[clang] [llvm] [Coroutines] Introduce [[clang::coro_only_destroy_when_complete]] (PR #71014)

[Wei Wang via cfe-commits]

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@@ -0,0 +1,59 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++20 \
+// RUN:     -disable-llvm-passes -emit-llvm %s -o - | FileCheck %s
+
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++20 \
+// RUN:     -O3 -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECK-O
+
+#include "Inputs/coroutine.h"
+
+using namespace std;
+
+struct A;
+struct A_promise_type {
+  A get_return_object();
+  suspend_always initial_suspend();
+  suspend_always final_suspend() noexcept;
+  void return_value(int);
+  void unhandled_exception();
+
+  std::coroutine_handle<> handle;
+};
+
+struct Awaitable{
+  bool await_ready();
+  int await_resume();
+  template <typename F>
+  void await_suspend(F);
+};
+Awaitable something();
+
+struct dtor {
+    dtor();
+    ~dtor();
+};
+
+struct [[clang::coro_only_destroy_when_complete]] A {
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apolloww wrote:

Since the attribute is on the return type, would that mean it would apply to any coroutine returning the particular type? Say user is using some library implementation (i.e. `folly::coro::Task`), they would not be able to use the attribute because it would mark all the coroutines this way.

https://github.com/llvm/llvm-project/pull/71014