RFR: Assembler write barriers should consistently check for forwarded objects

[Roman Kennke]

Am 10.07.2018 um 11:01 schrieb Aleksey Shipilev:
> On 07/10/2018 10:59 AM, Roman Kennke wrote:
>> Am 10.07.2018 um 10:56 schrieb Aleksey Shipilev:
>>> http://cr.openjdk.java.net/~shade/shenandoah/sbs-forwarded-check/webrev.01/
>>>
>>> This fixes the bug in write_barrier_impl in x86_64: we should check either for 0, or for
>>> HAS_FORWARDED when deciding to omit the read barrier. C1 write barrier tests HAS_FORWARDED and it
>>> seems most efficient when coalescing is not available. So, the rest homogenizes the check shape
>>> across architectures.
>>>
>>> Testing: tier3_gc_shenandoah (x86_64), build (aarch64)
>>>
>>> Thanks,
>>> -Aleksey
>>>
>>
>> Can you hold it back until I pushed the consolidation?
> 
> I think it is cleaner to go the other way around: we first push this thing that fixes the barriers,
> because it is also backportable, then we rebase and push consolidation, that is less backportable.
> But either way, I can redo the patch during backports...

Ok, then please push that change, and I'll re-do the consolidating patch.

Roman