Description:
------------
with opcache other than "Null coalescing operator" the "Null Coalescing Assignment" is not completly optimized out

function a()
{
 $test = $test ?? TRUE;
 return $test;
}

function b()
{
 $test ??= TRUE;
 return $test;
}

runtime difference with 50000000 calls:
a(): 3.1884
b(): 3.3666

function name:  a
number of ops:  2
----------------------------------------------------------------------------------
   5     0*       COALESCE                                         ~1      !0
   6     1*       RETURN                                                   <true>

function name:  b
number of ops:  3
----------------------------------------------------------------------------------
  11     0*       COALESCE                                         ~1      !0
         1*       ASSIGN                                           $2      !0, <true>
  12     2*       RETURN                                                   !0