Compiler ConstructionCompiler Construction0368-3133 0368-3133

Mooly Sagiv and Guy Golan-GuetaMooly Sagiv and Guy Golan-GuetaSchool of Computer ScienceSchool of Computer Science

Tel-Aviv UniversityTel-Aviv University

22

Executable

code

exe

Source

text

txt

Compiler

Semantic

Representation

Backend

(synthesis)

Frontend

(analysis)

ICProgram

ic

x86 executable

exeLexicalAnalysi

s

Syntax Analysi

s

Parsing

AST Symbol

Tableetc.

Inter.Rep.(IR)

CodeGeneration

33

HowHowLexicalAnalysi

s

Syntax Analysi

s

Parsing

AST Symbol

Tableetc.

Inter.Rep.(IR)

CodeGeneration

JFlex JavaCup Java

ICProgram

prog.ic

x86 assembly

prog.s

x86 assembly

prog.s

libic.a(libic + gc)

GNU assembler

prog.o GNUlinker prog.exe

script / Ant

44

50% exam50% exam50% project50% project

5 assignments – different weights5 assignments – different weightsPA1 - lexical analysisPA1 - lexical analysisPA2 - parsingPA2 - parsingPA3 - semantic analysisPA3 - semantic analysisPA4 - IR and IR loweringPA4 - IR and IR loweringPA5 - code generationPA5 - code generation

code checked both automatically and manuallycode checked both automatically and manually

GradingGrading

55

Teams of 2 or 3 studentsTeams of 2 or 3 students Email me before next recitationEmail me before next recitation

guyg.guyg@gmail.comguyg.guyg@gmail.com List of members (first name, last name, id, username on nova)List of members (first name, last name, id, username on nova) Team-account user nameTeam-account user name

There is adequate time to complete assignmentsThere is adequate time to complete assignments Start early and please follow directionsStart early and please follow directions

Submission in your home directoriesSubmission in your home directories

Project guidelinesProject guidelines

66

Goals:Goals: IC language overviewIC language overview Understand the scope of the projectUnderstand the scope of the project

TodayToday

IC

Language

ic

Executable

code

exeLexicalAnalysi

s

Syntax Analysi

s

Parsing

AST Symbol

Tableetc.

Inter.Rep.(IR)

CodeGeneration

77

IC language - main featuresIC language - main features Strongly-typedStrongly-typed

Primitive types for int, boolean, stringPrimitive types for int, boolean, string Reference typesReference types

Object orientedObject oriented Objects, virtual method callsObjects, virtual method calls InheritanceInheritance

Memory managementMemory management Dynamic heap allocation of objects and arraysDynamic heap allocation of objects and arrays Automatic deallocation (garbage collection)Automatic deallocation (garbage collection) Runtime safety checksRuntime safety checks

Null dereferenceNull dereference Division by 0Division by 0 Array access out of boundsArray access out of bounds

Adapted with permission from Prof. Radu Rugina (Cornell Adapted with permission from Prof. Radu Rugina (Cornell University)University)

88

Unsupported featuresUnsupported features

Access controlAccess controlEverything is publicEverything is public

InterfacesInterfacesMethod overloading Method overloading

(but still allow overriding)(but still allow overriding)ExceptionsExceptionsPackagesPackages

99

IC program structureIC program structure

Program is sequence of Program is sequence of classclass definitions definitionsClass is sequence of Class is sequence of fieldsfields and and methodsmethods

Static methods Static methods virtualvirtual methods methods Exactly one Exactly one mainmain method methodstatic void main(string[] args) {...}static void main(string[] args) {...}

1010

IC program structureIC program structure

VariablesVariables can be declared anywhere in a method can be declared anywhere in a method Check initialization before useCheck initialization before use

Object fields and Array elements are initializedObject fields and Array elements are initialized

stringsstrings are primitive types are primitive types ArraysArrays T[ ], T[ ][ ] T[ ], T[ ][ ]

1111

IC typesIC types Every class is a typeEvery class is a type Primitive types:Primitive types:

int :int : 1,-1,2,-2,…1,-1,2,-2,… boolean : true, falseboolean : true, false string : “hello”string : “hello”

References : References : nullnull Arrays : Arrays : int [] x = new int[5]; x.length==5;int [] x = new int[5]; x.length==5;

All variables must be declaredAll variables must be declared compiler infers types for expressionscompiler infers types for expressions

Type-safetyType-safety Well-typed programs do not result in runtime type errorsWell-typed programs do not result in runtime type errors

1212

SubtypingSubtyping

Inheritance induces subtyping relationInheritance induces subtyping relationType hierarchy gives acyclic graphType hierarchy gives acyclic graphSubtyping rules:Subtyping rules:

A extends B {…}A extends B {…}

A ≤ BA ≤ B A ≤ AA ≤ A

A ≤ B B ≤ CA ≤ B B ≤ C

A ≤ CA ≤ C nullnull ≤ A ≤ A

Subtyping does not extend to array typesSubtyping does not extend to array typesA subtype of B then A[] A subtype of B then A[] is notis not a subtype of B[] a subtype of B[]

1313

ExpressionsExpressions

Expression languageExpression language Every expression has a type and a valueEvery expression has a type and a value Loops:Loops: whilewhile ((exprexpr)) {{ stmt stmt }} Conditionals:Conditionals: ifif ((exprexpr)) stmt stmt elseelse stmt stmt Arithmetic operators: Arithmetic operators: + - * / %+ - * / % Relational compatison: Relational compatison: < > == <= >=< > == <= >= Logical operators: Logical operators: && ||&& || Unary operators: Unary operators: ! -! - Assignment:Assignment: xx = = expr expr break, continuebreak, continue

