[Bug target/88497] Improve Accumulation in Auto-Vectorized Code

[kelvin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88497

--- Comment #7 from kelvin at gcc dot gnu.org ---
Here is the original program that motivated my simplified reproducer:

extern void first_dummy ();
extern void dummy (double sacc, int n);
extern void other_dummy ();

extern float opt_value;
extern char *opt_desc;

#define M 128
#define N 512

double x [N];
double y [N];

int main (int argc, char *argv []) {
  double sacc;

  first_dummy ();
  for (int j = 0; j < M; j++) {

    sacc = 0.00;
    for (unsigned long long int i = 0; i < N; i++) {
      sacc += x[i] * y[i];
    }
    dummy (sacc, N);
  }
  opt_value = ((float) N) * 2 * ((float) M);
  opt_desc = "flops";
  other_dummy ();
}