$ cat test.pl
use 5.014;
use warnings;
use Benchmark qw(cmpthese);

foreach $a (undef, "", 0, 1, "x" x 60) {
    say "Testing for a = ", $a // "undef";

    cmpthese (-1, {
	def_eq  => sub { for (0..1000) { ! defined $a || $a eq ""   ? 1 : 0; }},
	def_len => sub { for (0..1000) { !(defined $a && length $a) ? 1 : 0; }},
	dor_eq  => sub { for (0..1000) { ($a // "") eq ""           ? 1 : 0; }},
	});
    }
$ perl test.pl
Testing for a = undef
           Rate  dor_eq  def_eq def_len
dor_eq   9135/s      --    -21%    -21%
def_eq  11499/s     26%      --     -1%
def_len 11605/s     27%      1%      --
Testing for a =
          Rate def_len  def_eq  dor_eq
def_len 7110/s      --     -8%    -25%
def_eq  7729/s      9%      --    -19%
dor_eq  9489/s     33%     23%      --
Testing for a = 0
           Rate def_len  def_eq  dor_eq
def_len  7518/s      --    -12%    -29%
def_eq   8533/s     14%      --    -19%
dor_eq  10577/s     41%     24%      --
Testing for a = 1
           Rate def_len  def_eq  dor_eq
def_len  7518/s      --    -12%    -29%
def_eq   8533/s     14%      --    -19%
dor_eq  10577/s     41%     24%      --
Testing for a = xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
           Rate def_len  def_eq  dor_eq
def_len  7450/s      --    -13%    -30%
def_eq   8533/s     15%      --    -20%
dor_eq  10676/s     43%     25%      --
$