The 4 Stages of the Compilation Process

The compilation process involves converting high-level source code into machine code that a computer can execute. It’s a multi-step process, and each stage plays an important role in ensuring that the code runs as expected. Here are the four main stages of the compilation process:

1. Lexical Analysis

The first step in the compilation process is lexical analysis. During this stage, the source code is read and converted into a sequence of tokens. A token is a basic unit of meaning, like keywords (if, while), variables, constants, operators (+, -), and punctuation.

During lexical analysis, the compiler also removes comments, annotations (like // or /*...*/), and whitespace (such as spaces, tabs, and newlines). These are ignored because they are not needed for understanding the logic of the program, but they help in writing human-readable code.

This step is performed by the lexer or scanner, which breaks down the source code into these tokens.

2. Syntax Analysis

The next stage is syntax analysis (also known as parsing). The compiler takes the tokens generated in the previous stage and checks whether they are arranged in a valid way according to the grammar (syntax) of the programming language.

A parser is used to create a parse tree or abstract syntax tree (AST). This tree represents the structure of the program, showing how different parts of the code relate to each other according to the language rules. For example, the parser will check if statements are correctly formed, like ensuring that an if statement has the proper condition and body.

The purpose is to ensure the code follows the language’s syntax rules and that the sequence of tokens makes sense logically in the structure of the program.

During the syntax analysis, if a syntax error is detected, the compilation process stops here and an error message is generated.

3. Code Generation

Once the program passes the syntax analysis and is considered structurally correct, the compiler moves to code generation. In this step, the compiler translates the high-level source code (like if (x > 5)) into machine code or intermediate code (such as bytecode for languages like Java).

The compiler uses the abstract syntax tree (AST) from the syntax analysis stage to generate the target code. This code can be directly executed by the computer’s processor or can be further processed into an executable program.

The purpose of code generation is to create an efficient machine-readable output (binary code) that the computer can execute.

4. Code Optimisation

Code optimisation is an optional but very important step where the generated code is improved for efficiency. The optimiser attempts to reduce the program’s runtime, memory usage, or both, without changing its functionality.

The optimisation process might involve eliminating redundant calculations, simplifying loops, or using more efficient data structures or algorithms. In some cases, it can rearrange the order of instructions to make the program run faster or take up less space.

The goal is to make the code run faster or more efficiently, improving its performance while keeping the logic of the program intact.

To Sum It Up…

• Lexical Analysis: Breaks down the source code into tokens and removes comments, annotations, and whitespace.
• Syntax Analysis: Checks the tokens against the syntax rules of the language, generating a parse tree or abstract syntax tree (AST).
• Code Generation: Translates the valid code into machine-readable or intermediate code.
• Code Optimisation: Improves the efficiency of the generated code, making it run faster or consume less memory.

Each of these stages is crucial in turning human-readable high-level code into a functional and efficient machine-executable program.

Task 1: Drag and Drop

Can you identify and describe the 4 stages of the compilation process?

Complete the fill in the gaps activity below to label the 4 stages of the compilation process with for each stage their input and output:

Compilation ProcessOpen in New Window

Task 2: Q&A

Answer the following question: