Support nn.Module forward hooks in torchdynamo (#92125)
Tweak dynamo behavior in 2 places when calling nn.Modules,
to route the call to __call__ instead of .forward(), since
__call__ is the codepath that eager users hit and will dispatch
to hooks correctly.
(1) inside NNModuleVariable.call_function, which covers the common case
of calling a module from code dynamo is already tracing
(2) at the OptimizedModule layer, which is the entrypoint
into a top-level nn.Module dynamo is about to compile
This exposes a new bug: NNModuleVariable used to special-case calling
module.forward() (which is a method) as a UserFunctionVariable with an extra
'self' arg. After tracing into module.__call__, there is no longer a special
case for the eventual call into .forward, and it gets wrapped in a
UserDefinedObjectVariable following standard behavior of ._wrap(). UDOV can't be
called, so this broke some tests.
- Fix: add a new special case in _wrap() that treats methods as a UserDefinedMethod
instead of UserDefinedObjectVariable. Now, the forward method can be called.
Also, fix NNModuleVar.call_method routing forward back to __call__
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92125
Approved by: https://github.com/ezyang, https://github.com/jansel, https://github.com/voznesenskym
