Understand the underlying development principles of PHP7: the conversion process from bytecode to machine code

Understand the underlying development principles of PHP7: the conversion process from bytecode to machine code

With the rapid development of the Internet, PHP as an efficient and scalable A powerful development language, it is favored by the majority of developers. The upgrade and update of the PHP language have always been the focus of developers. As the latest version, PHP7 not only has a significant improvement in performance, but also introduces changes in the underlying development principles. This article will start with the conversion process from bytecode to machine code to gain an in-depth understanding of the underlying development principles of PHP7.

In versions prior to PHP7, PHP was an interpreted language, and the code would be directly interpreted and executed by the parser. In PHP7, a brand new engine is introduced, namely Zend Engine 3.0, which compiles PHP code into bytecode, and then converts the bytecode into machine code through JIT (Just-In-Time) compilation technology to achieve for more efficient execution. This conversion process will be described in detail below.

First, let’s take a look at how to compile PHP code into bytecode. The PHP code will first be split into units through a lexical analyzer, such as identifiers, keywords, operators, etc. Then the relationship and structure between these units are analyzed through a syntax analyzer, and an Abstract Syntax Tree (AST) is generated. AST is a tree-like data structure that reflects the structure of PHP code. It consists of a series of nodes, each node represents a syntax structure unit.

Once the AST is generated, the next step is the process of converting the AST into bytecode. Bytecode is an intermediate form of code. Unlike machine code, it is not a binary code composed of 0s and 1s, but a specific serialization format that can be easily parsed and executed by the Zend engine. Bytecode is the actual carrier that the Zend engine reads and executes.

The code example is as follows:

<?php
   function sum($a, $b) {
      return $a + $b;
   }

   $result = sum(3, 4);
   echo "结果：{$result}
";
?>

In the above code, we define a simple function sum to calculate the sum of two numbers, and call this function to calculate The sum of 3 and 4. Here is the process of converting this code into bytecode:

1. The parser converts the source code into an abstract syntax tree consisting of a series of abstract syntax tree nodes.
2. The compiler generates the corresponding opcode based on the abstract syntax tree, and then generates bytecode.

The specific bytecode is as follows:

number 3
number 4
add
return

The above bytecode consists of a series of instructions, each instruction is an operation code (opcode) and an or multiple operands. For example, number 3 means pushing 3 onto the runtime stack, add means popping two numbers from the stack, adding them, and pushing the result back onto the stack. return means returning the result at the top of the stack.

Next, we will explore how bytecode is converted into machine code by the JIT compiler. A JIT compiler is a special compiler that dynamically converts bytecode into machine code at runtime. In PHP7, the Zend engine implements JIT compilation by calling the LLVM (Low-Level Virtual Machine) library.

The LLVM library is an open source compiler infrastructure that provides a flexible, modular compilation framework that can convert bytecode into machine code. It uses an intermediate representation (IR) form to translate bytecode from the source language into this intermediate representation, and then further converts it into machine code.

During the JIT compilation process, LLVM will first convert the bytecode into IR, and then perform a series of optimizations, such as constant propagation, loop expansion, etc., to finally generate efficient machine code. In this way, the execution efficiency of PHP programs has been greatly improved.

To summarize, PHP7 achieves more efficient execution by compiling PHP code into bytecode, and then converting the bytecode into machine code through the JIT compiler. In this process, lexical analyzers, syntax analyzers and compilers play an important role in converting source code into bytecode. The JIT compiler converts the bytecode into machine code by calling the LLVM library.

Understanding the underlying development principles of PHP7 is very important. It can help us better optimize the code and improve the performance of the program. With the continuous development of technology, understanding and mastering the underlying principles will become an indispensable skill for developers.

Reference:

• PHP Internals Book. (n.d.). Retrieved from https://www.phpinternalsbook.com/
• PHP and JIT - Nikita Popov . (2015, June). Retrieved from https://nikic.github.io/2015/06/19/PHP-7-0-JIT-FAQ.html

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