Add get_input() to DLR

[hcho3]

We need the ability to get the current value of an input when using the _assign operator in NNVM.

[wweic]

@hcho3 code looks good! Please add a unit test.

[zhiics]

Could you please explain a bit why GetInput is needed? Shouldn't users already know the input?

[hcho3]

Still need to test a few things. I'll take off "Draft" status once this PR is ready.

[hcho3]

@zhiics No, since the value of the input changes when the _assign operator is used. See this snippet:
https://github.com/dmlc/tvm/blob/39c8bc2a3da62701f28488920d63fdd2895fe060/nnvm/tests/python/compiler/test_top_assign.py#L21-L34

cc @kevinthesun

[zhiics]

@hcho3 I see. Thanks.

[hcho3]

The current logic for getting input names assumes that inputs always precede parameters, but it is not always true. One model I am looking at actually has some parameters before the input:

hybridsequential0_aux4
hybridsequential0_aux3
hybridsequential0_aux2
hybridsequential0_aux1
hybridsequential0_aux0
data
...

EDIT. Fixed by commit fb87ad4

[hcho3]

Also, std::set_difference assumes that both sets are sorted, but neither input_names nor weight_names are not sorted:

neo-ai-dlr/src/dlr.cc

Lines 196 to 203 in 0ce46d9

	std::vector<std::string> input_names;
	for (int i = 0; i < num_inputs_; i++) {
	input_names.push_back(tvm_graph_runtime_->GetInputName(i));
	}
	std::vector<std::string> weight_names = tvm_graph_runtime_->GetWeightNames();
	std::set_difference(input_names.begin(), input_names.end(),
	weight_names.begin(), weight_names.end(),
	std::inserter(input_names_, input_names_.begin()));

EDIT. Fixed by commit fb87ad4

[hcho3]

@wweic @ziyu-guo @zhiics I added a small unit test. Please review.

[ziyu-guo]

LGTM