Optimize for horizontal writing mode

Source/core/rendering/InlineBox.cpp

 /*
  * Copyright (C) 2003, 2004, 2005, 2006, 2007 Apple Inc. 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 290 matching lines @@
 
 void InlineBox::clearKnownToHaveNoOverflow()
 {
     m_bitfields.setKnownToHaveNoOverflow(false);
     if (parent() && parent()->knownToHaveNoOverflow())
         parent()->clearKnownToHaveNoOverflow();
 }
 
 FloatPoint InlineBox::locationIncludingFlipping()
 {
-    if (!renderer().style()->isFlippedBlocksWritingMode())
+    if (!UNLIKELY(renderer().document().hasVerticalWritingMode())
+        || !renderer().style()->isFlippedBlocksWritingMode()) {
         return FloatPoint(x(), y());
+    }
     RenderBlockFlow& block = root().block();
     if (block.style()->isHorizontalWritingMode())
         return FloatPoint(x(), block.height() - height() - y());
 
     return FloatPoint(block.width() - width() - x(), y());
 }
 
 void InlineBox::flipForWritingMode(FloatRect& rect)
 {
-    if (!renderer().style()->isFlippedBlocksWritingMode())
+    if (!UNLIKELY(renderer().document().hasVerticalWritingMode())

[pdr., 2014/10/21 22:11:26]

I'm not a huge fan of sprinkling unlikely's around because we may miss out on
wins both in this patch and in future refactorings. What do you think about
changing RenderStyle::isFlippedBlocksWritingMode to
RenderStyle::slowIsFlippedBlocksWritingMode and introducing
RenderObject::hasFlippedBlocksWritingMode?

I don't feel strongly about this, but De Morgan's might make this line easier to
read.
(!x || !y) -> (!(x && y))

[eae, 2014/10/21 22:21:46]

The entire point of this change is to short-circuit the conditions as early as
possible, changing the condition would require the second part to always be
evaluated negating much of the improvement. I do agree that it would make it
more readable though.

[pdr., 2014/10/21 22:38:14]

What do you think about the first part involving moving this code onto
RenderObject?

+        || !renderer().style()->isFlippedBlocksWritingMode()) {
         return;
+    }
     root().block().flipForWritingMode(rect);
 }
 
 FloatPoint InlineBox::flipForWritingMode(const FloatPoint& point)
 {
-    if (!renderer().style()->isFlippedBlocksWritingMode())
+    if (!UNLIKELY(renderer().document().hasVerticalWritingMode())
+        || !renderer().style()->isFlippedBlocksWritingMode()) {
         return point;
+    }
     return root().block().flipForWritingMode(point);
 }
 
 void InlineBox::flipForWritingMode(LayoutRect& rect)
 {
-    if (!renderer().style()->isFlippedBlocksWritingMode())
+    if (!UNLIKELY(renderer().document().hasVerticalWritingMode())
+        || !renderer().style()->isFlippedBlocksWritingMode()) {
         return;
+    }
     root().block().flipForWritingMode(rect);
 }
 
 LayoutPoint InlineBox::flipForWritingMode(const LayoutPoint& point)
 {
-    if (!renderer().style()->isFlippedBlocksWritingMode())
+    if (!UNLIKELY(renderer().document().hasVerticalWritingMode())
+        || !renderer().style()->isFlippedBlocksWritingMode()) {
         return point;
+    }
     return root().block().flipForWritingMode(point);
 }
 
 } // namespace blink
 
 #ifndef NDEBUG
 
 void showTree(const blink::InlineBox* b)
 {
     if (b)
         b->showTreeForThis();
 }
 
 void showLineTree(const blink::InlineBox* b)
 {
     if (b)
         b->showLineTreeForThis();
 }
 
 #endif