fix(minigraph): supports varnode forwarding

GitOrigin-RevId: 4494106f0a34d05c039211969444946cc6197bae

imperative/src/impl/proxy_graph/mini_graph.h

@@ -20,6 +20,7 @@
 #include "./proxy_graph_base.h"
 
 #include <optional>
+#include "megbrain/opr/utility.h"
 #include "range/v3/all.hpp"
 
 namespace mgb::imperative::proxy_graph {
@@ -83,7 +84,7 @@ TensorAdaptor(T&) -> TensorAdaptor<T, void>;
 template <typename T>
 TensorAdaptor(T*) -> TensorAdaptor<T, void>;
 
-SmallVector<Tensor*> to_raw_ptr_array(
+inline SmallVector<Tensor*> to_raw_ptr_array(
         const SmallVector<TensorPtr>& inputs, bool ensure_storage = true) {
     SmallVector<Tensor*> ret;
     for (auto&& i : inputs) {
@@ -243,6 +244,13 @@ public:
             vinputs[i] = opr_ref_keeper.back()->output(0);
         }
         auto ovars = OpDef::apply_on_var_node(opdef, vinputs);
+        if (!m_opr) {
+            // identity
+            mgb_assert(vinputs.size() == 1 && ovars.size() == 1);
+            mgb_assert(ovars[0] == vinputs[0]);
+            auto&& input = vinputs[0];
+            ovars[0] = opr::Identity::make(input).node();
+        }
         mgb_assert(m_opr);
         output_data.resize(m_opr->output().size());
         for (auto* v : ovars) {
@@ -343,7 +351,6 @@ public:
             } else {
                 mgb_assert(j < outputs.size());
                 auto&& tensor = outputs[j];
-                auto&& layout = tensor->layout();
                 if (var->m_mem_plan.chunk().owner_var != var) {
                     tensor->assign_from_dev_tensor(
                             var->m_dev_tensor);  // memory forwarding
@@ -613,6 +620,7 @@ class ExecMiniGraph : public ProxyGraph::MiniGraph {
             busy_oprs.pop_front();
             return m_opr;
         }
+        mgb_assert(false);
     }
 
     template <bool in_use>