Opcode Descriptions and Examples
PHP Manual

ASSIGN_REF

PHP code

<?php
/*
 * indicates that variable indicated by value1 is to be treated in the global scope for the remainder of the current scope.
 * opcode number: 39
 */
global $a;
?>

PHP opcodes

Function name: (null)

Compiled variables: !0=$a

line#op fetchextreturn operands
60 FETCH_Wgloballock  $0 'a'
 1 ASSIGN_REF     !0,$0
72 RETURN     1