Invitation to Computer Science 5 th Edition

1. Invitation to Computer Science 5thEdition Chapter 11 Compilers and Language Translation

2. Objectives In this chapter, you will learn about: • The compilation process • Phase I: Lexical analysis • Phase II: Parsing • Phase III: Semantics and code generation • Phase IV: Code optimization Invitation to Computer Science, 5th Edition

3. Introduction • Compiler • Translates high-level language into machine language prior to execution • Assembly language and machine language are related one to one • One to many • Relationship between a high-level language and machine language • Compiler goals • Correctness; efficient and concise Invitation to Computer Science, 5th Edition 3

4. The Compilation Process • Four phases of compilation • Phase I: Lexical analysis • Phase II: Parsing • Phase III: Semantic analysis and code generation • Phase IV: Code optimization Invitation to Computer Science, 5th Edition 4

5. Figure 11.1 General Structure of a Compiler Invitation to Computer Science, 5th Edition

6. Figure 11.2 Overall Execution Sequence of a High-level Language Program Invitation to Computer Science, 5th Edition

7. Phase I: Lexical Analysis • Lexical analyzer • Groups input characters into units called tokens • Scanner • Discards nonessential characters, such as blanks and tabs • Groups remaining characters into high-level syntactical units such as symbols, numbers, and operators Invitation to Computer Science, 5th Edition

8. Figure 11.3 Typical Token Classifications Invitation to Computer Science, 5th Edition

9. Phase II: Parsing • During the parsing phase: • Compiler determines whether the tokens recognized by the scanner during phase I fit together in a grammatically meaningful way • Parsing • Process of diagramming a high-level language statement • Done by a program called a parser Invitation to Computer Science, 5th Edition

10. Grammars, Languages, and BNF • Backus-Naur Form • Named after its designers John Backus and Peter Naur • Syntax of a language is specified as a set of rules, also called productions • Entire collection of rules is called a grammar • Lefthand side of a BNF rule is the name of a single grammatical category • Operator ::= means “is defined as,” and “definition,” also called righthand side Invitation to Computer Science, 5th Edition

11. Grammars, Languages, and BNF (continued) • Backus-Naur Form • Nonterminal: intermediate grammatical category used to help explain and organize the language • Goal symbol: final nonterminal • Language:collection of all statements that can be successfully parsed • Metasymbols:<, >, and ::= Invitation to Computer Science, 5th Edition

12. Parsing Concepts and Techniques • Parser • Receives as input the BNF description of a high-level language and a sequence of tokens recognized by the scanner • Look-ahead parsing algorithms • “Look down the road” a few tokens to see what would happen if a certain choice is made • Ambiguous • Grammar that allows the construction of two or more distinct parse trees for the same statement Invitation to Computer Science, 5th Edition

13. Figure 11.4 First Attempt at a Grammar for a Simplified Assignment Statement Invitation to Computer Science, 5th Edition

14. Figure 11.5 Parse Tree Produced by the Parser Invitation to Computer Science, 5th Edition

15. Figure 11.6 Second Attempt at a Grammar for Assignment Statements Invitation to Computer Science, 5th Edition

16. Figure 11.7 Two Parse Trees for the Statement x = x + y + z Invitation to Computer Science, 5th Edition

17. Figure 11.8 Third Attempt at a Grammar for Assignment Statements Invitation to Computer Science, 5th Edition

18. Figure 11.9 Grammar for a Simplified Version of an if-else Statement Invitation to Computer Science, 5th Edition

19. Figure 11.10 Parse Tree for the Statement if (x55y)x5z; else x5y; Invitation to Computer Science, 5th Edition

20. Phase III: Semantics and Code Generation • Semantic record • Data structure that stores information about a nonterminal • First part of code generation • Involves a pass over the parse tree to determine whether all branches of the tree are semantically valid • Code generation • Compiler must determine how transformation of grammatical objects can be accomplished in machine language Invitation to Computer Science, 5th Edition

21. Phase III: Semantics and Code Generation (continued) • Optimization • Compiler polishes and fine-tunes the translation so that it runs a little faster or occupies a little less memory Invitation to Computer Science, 5th Edition

22. Figure 11.11 Code Generation for the Assignment Statement x = x + y + z Invitation to Computer Science, 5th Edition

23. Phase IV: Code Optimization • Efficiency • Ability to write highly optimized programs that contained no wasted microseconds or unnecessary memory cells • Goal in compiler design today • Provide a wide array of compiler tools to simplify the programmer’s task and increase productivity • Integrated development environment • Compiler is embedded within a collection of supporting software development routines Invitation to Computer Science, 5th Edition

24. Phase IV: Code Optimization (continued) • Two types of optimization • Local optimization and global optimization • Possible local optimizations • Constant evaluation • Strength reduction • Eliminating unnecessary operations Invitation to Computer Science, 5th Edition

25. Figure 11.12 Optimized Code for the Assignment Statement x = x + y + z Invitation to Computer Science, 5th Edition

26. Summary • Compiler • Piece of system software that translates high-level languages into machine language • Goals of a compiler • Correctness and the production of efficient and concise code • Source program • High-level language program Invitation to Computer Science, 5th Edition

27. Summary (continued) • Object program • The machine language translation of the source program • Phases of the compilation process • Phase I: Lexical analysis • Phase II: Parsing • Phase III: Semantic analysis and code generation • Phase IV: Code optimization Invitation to Computer Science, 5th Edition