How does a Compiler Work?

A compiler is a program that translates high-level programming code (like C, C++, Java) into machine code (binary instructions) that a computer's processor can execute. It does this in multiple stages. Here's a breakdown of how a typical compiler works:

1. Lexical Analysis (Tokenization)

The compiler reads the source code and breaks it into small tokens (keywords, operators, identifiers, literals, etc.).
Example: int x = 5; → int, x, =, 5, ;
This step removes whitespace and comments.

2. Syntax Analysis (Parsing)

The compiler checks if the sequence of tokens follows the language’s grammar.
It builds a parse tree or abstract syntax tree (AST).
Example: int x = 5; → A tree showing x as an integer assigned to 5.

3. Semantic Analysis

Checks for meaningful correctness:
- Are variables declared before use?
- Are operations valid for the given data types?
- Ensures proper function calls and parameter matching.

4. Intermediate Code Generation

Translates the high-level source code into a generic intermediate representation (IR).
Example: Instead of directly converting to machine code, it might use an IR like LLVM IR or Three-Address Code (TAC).

5. Optimization

Improves performance by removing redundant code, simplifying expressions, and minimizing memory usage.

Example:

int a = 10;
int b = 20;
int c = a + b;

Might be optimized to:

int c = 30;

6. Code Generation

Converts the optimized IR into assembly language or machine code.
Example:
```
MOV R1, 10
MOV R2, 20
ADD R3, R1, R2
```

7. Linking & Loading

Linker combines different program modules and external libraries.
Loader places the executable into memory for execution.

Types of Compilers

Single-Pass Compiler – Processes the code once (e.g., early Pascal compilers).
Multi-Pass Compiler – Makes multiple passes for better optimization (e.g., GCC).
Just-in-Time (JIT) Compiler – Compiles at runtime for speed (e.g., Java’s JVM).

Would you like a deeper explanation of a specific phase? 🚀