Use macro for reduce on 2d blocks (#16344)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16344
Use macro for reduce on 2d blocks
i-am-not-moving-c2-to-c10
Reviewed By: houseroad
Differential Revision: D13808988
fbshipit-source-id: b68c0fb6079c1b6e203a072083aba7a95c202bc2
