Planning a compiler

• Source Language – A subset of C

• Target Language– Assembler

• Performance Criteria– Compiler speed– Code quality– Error diagnostics– Portability

• Re-target-ability (for a new target language)• Re-host-ability (run on a new machine)

– Maintainability

Approaches to compiler development

• Bootstrapping

– Using the facilities offered by a language to compile itself is the essence of bootstrapping

• Automatic generator

– Lex

– Yacc

A look at the C Compilers

• Three-quarters of the code in PCC(Portable C Compiler) is independent of the target machine.

• All these compilers are essentially two-pass.

– The PDP-11comipler has an optional third pass that does optimization ( peephole optimization ) on the assembly-language output

Lexical and syntax analysis intermediate code generation

Code generation

Post optimization

Postfix or prefix form for expressions assembly code otherwise

Assembly language

Source code

Assembly language

A Programming Project

• Main tasks

– Translate the source program in C into an intermediate representation such as quadruples

– Interpret the intermediate representation

– Implement a basic components of a compiler for a subset of C.

A Programming Project

• Suggested exercises– Design a symbol-table mechanism

(Required)• Search the symbol table for a given

name• Create a new entry for that name if

none is present• Delete from the symbol table all names

local to a given function

A Programming Project• Suggested exercises

– Write an interpreter for quadruples(Optional)– Write the lexical analyzer(Required)

• Select internal codes for the tokens• Decide the representation of constants• Count lines for later use by an error-message handler• Produce a listing of the source program if desired• Write a program to enter the reserved words into the symbol

table• Design the lexical analyzer to be a function called by the

parser• Error handling

A Programming Project

• Suggested exercises

– Write the semantic actions(Required)

• Do semantic analysis at this time. Converting integers to real numbers when necessary

– Write the parser(Required)

• LALR parser generator (Yacc)

– Write the error-handling routines (Optional)

A Programming Project

• Important Website about Lex/YACC– http://dinosaur.compilertools.net/ (Lex/Yacc P

ages) – http://www.cs.princeton.edu/software/lcc/pkg/– http://www.thefreecountry.com/compilers/cpp.

shtml– http://www.thefreecountry.com/programming/

compilerconstruction.shtml– http://www.gnu.org/software/gcc/gcc.html– http://gcc.gnu.org/install/index.html

A Yacc/Lex Example

Yacc/Lex for Pascal