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Intermediate Code Generation

Intermediate Code Generation. Intermediate Code Generation. Intermediate languages Declarations Expressions Statements. :=. a. +. *. *. -. -. b. b. c. c. Intermediate Languages. Syntax tree Postfix notation a b c - * b c - * + := Three-address code.

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Intermediate Code Generation

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  1. Intermediate Code Generation

  2. Intermediate Code Generation • Intermediate languages • Declarations • Expressions • Statements

  3. := a + * * - - b b c c Intermediate Languages • Syntax tree • Postfix notation a b c - * b c - * + := • Three-address code a := b * - c + b * - c

  4. Three-Address Code x := y op z where x, y, z are names, constants, or temporaries a := b * -c + b * -c t1 := -c t2 := b * t1 t3 := -c t4 := b * t3 t5 := t2 + t4 a := t5 x + y * z t1 := y * z t2 := x + t1

  5. Types of Three-Address Code • Assignment statement x := y op z • Assignment statement x := op y • Copy statement x := y • Unconditional jump goto L • Conditional jump if x relop y goto L • Procedural call param xcall preturn y

  6. Types of Three-Address Code • Indexed assignment x := y[i]x[i] := y • Address and pointer assignmentx := &yx := *y*x := y

  7. Implementation of Three-Address Code • Quadruples op arg1 arg2 result(0) - c t1(1) * b t1 t2(2) - c t3(3) * b t3 t4(4) + t2 t4 t5(5) := t5 a

  8. Implementation of Three-Address Code • Triples op arg1 arg2 (0) - c (1) * b (0)(2) - c (3) * b (2)(4) + (1) (3)(5) := a (4)

  9. Implementation of Three-Address Code • Indirect Triples statement op arg1 arg2 (0) (14) (14) - c (1) (15) (15) * b (14)(2) (16) (16) - c (3) (17) (17) * b (16)(4) (18) (18) + (15) (17)(5) (19) (19) := a (18)

  10. Comparison • Qualdruples • direct access of the location for temporaries • easier for optimization • Triples • space efficiency • Indirect Triples • easier for optimization • space efficiency

  11. New Names and Labels • Function newtemp returns a new name for each call • Function newlabel returns a new label for each call

  12. Assignments S  id “:=” E {emit(id.name ‘:=’ E.place);} E  E1 “+” E2{E.place := newtemp; emit(E.place ‘:=’ E1.place ‘+’ E2.place);} E  E1 “*” E2{E.place := newtemp; emit(E.place ‘:=’ E1.place ‘*’ E2.place);} E  “-” E1{E.place := newtemp; emit(E.place ‘:=’ ‘-’ E1.place);} E  “(” E1 “)” {E.place := E1.place} E  id{E.place := id.name}

  13. Array Accesses A[i]: base + (i - low)  w  (i  w) + (base - low  w) A[i1, i2]: base + ((i1 - low1)  n2 + i2 - low2)  w  (((i1n2) + i2)  w) + (base - ((low1n2) + low2)  w) c(id.place), width(id.place), limit(id.place, i)

  14. Array Accesses • Use inherited attributes L  id “[” Elist “]” | id Elist  Elist “,” E | E • Use synthesized attributesL  Elist “]” | id Elist  Elist “,” E | id “[” E

  15. Array Accesses Elist  id “[” E { Elist.place := E.place; Elist.ndim := 1; Elist.array := id.place; } Elist  Elist1 “,” E { t := newtemp; m := Elist1.ndim + 1; emit(t ‘:=’ Elist1.place ‘*’ limit(Elist1.array, m)); emit(t ‘:=’ t ‘+’ E.place); Elist.array := Elist1.array; Elist.place := t; Elist.ndim := m; }

  16. Array Accesses L  Elist “]” { L.place := newtemp; L.offset := newtemp; emit(L.place ‘:=’ c(Elist.array)); emit(L.offset ‘:=’ Elist.place ‘*’ width(Elist.array)) } L  id { L.place := id.place; L.offset := null }

  17. Array Accesses E  L { if L.offset = null then E.place := L.place; else begin E.place := newtemp; emit(E.place ‘:=’ L.place ‘[’ L.offset ‘]’); end } S  L “:=” E { if L.offset = null then emit(L.place ‘:=’ E.place); else emit(L.place ‘[’ L.offset ‘]’ ‘:=’ E.place); }

