Added interface reset_grad_inplace_version (#37573)

reset_inplace_version removes all inplace related records to VarBase/VariableWrapper, the essential purpose of which is to let you use inplace operations as if using its non-inplaced version, which of course will cause unexpected consequences if not used with care.

This is essentially a hack interface to satisfy one specific request

paddle/fluid/imperative/dygraph_grad_maker.h

@@ -365,9 +365,10 @@ class TracedGradOp {
       }
     }
 
-    VariableWrapper new_var_wrapper = *var_wrapper.get();
-    new_var_wrapper.ResetInplaceVersion();
-    return std::make_shared<VariableWrapper>(new_var_wrapper);
+    auto new_var_wrapper =
+        std::make_shared<VariableWrapper>(*var_wrapper.get());
+    new_var_wrapper->ResetInplaceVersion();
+    return new_var_wrapper;
   }
 
  private:

paddle/fluid/pybind/imperative.cc

@@ -1548,6 +1548,25 @@ void BindImperative(py::module *m_ptr) {
            [](imperative::VarBase &self, framework::proto::VarType::Type type) {
              self.MutableGradVarBase()->SetType(type);
            })
+      .def("_reset_grad_inplace_version",
+           [](imperative::VarBase &self) {
+             /*
+             *** This interfaceis a complete hack ***
+             reset_grad_inplace_version removes all inplace related records to
+             Grad VarBase/VariableWrapper,
+             the essential purpose of which is to let you use inplace operations
+             as if using its non-inplaced version,
+             which of course will cause unexpected consequences if not used with
+             care.
+             Make sure you fully understand what you're doing before make use of
+             this interface, and prepare for the worst.
+             */
+             if (self.HasGradVar()) {
+               auto grad_var = self.GradVarBase();
+               auto var_wrapper = grad_var->SharedVar();
+               if (var_wrapper) var_wrapper->ResetInplaceVersion();
+             }
+           })
       .def("_grad_ivar",
            [](const imperative::VarBase &self) {
              auto &grad_var = self.GradVarBase();

python/paddle/fluid/tests/unittests/test_reset_grad_inplace_version.py

+# Copyright (c) 2021 PaddlePaddle Authors. All Rights Reserved.
+# 
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+# 
+#     http://www.apache.org/licenses/LICENSE-2.0
+# 
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import numpy as np
+import paddle
+import paddle.fluid as fluid
+from paddle import _C_ops
+from paddle.fluid import framework
+import unittest
+paddle.set_device('cpu')
+
+
+def clear_grad(w, a):
+    @paddle.no_grad()
+    def warp(*_):
+        assert w.grad is not None
+        _C_ops.scale_(w.grad, 'scale', 0.5)
+        w._reset_grad_inplace_version()
+
+    return warp
+
+
+class TestInplaceAndClearGradient(unittest.TestCase):
+    def test(self):
+        input_data = np.ones([1, 1])
+        w = paddle.to_tensor(input_data, 'float32', stop_gradient=False)
+
+        _clear_grad = clear_grad(w, a="1")
+        w._register_backward_hook(_clear_grad)
+        for i in range(2):
+            print(" Step: ", i)
+            out0 = _C_ops.scale(w, 'scale', 0.1)
+            out = _C_ops.matmul_v2(out0, w, 'trans_x', False, 'trans_y', False)
+            out.backward()
+        assert w.grad[0] == 0.15
+
+
+if __name__ == '__main__':
+    unittest.main()