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 the 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
Answer: (D)
Explanation:
Total 300 additions (for each iteration 3 addition operations (p+c,q+a) or (p+b, q+c) , (i+2)
c=x+3;
z=c+a+b
303 addition operations and 2 dereference operations (for y->f1, y->f2).
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