value tracking

I would like to know what API i can use to tell that x cant be negative. I looked through the value tracking analysis API, nothing seems immediate.

int divBy4(int x) {
  if (x < 0) abort();
  return x/4; 

}

http://llvm.org/docs/doxygen/html/ValueTracking_8h.html

Thanks,
Trent

Hi Xin Tong,