Opcode Descriptions and Examples
PHP Manual

PRE_INC

PHP code

<?php
/*
 * increments variable indicated by value1 by 1 (before performing other operations) and stores in result
 * opcode number: 34
 */
++$a;
?>

PHP opcodes

Function name: (null)

Compiled variables: !0=$a

line#op fetchextreturn operands
60 PRE_INC     !0
71 RETURN     1

Opcode Descriptions and Examples
PHP Manual