more general fusion logic (#22015)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22015
Previous fusion logic only works for operators back-to-back in the linear order of protobuf file.
This diff generalizes to work for any predecessor-successor operators in the graph without any "interfering" use/def of the related blobs.
Reviewed By: csummersea
Differential Revision: D15916709
fbshipit-source-id: 82fe4911a8250845a8bea3427d1b77ce2442c495
