RFR(S): 8024919 G1: SPECjbb2013 crashes due to a broken object reference

[Igor Veresov]

C1 had passed incorrect new value to the post_barrer() in Unsafe.getAndSetObject() intrinsic.
Instead of the new value, on which G1 executes a bunch filters it passed the old value. That caused sporadic barrier omissions and missing rset entries as a result.

Huge thanks to Mikael Gerdin for helping to track this hard to reproduce issue.

Webrev: http://cr.openjdk.java.net/~iveresov/8024919/webrev.0/

igor