How does a compiler generate machine code?

A compiler generates machine code by translating high-level programming languages into low-level machine language instructions.

The process of generating machine code from high-level programming languages involves several stages. Initially, the compiler reads the source code, which is the program written in a high-level language. This stage is known as the lexical analysis or scanning. The compiler breaks down the source code into smaller pieces, called tokens. Tokens are the smallest units of a program, like keywords, identifiers, operators, and punctuation symbols.

After lexical analysis, the compiler moves to the syntax analysis or parsing stage. Here, the compiler checks the tokens for syntax errors and arranges them in a way that reflects their relationships. This arrangement is often represented as a parse tree or syntax tree. The syntax tree is a graphical representation that shows how the compiler groups tokens together to make statements or expressions.

Semantic analysis follows syntax analysis. In this stage, the compiler checks the parse tree for semantic errors. It verifies whether the expressions and statements are meaningful or valid in the context of the programming language rules. For example, it checks if the variables are declared before use, or if the function calls have the correct number and types of arguments.

Once the compiler is satisfied that the source code is both syntactically and semantically correct, it proceeds to the code generation stage. Here, the compiler translates the high-level language into machine code. This machine code is specific to a computer architecture and can be directly executed by the computer's CPU.

The final stage is code optimisation. Although this stage is optional, it is crucial for improving the efficiency of the generated machine code. The compiler attempts to optimise the code by eliminating unnecessary instructions, reducing the size of the code, or speeding up the execution time.

In summary, a compiler generates machine code through a multi-stage process that includes lexical analysis, syntax analysis, semantic analysis, code generation, and code optimisation. Each stage plays a crucial role in ensuring that the high-level source code is correctly translated into efficient and error-free machine code.