[8u-dev] Request for approval to backport: 8157306 and 8162496

[Vladimir Kozlov]

Hi!

I'd like to get an approval to backport this fix to jdk8u.

https://bugs.openjdk.java.net/browse/JDK-8157306 "Random infrequent null 
pointer exceptions in javac"
https://bugs.openjdk.java.net/browse/JDK-8162496 "missing precedence 
edge for anti_dependence"

http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/rev/f6c7981c093e
http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/rev/6f10754f85d9

Changes are applied cleanly to 8u sources. They were tested in JDK 9 for 
more then 2 weeks already.

No new tests were added since the problem showed with existing Hotspot 
jtreg tests for both bugs.

We found very dangerous problem which should be fixed in all releases. 
It is rare but cause incorrect behavior due to wrong ordering of 
depending stores and loads. The verification added for JDK-8162496 found 
several places which cause this.

Thanks,
Vladimir