diff --git a/llvm/include/llvm/ADT/StringExtras.h b/llvm/include/llvm/ADT/StringExtras.h
--- a/llvm/include/llvm/ADT/StringExtras.h
+++ b/llvm/include/llvm/ADT/StringExtras.h
@@ -312,23 +312,36 @@
 std::string convertToCamelFromSnakeCase(StringRef input,
                                         bool capitalizeFirst = false);
 
-namespace detail {
-
-template <typename IteratorT>
-inline std::string join_impl(IteratorT Begin, IteratorT End,
-                             StringRef Separator, std::input_iterator_tag) {
+template <typename IteratorT, typename UnaryFunction>
+inline std::string join(IteratorT Begin, IteratorT End, StringRef Separator,
+                        UnaryFunction F) {
   std::string S;
   if (Begin == End)
     return S;
 
-  S += (*Begin);
+  S += F(*Begin);
   while (++Begin != End) {
     S += Separator;
-    S += (*Begin);
+    S += F(*Begin);
   }
   return S;
 }
 
+/// Joins the strings in the range [R.begin(), R.end()), adding Separator
+/// between the elements.
+template <typename Range, typename UnaryFunction>
+inline std::string join(Range &&R, StringRef Separator, UnaryFunction F) {
+  return join(R.begin(), R.end(), Separator, F);
+}
+
+namespace detail {
+
+template <typename IteratorT>
+inline std::string join_impl(IteratorT Begin, IteratorT End,
+                             StringRef Separator, std::input_iterator_tag) {
+  return join(Begin, End, Separator, [](auto &&S) { return std::forward(S); });
+}
+
 template <typename IteratorT>
 inline std::string join_impl(IteratorT Begin, IteratorT End,
                              StringRef Separator, std::forward_iterator_tag) {
diff --git a/llvm/unittests/ADT/StringExtrasTest.cpp b/llvm/unittests/ADT/StringExtrasTest.cpp
--- a/llvm/unittests/ADT/StringExtrasTest.cpp
+++ b/llvm/unittests/ADT/StringExtrasTest.cpp
@@ -47,6 +47,19 @@
   Items = {"foo", "bar", "baz"};
   EXPECT_EQ("foo <sep> bar <sep> baz",
             join(Items.begin(), Items.end(), " <sep> "));
+
+  std::vector<unsigned> Integers = {1, 2, 3};
+  EXPECT_EQ("1 <sep> 2 <sep> 3",
+            join(Integers.begin(), Integers.end(), " <sep> ",
+                 [](auto I) { return StringRef(utostr(I)); }));
+
+  Integers = {4, 5, 6};
+  EXPECT_EQ("4 <sep> 5 <sep> 6", join(Integers, " <sep> ", [](auto I) {
+              return StringRef(utostr(I));
+            }));
+  EXPECT_EQ("4 <sep> 5 <sep> 6",
+            join(std::move(Integers), " <sep> ",
+                 [](auto I) { return StringRef(utostr(I)); }));
 }
 
 TEST(StringExtrasTest, JoinItems) {