[VPR] Rework get_channel_nodes() in RRSpatialLookup to filter out invalid nodes and avoid exposure on raw data

Author: tangxifan

vpr/src/device/rr_spatial_lookup.cpp

@@ -124,7 +124,9 @@ std::vector<RRNodeId> RRSpatialLookup::find_channel_nodes(int x,
     }
 
     for (const auto& node : rr_node_indices_[type][node_x][node_y][node_side]) {
-        channel_nodes.push_back(RRNodeId(node));
+        if (RRNodeId(node)) {
+            channel_nodes.push_back(RRNodeId(node));
+        }
     }
 
     return channel_nodes;

vpr/src/device/rr_spatial_lookup.h

@@ -71,10 +71,11 @@ class RRSpatialLookup {
      *
      * Note: 
      * - Return an empty list if there are no routing channel at the given (x, y) location
-     * - The node list returned may contain some holes (invalid ids), which means that
-     *   the routing track does not exist at a specific location
-     *   For example, if the 2nd element is an invalid id, it means the 2nd routing track does not exist
-     *   in a routing channel at (x, y) location
+     * - The node list returned only contain valid ids
+     *   For example, if the 2nd routing track does not exist in a routing channel at (x, y) location,
+     *   while the 3rd routing track does exist in a routing channel at (x, y) location,
+     *   the node list will not contain the node for the 2nd routing track, but the 2nd element in the list
+     *   will be the node for the 3rd routing track
      */
     std::vector<RRNodeId> find_channel_nodes(int x,
                                              int y,

vpr/src/route/router_lookahead_map.cpp

@@ -564,8 +564,6 @@ static RRNodeId get_start_node(int start_x, int start_y, int target_x, int targe
 
     /* find first node in channel that has specified segment index and goes in the desired direction */
     for (const RRNodeId& node_id : device_ctx.rr_graph.node_lookup().find_channel_nodes(start_lookup_x, start_lookup_y, rr_type)) {
-        if (!node_id) continue;
-
         VTR_ASSERT(temp_rr_graph.node_type(node_id) == rr_type);
 
         e_direction node_direction = rr_graph.node_direction(node_id);

vpr/src/route/router_lookahead_map_utils.cpp

@@ -405,8 +405,6 @@ t_chan_ipins_delays compute_router_chan_ipin_lookahead() {
             for (int iy = min_y; iy < max_y; iy++) {
                 for (auto rr_type : {CHANX, CHANY}) {
                     for (const RRNodeId& node_id : device_ctx.rr_graph.node_lookup().find_channel_nodes(ix, iy, rr_type)) {
-                        if (!node_id) continue;
-
                         //Find the IPINs which are reachable from the wires within the bounding box
                         //around the selected tile location
                         dijkstra_flood_to_ipins(node_id, chan_ipins_delays);