Does PHP optimize tail recursion?

I wrote a small piece of code that I believe should have succeeded if tail recursion was optimized, however it blew up the stack. Should I conclude PHP does not optimize tail recursion?

function sumrand($n,$sum) {
    if ($n== 0) {
        return $sum;
    }
    else {
        return (sumrand($n-1,$sum+rand(0,1)));
    }
}
echo sumrand(500000,0)."\n";