Add manual_cpp_binding to native_functions.yaml (#49092)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49092
Functions which specify manual_cpp_binding don't automatically
get C++ bindings generated for them in TensorBody.h or
Functions.h. This lets end users manually define the bindings
themselves, which may be helpful if there is a way to
short circuit the dispatcher entirely. contiguous() is switched
to use this mechanism.
Although manual_cpp_binding suggests that we don't generate the
binding at all, it is often the case that there is some "fast
path", but when this path is not satisfied, we should go back
to the slow dispatch. So we still generate a fallback method/function
which the user-defined binding can call into in case that we
have to go slowpath.
The correctness conditions for bindings manually written in this
way are subtle. Here are the ones I can think of off the top
of my head:
- Whatever condition is tested in the C++ body, must ALSO be
tested again in the native:: implementation on the other
side of the dispatcher. This is because you are NOT GUARANTEED
to hit the native:: implementation through the C++ binding,
you may go straight to the implementation via a boxed call.
- If a binding is written in this way, it is only safe to
skip dispatch if you would have returned the same tensor as
before. In any situation you would return a fresh tensor,
you MUST go to the slow path, because you need to actually
get to the autograd kernel.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Reviewed By: bhosmer
Differential Revision: D25428440
Pulled By: swolchok
fbshipit-source-id: 6e71767cb8d1086d56cd827c1d2d56cac8f6f5fe
