my @patterns=qw/foo bar baz blarch/;
my $tilly=qr/(@{[join "|",@patterns]})/;
my @chetlin=map qr/$_/,@patterns;
my $target="foo baz blarcy foo blarch"x400;

sub tilly {
    my $count;
    $count++ while ($target =~ /$tilly/g);
    print STDERR "tilly gives: $count\n" if ((caller)[1]!~/eval/);
}

sub chetlin {
    my $count;
    for (@chetlin) {$count++ while ($target =~ /$_/g) }
    print STDERR "chetlin gives: $count\n" if ((caller)[1]!~/eval/);
}

tilly();
chetlin();

use Benchmark;

timethese(-5, { tilly   => \&tilly,
                chetlin => \&chetlin,
});