[TVM Discuss] [Questions] Support of IfNode in graph runtime

Thanks @comaniac for your suggestion. I tried VM, but got segmentation fault when trying to run in VTA (just simulation). Struggle a while to debug, but does not figure it out. In addition, it seems VM does not support heterogenous execution. So just wonder if there are lots of works to supp

[TVM Discuss] [Questions] Support of IfNode in graph runtime

When there is an IfNode in the model, it will raise `if is not supported` errror. I saw the error comes from `src/relay/backend/graph_plan_memory.cc`: ```c++ void VisitExpr_(const IfNode* op) final {