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Chapter V: Compiler

Overview: To study the design and operation of compiler for high-level programming languages. Contents Basic compiler (one-pass compiler) functions Machine-dependent extension : (object-code generation & code optimization)

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Chapter V: Compiler

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  1. Overview: To study the design and operation of compiler for high-level programming languages. Contents Basic compiler (one-pass compiler) functions Machine-dependent extension: (object-code generation & code optimization) Compiler design alternative: multi-pass compiler, interpreters, p-code compilers & compiler-compilers. Chapter V: Compiler Compiler

  2. Example Basic compiler functions Compiler

  3. Basic compiler functions (cont.) • Source program • Regard each statement as a sequence of token. • The task of scanning the source statement, recognizing and classifying the various tokens, is known as lexical analysis. (scanner) • Recognized all tokens as some language construct by the grammar. • This process is called syntactic analysis or parsing. (parser) • Generation of object code. Compiler

  4. Compilation process • Scanning (lexical analysis) • Parsing (syntactic analysis) • Code generation • Ps. It can achieve in a single pass ! Compiler

  5. Grammars • A grammar for a programming language is a formal description of the syntax, of programs and individual statements written in the language. • The difference between syntax and semantics, • E.g., I := J + K X := Y + I where X,Y : Real I,J,K : IntegerThey are identical syntax.However, the semantic are quite different. Compiler

  6. Grammars (cont.) • BNF (Backus-Naur Form) • A kind of syntax description. • Simple. • Widely used. • It provide capabilities that are sufficient for most purposes. • BNF consists of a set of rules, each of which defines the syntax of some construct in the programming language. • E.g., <read> ::= READ ( <id-list>) Compiler

  7. Grammars (cont.) • <read> ::= READ ( <id-list>) • <id-list> ::= id | <id-list>, id • Character strings enclosed between < and > are called nonterminal symbol. • Character strings not enclosed between < and > are called terminal symbol (I.e, tokens). • E.g., READ(value, sum, x, y) Compiler

  8. Simplified Pascal grammar Compiler

  9. Simplified Pascal grammar (cont.) Compiler

  10. Simplified Pascal grammar (cont.) • To display the analysis of a source statement in terms of a grammar a a tree (parse tree or syntax tree). Compiler

  11. The parse tree for VARIANCE := SUMSQ DIV 100 – MEAN * MEAN Compiler

  12. Grammars (cont.) • Draw parse tree for • ALPHA – BETA * GAMMA • If there is more than one possible parse tree for a given statement, the grammar is said to be ambiguous. • The ambiguous grammar would leave doubt about what object code should be generated. Compiler

  13. Compiler

  14. Compiler

  15. Lexical analysis (scanning) • Scanning the program to be compiled and recognizing the tokens that make up the source statements. • Scanner are usually designed to recognize keywords, operators, and identifiers, integer, floating-point numbers, character strings, …,etc. • The identifier might be defined by the rules: • <ident> ::= <letter> | <ident> <letter> | <ident> <digit> • <letter> ::= A | B | C | D | … | Z • <digit> ::= 0 | 1 | 2 | 3 | … | 9 Compiler

  16. Token coding scheme Compiler

  17. Lexical scan Compiler

  18. The lexical scanning • It must deal with the following cases: • For example, • DO 10 I = 1, 100 • DO 10 I =1 • (FORTRAN ignores blank in the statement) • IF (THEN .EQ. ELSE) THEN IF = THENELSE THEN = IFENDIF • A number of tools have been developed for automatically constructing lexical scanners from specifications stated in a special-purpose language. Compiler

  19. Modeling Scanners as Finite Automata • The tokens of most programming languages can be recognized by a finite automation. • Starting state vs. final state. • If the automation stops in a final state, we say that it recognizes (or accept) the string being scanned, otherwise, it fails to recognize the string. Compiler

  20. Modeling Scanners as Finite Automata (cont.) Compiler

  21. Modeling Scanners as Finite Automata (cont.) Compiler

  22. Modeling Scanners as Finite Automata (cont.) Compiler

  23. Modeling Scanners as Finite Automata (cont.) Compiler

  24. The implementation of finite automata • Using algorithm code (for Fig. 5.8 (b)) Compiler

  25. The implementation of finite automata (cont.) • Using tabular representation Compiler

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