1. Compiler Construction
Chapter 8
Compiler Construction
Dr K. V. N. Sunitha

2. Intermediate Code Generation
Compiler Construction
Dr K. V. N. Sunitha

3. Intermediate Languages
There are three types of intermediate representation:
Syntax trees
Postfix notation
Three address code
DAG
Compiler Construction
Dr K. V. N. Sunitha

4. Compiler Construction
Syntax Tree
a = b* − (c − d) + b* − (c − d)
Compiler Construction
Dr K. V. N. Sunitha

5. Compiler Construction
Postfix Notation
a = b* − (c − d) + b* − (c − d)
Postfix form is as follows:
a b c d – - * b c d – - * + =
Compiler Construction
Dr K. V. N. Sunitha

6. Compiler Construction
Three-Address Code
Three address code for the statement a= b* − (c − d)+b* − c − d) is T1 = c − d T2 = − T1 T3 = b*T2 T4 = c − d T5 = − T4 T6 = b*T5 T7 = T3+T6 a = T7
Compiler Construction
Dr K. V. N. Sunitha

7. Compiler Construction
DAG
a = b* − (c − d) + b* − (c − d) is = + *
b - -
c d
Compiler Construction
Dr K. V. N. Sunitha

8. Implementing Three-Address Code
Quadruple
• a record structure with four fields
Triple
• a record structure with three fields
Indirect triples
• pointer to triples
Compiler Construction
Dr K. V. N. Sunitha

9. Types of Three-Address Statements
A := B op C A := op B A :=B goto L. if A relop B goto L A: = B[ i ] A:= &B A:= *B B fun(A1,A2,A3,....An)
Compiler Construction
Dr K. V. N. Sunitha

10. Three-Address Statement for the x or y not z
t1 = not z t2 = y and t1 t3 = x or t2
Compiler Construction
Dr K. V. N. Sunitha

11. Compiler Construction
If x < y Then 1 Else 0
Three address code is
if a < y go to 13
t1 = 0
go to 14
t1 = 1
Compiler Construction
Dr K. V. N. Sunitha

12. IR Translation of Conditional Statement
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 }
Compiler Construction
Dr K. V. N. Sunitha

13. IR Translation of While Loop
S → while E do S1 {S.begin = newlabel(); E.true = newlabel(); E.false = S.next; S1.next = S.next; S.code = gen(S.begin “:”) || || E.code || gen(E.true , “ :”) || S1.code || gen(“GOTO” , S.begin) }
Compiler Construction
Dr K. V. N. Sunitha