RFR: Assembler write barriers should consistently check for forwarded objects

[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...

-Aleksey