Convert recursion to iteration in clearClipRectsIncludingDescendants

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

Index: third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp b/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
index 3f8a6de6090b6dedea8057046b768ba5a7b09be4..05403b54b938ad0469cfb1ffbad9ce26ad82448f 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
@@ -177,28 +177,32 @@ ClipRects& PaintLayerClipper::getClipRects(
   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);
-
-  if (ClipRectsCache* cache = m_layer.clipRectsCache())
-    cache->clear(cacheSlot);
-
-  for (PaintLayer* layer = m_layer.firstChild(); layer;
-       layer = layer->nextSibling()) {
-    layer->clipper().clearClipRectsIncludingDescendants(cacheSlot);
+  std::stack<const PaintLayer*> layers;
+  layers.push(&m_layer);
+
+  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);
   }
 }