In-Depth Analysis of PHP7 Internals: A Complete Guide to Compilation and Execution Processes

1. Overview of PHP7 Internal Architecture

PHP is a widely-used scripting language for web development. In PHP7, significant performance enhancements have been achieved through improved memory management, better error handling, and the introduction of JIT compilation. Understanding how PHP7 works internally is essential for building efficient applications. This article dissects PHP7's internals, from source code compilation to execution.

2. Detailed Breakdown of the PHP Compilation Process

The compilation process in PHP can be divided into three main phases: lexical analysis, syntax analysis, and intermediate code generation. Let’s explore each in detail.

2.1 Lexical Analysis

During lexical analysis, PHP source code is broken down into tokens—basic units such as variables, numbers, strings, and operators. Each token consists of a type and a corresponding value.

$var1 = 10;
$var2 = "hello world";

Token list:

T_VARIABLE $var1  
T_WHITESPACE  
T_EQUAL =  
T_WHITESPACE  
T_LNUMBER 10  
T_SEMICOLON ;  
T_WHITESPACE  
T_VARIABLE $var2  
T_WHITESPACE  
T_EQUAL =  
T_WHITESPACE  
T_STRING "hello world"  
T_SEMICOLON ;  

2.2 Syntax Analysis

In this phase, tokens are organized into a parse tree (syntax tree), a hierarchical structure representing the code’s logic. This allows the interpreter to understand and execute the code effectively.

if ($a > $b) {
    $max = $a;
} else {
    $max = $b;
}

Corresponding syntax tree:

if  
├─ >  
│  ├─ $a  
│  └─ $b  
├─ =  
│  ├─ $max  
│  └─ $a  
└─ =  
   ├─ $max  
   └─ $b  

2.3 Intermediate Code Generation

At this stage, the syntax tree is converted into intermediate code—a platform-independent, abstract representation of the program. This code is later executed by the PHP virtual machine.

function get_user_name($userid) {
    $users = array(
        1 => "John",
        2 => "Mary",
        3 => "Bob"
    );
    if (isset($users[$userid])) {
        return $users[$userid];
    } else {
        return "Unknown";
    }
}

Intermediate code representation:

FUNCTION get_user_name  
PARAM $userid  
ADD_ARRAY $users,1,"John",2,"Mary",3,"Bob"  
IF isset,$users,$userid  
    GET_ARRAY $users,$userid  
    RETURN  
ELSE  
    STRING "Unknown"  
    RETURN  
ENDIF  
END_FUNCTION  

3. PHP Execution Process

After compilation, PHP enters the execution phase. The virtual machine executes the intermediate code, completing the program flow.

3.1 Interpreter Core

PHP’s interpreter consists of a language core and optional extensions. The core handles basic syntax and control structures, while extensions provide additional features that can be dynamically enabled.

3.2 JIT Compiler

PHP7 introduces a Just-In-Time (JIT) compiler, which converts frequently executed intermediate code segments into native machine code at runtime. This significantly boosts performance for computationally intensive scripts.

3.3 Virtual Machine Engine

The virtual machine simulates hardware-level operations, such as memory allocation, function calls, and thread management. It executes the intermediate code and returns results to the interpreter.

4. Conclusion

PHP7’s internals involve a multi-phase process: lexical and syntax analysis, intermediate code generation, and execution via a virtual machine, enhanced with a JIT compiler. Mastering these concepts provides developers with deeper insights into performance tuning and debugging of PHP applications.