int
foo (char* a, char* b, char* c, char* d)
{
    int sum = 0;
    for (int i = 0; i != 32; i++)
    {
        sum += (a[i] * b[i] + c[i] * d[i]);
    }
    return sum;
}


int
foo1 (char* a, char* b, char* c, char* d)
{
    int sum = 0;
    int sum1 = 0;
    for (int i = 0; i != 32; i++)
    {
        sum += a[i] * b[i]
        sum1 += c[i] * d[i];
    }
    return sum + sum1;
}

foo should be same as foo1, but it failed to be optimized to dot_prod_expr since current vect_recog_dot_prod_pattern only recognize sum += a[i] * b[i];

I think it can be extend to recog dot_prod_expr chain, as long as they're only used by the final sum reduction.