[libs][rr_graph] set T_linear for IPIN based on the most frequent switch connected to it

Author: amin1377

libs/librrgraph/src/utils/alloc_and_load_rr_indexed_data.cpp

@@ -2,6 +2,7 @@
 
 #include <algorithm>
 #include <cmath> /* Needed only for sqrt call (remove if sqrt removed) */
+#include <cstddef>
 #include <fstream>
 #include <iomanip>
 #include <numeric>
@@ -108,9 +109,6 @@ void alloc_and_load_rr_indexed_data(const RRGraphView& rr_graph,
         rr_indexed_data[RRIndexedDataId(i)].C_load = 0.;
     }
 
-    //TODO: SM: IPIN t_linear assumes wire_to_ipin_switch which corresponds to within die switch connection
-    rr_indexed_data[RRIndexedDataId(IPIN_COST_INDEX)].T_linear = rr_graph.rr_switch_inf(wire_to_ipin_switch).Tdel;
-
     std::vector<int> ortho_costs = find_ortho_cost_index(rr_graph, segment_inf_x, segment_inf_y, e_parallel_axis::X_AXIS);
 
     /* AA: The code below should replace find_ortho_cost_index call once we deprecate the CLASSIC lookahead as it is the only lookahead
@@ -531,12 +529,25 @@ static void load_rr_indexed_data_T_values(const RRGraphView& rr_graph,
     vtr::vector<RRIndexedDataId, std::vector<float>> switch_Cinternal_total(rr_indexed_data.size());
     vtr::vector<RRIndexedDataId, short> switches_buffered(rr_indexed_data.size(), LIBRRGRAPH_UNDEFINED_VAL);
 
+    std::map<short, int> ipin_switch_count;
+
     // Walk through the RR graph and collect all R and C values of all the nodes,
     // as well as their fan-in switches R, T_del, and Cinternal values.
     // The median of R and C values for each cost index is assigned to the indexed data.
     for (const RRNodeId rr_id : rr_graph.nodes()) {
         e_rr_type rr_type = rr_graph.node_type(rr_id);
 
+        if (rr_type == e_rr_type::IPIN) {
+            for (const RREdgeId edge : fan_in_list[rr_id]) {
+                short switch_index = rr_graph.rr_nodes().edge_switch(edge);
+                if (ipin_switch_count.find(switch_index) == ipin_switch_count.end()) {
+                    ipin_switch_count[switch_index] = 1;
+                } else {
+                    ipin_switch_count[switch_index]++;
+                }
+            }
+        }
+
         if (!is_chanxy(rr_type) && !is_chanz(rr_type)) {
             continue;
         }
@@ -590,6 +601,16 @@ static void load_rr_indexed_data_T_values(const RRGraphView& rr_graph,
         }
     }
 
+    int most_frequent_ipin_switch = -1;
+    for (const auto& [switch_index, count] : ipin_switch_count) {
+        if (count > most_frequent_ipin_switch_count) {
+            most_frequent_ipin_switch = switch_index;
+        }
+    }
+    VTR_ASSERT(most_frequent_ipin_switch != -1);
+    rr_indexed_data[RRIndexedDataId(IPIN_COST_INDEX)].T_linear = rr_graph.rr_switch_inf(RRSwitchId(most_frequent_ipin_switch)).Tdel;
+
+
     unsigned num_occurences_of_no_instances_with_cost_index = 0;
     for (size_t cost_index = CHANX_COST_INDEX_START; cost_index < rr_indexed_data.size(); cost_index++) {
         if (num_nodes_of_index[RRIndexedDataId(cost_index)] == 0) { // Segments don't exist.