[Bug tree-optimization/126906] back threader does not thread paths into unreachable edges but DOM does

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126906

--- Comment #9 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
Created attachment 65478
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=65478&action=edit
Testcase for PR105679