This is a straight backport of the early update references phase and all related code from JDK9. http://cr.openjdk.java.net/~rkennke/backport-uprefs/webrev.00/ <http://cr.openjdk.java.net/%7Erkennke/backport-uprefs/webrev.00/> Testing: hotspot_gc_shenandoah, specjvm compiler Ok?