Add comments around edge sorting.

Signed-off-by: Keith Rothman <[email protected]>

Author: litghost

vpr/src/route/rr_graph_storage.cpp

@@ -254,7 +254,7 @@ class edge_compare_src_node_and_configurable_first {
     const std::vector<t_rr_switch_inf>& rr_switch_inf_;
 };
 
-void t_rr_graph_storage::assign_edges() {
+void t_rr_graph_storage::assign_first_edges() {
     VTR_ASSERT(first_edge_.empty());
 
     // Last element is a dummy element
@@ -418,14 +418,19 @@ void t_rr_graph_storage::partition_edges() {
     VTR_ASSERT(remapped_edges_);
 
     const auto& device_ctx = g_vpr_ctx.device();
+    // This sort ensures two things:
+    //  - Edges are stored in ascending source node order.  This is required
+    //    by assign_first_edges()
+    //  - Edges within a source node have the configurable edges before the
+    //    non-configurable edges.
     std::stable_sort(
         edge_sort_iterator(this, 0),
         edge_sort_iterator(this, edge_src_node_.size()),
         edge_compare_src_node_and_configurable_first(device_ctx.rr_switch_inf));
 
     partitioned_ = true;
 
-    assign_edges();
+    assign_first_edges();
 
     VTR_ASSERT_SAFE(validate());
 }

vpr/src/route/rr_graph_storage.h

@@ -340,7 +340,7 @@ class t_rr_graph_storage {
 
     // Take allocated edges in edge_src_node_/ edge_dest_node_ / edge_switch_
     // sort, and assign the first edge for each
-    void assign_edges();
+    void assign_first_edges();
 
     // Verify that first_edge_ array correctly partitions rr edge data.
     bool verify_first_edges() const;