[Bug tree-optimization/78731] Possible bug with switch when optimization is turned on.

["wilson at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78731

--- Comment #2 from Jim Wilson <wilson at gcc dot gnu.org> ---
The compiler is failing in jump threading as called by dom2.  Jeff's 2015-09-30
patch is triggering in dom1, and changing the CFG just enough to prevent the
jump threading bug from triggering.  So it isn't a proper fix.

Disabling it, and bisecting again, I found bug 67892, another patch from Jeff,
which looks like a proper fix.  However, there is a problem.  The bug was
reported against gcc 5, fixed in gcc 6, and then closed, but is still broken in
gcc 5.  I think it is in the wrong state.  Presumably, it should still be open,
and then fixed in gcc 5 if reasonably safe, or documented as a known bug that
we won't fix in gcc 5.