RFR: 8199417: Modularize interpreter GC barriers

[Roman Kennke]

Hi Erik,

I like it.

As far as I can see, the patch currently only handles oop stores and
loads. Are you planning to add support for primitive access in the near
future? Or else I can probably do that, or help with it (I know where to
hook this up, based on Shenandoah experience).

Thanks, Roman


> The GC barriers for the interpreter are not as modular as they could be.
> They currently use switch statements to check which GC barrier set is
> being used, and call this or that barrier based on that, in a way that
> assumes GCs only use write barriers.
> 
> This patch modularizes this by generating accesses in the interpreter
> with declarative semantics. Accesses to the heap may now use store_at
> and load_at functions of the BarrierSetAssembler, passing along
> appropriate arguments and decorators. Each concrete BarrierSetAssembler
> can override the access completely or sprinkle some appropriate GC
> barriers as necessary.
> 
> Big thanks go to Martin Doerr and Roman Kennke, who helped plugging this
> into S390, PPC and AArch64 respectively.
> 
> Webrev:
> http://cr.openjdk.java.net/~eosterlund/8199417/webrev.00/
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8199417