Phases of a Compiler

 A compiler is a program that translates high-level source code into machine code. It works in multiple phases to perform lexical analysis, syntax checking, optimization, and code generation. The compilation process is generally divided into two major parts:

1. Analysis Phase (Front-End)
2. Synthesis Phase (Back-End)

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Phases of a Compiler

1. Lexical Analysis (Scanner)

• Converts source code into a stream of tokens.
• Removes whitespace and comments.
• Identifies keywords, identifiers, operators, literals.
• Example:

  c
  int x = 10;
  

  Tokenized as:
  • int (keyword)
  • x (identifier)
  • = (assignment operator)
  • 10 (integer literal)
  • ; (delimiter)

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2. Syntax Analysis (Parser)

• Checks whether the token sequence follows the grammatical rules of the programming language.
• Constructs a parse tree (syntax tree).
• Detects syntax errors.
• Example:
  • int x = 10; ✅ (Valid)
  • int = x 10; ❌ (Syntax Error)

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3. Semantic Analysis

• Ensures meaningful and valid operations.
• Checks for:
  • Type mismatches (e.g., int x = "hello"; ❌)
  • Undeclared variables
  • Function signature mismatches
• Example:

  c
  int x = "hello";  // Error: Type mismatch
  

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4. Intermediate Code Generation

• Converts the syntax tree into an intermediate representation (IR).
• IR is independent of machine architecture.
• Example (Three-Address Code):

  c
  a = b + c * d;
  

  Translates to:

  ini
  t1 = c * d
  t2 = b + t1
  a = t2
  

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5. Optimization

• Improves performance by reducing execution time and memory usage.
• Types:
  • Peephole Optimization (small local optimizations)
  • Loop Optimization (reducing redundant calculations in loops)
  • Constant Folding (3 * 4 → 12 at compile time)
• Example:

  c
  int a = 3 * 4;  // Compiler replaces it with 'int a = 12;'
  

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6. Code Generation

• Converts IR into assembly/machine code.
• Allocates registers, memory, and instructions for the target processor.
• Example:

  assembly
  MOV R1, b
  MOV R2, c
  MUL R3, R2, d
  ADD R4, R1, R3
  MOV a, R4
  

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7. Symbol Table Management

• Maintains a record of variable names, types, scopes, and memory locations.
• Used in semantic analysis, optimization, and code generation.

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8. Error Handling

• Detects and reports lexical, syntax, and semantic errors.
• Example Errors:
  • Lexical Error: inta x = 5; (invalid token inta)
  • Syntax Error: int x 5; (missing =)
  • Semantic Error: int x = "abc"; (type mismatch)

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Summary of Compiler Phases

Phase	Purpose
Lexical Analysis	Convert source code to tokens
Syntax Analysis	Check syntax correctness (parse tree)
Semantic Analysis	Ensure meaningful expressions (type checking)
Intermediate Code Generation	Convert to intermediate representation (IR)
Optimization	Improve performance
Code Generation	Produce machine/assembly code
Symbol Table Management	Store variable & function details
Error Handling	Detect and report errors