EXAMPLES for Syntax-Directed Definitions and Translations

Following are additional examples of syntax-directed definitions and translations.

EXAMPLE 1

Generate the three-address code for the following C program:

main()
{  int i = 1;
   int a[10];
   while(i <= 10)
   a[i] = ;
}

The three-address code for the above C program is:

1. i = 1

2. if i <= 10 goto(4)

3. goto(8)

4. t1 = i * width

5. t2 = addr(a) − width

6. t2[t1] = 0

7. goto(2)

where width is the number of bytes required for each element.

EXAMPLE 2

Generate the three-address code for the following program fragment:

while (A < C and B > D) do
  if A = 1 then C = C+1
    else
      while A <= D do
                 A = A + 3

The three-address code is:

1. if a < c goto(3)

2. goto(16)

3. if b >d goto(5)

4. goto(16)

5. if a = 1 goto(7)

6. goto(10)

7. t1 = c+1

8. c = t1

9. goto(1)

10. if a <= d goto

11. goto(1)

12. t2 = a+3

13. a = t2

14. goto(10)

15. goto(1)

EXAMPLE 3

Generate the three-address code for the following program fragment, where a and b are arrays of size 20 � 20, and there are four bytes per word.

begin
  add = 0;
  i = 1;
  j = 1;
  do
    begin
      add = add + a[i,j] * b[j,i]
      i = i + 1;
      j = j + 1;
    end
  while i <= 20 and j <= 20;
end

The three-address code is:

1. add = 0

2. i = 1

3. j = 1

4. t1 = i * 20

5. t1 = t1 + j

6. t1 = t1 * 4

7. t2 = addr(a) − 84

8. t3 = t2[t1]

9. t4 = j * 20

10. t4 = t4 + i

11. t4 = t4 * 4

12. t5 = addr(b) − 84

13. t6 = t5[t4]

14. t7 = t3 * t6

15. t7 = add + t7

16. t8 = i + 1

17. i = t8

18. t9 = j + 1

19. j = t9

20. if i <= 20 goto(22)

21. goto NEXT

22. if j <= 20 goto(4)

23. goto NEXT

EXAMPLE 4

Consider the program fragment:

sum = 0
for(i = 1; i<= 20; i++)
  sum = sum + a[i] + b[i];

and generate the three-address code for it. There are four bytes per word.

The three address code is:

1. sum = 0

2. i = 1

3. if i <= 20 goto(8)

4. goto NEXT

5. t1 = i+1

6. i = t1

7. goto(3)

8. t2 = i * 4

9. t3 = addr(a) − 4

10. t4 = t3[t2]

11. t5 = i * 4

12. t6 = addr(b) − 4

13. t7 = t6[t5]

14. t8 = sum + t4

15. t8 = t8 + t7

16. sum = t8

17. goto(5)