 seconds. (And it's the same story when I try it on the latest stable release, 5.32.1). I ran NYTProf on both 5.8.8 and 5.30.0, and it boils down to the difference in these two lines:

5.8.8

last if $text =~ /\G \s* \Z/gcmsx; # spent 181ms making 866465 calls to main::CORE:match, avg 208ns/c +all if ($text =~ /\G \s* ^ \s* begfoo \s+ (\S+?) \s* \( \s* (.*?) \s +* \) \s* ;/gcmsx) { $name = $1 } # spent 3.74s making 2547279 calls to main::CORE:match, avg 1µs/cal +l

5.30.0

last if $text =~ /\G \s* \Z/gcmsx; # spent 289ms making 866465 calls to main::CORE:match, avg 334ns/ca +ll if ($text =~ /\G \s* ^ \s* begfoo \s+ (\S+?) \s* \( \s* (.*?) \s +* \) \s* ;/gcmsx) { $name = $1 } # spent 103s making 2547279 calls to main::CORE:match, avg 41µs/ca +ll
Am I unwittingly doing something in my code that has been deprecated (I think I got this parsing/nibbling regex style using a block for looping from the original Effective Perl Programming), and now there's a better way? Thanks!

In reply to regex gotcha moving from 5.8.8 to 5.30.0? by mordibity

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