torch.utils.checkpoint.checkpoint + torch.cuda.amp (#49757)
Summary:
Adds a test to orphaned original PR (https://github.com/pytorch/pytorch/pull/40221).
Should fix https://github.com/pytorch/pytorch/issues/49738 and https://github.com/pytorch/pytorch/issues/47183
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49757
Reviewed By: mruberry
Differential Revision: D25689609
Pulled By: ngimel
fbshipit-source-id: 0a6adc11eb98382048ef9a9775e185dcdeff6010
