Index: lib/Analysis/MemorySSA.cpp
===================================================================
--- lib/Analysis/MemorySSA.cpp
+++ lib/Analysis/MemorySSA.cpp
@@ -1690,10 +1690,11 @@
                                                const MemoryUseOrDef *Template) {
   assert(!isa<PHINode>(I) && "Cannot create a defined access for a PHI");
   MemoryUseOrDef *NewAccess = createNewAccess(I, AA, Template);
-  assert(
-      NewAccess != nullptr &&
-      "Tried to create a memory access for a non-memory touching instruction");
-  NewAccess->setDefiningAccess(Definition);
+  if (Template)
+    assert(NewAccess != nullptr && "Tried to create a memory access for a "
+                                   "non-memory touching instruction");
+  if (NewAccess)
+    NewAccess->setDefiningAccess(Definition);
   return NewAccess;
 }
 
Index: lib/Analysis/MemorySSAUpdater.cpp
===================================================================
--- lib/Analysis/MemorySSAUpdater.cpp
+++ lib/Analysis/MemorySSAUpdater.cpp
@@ -484,15 +484,29 @@
                                         const ValueToValueMapTy &VMap,
                                         PhiToDefMap &MPhiMap,
                                         bool CloneWasSimplified) {
-  auto GetNewDefiningAccess = [&](MemoryAccess *MA) -> MemoryAccess * {
+  std::function<MemoryAccess *(MemoryAccess *)> GetNewDefiningAccess =
+      [&](MemoryAccess *MA) -> MemoryAccess * {
     MemoryAccess *InsnDefining = MA;
-    if (MemoryUseOrDef *DefMUD = dyn_cast<MemoryUseOrDef>(InsnDefining)) {
+    if (MemoryDef *DefMUD = dyn_cast<MemoryDef>(InsnDefining)) {
       if (!MSSA->isLiveOnEntryDef(DefMUD)) {
         Instruction *DefMUDI = DefMUD->getMemoryInst();
         assert(DefMUDI && "Found MemoryUseOrDef with no Instruction.");
         if (Instruction *NewDefMUDI =
-                cast_or_null<Instruction>(VMap.lookup(DefMUDI)))
+                cast_or_null<Instruction>(VMap.lookup(DefMUDI))) {
           InsnDefining = MSSA->getMemoryAccess(NewDefMUDI);
+          if (!CloneWasSimplified)
+            assert(InsnDefining && "Defining instruction cannot be nullptr.");
+          else if (!InsnDefining || isa<MemoryUse>(InsnDefining)) {
+            // The clone was simplified, it's no longer a MemoryDef, look up.
+            auto DefIt = DefMUD->getDefsIterator();
+            // Since simplified clones only occur in single block cloning, a
+            // previous definition must exist, otherwise NewDefMUDI would not
+            // have been found in VMap.
+            assert(DefIt != MSSA->getBlockDefs(DefMUD->getBlock())->begin() &&
+                   "Previous def must exist");
+            InsnDefining = GetNewDefiningAccess(&*(--DefIt));
+          }
+        }
       }
     } else {
       MemoryPhi *DefPhi = cast<MemoryPhi>(InsnDefining);
@@ -521,7 +535,8 @@
         MemoryAccess *NewUseOrDef = MSSA->createDefinedAccess(
             NewInsn, GetNewDefiningAccess(MUD->getDefiningAccess()),
             CloneWasSimplified ? nullptr : MUD);
-        MSSA->insertIntoListsForBlock(NewUseOrDef, NewBB, MemorySSA::End);
+        if (NewUseOrDef)
+          MSSA->insertIntoListsForBlock(NewUseOrDef, NewBB, MemorySSA::End);
       }
     }
   }
Index: test/Analysis/MemorySSA/loop-rotate-simplified-clone.ll
===================================================================
--- /dev/null
+++ test/Analysis/MemorySSA/loop-rotate-simplified-clone.ll
@@ -0,0 +1,28 @@
+; RUN: opt -verify-memoryssa -enable-mssa-loop-dependency -loop-rotate %s -S | FileCheck %s 
+
+; CHECK-LABEL: @test()
+define dso_local void @test() {
+entry:
+  br label %preheader
+
+preheader:
+  br label %l39
+
+l39:
+  %v40 = phi float (float)* [ @foo, %preheader ], [ %v43, %crit_edge ]
+  %v41 = call float %v40(float undef)
+  %v42 = load i32, i32* undef, align 8
+  br i1 undef, label %crit_edge, label %loopexit
+
+crit_edge:
+  %v43 = load float (float)*, float (float)** undef, align 8
+  br label %l39
+
+loopexit:
+  unreachable
+}
+
+; Function Attrs: readnone
+declare dso_local float @foo(float) #0 align 32
+
+attributes #0 = { readnone }