swift

a87a78c0 - [simplify-cfg] When determining/searching for the end of a switch_enums diamond using single successors, make sure we do not have single block self-loop.

[simplify-cfg] When determining/searching for the end of a switch_enums diamond using single successors, make sure we do not have single block self-loop. Otherwise, we infinite loop. rdar://52131975 (cherry picked from commit 378c6adbd625f1c1f568fa28116be3335506082f)