Remove clips where we can show that they are unnecessary.

Source/core/rendering/RenderBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 1499 matching lines @@
             BackgroundImageGeometry geometry;
             layerRenderer->calculateBackgroundImageGeometry(curLayer, rendererRect, geometry);
             layerRenderer->repaintRectangle(geometry.destRect());
             if (geometry.destRect() == rendererRect)
                 return true;
         }
     }
     return false;
 }
 
-bool RenderBox::pushContentsClip(PaintInfo& paintInfo, const LayoutPoint& accumulatedOffset)
+bool RenderBox::pushContentsClip(PaintInfo& paintInfo, const LayoutPoint& accumulatedOffset, ContentsClipBehavior contentsClipBehavior)
 {
     if (paintInfo.phase == PaintPhaseBlockBackground || paintInfo.phase == PaintPhaseSelfOutline || paintInfo.phase == PaintPhaseMask)
         return false;
 
     bool isControlClip = hasControlClip();
     bool isOverflowClip = hasOverflowClip() && !layer()->isSelfPaintingLayer();
 
     if (!isControlClip && !isOverflowClip)
         return false;
 
+    LayoutRect clipRect = isControlClip ? controlClipRect(accumulatedOffset) : overflowClipRect(accumulatedOffset, paintInfo.renderRegion);
+    RoundedRect clipRoundedRect(0, 0, 0, 0);
+    bool hasBorderRadius = style()->hasBorderRadius();
+    if (hasBorderRadius)
+        clipRoundedRect = style()->getRoundedInnerBorderFor(LayoutRect(accumulatedOffset, size()));
+
+    if (contentsClipBehavior == SkipContentsClipIfPossible) {
+        LayoutRect contentsVisualOverflow = contentsVisualOverflowRect();
+        if (contentsVisualOverflow.isEmpty())
+            return false;
+
+        LayoutRect conservativeClipRect = clipRect;
+        if (hasBorderRadius)
+            conservativeClipRect.intersect(clipRoundedRect.radiusCenterRect());
+        conservativeClipRect.moveBy(-accumulatedOffset);
+        if (hasLayer())
+            conservativeClipRect.move(scrolledContentOffset());
+        if (conservativeClipRect.contains(contentsVisualOverflow))
+            return false;
+    }
+
     if (paintInfo.phase == PaintPhaseOutline)
         paintInfo.phase = PaintPhaseChildOutlines;
     else if (paintInfo.phase == PaintPhaseChildBlockBackground) {
         paintInfo.phase = PaintPhaseBlockBackground;
         paintObject(paintInfo, accumulatedOffset);
         paintInfo.phase = PaintPhaseChildBlockBackgrounds;
     }
-    IntRect clipRect = pixelSnappedIntRect(isControlClip ? controlClipRect(accumulatedOffset) : overflowClipRect(accumulatedOffset, paintInfo.renderRegion));
     paintInfo.context->save();
-    if (style()->hasBorderRadius())
-        paintInfo.context->clipRoundedRect(style()->getRoundedInnerBorderFor(LayoutRect(accumulatedOffset, size())));
-    paintInfo.context->clip(clipRect);
+    if (hasBorderRadius)
+        paintInfo.context->clipRoundedRect(clipRoundedRect);
+    paintInfo.context->clip(pixelSnappedIntRect(clipRect));
     return true;
 }
 
 void RenderBox::popContentsClip(PaintInfo& paintInfo, PaintPhase originalPhase, const LayoutPoint& accumulatedOffset)
 {
     ASSERT(hasControlClip() || (hasOverflowClip() && !layer()->isSelfPaintingLayer()));
 
     paintInfo.context->restore();
     if (originalPhase == PaintPhaseOutline) {
         paintInfo.phase = PaintPhaseSelfOutline;
@@ skipping 2650 matching lines @@
 
