got it, thanks.

use Benchmark 'cmpthese';

cmpthese(-2, {
    predecl => '
        my $y;
        my $x;
        for $x (1..10000) { $y+=$x }
    ',
    lexical => '
        my $y;
        for my $x (1..10000) { $y+=$x }
    ',
    aliased => '
        my $y;
        for (1..10000) { $y+=$_ }
    ',
});
[download]

Seems you are right!

          Rate aliased lexical predecl
aliased 3733/s      --     -3%     -5%
lexical 3858/s      3%      --     -2%
predecl 3938/s      5%      2%      --
[download]