Back out "Back out "[Caffe2] Fix device_option propagation"" (#25908)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25908
Original commit changeset: f6e961e88c01
device_option propagation is completely broken in Caffe2 for cases when pass through operators are used. As an example Gather operator don't have gradient and passes through it's inputs, which results in incorrect detection of the components for sparse parameter aggregation (component will be empty instead of the real device).
This diff is trying to fix this issue.
Original diff had a problem, that Caffe2 is not handling cases when device option is present, but contains only metadata (for example one for auto-generated reduction ops in backward pass). This diff is addressing this issue by merging device options during the backward pass
Test Plan:
1. net_transform is finally working with Gather + FloatToHalf transformed model instead of failing because of incorrect number of components.
2. New unit-test.
3. Verify that previously broken benchmark is now passing
ezyang do you have suggestions what else I should test?
Reviewed By: ezyang
Differential Revision: D17281528
fbshipit-source-id: 4a1bc386f29f6a34fbf8008effde9d4890abebfa
