chore(mge): add VarNode.value

GitOrigin-RevId: 1dc0d0c711b3bc3e7bfb04fa933839928d579a8c

imperative/python/megengine/core/tensor/megbrain_graph.py

@@ -95,6 +95,10 @@ class VarNode(TensorBase):
     def shape(self):
         return self._node.shape
 
+    @property
+    def value(self):
+        return self._node.value
+
 
 class OpNode:
     def __init__(self, node: _imperative_rt.OperatorNode):

imperative/python/megengine/jit/tracing.py

@@ -399,7 +399,7 @@ class LazyEvalTensor(RawTensor):
         return self.__varnode.shape
 
     def numpy(self):
-        raise RuntimeError("cannot read value during symbolic tracing")
+        return self.__varnode.value
 
     def _dev_tensor(self):
         raise RuntimeError("cannot access data during symbolic tracing")

imperative/python/src/graph_rt.cpp

@@ -58,6 +58,19 @@ void init_graph_rt(py::module m) {
                     return nullptr;
                 }
                 return mgr.infer_shape_fallible(v);
+            })
+        .def_property_readonly("value", [](cg::VarNode* v) -> py::object {
+                auto&& mgr = v->owner_graph()->static_infer_manager();
+                auto&& type = mgr.get_infer_type(v);
+                using InferType = cg::static_infer::InferType;
+                if (!(type.value & (InferType::CONST | InferType::RT_STATIC))) {
+                    return py::none();
+                }
+                auto* val = mgr.infer_value_fallible(v);
+                if (!val) {
+                    return py::none();
+                }
+                return py::cast(*val).attr("numpy")();
             });
 
     py::class_<cg::OperatorNodeBase, GraphNodePtr<cg::OperatorNodeBase>>(m, "OperatorNode")