Index: llvm/include/llvm/ADT/STLExtras.h
===================================================================
--- llvm/include/llvm/ADT/STLExtras.h
+++ llvm/include/llvm/ADT/STLExtras.h
@@ -285,15 +285,16 @@
 
 template <typename ItTy, typename FuncTy,
           typename FuncReturnTy =
-            decltype(std::declval<FuncTy>()(*std::declval<ItTy>()))>
+              decltype(std::declval<FuncTy>()(*std::declval<ItTy>())),
+          bool IsReference = std::is_reference<FuncReturnTy>::value>
 class mapped_iterator
     : public iterator_adaptor_base<
-             mapped_iterator<ItTy, FuncTy>, ItTy,
-             typename std::iterator_traits<ItTy>::iterator_category,
-             typename std::remove_reference<FuncReturnTy>::type> {
+          mapped_iterator<ItTy, FuncTy>, ItTy,
+          typename std::iterator_traits<ItTy>::iterator_category,
+          typename std::remove_reference<FuncReturnTy>::type> {
 public:
   mapped_iterator(ItTy U, FuncTy F)
-    : mapped_iterator::iterator_adaptor_base(std::move(U)), F(std::move(F)) {}
+      : mapped_iterator::iterator_adaptor_base(std::move(U)), F(std::move(F)) {}
 
   ItTy getCurrent() { return this->I; }
 
@@ -303,6 +304,29 @@
   FuncTy F;
 };
 
+template <typename ItTy, typename FuncTy>
+class mapped_iterator<ItTy, FuncTy,
+                      decltype(std::declval<FuncTy>()(*std::declval<ItTy>())),
+                      false>
+    : public iterator_adaptor_base<
+          mapped_iterator<ItTy, FuncTy>, ItTy,
+          typename std::iterator_traits<ItTy>::iterator_category,
+          decltype(std::declval<FuncTy>()(*std::declval<ItTy>()))> {
+public:
+  mapped_iterator(ItTy U, FuncTy F)
+      : mapped_iterator::iterator_adaptor_base(std::move(U)), F(std::move(F)) {}
+
+  ItTy getCurrent() { return this->I; }
+
+  typename mapped_iterator::iterator_adaptor_base::reference operator*() const {
+    return V = F(*this->I);
+  }
+
+private:
+  FuncTy F;
+  mutable typename mapped_iterator::iterator_adaptor_base::value_type V;
+};
+
 // map_iterator - Provide a convenient way to create mapped_iterators, just like
 // make_pair is useful for creating pairs...
 template <class ItTy, class FuncTy>