Semantic analysis

Question 1

what grammar symbols associated with?

Answer 1

attributes

Question 2

how are these attributes evaluated?

Answer 2

semantic rules

Question 3

Evaluation of these semantic rules depends on :

Answer 3

Generate intermediate codes
put information on the symbol table
perform type checking
issues error messages
perform almost any activities

Question 4

A_________checks the source program for semantic errors

Answer 4

semantic analyzer

Question 5

A semantic analyzer collects information for ____________

Answer 5

Code Generation

Question 6

________________ is an important part of the semantic analyzer

Answer 6

Type-checking

Question 7

SDT

Answer 7

Syntax directed translation

Question 8

how are attributes stored in SDT?

Answer 8

The attributes are attached to the grammar symbols

Question 9

How are the values of the attributes calculated?

Answer 9

Semantic rules associated with grammar productions

Question 10

The flow of the semantic compiler

Answer 10

input string->parse tree-> dependency graph->semantic rule evaluation order

Question 11

Attribute values may represent :

Answer 11

Numbers
strings
memory locations
A data type for checking expressions
scoping information for declaration
A data type for checking expressions
scoping information for local declarations
Intermediate program representations

Question 12

Name two ways to represent semantic rules:

Answer 12

Syntax directed definitions.

& Translation Schemes

Question 13

SDD are ____ level

Translation schemes are closer to an _____________

Answer 13

higher implementation

Question 14

Explain SDD

syntax-directed definitions

Answer 14

Each production of A->alpha
is associated with the set of semantic rules
b=f(c1,c2,…….cn) where f is a function
b=> is synthesized attribute of A and c1,c2,c3,,,,,,,,,,cn are attributes of the grammar symbols in the production
b=>inherited attribute,one of the grammar symbols in aplha are attributes of the grammar symbols in the production (A-> alpha)

in either of the cases, we say b depends on c1,c2,c3,,,,,,,,,,,ck.

Question 15

what are Synthesized attributes

Answer 15

Synthesized attributes are the depends only on the attributes of the children
They are the most common attribute type
Synthesized attributes never take values from their parents nodes or any sibling nodes
the non terminal concerned must be in the head of the production
Terminals have synthesised attributes which are the lexical values

Question 16

what has Inherited attributes?

Answer 16

An Attributes’ node ‘s parents and/or siblings .They cannot be defined in terms of attributes value at children nodes

Inherited attributes are often used in compilers for passing contextual information forward ,for example,the type keyword in a variable declaration statement

Question 17

Attribute Grammar

Answer 17

A semantic rule=f(c1,c2,c3,,,,,,,,,cn) indicates that the attribute b depends on attributes c1,c2,…………cn.

Syntax-directed definition a semantic rule may just evaluate a value of an attribute it it may have some side effects such as printing values

Question 18

Side effects

Answer 18

Side effects:
Evaluation of semantic rules may generate intermediate codes,may perform type checking and may issue error messages.
These are known as side effects

Question 19

what are semantic rules with controlled side effects

Answer 19

Attribute grammars have no side
effects and allow any evaluation order consistent with dependency graph
whereas translation schemes impose left-to-right evaluation and allow
schematic actions to contain any program fragment

Question 20

ways to control side effects:

Answer 20

1. Permit incidental side effects that do not disturb attribute evaluation.
2. Impose restrictions on allowable evaluation orders, so that the same
   translation is produced for any allowable order

Question 21

what is the need for a dependency graph?

Answer 21

An SDD with both and synthesized attributes does not ensure any guaranteed order ,even it may not have an order at all
non terminals A and B with synthesized and inherited attributes A.s and B.i respectively along with the production and rules as:
Production
A →B

Semantic Rule
A.s = B.i
B.i= A.s+1

Question 22

what is the Dependency graph?

Answer 22

1.Dependency graph predicts the flow of information among the attribute instances in a particular parse tree

2.The inter dependencies among the inherited and synthesized attributes
at the node in the parse tree is depicted by dependency graph.

Question 23

Visualize a Dependency Graph

Answer 23

1. Each attribute is a node

2. We add edges from the node for attribute c to the node for the attribute