coroutines : Remove throwing_cleanup marks from the ramp [PR95822].

The FE contains a mechanism for cleaning up return expressions if a
function throws during the execution of cleanups prior to the return.

If the original function has a return value with a non-trivial DTOR
and the body contains a var with a DTOR that might throw, the function
decl is marked "throwing_cleanup".

However, we do not [in the coroutine ramp function, which is
synthesised], use any body var types with DTORs that might throw.

The original body [which will then contain the type with the throwing
DTOR] is transformed into the actor function which only contains void
returns, and is also wrapped in a try-catch block.

So (a) the 'throwing_cleanup' is no longer correct for the ramp and
   (b) we do not need to transfer it to the actor which only contains
       void returns.

gcc/cp/ChangeLog:

	PR c++/95822
	* coroutines.cc (morph_fn_to_coro): Unconditionally remove any
	set throwing_cleanup marker.

gcc/testsuite/ChangeLog:

	PR c++/95822
	* g++.dg/coroutines/pr95822.C: New test.

gcc/cp/coroutines.cc

@@ -4029,6 +4029,17 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
       TREE_OPERAND (body_start, 0) = push_stmt_list ();
     }
 
+  /* If the original function has a return value with a non-trivial DTOR
+     and the body contains a var with a DTOR that might throw, the decl is
+     marked "throwing_cleanup".
+     We do not [in the ramp, which is synthesised here], use any body var
+     types with DTORs that might throw.
+     The original body is transformed into the actor function which only
+     contains void returns, and is also wrapped in a try-catch block.
+     So (a) the 'throwing_cleanup' is not correct for the ramp and (b) we do
+     not need to transfer it to the actor which only contains void returns.  */
+  cp_function_chain->throwing_cleanup = false;
+
   /* Create the coro frame type, as far as it can be known at this stage.
      1. Types we already know.  */
 

gcc/testsuite/g++.dg/coroutines/pr95822.C

@@ -0,0 +1,29 @@
+#include <coroutine>
+
+struct task {
+  struct promise_type {
+    auto initial_suspend() noexcept { return std::suspend_always{}; }
+    auto final_suspend() noexcept { return std::suspend_always{}; }
+    void return_void() {}
+    task get_return_object() { return task{}; }
+    void unhandled_exception() noexcept {}
+  };
+
+  ~task() noexcept {}
+
+  bool await_ready() const noexcept { return false; }
+  void await_suspend(std::coroutine_handle<>) noexcept {}
+  void await_resume() noexcept {}
+};
+
+struct Error {
+   Error() { };
+  ~Error() noexcept(false) {}
+};
+
+task g();
+
+task f() {
+  Error error;
+  co_await g();
+}