[GitHub] [incubator-mxnet] samskalicky commented on pull request #19812: [2.0.alpha] fixed backend_opts to be empty dictionary instead of None

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samskalicky commented on pull request #19812:
URL: https://github.com/apache/incubator-mxnet/pull/19812#issuecomment-771234624


   > Thank you! Could you please add a test? It looks like this was completely untested?
   
   Looking at the flow, it seems to only happen when calling `optimize_for` twice. After each call the `backend` and `backend_opts` are cleared:
   https://github.com/apache/incubator-mxnet/blob/49edbfc82cb0ce3b823051e1acc26388bc79686c/python/mxnet/gluon/block.py#L1398-L1401
   
   And then the "clearing" sets the `backend_opts` to None. So on the 2nd call, if the user does not provide any options it would run into this scenario. In the lib_subgraph extensions example we call optimize_for once to partition, and then a 2nd time to run a graph pass:
   https://github.com/apache/incubator-mxnet/blob/49edbfc82cb0ce3b823051e1acc26388bc79686c/example/extensions/lib_subgraph/test_subgraph.py#L65-L78
   
   But in the unittests, we only use the `default` subgraph backends:
   https://github.com/apache/incubator-mxnet/blob/49edbfc82cb0ce3b823051e1acc26388bc79686c/tests/python/unittest/test_subgraph_op.py#L267
   
   So theres no way to duplicate exactly what is being done in the example. But, we do build the `lib_subgraph` library in the CMakeLists.txt:
   https://github.com/apache/incubator-mxnet/blob/49edbfc82cb0ce3b823051e1acc26388bc79686c/CMakeLists.txt#L814
   
   So we could add a test in unittests to use this library. But I think we decided not to do this in the past since people were running the unittests on pip wheels that didnt have the libraries packaged into the wheel. Thoughts?


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