1. Compiler Chapter 9. Intermediate Languages
Sung-Dong Kim
Dept. of Computer Engineering,
Hansung University

2. 1. Introduction (1) Compiler model Source Program Back-End IL
Lexical Analyzer
Source
Program
tokens
Syntax Analyzer
AST
Back-End
Semantic Analyzer
Intermediate
Code Generator IL
Code Optimizer
Object Program
Target Code Generator
Front-End
Front-End - language dependant part
Back-End - machine dependant part
(2011-1) Compiler

3. 1. Introduction (2) Intermediate language Advantages
Link front end and back end of the compiler
Advantages
Modularity
Portability
Bridge between semantic gaps
Machine-independent code optimization
Interpreter can execute on interpretive compiling system
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4. 1. Introduction (3) Disadvantages Compile time
Inefficient code  code optimization
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5. 1. Introduction (4) Types of IL
Polish notation – postfix representation, IR
3-address code – Triple, Quadruple, Indirect Triple
Tree structure code – AST, TCOL, Diana
Virtual machine code – P-code, EM-code, U-code, Bytecode
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6. 2. Polish notation (1) Developed by Lucasiewiez Usage
Intermediate code for arithmetic expression in Fortran compiler
Intermediate code for interpreter like BASIC
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7. 2. Polish notation (2) Postfix notation Operand precedes operator
No parenthesis
Operator stack
Easy to change and fast
Appropriate for interpreter
Not appropriate for optimization
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8. 3. 3-address code (1) 구성 예 4: a = b * (c + d) 가장 널리 이용 최적화 컴파일러
1개의 연산자
2개의 피연산자
예 4: a = b * (c + d)
가장 널리 이용
최적화 컴파일러
A := B op C
(t1 := c + d)
(t2 := b * t1)
(a := t2 )
(2011-1) Compiler

9. 3. 3-address code (2) Implementation Triple Indirect triple Quadruple
(operator, operand1, operand2)
Not appropriate for optimization
Indirect triple
Table for triple’s execution order
Quadruple
(operator, operand1, operand2, result)
Appropriate for optimization
(2011-1) Compiler

10. 3. 3-address code (3) RTL (Register Transfer Language)
IL for GNU’s C, C++ compiler
All operations use register
Based on list concept of LISP
Ex 7:
(set (reg:SI 69) (mem:SI (plus:SI (reg:SI 65) (const_int –4))))
(set (reg:SI 70) (mem:SI (plus:SI (reg:SI 65) (const_int –8))))
(set (reg:SI 68) (plus:SI (reg:SI 69) (reg:SI 70)))
(set (mem:SF (plus:SI (reg:SI 65) (const_int –12)))
(float:SF (reg:SI 68)))
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11. 4. Tree structure code (1) Advantages Parse tree
Represent program’s meaning (semantics)
Easy to construct
Most appropriate for optimized compiler
Parse tree
Syntax-directed
Many useless information
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12. 4. Tree structure code (2) Abstract syntax tree (AST) Very effective
Specify terminal/non-terminal nodes
Compile-compiler project
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13. 5. Virtual machine code (1)
Portable compiler
Virtual machine connects front- and back-end  instruction set
Abstract machine
No general register
Stack machine
Virtual machine code
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14. 5. Virtual machine code (1)
P-code
Intermediate output of Pascal-P compiler
P machine
Stack machine
4 registers: PC, SP, MP, NP
Memory: CODE, STORE
stack
heap
constant area
CODE
STORE PC MP SP NP
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15. 5. Virtual machine code (2)
U-code
Intermediate code for portable Pascal compiler developed by Stanford
Based on virtual stack machine
All operations are performed on stack
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16. 5. Virtual machine code (3)
Types of operations
Unary instruction: notop, neg
Binary instruction : add, sub, …
Stack instruction : lod, str, ldc, ldr
Constrol instruction : ujp, tjp, fjp
Range check instruction : chkh, chkl
Indirect-address instruction : ixa, sta
Procedure instruction : cal, ret, …
Other instruction: bgn, sym
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17. 5. Virtual machine code (4)
Bytecode
Intermediate language for Java
Instructions for Java Virtual Machine (JVM)
Portability
Interpreter, JIT (Just-In-Time) compiler
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18. 5. Virtual machine code (5)
Features
Small, simple: transferred on the network
Instructions for array, class, exception, thread, …
Instructions for data types (iadd, fadd, …)
Instructions with composite function (pop2)
(2011-1) Compiler

19. 6. Selection of IL (1) Recent approach: several ILs ILS:
Automatically acquired from source
Source language dependent and high level
Source
Front-End
ILS
ILS-ILT
ILT
Back-End
Target
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20. 6. Selection of IL (2) ILT: ILS to ILT :
Easy to translate into target machine
Target machine dependent and low level
ILS to ILT :
Translate from ILS into ILT
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