Understand the opcodes of PHP principles_PHP tutorial-PHP Tutorial-php.cn

Understand the opcodes of PHP principles_PHP tutorial

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Release： 2016-07-21 15:34:05

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Opcondes is an intermediate language compiled from PHP scripts, just like Java's Byte Code, or .NET's MSL. (I have never understood it~)

Give an example in the article

Copy the code The code is as follows:

 
  echo "Hello World"; 
 $a = 1 + 1; 
 echo $a; 
 ?> 

PHP executes this code It will go through the following 4 steps (to be precise, it should be PHP's language engine Zend)

Copy the code The code is as follows:

 
Scanning (Lexing) (scanning), converts PHP code into language fragments (Tokens) 
Parsing (grammar analysis), converts Tokens into simple and meaningful expressions 
Compilation (Compilation), compile the expression into Opocdes 
　4.Execution (execute the compiled result), execute Opcodes sequentially, one at a time, thereby realizing the function of the PHP script. 

Among them, he also mentioned: "Some Cache now, such as APC, can enable PHP to cache Opcodes. In this way, every time a request comes, there is no need to repeat the previous three steps. This can greatly improve the execution speed of PHP. " This may be one of the reasons why PHP execution speed is faster ~

So what is Lexing? Students who have studied the principles of compilation should be familiar with the lexicon in the principles of compilation. If you have some understanding of the analysis steps, Lex is a basis table for lexical analysis. Zend/zend_language_scanner.c will perform lexical analysis on the input PHP code based on Zend/zend_language_scanner.l (Lex file) to obtain "words" one by one. PHP4.2 has provided a function called token_get_all. This function can Let’s talk about Scanning a piece of PHP code into Tokens;
If you use this function to process the PHP code we mentioned at the beginning, you will get the following results:

Copy code The code is as follows:

 
Array 
( 
[0] => Array 
( 
[0] => 367 
[1] => Array 
( 
[0] => 316 
[1] => echo 
) 
[2] => Array 
( 
[0] = > 370 
[1] => 
) 
[3] => Array 
( 
[0] => 315 
[1] => " Hello World" 
) 
[4] => ; 
[5] => Array 
( 
[0] => 370 
[1] => 
) 
[6] => = 
[7] => Array 
( 
[0] => 370 
[1] => ) 
[8] => Array 
( 
[0] => 305 
[1] => 1 
) 
[9] => Array 
( 
[0] => 370 
[1] => 
) 
[10] => + 
[11] => Array 
( 
[0] => 370 
[1] => [1] => 1 
) 
[13] => ; 
[14] => Array 
( 
[0] => 370 
[1 ] => 
) 
[15] => Array 
( 
[0] => 316 
[1] => echo 
) 
[ 16] => Array 
( 
[0] => 370 
[1] => 
 
Analyzing this return result, we can find that the strings, characters, and spaces in the source code will be returned unchanged. Characters in each source code will appear in the corresponding order. However, other items such as tags, operators, and statements will be converted into an Array containing two parts: Token ID (that is, the corresponding code for changing the Token inside Zend, such as T_ECHO, T_STRING), and the original code in the source code. content. 
Next, comes the Parsing stage. Parsing will first discard the excess spaces in the Tokens Array, and then convert the remaining Tokens into simple expressions one by one 



 Copy the code 

 The code is as follows: 

1.echo a constant string
2.add two numbers together
3.store the result of the prior expression to a variable

4.echo a variable Then the Compilation stage is changed. It will compile Tokens into op_arrays one by one. Each op_arrayd contains the following 5 parts:

Copy the code

 The code is as follows:

1. The identification of the Opcode number indicates the operation type of each op_array, such as add, echo
2. The result stores the Opcode result
3. Operand 1 Operand for Opcode

4. Operand 2 5. Extended value 1 integer used to distinguish overloaded operators For example, our PHP code will be parsed into:

Copy code 

 The code is as follows:

* ZEND_ECHO 'Hello World'
* ZEND_ADD ~0 1 1
* ZEND_ASSIGN !0 ~0

* ZEND_ECHO !0
Haha, you may ask, where did our $a go?

Well, this is about introducing the operands. Each operand is composed of the following two parts:

a)op_type: IS_CONST, IS_TMP_VAR, IS_VAR, IS_UNUSED, or IS_CVb) u, a union, stores the value (const) or lvalue (var) of the operand in different types depending on the op_type. For var, each var is different

IS_TMP_VAR, as the name suggests, this is a temporary variable that saves some results of op_array for use in the next op_array. The u of this type of operand stores a handle (integer) pointing to the variable table. This type of operand is generally used~ The beginning, such as ~0, represents the unknown temporary variable No. 0 in the variable table

IS_VAR This is our general sense of the variable, they start with $ to represent

IS_CV represents ZE2.1 /A cache mechanism used by compilers after PHP5.1. This variable stores the address of the variable referenced by it. When a variable is referenced for the first time, it will be CVd. In the future, the variable will be Reference does not need to look up the active symbol table again, CV variables to! The beginning indicates.

It seems that our $a has been optimized to !0.
Summary:

The execution order of 1.php is: -> php program
　　　--> Scanning (scanning and conversion into Tokens (language fragments))
　　　-> ; Parsing (grammar analysis, converting Tokens into simple and meaningful expressions)
-> Compilation (compilation, compiling expressions into Opocdes (operation codes))
-> Execution (sequential execution Compiled results)
2. The caching mechanism of APC (Alternative PHP Cache) can cache Opcodes. In this way, the next time a request comes, there is no need to repeat the previous three steps, which can greatly improve the performance of PHP. Execution speed. This may be one of the reasons why PHP executes faster

Supplement:
apc, zend optimize is able to speed up PHP
because it can cache opcode
It is not a built-in function of the zend engine itself
The zend engine defaults to any item in a reincarnation.