         // In flipped blocks writing modes, the physical sides are inverted. For example in vertical-rl, the right
         // border is at the lower x coordinate value.
         overflowMinX = min(overflowMinX, borderBox.x() - ((!isFlipped || isHorizontal) ? borderOutsets.left() : borderOutsets.right()));
         overflowMaxX = max(overflowMaxX, borderBox.maxX() + ((!isFlipped || isHorizontal) ? borderOutsets.right() : borderOutsets.left()));
         overflowMinY = min(overflowMinY, borderBox.y() - ((!isFlipped || !isHorizontal) ? borderOutsets.top() : borderOutsets.bottom()));
         overflowMaxY = max(overflowMaxY, borderBox.maxY() + ((!isFlipped || !isHorizontal) ? borderOutsets.bottom() : borderOutsets.top()));
     }
 
     // Add in the final overflow with shadows and outsets combined.
-    addVisualOverflow(LayoutRect(overflowMinX, overflowMinY, overflowMaxX - overflowMinX, overflowMaxY - overflowMinY));
+    LayoutRect visualEffectOverflow(overflowMinX, overflowMinY, overflowMaxX - overflowMinX, overflowMaxY - overflowMinY);
+    addVisualOverflow(visualEffectOverflow);
 }
 
 void RenderBox::addOverflowFromChild(RenderBox* child, const LayoutSize& delta)
 {
     // Never allow flow threads to propagate overflow up to a parent.
     if (child->isRenderFlowThread())
         return;
 
     // Only propagate layout overflow from the child if the child isn't clipping its overflow.  If it is, then
     // its overflow is internal to it, and we don't care about it.  layoutOverflowRectForPropagation takes care of this
     // and just propagates the border box rect instead.
     LayoutRect childLayoutOverflowRect = child->layoutOverflowRectForPropagation(style());
     childLayoutOverflowRect.move(delta);
     addLayoutOverflow(childLayoutOverflowRect);
 
     // Add in visual overflow from the child.  Even if the child clips its overflow, it may still
     // have visual overflow of its own set from box shadows or reflections.  It is unnecessary to propagate this
     // overflow if we are clipping our own overflow.
-    if (child->hasSelfPaintingLayer() || hasOverflowClip())
+    if (child->hasSelfPaintingLayer())
         return;
     LayoutRect childVisualOverflowRect = child->visualOverflowRectForPropagation(style());
     childVisualOverflowRect.move(delta);
-    addVisualOverflow(childVisualOverflowRect);
+    addContentsVisualOverflow(childVisualOverflowRect);
 }
 
 void RenderBox::addLayoutOverflow(const LayoutRect& rect)
 {
     LayoutRect clientBox = noOverflowRect();
     if (clientBox.contains(rect) || rect.isEmpty())
         return;
 
     // For overflow clip objects, we don't want to propagate overflow into unreachable areas.
     LayoutRect overflowRect(rect);
@@ skipping 44 matching lines @@
     LayoutRect borderBox = borderBoxRect();
     if (borderBox.contains(rect) || rect.isEmpty())
         return;
 
     if (!m_overflow)
         m_overflow = adoptPtr(new RenderOverflow(noOverflowRect(), borderBox));
 
     m_overflow->addVisualOverflow(rect);
 }
 
+void RenderBox::addContentsVisualOverflow(const LayoutRect& rect)
+{
+    if (!hasOverflowClip()) {
+        addVisualOverflow(rect);
+        return;
+    }
+
+    if (!m_overflow)
+        m_overflow = adoptPtr(new RenderOverflow(clientBoxRect(), borderBoxRect()));
+    m_overflow->addContentsVisualOverflow(rect);
+}
+
 void RenderBox::clearLayoutOverflow()
 {
     if (!m_overflow)
         return;
 
-    if (!hasVisualOverflow()) {
+    if (!hasVisualOverflow() && contentsVisualOverflowRect().isEmpty()) {
         m_overflow.clear();
         return;
     }
 
     m_overflow->setLayoutOverflow(noOverflowRect());
 }
 
 inline static bool percentageLogicalHeightIsResolvable(const RenderBox* box)
 {
     return RenderBox::percentageLogicalHeightIsResolvableFromBlock(box->containingBlock(), box->isOutOfFlowPositioned());
@@ skipping 369 matching lines @@
     }
 
     if (didSplitParentAnonymousBoxes)
         markBoxForRelayoutAfterSplit(this);
 
     ASSERT(beforeChild->parent() == this);
     return beforeChild;
 }
 
 } // namespace WebCore