1. Compiler Structures 1. Overview Objective
, Semester 2,
1. Overview
Objective
what are the main features (structures) in a compiler?

2. Overview
1. What is a Compiler? 2. Structure of a Compiler 3. Example Compilation 4. Compiler Design Issues 5. Compilers and Interpreters

3. 1. What is a Compiler?
A compiler reads a program written in one language and translates it into another language.
The source language is high-level (e.g. C), and the target language is low-level (e.g. machine code).
program
in a source
language
program
in a target
language
compiler

4. The target program is run later.
Input
Compiler
Target
Program
Source
Program
Target
Program
Compile-time
Error messages
Runtime
Error messages
Output

5. 2. Structure of a Compiler
Source Program
2. Structure of a Compiler ?
Target Lang. Prog.

6. Structure of a Compiler
Source Program
Structure of a Compiler
Front End
Intermediate Code
Back End
Target Lang. Prog.

7. Structure of a Compiler
Source Program
Structure of a Compiler
Lexical Analyzer
Front
End
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Back End
Target Lang. Prog.

8. Structure of a Compiler
Source Program
Structure of a Compiler
Lexical Analyzer
Front
End
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
This course will
concentrate on the
"front end" tasks
performed by a
compiler.
Intermediate Code
Code Optimizer
Back
End
Target Code Generator
Target Lang. Prog.

9. 3. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Source Code:
cur_time = start_time + cycles * 60
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

10. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Source Code:
cur_time = start_time + cycles * 60
Lexical Analysis:
ID(1) ASSIGN ID(2) ADD ID(3) MULT INT(60)
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

11. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Source Code:
cur_time = start_time + cycles * 60
Lexical Analysis:
ID(1) ASSIGN ID(2) ADD ID(3) MULT INT(60)
Syntax Analysis:
ASSIGN
ID(1) ADD
ID(2) MULT
ID(3) INT(60)
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

12. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Syntax Analysis:
ASSIGN
ID(1) ADD
ID(2) MULT
ID(3) INT(60)
Sematic Analysis:
ID(3) int2float
INT(60)
Lexical Analyzer
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

13. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Sematic Analysis:
ASSIGN
ID(1) ADD
ID(2) MULT
ID(3) int2float
INT(60)
Intermediate Code:
temp1 = int2float(60)
temp2 = id3 * temp1
temp3 = id2 + temp2
id1 = temp3
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

14. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Intermediate Code:
temp1 = int2float(60)
temp2 = id3 * temp1
temp3 = id2 + temp2
id1 = temp3
Optimized Code (step 0):
Lexical Analyzer
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

15. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Intermediate Code:
temp1 = int2float(60)
temp2 = id3 * temp1
temp3 = id2 + temp2
id1 = temp3
Optimized Code (step 1):
temp1 = 60.0
Lexical Analyzer
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

16. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Intermediate Code:
temp1 = int2float(60)
temp2 = id3 * temp1
temp3 = id2 + temp2
id1 = temp3
Optimized Code (step 2):
temp2 = id3 * 60.0
Lexical Analyzer
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

17. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Intermediate Code:
temp1 = int2float(60)
temp2 = id3 * temp1
temp3 = id2 + temp2
id1 = temp3
Optimized Code (step 3):
temp2 = id3 * 60.0
id1 = id2 + temp2
Lexical Analyzer
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

18. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Intermediate Code:
temp1 = int2float(60)
temp2 = id3 * temp1
temp3 = id2 + temp2
id1 = temp3
Optimized Code:
temp1 = id3 * 60.0
id1 = id2 + temp1
Lexical Analyzer
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

19. Example Compilation Source Program Lexical Analyzer Syntax Analyzer
Intermediate Code:
temp1 = int2float(60)
temp2 = id3 * temp1
temp3 = id2 + temp2
id1 = temp3
Optimized Code:
temp1 = id3 * 60.0
id1 = id2 + temp1
Target Code:
MOVF id3, R2
MULF #60.0, R2
MOVF id2, R1
ADDF R2, R1
MOVF R1, id1
Lexical Analyzer
Syntax Analyzer
Semantic Analyzer
Int. Code Generator
Intermediate Code
Code Optimizer
Target Code Generator
Target Lang. Prog.

20. 4. Compiler Design Issues
Correctness
does the target do the 'same' as the source?
Speed (compile time and runtime)
code optimizations
multiple passes over code
Memory space required
Good feedback to user
error reporting

21. 5. Compilers and Interpreters
A compiler generates a target program that can be run later.
Input
Compiler
Target
Program
Source
Program
Target
Program
Compile-time
Error messages
Runtime
Error messages
Output

22. An interpreter 'compiles' and runs the source program all at once
it usually executes the intermediate code
Source
Program
interpreter
Output
Input
Error messages