1. Compiler Designs and Constructions
Chapter 11: Intermediate Code Generation(part II)
Compiler Designs and Constructions
Chapter 11: Intermediate Code Generation(part II)
Objectives:
Dr. Mohsen Chitsaz
Chapter 11: Intermediate Code Generation (part II)
COSC 470

2. Method II Flow of Control
Translation of Boolean Expression (Position Reached)
True (Exit)
False (Exit)
Chapter 11: Intermediate Code Generation (part II)

3. Method II Flow of Control
Example:
IF (a<b OR c>d) THEN
N = M+K;
IF a<b GOTO 4
IF c>d GOTO 4
GOTO 6
T1 = M + K
N = T1
True 4
False 6
Chapter 11: Intermediate Code Generation (part II)

4. Chapter 11: Intermediate Code Generation (part II)
Address of Jump?
Functions:
Backpatch (P, I)
Quadruple P takes I as a target
Makelist (i)
Create a new list with element I, (an index into the array of quadruples)
Makelist returns a pointer
Merge (P1, P2)
Concatenate pointer P1 and P2 into one list, returns a pointer to the new list
Chapter 11: Intermediate Code Generation (part II)

5. Chapter 11: Intermediate Code Generation (part II)
Example
WHILE (a=b AND a=c) DO {
N = a+b;
c = N; }
IF a=b GOTO __
GOTO __
IF a=c GOTO __
T1 = a+b
N = T1
C=N
Marker1 (True)=1-> 3
Marker2 (True)=3-> 5
Marker3 (False)=2-> 9
Marker4 (False)=4-> 9
How do I know
the address?
Chapter 11: Intermediate Code Generation (part II)

6. Chapter 11: Intermediate Code Generation (part II)
E. True Target Location (Jump) (MARKER)
E.False
E  E1 AND E2
To find the jump address, we need to check E2
Modify the Grammar:
E  E1 OR M E2
E  E1 AND M E2
E  Not E1
E  (E1)
E  id
E  id1 Relop id2
M 
Chapter 11: Intermediate Code Generation (part II)

7. Chapter 11: Intermediate Code Generation (part II)
M.Quad = NextQuad
E  id1 Relap id2
E.True = Makelist (NextQuad)
E.False = Makelist (NextQuad+1)
Gen (IF id1.Place Relap id2.Place GOTO )
Gen (GOTO )
E  id
Gen (IF id1.Place GOTO )
Gen (GOTO )
Chapter 11: Intermediate Code Generation (part II)

8. Chapter 11: Intermediate Code Generation (part II)
E  (E1)
E.True = E1.True
E.False = E1.False
E  Not E1
E.True = E1.False
E.False=E1.True
E  E1 AND M E2
Backpatch (E1.True, M.Quad)
E.True := E2.True
E.False := Merge (E1.False, E2.False)
Chapter 11: Intermediate Code Generation (part II)

9. Chapter 11: Intermediate Code Generation (part II)
E  E1 OR M E2
Backpatch (E1.False, M.Quad)
E.True := Merge (E1.True, E2.True)
E.False := E2.False
Chapter 11: Intermediate Code Generation (part II)

10. Chapter 11: Intermediate Code Generation (part II)
Practice:
1- Build the Parse Tree
2- Add attributes
a<b OR c<d AND e>f
Chapter 11: Intermediate Code Generation (part II)

11. Chapter 11: Intermediate Code Generation (part II)
0. IF a<b GOTO___ True
GOTO 2
IF c<d GOTO 4
GOTO___ False
IF c>f GOTO ___ True
GOTO ___ False
E  E1 AND M E
Backpatch(2,4)
E  E1 OR M E2
Backpatch (1,2)
Chapter 11: Intermediate Code Generation (part II)

12. Chapter 11: Intermediate Code Generation (part II)
Flow of Control
Statement  IF (exp)
Statement
ELSE
Statement  WHILE (exp)
Statement  {State_list}
Statement  Assignment_Statement
State_list  State_list; Statement
State_list  Statement
Chapter 11: Intermediate Code Generation (part II)

13. Chapter 11: Intermediate Code Generation (part II)
Flow of Control
What should we do with nested WHILE loop?
WHILE
{ WHILE
. {
. .
. } }
Chapter 11: Intermediate Code Generation (part II)

14. Chapter 11: Intermediate Code Generation (part II)
Method 1: Using Stack
Method 2: Using Markers
Statement  WHILE M1(exp) M2 Statement M
Example:
WHILE (a>b)
WHILE (c>d) ..
END
Chapter 11: Intermediate Code Generation (part II)

15. Chapter 11: Intermediate Code Generation (part II)
Method 1
0. IF a> b GOTO 2
GOTO ___
2. IF c<d GOTO 4
GOTO __
GOTO 2
False2:
GOTO 0
False1:
Chapter 11: Intermediate Code Generation (part II)

16. Chapter 11: Intermediate Code Generation (part II)
Method 2
Statement  WHILE M1(exp) M2 Statement
Chapter 11: Intermediate Code Generation (part II)

