Micro performance optimisation in map matching (#6976)

Author: SiarheiFedartsou

CHANGELOG.md

@@ -24,6 +24,7 @@
     - NodeJS:
       - CHANGED: Use node-api instead of NAN. [#6452](https://github.com/Project-OSRM/osrm-backend/pull/6452)
     - Misc:
+      - CHANGED: Micro performance optimisation in map matching. [#6976](https://github.com/Project-OSRM/osrm-backend/pull/6976)
       - CHANGED: Re-use priority queue in StaticRTree. [#6952](https://github.com/Project-OSRM/osrm-backend/pull/6952)
       - CHANGED: Optimise encodePolyline function. [#6940](https://github.com/Project-OSRM/osrm-backend/pull/6940)
       - CHANGED: Avoid reallocations in base64 encoding. [#6951](https://github.com/Project-OSRM/osrm-backend/pull/6951)

src/engine/routing_algorithms/map_matching.cpp

@@ -401,6 +401,7 @@ SubMatchingList mapMatching(SearchEngineData<Algorithm> &engine_working_data,
         auto trace_distance = 0.0;
         matching.nodes.reserve(reconstructed_indices.size());
         matching.indices.reserve(reconstructed_indices.size());
+        matching.alternatives_count.reserve(reconstructed_indices.size());
         for (const auto &idx : reconstructed_indices)
         {
             const auto timestamp_index = idx.first;
@@ -428,7 +429,7 @@ SubMatchingList mapMatching(SearchEngineData<Algorithm> &engine_working_data,
 
         matching.confidence = confidence(trace_distance, matching_distance);
 
-        sub_matchings.push_back(matching);
+        sub_matchings.emplace_back(std::move(matching));
         sub_matching_begin = sub_matching_end;
     }