Remove Empty html tags from string - PHP

The below function is used to remove empty html tags from html content.
Note : This function is only removed the empty html tag without any attribute.

Example :
1.<p>GvSubhu<p></p></p> => <p>GvSubhu</p>
2.<p>GvSubhu<p></p><a href="#"></a></p> => <p>GvSubhu</p><a href="#"></a>

Code :

function remove_empty_tags ($str)
{
    if (!is_string ($str) || trim ($str) == '')
            return $str;

    return preg_replace ( '/<([^</>]*)>([s]*?|(?R))</1>/imsU', $repto, $str );
}

$str="<b>This is <p></p>GvSubhu</b><pre></pre>";

echo htmlentities(remove_empty_tags ($str));

Output :
<b>This is GvSubhu</b>