Comment by archgoon

So fun fact, if you compile

  int sum(int n) {
      int sum = 0;
      for(int i = 0; i < n; i++) {
          sum +=i;
      }
      return sum;
  }

clang, with -O2, will turn this into the polynomial (n+1)*n//2. It can also do similar transformations for multiple loops.

https://godbolt.org/z/so6neac33

So if you do a brute force solution which could have been reduced to a polyomial, clang has a shot of doing just that.