Code Generation and Optimization - Compiler Design - Computer Science & Information Technology Previous Year Questions

1

2013 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2013 [Session 1]

Suppose the instruction set architecture of the processor has only two registers. The only allowed compiler optimization is code motion, which moves statements from one place to another while preserving correctness. What is the minimum number of spills to memory in the compiled code?

A

0

B

1

C

2

D

3

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2

2013 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2013 [Session 1]

What is the minimum number of registers needed in the instruction set architecture of the processor to compile this code segment without any spill to memory? Do not apply any optimization other than optimizing register allocation.

A

3

B

4

C

5

D

6

Check answer

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3

2014 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2014 [Session 1]

Which one of the following is FALSE?

A

A basic block is a sequence of instructions where control enters the sequence at the beginning and exits at the end.

B

Available expression analysis can be used for common subexpression elimination.

C

Live variable analysis can be used for dead code elimination.

D

x = 4 * 5 ⇒ x = 20 is an example of common subexpression elimination.

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4

2014 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2014 [Session 3]

One of the purposes of using intermediate code in compilers is to

A

make parsing and semantic analysis simpler.

B

improve error recovery and error reporting.

C

increase the chances of reusing the machine-independent code optimizer in other compilers.

D

improve the register allocation.

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5

2014 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2014 [Session 3]

Consider the basic block given below.
a = b + c
c = a + d
d = b + c
e = d - b
a = e + b
The minimum number of nodes and edges present in the DAG representation of the above basic block respectively are

A

6 and 6

B

8 and 10

C

9 and 12

D

4 and 4

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6

2015 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2015 [Session 2]

Consider the intermediate code given below.
(1)  i = 1
(2)  j = 1
(3)  t1 = 5 * i
(4)  t2 = t1 + j
(5)  t3 = 4 * t2
(6)  t4 = t3
(7)  a[t4] = -1
(8)  j = j + 1
(9)  if j <= 5 goto (3)
(10)  i=i+1
(11)  if i < 5 goto (2)
The number of nodes and edges in the control-flow-graph constructed for the above code, respectively, are

A

5 and 7

B

6 and 7

C

5 and 5

D

7 and 8

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7

2021 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2021 [Session 2]

Consider the following ANSI C code segment:
z = x + 3 + y->f1 + y->f2;
for (i = 0; i < 200; i = i + 2) {
if (z > i) {
p = p + x + 3;
q = q + y->f1;
} else {
p = p + y->f2;
q = q + x + 3;
}
}
Assume that the variable y points to a struct (allocated on the heap) containing two fields f1 and f2, and the local variables x, y, z, p, q, and i are allotted registers. Common sub-expression elimination (CSE) optimization is applied on the code. The number of addition and dereference operations (of the form y->f1 or y->f2) in the optimized code, respectively, are:

A

403 and 102

B

203 and 2

C

303 and 102

D

303 and 2

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8

2021 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2021 [Session 2]

For a statement \(S\) in a program, in the context of liveness analysis, the following sets are defined:

\(USE(S)\) : the set of variables used in \(S\)

\(IN(S)\) : the set of variables that are live at the entry of \(S\)

\(OUT(S)\) : the set of variables that are live at the exit of \(S\)

Consider a basic block that consists of two statements, \(S_1\) followed by \(S_2\). Which one of the following statements is correct?

A

\(OUT(S_1) = IN(S_2)\)

B

\(OUT(S_1) = IN(S_1) \cup USE(S_1)\)

C

\(OUT(S_1) = IN(S_2) \cup OUT(S_2)\)

D

\(OUT(S_1) = USE(S_1) \cup IN(S_2)\)

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9

2024 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2024 [Session 1]

Consider the following pseudo-code.
L1: t1 = -1
L2: t2 = 0
L3: t3 = 0
L4: t4 = 4 * t3
L5: t5 = 4 * t2
L6: t6 = t5 * M
L7: t7 = t4 + t6
L8: t8 = a[t7]
L9: if t8 <= max goto L11
L10: t1 = t8
L11: t3 = t3 + 1
L12: if t3 < M goto L4
L13: t2 = t2 + 1
L14: if t2 < N goto L3
L15: max = t1
Which one of the following options CORRECTLY specifies the number of basic blocks and the number of instructions in the largest basic block, respectively ?

A

6 and 6

B

6 and 7

C

7 and 7

D

7 and 6

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10

2024 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2024 [Session 2]

Consider the following expression: x[i] = (p + r) * -s[i] + u/w. The following sequence shows the list of triples representing the given expression, with entries missing for triples (1), (3), and (6).

(0)	+	p	r
(1)
(2)	uminus	(1)
(3)
(4)	/	u	w
(5)	+	(3)	(4)
(6)
(7)	=	(6)	(5)

Which one of the following options fills in the missing entries CORRECTLY?

A

(1) []= s i (3) * (0) (2) (6) []= x i

B

(1) []= s i (3) - (0) (2) (6) =[] x (5)

C

(1) =[] s i (3) * (0) (2) (6) []= x (5)

D

(1) =[] s i (3) - (0) (2) (6) =[] x i

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11

2025 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2025 [Session 1]

Which ONE of the following techniques used in compiler code optimization uses live variable analysis?

A

Run-time function call management

B

Register assignment to variables

C

Strength reduction

D

Constant folding

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12

2025 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2025 [Session 1]

Refer to the given 3-address code sequence. This code sequence is split into basic blocks. The number of basic blocks is ______. (Answer in integer)

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13

2025 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science & Information Technology (CS) 2025 [Session 2]

Consider the following statements about the use of backpatching in a compiler for intermediate code generation:
(I) Backpatching can be used to generate code for Boolean expression in one pass.
(II) Backpatching can be used to generate code for flow-of-control statements in one pass.
Which ONE of the following options is CORRECT?

A

Only (I) is correct.

B

Only (II) is correct.

C

Both (I) and (II) are correct.

D

Neither (I) nor (II) is correct.

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14

2026 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science and Information Technology (CS) 2026

Consider the control flow graph shown in the figure.
Which one of the following options correctly lists the set of redundant expressions (common subexpressions) in the basic blocks B4 and B5?
Note: All the variables are integers.

A

B4: { b + i }
B5: { c + m }

B

B4: { g * k }
B5: { c + m }

C

B4: { g * k, b + i }
B5: { }

D

B4: { g * k }
B5: { }

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15

2026 · Computer Science & Information Technology · Compiler Design · Code Generation and Optimization

Computer Science and Information Technology (CS) 2026

Consider the control flow graph given below.
[Image of control flow graph]
Which one of the following options is the set of live variables at the exit point of each basic block?

A

B1:{a, b, c, e, f}, B2:{d, e}, B3:{b, c, e, f}, B4:∅

B

B1:∅, B2:{d, e}, B3:{a, c, f}, B4:∅

C

B1:{a, b, c, e, f}, B2:{d, e}, B3:{c, e, f}, B4:∅

D

B1:∅, B2:{d, e, f}, B3:{a, b, c, e, f}, B4:∅

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