Course OverviewMooly Sagiv

msagiv@post.tau.ac.ilSchrierber 31703-640-7606

Wed 10:00-12:00

html://www.math.tau.ac.il/~msagiv/courses/wcc01.htmlTextbook:Modern Compiler Implementation in C

Andrew AppelISBN 0-521-58390-X

Outline• High level programming languages

• Interpreter vs. Compiler

• Abstract Machines

• Why study compilers?

• Main Compiler Phases

High Level Programming Languages• Imperative

– Algol, PL1, Fortran, Pascal, Ada, Modula, and C– Closely related to “von Neumann” Computers

• Object-oriented – Simula, Smalltalk, Modula3, C++, Java– Data abstraction and ‘evolutionary’

form of program development• Class An implementation of an abstract data type (data+code)• Objects Instances of a class• Fields Data (structure fields)

• Methods Code (procedures/functions with overloading)• Inheritance Refining the functionality of a class with different fields

and methods

• Functional • Logic Programming

Other Languages• Hardware description languages

– VHDL

– The program describes Hardware components

– The compiler generates hardware layouts

• Shell-languages Shell, C-shell, REXX

– Include primitives constructs from the current software environment

• Graphics and Text processing TeX, LaTeX, postscript– The compiler generates page layouts

• Web/Internet

– HTML, MAWL, Telescript, JAVA

• Intermediate-languages

– P-Code, Java bytecode, IDL

Interpreter• Input

– A program– An input for the program

• Output– The required output

interpreter

source-program

program’s input program’s input

Example

C interpreter

int x;scanf(“%d”, &x);x = x + 1 ;printf(“%d”, x);

5 6

Compiler• Input

– A program

• Output– An object program that reads the input and

writes the output

compiler

source-program

program’s input program’s inputobject-program

Example

Sparc-cc-compiler

int x;scanf(“%d”, &x);x = x + 1 ;printf(“%d”, x);

5 6

add %fp,-8, %l1mov %l1, %o1call scanfld [%fp-8],%l0add %l0,1,%l0st %l0,[%fp-8] ld [%fp-8], %l1 mov %l1, %o1 call printf

assembler/linker

object-program

Interpreter vs. Compiler

• Conceptually simpler (the definition of the programming language)

• Easier to port• Can provide more

specific error report• Normally faster

• More efficient– Compilation is done once

for all the inputs --- many computations can be performed at compile-time

– Sometimes evencompile-time + execution-time < interpretation-time

• Can report errors before input is given

Interpreters provide specific error report• Input-program

• Input data y=0

scanf(“%d”, &y);if (y < 0)

x = 5;... if (y <= 0)

z = x + 1;

Compilers are usually more efficient

Sparc-cc-compiler

scanf(“%d”, &x);y = 5 ;z = 7 ;x = x +y*z;printf(“%d”, x);

add %fp,-8, %l1 mov %l1, %o1call scanfmov 5, %l0st %l0,[%fp-12]mov 7,%l0st %l0,[%fp-16]ld [%fp-8], %l0ld [%fp-8],%l0add %l0, 35 ,%l0st %l0,[%fp-8] ld [%fp-8], %l1 mov %l1, %o1 call printf

Compilers can provide errors beforeactual input is given

• Input-program

• Compiler-Output “line 4: improper pointer/integer combination: op =''

int a[100], x, y ;scanf(“%d”, y) ;if (y < 0)

/* line 4*/ y = a ;

Compilers can provide errors beforeactual input is given

• Input-program

• Compiler-Output “line 88: x may be used before set''

scanf(“%”, y);if (y < 0)

x = 5;... if (y <= 0)/* line 88 */ z = x + 1;

Abstract Machines• A compromise between compilers and interpreters• An intermediate program representation• The intermediate representation is interpreted• Example: Zurich P4 Pascal Compiler(1981)

• Other examples: Java bytecode, MS .NET• The intermediate code can be compiled

Pascal compiler

Pascal Program

P-code

interpreter program’s inputprogram’s input

Why Study Compilers• Become a compiler writer

– New programming languages– New machines– New compilation modes: “just-in-time”

• Using some of the techniques in other contexts• Design a very big software program using a

reasonable effort• Learn applications of many CS results (formal

languages, decidability, graph algorithms, dynamic programming, ...

• Better understating of programming languages and machine architectures

• Become a better programmer

Course Requirements

• Compiler Project 50%– Develop a Tiger Front-End in C– Tight schedule

• Bonus 15%

• Final exam 50%

Compiler Phases

• The compiler program is usually written as sequence of well defined phases

• The interfaces between the phases is well defined (another language)

• It is sometimes convenient to use auxiliary global information (e.g., symbol table)

• Advantages of the phase separation:– Modularity

– Simplicity

– Reusabilty

Basic Compiler PhasesSource program (string)

Fin. Assembly

lexical analysis

syntax analysis

semantic analysis

Translate

Instruction selection

Register Allocation

Tokens

Abstract syntax tree

Intermediate representation

Assembly

Finite automata

Pushdown automata

Memory organization

graph algorithms

Dynamic programming

Example:straight-line programming

Stm ::=Stm ; Stm //(CompoundStm)Stm ::=id := Exp // (AssignStm)Stm ::= print (ExpList) // (PrintStm)Exp ::= id // (IdExp)Exp ::= num // (NumExp)Exp ::= Exp Binop Exp // (OpExp)Exp ::= (Stm, Exp) // (EseqExp)ExpList ::= Exp, ExpList // (PairExpList)ExpList ::= Exp // (LastExpList)Binop ::= + // (Plus)Binop ::= - // (Minus)Binop ::= * // (Times)Binop ::= / // (Div)

Example Input

a := 5 + 3;b := (

print(a, a-1), 10 * a);print(b)

Questions

• How to check that a program is correct?

• How to internally represent the compiled program?

Lexical Analysis

a\b := 5 + 3 ;\nb := (print(a, a-1), 10 * a) ;\nprint(b)

• Input string

• Tokens

id (“a”) assign num (5) + num(3) ;id(“b”) assign

print(id(“a”) , id(“a”) - num(1)), num(10) * id(“a”)) ;print(id(“b”))

Syntax Analysis• Tokens

• Abstract Syntax tree

id (“a”) assign num (5) + num(3) ;id(“b”) assign

print(id(“a”) , id(“a”) - num(1)), num(10) * id(“a”)) ;print(id(“b”))

CompoundStm

AssignStmCompoundStm

id opExp

numExp numExpPlus

5 3

a

AssignStm

id eseqExp

PrintStm

opExp

b

Summary

• Phases drastically simplifies the problem of writing a good compiler

• The Textbook offers a reasonable partition into phases with interface definition (in C)

• Every week we will study a new compiler phase