fix old traceback conversion

Author: duck2

vpr/src/base/old_traceback.cpp

@@ -8,7 +8,7 @@
 
 std::pair<t_trace*, t_trace*> traceback_from_route_tree_recurr(t_trace* head, t_trace* tail, const RouteTreeNode& node);
 static void traceback_to_route_tree_x(
-    std::unordered_map<RRNodeId, vtr::optional<RouteTreeNode&>> rr_node_to_rt_node,
+    std::unordered_map<RRNodeId, vtr::optional<RouteTreeNode&>>& rr_node_to_rt_node,
     t_trace* trace,
     RouteTreeNode& parent,
     RRSwitchId parent_switch);
@@ -23,7 +23,7 @@ vtr::optional<RouteTree> traceback_to_route_tree(t_trace* head) {
     if (head == nullptr)
         return vtr::nullopt;
 
-    RouteTreeNode root(RRNodeId(head->index), RRSwitchId(OPEN), vtr::nullopt);
+    RouteTreeNode root(RRNodeId(head->index), RRSwitchId::INVALID(), vtr::nullopt);
     std::unordered_map<RRNodeId, vtr::optional<RouteTreeNode&>> rr_node_to_rt_node;
 
     rr_node_to_rt_node[RRNodeId(head->index)] = root;
@@ -34,18 +34,18 @@ vtr::optional<RouteTree> traceback_to_route_tree(t_trace* head) {
     RouteTree tree(std::move(root));
     tree.reload_timing();
 
-    /* We built the tree using an external lookup, but returning by value should either copy
+    /* We built the tree using a (hacky) external lookup, but returning by value should either copy
      * or move, which will make the tree update its own lookup */
     return tree;
 }
 
 /* Add the path indicated by the trace to parent */
-static void traceback_to_route_tree_x(std::unordered_map<RRNodeId, vtr::optional<RouteTreeNode&>> rr_node_to_rt_node, t_trace* trace, RouteTreeNode& parent, RRSwitchId parent_switch) {
+static void traceback_to_route_tree_x(std::unordered_map<RRNodeId, vtr::optional<RouteTreeNode&>>& rr_node_to_rt_node, t_trace* trace, RouteTreeNode& parent, RRSwitchId parent_switch) {
     auto& device_ctx = g_vpr_ctx.device();
     const auto& rr_graph = device_ctx.rr_graph;
     RRNodeId inode = RRNodeId(trace->index);
 
-    RouteTreeNode new_node = parent.emplace_child(inode, parent_switch, parent);
+    RouteTreeNode& new_node = parent.emplace_child(inode, parent_switch, parent);
     new_node.net_pin_index = trace->net_pin_index;
     new_node.R_upstream = std::numeric_limits<float>::quiet_NaN();
     new_node.C_downstream = std::numeric_limits<float>::quiet_NaN();
@@ -59,7 +59,7 @@ static void traceback_to_route_tree_x(std::unordered_map<RRNodeId, vtr::optional
     rr_node_to_rt_node[new_node.inode] = new_node;
 
     if (rr_graph.node_type(inode) == SINK) {
-        /* The traceback returns to the previous branch point if there is more than one SINK, else we are at the base case */
+        /* The traceback returns to the previous branch point if there is more than one SINK, otherwise we are at the last SINK */
         if (trace->next) {
             RRNodeId next_rr_node = RRNodeId(trace->next->index);
             RouteTreeNode& branch = rr_node_to_rt_node.at(next_rr_node).value();