Index: include/llvm/Analysis/MemorySSAUpdater.h
===================================================================
--- include/llvm/Analysis/MemorySSAUpdater.h
+++ include/llvm/Analysis/MemorySSAUpdater.h
@@ -60,6 +60,7 @@
   MemorySSA *MSSA;
   SmallVector<MemoryPhi *, 8> InsertedPHIs;
   SmallPtrSet<BasicBlock *, 8> VisitedBlocks;
+  SmallPtrSet<MemoryPhi *, 8> NonOptPhis;
 
 public:
   MemorySSAUpdater(MemorySSA *MSSA) : MSSA(MSSA) {}
Index: lib/Analysis/MemorySSA.cpp
===================================================================
--- lib/Analysis/MemorySSA.cpp
+++ lib/Analysis/MemorySSA.cpp
@@ -1415,7 +1415,7 @@
     auto *Defs = getOrCreateDefsList(BB);
     // If we got asked to insert at the end, we have an easy job, just shove it
     // at the end. If we got asked to insert before an existing def, we also get
-    // an terator. If we got asked to insert before a use, we have to hunt for
+    // an iterator. If we got asked to insert before a use, we have to hunt for
     // the next def.
     if (WasEnd) {
       Defs->push_back(*What);
@@ -1434,7 +1434,7 @@
   BlockNumberingValid.erase(BB);
 }
 
-// Move What before Where in the IR.  The end result is taht What will belong to
+// Move What before Where in the IR.  The end result is that What will belong to
 // the right lists and have the right Block set, but will not otherwise be
 // correct. It will not have the right defining access, and if it is a def,
 // things below it will not properly be updated.
Index: lib/Analysis/MemorySSAUpdater.cpp
===================================================================
--- lib/Analysis/MemorySSAUpdater.cpp
+++ lib/Analysis/MemorySSAUpdater.cpp
@@ -165,6 +165,10 @@
 template <class RangeType>
 MemoryAccess *MemorySSAUpdater::tryRemoveTrivialPhi(MemoryPhi *Phi,
                                                     RangeType &Operands) {
+  // Bail out on non-opt Phis.
+  if (NonOptPhis.count(Phi))
+    return Phi;
+
   // Detect equal or self arguments
   MemoryAccess *Same = nullptr;
   for (auto &Op : Operands) {
@@ -307,6 +311,11 @@
     auto *Defs = MSSA->getWritableBlockDefs(NewDef->getBlock());
     auto DefIter = NewDef->getDefsIterator();
 
+    // The temporary Phi is being fixed, unmark it for not to optimize.
+    if (MemoryPhi *Phi = dyn_cast_or_null<MemoryPhi>(NewDef))
+      if (NonOptPhis.count(Phi))
+        NonOptPhis.erase(Phi);
+
     // If there is a local def after us, we only have to rename that.
     if (++DefIter != Defs->end()) {
       cast<MemoryDef>(DefIter)->setDefiningAccess(NewDef);
@@ -366,6 +375,11 @@
 template <class WhereType>
 void MemorySSAUpdater::moveTo(MemoryUseOrDef *What, BasicBlock *BB,
                               WhereType Where) {
+  // Mark MemoryPhi users of What not to be optimized.
+  for (auto *U : What->users())
+    if (MemoryPhi *PhiUser = dyn_cast_or_null<MemoryPhi>(U))
+      NonOptPhis.insert(PhiUser);
+
   // Replace all our users with our defining access.
   What->replaceAllUsesWith(What->getDefiningAccess());
 
Index: test/Transforms/GVNHoist/non-trivial-phi.ll
===================================================================
--- /dev/null
+++ test/Transforms/GVNHoist/non-trivial-phi.ll
@@ -0,0 +1,34 @@
+; RUN: opt -gvn-hoist %s -S -o - | FileCheck %s
+
+; CHECK: store
+; CHECK-NOT: store
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+
+define void @f(i8* %p) {
+entry:
+  switch i4 undef, label %if.then30 [
+    i4 4, label %if.end
+    i4 0, label %if.end
+  ]
+
+if.end:
+  br label %if.end19
+
+if.end19:
+  br i1 undef, label %e, label %e.thread
+
+e.thread:
+  store i8 0, i8* %p, align 4
+  br label %if.then30
+
+if.then30:
+  call void @g()
+  unreachable
+
+e:
+  store i8 0, i8* %p, align 4
+  unreachable
+}
+
+declare void @g()