Add a maximum width for expansion to help small cells in Coriolis

pycoloquinte/coloquinte.py

@@ -864,7 +864,7 @@ def main():
         if args.density <= 0.0 or args.density >= 1.0:
             raise RuntimeError(
                 "Target density should be strictly between 0 and 1.")
-        circuit.expand_cells_to_density(args.density, 0.0)
+        circuit.expand_cells_to_density(args.density, 0.0, 1.0)
     print(circuit.report())
 
     sys.stdout.flush()

pycoloquinte/module.cpp

@@ -313,7 +313,10 @@ Construct a circuit.
           "Run the detailed placement algorithm")
       .def("expand_cells_to_density", &Circuit::expandCellsToDensity,
            py::arg("target_density"), py::arg("row_side_margin") = 0.0,
-           "Expand the standard cells to reach the target density")
+           py::arg("max_expanded_size") = 1.0,
+           "Expand the standard cells to reach the target density, "
+           "with a margin in each row (in cell heights) and a maximum cell "
+           "expansion (in row widths)")
       .def("expand_cells_by_factor", &Circuit::expandCellsByFactor,
            py::arg("expansion_factor"), py::arg("max_density") = 1.0,
            py::arg("row_side_margin") = 0.0,

src/coloquinte.cpp

@@ -626,7 +626,8 @@ long long Circuit::computeRowPlacementArea(double rowSideMargin) const {
   return rowArea;
 }
 
-void Circuit::expandCellsToDensity(double targetDensity, double rowSideMargin) {
+void Circuit::expandCellsToDensity(double targetDensity, double rowSideMargin,
+                                   double maxExpandedWidth) {
   // Compute placeable cell area
   long long cellArea = 0LL;
   for (int i = 0; i < nbCells(); ++i) {
@@ -635,6 +636,7 @@ void Circuit::expandCellsToDensity(double targetDensity, double rowSideMargin) {
     }
   }
 
+  // Compute available area
   long long rowArea = computeRowPlacementArea(rowSideMargin);
 
   // Compute the density and return if no further work is needed
@@ -645,6 +647,13 @@ void Circuit::expandCellsToDensity(double targetDensity, double rowSideMargin) {
   if (density >= targetDensity) {
     return;
   }
+
+  // Compute maximum width of the rows
+  int maxRowWidth = 0;
+  for (const Row &row : rows_) {
+    maxRowWidth = std::max(maxRowWidth, row.width());
+  }
+
   double expansionFactor = targetDensity / density;
 
   // Apply the expansion
@@ -657,6 +666,11 @@ void Circuit::expandCellsToDensity(double targetDensity, double rowSideMargin) {
         continue;
       }
       double fracW = w * expansionFactor;
+      // Force the expansion to a maximum
+      if (fracW > (double)maxRowWidth) {
+        fracW = (double)maxRowWidth;
+      }
+
       int newW = (int)fracW;
       // Now, since we round down, we got some area missing
       missingArea += h * (fracW - newW);

src/coloquinte.hpp

@@ -1001,8 +1001,11 @@ class Circuit {
    * @param rowSideMargin Margin applied to each row before computing available
    * area, in standard cell heights. Usually better than tweaking the density to
    * make the placement feasible.
+   * @param maxExpandedWidth Maximum width of a cell after expansion, in maximum
+   * row width.
    */
-  void expandCellsToDensity(double targetDensity, double rowSideMargin = 0.0);
+  void expandCellsToDensity(double targetDensity, double rowSideMargin = 0.0,
+                            double maxExpandedWidth = 1.0);
 
   /**
    * @brief Apply cell size modifications to the circuit, with individual