What is EXT_NOP and EXT_STMT, PHP Opcode - php

Question

I'm trying to understand more deep and php internals by just executing native php functions against to my implementations.
But in every opcode dump I see these two following opcodes :
EXT_NOP : http://php.net/manual/tr/internals2.opcodes.ext-nop.php
EXT_STMT : http://php.net/manual/tr/internals2.opcodes.ext-stmt.php
as you see in docs there is no detailed explanation.
Even in following example which given in the doc my dumps are different than the doc's spesification. I really want to know why are these two stands in every dump ? What is their functionality ?
<?php
/*
* no operation
* opcode number: 0
*/
function A(){};
?>
Env Spesification :
LXC
Linux web 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt11-1+deb8u5 (2015-10-09) x86_64 GNU/Linux
PHP 5.6.15-1~dotdeb+7.1 (cli) (built: Nov 3 2015 16:29:58)
Copyright (c) 1997-2015 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2015 Zend Technologies
with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2015, by Zend Technologies
with Xdebug v2.3.3, Copyright (c) 2002-2015, by Derick Rethans
OpCode Dump :
➜ php -d vld.active=1 -d vld.execute=0 -f nop.php
Finding entry points
Branch analysis from position: 0
Jump found. Position 1 = -2
filename: /root/web/www/optest/nop.php
function name: (null)
number of ops: 5
compiled vars: none
line #* E I O op fetch ext return operands
-------------------------------------------------------------------------------------
2 0 E > EXT_STMT
1 NOP
2 NOP
4 3 EXT_STMT
4 > RETURN 1
branch: # 0; line: 2- 4; sop: 0; eop: 4; out1: -2
path #1: 0,
Function a:
Finding entry points
Branch analysis from position: 0
Jump found. Position 1 = -2
filename: /root/web/www/optest/nop.php
function name: A
number of ops: 3
compiled vars: none
line #* E I O op fetch ext return operands
-------------------------------------------------------------------------------------
2 0 E > EXT_NOP
1 EXT_STMT
2 > RETURN null
branch: # 0; line: 2- 2; sop: 0; eop: 2; out1: -2
path #1: 0,
End of function a

Answer 1

EXT_NOP is used in the cases where previously there was something to do (ie a function declaration), but the engine has internally already taken care of this, and replaced the original opcode with EXT_NOP. NOP stands for "no operation". NOP is slightly different from EXT_NOP, as it's generated at different times, but it does the same thing: Nothing.
EXT_STMT is created in between statements, and allows debuggers (such as Xdebug) to stop in safe locations. Xdebug uses a "statement handler" (https://github.com/derickr/xdebug/blob/master/xdebug.c#L2534) to hook into the Zend Engine. The Zend Engine calls this handler for each EXT_STMT opcode it encounters.