new subtree with 9 nodes and after that a Renormalize pass is needed to simplified it back to a tensor. The new algorithm will
create the tensor while visiting in the pass, therefore only a single node is created and no Renormalize will be needed for this pass
(if other passes requires then Renormalize will still be called but no further infer is needed for the created tensor)

Signed-off-by: Hoai Linh Tran h00472437 <hoai.linh.tran@huawei.com>

Code review

1. Remove the records of user graphs;
2. Remove the records of user value nodes;
3. Remove the records of user cnodes;
4. Add the records of users, and the API to access the users of graph, value node, and cnode;
5. Fix issue:User cnode record may point to its own graph, when combine the user(caller) and used one(callee);
6. Fix issue:User graphs never update itself after its first creation.

Merge pull request !662 from zhangbuxue/fix-reviewboot

This reverts commit ea6958c50a.

This reverts commit 252ed4f7c9.

Merge pull request !340 from ougongchang/master

clean clang format errors and cpplint errors

add some test cases for histogram summary operator

use unpack graph primitive instead

add testcases for all grad interface

remove debug log

format code

remove dumpfuncgraph

resolve clang-format

resolve reviews

resolve cpplint

fix review

Signed-off-by: leonwanghui <leon.wanghui@huawei.com>