[VPR] Patch comments and remove the inproper assert (which should be enabled later when remove_node() API is available in rr_spatial_lookup)

Author: tangxifan

vpr/src/base/vpr_context.h

@@ -165,6 +165,9 @@ struct DeviceContext : public Context {
 
     /* TODO: remove this interface from device_context once the code refactoring is completed
      * because it should be part of the rr_graph view
+     * TODO: Currently, we use reference pointers to ensure that the rr_spatial_lookup is always
+     * synchronized with the rr_node_indices but this causes a lot of confusion for developers
+     * The temporary fix should be patched as soon as possible.
      */
     RRSpatialLookup rr_spatial_lookup{rr_node_indices};
 

vpr/src/device/rr_spatial_lookup.cpp

@@ -80,7 +80,6 @@ void RRSpatialLookup::add_node(RRNodeId node,
                                t_rr_type type,
                                int ptc,
                                e_side side) {
-    VTR_ASSERT(node);
     VTR_ASSERT_SAFE(3 == rr_node_indices_[type].ndims());
 
     /* Expand the fast look-up if the new node is out-of-range

vpr/src/device/rr_spatial_lookup.h

@@ -42,6 +42,8 @@ class RRSpatialLookup {
      *     - track number of a routing wire in a channel. They would normally go from 0
      *       to channel_width - 1 at that (x,y)
      *
+     * An invalid id will be returned if the node does not exist
+     *
      * Note that for segments (CHANX and CHANY) of length > 1, the segment is
      * given an rr_index based on the (x,y) location at which it starts (i.e.
      * lowest (x,y) location at which this segment exists).
@@ -71,8 +73,6 @@ class RRSpatialLookup {
      *   - track index in a routing channel when type is CHANX/CHANY
      * - side is the side of node on the tile, applicable to OPIN/IPIN 
      *
-     * An invalid id will be returned if the node does not exist
-     *
      * Note that a node added with this call will not create a node in the rr_graph_storage node list
      * You MUST add the node in the rr_graph_storage so that the node is valid  
      *