Request for review: 7010665 - Misplaced membar in C1 implementation of Unsafe.get/putXXX

[David Holmes]

http://cr.openjdk.java.net/~dholmes/7010665/

The memory barriers were misplaced in the intrinsic versions of the 
Unsafe.get/put<type>Volatile methods

get
  old: -> membar_acquire(), load; membar()
  new: -> load; membar_acquire()

put
  old: -> membar_release(); store
  new: -> membar_release(); store; membar()

These now match the C1 handling of Java volatile variables (see 
LIRGenerator::do_StoreField and LIRGenerator::do_LoadField in the same 
file).

The non-intrinsic versions are being fixed as part of 7009756.

Thanks,
David