Undefined Behavior: Long Live Poison!
http://llvm.org/devmtg/2016-11/Slides/Lopes-LongLivePoison.pdf [llvm.org]
2017-01-05 04:49
Replacing undef with poison in llvm. Not a lot of context, unfortunately, for those unfamiliar with llvm internals.
Followup email: http://lists.llvm.org/pipermail/llvm-dev/2016-December/107840.html