RFR (XS): 8214523: Fix nmethod asserts for concurrent nmethod unloading

[Erik Österlund]

By popular demand, I decided to CC hotspot-dev. And Coleen.

/Erik

On 2018-11-30 11:29, Erik Österlund wrote:
> Hi,
> 
> There are some asserts in nmethod.cpp that do not play well with 
> concurrent nmethod unloading. This patch adjusts said asserts and makes 
> nmethod::maybe_invalidate_installed_code() return early if the nmethod 
> is not JVMCI compiled, to dodge JVMCI requirements on locking, that is 
> far from supported right now anyway for concurrent unloading.
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8214523
> 
> Webrev:
> http://cr.openjdk.java.net/~eosterlund/8214523/webrev.00/
> 
> Thanks,
> /Erik