I've been benchmarking code all morning and this doesn't seem right. By itself
tr is slower than eq in comparing 13 character strings. I understand and
completely agree with that. What is strange to me is that tr is faster in a
loop than eq. The tr command in the eq loop should never execute. What's
happening? 
use strict;
use warnings;
use Benchmark qw(cmpthese);

my $string = '0'x13;
cmpthese(0, {
    'eq_loop' => q(for (0..12) {
         next if ($string eq '0000000000000');
         $_ = ($string =~ tr/1/1/);
     }),
    'tr_loop' => q(for (0..12) {
         next unless ($_ = ($string =~ tr/1/1/));
    }),
    'eq' => q($string eq '0000000000000';),
    'tr' => q($string =~ tr/1/1/;),
});

[download]

Benchmark: running eq, eq_loop, tr, tr_loop, each for at least 3 CPU seconds...
        eq:  4 wallclock secs ( 3.30 usr +  0.00 sys =  3.30 CPU) @ 1173221.21/s (n=3871630)
   eq_loop:  4 wallclock secs ( 3.00 usr +  0.00 sys =  3.00 CPU) @ 16577.00/s (n=49731)
        tr:  3 wallclock secs ( 3.08 usr +  0.00 sys =  3.08 CPU) @ 536228.57/s (n=1651584)
   tr_loop:  4 wallclock secs ( 3.17 usr +  0.00 sys =  3.17 CPU) @ 18796.53/s (n=59585)
             Rate eq_loop tr_loop      tr      eq
eq_loop   16577/s      --    -12%    -97%    -99%
tr_loop   18797/s     13%      --    -96%    -98%
tr       536229/s   3135%   2753%      --    -54%
eq      1173221/s   6977%   6142%    119%      --

In reply to tr faster than eq? by Keystroke

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