Refine the activation type of GRUOp by following comments

paddle/operators/gru_op.h

@@ -90,6 +90,10 @@ class GRUKernel : public framework::OpKernel<T> {
     }
     auto batch_starts = batch_gate->lod()[0];
     size_t num_batch = batch_starts.size() - 1;
+    auto active_node = math::detail::GetActivationType(
+        context.Attr<std::string>("activation"));
+    auto active_gate = math::detail::GetActivationType(
+        context.Attr<std::string>("gate_activation"));
     for (size_t n = 0; n < num_batch; n++) {
       int bstart = static_cast<int>(batch_starts[n]);
       int bend = static_cast<int>(batch_starts[n + 1]);
@@ -102,11 +106,8 @@ class GRUKernel : public framework::OpKernel<T> {
       gru_value.gate_value = gate_t.data<T>();
       gru_value.reset_output_value = reset_hidden_prev_t.data<T>();
       math::GRUUnitFunctor<DeviceContext, T>::compute(
-          dev_ctx, gru_value, frame_size, cur_batch_size,
-          math::detail::GetActivationType(
-              context.Attr<std::string>("activation")),
-          math::detail::GetActivationType(
-              context.Attr<std::string>("gate_activation")));
+          dev_ctx, gru_value, frame_size, cur_batch_size, active_node,
+          active_gate);
       gru_value.prev_out_value = gru_value.output_value;
     }
 
@@ -192,6 +193,10 @@ class GRUGradKernel : public framework::OpKernel<T> {
 
     auto batch_starts = batch_hidden_grad.lod()[0];
     size_t num_batch = batch_starts.size() - 1;
+    auto active_node = math::detail::GetActivationType(
+        context.Attr<std::string>("activation"));
+    auto active_gate = math::detail::GetActivationType(
+        context.Attr<std::string>("gate_activation"));
     for (int n = static_cast<int>(num_batch) - 1; n >= 0; n--) {
       int bstart = static_cast<int>(batch_starts[n]);
       int bend = static_cast<int>(batch_starts[n + 1]);
@@ -222,11 +227,8 @@ class GRUGradKernel : public framework::OpKernel<T> {
       }
 
       math::GRUUnitGradFunctor<DeviceContext, T>::compute(
-          dev_ctx, gru_value, gru_grad, frame_size, cur_batch_size,
-          math::detail::GetActivationType(
-              context.Attr<std::string>("activation")),
-          math::detail::GetActivationType(
-              context.Attr<std::string>("gate_activation")));
+          dev_ctx, gru_value, gru_grad, frame_size, cur_batch_size, active_node,
+          active_gate);
     }
     if (input_grad) {
       input_grad->mutable_data<T>(context.GetPlace());