[Bug tree-optimization/121762] pass_fold_builtins and pass_optimize_widening_mul and pass_gimple_isel should be merged or moved other places

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121762

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
>BUILT_IN_UNREACHABLE -> forwprop with late set

I am not even positive this is needed any more can be just removed.  
So basically both VRP and DOM do something about this.

DOM does it via dom_opt_dom_walker::set_global_ranges_from_unreachable_edges  .
And then VRP cleans up the edge.

VRP does it via m_unreachable.maybe_register .

Let me think about this and try to remove it.