diff --git a/imperative/src/impl/ops/broadcast.cpp b/imperative/src/impl/ops/broadcast.cpp
index 2895688b53ecda1fb8d03a06a4cecdff3748bd1c..b63883e2ef8ead62f8ddba7c75c186beba2755cc 100644
--- a/imperative/src/impl/ops/broadcast.cpp
+++ b/imperative/src/impl/ops/broadcast.cpp
@@ -12,6 +12,8 @@
 #include "megbrain/imperative/ops/autogen.h"
 #include "megbrain/opr/tensor_manip.h"
 
+#include "megbrain/graph/helper.h"
+
 #include "../op_trait.h"
 
 namespace mgb {
@@ -83,10 +85,46 @@ std::tuple<SmallVector<LogicalTensorDesc>, bool> infer_output_attrs_fallible(
     return {{{TensorLayout(out_shape, src.layout.dtype), src.comp_node}}, true};
 }
 
+std::tuple<SmallVector<MemoryDesc>, SmallVector<MemoryDesc>> infer_output_mem_desc(
+        const OpDef& def,
+        const SmallVector<TensorPtr>& inputs_tensors,
+        const SmallVector<MemoryDesc>& inputs_mems) {
+    auto& input = inputs_tensors[0];
+    TensorShape target_shape;
+    cg::copy_tensor_value_to_shape(target_shape, inputs_tensors[1]->get_value().proxy_to_default_cpu());
+    // TODO: memory forward
+    // if (input->shape().eq_shape(target_shape)) {
+    //     return {{{input->layout(), 0, input->comp_node(), StorageIdentifier::make(&inputs_mems[0])}}, {}};
+    // }
+    return {{{{target_shape, input->dtype()}, 0, input->comp_node(), StorageIdentifier::make(0)}}, {}};
+}
+
+void execute(
+        const OpDef& def,
+        SmallVector<TensorPtr> inputs,
+        SmallVector<TensorPtr> outputs,
+        SmallVector<TensorPtr> workspace) {
+    if (outputs[0]->layout().is_empty()) {
+        return;
+    }
+    if (inputs[0]->shape().eq_shape(outputs[0]->shape())) {
+        mgb_assert(inputs[0]->layout().eq_layout(outputs[0]->layout()));
+        // TODO: memory forward
+        // mgb_assert(inputs[0]->offset() == outputs[0]->offset());
+        // mgb_assert(inputs[0]->blob() == outputs[0]->blob());
+        outputs[0]->dev_tensor().copy_from_fixlayout(inputs[0]->dev_tensor());
+    } else {
+        TensorLayout input_layout = inputs[0]->layout().broadcast(outputs[0]->shape());
+        outputs[0]->dev_tensor().copy_from_fixlayout(inputs[0]->dev_tensor().sub(SubTensorSpec::make_from_layout(input_layout)));
+    }
+}
+
 OP_TRAIT_REG(Broadcast, Broadcast, opr::Broadcast)
     .make_from_op_node(make_from_op_node)
     .apply_on_var_node(apply_on_var_node)
     .infer_output_attrs_fallible(infer_output_attrs_fallible)
+    .infer_output_mem_desc(infer_output_mem_desc)
+    .execute(execute)
     .fallback();
 } // broadcast
 
diff --git a/imperative/src/impl/ops/reduce.cpp b/imperative/src/impl/ops/reduce.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..b9aa65203e9454dbd1d87ab6699eb747065de5ab
--- /dev/null
+++ b/imperative/src/impl/ops/reduce.cpp
@@ -0,0 +1,47 @@
+/**
+ * \file imperative/src/impl/ops/reduce.cpp
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2021 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#include "megbrain/imperative/ops/autogen.h"
+#include "megbrain/opr/basic_arith.h"
+
+#include "../op_trait.h"
+#include "../dnn_op_helper.h"
+
+namespace mgb {
+namespace imperative {
+namespace {
+namespace reduce {
+auto apply_on_var_node(const OpDef& def, const VarNodeArray& inputs) {
+    auto&& reduce = static_cast<const Reduce&>(def);
+    OperatorNodeConfig config{reduce.make_name()};
+    if (inputs.size() > 1) {
+        return opr::Reduce::make(inputs[0], reduce.param(), inputs[1], config);
+    } else {
+        return opr::Reduce::make(inputs[0], reduce.param(),
+                                 (cg::VarNode*)nullptr, config);
+    }
+}
+
+std::shared_ptr<OpDef> make_from_op_node(cg::OperatorNodeBase* node_) {
+    auto* node = &node_->cast_final_safe<opr::Reduce>();
+    return Reduce::make(node->param());
+}
+
+OP_TRAIT_REG(Reduce, Reduce, opr::Reduce)
+        .make_from_op_node(make_from_op_node)
+        .apply_on_var_node(apply_on_var_node)
+        .fallback();
+}  // namespace reduce
+}  // namespace
+}  // namespace imperative
+}  // namespace mgb
+
+// vim: syntax=cpp.doxygen foldmethod=marker foldmarker=f{{{,f}}}
diff --git a/imperative/src/impl/ops/specializations.cpp b/imperative/src/impl/ops/specializations.cpp
index edb76da194df8ba2ceb585cfeee8f833358b8391..ac8a50bea08382776f4e2abb08d5b08817d6cdfa 100644
--- a/imperative/src/impl/ops/specializations.cpp
+++ b/imperative/src/impl/ops/specializations.cpp
@@ -116,31 +116,6 @@ OP_TRAIT_REG(TopK, TopK).apply_on_var_node(apply_on_var_node).fallback();
 }  // namespace top_k
 }  // namespace
 
-namespace {
-namespace reduce {
-auto apply_on_var_node(const OpDef& def, const VarNodeArray& inputs) {
-    auto&& reduce = static_cast<const Reduce&>(def);
-    OperatorNodeConfig config{reduce.make_name()};
-    if (inputs.size() > 1) {
-        return opr::Reduce::make(inputs[0], reduce.param(), inputs[1], config);
-    } else {
-        return opr::Reduce::make(inputs[0], reduce.param(),
-                                 (cg::VarNode*)nullptr, config);
-    }
-}
-
-std::shared_ptr<OpDef> make_from_op_node(cg::OperatorNodeBase* node_) {
-    auto* node = &node_->cast_final_safe<opr::Reduce>();
-    return Reduce::make(node->param());
-}
-
-OP_TRAIT_REG(Reduce, Reduce, opr::Reduce)
-        .make_from_op_node(make_from_op_node)
-        .apply_on_var_node(apply_on_var_node)
-        .fallback();
-}  // namespace reduce
-}  // namespace
-
 namespace {
 namespace adaptive_pooling {
 auto apply_on_var_node(const OpDef& def, const VarNodeArray& inputs) {