Index: include/llvm/Support/Error.h
===================================================================
--- include/llvm/Support/Error.h
+++ include/llvm/Support/Error.h
@@ -302,6 +302,14 @@
     return Tmp;
   }
 
+  friend raw_ostream &operator<<(raw_ostream &OS, const Error &E) {
+    if (auto P = E.getPtr())
+      P->log(OS);
+    else
+      OS << "success";
+    return OS;
+  }
+
   ErrorInfoBase *Payload = nullptr;
 };
 
Index: include/llvm/Support/FormatVariadic.h
===================================================================
--- include/llvm/Support/FormatVariadic.h
+++ include/llvm/Support/FormatVariadic.h
@@ -237,6 +237,8 @@
 //      for type T containing a method whose signature is:
 //      void format(const T &Obj, raw_ostream &Stream, StringRef Options)
 //      Then this method is invoked as described in Step 1.
+//   3. If an appropriate operator<< for raw_ostream exists, it will be used.
+//      For this to work, (raw_ostream& << const T&) must return raw_ostream&.
 //
 // If a match cannot be found through either of the above methods, a compiler
 // error is generated.
@@ -258,13 +260,6 @@
       std::make_tuple(detail::build_format_adapter(std::forward<Ts>(Vals))...));
 }
 
-// Allow a formatv_object to be formatted (no options supported).
-template <typename T> struct format_provider<formatv_object<T>> {
-  static void format(const formatv_object<T> &V, raw_ostream &OS, StringRef) {
-    OS << V;
-  }
-};
-
 } // end namespace llvm
 
 #endif // LLVM_SUPPORT_FORMATVARIADIC_H
Index: include/llvm/Support/FormatVariadicDetails.h
===================================================================
--- include/llvm/Support/FormatVariadicDetails.h
+++ include/llvm/Support/FormatVariadicDetails.h
@@ -38,6 +38,17 @@
   }
 };
 
+template <typename T>
+class stream_operator_format_adapter : public format_adapter {
+  T Item;
+
+public:
+  explicit stream_operator_format_adapter(T &&Item)
+      : Item(std::forward<T>(Item)) {}
+
+  void format(llvm::raw_ostream &S, StringRef Options) override { S << Item; }
+};
+
 template <typename T> class missing_format_adapter;
 
 // Test if format_provider<T> is defined on T and contains a member function
@@ -59,6 +70,23 @@
       (sizeof(test<llvm::format_provider<Decayed>>(nullptr)) == 1);
 };
 
+// Test if raw_ostream& << T -> raw_ostream& is findable via ADL.
+template <class T> class has_StreamOperator {
+public:
+  using ConstRefT = const typename std::decay<T>::type &;
+
+  template <typename U>
+  static char test(typename std::enable_if<
+                   std::is_same<decltype(std::declval<llvm::raw_ostream &>()
+                                         << std::declval<U>()),
+                                llvm::raw_ostream &>::value,
+                   int *>::type);
+
+  template <typename U> static double test(...);
+
+  static bool const value = (sizeof(test<ConstRefT>(nullptr)) == 1);
+};
+
 // Simple template that decides whether a type T should use the member-function
 // based format() invocation.
 template <typename T>
@@ -77,15 +105,24 @@
           bool, !uses_format_member<T>::value && has_FormatProvider<T>::value> {
 };
 
+// Simple template that decides whether a type T should use the operator<<
+// based format() invocation.  This takes last priority.
+template <typename T>
+struct uses_stream_operator
+    : public std::integral_constant<bool, !uses_format_member<T>::value &&
+                                              !uses_format_provider<T>::value &&
+                                              has_StreamOperator<T>::value> {};
+
 // Simple template that decides whether a type T has neither a member-function
 // nor format_provider based implementation that it can use.  Mostly used so
 // that the compiler spits out a nice diagnostic when a type with no format
 // implementation can be located.
 template <typename T>
 struct uses_missing_provider
-    : public std::integral_constant<bool,
-                                    !uses_format_member<T>::value &&
-                                        !uses_format_provider<T>::value> {};
+    : public std::integral_constant<bool, !uses_format_member<T>::value &&
+                                              !uses_format_provider<T>::value &&
+                                              !uses_stream_operator<T>::value> {
+};
 
 template <typename T>
 typename std::enable_if<uses_format_member<T>::value, T>::type
@@ -100,6 +137,13 @@
   return provider_format_adapter<T>(std::forward<T>(Item));
 }
 
+template <typename T>
+typename std::enable_if<uses_stream_operator<T>::value,
+                        stream_operator_format_adapter<T>>::type
+build_format_adapter(T &&Item) {
+  return stream_operator_format_adapter<T>(std::forward<T>(Item));
+}
+
 template <typename T>
 typename std::enable_if<uses_missing_provider<T>::value,
                         missing_format_adapter<T>>::type
Index: unittests/Support/ErrorTest.cpp
===================================================================
--- unittests/Support/ErrorTest.cpp
+++ unittests/Support/ErrorTest.cpp
@@ -716,6 +716,25 @@
             0);
 }
 
+TEST(Error, Stream) {
+  {
+    Error OK = Error::success();
+    std::string Buf;
+    llvm::raw_string_ostream S(Buf);
+    S << OK;
+    EXPECT_EQ("success", S.str());
+    consumeError(std::move(OK));
+  }
+  {
+    Error E1 = make_error<CustomError>(0);
+    std::string Buf;
+    llvm::raw_string_ostream S(Buf);
+    S << E1;
+    EXPECT_EQ("CustomError { 0}", S.str());
+    consumeError(std::move(E1));
+  }
+}
+
 TEST(Error, ErrorMatchers) {
   EXPECT_THAT_ERROR(Error::success(), Succeeded());
   EXPECT_NONFATAL_FAILURE(
Index: unittests/Support/FormatVariadicTest.cpp
===================================================================
--- unittests/Support/FormatVariadicTest.cpp
+++ unittests/Support/FormatVariadicTest.cpp
@@ -671,3 +671,12 @@
   EXPECT_EQ(0, R.Copied);
   EXPECT_EQ(0, R.Moved);
 }
+
+namespace adl {
+struct X {};
+raw_ostream &operator<<(raw_ostream &OS, const X &) { return OS << "X"; }
+} // namespace adl
+TEST(FormatVariadicTest, FormatStreamable) {
+  adl::X X;
+  EXPECT_EQ("X", formatv("{0}", X).str());
+}