[8u] RFR and RFA: 8172850: Anti-dependency on membar causes crash in register allocator due to invalid instruction scheduling

[Roland Westrelin]

I'd like to backport 8172850 to 8u because I'd also like to backport a
change that depends on it: 8209639. The change doesn't apply cleanly. So
here is an updated webrev:

http://cr.openjdk.java.net/~roland/8172850-8u/webrev.00/

Initial change:

https://bugs.openjdk.java.net/browse/JDK-8172850
http://hg.openjdk.java.net/jdk9/hs/hotspot/rev/6bf44f4e2a1e

Roland.