diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -576,10 +576,10 @@
   "thread-local storage is not supported for the current target">;
 
 def warn_maybe_falloff_nonvoid_function : Warning<
-  "control may reach end of non-void function">,
+  "not all control paths in this function return a value; non-void function must return a value">,
   InGroup<ReturnType>;
 def warn_falloff_nonvoid_function : Warning<
-  "control reaches end of non-void function">,
+  "function does not return a value; non-void function must return a value">,
   InGroup<ReturnType>;
 def err_maybe_falloff_nonvoid_block : Error<
   "control may reach end of non-void block">;
diff --git a/llvm/lib/IR/LegacyPassManager.cpp b/llvm/lib/IR/LegacyPassManager.cpp
--- a/llvm/lib/IR/LegacyPassManager.cpp
+++ b/llvm/lib/IR/LegacyPassManager.cpp
@@ -1626,13 +1626,12 @@
 /// RequiredPass is run on the fly by Pass Manager when P requests it
 /// through getAnalysis interface.
 void MPPassManager::addLowerLevelRequiredPass(Pass *P, Pass *RequiredPass) {
+  assert(RequiredPass && "No required pass?");
   assert(P->getPotentialPassManagerType() == PMT_ModulePassManager &&
          "Unable to handle Pass that requires lower level Analysis pass");
   assert((P->getPotentialPassManagerType() <
           RequiredPass->getPotentialPassManagerType()) &&
          "Unable to handle Pass that requires lower level Analysis pass");
-  if (!RequiredPass)
-    return;
 
   FunctionPassManagerImpl *FPP = OnTheFlyManagers[P];
   if (!FPP) {