Symbol Tables for Compiler: Implementation Techniques

1. Symbol Tables

2. Contents • Introduction • A Simple Compiler • Scanning – Theory and Practice • Grammars and Parsing • LL(1) Parsing • Lex and yacc • LR Parsing • Semantic Processing • Symbol Tables • Run-time Storage Organization • Code Generation and Local Code Optimization • Global Optimization

3. A Symbol Table Interface

5. A Symbol Table Interface (cont’d.)

6. A Symbol Table Interface (cont’d.)

7. Basic Implementation Techniques • Unordered List • Ordered List • Binary Search Trees • The expected search time is O(log(n)) • For a balanced tree, the worst-case performance is O(n).

8. Basic Implementation Techniques (cont’d.) • Hash Tables • Hash function • Resolving collisions • Linear • If position h(n) is occupied, try (h(n)+1) mod m • Add-the-hash rehash • If position h(n) is occupied, try (2*h(n)) mod m • Quadratic rehash • If position h(n) is occupied, try (h(n)+1**2) mod m • Collision resolution by chaining

9. Basic Implementation Techniques (cont’d.) • String Space Arrays • A fixed-size array

10. Basic Implementation Techniques (cont’d.) • Segmented String Space Arrays • A dynamic-allocation array

11. Block-Structured Symbol Tables • Block structured languages

12. Block-Structured Symbol Tables (cont’d.) • Visibility rules

13. Block-Structured Symbol Tables (cont’d.) • An Individual Table for Each Scope

14. Block-Structured Symbol Tables (cont’d.)

15. Block-Structured Symbol Tables (cont’d.)

16. Block-Structured Symbol Tables (cont’d.)