Compiler design and lexical analyser
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The document discusses the different phases of a compiler: 1) The front end checks the syntax and semantics of the source code and the back end translates it to assembly code. 2) The front end contains lexical analysis, preprocessing, syntax analysis, and semantic analysis. The back end contains analysis, optimization, and code generation. 3) Optimization aims to improve the intermediate code to increase performance by reducing complexity and leading to faster execution.
![ Declarations of ordinary C variables
,constants and Libraries.
%{
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
%}
flex definitions :- name definition
Digit [0-9] (Regular Definition)
14](https://image.slidesharecdn.com/compilerdesign-170426184632/85/Compiler-design-and-lexical-analyser-14-320.jpg)
![ Also called as Hierarchial Analysis
A syntax tree[also called as parse tree] is generated
where
◦ Operators Interior nodes
◦ Operands Children of node for operators.
=
A + Interior
B C Children](https://image.slidesharecdn.com/compilerdesign-170426184632/85/Compiler-design-and-lexical-analyser-19-320.jpg)
![Concrete Parse tree
Abstract syntax tree
Converted into a linear sequence of instructions
Results in 3AC [ 3 Address Code]](https://image.slidesharecdn.com/compilerdesign-170426184632/85/Compiler-design-and-lexical-analyser-22-320.jpg)
Compiler design and lexical analyser
- 1. Harcourt butler technical University Kanpur
- 2. A compiler is a program that reads a program written in one language and translates into equivalent target language Source- - Target | | | Error Message COMPILER
- 4. The Front end checks whether the program is correctly written in terms of the programming language syntax and semantics The back end is responsible for translating the source into assembly code.
- 5. Front End : Lexical Analysis Preprocessing Syntax Analysis Semantic Analysis
- 6. Back End Analysis Optimization Code generation
- 7. Lexical Analyzer Syntax Analyzer Semantic Analyzer Intermediate code generator Code optimizer Code generator
- 8. Lexical Syntax Semantic Code Generator Code Optimizer Intermediate Code Generator Symbol Table manager Error Handler
- 9. Also called Linear Analysis Characters read from left to right and grouped into tokens that are a sequence of characters with a collective meaning Scans Input Removes White spaces and comments Manufacture Tokens Generate Error if Any
- 10. ◦ Example ◦ A=B+C ◦ Variable tokens - A ,B, C ◦ Symbolic token -- = +
- 11. 11 Lex(Flex in recent implementation)
- 12. 12 The main job of a lexical analyzer (scanner) is to break up an input stream into tokens(tokenize input streams). Ex :- a = b + c * d; ID ASSIGN ID PLUS ID MULT ID SEMI Lex is an utility to help you rapidly generate your scanners
- 13. PLLab, NTHU,Cs2403 Programming Languages 13 (optional) (required) Lex source is separated into three sections by %% delimiters The general format of Lex source is The absolute minimum Lex program is thus {definitions} %% {transition rules} %% {user Code} %%
- 14. Declarations of ordinary C variables ,constants and Libraries. %{ #include <math.h> #include <stdio.h> #include <stdlib.h> %} flex definitions :- name definition Digit [0-9] (Regular Definition) 14
- 15. 15 Lex compiler C compiler a.out Lex source program lex.yy.c input lex.yy.c a.out tokens
- 16. 16 yytext -- a string containing the lexeme yyleng -- the length of the lexeme yyin -- the input stream pointer ◦ the default input of default main() is stdin yyout -- the output stream pointer ◦ the default output of default main() is stdout.
- 17. 17 yylex() ◦ The default main() contains a call of yylex() yymore() ◦ return the next token yyless(n) ◦ retain the first n characters in yytext yywarp() ◦ is called whenever Lex reaches an end-of-file ◦ The default yywarp() always returns 1
- 18. PLLab, NTHU,Cs2403 Programming Languages 18 Name Function char *yytext pointer to matched string int yyleng length of matched string FILE *yyin input stream pointer FILE *yyout output stream pointer int yylex(void) call to invoke lexer, returns token char* yymore(void) return the next token int yyless(int n) retain the first n characters in yytext int yywrap(void) wrapup, return 1 if done, 0 if not done ECHO write matched string REJECT go to the next alternative rule INITAL initial start condition BEGIN condition switch start condition
- 19. Also called as Hierarchial Analysis A syntax tree[also called as parse tree] is generated where ◦ Operators Interior nodes ◦ Operands Children of node for operators. = A + Interior B C Children
- 20. Characters grouped as tokens in Lexical Analysis are recorded as Tables. Checks for semantic errors Collect TYPE information for the subsequent code generation phase
- 21. Sophisticated compilers typically perform multiple passes over various intermediate forms. Many algorithms for code optimization are easier to apply one at a time The input to one optimization relies on the processing performed by another optimization
- 22. Concrete Parse tree Abstract syntax tree Converted into a linear sequence of instructions Results in 3AC [ 3 Address Code]
- 23. This phase attempts to improve the intermediate code inorder to increase the running time Reduce the complexity of the code generated Leading to a faster execution of the program Increased Performance
- 24. Platform Dependant/ Platform Independent Optimization can be automated by compilers or performed by programmers Usually, the most powerful optimization is to find a superior algorithm. Include activities like ◦ Optimization of LOOPS ◦ Optimization of Bottlenecks
- 25. Succeeding step of Intermediate code optimizer Consists of re-locatable machine code/assembly code Intermediate instructions are converted into a a sequence of machine instructions
- 26. THANK YOU