[Bug c++/95615] New: [coroutines] Coroutine frame and promise is leaked if exception thrown from promise.initial_suspend()

["lewissbaker.opensource at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95615

            Bug ID: 95615
           Summary: [coroutines] Coroutine frame and promise is leaked if
                    exception thrown from promise.initial_suspend()
           Product: gcc
           Version: 10.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lewissbaker.opensource at gmail dot com
  Target Milestone: ---

If an exception is thrown from any of the following:
- promise_type constructor
- promise.get_return_object()
- promise.initial_suspend()
- initSuspendAwaitable.await_ready()
- initSuspendAwaitable.await_suspend()

Then I believe the compiler is required to automatically
destroy the promise (if constructor completed successfully),
destroy the return return-object (if get_return_object() completed
successfully) and free the coroutine frame before letting the
exception propagate to the caller.

However, it seems that this cleanup logic is not currently
begin called by GCC in these situations.

For example, see https://godbolt.org/z/kQWjpF which shows the
behaviour when an exception is thrown from promise.initial_suspend()'s
await_suspend() method (other variants are commented out in the code).


The wording described in [dcl.fct.def.coroutine] p5 in conjunction with p11
seems to indicate that the promise object should be destroyed as the
exception propagates out of the coroutine.