Optimize PaintInvalidatorContext::mapLocalRectToVisualRectInBacking()

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

 // Copyright 2014 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/layout/PaintInvalidationState.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutInline.h"
 #include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/api/LayoutAPIShim.h"
 #include "core/layout/api/LayoutPartItem.h"
 #include "core/layout/svg/LayoutSVGRoot.h"
 #include "core/layout/svg/SVGLayoutSupport.h"
 #include "core/paint/PaintInvalidator.h"
 #include "core/paint/PaintLayer.h"
 #include "core/paint/PaintPropertyTreeBuilder.h"
+#include "platform/graphics/paint/GeometryMapper.h"
 
 namespace blink {
 
 static bool supportsCachedOffsets(const LayoutObject& object) {
   // Can't compute paint offsets across objects with transforms, but if they are
   // paint invalidation containers, we don't actually need to compute *across*
   // the container, just up to it. (Also, such objects are the containing block
   // for all children.)
   return !(object.hasTransformRelatedProperty() &&
            !object.isPaintInvalidationContainer()) &&
@@ skipping 597 matching lines @@
   ASSERT_NOT_REACHED();
 }
 
 #endif  // CHECK_FAST_PATH_SLOW_PATH_EQUALITY
 
 static const PaintPropertyTreeBuilderContext& dummyTreeBuilderContext() {
   DEFINE_STATIC_LOCAL(PaintPropertyTreeBuilderContext, dummyContext, ());
   return dummyContext;
 }
 
+static GeometryMapper& dummyGeometryMapper() {

[chrishtr, 2017/03/22 17:54:31]

Is it somehow guaranteed that this GeometryMapper is never used?

[Xianzhu, 2017/03/22 18:50:02]

Yes because the adapter's mapLocalRectToVisualRectInBacking() overrides the
method in PaintInvalidatorContext's. The overriding method uses
PaintInvaldiationState to map the rect.

Create a followup patch to enforce it.

[chrishtr, 2017/03/22 18:56:21]

Ok, please add a comment saying that it's guaranteed by code structure that this
dummy object
is never called.

[Xianzhu, 2017/03/22 19:20:43]

Done.

+  DEFINE_STATIC_LOCAL(std::unique_ptr<GeometryMapper>, dummyMapper,
+                      (GeometryMapper::create()));

[wkorman, 2017/03/22 18:33:40]

We saw pdr@ recently make a perf improvement by adding fast-malloc to an
instance, should we consider similar for GeometryMapper?
https://codereview.chromium.org/2744243010

Maybe it's not worth it just b/c we allocate comparatively few and not in hot
code path.

[Xianzhu, 2017/03/22 18:51:38]

I think it's not worth it.

+  return *dummyMapper;
+}
+
 PaintInvalidatorContextAdapter::PaintInvalidatorContextAdapter(
     const PaintInvalidationState& paintInvalidationState)
-    : PaintInvalidatorContext(dummyTreeBuilderContext()),
+    : PaintInvalidatorContext(dummyTreeBuilderContext(), dummyGeometryMapper()),
       m_paintInvalidationState(paintInvalidationState) {
   forcedSubtreeInvalidationFlags =
       paintInvalidationState.m_forcedSubtreeInvalidationFlags;
   paintInvalidationContainer =
       &paintInvalidationState.paintInvalidationContainer();
   paintingLayer = &paintInvalidationState.paintingLayer();
 }
 
 void PaintInvalidatorContextAdapter::mapLocalRectToVisualRectInBacking(
     const LayoutObject& object,
     LayoutRect& rect) const {
   DCHECK(&object == &m_paintInvalidationState.currentObject());
   m_paintInvalidationState.mapLocalRectToVisualRectInBacking(rect);
 }
 
 }  // namespace blink