Description:
------------
PHP version was from a pull of the 5.6 branch this morning.

sapi/cli/php -v
PHP 5.6.1-dev (cli) (built: Aug 27 2014 11:35:34) (DEBUG)

Configured with --disable-all --enable-debug --enable-bcmath and --with-gmp 

I believe there may be a refcount issue with either the shift-left-assign or or-assign operators. I can reliably exhaust available memory with a function using these operators.

In the provided script import() works as intended and does not use the assign-ops, whereas import2() uses assign-ops and causes memory exhaustion.

Test script:
---------------
function import($bin)
{
    $c = unpack('C*', $bin);

    $i = count($c);
    $ret = gmp_init($c[$i--]);
    while ($i > 0) {
        $ret = ($ret << 8) | $c[$i--];
    }

    return $ret;
}

function import2($bin)
{
    $c = unpack('C*', $bin);

    $i = count($c);
    $ret = gmp_init($c[$i--]);
    while ($i > 0) {
        $ret <<= 8;
        $ret |= $c[$i--];
    }

    return $ret;
}

print "import 1 x 10000\n";
for ($i = 0; $i < 10000; $i++) {
    import(str_repeat('a', 100));
}

print "import 2 x 10000\n";
for ($i = 0; $i < 10000; $i++) {
    import2(str_repeat('a', 100));
}


Expected result:
----------------
import 1 x 10000
import 2 x 10000

Process finished with exit code 0

Actual result:
--------------
import 1 x 10000
import 2 x 10000

Fatal error: Allowed memory size of 134217728 bytes exhausted at gmp.c:384 (tried to allocate 48 bytes) in test.php on line 24

Process finished with exit code 255