In generating the code for symmetric transfer, a temporary object is created to store the returned handle from await_suspend() call of the awaiter. Previously this temp won't be cleaned up until very later, which ends up causing this temp to be spilled to the heap. However, we know that this temp will no longer be needed after we obtained the address. We can clean it up right after the call to address member.
I don't know that much about the code-generation here, but when cleanups escape into a surrounding scope, you can usually test that the cleanup is emitted before some call tied to a later statement in that scope. You don't have to test for every last instruction in the function.