grt/cugr: tidy via-demand comments and fix stale wording

Signed-off-by: Eder Monteiro <emrmonteiro@precisioninno.com>

Author: eder-matheus

src/grt/src/cugr/src/Design.cpp

@@ -355,12 +355,8 @@ void Design::setUnitCosts()
 odb::dbTechVia* Design::chooseViaForPair(odb::dbTechLayer* lower_tl,
                                          odb::dbTechLayer* upper_tl) const
 {
-  // Select the via whose footprint best approximates what drt will place.
-  // odb::dbBlock::getDefaultVias fabricates a default from the first via in db
-  // order when no OR_DEFAULT is set, which is arbitrary; instead rank all vias
-  // connecting the pair. drt's initDefaultVias always takes the single-cut
-  // group first, so order by: OR_DEFAULT, then fewest cuts, then the
-  // LEF-default flag, then the smallest metal enclosure.
+  // Rank vias connecting the pair by a drt-like priority: OR_DEFAULT, then
+  // fewest cuts, then LEF-default, then smallest enclosure.
   odb::dbTechLayer* cut_tl = lower_tl->getUpperLayer();
   odb::dbTechVia* best = nullptr;
   std::tuple<bool, int, bool, int64_t> best_key;
@@ -393,8 +389,7 @@ odb::dbTechVia* Design::chooseViaForPair(odb::dbTechLayer* lower_tl,
 void Design::computeViaDemandLengths()
 {
   const int num_layers = getNumLayers();
-  // Legacy proxy: min-area stub length inflated by the flat via_multiplier.
-  // Used as the fallback when the tech has no default via for a layer pair.
+  // Fallback proxy (min-area stub x via_multiplier) for pairs with no via.
   via_demand_length_lower_.assign(num_layers, 0.0);
   via_demand_length_upper_.assign(num_layers, 0.0);
 
@@ -412,8 +407,7 @@ void Design::computeViaDemandLengths()
 
     double num_lower = lower.getMinLength() * constants_.via_multiplier;
     double num_upper = upper.getMinLength() * constants_.via_multiplier;
-    // Union all boxes on each routing layer: a via may have several rects on a
-    // layer, and the footprint is their combined extent, not the last one.
+    // Union the boxes on each layer; a via may have several rects per layer.
     odb::Rect lo_box, up_box;
     lo_box.mergeInit();
     up_box.mergeInit();
@@ -436,8 +430,7 @@ void Design::computeViaDemandLengths()
     via_demand_length_upper_[i] = num_upper;
 
     if (debug) {
-      // Enclosure sizes are the via pad extents (x*y DBU); demand is the
-      // per-via fraction of one track for a uniform gcell.
+      // Report enclosures, lengths, and per-track demand for each pair.
       const int gcell = default_gridline_spacing_;
       const std::string via_src
           = via != nullptr ? via->getName() : std::string("min_area-fallback");
@@ -475,15 +468,13 @@ double Design::viaDemandLength(const MetalLayer& layer,
                                const int dy) const
 {
   const int pitch = layer.getPitch();
-  // getSpacing() is 0 on techs that give spacing only via a parallel table;
-  // fall back to the table-derived default so the spacing term is not lost.
+  // getSpacing() is 0 on parallel-table-only techs; use default spacing then.
   const int spacing
       = layer.getSpacing() > 0 ? layer.getSpacing() : layer.getDefaultSpacing();
   // Split the pad into extent along the routing direction and across tracks.
   const int along = (layer.getDirection() == MetalLayer::H) ? dx : dy;
   const int perp = (layer.getDirection() == MetalLayer::H) ? dy : dx;
-  // A via blocks whole tracks perpendicular to the routing direction; round the
-  // keep-out (via metal + spacing on both sides) up to an integer track count.
+  // A via blocks whole tracks; ceil the keep-out to an integer track count.
   const double tracks_blocked
       = pitch > 0 ? std::ceil(static_cast<double>(perp + 2 * spacing) / pitch)
                   : 1.0;

src/grt/src/cugr/src/Design.h

@@ -58,8 +58,7 @@ class Design
   {
     return layers_[layer_index];
   }
-  // Effective via demand length (enclosure_along * tracks_blocked) for the via
-  // between routing layers i and i+1, charged to the lower/upper layer.
+  // Effective via demand length charged to the lower / upper layer of via i.
   double getViaDemandLengthLower(int i) const
   {
     return via_demand_length_lower_[i];
@@ -97,15 +96,12 @@ class Design
   void readDesignObstructions();
   void computeGrid();
   void setUnitCosts();
-  // Fill via_demand_length_{lower,upper}_ from the tech's default vias.
+  // Fill via_demand_length_{lower,upper}_ from each pair's via geometry.
   void computeViaDemandLengths();
-  // Pick the via connecting two routing layers, ranked to approximate drt:
-  // OR_DEFAULT, then fewest cuts, then LEF-default, then smallest enclosure.
+  // Pick the via for a layer pair, ranked to approximate drt's choice.
   odb::dbTechVia* chooseViaForPair(odb::dbTechLayer* lower_tl,
                                    odb::dbTechLayer* upper_tl) const;
-  // Effective demand length of a via pad on one layer: its enclosure extent
-  // along the routing direction scaled by the number of tracks it blocks
-  // across.
+  // Via pad demand length: extent along routing dir x tracks blocked across.
   double viaDemandLength(const MetalLayer& layer, int dx, int dy) const;
 
   // debug functions
@@ -115,9 +111,7 @@ class Design
   int lib_dbu_;
   BoxT die_region_;
   std::vector<MetalLayer> layers_;
-  // Indexed by the via's lower routing-layer; lower_ is charged to layer i,
-  // upper_ to layer i+1. Falls back to min_length * via_multiplier when the
-  // tech exposes no default via for the pair.
+  // Effective via demand length per lower layer i (lower_ = i, upper_ = i+1).
   std::vector<double> via_demand_length_lower_;
   std::vector<double> via_demand_length_upper_;
   std::vector<CUGRNet> nets_;

src/grt/src/cugr/src/GridGraph.cpp

@@ -297,9 +297,7 @@ CapacityT GridGraph::viaDemand(const int layer_index,
                                const int l,
                                const int edge_sum) const
 {
-  // Design digested the via geometry into an effective length per layer role;
-  // spread it over the two flanking edges (lower role for the via's lower
-  // layer, upper role for the upper layer).
+  // Spread the layer's precomputed via demand length over its two edges.
   const double via_num = (l == layer_index)
                              ? design_->getViaDemandLengthLower(layer_index)
                              : design_->getViaDemandLengthUpper(layer_index);

src/grt/src/cugr/src/GridGraph.h

@@ -354,8 +354,7 @@ class GridGraph
   void commitTree(const std::shared_ptr<GRTreeNode>& tree,
                   bool rip_up = false,
                   const std::vector<double>& net_costs = {});
-  // Per-via demand on layer `l` (lower or upper role) of the via at
-  // `layer_index`, spread over its two flanking edges (`edge_sum`).
+  // Per-via demand on layer `l` of via `layer_index`, spread over `edge_sum`.
   CapacityT viaDemand(int layer_index, int l, int edge_sum) const;
 
   utl::Logger* logger_;