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.