Introduction

D. M. Akbar Hussain: Department of Software & Media Technology

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Compiler is tool: which translate notations from one system to another, usually from source code (high level code) to machine code (object code, target code, low level code).

IntroductionIntroduction


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CompilerCompiler

CompilerCompiler

Error Messages

Source Code

Target Code

?


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What is InvolvedWhat is Involved

• Programming Languages

• Components of a Compiler

• Applications

• Formal Languages


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Programming LanguagesProgramming Languages

• We use natural languages to communicate

• We use programming languages to speak with computers


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Component of CompilersComponent of Compilers

• Analysis

• Lexical Analysis

• Syntax Analysis

• Semantic Analysis

• Synthesis

• Intermediate Code Generation

• Code Optimization

• Code Generation


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The InputThe Input

Read string input– sequence of characters– Character set:

• ASCII• ISO Latin-1• ISO 10646 (16-bit = unicode) Ada, Java• Others (EBCDIC, JIS, etc)


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The OutputThe Output

Tokens: kind, name

– Punctuation ( ) ; , [ ]

– Operators + - ** :=

– Keywords begin end if while try catch

– Identifiers Square_Root

– String literals “press Enter to continue”

– Character literals ‘x’

– Numeric literals • Integer • Floating_point


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Lexical AnalysisLexical Analysis

Free form languagesAll modern languages are free form – White space, tabs, new line, carriage return does not

matter just Ignore these.– Ordering of token is only important

Fixed format languages– Layout is critical

• Fortran, label in cols 1-6• COBOL, area A B• Lexical analyzer must know about layout to find tokens


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Relevant FormalismsRelevant Formalisms

Type 3 (Regular) Grammars Regular Expressions Finite State Machines

Useful for program construction, even if hand-written


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Interface to Lexical AnalyzerInterface to Lexical Analyzer

Either: Convert entire file to a file of tokens– Lexical analyzer is separate phase

Or: Parser calls lexical analyzer to supply next token– This approach avoids extra I/O– Parser builds tree incrementally, using successive tokens as tree

nodes


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Performance IssuesPerformance Issues

Speed– Lexical analysis can become bottleneck

– Minimize processing per character• Skip blanks fast

• I/O is also an issue (read large blocks)

– We compile frequently• Compilation time is important

– Especially during development

– Communicate with parser through global variables


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SyntaxSyntax Analysis Analysis (SA) (SA)


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SemanticSemantic Analyser Analyserzerzer


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Intermediate Code GenerationIntermediate Code Generation


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Code OptimizationCode Optimization


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Code GenerationCode Generation


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Data structure toolsData structure tools

Syntax tree: Literal table: Symbol table:


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Error handlerError handler

One of the difficult part of a compiler. Must handle a wide range of errors Must handle multiple errors. Must not get stuck. Must not get into an infinite loop (typical simple-minded

strategy:count errors, stop if count gets too high).


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Kinds of errorsKinds of errors

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Sample compilerSample compiler

TINY: Pages 22-26, 4-pass compiler for the TINY language based on Pascal.

C-Minus based on C : Pages 26-27 and Appendix A.


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TINY ExampleTINY Example

read x;

if x > 0 then

fact := 1;

repeat

fact := fact * x;

x := x - 1

until x = 0;

write fact

end


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C-Minus ExampleC-Minus Example

int fact( int x ){ if (x > 1) return x * fact(x-1); else return 1;}

void main( void ){ int x; x = read(); if (x > 0) write( fact(x) );}


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Structure of the TINY CompilerStructure of the TINY Compiler

globals.h main.c

util.h util.c

scan.h scan.c

parse.h parse.c

symtab.h symtab.c

analyze.h analyze.c

code.h code.c

cgen.h cgen.c


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Conditional Compilation OptionsConditional Compilation Options

NO_PARSE: Builds a scanner-only compiler.

NO_ANALYZE: Builds a compiler that parses and scans only.

NO_CODE: Builds a compiler that performs semantic analysis, but generates no code.


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Listing Options (built in - not flags)Listing Options (built in - not flags)

EchoSource: Echoes the TINY source program to the listing, together with line numbers.

TraceScan: Displays information on each token as the scanner recognizes it.

TraceParse: Displays the syntax tree in a linearlised format. TraceAnalyze: Displays summary information on the symbol table

and type checking. TraceCode: Prints code generation-tracing comments to the code

file.

Introduction

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