https://stackoverflow.com/q/48961457/9300627

regbench.pl

use warnings;
use strict;
use Benchmark qw/cmpthese/;

for my $r (10,100,1_000,10_000) {
	print "   ___ $r ___\n";
	my $str = "foo;bar;" x $r;
	cmpthese(-1, {
		orig => sub { # https://stackoverflow.com/q/48961457/9300627
			$str=~s/\b([^;]+)(?=.*;\1;);//gr;
		},
		revo => sub { # https://stackoverflow.com/a/48961672/9300627
			$str=~s/(?<![^;])([^;]++;)(?=(?>[^;]*;)*?\1)//gr;
		},
		split => sub { # https://stackoverflow.com/a/48961541/9300627
			my %seen;
			join ';', grep { !$seen{$_}++ } split /;/, $str;
		},
	});
}

__END__

   ___ 10 ___
          Rate  revo  orig split
revo  142174/s    --   -8%  -64%
orig  154984/s    9%    --  -61%
split 398221/s  180%  157%    --
   ___ 100 ___
         Rate  orig  revo split
orig  11294/s    --  -22%  -77%
revo  14499/s   28%    --  -70%
split 48762/s  332%  236%    --
   ___ 1000 ___
        Rate  orig  revo split
orig   316/s    --  -80%  -94%
revo  1614/s  411%    --  -69%
split 5288/s 1573%  228%    --
   ___ 10000 ___
        Rate   orig   revo  split
orig  3.88/s     --   -98%   -99%
revo   160/s  4020%     --   -70%
split  532/s 13609%   233%     --