use Benchmark
Benchmark::cmpthese( -10, {
  non => sub{my $g = 10; my $lim = 10;
             for ( my $i = 1; $i < $lim; ++$i ) { --$g }},
  wit => sub{my $g = 10; my $lim = 10;
             for ( my $i = 1; $i < $lim; ++$i ) { --$lim }}
} )

__END__

        Rate  non  wit
non 507747/s   -- -26%
wit 685879/s  35%   --