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

1. Introduction (1)  Compiler model (2012-1) Compiler 2 Source Program Lexical Analyzer Syntax Analyzer Semantic Analyzer Intermediate Code Generator tokens AST Front-End Code Optimizer Target Code Generator Back-End IL Object Program Front-End - language dependant part Back-End - machine dependant part

1. Introduction (2)  Intermediate language  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 (2012-1) Compiler 3

1. Introduction (3)  Disadvantages  Compile time  Inefficient code  code optimization (2012-1) Compiler 4

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 (2012-1) Compiler 5

2. Polish notation (1)  Developed by Lucasiewiez  Usage  Intermediate code for arithmetic expression in Fortran compiler  Intermediate code for interpreter like BASIC (2012-1) Compiler 6

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 (2012-1) Compiler 7

3. 3-address code (1)  구성  1 개의 연산자  2 개의 피연산자  예 4: a = b * (c + d)  가장 널리 이용  최적화 컴파일러 (2012-1) Compiler 8 A := B op C (t1 := c + d) (t2 := b * t1) (a := t2 )

3. 3-address code (2)  Implementation  Triple  (operator, operand1, operand2)  Not appropriate for optimization  Indirect triple  Table for triple’s execution order  Quadruple  (operator, operand1, operand2, result)  Appropriate for optimization (2012-1) Compiler 9

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: (2012-1) Compiler 10 (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)))

4. Tree structure code (1)  Advantages  Represent program’s meaning (semantics)  Easy to construct  Most appropriate for optimized compiler  Parse tree  Syntax-directed  Many useless information (2012-1) Compiler 11

4. Tree structure code (2)  Abstract syntax tree (AST)  Very effective  Specify terminal/non-terminal nodes  Compile-compiler project (2012-1) Compiler 12

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 (2012-1) Compiler 13

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 (2012-1) Compiler 14 stack heap constant area CODE STORE PC MP SP NP

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 (2012-1) Compiler 15

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 (2012-1) Compiler 16

5. Virtual machine code (4)  Bytecode  Intermediate language for Java  Instructions for Java Virtual Machine (JVM)  Portability  Interpreter, JIT (Just-In-Time) compiler (2012-1) Compiler 17

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) (2012-1) Compiler 18

6. Selection of IL (1)  Recent approach: several ILs  IL S :  Automatically acquired from source  Source language dependent and high level (2012-1) Compiler 19 Source Front-End IL S IL S -IL T IL T Back-End Target

6. Selection of IL (2)  IL T :  Easy to translate into target machine  Target machine dependent and low level  IL S to IL T :  Translate from IL S into IL T (2012-1) Compiler 20