RFR: JDK-8213199: GC abstraction for Assembler::needs_explicit_null_check()

[Kim Barrett]

> On Oct 31, 2018, at 1:27 PM, Roman Kennke <rkennke at redhat.com> wrote:
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8213199
> Full webrev:
> http://cr.openjdk.java.net/~rkennke/JDK-8213199/webrev.00/
> 
> Testing: passes hotspot/jtreg:tier3 on x86/fastdebug
> 
> Can I please get reviews on this? Also, any suggestions for improvement
> are very welcome!
> 
> Thanks,
> Roman

I think BarrierSetAssembler::needs_explicit_null_check() should be const.

Other than that, looks good.