RFR: Guard interpreter keep alive barrier with ShenandoahKeepAliveBarrier

[Roman Kennke]

Am 16.01.2018 um 18:52 schrieb Aleksey Shipilev:
> On 01/16/2018 06:49 PM, Roman Kennke wrote:
>> Am 16.01.2018 um 18:47 schrieb Aleksey Shipilev:
>>> So the better fix would probably revisit all uses of keep_alive_barrier, and protect their relevant
>>> blocks, then putting the assert(ShenandoahKeepAliveBarrier) in MacroAssembler::keep_alive_barrier?
>>>
>>> -Aleksey
>>>
>>
>> Yes, that is what I mean with 'this should need more refactoring' ;-) Only the code that I touched
>> uses it, so we should infact move all that code under keep_alive_barrier() instead. Want me to do
>> that now? Or wait until codegen for interpreter arrives and do it really properly?
> 
> I think it does not matter at this point. We usually use Shenandoah*Barrier as the performance
> investigation tool, which means we do care about what compilers do. We are not really interested in
> what interpreters do perf-wise. So, a better move resource-wise would be to make it right once,
> after codegen interfaces arrive.
> 
> Or, does it affect Traversal GC perf?
> 

No, not really. It just means we keep alive more weakrefs than we need to.

Ok, let's drop it for now.

Roman