RFR: 8212996: Use AS_NO_KEEPALIVE when accessing dead java.lang.invoke.CallSites during nmethod unloading

[Erik Österlund]

Hi,

When nmethods are unloaded, they may have dead 
java.lang.invoke.CallSites loaded, and then we follow their dead 
java.lang.invoke.MethodHandleNatives.CallSiteContext, so that its 
dependency context can be cleaned. These dead oops should be loaded with 
AS_NO_KEEPALIVE accessors, otherwise GC barriers can become very unhappy.

Webrev:
http://cr.openjdk.java.net/~eosterlund/8212996/webrev.00/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8212996

Thanks,
/Erik