[vpr][place][net_cost] fix typos

Author: amin1377

vpr/src/place/net_cost_handler.cpp

@@ -155,7 +155,7 @@ NetCostHandler::NetCostHandler(const t_placer_opts& placer_opts,
 }
 
 void NetCostHandler::alloc_and_load_chan_w_factors_for_place_cost_() {
-    float place_cost_exp = placer_opts_.place_cost_exp;
+    const double place_cost_exp = static_cast<double>(placer_opts_.place_cost_exp);
     auto& device_ctx = g_vpr_ctx.device();
 
     const int grid_height = device_ctx.grid.height();
@@ -197,7 +197,7 @@ void NetCostHandler::alloc_and_load_chan_w_factors_for_place_cost_() {
             }
 
             chanx_place_cost_fac_[high][low] = (high - low + 1.) / chanx_place_cost_fac_[high][low];
-            chanx_place_cost_fac_[high][low] = pow((double)chanx_place_cost_fac_[high][low], (double)place_cost_exp);
+            chanx_place_cost_fac_[high][low] = pow((double)chanx_place_cost_fac_[high][low], place_cost_exp);
         }
     }
 
@@ -227,7 +227,7 @@ void NetCostHandler::alloc_and_load_chan_w_factors_for_place_cost_() {
             }
 
             chany_place_cost_fac_[high][low] = (high - low + 1.) / chany_place_cost_fac_[high][low];
-            chany_place_cost_fac_[high][low] = pow((double)chany_place_cost_fac_[high][low], (double)place_cost_exp);
+            chany_place_cost_fac_[high][low] = pow((double)chany_place_cost_fac_[high][low], place_cost_exp);
         }
     }
 
@@ -268,22 +268,27 @@ void NetCostHandler::alloc_and_load_for_fast_vertical_cost_update_() {
     * the block on the lower left connection of the block is added twice, that part needs to be removed.
     */
     for (const auto& src_rr_node : rr_graph.nodes()) {
-        for (auto edge_range: {rr_graph.configurable_edges(src_rr_node), rr_graph.non_configurable_edges(src_rr_node)}) {
-            for (const auto& rr_edge_idx : edge_range) {
-                const auto& sink_rr_node = rr_graph.edge_sink_node(src_rr_node, rr_edge_idx);
-                if (rr_graph.node_layer(src_rr_node) != rr_graph.node_layer(sink_rr_node)) {
-                    // We assume that the nodes driving the inter-layer connection or being driven by it
-                    // are not stretched across multiple tiles
-                    int src_x = rr_graph.node_xhigh(src_rr_node);
-                    int src_y = rr_graph.node_yhigh(src_rr_node);
-                    VTR_ASSERT(rr_graph.node_xlow(src_rr_node) == src_x && rr_graph.node_ylow(src_rr_node) == src_y);
-
-                    tile_num_inter_die_conn[src_x][src_y]++;
-                }
+        for (const auto& rr_edge_idx : rr_graph.edges(src_rr_node)) {
+            const auto& sink_rr_node = rr_graph.edge_sink_node(src_rr_node, rr_edge_idx);
+            if (rr_graph.node_layer(src_rr_node) != rr_graph.node_layer(sink_rr_node)) {
+                // We assume that the nodes driving the inter-layer connection or being driven by it
+                // are not stretched across multiple tiles
+                int src_x = rr_graph.node_xhigh(src_rr_node);
+                int src_y = rr_graph.node_yhigh(src_rr_node);
+                VTR_ASSERT(rr_graph.node_xlow(src_rr_node) == src_x && rr_graph.node_ylow(src_rr_node) == src_y);
+
+                tile_num_inter_die_conn[src_x][src_y]++;
             }
         }
     }
 
+    int num_layers = device_ctx.grid.get_num_layers();
+    for (size_t x = 0; x < device_ctx.grid.width(); x++) {
+        for (size_t y = 0; y < device_ctx.grid.height(); y++) {
+            tile_num_inter_die_conn[x][y] /= (num_layers-1);
+        }
+    }
+
     // Step 2: Calculate prefix sum of the inter-die connectivity up to and including the channel at (x, y).
     acc_tile_num_inter_die_conn_[0][0] = tile_num_inter_die_conn[0][0];
     // Initialize the first row and column

vpr/src/place/net_cost_handler.h

@@ -198,12 +198,14 @@ class NetCostHandler {
     vtr::NdOffsetMatrix<float, 2> chanx_place_cost_fac_; // [-1...device_ctx.grid.width()-1]
     vtr::NdOffsetMatrix<float, 2> chany_place_cost_fac_; // [-1...device_ctx.grid.height()-1]
     /**
-      @brief This data structure stores the cumulative number of inter-die connections from the lower-left corner. 
-      * It is later used to calculate the chanZ factor, which functions similarly to chanx_place_cost_fac_ and chany_place_cost_fac_, 
-      * but applies to the height of the bounding box. The chanZ factor is calculated during block placement because storing it in the 
-      * same way as the X and Y cost factors would require a 4D array and population it is an O(n^2) operation.
+     * @brief The matrix below is used to calculate a chanz_place_cost_fac based on the average channel width in 
+     * the cross-die-layer direction over a 2D (x,y) region. We don't assume the inter-die connectivity is the same at all (x,y) locations, so we
+     * can't compute the full chanz_place_cost_fac for all possible (xlow,ylow)(xhigh,yhigh) without a 4D array, which would
+     * be too big: O(n^2) in circuit size. Instead we compute a prefix sum that stores the number of inter-die connections per layer from
+     * (x=0,y=0) to (x,y). Given this, we can compute the average number of inter-die connections over a (xlow,ylow) to (xhigh,yhigh) 
+     * region in O(1) (by adding and subtracting 4 entries)
      */
-    vtr::NdMatrix<int, 2> acc_tile_num_inter_die_conn_;
+    vtr::NdMatrix<int, 2> acc_tile_num_inter_die_conn_; // [0..grid_width-1][0..grid_height-1]
 
 
   private: