Speed up calling an async function that doesn't suspend #161170

Feature or enhancement

Now on await f() Python creates a coroutine object on heap and then calls coro.send(None).

If an async function doesn't suspend (directly or indirectly awaits for non-ready future in asyncio world), the coroutine is still created and send() is still called.
Very many async functions have a happy path that, for example, returns data from a memory buffer and runs I/O only if the buffer is empty. Or get an item from a queue without suspending if the queue is not empty.

The interpreter could emulate this first send(None) on the stack and lazily materialize the coroutine only if an asyc function suspends, or other conditions are met: a coroutine object is explicitly requested with immediate awaiting, C extension calls async function, an instrumentation is applied, etc.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

#91121 propose an alternative approach by introducing a new vectorcall flag.

Linked PRs

• gh-161170: Lazily materialize coroutine objects for immediate awaits #161171