How is “my” faster than “local” in Perl?

Question

Quoting from PerlMonks: The difference between my and local,

But in real life, they work virtually the same? Yes. Sort of. So when shoul

Answer 1

local is probably slower because of the need to save the old value, but the speed of local vs my should not come into the discussion at all. The speed savings is minuscule:

           Rate local    my
local 7557305/s    --   -2%
my    7699334/s    2%    --

and the features of the two are radically different. The results above come from the following benchmark:

#!/usr/bin/perl

use strict;
use warnings;

use Benchmark;

our $x;

my %subs = (
    local => sub {
        local $x = 42;
        return $x;
    },
    my => sub {
        my $x = 42;
        return $x;
    }
);

for my $sub (keys %subs) {
    print "$sub: ", $subs{$sub}(), "\n";
}

Benchmark::cmpthese -1, \%subs;