I've encountered a memory leak in gmp_cmp if a literal string is used as the second value inside of loops. A workaround is to initialize first, then use the variable. I wasn't able to generate a minimum code sample, it's something more complicated, but I was able to fix it as follows:

<?php

$x = gmp_init(strval(mt_rand()));

// Depending on surrounding code, may have leaks
while (true)
{
    if (!gmp_cmp($x, '1'))
        print 'one'."\n";
}

// Usually doesn't have leaks
$one = gmp_init('1');

while (true)
{
    if (!gmp_cmp($x, $one))
        print 'one'."\n";
}

?>