1  /* { dg-do compile } */
       2  /* { dg-require-effective-target vect_double } */
       3  
       4  double dotprod(const double *a, const double *b, unsigned long long n)
       5  {
       6    double d1 = 0.0;
       7    double d2 = 0.0;
       8  
       9    for (unsigned long long i = 0; i < n; i += 2) {
      10      d1 += a[i] * b[i];
      11      d2 += a[i + 1] * b[i + 1];
      12    }
      13  
      14    return (d1 + d2);
      15  }
      16  
      17  /* We should use a SLP reduction even without -ffast-math by using a
      18     VF of one.  */
      19  /* { dg-final { scan-tree-dump "vectorizing stmts using SLP" "vect" { xfail vect_variable_length } } } */
      20  /* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */