Lecture 2

Classification of Compilers

1. Single Pass Compilers

2. Two Pass Compilers

3. Multipass Compilers

Single Pass Compiler

• Source code directly transforms into machine code.– For example Pascal

sourcecode

targetcode

Front EndCompiler

Two Pass Compiler

• Use intermediate representation – Why?

sourcecode

targetcode

Front End Back EndIR

Front End

Two pass compiler

• intermediate representation (IR) • front end maps legal code into IR • back end maps IR onto target machine • simplify retargeting • allows multiple front ends • multiple passes better code

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© Oscar Nierstrasz

Multipass compiler

• analyzes and changes IR • goal is to reduce runtime • must preserve values

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Comparison

• One pass compilers are generally faster than Multipass Compilers

• Multipass ensures the correctness of small program rather than the correctness of a large program (high quality code)