[PATCH] D51741: [coro]Pass rvalue reference for named local variable to return_value

[Tanoy Sinha via Phabricator via cfe-commits]

tks2103 updated this revision to Diff 164265.
tks2103 added a comment.

get NRVOCandidate to determine if we should try to move return var


Repository:
  rC Clang

https://reviews.llvm.org/D51741

Files:
  lib/Sema/SemaCoroutine.cpp
  test/SemaCXX/coroutine-rvo.cpp


Index: test/SemaCXX/coroutine-rvo.cpp
===================================================================
--- /dev/null
+++ test/SemaCXX/coroutine-rvo.cpp
@@ -0,0 +1,69 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin9 %s -stdlib=libc++ -std=c++1z -fcoroutines-ts -fsyntax-only
+
+namespace std::experimental {
+template <class Promise = void> struct coroutine_handle {
+  coroutine_handle() = default;
+  static coroutine_handle from_address(void *) noexcept;
+};
+
+template <> struct coroutine_handle<void> {
+  static coroutine_handle from_address(void *) noexcept;
+  coroutine_handle() = default;
+  template <class PromiseType>
+  coroutine_handle(coroutine_handle<PromiseType>) noexcept;
+};
+
+template <class... Args>
+struct void_t_imp {
+  using type = void;
+};
+template <class... Args>
+using void_t = typename void_t_imp<Args...>::type;
+
+template <class T, class = void>
+struct traits_sfinae_base {};
+
+template <class T>
+struct traits_sfinae_base<T, void_t<typename T::promise_type>> {
+  using promise_type = typename T::promise_type;
+};
+
+template <class Ret, class... Args>
+struct coroutine_traits : public traits_sfinae_base<Ret> {};
+}
+
+struct suspend_never {
+  bool await_ready() noexcept;
+  void await_suspend(std::experimental::coroutine_handle<>) noexcept;
+  void await_resume() noexcept;
+};
+
+struct MoveOnly {
+  MoveOnly() {};
+  MoveOnly(const MoveOnly&) = delete;
+  MoveOnly(MoveOnly&&) noexcept {};
+  ~MoveOnly() {};
+};
+
+template <typename T>
+struct task {
+  struct promise_type {
+    auto initial_suspend() { return suspend_never{}; }
+    auto final_suspend() { return suspend_never{}; }
+    auto get_return_object() { return task{}; }
+    static void unhandled_exception() {}
+    void return_value(T&& value) {}
+  };
+};
+
+task<MoveOnly> f() {
+  MoveOnly value;
+  co_return value;
+}
+
+int main() {
+  f();
+  return 0;
+}
+
+// expected-no-diagnostics
Index: lib/Sema/SemaCoroutine.cpp
===================================================================
--- lib/Sema/SemaCoroutine.cpp
+++ lib/Sema/SemaCoroutine.cpp
@@ -841,6 +841,19 @@
     E = R.get();
   }
 
+  // Move the return value if we can
+  if (E) {
+    auto NRVOCandidate = this->getCopyElisionCandidate(E->getType(), E, CES_AsIfByStdMove);
+    if (NRVOCandidate) {
+      InitializedEntity Entity =
+          InitializedEntity::InitializeResult(Loc, E->getType(), NRVOCandidate);
+      ExprResult MoveResult =
+          this->PerformMoveOrCopyInitialization(Entity, NRVOCandidate, E->getType(), E);
+      if (MoveResult.get())
+        E = MoveResult.get();
+    }
+  }
+
   // FIXME: If the operand is a reference to a variable that's about to go out
   // of scope, we should treat the operand as an xvalue for this overload
   // resolution.


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