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 (compile time)
Value of expressions (run time)
Location of variables (compile time)
Object code of procedure (compile time)
Number of Significant digits (design time)

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
E1  E2 + T
E1.tree =
mkOpNode(+, E2.tree, T.tree)
E  T
E.tree = T.tree
F  number
F.tree = mkNumNode(number.lexval)

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

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

14. Kinds of Declarations
Sequential – each declaration is available starting with the next line C
Collateral – each declaration is evaluated in the environment preceding the declaration group. Declared identifiers are available only after all finishes.
scheme ML
Recursive - requires the function name to be added to the symbol table before processing the body of the function. C functions and type declarations are recursive.

15. Example - Sequential/Colateral order is not important with in group
int i = 1;
void f(void) {
int i = 2, j = i + 1; … }
Is j 2 or 3?

16. 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

17. Example - Recursive void f(void) { … g() … } void g(void) { … f() … }
Resolved by using prototype.
Some languages have issue with using g before g is defined. (pascal)

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

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

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

21. 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. I.E. equivalent only if they are identical.
Example
typedef link = *cell
link next;
cell * p;
Name Equivalence
two expressions use the same name

22. 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

23. Name Equivalence typedef int t1; typedef int t2; t2 x; t2 y; t1 z;
x and y are the same type.
z is not the same type.