Optimize for horizontal writing mode

Source/core/rendering/InlineBox.cpp

Index: Source/core/rendering/InlineBox.cpp
diff --git a/Source/core/rendering/InlineBox.cpp b/Source/core/rendering/InlineBox.cpp
index 05ef4904bbff1806637c720f74cfa6d33f557b18..7c5d6351b87653bd4f6bd7d0fed6e0cebeb9a277 100644
--- a/Source/core/rendering/InlineBox.cpp
+++ b/Source/core/rendering/InlineBox.cpp
@@ -308,8 +308,10 @@ void InlineBox::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());
@@ -319,29 +321,37 @@ FloatPoint InlineBox::locationIncludingFlipping()
 
 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);
 }