1
Evaluating a constant expression at compile time is called
Correct Answer
constant folding
☑ MCQ PRACTICE
Compiler Design Unit 5
Practice objective questions for quick revision and examination preparation. Try answering each question before revealing the answer.
Compiler Design MCQs - Unit 5
2
Dead code is code
Correct Answer
whose result is never used
3
Common subexpression elimination
Correct Answer
avoids recomputing an expression whose value is already available
4
Copy propagation replaces uses of x by y after the statement
Correct Answer
x = y
5
Moving a loop-invariant computation outside the loop is called
Correct Answer
code motion
6
Replacing a multiplication in a loop by repeated addition uses
Correct Answer
induction variables (strength reduction)
7
Data-flow analysis is used to
Correct Answer
collect information about the values at various points in a program
8
Reaching-definitions analysis is a
Correct Answer
forward data-flow problem
9
Live-variable analysis is a
Correct Answer
backward data-flow problem
10
The meet operator for available expressions is
Correct Answer
intersection
11
The meet operator for reaching definitions is
Correct Answer
union
12
The data-flow equation for a block B is
Correct Answer
OUT[B] = GEN[B] ∪ (IN[B] − KILL[B])
13
A data-flow framework consists of a domain, a direction, a semilattice and
Correct Answer
transfer functions
14
Constant propagation
Correct Answer
replaces a variable by its constant value when the value is known
15
Partial-redundancy elimination removes expressions that are redundant along
Correct Answer
some but not all paths
16
A loop in a flow graph has a single entry node called the
Correct Answer
header
17
A node d dominates a node n if
Correct Answer
every path from the entry to n goes through d
18
A back edge is an edge a → b in which
Correct Answer
b dominates a
19
A natural loop is defined by a
Correct Answer
back edge
20
A loop-invariant expression is one whose value
Correct Answer
does not change during the execution of the loop
21
Machine-independent optimization is usually applied to
Correct Answer
intermediate code
22
Iterative data-flow algorithms continue until
Correct Answer
no further change occurs (a fixed point is reached)
23
Loop-invariant code motion improves performance by
Correct Answer
computing invariant expressions once outside the loop
24
In available-expressions analysis, an expression is available at a point if it
Correct Answer
has been computed on every path to that point and not killed since
25
A flow graph whose loops can all be identified by back edges and dominators is called
Correct Answer
reducible
Fill in the Blanks
26
Evaluating constant expressions at compile time is called constant ______.
Correct Answer
folding
27
Code whose result is never used is called ______ code.
Correct Answer
dead
28
Moving a loop-invariant computation out of a loop is called code ______.
Correct Answer
motion
29
The meet operator for reaching definitions is ______.
Correct Answer
union
30
The meet operator for available expressions is ______.
Correct Answer
intersection
31
Live-variable analysis is a ______ data-flow problem.
Correct Answer
backward
32
In the equation OUT[B] = GEN[B] ∪ (IN[B] − ______[B]), the missing term is the set of killed definitions.
Correct Answer
KILL
33
Iterative data-flow algorithms stop when a ______ point is reached.
Correct Answer
fixed
34
Constant propagation replaces a variable by its known constant ______.
Correct Answer
value
35
Partial-redundancy elimination removes expressions that are redundant along ______ paths.
Correct Answer
some
36
A node d ______ a node n if every path from the entry to n passes through d.
Correct Answer
dominates
37
An edge a → b whose head b dominates its tail a is called a ______ edge.
Correct Answer
back
38
A back edge defines a ______ loop.
Correct Answer
natural
39
The single entry node of a loop is called the loop ______.
Correct Answer
header
40
After the statement x = y, copy propagation replaces uses of x by ______.
Correct Answer
y