Six Phases of compiler – Lexical /Syntax /Semantic /Intermediate code generation/code optimization

Six Phases of compiler – Lexical /Syntax /Semantic /Intermediate code generation/code optimization

 Six Phases of Compiler

A compiler translates high-level code into machine code through six main phases:

Lexical Analysis
Syntax Analysis
Semantic Analysis
Intermediate Code Generation
Code Optimization
Code Generation

 Lexical Analysis (Scanning)

Input: Source Code (High-level language)
Output: Tokens
Purpose: Converts the source code into tokens (smallest units of the program).
Performs:
 Removes whitespaces, comments
 Identifies keywords, identifiers, operators, symbols
 Stores tokens in Symbol Table

Example:
Input: int x = 10;
Output:

 Syntax Analysis (Parsing)

Input: Tokens from Lexical Analysis
Output: Parse Tree (Syntax Tree)
Purpose: Checks if the code follows the grammar rules (using parsing techniques like LL(1), LR(1)).
Performs:
 Builds Parse Tree
 Detects Syntax Errors

Example:
Input: int x = 10;
Output: Parse Tree

 If we write int = x 10;, the compiler will show a syntax error.

 Semantic Analysis

Input: Parse Tree
Output: Annotated Parse Tree
Purpose: Checks meaning and correctness of the program.
Performs:
 Type Checking (int x = “hello”; is invalid)
 Variable declaration checking
 Function parameter matching

Example:
Code:

Error: Type Mismatch

 Intermediate Code Generation

Input: Annotated Parse Tree
Output: Intermediate Code (3-address code, AST)
Purpose: Generates a machine-independent representation of the program.
Performs:
 Converts code to Intermediate Representation (IR)
 Uses Three-Address Code (TAC)

Example:
Code:

TAC Output:

 Code Optimization

Input: Intermediate Code
Output: Optimized Intermediate Code
Purpose: Makes the code faster and memory-efficient.
Performs:
Constant Folding → 5 + 3 → 8
Dead Code Elimination → Removes unreachable code
Loop Optimization → Moves invariant expressions out of loops

Example:
Before Optimization:

After Optimization:

 Code Generation

Input: Optimized Intermediate Code
Output: Target Machine Code (Assembly/Binary)
Purpose: Converts IR to actual machine code for execution.
Performs:
Register Allocation
Instruction Selection
Machine-specific code generation

Example:
IR:

Assembly Code (x86):

 Summary of Compiler Phases

 Final Notes

Lexical, Syntax, and Semantic Analysis → Detect errors.
Intermediate Code & Optimization → Improve efficiency.
Code Generation → Final machine-executable code.

 Would you like a detailed example on any specific phase?

Six Phases of compiler – Lexical /Syntax /Semantic /Intermediate code generation/code optimization