1 files changed, 125 insertions, 0 deletions
diff --git a/llvm/include/llvm/ADT/STLExtras.h b/llvm/include/llvm/ADT/STLExtras.h
index 7c2a147bc88..807ec59061d 100644
--- a/llvm/include/llvm/ADT/STLExtras.h
+++ b/llvm/include/llvm/ADT/STLExtras.h
@@ -55,6 +55,131 @@ struct greater_ptr : public std::binary_function<Ty, Ty, bool> {
   }
 };
 
+/// An efficient, type-erasing, non-owning reference to a callable. This is
+/// intended for use as the type of a function parameter that is not used
+/// after the function in question returns.
+///
+/// This class does not own the callable, so it is not in general safe to store
+/// a function_ref.
+template<typename Fn> class function_ref;
+
+#if LLVM_HAS_VARIADIC_TEMPLATES
+
+template<typename Ret, typename ...Params>
+class function_ref<Ret(Params...)> {
+  Ret (*callback)(void *callable, Params ...params);
+  void *callable;
+
+  template<typename Callable>
+  static Ret callback_fn(void *callable, Params ...params) {
+    return (*reinterpret_cast<Callable*>(callable))(
+        std::forward<Params>(params)...);
+  }
+
+public:
+  template<typename Callable>
+  function_ref(Callable &&callable)
+      : callback(callback_fn<typename std::remove_reference<Callable>::type>),
+        callable(reinterpret_cast<void *>(&callable)) {}
+  Ret operator()(Params ...params) const {
+    return callback(callable, std::forward<Params>(params)...);
+  }
+};
+
+#else
+
+template<typename Ret>
+class function_ref<Ret()> {
+  Ret (*callback)(void *callable);
+  void *callable;
+
+  template<typename Callable>
+  static Ret callback_fn(void *callable) {
+    return (*reinterpret_cast<Callable*>(callable))();
+  }
+
+public:
+  template<typename Callable>
+  function_ref(Callable &&callable)
+      : callback(callback_fn<typename std::remove_reference<Callable>::type>),
+        callable(reinterpret_cast<void *>(&callable)) {}
+  Ret operator()() const { return callback(callable); }
+};
+
+template<typename Ret, typename Param1>
+class function_ref<Ret(Param1)> {
+  Ret (*callback)(void *callable, Param1 param1);
+  void *callable;
+
+  template<typename Callable>
+  static Ret callback_fn(void *callable, Param1 param1) {
+    return (*reinterpret_cast<Callable*>(callable))(
+        std::forward<Param1>(param1));
+  }
+
+public:
+  template<typename Callable>
+  function_ref(Callable &&callable)
+      : callback(callback_fn<typename std::remove_reference<Callable>::type>),
+        callable(reinterpret_cast<void *>(&callable)) {}
+  Ret operator()(Param1 param1) {
+    return callback(callable, std::forward<Param1>(param1));
+  }
+};
+
+template<typename Ret, typename Param1, typename Param2>
+class function_ref<Ret(Param1, Param2)> {
+  Ret (*callback)(void *callable, Param1 param1, Param2 param2);
+  void *callable;
+
+  template<typename Callable>
+  static Ret callback_fn(void *callable, Param1 param1, Param2 param2) {
+    return (*reinterpret_cast<Callable*>(callable))(
+        std::forward<Param1>(param1),
+        std::forward<Param2>(param2));
+  }
+
+public:
+  template<typename Callable>
+  function_ref(Callable &&callable)
+      : callback(callback_fn<typename std::remove_reference<Callable>::type>),
+        callable(reinterpret_cast<void *>(&callable)) {}
+  Ret operator()(Param1 param1, Param2 param2) {
+    return callback(callable,
+                    std::forward<Param1>(param1),
+                    std::forward<Param2>(param2));
+  }
+};
+
+template<typename Ret, typename Param1, typename Param2, typename Param3>
+class function_ref<Ret(Param1, Param2, Param3)> {
+  Ret (*callback)(void *callable, Param1 param1, Param2 param2, Param3 param3);
+  void *callable;
+
+  template<typename Callable>
+  static Ret callback_fn(void *callable, Param1 param1, Param2 param2,
+                         Param3 param3) {
+    return (*reinterpret_cast<Callable*>(callable))(
+        std::forward<Param1>(param1),
+        std::forward<Param2>(param2),
+        std::forward<Param3>(param3));
+  }
+
+public:
+  template<typename Callable>
+  function_ref(Callable &&callable)
+      : callback(callback_fn<typename std::remove_reference<Callable>::type>),
+        callable(reinterpret_cast<void *>(&callable)) {}
+  Ret operator()(Param1 param1, Param2 param2, Param3 param3) {
+    return callback(callable,
+                    std::forward<Param1>(param1),
+                    std::forward<Param2>(param2),
+                    std::forward<Param3>(param3));
+  }
+};
+
+#endif
+
 // deleter - Very very very simple method that is used to invoke operator
 // delete on something.  It is used like this:
 //