TODO list for supporting dynamic shape

[zheng-da]

MXNet doesn't support operators that don't allow static shape inference, such as unique and boolean_index. One possible solution is proposed in https://cwiki.apache.org/confluence/display/MXNET/Dynamic+shape

This task can be broken into multiple steps:

• support such an operator in the imperative execution. A possible modification in the imperative execution is shown here: https://github.com/apache/incubator-mxnet/pull/12400
• support such an operator in CachedOp. This step requires writing a new executor that runs operators in a computation graph one by one without shape inference and memory planning. We can start with executing operators synchronously, but eventually, we should execute them asynchronously.
• an optimization is to use the subgraph API to split the computation graph into subgraphs so that a subgraph either contain only operators allowing static shape inference or operators with dynamic shape.

[vrakesh]

@zheng-da thanks for the detailed proposal on supporting dynamic shapes

@mxnet-label-bot [Feature request]

[vrakesh]

@mxnet-label-bot [Operator]

[chinakook]

I think that a good solution to support pseudo-dynamic (in most cases it's enough) shape is to support infer_shape_partial (through defer shape inference) in HybridBlock.