Index: include/llvm/Analysis/MemorySSAUpdater.h
===================================================================
--- include/llvm/Analysis/MemorySSAUpdater.h
+++ include/llvm/Analysis/MemorySSAUpdater.h
@@ -261,6 +261,7 @@
   MemoryAccess *recursePhi(MemoryAccess *Phi);
   template <class RangeType>
   MemoryAccess *tryRemoveTrivialPhi(MemoryPhi *Phi, RangeType &Operands);
+  void tryRemoveTrivialPhis(ArrayRef<WeakVH> UpdatedPHIs);
   void fixupDefs(const SmallVectorImpl<WeakVH> &);
   // Clone all uses and defs from BB to NewBB given a 1:1 map of all
   // instructions and blocks cloned, and a map of MemoryPhi : Definition
Index: lib/Analysis/MemorySSAUpdater.cpp
===================================================================
--- lib/Analysis/MemorySSAUpdater.cpp
+++ lib/Analysis/MemorySSAUpdater.cpp
@@ -355,12 +355,9 @@
   }
 
   // Optimize potentially non-minimal phis added in this method.
-  for (unsigned Idx = NewPhiIndex; Idx < NewPhiIndexEnd; ++Idx) {
-    if (auto *MPhi = cast_or_null<MemoryPhi>(InsertedPHIs[Idx])) {
-      auto OperRange = MPhi->operands();
-      tryRemoveTrivialPhi(MPhi, OperRange);
-    }
-  }
+  int NewPhiSize = NewPhiIndexEnd - NewPhiIndex;
+  if (NewPhiSize > 0)
+    tryRemoveTrivialPhis(ArrayRef<WeakVH>(&(InsertedPHIs[NewPhiIndex]), NewPhiSize));
 
   // Now that all fixups are done, rename all uses if we are asked.
   if (RenameUses) {
@@ -1215,6 +1212,14 @@
   }
 }
 
+void MemorySSAUpdater::tryRemoveTrivialPhis(ArrayRef<WeakVH> UpdatedPHIs) {
+  for (auto &VH : UpdatedPHIs)
+    if (auto *MPhi = cast_or_null<MemoryPhi>(VH)) {
+      auto OperRange = MPhi->operands();
+      tryRemoveTrivialPhi(MPhi, OperRange);
+    }
+}
+
 MemoryAccess *MemorySSAUpdater::createMemoryAccessInBB(
     Instruction *I, MemoryAccess *Definition, const BasicBlock *BB,
     MemorySSA::InsertionPlace Point) {