SvREFCNT is exposed in Devel::Peek (no need to go to CPAN), which is a bit easier to use than embedding XS. For example:

use Devel::Peek qw(SvREFCNT);

$x = 42;
$y = \$x;

$refs_for_x = SvREFCNT($x);
print "$refs_for_x\n";
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Prints 2.