Intermediate Code Generation(Compiler Design) MCQs

Intermediate Code Generation” from Compiler Design for the GATE exam

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1.

Which of the following is not a form of intermediate code representation?
A) Three-address code
B) Syntax tree
C) Parse tree
D) Assembly code

✅ Answer: D) Assembly code
Solution:
Assembly code is machine-dependent, while the other three are machine-independent intermediate representations (IRs) used before code generation.

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2.

Which one of the following is a valid three-address statement?
A) x = y + z * 2
B) x = y + z + w
C) x = y + z; w = x * 3
D) x = y + (z * w)

✅ Answer: A) x = y + z * 2
Solution:
A single three-address instruction contains at most one operator on the right side. Option (A) can be broken into:
t1 = z * 2; x = y + t1.

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3.

Intermediate code is mainly generated to:
A) Optimize parsing speed
B) Provide machine independence
C) Increase code size
D) Reduce semantic errors

✅ Answer: B) Provide machine independence
Solution:
IR acts as a bridge between front end and back end, allowing portability across architectures.

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4.

Which of the following correctly represents a quadruple format?
A) (operator, operand1, operand2, result)
B) (operand1, operand2, operator, result)
C) (operator, result, operand1, operand2)
D) (result, operator, operand1, operand2)

✅ Answer: A) (operator, operand1, operand2, result)
Solution:
In quadruples, operator precedes operands; the result field stores the location where output is kept.

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5.

In triples, how are intermediate results represented?
A) Using temporary variable names
B) Using numeric position labels
C) Using symbol table indices
D) Using direct registers

✅ Answer: B) Using numeric position labels
Solution:
Triples replace temporary variables with statement numbers, saving storage but complicating code movement.

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6.

Given expression: x = (a + b) * (c - d), how many three-address statements are required?
A) 1
B) 2
C) 3
D) 4

✅ Answer: C) 3
Solution:
t1 = a + b
t2 = c - d
x = t1 * t2
→ 3 instructions.

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7.

In quadruple representation, if statement 3 is (*, T1, T2, T3), then it means:
A) T3 = T1 * T2
B) T1 = T2 * T3
C) T2 = T1 * T3
D) T1 = T3 * T2

✅ Answer: A) T3 = T1 * T2
Solution:
The order in quadruples is (operator, operand1, operand2, result).

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8.

Which of the following is most suitable for implementing optimization techniques?
A) Target code
B) Intermediate code
C) Assembly code
D) Source code

✅ Answer: B) Intermediate code
Solution:
Most optimizations are easier and machine-independent at the IR level before final code generation.

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9.

The Directed Acyclic Graph (DAG) representation of expressions helps in:
A) Parsing
B) Code generation only
C) Common subexpression elimination
D) Constant folding only

✅ Answer: C) Common subexpression elimination
Solution:
DAG merges identical subexpressions, avoiding redundant computation.

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10.

Three-address code instruction goto L1 if x < y is equivalent to:
A) Conditional jump
B) Unconditional jump
C) Function call
D) Return statement

✅ Answer: A) Conditional jump
Solution:
This instruction transfers control to label L1 only if the condition x < y is true.

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11.

Which of the following is a benefit of generating an intermediate code?
A) Faster compilation
B) Easier debugging
C) Machine independence and optimization
D) Reduced lexical errors

✅ Answer: C) Machine independence and optimization
Solution:
Intermediate representation separates front-end and back-end concerns, improving portability and optimization.

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12.

In three-address code, how many operands are used at most in one instruction?
A) 1
B) 2
C) 3
D) 4

✅ Answer: C) 3
Solution:
The name “three-address” means each instruction can have up to three operands (two sources + one destination).

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13.

For the expression x = a * b + c * d, how many temporary variables are required in three-address form?
A) 1
B) 2
C) 3
D) 4

✅ Answer: B) 2
Solution:
t1 = a * b
t2 = c * d
x = t1 + t2
→ two temporaries.

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14.

A quadruple and triple differ mainly in:
A) Type of operations supported
B) Number of operands
C) Way intermediate results are represented
D) Control flow

✅ Answer: C) Way intermediate results are represented
Solution:
Triples use statement numbers; quadruples use explicit temporary variables.

