Classification of Compilers Single Pass Compilers Two Pass Compilers Multipass Compilers

1. Lecture 2

2. Classification of Compilers
1. Single Pass Compilers
2. Two Pass Compilers
3. Multipass Compilers

3. Single Pass Compiler
• Source code directly transforms into
machine code.
– For example Pascal
source
code
target
code
Front EndCompiler

4. Two Pass Compiler
• Use intermediate representation
– Why?
source
code
target
code
Front End Back End
IR
Front End

5. 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
5

6. © Oscar Nierstrasz
Multipass compiler
• analyzes and changes IR
• goal is to reduce runtime
• must preserve values
6

7. 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)