Compiler Design Lecture Notes

Overview of Compiler Phases

• Introduction to compiler phases with an illustration.
• Expected outcomes of the lecture:
  • Brief overview of various compiler phases.
  • Tools for implementing these phases.

Language Translator Phases

• Four different phases of a language translator:
  1. Preprocessor
  2. Compiler
  3. Assembler
  4. Linker and Loader
• Preprocessor converts human-readable code to pure high-level language (removes directives).
• Compiler produces equivalent assembly language code.

Focus for Today

• Analyze an arithmetic expression through the compiler phases instead of the entire code.

Phase 1: Lexical Analysis

• Lexical Analyzer Tasks:
  • Takes lexems as input and generates tokens.
  • Lexems: Similar to words that convey meaning when grouped.
  • Tokens: Meanings of lexems.
• Example of lexems and tokens in an arithmetic expression:
  • x (identifier), = (assignment operator), a (identifier), + (arithmetic operator).
• Regular Expressions: Used to identify tokens (e.g., identifiers).
• Finite Automata: Illustrates regex for identifiers.
  • Cannot start with digits.

Phase 2: Syntax Analysis

• Syntax Analyzer (Parser):
  • Receives token stream and uses context-free grammars (CFG) to create a parse tree.
• Parse Tree Formation:
  • Production rules used to derive the parse tree.
  • Example: s -> id = e ; (expression assignment).
• Yield of Parse Tree:
  • Traversal yields same expression as input; indicates no syntax errors.

Phase 3: Semantic Analysis

• Semantic Analyzer Tasks:
  • Produces semantically verified parse tree.
  • Checks for type errors, array bounds, scope resolution, etc.
  • Ensures that the parse tree is meaningful.

Phase 4: Intermediate Code Generation

• Intermediate Code Generator:
  • Produces intermediate code from the semantically verified parse tree.
  • Example: Three-address code.
• Three-Address Code:
  • Each statement has at most three addresses, indicating temporary variables.

Phase 5: Code Optimization

• Code Optimizer Tasks:
  • Optimizes the intermediate code.
  • Can be machine dependent or independent.
• Example Optimization:
  • Reducing statements by optimizing assignments.

Phase 6: Target Code Generation

• Target Code Generator:
  • Produces assembly code from optimized code.
  • Example of assembly code segment explained step-by-step.

Tools for Compiler Implementation

• Lex: Standard lexical analyzer generator.
• Yacc: Yet Another Compiler Compiler, used for syntax analysis.
• Lance C Compiler: Software platform for implementing the front end of a C language compiler for embedded processors.
• Research paper suggestion: "Lance: A C Compiler Platform for Embedded Processors" by Dr. Reiner Leipers.

Conclusion

• Overview of compiler phases and tools for implementation.
• Next session topic: Symbol table.