cmpthese(-1, {
    'ampersand' => '
            use constant foo => 2; 
            sub a { my $x = 0; for (1..10000) { $x += &foo } }
            a(%ENV, %ENV, %ENV)
        ',
    'no_amp' => '
            use constant foo => 2; 
            sub a { my $x = 0; for (1..10000) { $x += foo } }
            a(%ENV, %ENV, %ENV)
        ',
});
__END__
           Rate ampersand    no_amp
ampersand 330/s        --      -61%
no_amp    849/s      157%        --