[Bug libstdc++/109205] vector.resize( v.size() + 100 ) does unnecessary comparison

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109205

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So the IR looks like:
  _4 = MEM[(const struct vector *)v_3(D)].D.25711._M_impl.D.25018._M_finish;
  _6 = MEM[(const struct vector *)v_3(D)].D.25711._M_impl.D.25018._M_start;
  _7 = _4 - _6;
  _8 = (long unsigned int) _7;
  _1 = _8 + 100;

GCC does not know this statement holds true:
  if (v.end() < v.begin()) __builtin_unreachable();

If you add that, then it will optimize away the comparison.