Overlap Iterations in Dependence testing

[Prashant Singh Rawat]

In gcc 4.6.0, The part of dump (*.ckdd) finding the dependency using
Banerjee's Solver for the program
| int a[256];
| int main ()
| {
|    int i;
|     for (i=0; i<200; i++)
|        a[i+21] = a[i*2] + 2;
| }

gives,
chrec_a = {0, +, 2}_1
chrec_b = {21, +, 1}_1

and the overlap_iterations are :
overlap_iterations_a = [11 + 1 * x_1]
overlap_iterations_b = [1 + 2 * x_1]

What I understood was that overlap_iterations give the solution to the
Diophantine equation. In that light, is this solution not incorrect?
Or there is something wrong with my understanding?
Also, what does last_conflict hold? The last iteration number of
source that causes conflict, or the total number of iterations that
cause conflict?
In case of variable dependence distance, even the last_conflict seems
to have wrong value. In this example, it is 63. Why?



--
With regards,
Prashant Singh Rawat
http://www.cse.iitb.ac.in/~prashantr