$complex_re = /^($ip) ($host) ($msg)$/ if (
    $ip   = /\d+\.\d+\.\d+\.\d+/,
    $host = /[\-\.\w]+/,
    $msg  = /.*/
);

##</code><code>##

my $complex_re = eval {
    my $ip   = qr/\d+\.\d+\.\d+\.\d+/;
    my $host = qr/[\-\.\w]+/;
    my $msg  = qr/.*/;

    return /^($ip) ($host) ($msg)$/;
);

##</code><code>##

                 Rate    with eval without eval
with eval    116279/s           --          -5%
without eval 121951/s           5%           --