Question 1

What is Preprocessor?

Accepted Answer

A preprocessor is a program that processes the source code before the compiler proper, handling directives like macro expansion, file inclusion, and conditional compilation.

Question 2

Define Regular Expression.

Accepted Answer

A Regular Expression is a notation for specifying patterns of strings over an alphabet, used in lexical analysis to define the patterns of tokens.

Question 3

What is Ambiguous Grammar?

Accepted Answer

An Ambiguous Grammar is a grammar for which some string in its language has more than one parse tree (or equivalently, more than one leftmost or rightmost derivation).

Question 4

Define Handle.

Accepted Answer

A Handle is a substring of the current right-sentential form that matches the RHS of some production and whose reduction to the LHS is a step in the reverse rightmost derivation.

Question 5

What is Semantic Analysis?

Accepted Answer

Semantic Analysis is the compiler phase that checks the source program for semantic correctness (type compatibility, scope rules, declarations) beyond what grammar rules can express.

Question 6

Define Activation Record.

Accepted Answer

An Activation Record (stack frame) is a block of memory allocated on the runtime stack to hold information needed for a single execution (activation) of a procedure.

Question 7

What is Intermediate Code?

Accepted Answer

Intermediate Code is a machine-independent, source-language-independent representation of the source program, generated between the front end and back end of the compiler.

Question 8

Define DAG (Directed Acyclic Graph).

Accepted Answer

A DAG (Directed Acyclic Graph) is a directed graph with no cycles, used in compilers to represent the structure of basic blocks and to identify common subexpressions.

Question 9

What is Peephole Optimization?

Accepted Answer

Peephole Optimization is a machine-code level optimization that examines a small sliding window (peephole) of consecutive instructions and replaces them with shorter or faster equivalent sequences.

Question 10

Define Register Allocation.

Accepted Answer

Register Allocation is the compiler phase that maps program variables (and temporaries) in intermediate code to a limited number of machine registers, minimizing costly memory accesses.

Question 11

Explain the concept of Finite Automata and its role in lexical analysis.

Accepted Answer

Finite Automata (FA) are abstract machines that recognize regular languages. They form the mathematical foundation of lexical analyzers, which are implemented as DFAs to recognize token patterns.

Question 12

Describe the construction of Predictive Parsing Table.

Accepted Answer

The Predictive Parsing Table M[A,a] is constructed using FIRST and FOLLOW sets; entry M[A,a] specifies which production to use when the current non-terminal is A and the lookahead is a.

Question 13

Explain the concept of operator precedence parsing.

Accepted Answer

Operator Precedence Parsing is a shift-reduce parsing method for operator grammars that uses precedence relations (⋖, ≐, ⋗) between terminal symbols to identify handles without building the full LR automaton.

Question 14

Discuss the runtime environment in compilers.

Accepted Answer

The runtime environment manages memory layout, activation record management, parameter passing, and scope resolution during program execution, supporting features like recursion, dynamic allocation, and nested procedures.

Question 15

Explain the concept of Intermediate Code Generation with examples (TAC, Quadr…

Accepted Answer

Intermediate Code Generation produces a machine-independent IR (Three-Address Code, Quadruples, Triples) from the annotated parse tree, forming the bridge between the compiler's front end and back end.

Question 16

Describe the concept of Data Flow Analysis.

Accepted Answer

Data Flow Analysis is a framework for gathering information about the flow of data values along program paths in the control flow graph, used to enable global optimizations.

Question 17

Explain the different types of code generation techniques.

Accepted Answer

Code generation translates optimized intermediate code into target machine code, performing instruction selection, register allocation, and instruction scheduling.

Question 18

(a) Explain the construction of NFA from Regular Expression. (b) Describe the…

Accepted Answer

Thompson's construction builds an NFA from a regular expression bottom-up. The subset construction (powerset construction) converts a NFA to an equivalent DFA by treating sets of NFA states as single DFA states.

Question 19

Explain LL(1) parsing in detail. Construct LL(1) parse table for the followin…

Accepted Answer

LL(1) parsing requires eliminating left recursion and applying left factoring to the grammar, then computing FIRST/FOLLOW sets to build the parsing table. The given grammar E→E+T|T, T→T*F|F, F→(E)|id must be transformed before an LL(1) table can be built.

Question 20

Explain the LALR parsing in detail. Construct LALR parsing table for a given …

Accepted Answer

LALR parsing merges LR(1) states with identical cores (LR(0) items) to produce a compact parser almost as powerful as canonical LR(1). It is the standard parsing method used in tools like yacc and bison.

Question 21

(a) Explain Type Checking. (b) Discuss Backpatching with an example. (c) Expl…

Accepted Answer

Type Checking enforces type safety rules; Backpatching resolves forward references in jump instructions during code generation; Boolean expression translation generates conditional jump code for if-then-else and loops.

Question 22

Explain Code Generation in detail. Discuss register allocation and assignment…

Accepted Answer

Code generation translates IR to target machine code through instruction selection, register allocation (graph coloring), and instruction scheduling. DAG representation of basic blocks enables common subexpression elimination and efficient register use.

Compiler Design