GATE | GATE-CS-2006 | Question 60
Consider the following C code segment.
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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 of common sub-expression elimination in this code
(C) There is scope of strength reduction in this code
(D) There is scope of dead code elimination in this code
Answer: (D)
Explanation: Question asks about false statement
4*j is common subexpression elimination so B is true. 5*i can be moved out of inner loop so can be i%2. Means, A is true as we have loop invariant computation. Next, 4*j as well as 5*i can be replaced with a = - 4; before j loop then a = a + 4; where 4*j is computed, likewise for 5*i. C is true as there is scope of strength reduction. By choice elimination, we have D.
