Add .reserve(...) to assembleGeometry function (Project-OSRM#6983)

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: Add .reserve(...) to assembleGeometry function. [#6983](https://github.com/Project-OSRM/osrm-backend/pull/6983)
       - CHANGED: Get rid of boost::optional leftovers. [#6977](https://github.com/Project-OSRM/osrm-backend/pull/6977)
       - CHANGED: Use Link Time Optimisation whenever possible. [#6967](https://github.com/Project-OSRM/osrm-backend/pull/6967)
       - CHANGED: Use struct instead of tuple to define UnpackedPath. [#6974](https://github.com/Project-OSRM/osrm-backend/pull/6974)

include/engine/guidance/assemble_geometry.hpp

@@ -37,6 +37,14 @@ inline LegGeometry assembleGeometry(const datafacade::BaseDataFacade &facade,
 {
     LegGeometry geometry;
 
+    // each container will at most have `leg_data.size()` + 1/2 elements in it
+    // these additional 1/2 elements come from processing of very first and very last segment
+    geometry.locations.reserve(leg_data.size() + 2);
+    geometry.segment_distances.reserve(leg_data.size() + 1);
+    geometry.segment_offsets.reserve(leg_data.size() + 1);
+    geometry.annotations.reserve(leg_data.size() + 1);
+    geometry.node_ids.reserve(leg_data.size() + 2);
+
     // segment 0 first and last
     geometry.segment_offsets.push_back(0);
     geometry.locations.push_back(source_node.location);