GATE 2021 CS – Question 60

Compiler Design · Code Optimization and Data Flow Analysis · 2 marks · Numerical answer

Consider the following C code segment:

a = b + c;
e = a + 1;
d = b + c;
f = d + 1;
g = e + f;

In a compiler, this code segment is represented internally as a directed acyclic graph (DAG). The number of nodes in the DAG is ______.

Show answer and explanation

Correct answer: 6

Explanation

Leaves: b, c, 1 (3 nodes). Internal nodes: b+c (shared by a and d), (b+c)+1 (shared by e and f), and g = e+f. Total = 3 + 3 = 6.