Convert recursion to iteration in clearClipRectsIncludingDescendants

third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 159 matching lines @@
   // before we call calculateClipRects so that calculateClipRects will hit
   // the cache.
   ClipRects* parentClipRects = nullptr;
   if (context.rootLayer != &m_layer && m_layer.parent())
     parentClipRects = &m_layer.parent()->clipper().getClipRects(context);
   RefPtr<ClipRects> clipRects = ClipRects::create();
   calculateClipRects(context, *clipRects);
   return storeClipRectsInCache(context, parentClipRects, *clipRects);
 }
 
-void PaintLayerClipper::clearClipRectsIncludingDescendants() {
+void PaintLayerClipper::clearCache(ClipRectsCacheSlot cacheSlot) {

[wkorman, 2017/01/06 02:51:50]

Current unit tests in PaintLayerClipperTest look fairly limited, worth adding
some test cases to make sure this is still doing the right thing, and that the
various slots are cleared out when we expect? This Clipper business is
surprisingly complicated. I figure our layout test coverage means the core logic
will be tested as is, but it seems possible we could pass those despite some
caching missteps.

+  if (cacheSlot == NumberOfClipRectsCacheSlots)
+    m_layer.clearClipRectsCache();
+  else if (ClipRectsCache* cache = m_layer.clipRectsCache())
+    cache->clear(cacheSlot);
+
   if (m_geometryMapper)
     m_geometryMapper.reset(new GeometryMapper);
-  m_layer.clearClipRectsCache();
+}
 
-  for (PaintLayer* layer = m_layer.firstChild(); layer;
-       layer = layer->nextSibling()) {
-    layer->clipper().clearClipRectsIncludingDescendants();
-  }
+void PaintLayerClipper::clearClipRectsIncludingDescendants() {
+  clearClipRectsIncludingDescendants(NumberOfClipRectsCacheSlots);
 }
 
 void PaintLayerClipper::clearClipRectsIncludingDescendants(
     ClipRectsCacheSlot cacheSlot) {
-  if (m_geometryMapper)
-    m_geometryMapper.reset(new GeometryMapper);
+  std::stack<const PaintLayer*> layers;
+  layers.push(&m_layer);
 
-  if (ClipRectsCache* cache = m_layer.clipRectsCache())
-    cache->clear(cacheSlot);
-
-  for (PaintLayer* layer = m_layer.firstChild(); layer;
-       layer = layer->nextSibling()) {
-    layer->clipper().clearClipRectsIncludingDescendants(cacheSlot);
+  while (!layers.empty()) {
+    const PaintLayer* currentLayer = layers.top();
+    layers.pop();
+    currentLayer->clipper().clearCache(cacheSlot);
+    for (const PaintLayer* layer = currentLayer->firstChild(); layer;
+         layer = layer->nextSibling())
+      layers.push(layer);
   }
 }
 
 LayoutRect PaintLayerClipper::localClipRect(
     const PaintLayer* clippingRootLayer) const {
   ClipRectsContext context(clippingRootLayer, PaintingClipRects);
   if (m_geometryMapper) {
     ClipRect clipRect = applyOverflowClipToBackgroundRectWithGeometryMapper(
         context, clipRectWithGeometryMapper(context, false));
 
@@ skipping 342 matching lines @@
     const LayoutSize& subpixelAccumulation) const {
   DCHECK(!m_geometryMapper);
   ClipRectsContext context(rootLayer, PaintingClipRects,
                            IgnoreOverlayScrollbarSize, subpixelAccumulation);
   if (respectOverflowClip == IgnoreOverflowClip)
     context.setIgnoreOverflowClip();
   return getClipRects(context);
 }
 
 }  // namespace blink