1414

ObjectsObjects

Instances of classes are Instances of classes are objectsobjectsclass Point {class Point {

int x; // initialized to 0int x; // initialized to 0

int y;int y;}}

new Point()new Point() allocates object of class allocates object of class PointPoint on heap and initializes fieldson heap and initializes fields No argumentsNo arguments

An object can be thought of as a struct (record) An object can be thought of as a struct (record) with a slot for each fieldwith a slot for each field

0 0x y

1515

MethodsMethodsclass Point {class Point {int x;int x;int y;int y;Point movePoint(int newx, int newy) {Point movePoint(int newx, int newy) {

x = newx;x = newx;y = newy;y = newy;return return thisthis;;

}} -- close method -- close method}} -- close class -- close class

Methods can refer to the current object using Methods can refer to the current object using thisthis

1616

class TestPoint {class TestPoint {Point p;Point p;Point q;Point q;boolean test() {boolean test() {

p = new Point();p = new Point();q = q = pp.movePoint(1,2);.movePoint(1,2);return p==q;return p==q;

}}}}

class Point {class Point {int x;int x;int y;int y;Point movePoint(int newx, int newy) {Point movePoint(int newx, int newy) {

x = newx;x = newx;y = newy;y = newy;return return thisthis;;

} } }}

0 0x y

p

1 2x y

pq

ExampleExample

1 2x y

pthis

1717

Method implementationMethod implementation

Each object knows how to access method codeEach object knows how to access method code As if object contains slot pointing to the codeAs if object contains slot pointing to the code

In reality implementations save space by sharing these In reality implementations save space by sharing these pointers among instances of the same classpointers among instances of the same class

0 0x y

*movePoint

0 0x y

*movePoint

methods

1818

Inheritance exampleInheritance example We can extend points to colored points:We can extend points to colored points:

class ColoredPoint extends Point {class ColoredPoint extends Point {int color;int color;Point movePoint(int newx, int newy) {Point movePoint(int newx, int newy) {

color = 0;color = 0;x = newx;x = newx;y = newy;y = newy;return this;return this;

}}}}

0 0x y

*movePoint

methods0color

1919

Method invocation and inheritanceMethod invocation and inheritance

Example:Example:

Point p;Point p;

p = new ColoredPoint();p = new ColoredPoint();

p.movePoint(1,2);p.movePoint(1,2); pp has has staticstatic type type PointPoint pp has has dynamicdynamic type type ColoredPointColoredPoint p.movePointp.movePoint invokes invokes ColoredPointColoredPoint

implementationimplementation

2020

IC memory managementIC memory management

Memory allocated every time Memory allocated every time newnew is used is used Memory deallocated automatically by Memory deallocated automatically by

reclaiming reclaiming unreachableunreachable objects objectsDone by a garbage collector (GC) Done by a garbage collector (GC) Use off-the-shelf GCUse off-the-shelf GC

0 0x y

a…a = b

1 2x y

b

0 0x y

1 2x y

ba

unreachableobject

2121

Library functionsLibrary functions libic provides:libic provides:

I/O operationsI/O operations datatype conversionsdatatype conversions system level-operationssystem level-operations

class Library {class Library { static void println(string s); static void println(string s); // prints string s followed by a newline.// prints string s followed by a newline. static void print(string s); static void print(string s); // prints string s. // prints string s. static void printi(int i); static void printi(int i); // prints integer i.// prints integer i. static void printb(boolean b); static void printb(boolean b); // prints boolean b.// prints boolean b. static int readi(); static int readi(); // reads one character from the input.// reads one character from the input. static string readln(); static string readln(); // reads one line from the input.// reads one line from the input. static boolean eof(); static boolean eof(); // checks end-of-file on standard input.// checks end-of-file on standard input. static int stoi(string s, int n); static int stoi(string s, int n); // returns the integer that s represents// returns the integer that s represents // or n if s is not an integer.// or n if s is not an integer. static string itos(int i); static string itos(int i); // returns a string representation of i.// returns a string representation of i. static int[] stoa(string s);static int[] stoa(string s); // an array with the ascii codes of chars in s.// an array with the ascii codes of chars in s. static string atos(int[] a);static string atos(int[] a); // builds a string from the ascii codes in a.// builds a string from the ascii codes in a. static int random(int n); static int random(int n); // returns a random number between 0 and n-1.// returns a random number between 0 and n-1. static int time(); static int time(); // number of milliseconds since program start.// number of milliseconds since program start. static void exit(int n); static void exit(int n); // terminates the program with exit code n.// terminates the program with exit code n.}}

2222

For next weekFor next week

Split into teamsSplit into teams Send me email with team members and Send me email with team members and

representative accountrepresentative account Read IC language specificationRead IC language specification Get acquainted with JavaGet acquainted with Java

J2SE 1.5 (or higher) (or higher) Eclipse IDE

Install and play with JFLex and Java CupInstall and play with JFLex and Java Cup

2323

Next weekNext week

Lexical analysisLexical analysisJFLexJFLex

Lexical analyzer generator in JavaLexical analyzer generator in Java

Explain PA1Explain PA1