hg: shenandoah/jdk9/hotspot: Cherry-pick JDK-8167298 change, modify ReferenceCAS to be more aggressive, turn back C2 opto.

[ashipile at redhat.com]

Changeset: 658bdee8b6ab
Author:    shade
Date:      2016-10-31 16:26 +0100
URL:       http://hg.openjdk.java.net/shenandoah/jdk9/hotspot/rev/658bdee8b6ab

Cherry-pick JDK-8167298 change, modify ReferenceCAS to be more aggressive, turn back C2 opto.

! src/share/vm/adlc/formssel.cpp
! src/share/vm/gc/shenandoah/shenandoah_globals.hpp
! test/gc/shenandoah/cas/ReferenceCAS.java