D. M. Akbar Hussain: Department of Software & Media Technology 1 Compiler is tool: which translate notations from one system to another, usually from source.

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

1

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


2

CompilerCompiler

CompilerCompiler

Error Messages

Source Code

Target Code

?


3

What is InvolvedWhat is Involved

• Programming Languages

• Components of a Compiler

• Applications

• Formal Languages


4

Programming LanguagesProgramming Languages

• We use natural languages to communicate

• We use programming languages to speak with computers


5

Component of CompilersComponent of Compilers

• Analysis

• Lexical Analysis

• Syntax Analysis

• Semantic Analysis

• Synthesis

• Intermediate Code Generation

• Code Optimization

• Code Generation


6

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)


7

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


8

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


9

Relevant FormalismsRelevant Formalisms

Type 3 (Regular) Grammars Regular Expressions Finite State Machines

Useful for program construction, even if hand-written


10

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


11

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


12

SyntaxSyntax Analysis Analysis (SA) (SA)


13

SemanticSemantic Analyser Analyserzerzer


14

Intermediate Code GenerationIntermediate Code Generation


15

Code OptimizationCode Optimization


16

Code GenerationCode Generation


17

Data structure toolsData structure tools

Syntax tree: Literal table: Symbol table:


18

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).


19

Kinds of errorsKinds of errors

?


20

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.


21

TINY ExampleTINY Example

read x;

if x > 0 then

fact := 1;

repeat

fact := fact * x;

x := x - 1

until x = 0;

write fact

end


22

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) );}


23

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


24

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.


25

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.

D. M. Akbar Hussain: Department of Software & Media Technology 1 Compiler is tool: which translate notations from one system to another, usually from source.

Documents

D. M. Akbar Hussain: Department of Software & Media Technology 1 Compiler is tool: which translate notations from one system to another, usually from source.