2. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 1 제 9 장 중 간 언어 컴파일러 입문

3. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 2 Contents Introduction Polish Notation Three Address Code Tree Structured Code Abstract Machine Code Concluding Remarks

4. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 3 Compiler Model Source Program Lexical Analyzer Syntax Analyzer Semantic Analyzer Intermediate Code Generator tokens AST Front-End Code Optimizer Target Code Generator IC Back-End IL Object Program Front-End- language dependant part Back-End- machine dependant part Introduction

5. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 4 IL 의 필요성 –Modular Construction –Automatic Construction –Easy Translation –Portability –Optimization –Bootstrapping IL 의 분류 –P–Polish Notation --- Postfix, IR –T–Three Address Code --- Quadruple, Triple, Indirect triple –T–Tree Structured Code --- PT, AST, TCOL –A–Abstract Machine Code --- P-code, EM-code, U-code, Bytecode

6. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 5 Two level Code Generation IL S – 소스로부터 자동화에 의해 얻을 수 있는 형태 – 소스 언어에 의존적이며 high level 이다. IL T – 후단부의 자동화에 의해 목적기계로의 번역이 매우 쉬운 형태 – 목적기계에 의존적이며 low level 이다. IL S to IL T –IL S 에서 IL T 로의 번역이 주된 작업임. Source Front-End IL S IL S -IL T IL T Back-End Target

7. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 6 ☞ Polish mathematician Lucasiewiez invented the parenthesis-free notation. Postfix(Suffix) Polish Notation earliest IL popular for interpreted language - SNOBOL, BASIC –general form : e 1 e 2... e k OP (k ≥ 1) where, OP: k_ary operator e i : any postfix expression (1 ≤ i ≤ k) Polish Notation

8. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 7 –example : if a then if c-d then a+c else a*c else a+b 〓〉 a L1 BZ c d - L2 BZ a c + L3 BR L2: a c * L3 BR L1: a b + L3: –note 1) high level:source to IL - fast & easy translation IL to target - difficulty 2) easy evaluation - operand stack 3) optimization 부적당 - 다른 IL 로의 translation 필요 4) parentheses free notation - arithmetic expression –interpretive language 에 적합 Source Translator Postfix Evaluator Result

9. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 8 Internal Representation(IR) –low-level prefix polish notation - addressing structure of target machine compiler-compiler IL - table driven code generation –IR program - a sequence of root-level IR expression –IR expression: OP e1 e2...... e k (k ≥ 1) where, OP: k-ary operator - 1-1 correspondence with target machine instruction. ┌─ root-level operator - not appear in an operand │ ⇒ root-level IR expression. └─ internal operator - appear in an operand ⇒ internal IR expression. e i : operand --- single symbol or internal IR expression.

10. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 9 –example D := E ⇔ := + d r ↑ + e r where,r : local base register d, e : location of variable D and E + : additive operator ↑ : unary operator giving the value of the location := : assignment operator(root-level) –example FOR D := E TO F DO Loop body; := + d r ↑+ e r := + temp r ↑+ f r j L2 :L1 Loop body := + d r + ↑+ d r 1 :L2 <= L1 ? ↑+ d r ↑+ temp r D := E; TEMP := F; GOTO 2 1: Loop body D := D + 1; 2: IF D <= TEMP THEN GOTO 1;

11. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 10 –Note 1) Shift-reduce parser --- prefix : fewer states than postfix 2) Several addressing mode ┌─ prefix : operator 만 보고 결정 (no backup) └─ postfix : backup 필요 ex) assumption: first operand computed in register r. r.1 ::= (/ d. 1 r. 2) r.1 ::= (+ r. 1 r. 2) ┌ prefix - [r -> /. d r] │ first operand changed to d and continue └ postfix - [r ->. d r /] [r ->. r r +] shift r, shift r and block([r -> r r. +]) ⇒ backup 3) Easy translation IR to target - easy source to IR - difficulty

12. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 11 most popular IL, optimizing compiler General form: A := B op C where,A : result address B, C : operand addresses op : operator (1) Quadruple - 4-tuple notation,,, (2) Triple - 3-tuple notation,, (3) Indirect triple - execution order table & triples Three Address Code

13. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 12 –example A ← B + C * D / E F ← C * D

14. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 13 Note Quadruple vs. Triple –quadruple - optimization 용이 –triple - removal of temporary addresses ⇒ Indirect Triple extensive code optimization 용이 – IL rearrange 가능 (triple 제외 ) easy translation - source to IL difficult to generate good code –quadruple to two-address machine –triple to three-address machine

15. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 14 Abstract Syntax Tree –parse tree 에서 redundant 한 information 제거. ┌ leaf node --- variable name, constant └ internal node --- operator –[ 예제 8] --- Text p.377 { x = 0; y = z + 2 * y; while ((x<n) and (v[x] != z)) x = x+1; return x; } Tree Structured Code

16. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 15 Tree Structured Common Language(TCOL) –Variants of AST - containing the result of semantic analysis. –TCOL operator - type & context specific operator –Context ┌ value ----- rhs of assignment statement ├ location ----- lhs of assignment statement ├ boolean----- conditional control statement └ statement----- statement ex). : operand --- location result --- value while : operand --- boolean, statement result --- statement

17. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 16 Example) int a; float b;... b = a + 1; –Representation ----- graph orientation ┌ internal notation ------efficient └ external notation ------ debug, interface linear graph notation Example) int a; float b;... b = a + 1; AST:assign badd a1 TCOL:assign bfloat addi a 1.

18. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 17 Note –AST ----- automatic AST generation(output of parser) Parser Generator┌ leaf node specification └ operator node specification –TCOL ----- automatic code generation : PQCC (1) intermediate level:high level --- parse tree like notation control structure low level --- data access (2) semantic specification:dereferencing, coercion, type specific operator dynamic subscript and type checking (3) loop optimization -----high level control structure easy reconstruction (4) extensibility ----- define new TCOL operator

19. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 18 Motivation ┌ rapid development of machine architectures └ proliferation of programming languages –portable & adaptable compiler design --- P_CODE porting --- rewriting only back-end –compiler building system --- EM_CODE M front-ends N back-ends + M compilers for N target machines Abstract Machine Code

20. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 19 Model front -end back -end target machine abstract machine interpreter source program interface target code abstract machine code

21. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 20 Pascal-P Code Pascal P Compiler --- portable compiler producing P_CODE for an abstract machine(P_Machine). P_Machine ----- hypothetical stack machine designed for Pascal language. (1) Instruction --- closely related to the PASCAL language. (2) Registers┌ PC --- program counter │ NP --- new pointer │ SP --- stack pointer └ MP --- mark pointer (3) Memory ┌ CODE --- instruction part └ STORE --- data part(constant area, stack, heap)

22. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 21 CODEPC STORE stack heap MP current activation record SP NP constant area

23. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 22 Ucode  Ucode  the intermediate form used by the Stanford Portable Pascal compiler.  stack-based and is defined in terms of a hypothetical stack machine.  Ucode Interpreter : Appendix B.  Addressing  stack addressing ===> a tuple : (B, O)  B : the block number containing the address  O : the offset in words from the beginning of the block, offsets start at 1.  label  to label any Ucode instruction with a label field.  All targets of jumps and procedures must be labeled.  All labels must be unique for the entire program.

24. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 23  Example :  Consider the following skeleton : program main procedure P procedure Q var i : integer; j : integer;  block number  main : 1  P : 2  Q : 3  variable addressing  i : (3,1)  j : (3,2)

25. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 24  Ucode Operations (35 개 )  Unary--- notop, neg  Binary--- add, sub, mult, divop, modop, swp andop, orop, gt, lt, ge, le, eq, ne  Stack Operations--- lod, str, ldr, ldp  Immediate Operation--- ldc  Control Flow--- ujp, tjp, fjp, cal, ret  Range Checking--- chkh, chkl  Indirect Addressing--- ixa, sta  Procedure Specification--- proc, endop  Program Specification--- bgn  Procedure Calling Sequence--- cal  Symbol Table Information --- sym

26. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 25  Example :  x = a + b * c; lod1 1 /* a */ lod1 2 /* b */ lod1 3 /* c */ mult add str 1 4 /* x */  if (a>b) a = a + b; lod1 1 /* a */ lod1 2 /* b */ gt fjp next lod1 1 /* a */ lod1 2 /* b */ add str 1 1 /* a */ next

27. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 26  Indirect Addressing  is used to access both array elements and var parameters.  ixa --- indirect load  replace stacktop by the value of the item at location stacktop.  to retrieve A[i] : lodi /* actually (Bi, Oi)) */ ldr A /* also (block number, offset) */ add /* effective address */ ixa /* indirect load gets contents of A[i] */  to retrieve var parameter x : lod x /* loads address of actual - since x is var */ ixa /* indirect load */

28. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 27 sta --- indirect store –sta stores stacktop into the address at stack[stacktop-1], both items are popped. –A[i] = j; lod i ldr A add lod j sta –x := y, where x is a var parameter lod x lod y sta

29. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 28  Procedure Calling Sequence  procedure definition :  procedure A(var a : integer; b,c : integer);  procedure call :  A(x, expr1, expr2);  calling sequence : ldp ldr x /* load the address of actual for var parameter */ … /* code to evaluate expr1 --- left on the stack */ … /* code to evaluate expr2 --- left on the stack */ cal A

30. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 29  Ucode Interpreter  The Ucode interpreter is called ucodei, it’s source is on plac.dongguk.ac.kr.  The interpreter uses the following files :  *.ucode : file containing the Ucode program.  *.lst : Ucode listing and output from the program.  Ucode format label-field op-code operand-field 1-10 12-m m+2  m is exactly enough to hold opcode.  label field --- a 10 character label( make sure its 10 characters pad with blanks )  op-code --- starts at 12 column.

31. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 30 Programming Assignment #3 부록 B 에 수록된 Ucode 인터프리터를 각자 PC 에 설치하고 100 이하의 소수 (prime number) 를 구하는 프로그램을 Ucode 로 작성하시오. – 다른 문제의 프로그램을 작성해서 제출해도 됨. –Ucode 인터프리터 출력 리스트를 제출. 참고 : –#1 : recursive-decent parser –#2 : MiniPascal LR parser

32. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 31 IL criteria –intermediate level –input language --- high level –output machine --- low level –efficient processing –translation --- source to IL, IL to target –interpretation –optimization –extensibility –external representation –clean separation –language dependence & machine dependence Concluding Remarks

33. PL&C Lab, DongGuk University Compiler Lecture Note, Intermediate LanguagePage 32 A : 좋다 B : 보통이다 C : 나쁘다