Expose torch._will_engine_execute_node (#84773)
Addresses: https://github.com/pytorch/pytorch/issues/83617
This PR a way to query the TLS graph task's exec_info which is a map mapping the Node to a bool indicating whether it will be executed in the current backward pass (as determined by the inputs= argument for .grad of .backward).
- this works with both custom Function nodes and normal codegened nodes
- to be able to verify whether the pyobject passed is an actual node, we now store pointers to PyTypeObjects into a set on registration.
- error out when .backward without inputs= to avoid silently returning True
Alternatives:
- not sure if it is possible to bind to Python from a raw pointer to Node. At least we wouldn't be able to use existing logic, and the Python object should only hold a weak reference to the Node.
- other solutions to the motivating issue seem to require more extensive modification to the engine
See the issue linked for an example of usage
Pull Request resolved: https://github.com/pytorch/pytorch/pull/84773
Approved by: https://github.com/albanD
