RFR: 8252505: C1/C2 compiler support for blackholes

[Vladimir Ivanov]

>> Even if there are no instructions issued, some of the unfortunate effects of a call may be still there (e.g., spills around the place where the node is scheduled, memory state is effectively killed). Fixing that would involve overriding calling conventions, in_RegMask()/out_RegMask(), customize memory effects.
> 
> Is that even a downside? It does at least allow everything in flight to
> become visible. It's certainly an improvement over what we have at the
> moment.

I'm under the impression that the main driver for this feature is 
performance, so I consider anything which affects performance a downside.

> But Aleksey, there is an alternative: a store that doesn't do anything.
> Did you consider that instead? I guess the problem is that there'd be a lot
> more nodes.

Yes, wiring the node into memory graph should work as well.

I don't see why a single node (covering all basic types) can't do the job.

Best regards,
Vladimir Ivanov