Currently MXNet relies on topological ordering of the graph when communicating between frontend languages and backend. This makes it hard to apply fusions in the graph, as they could change the topological order of graph inputs and so break passing of the inputs from frontend.

This could be solved by either moving to passing dictionaries (name, value) from frontend to the engine (which requires changing of C API) or making mappings inside Executor and CachedOp from the original topological ordering to the new one.