[Bug ipa/71207] [5/6/7 Regression] gcc 5.3 and 6.1 generates wrong code with -O2

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71207

--- Comment #6 from Martin Liška <marxin at gcc dot gnu.org> ---
Created attachment 40512
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40512&action=edit
Patch candidate

Btw. I really believe this should be marked as P1 because it creates invalid
builtin_unreachable calls.