Loop-Unroll optimization

I am trying loop-unroll optimization but it is not affecting the bit code. When I looked the loop unroll code it seems to be expecting three parameter(UnrollThreshold, UnrollCount, UnrollAllowPartial) from the user. Do I need to pass these parameter to activate loop unroll?

The loop that I am trying it on is:

for(i=0; i< 1000; i++)
c[i] = a[i] + b[i];