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15.

If the expression is p = q + r * s, what is the first operator executed?
A) +
B) *
C) =
D) Depends on compiler

✅ Answer: B) *
Solution:
Operator precedence ensures multiplication before addition.

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16.

A syntax-directed translation scheme that generates three-address code during parsing belongs to:
A) Semantic analysis
B) Intermediate code generation
C) Code optimization
D) Syntax analysis

✅ Answer: B) Intermediate code generation
Solution:
This phase attaches translation actions to grammar rules that produce IR during parsing.

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17.

The intermediate code generation phase takes input from:
A) Syntax analyzer
B) Lexical analyzer
C) Semantic analyzer
D) All of these

✅ Answer: D) All of these
Solution:
Intermediate code requires token information (lexical), syntax structure (parser), and semantic validation.

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18.

Which of the following does not belong to three-address code forms?
A) x = y + z
B) x = -y
C) x = y
D) x = y + z + w

✅ Answer: D) x = y + z + w
Solution:
Only one operator per instruction; this one requires breaking into multiple statements.

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19.

Which IR form explicitly shows computation order?
A) Syntax tree
B) DAG
C) Quadruples
D) Symbol table

✅ Answer: C) Quadruples
Solution:
Quadruples maintain an ordered list of operations for sequential computation.

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20.

The label field in intermediate code is used for:
A) Arithmetic operations
B) Control flow
C) Temporary variable naming
D) Symbol table lookup

✅ Answer: B) Control flow
Solution:
Labels denote jump targets in control flow statements like loops and conditionals.

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21.

For Boolean expression x && y || z, short-circuit evaluation in intermediate code uses:
A) Backpatching
B) Constant folding
C) Loop unrolling
D) Dead code elimination

✅ Answer: A) Backpatching
Solution:
Backpatching is used to fill jump addresses later during Boolean expression translation.

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22.

In quadruple (+, op1, op2, result), which operation occurs first?
A) Assignment
B) Addition
C) Both simultaneously
D) Depends on operator precedence

✅ Answer: B) Addition
Solution:
Operator field represents the arithmetic operation performed before storing result.

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23.

Intermediate code generation helps in separating:
A) Syntax and semantics
B) Machine-dependent and machine-independent phases
C) Front end and back end of compiler
D) Both B and C

✅ Answer: D) Both B and C
Solution:
IR forms a bridge between the machine-independent front end and machine-dependent back end.

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24.

A DAG node with two parents represents:
A) Common subexpression
B) Redundant variable
C) Constant propagation
D) Unreachable code

✅ Answer: A) Common subexpression
Solution:
When two expressions share the same computation, they point to a single DAG node.

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25.

In a DAG representation, leaf nodes represent:
A) Operators
B) Constants or variables
C) Temporary results
D) Control links

✅ Answer: B) Constants or variables
Solution:
Leaves store operands (variables or constants), while internal nodes represent operators.

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Intermediate Code Generation – Compiler Design

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26.
The intermediate code for if (a < b) x = y + z; else x = y - z; will include how many labels?
A) 1
B) 2
C) 3
D) 4

✅ Answer: C) 3
Solution:
Typically, if-else requires three labels: one for the true branch, one for the false branch, and one for the exit point.

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27.
For while (i < 5) i = i + 1;, the three-address code will have how many jump statements?
A) 1
B) 2
C) 3
D) 4

✅ Answer: B) 2
Solution:
One jump to test the condition and another unconditional jump to loop back.

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28.
In the intermediate representation of an expression tree, internal nodes represent:
A) Variables
B) Operators
C) Temporary variables
D) Constants

✅ Answer: B) Operators
Solution:
Internal nodes denote operations, while leaves hold operands.

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29.
Which statement about quadruples is incorrect?
A) Easy to reorder
B) Difficult to maintain temporary variables
C) Each operation stored explicitly
D) No explicit temporaries used

✅ Answer: D) No explicit temporaries used
Solution:
Quadruples do use explicit temporaries; that’s what differentiates them from triples.

