optimize code

paddle/fluid/operators/math/selected_rows_functor.cc

@@ -12,6 +12,7 @@ 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. */
 
+#include <map>
 #include <set>
 
 #include "paddle/fluid/operators/math/math_function.h"
@@ -228,6 +229,11 @@ struct MergeAdd<platform::CPUDeviceContext, T> {
     }
     std::vector<int64_t> merge_rows(merged_row_set.begin(),
                                     merged_row_set.end());
+    std::map<int64_t, size_t> rows_to_id;
+    for (size_t i = 0; i < merge_rows.size(); ++i) {
+      rows_to_id[merge_rows[i]] = i;
+    }
+
     out.set_rows(merge_rows);
     out.set_height(input_height);
     out.mutable_value()->mutable_data<T>(
@@ -245,7 +251,7 @@ struct MergeAdd<platform::CPUDeviceContext, T> {
       auto& input_rows = input->rows();
 
       for (size_t i = 0; i < input_rows.size(); i++) {
-        size_t out_i = FindPos(merge_rows, input_rows[i]);
+        size_t out_i = rows_to_id[input_rows[i]];
         for (int64_t j = 0; j < input_width; j++) {
           out_data[out_i * input_width + j] += input_data[i * input_width + j];
         }