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";
}

[download]

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

[download]

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

[download]
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

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.