[Bug target/61837] missed loop invariant expression optimization

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61837

--- Comment #8 from Segher Boessenkool <segher at gcc dot gnu.org> ---
-funswitch-loops changes things like

  for (...) {
    if (...)
      ...1;
    else
      ...2;
  }

into

  if (...) {
    for (...)
      ...1;
  } else {
    for (...)
      ...2;
  }

which often is not a good idea.  This is why this is not done at -O2:
-O2 is only for optimisations that almost never hurt performance.