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30.
For expression x = a * b + c * d + e, number of three-address instructions = ?
A) 3
B) 4
C) 5
D) 6

✅ Answer: B) 4
Solution:
t1 = a * b
t2 = c * d
t3 = t1 + t2
x = t3 + e → 4 statements.

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31.
In a triple, intermediate results are identified by:
A) Temporary variables
B) Statement numbers
C) Stack addresses
D) Register names

✅ Answer: B) Statement numbers
Solution:
Each statement can refer to previous computations by their index.

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32.
An advantage of indirect triples over triples is:
A) Faster arithmetic
B) Easier code reordering
C) Reduced memory usage
D) Simpler parsing

✅ Answer: B) Easier code reordering
Solution:
Indirect triples maintain a table of pointers, allowing rearrangement of computation order.

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33.
Which of the following is not a benefit of intermediate code?
A) Portability
B) Simpler optimization
C) Faster execution
D) Machine independence

✅ Answer: C) Faster execution
Solution:
Intermediate code is slower than final machine code; it’s meant for translation, not execution.

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34.
In three-address code, instruction x = *y denotes:
A) Value of y assigned to x
B) Content of memory at y assigned to x
C) Address of y assigned to x
D) Value of x assigned to memory at y

✅ Answer: B) Content of memory at y assigned to x
Solution:
The * operator indicates pointer dereferencing.

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35.
For instruction *x = y, the meaning is:
A) Assign y to x
B) Assign y to address pointed by x
C) Assign x to y
D) Load address of y to x

✅ Answer: B) Assign y to address pointed by x
Solution:
The left-hand * means “store in memory at address x”.

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36.
Intermediate code generation comes after which compiler phase?
A) Code optimization
B) Syntax analysis
C) Semantic analysis
D) Code generation

✅ Answer: C) Semantic analysis
Solution:
IR is generated once syntax and semantics are validated.

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37.
Which of the following intermediate forms is closest to assembly language?
A) Syntax tree
B) Three-address code
C) Quadruple
D) Postfix notation

✅ Answer: B) Three-address code
Solution:
Three-address code resembles low-level assembly with simple operations.

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38.
For expression a = b + c * d / e, number of temporaries required = ?
A) 1
B) 2
C) 3
D) 4

✅ Answer: C) 3
Solution:
t1 = c * d; t2 = t1 / e; a = b + t2.

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39.
In DAG representation, leaf nodes represent:
A) Operators
B) Constants or variables
C) Temporaries only
D) Control instructions

✅ Answer: B) Constants or variables
Solution:
Leaf nodes are operands; inner nodes are operations.

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40.
The postfix form of expression (x + y) * (z - w) is:
A) x y + z w - *
B) x y z w + - *
C) x y z w * + -
D) x + y - z * w

✅ Answer: A) x y + z w - *
Solution:
Convert infix to postfix following operator precedence and parentheses.

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41.
Which operation is represented by three-address code param a?
A) Parameter passing
B) Return value
C) Function definition
D) Variable initialization

✅ Answer: A) Parameter passing
Solution:
param instructions push function arguments on stack before call.

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42.
In function calls, the instruction call p, 3 denotes:
A) Call procedure p with 3 arguments
B) Call procedure p at line 3
C) Recursive call
D) Call 3 times

✅ Answer: A) Call procedure p with 3 arguments
Solution:
The number indicates count of parameters passed.

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43.
In intermediate code, return x means:
A) End program
B) Return control and value x to caller
C) Go to start of procedure
D) Terminate compiler

✅ Answer: B) Return control and value x to caller
Solution:
Used to end function execution and send value to the calling routine.

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44.
Backpatching is used to:
A) Optimize arithmetic expressions
B) Fill in jump addresses
C) Remove redundant labels
D) Translate literals

✅ Answer: B) Fill in jump addresses
Solution:
In control flow translation, jump targets are unknown initially and are later patched.

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45.
Which data structure supports backpatching most efficiently?
A) Stack
B) Queue
C) Linked list
D) Symbol table

✅ Answer: C) Linked list
Solution:
Backpatching lists maintain pointers to instructions waiting for target labels.

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46.
The IR best suited for machine-dependent optimization is:
A) Three-address code
B) DAG
C) Syntax tree
D) Machine code

✅ Answer: A) Three-address code
Solution:
It’s closer to machine code and allows instruction-level optimization.

