[Eager] Support is empty (#43032)

* support is empty

* fix error

* fix code error

* change to fake empty

* using fake empty first

* using fake empty first

paddle/fluid/eager/accumulation/accumulation_node.cc

@@ -28,7 +28,11 @@
 namespace egr {
 
 static void CopyOrAddTensor(paddle::experimental::Tensor* tensor,
-                            const paddle::experimental::Tensor& t) {
+                            const paddle::experimental::Tensor& t,
+                            bool is_fake_empty) {
+  if (is_fake_empty) {
+    *tensor = t;
+  } else {
     if (!tensor->defined() || !tensor->initialized()) {
       // Simply copy tensor->impl
       *tensor = t;
@@ -36,7 +40,8 @@ static void CopyOrAddTensor(paddle::experimental::Tensor* tensor,
       // Accumulation
       if (LIKELY(t.is_dense_tensor())) {
         if (LIKELY(tensor->is_dense_tensor())) {
-        paddle::imperative::TensorAdd<paddle::experimental::Tensor>(t, tensor);
+          paddle::imperative::TensorAdd<paddle::experimental::Tensor>(t,
+                                                                      tensor);
         } else {
           // TODO(jiabin): Support Other TensorBase later
           // TODO(zhanlve): Replace SelectedRowsAddTensor with
@@ -48,7 +53,8 @@ static void CopyOrAddTensor(paddle::experimental::Tensor* tensor,
         }
       } else {
         // TODO(jiabin): Support Other TensorBase later
-      // TODO(zhanlve): Replace SelectedRowsAddTensor with add_dygraph_function
+        // TODO(zhanlve): Replace SelectedRowsAddTensor with
+        // add_dygraph_function
         // once it's supported
         if (tensor->is_dense_tensor()) {
           paddle::imperative::SelectedRowsAddToTensor(t, tensor);
@@ -58,6 +64,7 @@ static void CopyOrAddTensor(paddle::experimental::Tensor* tensor,
         }
       }
     }
+  }
 }
 
 paddle::small_vector<std::vector<paddle::experimental::Tensor>,
@@ -91,7 +98,8 @@ GradNodeAccumulation::operator()(
 
   if (!weak_grad_.expired() && !is_new_grad) {
     auto grad = weak_grad_.lock();
-    CopyOrAddTensor(grad.get(), grad_out);
+    CopyOrAddTensor(grad.get(), grad_out, is_fake_empty_);
+    is_fake_empty_ = false;
   }
 
   // Apply Reduce Hooks

paddle/fluid/eager/accumulation/accumulation_node.h

@@ -64,14 +64,16 @@ class GradNodeAccumulation : public GradNodeBase {
         new GradNodeAccumulation(nullptr));
   }
 
+  void SetFakeEmpty(bool is_fake_empty) { is_fake_empty_ = is_fake_empty; }
+
  private:
+  // TODO(Jiabin): remove this when we make our clear gradient really cleared;
+  bool is_fake_empty_ = {false};
   std::weak_ptr<paddle::experimental::Tensor> weak_grad_;
-
+  std::vector<std::shared_ptr<TensorVoidHook>> reduce_hooks_;
   std::function<paddle::experimental::Tensor(
       const paddle::experimental::Tensor&)>
       retain_grad_hook_;
-
-  std::vector<std::shared_ptr<TensorVoidHook>> reduce_hooks_;
 };
 
 }  // namespace egr

paddle/fluid/pybind/eager_method.cc

@@ -494,7 +494,8 @@ static PyObject* tensor_clear_gradient(TensorObject* self, PyObject* args,
   }
 
   paddle::experimental::Tensor* grad;
-  if (egr::egr_utils_api::IsLeafTensor(self->tensor)) {
+  bool is_leaf = egr::egr_utils_api::IsLeafTensor(self->tensor);
+  if (is_leaf) {
     grad = egr::EagerUtils::mutable_grad(self->tensor);
     PADDLE_ENFORCE(grad != nullptr,
                    paddle::platform::errors::Fatal(
@@ -518,6 +519,11 @@ static PyObject* tensor_clear_gradient(TensorObject* self, PyObject* args,
       if (grad->initialized()) {
         if (set_to_zero) {
           grad->set_impl(paddle::experimental::zeros_like(*grad).impl());
+          if (is_leaf) {
+            std::static_pointer_cast<egr::GradNodeAccumulation>(
+                egr::EagerUtils::grad_node(self->tensor))
+                ->SetFakeEmpty(true);
+          }
         } else {
           VLOG(4) << "Gradient of " << self->tensor.name()
                   << " is initialized, will be released.";