Perl 5.22 introduced the 'refaliasing' feature. The simplest solution to the example is:

use v5.22;
use warnings;
use feature 'refaliasing';

# Silence warnings if desired:
no warnings 'experimental::refaliasing';

my ($x, $y);
\$x = \$y; # alias here
$x = 5;
say $y; # prints 5
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