RFR: JDK-8221766: Load-reference barriers for Shenandoah

[Roman Kennke]

> I don't think it should be part of this cleanup.

Fair enough.
I have run several tests today, and removing the is_Phi() call doesn't 
seem to negatively impact Shenandoah.

Updated webrevs:
Incremental:
http://cr.openjdk.java.net/~rkennke/JDK-8221766/webrev.01.diff/
Full:
http://cr.openjdk.java.net/~rkennke/JDK-8221766/webrev.01/

Ok now?

Thanks,
Roman


> Please, file separate RFE to push this change with separate review and 
> testing.
> 
> Thanks,
> Vladimir
> 
> On 4/3/19 4:18 AM, Roland Westrelin wrote:
>>
>> Hi Vladimir,
>>
>>> opto/loopnode.cpp new is_Phi check was added. Please, explain.
>>
>> When we expand barriers, if we find a null check nearby we move the
>> barrier close to the null check so there's a better chance of converting
>> it to an implicit null check. That happens as part of a pass of loop
>> opts. I think that's where that change comes from but I don't remember
>> the details. In general we need the control that's assigned to a load to
>> not be too conservative.
>>
>> Anyway, that change is not required for correctness. But it looks
>> reasonable to me.
>>
>> Roland.
>>