Optimize number of rowspan cells required to distribute their height in rows.

Source/core/rendering/RenderTableSection.cpp

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 510 matching lines @@
 
     m_rowPos.resize(m_grid.size() + 1);
 
     // We ignore the border-spacing on any non-top section as it is already included in the previous section's last row position.
     if (this == table()->topSection())
         m_rowPos[0] = table()->vBorderSpacing();
     else
         m_rowPos[0] = 0;
 
     SpanningRenderTableCells rowSpanCells;
+#ifndef NDEBUG
+    HashSet<const RenderTableCell*> uniqueCells;
+#endif
 
     for (unsigned r = 0; r < m_grid.size(); r++) {
         m_grid[r].baseline = 0;
         LayoutUnit baselineDescent = 0;
 
         // Our base size is the biggest logical height from our cells' styles (excluding row spanning cells).
         m_rowPos[r + 1] = max(m_rowPos[r] + minimumValueForLength(m_grid[r].logicalHeight, 0, viewRenderer).round(), 0);
 
         Row& row = m_grid[r].row;
         unsigned totalCols = row.size();
+        RenderTableCell* lastRowSpanCell = 0;
 
         for (unsigned c = 0; c < totalCols; c++) {
             CellStruct& current = cellAt(r, c);
             for (unsigned i = 0; i < current.cells.size(); i++) {
                 cell = current.cells[i];
                 if (current.inColSpan && cell->rowSpan() == 1)
                     continue;
 
                 if (RuntimeEnabledFeatures::rowSpanLogicalHeightSpreadingEnabled()) {
                     if (cell->rowSpan() > 1) {
                         // For row spanning cells, we only handle them for the first row they span. This ensures we take their baseline into account.
-                        if (cell->rowIndex() == r) {
+                        if (lastRowSpanCell != cell && cell->rowIndex() == r) {
+#ifndef NDEBUG
+                            ASSERT(!uniqueCells.contains(cell));
+                            uniqueCells.add(cell);
+#endif
+
                             rowSpanCells.append(cell);
+                            lastRowSpanCell = cell;
 
                             // Find out the baseline. The baseline is set on the first row in a rowSpan.
                             updateBaselineForCell(cell, r, baselineDescent);
                         }
                         continue;
                     }
 
                     ASSERT(cell->rowSpan() == 1);
                 } else {
                     // FIXME: We add all the logical row of a rowspan to the last rows
@@ skipping 1133 matching lines @@
     if (!style()->isLeftToRightDirection())
         cellLocation.setX(table()->columnPositions()[table()->numEffCols()] - table()->columnPositions()[table()->colToEffCol(cell->col() + cell->colSpan())] + horizontalBorderSpacing);
     else
         cellLocation.setX(table()->columnPositions()[effectiveColumn] + horizontalBorderSpacing);
 
     cell->setLogicalLocation(cellLocation);
     view()->addLayoutDelta(oldCellLocation - cell->location());
 }
 
 } // namespace WebCore