Index: include/clang/AST/Decl.h
===================================================================
--- include/clang/AST/Decl.h
+++ include/clang/AST/Decl.h
@@ -1599,6 +1599,7 @@
   unsigned HasImplicitReturnZero : 1;
   unsigned IsLateTemplateParsed : 1;
   unsigned IsConstexpr : 1;
+  unsigned IsMarkedForPendingInstantiation : 1;
 
   /// \brief Indicates if the function uses __try.
   unsigned UsesSEHTry : 1;
@@ -1691,7 +1692,8 @@
       HasWrittenPrototype(true), IsDeleted(false), IsTrivial(false),
       IsDefaulted(false), IsExplicitlyDefaulted(false),
       HasImplicitReturnZero(false), IsLateTemplateParsed(false),
-      IsConstexpr(isConstexprSpecified), UsesSEHTry(false),
+      IsConstexpr(isConstexprSpecified),
+      IsMarkedForPendingInstantiation(false), UsesSEHTry(false),
       HasSkippedBody(false), EndRangeLoc(NameInfo.getEndLoc()),
       TemplateOrSpecialization(),
       DNLoc(NameInfo.getInfo()) {}
@@ -1872,6 +1874,15 @@
   bool isConstexpr() const { return IsConstexpr; }
   void setConstexpr(bool IC) { IsConstexpr = IC; }
 
+  /// \brief Whether this function has been put on the pending instatiations
+  /// list.
+  bool isMarkedForPendingInstantiation() const {
+    return IsMarkedForPendingInstantiation;
+  }
+  void setMarkedForPendingInstantiation(bool IM = true) {
+    IsMarkedForPendingInstantiation = IM;
+  }
+
   /// \brief Indicates the function uses __try.
   bool usesSEHTry() const { return UsesSEHTry; }
   void setUsesSEHTry(bool UST) { UsesSEHTry = UST; }
Index: lib/CodeGen/CGClass.cpp
===================================================================
--- lib/CodeGen/CGClass.cpp
+++ lib/CodeGen/CGClass.cpp
@@ -2874,10 +2874,16 @@
 
   // We can devirtualize calls on an object accessed by a class member access
   // expression, since by C++11 [basic.life]p6 we know that it can't refer to
-  // a derived class object constructed in the same location.
+  // a derived class object constructed in the same location. However, we avoid
+  // devirtualizing a call to a function that can be instantiated implicitly,
+  // unless we know that we will be instantiating it in this TU. If this
+  // function does not get instantiated, the devirtualization will create a
+  // direct call to a function whose body may not exist.
   if (const MemberExpr *ME = dyn_cast<MemberExpr>(Base))
     if (const ValueDecl *VD = dyn_cast<ValueDecl>(ME->getMemberDecl()))
-      return VD->getType()->isRecordType();
+      return VD->getType()->isRecordType() &&
+                  (MD->isMarkedForPendingInstantiation() ||
+                   !MD->isImplicitlyInstantiable());
 
   // We can always devirtualize calls on temporary object expressions.
   if (isa<CXXConstructExpr>(Base))
Index: lib/Sema/Sema.cpp
===================================================================
--- lib/Sema/Sema.cpp
+++ lib/Sema/Sema.cpp
@@ -680,6 +680,9 @@
       // Load pending instantiations from the external source.
       SmallVector<PendingImplicitInstantiation, 4> Pending;
       ExternalSource->ReadPendingInstantiations(Pending);
+      for (auto PII : Pending) 
+        if (FunctionDecl *Func = dyn_cast<FunctionDecl>(PII.first))
+          Func->setMarkedForPendingInstantiation();
       PendingInstantiations.insert(PendingInstantiations.begin(),
                                    Pending.begin(), Pending.end());
     }
Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -13082,6 +13082,7 @@
         // call to such a function.
         InstantiateFunctionDefinition(PointOfInstantiation, Func);
       else {
+        Func->setMarkedForPendingInstantiation();
         PendingInstantiations.push_back(std::make_pair(Func,
                                                        PointOfInstantiation));
         // Notify the consumer that a function was implicitly instantiated.
Index: lib/Sema/SemaTemplateInstantiateDecl.cpp
===================================================================
--- lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -3531,6 +3531,7 @@
   // Postpone late parsed template instantiations.
   if (PatternDecl->isLateTemplateParsed() &&
       !LateTemplateParser) {
+    Function->setMarkedForPendingInstantiation();
     PendingInstantiations.push_back(
       std::make_pair(Function, PointOfInstantiation));
     return;
@@ -3582,6 +3583,7 @@
     } else if (Function->getTemplateSpecializationKind()
                  == TSK_ExplicitInstantiationDefinition) {
       assert(!Recursive);
+      Function->setMarkedForPendingInstantiation();
       PendingInstantiations.push_back(
         std::make_pair(Function, PointOfInstantiation));
     } else if (Function->getTemplateSpecializationKind()
Index: test/CodeGen/no-devirt.cpp
===================================================================
--- test/CodeGen/no-devirt.cpp
+++ test/CodeGen/no-devirt.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 %s -triple %itanium_abi_triple -emit-llvm -o - | FileCheck %s
+template < typename T, int N = 0 > class TmplWithArray {
+public:
+  virtual T& operator [] (int idx);
+  virtual T& func1 (int idx);
+  virtual T& func2 (int idx);
+  T ar[N+1];
+};
+class Wrapper {
+  TmplWithArray<bool, 10> data;
+  bool indexIt(int a);
+};
+bool Wrapper::indexIt(int a)
+{
+   if (a > 6) return data[a] ;      // Should not devirtualize
+   if (a > 4) return data.func1(a); // Should devirtualize
+   return data.func2(a);            // Should devirtualize
+}
+template <typename T, int N> T& TmplWithArray<T, N >::operator[](int idx) {
+  return ar[idx];
+}
+template <typename T, int N> T& TmplWithArray<T, N >::func1(int idx) {
+  return ar[idx];
+}
+// CHECK-NOT: call {{.*}} @_ZN13TmplWithArrayIbLi10EEixEi
+// CHECK-DAG: call {{.*}} @_ZN13TmplWithArrayIbLi10EE5func1Ei
+// CHECK-DAG: call {{.*}} @_ZN13TmplWithArrayIbLi10EE5func2Ei