1 October 16, 2015 1 October 16, 2015October 16, 2015October 16, 2015 Azusa, CA Sheldon X. Liang Ph....

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April 21, 20231

April 21, 2023April 21, 2023 Azusa, CAAzusa, CA

Sheldon X. Liang Ph. D.

Computer Science at Computer Science at Azusa Pacific UniversityAzusa Pacific University

Azusa Pacific University, Azusa, CA 91702, Tel: (800) 825-5278 Department of Computer Science, http://www.apu.edu/clas/computerscience/

CS400 Compiler ConstructionCS400 Compiler Construction

http://www.apu.edu/clas/computerscience/

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• Building a compiler involves:– Defining the syntax of a programming language

– Develop a source code parser: for our compiler we will use predictive parsing (greedy eater)

– Implementing syntax directed translation to generate intermediate code: our target is the JVM abstract stack machine

– Generating Java bytecode for the JVM

– Optimize the Java bytecode (optional)

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CS@APU: CS400 Compiler ConstructionCS@APU: CS400 Compiler Construction

Building a Simple CompilerBuilding a Simple Compiler

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Symbol TableSymbol Table

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Keep in mind following questionsKeep in mind following questions

• Symbol table– A data structure– Hold information – Collected incrementally

• Why we need s-table– Keep track of semantics of variable– Character string (lexeme)– Variables’ type – Its position in storage

• What further use of s-table– Forward reference– Scope information– Storage allocation, size…

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Content in Symbol TablesContent in Symbol Tables

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insert(s, t): returns array index to new entry for string s token t

lookup(s): returns array index to entry for string s or 0

The symbol table is globally accessible (to all phases of the compiler)

Each entry in the symbol table contains a string and a token value:struct entry{ char *lexptr; /* lexeme (string) */ int token;};struct entry symtable[];

Possible implementations:- simple C code (see textbook)- hashtables

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Symbol TableSymbol Table


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Two Common Approaches(1/3)Two Common Approaches(1/3)

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Forward ReferenceForward Reference

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factor ( expr ) | id { print(id.string) }

#define ID 259 /* token returned by lexan() */

factor(){ if (lookahead == ‘(‘) { match(‘(‘); expr(); match(‘)’); } else if (lookahead == ID) { printf(“ %s “, symtable[tokenval].lexptr); match(NUM); } else error();}

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IdentifiersIdentifiers


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/* global.h */#define DIV 257 /* token */#define MOD 258 /* token */#define ID 259 /* token */

/* init.c */insert(“div”, DIV);insert(“mod”, MOD);

/* lexer.c */int lexan(){ … tokenval = lookup(lexbuf); if (tokenval == 0) tokenval = insert(lexbuf, ID); return symtable[p].token;}

We simply initialize the global symbol

table with the set of keywords

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Handling Reserved KeywordsHandling Reserved Keywords


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morefactors div factor { print(‘DIV’) } morefactors | mod factor { print(‘MOD’) } morefactors | …

/* parser.c */morefactors(){ if (lookahead == DIV) { match(DIV); factor(); printf(“DIV”); morefactors(); } else if (lookahead == MOD) { match(MOD); factor(); printf(“MOD”); morefactors(); } else …}

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Handling Reserved KeywordsHandling Reserved Keywords


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push 5rvalue 2+rvalue 3*…

16

7

0

11

7

…

Instructions Stack Data

1

2

3

4

123456

pc

top…

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Abstract Stack MachinesAbstract Stack Machines


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• Abstract stack machine architecture– Emulated in software with JVM interpreter

– Just-In-Time (JIT) compilers

– Hardware implementations available

• Java bytecode– Platform independent

– Small

– Safe

• The JavaTM Virtual Machine Specification, 2nd ed.http://java.sun.com/docs/books/vmspec

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The JVMThe JVM


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Got it with following questionsGot it with following questions• Symbol table

– A data structure– Hold information – Collected incrementally

• Why we need s-table– Keep track of semantics of variable– Character string (lexeme)– Variables’ type – Its position in storage

• What further use of s-table– Forward reference– Scope information– Storage allocation, size…

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Thank you very much!

Questions?

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A Simple Syntax-Directed TranslatorA Simple Syntax-Directed Translator


1 October 16, 2015 1 October 16, 2015October 16, 2015October 16, 2015 Azusa, CA Sheldon X. Liang Ph....

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