Save the weight shape info the first time we have chance to extract it (#21233)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21233
It is possible that OnnxifiOp is created in a thread where weights have been cleaned from the workspace, which is legit use case as we can create the backend once and lower all the weights. So we need to extract the weight shape info the first time we create the backend and save it.
Reviewed By: bertmaher, rdzhabarov
Differential Revision: D15587237
fbshipit-source-id: 1f264dc32c0398c42b618e9c41c119eb13e1c9f1
