Move TensorOptions ops to c10 (#39492)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39492
This PR adds use_c10_dispatcher: full to ops taking TensorOptions. To allow this, since the c10 operator library doesn't know about TensorOptions, we need to register the operator kernels as optional<ScalarType>, optional<Device>, optional<Layout>, optional<bool> instead, and also call them this way.
Changes:
Add use_c10_dispatcher: full to those ops
Write hacky_wrapper_for_legacy_signatures which takes an old-style kernel (i.e. one written to take TensorOptions) an creates a wrapper kernel for it that takes the scattered optional<ScalarType>, optional<Device>, optional<Layout>, optional<bool> instead.
Change codegen so that all op registrations are wrapped into hacky_wrapper_for_legacy_signatures. This is added to all ops but is a no-op if the op doesn't take TensorOptions. This allows us in the future to just change a kernel signature from TensorOptions to the scattered version and have it work without having to touch codegen.
Change codegen so that the frontend calls those operators with expanded arguments instead of with a TensorOptions object. This is required because now the kernels are written in this way.
This PR does not remove TensorOptions special cases from codegen, but instead it separates kernels from the codegen/frontend issues. After this, kernels can be worked on separately without having to touch codegen and codegen can be worked on without having to touch kernels.
Codegen diff: P133121032
ghstack-source-id: 106426630
Test Plan: waitforsandcastle
Differential Revision: D21581908
fbshipit-source-id: 6d4a9f526fd70fae40581bf26f3ccf794ce6a89e
