change map to unordered_map

paddle/fluid/operators/split_ids_op.h

@@ -14,7 +14,7 @@ limitations under the License. */
 
 #pragma once
 
-#include <map>
+#include <unordered_map>
 #include <vector>
 #include "paddle/fluid/framework/op_registry.h"
 #include "paddle/fluid/operators/math/selected_rows_functor.h"
@@ -69,7 +69,7 @@ class SplitIdsOpKernel : public framework::OpKernel<T> {
       auto outs = ctx.MultiOutput<framework::SelectedRows>("Out");
       const size_t shard_num = outs.size();
       // get rows for outputs
-      std::map<int64_t, size_t> id_to_index;
+      std::unordered_map<int64_t, size_t> id_to_index;
       for (size_t i = 0; i < ids_rows.size(); ++i) {
         id_to_index[ids_rows[i]] = i;
         size_t shard_id = static_cast<size_t>(ids_rows[i]) % shard_num;