Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4720,6 +4720,15 @@
       return false;
     MapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
 
+    // No more than two unique results can be selected between.
+    if (UniqueResults.size() > 2)
+      return false;
+
+    // No result may have more than one case that selects it.
+    for (const auto &RI : UniqueResults)
+      if (RI.second.size() > 1)
+        return false;
+
     // Check the PHI consistency.
     if (!PHI)
       PHI = Results[0].first;