Fix code and add unittests according to reviews

Author: liym27

paddle/fluid/operators/set_value_op.h

@@ -21,6 +21,7 @@
 #include <utility>
 #include "paddle/fluid/framework/eigen.h"
 #include "paddle/fluid/framework/op_registry.h"
+#include "paddle/fluid/framework/tensor_util.h"
 #include "paddle/fluid/operators/assign_value_op.h"
 #include "paddle/fluid/operators/elementwise/elementwise_op_function.h"
 #include "paddle/fluid/platform/enforce.h"
@@ -83,6 +84,10 @@ class SetValueKernel : public framework::OpKernel<T> {
  public:
   void Compute(const framework::ExecutionContext& ctx) const {
     const int rank = ctx.Output<framework::LoDTensor>("Out")->dims().size();
+
+    // TODO(liym27): A more elegent code to do this. C++ has to make template
+    //  integer as constant, but we had better have alternative writing in the
+    //  future.
     switch (rank) {
       case 1:
         SetValueCompute<1>(ctx);
@@ -127,7 +132,18 @@ class SetValueKernel : public framework::OpKernel<T> {
     auto& eigen_place =
         *ctx.template device_context<DeviceContext>().eigen_device();
 
-    out->ShareDataWith(*in);
+    // Here copy data from input to avoid data loss at PE and Graph level.
+    // TODO(liym27): Speed up in the future version.
+    // - Q: Why don't call ShareDataWith to speed up?
+    // - A: Because it's not supported to ShareDataWith on OP's input and output
+    // https://github.com/PaddlePaddle/Paddle/wiki/ShareDataWith-and-ShareBufferWith-are-prohibited-in-OP
+    // - Q: Why don't delete Input, after all, the input and output are the same
+    // Tensor at program level?
+    // - A: If deleting Input, the graph will be complex, such as there will
+    // be two ops points to the output in graph: op1 -> output <- set_value.
+    // In this case, we have to find a way to handle the running order of
+    // set_value is what we want.
+    TensorCopy(*in, place, out);
 
     Tensor slice_t(dtype), pad_t(dtype);
     slice_t.mutable_data<T>(slice_dims, place);

python/paddle/fluid/tests/unittests/dygraph_to_static/test_slice.py

@@ -23,6 +23,7 @@
 np.random.seed(SEED)
 prog_trans = paddle.jit.ProgramTranslator()
 
+
 @paddle.jit.to_static
 def test_slice_without_control_flow(x):
     # Python slice will not be transformed.
@@ -84,7 +85,7 @@ def test_slice_in_for_loop(x, iter_num=3):
 
 
 @paddle.jit.to_static
-def test_setitem(x):
+def test_set_value(x):
     x = paddle.to_tensor(x)
     x[0] = paddle.full(shape=[1], fill_value=2, dtype="float32")
     x[1:2, 0:1] = 10
@@ -140,12 +141,12 @@ def init_dygraph_func(self):
         self.dygraph_func = test_slice_in_for_loop
 
 
-class TestSetitem(TestSliceWithoutControlFlow):
+class TestSetValue(TestSliceWithoutControlFlow):
     def init_input(self):
-        self.input = np.full([3,4,5], 5).astype('float32')
+        self.input = np.full([3, 4, 5], 5).astype('float32')
 
     def init_dygraph_func(self):
-        self.dygraph_func = test_setitem
+        self.dygraph_func = test_set_value
 
 
 if __name__ == '__main__':

python/paddle/fluid/tests/unittests/test_setitem_op.py renamed to python/paddle/fluid/tests/unittests/test_set_value_op.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# Test setitem op in static mode
+# Test set_value op in static mode
 
 from __future__ import print_function