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47.
In a three-address code, instruction x = y represents:
A) Assignment
B) Comparison
C) Pointer dereference
D) Function call

✅ Answer: A) Assignment
Solution:
Simple data transfer operation assigning value of y to x.

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48.
Intermediate code generation simplifies:
A) Lexical analysis
B) Code portability
C) Parsing speed
D) Assembly generation

✅ Answer: B) Code portability
Solution:
IR abstracts machine details, allowing reuse of front end for multiple targets.

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49.
What is the intermediate representation of array access a[i] = b + c?
A) t1 = b + c; a[i] = t1
B) a = i + b + c
C) t1 = a + b; i = t1 + c
D) a = b + c[i]

✅ Answer: A) t1 = b + c; a[i] = t1
Solution:
One temp for right-hand side expression, then assignment to array element.

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50.
Intermediate code of pointer assignment *p = q + r is:
A) t1 = q + r; *p = t1
B) p = q + r; *t1 = p
C) q = *r + p
D) p = *q + r

✅ Answer: A) t1 = q + r; *p = t1
Solution:
Evaluates arithmetic first, then stores result into location pointed by p.

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51.
What does SSA (Static Single Assignment) form ensure?
A) No loops exist
B) Each variable is assigned once
C) All variables are constant
D) Recursion is avoided

✅ Answer: B) Each variable is assigned once
Solution:
SSA simplifies optimization by unique variable assignment.

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52.
An intermediate representation should be:
A) Machine-specific
B) Readable only by assembler
C) Easy to translate and optimize
D) Dependent on syntax

✅ Answer: C) Easy to translate and optimize
Solution:
It acts as a bridge allowing efficient translation and optimization.

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53.
Three-address code t1 = x < y represents:
A) Conditional expression
B) Assignment
C) Function call
D) Array access

✅ Answer: A) Conditional expression
Solution:
Comparison generates Boolean result for use in later branches.

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54.
The intermediate code for if (x <= y) z = 10; can be:
A) if x <= y goto L1; L1: z = 10
B) goto L1 if x <= y; z = 10
C) ifFalse x <= y goto L2; z = 10
D) goto L1; z = 10

✅ Answer: C) ifFalse x <= y goto L2; z = 10
Solution:
The false condition branches to label after assignment.

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55.
The postfix for expression a + b * (c + d) is:
A) a b c d + * +
B) a b + c d * +
C) a b c + d * +
D) a b c + d + *

✅ Answer: A) a b c d + * +
Solution:
Parentheses evaluated first, maintaining precedence.

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56.
Intermediate code improves compiler retargeting because:
A) It directly executes
B) It abstracts machine details
C) It requires fewer instructions
D) It optimizes parsing

✅ Answer: B) It abstracts machine details
Solution:
Machine independence allows reuse of compiler front-end.

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57.
Which of the following best defines “basic block”?
A) Sequence with single entry and single exit
B) Looping structure
C) Group of unrelated statements
D) Data segment

✅ Answer: A) Sequence with single entry and single exit
Solution:
Basic blocks are atomic units for optimization and control flow analysis.

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58.
In a three-address code sequence, each instruction:
A) Performs one operation
B) Performs multiple operations
C) Represents full program logic
D) Includes nested conditions

✅ Answer: A) Performs one operation
Solution:
Each TAC represents a simple operation for optimization ease.

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59.
Intermediate representation between high-level and assembly code is:
A) Syntax tree
B) Abstract machine code
C) Intermediate code
D) Bytecode

✅ Answer: C) Intermediate code
Solution:
It sits between source-level constructs and target-level instructions.

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60.
Which of the following is machine-dependent?
A) Parse tree
B) Intermediate code
C) Target code
D) Syntax tree

✅ Answer: C) Target code
Solution:
Target code depends on processor architecture.

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61.
In three-address code, goto L1 means:
A) Conditional branch
B) Unconditional branch
C) Function call
D) Return statement

✅ Answer: B) Unconditional branch
Solution:
Transfers control directly to label L1.

