fix to skip node not in graph.

[chinakook]

fix to skip node not in graph because some network cannot be hybridized with some var unused.

Thanks for contributing to TVM! Please refer to guideline https://tvm.apache.org/docs/contribute/ for useful information and tips. After the pull request is submitted, please request code reviews from Reviewers by @ them in the pull request thread.

[icemelon]

Could you add some test case for it?

[chinakook]

@icemelon9 what kind of tests, please? Failure case I've met with?

[tqchen]

I am going to merge this for now, given it is a change to the nnvm code. However, based on my current impression, I am not really sure if such relaxation should be done, given that node2index is supposed to only contain nodes in the graph, @chinakook would be great if you can comment a bit.

[chinakook]

@tqchen As I'v just tested, It's a op named _FusedOp that cannot be CHECK success.

[tqchen]

i see, perhaps you also want to confirm with the mxnet community as well to make sure it is the intended behavior cc @szha

[chinakook]

I'm sure some network will be fail to hybridize after this apache/mxnet#15167 PR. So we can add e.node->op()->name.compare("_FusedOp")==0 at first. However, this op name is specified to mxnet but not tvm.

[ptrendx]

This is not right and should be reverted IMO - the problem in the original issue (apache/mxnet#18624) was a genuine bug in the fusion graph pass that generated a cycle in the graph. Omitting such node from indexed graph would result in incorrect result being produced.

[tqchen]

@ptrendx feel free to send a PR to revert the change then

[ptrendx]

@tqchen PR #6680 done.