RFR(XS): 8143930: C1 LinearScan asserts when compiling two back-to-back CompareAndSwapLongs

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8143930/webrev.00/

The problem is that loading values in pinned registers and then computing the address for the CAS puts too much pressure on registers. The fix consists in loading values in pinned registers right before the CAS.

Roland.