The current implementation is: bool isRootLayer() const { return renderer()->isRenderView(); } Our renderer() won't change during the RenderLayer lifetime time, nor will its type. This means we could easily cache this information in the constructor. Adding this caching seems to help with painting time on http://dglazkov.github.com/performance-tests/biggrid.html.
Created attachment 146373 [details] Proposed new caching.
Comment on attachment 146373 [details] Proposed new caching. Much more readable now too!
Comment on attachment 146373 [details] Proposed new caching. Clearing flags on attachment: 146373 Committed r119761: <http://trac.webkit.org/changeset/119761>
All reviewed patches have been landed. Closing bug.