Compiler Chap'1 Introduction to Compiler

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CompilerChap.1 Introduction to Compiler

• Internet Management Technology Lab.

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Contents

• Introduction
• Conceptual view of the compilation process
• The phases of a compiler

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Introduction

• Definition of compiler
• A program which accepts phrases written in an
  input language (source language) and produces
  equivalent phrases in the desired output language
  (target language)
• e.g. assembler assembly ? machine language
• Characteristics of compiler
• Directed by a simple understanding of the phrase
  structure (grammar) of an input language
• Usually contains complex mapping algorithms
• Generates a target code for efficiency while an
  interpreter does not generate a target code for
  flexibility

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Conceptual View of Compilation Process
ltA language-processing systemgt
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The phases of a compiler Architecture
ltAnalysis of the source programgt
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The phases of a compiler Lexical Analysis

• Lexical Analysis Phase
• Reads in the characters from the source program
• Groups the characters into grammatically
  significant chunks called lexemes or tokens
• A token is a logically cohesive sequence of
  characters - keyword, constant, operator,
  identifier, etc.
• Outputs the tokens to the syntax analysis phase
• Performed by a lexer (or scanner) and the
  efficiency is one of the important issues
• Example Find tokens from the following example

if( a lt 3.5 )        bottom a else
       bottom
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The phases of a compiler Syntax Anaysis

• Syntax Analysis phase
• Imposes a hierarchical structure on the token
  stream by the language syntax
• Optionally builds an Abstract Syntax Tree (AST)
• AST represents the structure of the source
  program
• AST is one of the Intermediate representation
  form
• Performed by a parser

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The phases of a compiler Intermediate Rep.

• AST from the example 1

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The phases of a compiler Semantic Analysis

• Semantic Analysis Phase
• Checks the meaning of the constructs
• Most of the semantic analysis is done by a parser
  
• Some could be done by lexer or code generator
• Parser and part of code generator performing
  semantic analysis is called constrainer by
  pittman
• Type checking, uniqueness
• Int a, real b
• a b

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The phases of a compiler Optimization

• Code optimization Phase
• Optional phase for performance enhancement such
  as
• Reducing execution time
• Saving memory space
• Reducing communication bandwidth
• Performed by a code optimizer

for(j 0 j lt MAX j)    m 24   
sum sum xj m could be rewritten as
m 24 for(j 0 j lt MAX j)    sum
xj m
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The phases of a compiler Code Generation

• Code Generation Phase
• Translates intermediate representation (or output
  from the parser) into a target code
• Performed by a code generator
• e.g.
• a a 1
• Generates the following assembly-like pseudo code

LD                 R1, a ADD               R1,
R1, 1 ST          a, R1
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Homework I

• Compare compiler and interpreter with regard to
  the space complexity and the time complexity,
  then discuss the applications areas where using
  interpreters are better than compilers.
• How the compiler architecture presented in class
  could be modified for better flexibilities?
• How each 4 modules in the architecture
  contributes to the syntax analysis and semantic
  analysis respectively?
• What are the advantages of having the phases such
  as lexical analysis phase, syntax analysis phase,
  and so on be separately modularized ?