[Bug tree-optimization/40748] simple switch/case, if/else and arithmetics result in different code

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40748

--- Comment #7 from Martin Liška <marxin at gcc dot gnu.org> ---
> {
>       if (i == 0) return 0;
>       if (i == 1) return 1;
>       if (i == 2) return 2;
>       if (i == 3) return 3;
>       if (i == 4) return 4;
>       if (i == 5) return 4;
>       if (i == 6) return 4;
>       return 4;
> }

Here we produce:

  <bb 2> [local count: 1073741824]:
  if (i_2(D) <= 6)
    goto <bb 3>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 3> [local count: 536870913]:
  _4 = CSWTCH.1[i_2(D)];

  <bb 4> [local count: 1073741824]:
  # _1 = PHI <4(2), _4(3)>
  return _1;

Am I right that we can do better with:

  if (i_2(D) <= 3)
...