Definition

Compilation happens in six logical phases, front-end (language-dependent) followed by back-end (machine-dependent), with the symbol table and error handler interacting across all phases.

Key Points (in order)

1. Lexical Analysis — source code → stream of tokens (removes whitespace/comments)
2. Syntax Analysis — tokens → parse tree, checked against grammar rules
3. Semantic Analysis — parse tree checked for meaning (type checking, scope rules) → annotated tree
4. Intermediate Code Generation — produces machine-independent code (e.g., three-address code)
5. Code Optimization — improves intermediate code for speed/space, without changing meaning
6. Code Generation — intermediate code → target machine code

• Symbol Table Management and Error Handling run throughout all phases, not as separate sequential steps.
• Front-end = phases 1–3 (analysis); Back-end = phases 4–6 (synthesis).

Example

For x = a + b * 2:

• Lexer: id(x) = id(a) + id(b) * num(2)
• Parser: builds expression tree respecting precedence
• Semantic: checks a, b, x are declared & type-compatible
• Intermediate: t1 = b*2; t2 = a+t1; x = t2

📌 CSS Frequency: High — diagram/labeling question almost every attempt; sometimes asked to trace one phase with an example expression.

Model Answer (short)

"A compiler works in six phases: lexical analysis (tokenization), syntax analysis (parsing), semantic analysis (type/scope checking), intermediate code generation, code optimization, and code generation. The symbol table and error handler support every phase. The first three phases form the analysis (front-end); the last three form the synthesis (back-end), which allows retargeting to different machines by only rewriting the back-end."