Optimize collapsed border calculation (step 2)

third_party/WebKit/Source/core/layout/LayoutTable.cpp

Index: third_party/WebKit/Source/core/layout/LayoutTable.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutTable.cpp b/third_party/WebKit/Source/core/layout/LayoutTable.cpp
index c0bb217186c7c7920a379781fad95237bbd71264..e89e3838665c20bf8a72b020b9e78c2397f6ddd1 100644
--- a/third_party/WebKit/Source/core/layout/LayoutTable.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutTable.cpp
@@ -103,12 +103,12 @@ void LayoutTable::StyleDidChange(StyleDifference diff,
   if (!old_style)
     return;
 
-  if (old_style->BorderCollapse() != StyleRef().BorderCollapse()) {
-    InvalidateCollapsedBorders();
-  } else {
-    LayoutTableBoxComponent::InvalidateCollapsedBordersOnStyleChange(
-        *this, *this, diff, *old_style);
-  }
+  if (old_style->BorderCollapse() != StyleRef().BorderCollapse())
+    SetNeedsInvalidateCollapsedBordersForAllCells();
+  else if (LayoutTableBoxComponent::
+               NeedsInvalidateCollapsedBordersOnStyleChange(*this, *this, diff,
+                                                            *old_style))
+    InvalidateCollapsedBordersOfAffectedCells();
 
   if (LayoutTableBoxComponent::DoCellsHaveDirtyWidth(*this, *this, diff,
                                                      *old_style))
@@ -807,6 +807,40 @@ void LayoutTable::InvalidateCollapsedBordersForAllCellsIfNeeded() {
   }
 }
 
+void LayoutTable::InvalidateCollapsedBordersOfAffectedCells() {
+  DCHECK(CollapseBorders());
+  if (NeedsInvalidateCollapsedBordersForAllCells())
+    return;
+
+  RecalcSectionsIfNeeded();
+  InvalidateCollapsedBorders();
+
+  auto* top_section = TopNonEmptySection();
+  if (!top_section)
+    return;
+
+  // Invalidate cells in the top row.
+  top_section->InvalidateCellCollapsedBordersIntersectingRow(0);
+
+  LayoutTableSection* bottom_section = nullptr;
+  for (auto* section = top_section; section;
+       section = SectionBelow(section, kSkipEmptySections)) {
+    auto num_effective_columns = section->NumEffectiveColumns();
+    for (unsigned r = 0; r < section->NumRows(); ++r) {
+      if (auto* cell = section->PrimaryCellAt(r, 0))
+        cell->InvalidateCollapsedBorderValues();
+      if (auto* cell = section->PrimaryCellAt(r, num_effective_columns - 1))
+        cell->InvalidateCollapsedBorderValues();
+    }
+    bottom_section = section;
+  }
+
+  if (bottom_section != top_section || bottom_section->NumRows() > 1) {
+    bottom_section->InvalidateCellCollapsedBordersIntersectingRow(
+        bottom_section->NumRows() - 1);
+  }
+}
+
 // Collect all the unique border values that we want to paint in a sorted list.
 // During the collection, each cell saves its recalculated borders into the
 // cache of its containing section, and invalidates itself if any border
@@ -1495,56 +1529,16 @@ LayoutTableSection* LayoutTable::BottomSection() const {
 
 LayoutTableCell* LayoutTable::CellAbove(const LayoutTableCell* cell) const {
   RecalcSectionsIfNeeded();
-
-  // Find the section and row to look in

[wkorman, 2017/04/27 22:05:36]

Is the simplified logic here and in CellBelow beneath essentially identical, and
we're just using the new helper methods so as to share logic?

-  unsigned r = cell->RowIndex();
-  LayoutTableSection* section = nullptr;
-  unsigned r_above = 0;
-  if (r > 0) {
-    // cell is not in the first row, so use the above row in its own section
-    section = cell->Section();
-    r_above = r - 1;
-  } else {
-    section = SectionAbove(cell->Section(), kSkipEmptySections);
-    if (section) {
-      DCHECK(section->NumRows());
-      r_above = section->NumRows() - 1;
-    }
-  }
-
-  // Look up the cell in the section's grid, which requires effective col index
-  if (section) {
-    unsigned eff_col =
-        AbsoluteColumnToEffectiveColumn(cell->AbsoluteColumnIndex());
-    return section->PrimaryCellAt(r_above, eff_col);
-  }
-  return nullptr;
+  return cell->Section()->PrimaryCellAboveInTable(
+      cell->RowIndex(),
+      AbsoluteColumnToEffectiveColumn(cell->AbsoluteColumnIndex()));
 }
 
 LayoutTableCell* LayoutTable::CellBelow(const LayoutTableCell* cell) const {
   RecalcSectionsIfNeeded();
-
-  // Find the section and row to look in
-  unsigned r = cell->RowIndex() + cell->RowSpan() - 1;
-  LayoutTableSection* section = nullptr;
-  unsigned r_below = 0;
-  if (r < cell->Section()->NumRows() - 1) {
-    // The cell is not in the last row, so use the next row in the section.
-    section = cell->Section();
-    r_below = r + 1;
-  } else {
-    section = SectionBelow(cell->Section(), kSkipEmptySections);
-    if (section)
-      r_below = 0;
-  }
-
-  // Look up the cell in the section's grid, which requires effective col index
-  if (section) {
-    unsigned eff_col =
-        AbsoluteColumnToEffectiveColumn(cell->AbsoluteColumnIndex());
-    return section->PrimaryCellAt(r_below, eff_col);
-  }
-  return nullptr;
+  return cell->Section()->PrimaryCellBelowInTable(
+      cell->RowIndex(),
+      AbsoluteColumnToEffectiveColumn(cell->AbsoluteColumnIndex()));
 }
 
 LayoutTableCell* LayoutTable::CellBefore(const LayoutTableCell* cell) const {