RFR: Extract Shenandoah superword check into ShenandoahBarrierSetC2

[Roman Kennke]

FWIW, specjvm also did not show any problems with the whole thing removed.

Roman


> It's probably worth pointing out that I found a few of our tests trigger
> the condition that we're checking in the test *and* don't fail in any
> way. And our testsuite passes (including a few tests that trigger the
> condition). Might be worth to investigate if we actually still need the
> code at all?
> 
> Roman
> 
>> We have a check in superword.cpp to prevent superword optimization if we
>> find a WB between the pre- and main-loop. This seems to be a rare
>> situation. I'd:
>> - put it inside #if INCLUDE_SHENANDOAHGC
>> - and UseShenandoahGC
>> - and extract the actual body of code into ShenandoahBarrierSetC2.cpp
>>
>> Not sure if it's worth to make a real abstraction for it. It seems quite
>> specific.
>>
>> http://cr.openjdk.java.net/~rkennke/shenandoah-superword/webrev.00/
>>
>> Testing: tier3_gc_shenandoah
>>
>> Roman
>>
>