2 include files:

[A.inc]
<?php
   class A { }
?>

[B.inc]
<?php
   require_once 'A.inc'; 
   class B extends A { }
?>

If A.inc is included before B.inc, then A is in EG(class_table) already
and early binding kicks in leaving us with an op_array for B.inc containing:

INCLUDE_OR_EVAL
NOP
NOP
RETURN
ZEND_HANDLE_EXCEPTION

And if B.inc is included before A.inc, then B.inc compiles to:

INCLUDE_OR_EVAL
ZEND_FETCH_CLASS
ZEND_DECLARE_INHERITED_CLASS
RETURN
ZEND_HANDLE_EXCEPTION