Optimize RenderTable::colToEffCol() for tables without colspans

Source/core/rendering/RenderTable.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, 2007, 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 44 matching lines @@
     : RenderBlock(element)
     , m_head(0)
     , m_foot(0)
     , m_firstBody(0)
     , m_currentBorder(0)
     , m_collapsedBordersValid(false)
     , m_hasColElements(false)
     , m_needsSectionRecalc(false)
     , m_columnLogicalWidthChanged(false)
     , m_columnRenderersValid(false)
+    , m_hasCellColspanThatDeterminesTableWidth(false)
     , m_hSpacing(0)
     , m_vSpacing(0)
     , m_borderStart(0)
     , m_borderEnd(0)
 {
     setChildrenInline(false);
     m_columnPos.fill(0, 1);
 
 }
 
@@ skipping 753 matching lines @@
     }
 
     m_columnPos.grow(numEffCols() + 1);
 }
 
 void RenderTable::appendColumn(unsigned span)
 {
     unsigned newColumnIndex = m_columns.size();
     m_columns.append(ColumnStruct(span));
 
+    // Unless the table has cell(s) with colspan that exceed the number of columns afforded
+    // by the other rows in the table we can use the fast path when mapping columns to effective columns.
+    m_hasCellColspanThatDeterminesTableWidth = m_hasCellColspanThatDeterminesTableWidth || span > 1;
+
     // Propagate the change in our columns representation to the sections that don't need
     // cell recalc. If they do, they will be synced up directly with m_columns later.
     for (RenderObject* child = firstChild(); child; child = child->nextSibling()) {
         if (!child->isTableSection())
             continue;
 
         RenderTableSection* section = toRenderTableSection(child);
         if (section->needsCellRecalc())
             continue;
 
@@ skipping 54 matching lines @@
 }
 
 void RenderTable::recalcSections() const
 {
     ASSERT(m_needsSectionRecalc);
 
     m_head = 0;
     m_foot = 0;
     m_firstBody = 0;
     m_hasColElements = false;
+    m_hasCellColspanThatDeterminesTableWidth = hasCellColspanThatDeterminesTableWidth();
 
     // We need to get valid pointers to caption, head, foot and first body again
     RenderObject* nextSibling;
     for (RenderObject* child = firstChild(); child; child = nextSibling) {
         nextSibling = child->nextSibling();
         switch (child->style()->display()) {
         case TABLE_COLUMN:
         case TABLE_COLUMN_GROUP:
             m_hasColElements = true;
             break;
@@ skipping 528 matching lines @@
 const BorderValue& RenderTable::tableEndBorderAdjoiningCell(const RenderTableCell* cell) const
 {
     ASSERT(cell->isFirstOrLastCellInRow());
     if (hasSameDirectionAs(cell->row()))
         return style()->borderEnd();
 
     return style()->borderStart();
 }
 
 }