[Bug tree-optimization/83857] [8 Regression] internal compiler error: in exact_div, at poly-int.h:2139

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83857

--- Comment #5 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> 
---
Slightly reduced testcase:

f (double *x, double y)
{
  double a = 0;
  for (int i = 0; i < 100; ++i)
    {
      a += y;
      x[i * 2] += a;
      x[i * 2 + 1] += a;
    }
  return a - y;
}

The problem is that we need the phi to be treated as an SLP operation
when calculating ncopies.