  18. An Example x := A[y, z] n1 = 10, n2 = 20, w = 4 c = baseA - ((1 20) + 1)  4 = baseA - 84 t1 := y * 20 t1 := t1 + z t2 := c t3 := t1 * 4 t4 := t2[t3] x := t4

  19. Type Conversion E  E1 + E2 {E.place := newtemp; if E1.type = int and E2.type = int then begin emit(E.place ‘:=’ E1.place ‘int+’ E2.place); E.type := int; end else if E1.type = real and E2.type = real then begin emit(E.place ‘:=’ E1.place ‘real+’ E2.place); E.type := real; end else if E1.type = int and E2.type = real then begin u := newtemp; emit(u ‘:=’ ‘inttoreal’ E1.place); emit(E.place ‘:=’ u ‘real+’ E2.place); E.type := real; end else if … }

  20. Flow-of-Control Statements S  if E then S1 | if E then S1else S2 | while E do S1 | switch E begin case V1: S1 case V2: S2 … case Vn-1: Sn-1 default: Sn end

  21. E.true E.code E.false E.true: S1.code E.false: Conditional Statements S  if E then S1 { E.true := newlabel; E.false := S.next; S1.next := S.next; S.code := E.code || gen(E.true ‘:’) || S1.code }

  22. Conditional Statements S  if E then S1 else S2 { E.true := newlabel; E.false := newlabel; S1.next := S.next; S2.next := S.next; S.code := E.code || gen(E.true ‘:’) || S1.code || gen(‘goto’ S.next) || gen(E.false ‘:’) || S2.code } E.true E.code E.false E.true: S1.code goto S.next E.false: S2.code S.next:

  23. Loop Statements S  while E do S1 { S.begin := newlabel; E.true := newlabel; E.false := S.next; S1.next := S.begin; S.code := gen(S.begin ‘:’) || E.code || gen(E.true ‘:’) || S1.code || gen(‘goto’ S.begin) } S.begin: E.true E.code E.false E.true: S1.code goto S.begin E.false:

  24. Boolean Expressions E  E1or E2 {E1.true := E.true; E1.false := newlabel; E2.true := E.true; E2.false := E.false; E.code := E1.code || gen(E1.false ‘:’) || E2.code; } E  E1and E2 {E1.true := newlabel; E1.false := E.false; E2.true := E.true; E2.false := E.false; E.code := E1.code || gen(E1.true ‘:’) || E2.code; } E  not E1 {E1.true := E.false; E1.false := E.true; E.code := E1.code; }

  25. Boolean Expressions E  “(” E1 “)” { E1.true := E.true; E1.false := E.false; E.code := E1.code; } E  id1relopid2 { E.code := gen(‘if’ id1.place relop.op id2.place ‘goto’ E.true) || gen(‘goto’ E.false); } E  true { E.code := gen(‘goto’ E.true); } E  false { E.code := gen(‘goto’ E.false); }

  26. An Example a < b or c < d and e < f if a < b goto Ltrue goto L1 L1: if c < d goto L2 goto Lfalse L2: if e < f goto Ltrue goto Lfalse

  27. An Example Lbegin: if a < b goto L1 goto Lnext L1: if c < d goto L2 goto L3 L2: t1 := y + z x := t1 goto Lbegin L3: t2 := y - z x := t2 goto Lbegin Lnext: while a < b do if c < d then x := y + z else x := y - z

  28. Case Statements • Conditional goto’s • less than 10 cases • Jump table • more than 10 cases • dense value range • Hash table • more than 10 cases • sparse value range

  29. Conditional Goto’s code to evaluate E into t goto test L1: code for S1 goto next … Ln-1: code for Sn-1 goto next Ln: code for Sn goto next test: if t = V1 goto L1 … if t = Vn-1 goto Ln-1 goto Ln next:

  30. Jump Table code to evaluate E into t if t < Vmin goto Ldefault if t > Vmax goto Ldefault i := t - Vmin L := jumpTable[i] goto L

  31. Hash Table code to evaluate E into t i := hash(t) L := hashTable[i] goto L

  32. Procedure Calls S  callid “(” Elist “)” { for each item p on queue do emit(‘param’ p); emit(‘call’ id.place); } Elist  Elist “,” E { append E.place to the end of queue; } Elist  E { initialize queue to contain only E.place; }

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