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A more detailed comment explains why we need to re-compute NoC costs from scratch.

Two member function in xy_routing are now normal functions rather than static ones.

Author: soheilshahrouz

vpr/src/noc/xy_routing.h

@@ -140,7 +140,7 @@ class XYRouting : public NocRouting {
      * that is currently being visited on the FPGA
      * @return RouteDirection The direction to travel next
      */
-    static RouteDirection get_direction_to_travel(int sink_router_x_position, int sink_router_y_position, int curr_router_x_position, int curr_router_y_position);
+    RouteDirection get_direction_to_travel(int sink_router_x_position, int sink_router_y_position, int curr_router_x_position, int curr_router_y_position);
 
     /**
      * @brief Given the direction to travel next, this function determines
@@ -166,7 +166,7 @@ class XYRouting : public NocRouting {
      * @return true A suitable link was found that we can traverse next
      * @return false No suitable link was found that could be traversed
      */
-    static bool move_to_next_router(NocRouterId& curr_router_id, int curr_router_x_position, int curr_router_y_position, RouteDirection next_step_direction, std::vector<NocLinkId>& flow_route, std::unordered_set<NocRouterId>& visited_routers, const NocStorage& noc_model);
+    bool move_to_next_router(NocRouterId& curr_router_id, int curr_router_x_position, int curr_router_y_position, RouteDirection next_step_direction, std::vector<NocLinkId>& flow_route, std::unordered_set<NocRouterId>& visited_routers, const NocStorage& noc_model);
 };
 
 #endif

vpr/src/place/place_checkpoint.cpp

@@ -44,7 +44,11 @@ void restore_best_placement(t_placement_checkpoint& placement_checkpoint, std::s
                                    timing_info.get(),
                                    &costs);
 
-        // If NoC is enabled, re-compute NoC costs and re-initialize NoC internal data structures
+        /* If NoC is enabled, re-compute NoC costs and re-initialize NoC internal data structures.
+         * If some routers have different locations than the last placement, NoC-related costs and
+         * internal data structures that are used to keep track of each flow's cost are no longer valid,
+         * and need to be re-computed from scratch.
+         */
         if (noc_opts.noc) {
             reinitialize_noc_routing(noc_opts, costs);
         }