Compiler Fundamentals: Understanding the Compilation Process, Study notes of Computer Science

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Compilers

CS414-2008S-

Compiler Basics & Lexical Analysis

David Galles

Department of Computer Science University of San Francisco

01-0:

Syllabus Office Hours Course Text Prerequisites Test Dates & Testing Policies Projects

Teams of up to 2 Grading Policies Questions?

01-2:

Notes on the Class Projects are non-trivial

Using new tools (JavaCC) Managing a large scale project Lots of complex classes & advancedprogramming techniques.

01-3:

Notes on the Class Projects are non-trivial

Using new tools (JavaCC) Managing a large scale project Lots of complex classes & advancedprogramming techniques. START EARLY!

Projects will take longer than you think(especially starting with the semantic analyzerproject) ASK QUESTIONS!

01-5:

What is a compiler?

Parser

Lexical Analyzer

Linker

SourceFile

TokenStream

Semantic Analyzer^ Assembly TreeGenerator

AbstractAssemblyTree

AbstractSyntax Tree

Code Generator

Assembly Assembler

RelocatableObjectCode

Libraries

Machine code

More Accurate View

01-6:

What is a compiler?

Parser

Lexical Analyzer

Linker

SourceFile

TokenStream

Semantic

Analyzer Assembly

Tree Generator

AbstractAssemblyTree

AbstractSyntax

Tree

Code Generator

Assembly Assembler

RelocatableObjectCode

Libraries

Machine

code

Front

end Back

End

01-8:

Why Use Decomposition?

01-9:

Why Use Decomposition?

Software Engineering!

Smaller units are easier to write, test and debug Code Reuse

Writing a suite of compilers (C, Fortran, C++,etc) for a new architecture Create a new language – want compilersavailable for several platforms

01-11:

Lexical Analysis Converting input file to stream of tokens

void main() {

IDENTIFIER(void)

print(4);

IDENTIFIER(main)

}^

LEFT-PARENTHESISRIGHT-PARENTHESISLEFT-BRACEIDENTIFIER(print)LEFT-PARENTHESISINTEGER-LITERAL(4)RIGHT-PARENTHESISSEMICOLONRIGHT-BRACE

01-12:

Lexical Analysis

Brute-Force Approach

Lots of nested if statements if (c = nextchar() == ’P’) { if (c = nextchar() == ’R’) { if (c = nextchar() == ’0’) {

if (c = nextchar() == ’G’) {/*

Code to handle the rest of eitherPROGRAM or any identifier that startswith PROG/ } else if (c == ’C’) {/

Code to handle the rest of eitherPROCEDURE or any identifier that startswith PROC*/ ...

01-14:

Deterministic Finite Automata Set of states Initial State Final State(s) Transitions

DFA for else, end, identifiersCombine DFA

01-15:

DFAs and Lexical Analyzers Given a DFA, it is easy to create C code toimplement it DFAs are easier to understand than C code^ Visual – almost like structure charts ... However, creating a DFA for a complete lexicalanalyzer is still complex

01-17:

Formal Languages Alphabet

: Set of all possible symbols

(characters) in the input file

Think of

as the set of symbols on the

keyboard

String

w

: Sequence of symbols from an alphabet

String length

|w

|^ Number of characters in a

string:

|car

|^ = 3,

|abba

|^ = 4

Empty String

ǫ: String of length 0:

|^ = 0

Formal Language

: Set of strings over an

alphabet Formal Language

Programming language – Formal

Language is only a set of strings.

01-18:

Formal Languages

Example formal languages:

Integers

{^0

,^23

,^44

Floating Point Numbers

{^3

.^4 ,

Identifiers {foo, bar,