Detailed explanation of OpCode principle in PHP

This article mainly introduces the OpCode principle of PHP, and analyzes the relevant compilation mechanism and operating principle of the PHP program in more detail. Friends in need can refer to it

OpCode is a kind of PHP script compiled Intermediate language, like Java's ByteCode, or .NET's MSL. This article is mainly based on "Understanding OPcode" and the Internet. It is specially recorded based on personal understanding and modification:

PHP code:

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

PHP will go through the following 4 steps when executing this code:

1. Scanning (Lexing), convert PHP code into language fragments (Tokens)
2. Parsing, convert Tokens into simple And meaningful expression
3. Compilation, compiles the expression into Opocdes
4. Execution, executes Opcodes sequentially, one at a time, thereby realizing the function of PHP script.

Note: Some current caches, such as APC, can enable PHP to cache Opcodes. In this way, every time a request comes, there is no need to repeat the first three steps, which can greatly improve the execution speed of PHP. .

First, Zend/zend_language_scanner.c will perform lexical analysis on the input PHP code based on Zend/zend_language_scanner.l (Lex file), thereby obtaining "words" one by one, which PHP4.2 began to provide There is a function called token_get_all. This function can scan a piece of PHP code into Tokens;

will get the following results:

Array
(
  [0] => Array
    (
      [0] => 367
      [1] => <?php
      [2] => 1
    )
  [1] => Array
    (
      [0] => 370
      [1] =>
      [2] => 2
    )
  [2] => Array
    (
      [0] => 316
      [1] => echo
      [2] => 2
    )
  [3] => Array
    (
      [0] => 370
      [1] =>
      [2] => 2
    )
  [4] => Array
    (
      [0] => 315
      [1] => "Hello World"
      [2] => 2
    )
  [5] => ;
  [6] => Array
    (
      [0] => 370
      [1] =>
      [2] => 2
    )
  [7] => Array
    (
      [0] => 309
      [1] => $a
      [2] => 3
    )
  [8] => Array
    (
      [0] => 370
      [1] =>
      [2] => 3
    )
  [9] => =
  [10] => Array
    (
      [0] => 370
      [1] =>
      [2] => 3
    )
  [11] => Array
    (
      [0] => 305
      [1] => 1
      [2] => 3
    )
  [12] => Array
    (
      [0] => 370
      [1] =>
      [2] => 3
    )
  [13] => +
  [14] => Array
    (
      [0] => 370
      [1] =>
      [2] => 3
    )
  [15] => Array
    (
      [0] => 305
      [1] => 1
      [2] => 3
    )
  [16] => ;
  [17] => Array
    (
      [0] => 370
      [1] =>
      [2] => 3
    )
  [18] => Array
    (
      [0] => 316
      [1] => echo
      [2] => 4
    )
  [19] => Array
    (
      [0] => 370
      [1] =>
      [2] => 4
    )
  [20] => Array
    (
      [0] => 309
      [1] => $a
      [2] => 4
    )
  [21] => ;
  [22] => Array
    (
      [0] => 370
      [1] =>
      [2] => 4
    )
  [23] => Array
    (
      [0] => 369
      [1] => ?>
      [2] => 5
    )
)

The returned result, 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.

The next step is 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

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, change the Compilation stage, it Tokens will be compiled into op_arrays one by one. Each op_arrayd contains the following 5 parts:

1. The identification of the Opcode number indicates the operation type of each op_array, such as add, echo
2. Result Store the Opcode result
3. Operand 1 is the operand of Opcode
4. Operand 2
5. The extended value is an integer to distinguish the overloaded operator

For example , the PHP code will be Parsed into:

[root@localhost html]# /usr/local/php/bin/php -dvld.active=1 hello.php
Branch analysis from position: 0
Return found
filename:    /var/www/html/hello.php
function name: (null)
number of ops: 6
compiled vars: !0 = $a
line   # op              fetch     ext return operands
-------------------------------------------------------------------------------
  2   0 ECHO                           'Hello+world'
  3   1 ADD                       ~0   1, 1
     2 ASSIGN                          !0, ~0
  4   3 ECHO                           !0
  6   4 RETURN                          1
     5* ZEND_HANDLE_EXCEPTION
Hello world2

Each operand is composed of the following two parts:

a) op_type: IS_CONST, IS_TMP_VAR, IS_VAR, IS_UNUSED, or IS_CV

b) u, a union, which stores the value (const) or lvalue (var) of the operand in different types according to the op_type. )

As 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 IS_VAR at No. 0 in the variable table. This is our general variable. They begin with $ to represent IS_CV, which represents the type used by compilers after ZE2.1/PHP5.1. cache mechanism, this variable stores the address of the variable referenced by it. When a variable is referenced for the first time, it will be CVd. Subsequent references to this variable do not need to look up the active symbol table again. CV variables are represented by starting with !.

$a variable is optimized to !0.

Summary: The above is the entire content of this article, I hope it will be helpful to everyone's study.

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