Optimize for horizontal writing mode

Source/core/dom/Document.h

Index: Source/core/dom/Document.h
diff --git a/Source/core/dom/Document.h b/Source/core/dom/Document.h
index 1dc82d0421ca71ffdd68fc136f47d99e86112afe..57bb6d8e0fbc70928ed531bb9511e7e0046bc58a 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -782,6 +782,9 @@ public:
     void setDirectionSetOnDocumentElement(bool b) { m_directionSetOnDocumentElement = b; }
     void setWritingModeSetOnDocumentElement(bool b) { m_writingModeSetOnDocumentElement = b; }
 
+    bool hasVerticalWritingMode() const { return m_hasVerticalWritingMode; }

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

Would we still see the perf benefit if we moved the unlikely in here? This would
be a bit cleaner and I think it'll all inline.

Bikeshed: I can see someone not realizing that this is for the entire document.
What do you think about containsAnyVerticalWritingModes or similar?

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

The effect of the UNLIKELY macro is minimal, it didn't show a statistically
significant improvement on any of the tests. I'm guessing it adds 0.1-0.5% by
priming the branch predictor. The macro only works for conditions (afaik) so I'm
not sure how it could be used here.
That is a much better name, thanks!

+    void setHasVerticalWritingMode(bool b) { m_hasVerticalWritingMode = b; }
+
     bool execCommand(const String& command, bool userInterface = false, const String& value = String());
     bool queryCommandEnabled(const String& command);
     bool queryCommandIndeterm(const String& command);
@@ -1331,6 +1334,7 @@ private:
 
     bool m_directionSetOnDocumentElement;
     bool m_writingModeSetOnDocumentElement;
+    bool m_hasVerticalWritingMode;
     DocumentTiming m_documentTiming;
     RefPtrWillBeMember<MediaQueryMatcher> m_mediaQueryMatcher;
     bool m_writeRecursionIsTooDeep;