17. Chapter 11: Intermediate Code Generation (part II)
Grammar
Statement  IF (exp) M1 Statement1 N
ELSE M2 Statement2
Backpatch(E.True, M1.Quad)
Backpatch (E.False, M2.Quad)
Statement.Next: Merge (S1.Next, N.Next, S2.Next)
{ Next is the next statement to Jump}
N 
N.Next = Makelist (NextQuad)
Gen (GOTO)
Chapter 11: Intermediate Code Generation (part II)

18. Chapter 11: Intermediate Code Generation (part II)
Grammar
M 
M.Quad = NextQuad
Statement  IF (exp) M Statement
Backpatch (E.True, M.Quad);
S.Next = Merge (E.False, S.Next)
Statement  WHILE M1(exp) M2 Statement
Gen (GOTO M1.Quad)
Backpatch(S.Next, M1.Quad)
Backpatch(E.True, M2.Quad)
S.Next = E.False
Chapter 11: Intermediate Code Generation (part II)

19. Chapter 11: Intermediate Code Generation (part II)
Grammar
Statement  { State_list }
S.Next = L.Next
Statement  Assignment_Statement
S.Next = Makelist (NextQuad);
State_list  State_List1; M Statement
Backpatch (L1.Next, M.Quad)
L.Next := S.Next
State_List  Statement
Chapter 11: Intermediate Code Generation (part II)

20. Chapter 11: Intermediate Code Generation (part II)
Practice:
1- Build parse tree
2- Add attributes
WHILE (a< b)
IF (c > d)
a = b + c;
Chapter 11: Intermediate Code Generation (part II)

21. Chapter 11: Intermediate Code Generation (part II)
WHILE (a< b) DO
IF (c > d) THEN
a = b + c;
0. IF a< b GOTO 2
GOTO 7
IF c>d GOTO 4
GOTO 0
T1 = b+c
a = T1
GOTO
Chapter 11: Intermediate Code Generation (part II)

22. Chapter 11: Intermediate Code Generation (part II)
Static Array
List: Array [1..20, 1..30] of datatype;
How much space do we need?
How do we store this array?
Row Major
Column Major
Where is List [20,30] started?
List [I,j] is stored at
= +((I-1) * 30) * bpw + (j-1) * bpw
= +30i + j – 31 (bpw)?
Base Register –31  Compiled Time (Fixed)
Index Register 30i+j  Calculated
Chapter 11: Intermediate Code Generation (part II)

23. Chapter 11: Intermediate Code Generation (part II)
Example
B = List [I,j]
0- T1 = i+*30
1- T1 = T1 + j  Index Register
2- T2 = -31 * 4  Assume bpw = 4
3- T3 = 4* T1
4- T4 = T2 [T3]
5- B = T4
Chapter 11: Intermediate Code Generation (part II)

24. Chapter 11: Intermediate Code Generation (part II)
Array
Code for Array
[]= A i T1 T1 = A[i]
= B T1 T1 = B
For K dimensional array: (Row Major)
A [i1,i2,…ik]
=(i1-1) d2,d3…dk+(i2-1)d3,d4…dk + …+(ik-1-1)dk+(ik-1)
= i1d2d3…dk+i2d3d4…dk+…+dk+1
=(d2d3…dk+d3d4…dk+…+dk+1)
Fixed = D
If Address of A is THEN D is computed at Compile Time
Chapter 11: Intermediate Code Generation (part II)

25. Chapter 11: Intermediate Code Generation (part II)
Array
A L=E
E  E+E
E  (E)
E  L
E  elist ]
L  id
elist  elist, E
elist  id [ E
Chapter 11: Intermediate Code Generation (part II)

26. Chapter 11: Intermediate Code Generation (part II)
Array
elist  id [ E
elist.Place = E.Place
elist.Ndim = 1;
elist.Array = id.Place
elist  elist1, E
T=NewTemp();
M=elist.Ndim + 1;
Gen (t ‘=‘ elist1.Place ‘*’ Limit (elist1.Array, M))
Gen (t ‘=‘ t ‘+’ E.Place);
elist.Array = elist1.Array
elist.Place = t
elist.Ndim = M
Chapter 11: Intermediate Code Generation (part II)

27. Chapter 11: Intermediate Code Generation (part II)
Array
L  id
L.Place = id.Place
L.offset = Null
L  elist ]
L.Place = NewTemp();
L.offset = NewTemp();
Gen (L.offset ‘=‘ ‘bpw’ ‘*’ elist.Place)
E  L
IF (L.offset = Null)
E.Place = L.Place
ELSE {
T = NewTemp();
Gen (T ‘=‘ L.Place ‘[‘ L.offset ‘]’);
E.Place = T }
Chapter 11: Intermediate Code Generation (part II)

28. Chapter 11: Intermediate Code Generation (part II)
Array
E  (E1)
E.Place = E1.Place
E  E1 + E2
T = NewTemp()
Gen (T ‘=‘ E1.Place + E2.Place);
E.Place = T
A  L = E
IF L.offset = Null
Gen(L.Place ‘=‘ E.Place)
ELSE
Gen (L.Place ‘[‘ L.offset ‘]’ := E.Place)
Chapter 11: Intermediate Code Generation (part II)