1. Semantic Analysis
Chapter 6

2. Two Flavors Static (done during compile time)
Ada
Dynamic (done during run time)
LISP
Smalltalk
Optimization

3. Static Semantic Analysis
Build symbol table
Keep track of declarations
Perform type checking

4. Static Analysis Description Implementation Attributes (properties)
Attribute equations (semantic rules)
Application of rules
Syntax-directed semantics

5. General Attribute Property of the Language Data type
Value of expressions
Location of variables in memory
Object code of procedure
Number of Significant digits

6. Specific Attributes Parameters/Arguments type
Parameters/Arguments number
Array subscript type
Array subscript number
Continue with no place to continue to
Variable undeclared
Variable duplicately declared
Scope
Incorrect structure reference

7. Specific Attributes Cont.
Break inappropriate
Incorrect Return
Wrong type
Array
None when needed (void)
No main
Two main’s
Constant on left side
Expression types

8. Binding Time of Attributes
Static - prior to execution
Fortran
Dynamic - during execution
Combination C
Java
Pascal

9. Attribute Grammars
X is grammar symbol, Xa is an attribute for this symbol
X ABCD (grammar)
X.x = A.a B.b C.c D.d
(attribute grammar)

10. Attribute Grammar Example
E1  E2 + T
E1.type = E2.type + T.type

11. Attribute Grammar Example
decl  type var-list
var-list.dtype =type.dtype
type  int type.dtype = integer
type  float type.dtype = float
var-list1  id, var-list2
id.dtype = var-list1.dtype
var-list2.dtype = var-list1.dtype
var-list  id id.dtype = var-list.dtype

12. Attribute Grammar Comments
Symbols may have more than one attribute
The grammar is not the master
More of a guide

13. Attribute Grammar Example
E1  E2 + T
E1.tree =
mkOpNode(+, E2.tree, T.tree)
E  T
E.tree = T.tree
F  number
F.tree = mkNumNode(number.lexval)

14. Attribute Up and Down Dependency Tree
Synthesized
Point from child to parent
Inherited
Point child to child or parent to child

15. Symbol Tables Lists of Lists Hash …
Collision resolving by use of buckets
Collision resolving by probing …

16. Symbol Tables Keep track of identifiers
Must deal with scope efficiently

17. Code Fragment int f(int size) { char i, temp; … { double j, i; }
{ char * j;
*j = i = 5;

18. Static vs Dynamic Scope
int i = 1;
void f(void)
{ printf(“%d\n”,i); }
void main(void)
{ int i = 2;
f();
return;
What is printed?

19. Kinds of Declarations sequential collateral recursive C scheme ML
requires the function name to be added to the symbol table before processing the body of the function

20. Example - Sequential/Colateral
int i = 1;
void f(void) {
int i = 2, j = i + 1; … }
Is j 2 or 3?

21. Example - Recursive int gcd(int n, int m) { if (m == 0) return n;
else return gcd(m, n%m); }
gcd must be added to the symbol table before processing the body

22. Example - Recursive void f(void) { … g() … } void g(void) { … f() … }
Resolved by using prototype.
Actually, this didn’t create a problem.

23. Data Types – Type Checking
Explicit datatype
int x
Implicit datatype
#define x 5

24. Implementation of Types
Hardware implementation
int
double
float
Software implementation
boolean
char
enum – can be integers to save space

25. More Complicated Types
Arrays
base(b)+i*esize
base(ar)+(i1*r2 +i2)*esize
Records
allocate memory sequentially
base+displacement

26. Type Checking Statements
S  id = E
S.type = if id.type = E.type then void
else error
S  if E then S1
S.type=if E.type=boolean then S1.type

27. Equivalence of type Expressions
Structural Equivalence
two expressions are either the same basic type, or are formed by applying the same constructor to structurally equivalent types. IE equivalent only if they are identical.
Name Equivalence
The following is structurally equivalent, not name
typedef link = *cell
link next;
cell * p;

28. Name Equivalence typedef int t1; typedef int t2;
t2 and t1 are not the same type.
int typeEqual(t1, t2)
{ if (t1 and t2 are simple types)
return t1 == t2;
if (t1 and t2 are type names)
else return 0;} in case you read the text