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Concepts%20of%20Compiler%20Design

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Title: Concepts%20of%20Compiler%20Design


1
Introduction
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).
2
Compiler
Source Code
Compiler
Target Code
?
Error Messages
3
What is Involved
  • Programming Languages
  • Components of a Compiler
  • Applications
  • Formal Languages

4
Programming Languages
  • We use natural languages to communicate
  • We use programming languages to speak with
    computers

5
Component of Compilers
  • Analysis
  • Lexical Analysis
  • Syntax Analysis
  • Semantic Analysis
  • Synthesis
  • Intermediate Code Generation
  • Code Optimization
  • Code Generation

6
The 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 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 Analysis
  • Free form languages
  • All 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 Formalisms
  • Type 3 (Regular) Grammars
  • Regular Expressions
  • Finite State Machines
  • Useful for program construction, even if
    hand-written

10
Interface 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 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
Syntax Analysis (SA)

13
Semantic Analyserzer
14
Intermediate Code Generation
15
Code Optimization
16
Code Generation
17
Data structure tools
  • Syntax tree
  • Literal table
  • Symbol table

18
Error 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 strategycount errors, stop if
    count gets too high).

19
Kinds of errors
?
20
Sample 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 Example
  • read x
  • if x gt 0 then
  • fact 1
  • repeat
  • fact fact x
  • x x - 1
  • until x 0
  • write fact
  • end

22
C-Minus Example
  • int fact( int x )
  • if (x gt 1)
  • return x fact(x-1)
  • else
  • return 1
  • void main( void )
  • int x
  • x read()
  • if (x gt 0) write( fact(x) )

23
Structure 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 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)
  • 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.
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