@matches= $string =~ /$regex/gk;

##</code><code>##

#!/usr/bin/perl -w
use strict;
use Benchmark qw( timethis cmpthese );

my %t;
my $pref= "no&";
my $str= "match" . ( "garbage" x 500 );
for( 0, 1 ) {
    $t{$pref."?:"}= timethis( -3, sub {
        $str =~ /(?:match)+/;
    } );
    $t{$pref."()"}= timethis( -3, sub {
        $str =~ /(match)+/;
    } );
    eval '$&';
    $pref= "amp";
}
cmpthese( \%t );
__END__
           Rate amp() no&() amp?: no&?:
amp()  439813/s    --   -0%   -1%  -81%
no&()  441612/s    0%    --   -0%  -81%
amp?:  443563/s    1%    0%    --  -81%
no&?: 2354611/s  435%  433%  431%    --