[gcc r11-10642] c++: co_await and move-only type [PR105406]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:657fb0db2648a8cd7ba355fdec570fe2f08448ac

commit r11-10642-g657fb0db2648a8cd7ba355fdec570fe2f08448ac
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Mar 15 17:02:15 2023 -0400

    c++: co_await and move-only type [PR105406]
    
    Here we were building a temporary MoveOnlyAwaitable to hold the result of
    evaluating 'o', but since 'o' is an lvalue we should build a reference
    instead.
    
            PR c++/105406
    
    gcc/cp/ChangeLog:
    
            * coroutines.cc (build_co_await): Handle lvalue 'o'.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/coroutines/co-await-moveonly1.C: New test.

Diff:
---
 gcc/cp/coroutines.cc                               |  9 +++-
 .../g++.dg/coroutines/co-await-moveonly1.C         | 63 ++++++++++++++++++++++
 2 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index ea3850082cf..b20e773bff6 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -1016,9 +1016,13 @@ build_co_await (location_t loc, tree a, suspend_point_kind suspend_kind)
     }
   else
     {
-      e_proxy = get_awaitable_var (suspend_kind, o_type);
+      tree p_type = o_type;
+      if (glvalue_p (o))
+	p_type = cp_build_reference_type (p_type, !lvalue_p (o));
+      e_proxy = get_awaitable_var (suspend_kind, p_type);
       o = cp_build_modify_expr (loc, e_proxy, INIT_EXPR, o,
 				tf_warning_or_error);
+      e_proxy = convert_from_reference (e_proxy);
     }
 
   /* I suppose we could check that this is contextually convertible to bool.  */
@@ -1111,6 +1115,9 @@ build_co_await (location_t loc, tree a, suspend_point_kind suspend_kind)
     }
   TREE_VEC_ELT (awaiter_calls, 2) = awrs_call; /* await_resume().  */
 
+  if (REFERENCE_REF_P (e_proxy))
+    e_proxy = TREE_OPERAND (e_proxy, 0);
+
   tree await_expr = build5_loc (loc, CO_AWAIT_EXPR,
 				TREE_TYPE (TREE_TYPE (awrs_func)),
 				a, e_proxy, o, awaiter_calls,
diff --git a/gcc/testsuite/g++.dg/coroutines/co-await-moveonly1.C b/gcc/testsuite/g++.dg/coroutines/co-await-moveonly1.C
new file mode 100644
index 00000000000..e2831c104bf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/co-await-moveonly1.C
@@ -0,0 +1,63 @@
+// PR c++/105406
+// { dg-do compile { target c++20 } }
+
+#include <coroutine>
+#include <exception>
+
+// A move-only awaitable
+class MoveOnlyAwaitable {
+public:
+    MoveOnlyAwaitable() = default;
+    MoveOnlyAwaitable(MoveOnlyAwaitable &&) = default;
+    MoveOnlyAwaitable &operator=(MoveOnlyAwaitable &&) = default;
+
+    MoveOnlyAwaitable(const MoveOnlyAwaitable &) = delete;
+    MoveOnlyAwaitable &operator=(const MoveOnlyAwaitable &) = delete;
+
+    bool await_ready() const noexcept { return false; }
+    void await_suspend(std::coroutine_handle<>) noexcept {}
+    void await_resume() {}
+};
+
+struct task {
+    struct promise_type {
+        auto initial_suspend() const { return std::suspend_never{}; }
+        auto final_suspend() const noexcept { return std::suspend_never(); }
+        auto get_return_object() { return task{}; }
+        void return_void() {}
+        void unhandled_exception() {}
+
+        template<typename T>
+        T &&await_transform(T &&t) {
+            return static_cast<T &&>(t);
+        }
+
+
+    };
+
+    bool await_ready() const { return false; }
+    void await_suspend(std::coroutine_handle<> awaiter) {}
+    void await_resume() {}
+};
+
+task myCoroutine() {
+    // GCC: OK
+    // clang: OK
+    {
+        co_await MoveOnlyAwaitable();
+    }
+    // GCC: OK
+    // clang: OK
+    {
+        auto moveonly = MoveOnlyAwaitable();
+        co_await std::move(moveonly);
+    }
+
+    // GCC <= 11.2: OK
+    // GCC 11.3:ERROR:  error: use of deleted function 'MoveOnlyAwaitable::MoveOnlyAwaitable(const MoveOnlyAwaitable&)
+    // clang: OK
+    {
+        auto moveonly = MoveOnlyAwaitable();
+        co_await moveonly;
+    }
+}