Question

Consider the following C code segment.
for (i = 0; i < n; i ++)
{
for (j = 0; j < n; j ++)
{
if (i % 2)
{ x + = (4 * j + 5 * i);
y + = (7 + 4 *j);
}
}
}
which one of the following is false?

• A. The code contains loop invariant computation
• B. There is scope strength reduction in this code
• C. There is scope of dead code elimination in this code
• D. There is scope of common sub-expression elimination in this code

Answer 1

The correct option is C There is scope of dead code elimination in this code

(a) i%2 is inner loop invariant, it can be moved before inner loop.

(b) 4*j is common sub-expression apeared in two statements.

(c) 4*j can be reduced to j<<2 by strength reduction

(d) There is no dead code in given code segment.
So there is no scope of dead code elimination in this code.
Hence only option (d) is FALSE.