Don't bother checking for paint properties for classes that never need them.

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintPropertyTreeBuilder.h"
 
 #include <memory>
 #include "core/dom/DOMNodeIds.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
@@ skipping 1189 matching lines @@
       paint_properties.SetCompositorElementId(
           CreateDomNodeBasedCompositorElementId(object));
     }
   } else {
     object.GetMutableForPainting().ClearPaintProperties();
     if (had_paint_properties)
       full_context.force_subtree_update = true;
   }
 }
 
+static inline bool MightNeedPaintProperties(const LayoutObject& object) {
+  return object.IsBoxModelObject() || object.IsSVG();

[pdr., 2017/05/15 21:32:45]

Why is IsSVG() needed?

[chrishtr, 2017/05/15 21:36:22]

NeedsSVGLocalToBorderBoxTransform, NeedsTransformForNonRootSVG and NeedsEffect
all
trigger on SVG roots or children.

+}
+
 void PaintPropertyTreeBuilder::UpdatePropertiesForSelf(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& full_context) {
   PaintPropertyTreeBuilderFragmentContext& context = full_context.fragments[0];
   if (object.IsSVGHiddenContainer()) {
     // SVG resources are painted within one or more other locations in the
     // SVG during paint, and hence have their own independent paint property
     // trees, paint offset, etc.
     context = PaintPropertyTreeBuilderFragmentContext();
   }
 
-  UpdatePaintProperties(object, full_context);
+  bool might_need_paint_properties = MightNeedPaintProperties(object);

[pdr., 2017/05/15 21:32:45]

It's important that this does not change between updates. In other words, a
layoutobject cannot change from not might-need-paint-properties to needing paint
properties. I think it would be useful if this variable and function reflected
that. Something like "ObjectTypeMightNeedPaintProperties"?

[chrishtr, 2017/05/15 21:36:22]

Indeed. Changed.

+
+  if (might_need_paint_properties)

[pdr., 2017/05/15 21:32:45]

Is the perf win just reducing the calls to this fn by one?

[chrishtr, 2017/05/15 21:36:22]

No. the perf win is not calling UpdatePaintProperties, which will
call a whole bunch of other functions, some of which call others
and have a bit of non-trivial logic, just to verify that text
nodes etc have no paint properties.

+    UpdatePaintProperties(object, full_context);
 
   bool is_actually_needed = false;
 #if DCHECK_IS_ON()
   is_actually_needed = full_context.is_actually_needed;
 #endif
 
   // This is not in FindObjectPropertiesNeedingUpdateScope because paint offset
   // can change without needsPaintPropertyUpdate.
   UpdateForObjectLocationAndSize(
       object, full_context.container_for_absolute_position, is_actually_needed,
       context, full_context.force_subtree_update);
 
 #if DCHECK_IS_ON()
   FindObjectPropertiesNeedingUpdateScope check_needs_update_scope(
       object, full_context.force_subtree_update);
 #endif
 
-  if (object.IsBoxModelObject() || object.IsSVG()) {
+  if (might_need_paint_properties) {
     UpdateTransform(object, context, full_context.force_subtree_update);
     UpdateCssClip(object, context, full_context.force_subtree_update);
     if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
       UpdateEffect(object, context, full_context.force_subtree_update);
       UpdateFilter(object, context, full_context.force_subtree_update);
     }
     UpdateLocalBorderBoxContext(object, context,
                                 full_context.force_subtree_update);
     if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
       UpdateScrollbarPaintOffset(object, context,
                                  full_context.force_subtree_update);
     }
   }
 }
 
 void PaintPropertyTreeBuilder::UpdatePropertiesForChildren(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
-  if (!object.IsBoxModelObject() && !object.IsSVG())
+  if (!MightNeedPaintProperties(object))
     return;
 
   for (auto& fragment_context : context.fragments) {
 #if DCHECK_IS_ON()
     FindObjectPropertiesNeedingUpdateScope check_needs_update_scope(
         object, context.force_subtree_update);
 #endif
     UpdateOverflowClip(object, fragment_context, context.force_subtree_update);
     UpdatePerspective(object, fragment_context, context.force_subtree_update);
     UpdateSvgLocalToBorderBoxTransform(object, fragment_context,
                                        context.force_subtree_update);
     UpdateScrollAndScrollTranslation(object, fragment_context,
                                      context.force_subtree_update);
     UpdateOutOfFlowContext(object, fragment_context,
                            context.force_subtree_update);
 
     context.force_subtree_update |= object.SubtreeNeedsPaintPropertyUpdate();
   }
 
   if (object.CanContainAbsolutePositionObjects())
     context.container_for_absolute_position = &object;
 }
 
 }  // namespace blink