[PATCH v2] gimple ssa: Teach switch conversion to optimize powers of 2 switches

[Filip Kastl]

> Meanwhile I'll look into source code of the rest of the switch conversion pass.
> Switch conversion pass inserts conditions similar to what I'm doing so someone
> before me may have already solved how to properly fix dominators in this
> situation.

Oh nevermind.  Switch conversion (gen_inbound_check ()) actually uses
iterate_fix_dominators.