Intermediate Language  Compiler Model Front-End− language dependant part Back-End− machine dependant part [1/34]

 IL 의 필요성  Modular Construction  Automatic Construction  Easy Translation  Portability  Optimization  Bootstrapping  IL 의 분류  Polish Notation --- Postfix, IR  Three Address Code --- Quadruple, Triple, Indirect triple  Tree Structured Code --- PT, AST, TCOL  Abstract Machine Code --- P-code, EM-code, U-code, Byte-code Intermediate Language [2/34]

Intermediate Language  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. [3/34]

 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) Intermediate Language [4/34]

Intermediate Language  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 [5/34]

 most popular IL, optimizing compiler  General form: 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 Intermediate Language A := B op C [6/34]

Intermediate Language  example  a = b + c * d / e;  f = c * d; [7/34]

 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 Intermediate Language [8/34]

Intermediate Language  Abstract Syntax Tree  parse tree 에서 redundant 한 information 제거.  Leaf node-- variable name, constant  Internal node-- operator  [ 예제 9.8] { x = 0; y = z + 2 * y; while ((x<n) && (v[x] != z)) x = x+1; return x; } [9/34]

 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 Intermediate Language [10/34]

Example)int a; float b;... b = a + 1;  Representation ---- graph orientation internal notation efficient external notation ---- debug, interface linear graph notation Intermediate Language [11/34]

 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) Intermediate Language [12/34]

Intermediate Language [13/34]

 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. Intermediate Language [14/34]

 Example :  Consider the following skeleton : int x; void main() { int i; int j; //..... }  block number - 전역변수 : 1 - 함수 내 지역변수 : 2  variable addressing - x : (1,1) - i : (2,1) - j : (2,2) Intermediate Language [15/34]

 Ucode Operations (39 개 )  Unary --- notop, neg, inc, dec, dup  Binary --- add, sub, mult, div, mod, swp and, or, gt, lt, ge, le, eq, ne  Stack Operations --- lod, str, ldc, lda  Control Flow --- ujp, tjp, fjp  Range Checking --- chkh, chkl  Indirect Addressing --- ldi (load indirect), sti (store indirect)  Procedure --- cal, ret, retv, ldp, proc, end  Etc. --- nop, bgn, sym Intermediate Language [16/34]

 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... Intermediate Language [17/34]

 Indirect Addressing  is used to access the array elements.  ldi --- indirect load  replace stacktop by the value of the item at location stacktop.  to retrieve A[i] : lod i // actually (Bi, Oi)) lda A // also (block number, offset) add // effective address ldi // indirect load gets contents of A[i] Intermediate Language [18/34]

 sti --- indirect store  sti stores stacktop into the address at stack[stacktop-1], both items are popped.  A[i] = j; lod i lda A add lod j Sti Intermediate Language [19/34]

 Procedure Calling Sequence  function definition :  void func(int x, int array[]) { }  function call :  func(a, list);  calling sequence : ldp // load parameter lod a // load the value of actual parameter lda list // load the address of actual parameter call func // call func Intermediate Language [20/34]