Description:
------------
see https://3v4l.org/BeuOd

issue present since PHP 7.4, but not documented in https://github.com/php/php-src/blob/PHP-7.4/NEWS nor UPGRADING

minimalistic test script below should be part of php core test

Test script:
---------------
<?php

class X {
    public $r;
    public $r2;
    
    public function __destruct() {
        $this->r2 = null;
    }
}

function getCircle() {
    $a = new X();
    $b = new X();
    $c = new X();
    $a->r = $c;
    $b->r = $a;
    $c->r = $b;
    
    return $a;
}

$zeroMemory = memory_get_usage();

$u = getCircle();
$u->r2 = getCircle();
$u = null;
gc_collect_cycles();
var_dump(memory_get_usage()- $zeroMemory);

Expected result:
----------------
int(0)

Actual result:
--------------
int(480)