Index: lib/Analysis/BasicAliasAnalysis.cpp
===================================================================
--- lib/Analysis/BasicAliasAnalysis.cpp
+++ lib/Analysis/BasicAliasAnalysis.cpp
@@ -1536,6 +1536,10 @@
       V1Srcs.push_back(PV1);
   }
 
+  // It's possible for a phi in unreachable code to have no inputs.
+  if (V1Srcs.empty())
+    return MayAlias;
+
   // If this PHI node is recursive, set the size of the accessed memory to
   // unknown to represent all the possible values the GEP could advance the
   // pointer to.