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62.
Intermediate code simplifies optimization because:
A) It is high level
B) It is architecture neutral
C) It is machine code
D) It uses registers

✅ Answer: B) It is architecture neutral
Solution:
Machine independence enables general optimization techniques.

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63.
An instruction x = -y in three-address code performs:
A) Logical negation
B) Arithmetic negation
C) Address inversion
D) Bitwise complement

✅ Answer: B) Arithmetic negation
Solution:
Unary minus operator negates the numeric value.

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64.
In quadruples, the result of one instruction can be used in another by:
A) Copying operand value
B) Using result field reference
C) Recomputing expression
D) Using access links

✅ Answer: B) Using result field reference
Solution:
Result names are used as operands in subsequent instructions.

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65.
The number of temporaries for x = a + b + c + d is:
A) 1
B) 2
C) 3
D) 4

✅ Answer: C) 3
Solution:
t1 = a + b; t2 = t1 + c; x = t2 + d.

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66.
For Boolean if (x && y) z = 1;, how many conditional jumps required?
A) 1
B) 2
C) 3
D) 4

✅ Answer: B) 2
Solution:
One check for x, and another for y if first is true.

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67.
Which IR form helps eliminate redundant subexpressions easily?
A) DAG
B) Quadruple
C) Three-address code
D) Postfix

✅ Answer: A) DAG
Solution:
DAG merges identical operations into single nodes.

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68.
Three-address code supports maximum of:
A) 2 operands
B) 3 operands
C) 4 operands
D) Unlimited operands

✅ Answer: B) 3
Solution:
Typically two operands and one result field.

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69.
Which field is not present in a triple representation?
A) Operator
B) Operand 1
C) Operand 2
D) Result

✅ Answer: D) Result
Solution:
Triples omit result field; results are implicit by position.

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70.
A phi (Φ) function in SSA form merges:
A) Loops
B) Control flow
C) Variable values from different paths
D) Constants

✅ Answer: C) Variable values from different paths
Solution:
Φ-function combines multiple assignments into one variable in SSA.

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71.
Intermediate code for function call sum(a,b) is:
A) param a; param b; call sum,2
B) sum a b,2
C) call sum(a,b)
D) param 2; call a,b

✅ Answer: A) param a; param b; call sum,2
Solution:
Standard form for procedure call with parameters.

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72.
Which is most suitable for register allocation optimization?
A) DAG
B) Quadruple
C) Three-address code
D) Parse tree

✅ Answer: C) Three-address code
Solution:
It closely matches register-level operations.

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73.
if x < y goto L1 is an example of:
A) Arithmetic TAC
B) Control TAC
C) Boolean TAC
D) Logical TAC

✅ Answer: B) Control TAC
Solution:
Conditional transfer of control.

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74.
In three-address code, which statement represents pointer arithmetic?
A) t1 = &a
B) t2 = *p
C) p = p + 1
D) return p

✅ Answer: C) p = p + 1
Solution:
Incrementing a pointer is pointer arithmetic.

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75.
For nested loops, backpatching handles:
A) Variable lifetimes
B) Jump addresses for loops
C) Function calls
D) Parameter stack

✅ Answer: B) Jump addresses for loops
Solution:
Patching labels ensures correct looping control.

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76.
Intermediate code for for(i=0;i<3;i++) uses how many labels?
A) 2
B) 3
C) 4
D) 5

✅ Answer: B) 3
Solution:
Initialization, condition, and increment need labels.

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77.
Which IR is easiest to interpret directly?
A) Postfix
B) DAG
C) Three-address code
D) Syntax tree

✅ Answer: A) Postfix
Solution:
Postfix is easily evaluated using a stack.

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78.
Expression x = a + b * c - d requires how many TACs?
A) 2
B) 3
C) 4
D) 5

✅ Answer: B) 3
Solution:
t1 = b * c; t2 = a + t1; x = t2 - d.

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79.
The TAC instruction t1 = y < z is used in:
A) Boolean expression evaluation
B) Constant folding
C) Loop unrolling
D) Array indexing

✅ Answer: A) Boolean expression evaluation
Solution:
Generates condition results for later jumps.

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80.
Which IR allows common subexpression elimination?
A) Quadruple
B) DAG
C) Triple
D) Syntax tree

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