o  - pretend to optimize your code, but actually introduce bugs

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;

use Benchmark 'cmpthese';

my $str = 'xyz';
my $re = qr{^xyz$};

cmpthese 0 => {
    use_m => \&use_m,
    as_qr => \&as_qr,
    use_o => \&use_o,
    raw_m => \&raw_m,
    raw_o => \&raw_o,
};

sub use_m {
    $str =~ m/$re/ and return;
}

sub as_qr {
    $str =~ $re and return;
}

sub use_o {
    $str =~ m/$re/o and return;
}

sub raw_m {
    $str =~ m/^xyz$/ and return;
}

sub raw_o {
    $str =~ m/^xyz$/o and return;
}

##</code><code>##

            Rate as_qr use_m use_o raw_m raw_o
as_qr  2729934/s    --   -0%  -71%  -73%  -73%
use_m  2734042/s    0%    --  -71%  -73%  -73%
use_o  9454792/s  246%  246%    --   -6%   -7%
raw_m 10094766/s  270%  269%    7%    --   -1%
raw_o 10207253/s  274%  273%    8%    1%    --