RFR: JDK-8223244: Fix usage of ARRAYCOPY_DISJOINT decorator

[David Holmes]

Hi Roman,

Not a review as I'm not familiar with the code, but I did take a look 
and have one comment ...

On 3/05/2019 1:19 am, Roman Kennke wrote:
>   In stubGenerator_x86_64.cpp, the ARRAYCOPY_DISJOINT decorator is 
> missing in one place, and wrongly added in another. This should be 
> fixed, because Shenandoah will rely on correct DISJOINT decorator soon, 
> when we implement JDK-8222859.
> 
> Specifically, the conjoint routine pretends to be disjoint. The 
> checkcast routine omits the disjoint decorator, even though it is always 
> disjoint (otherwise it wouldn't need checkcast).

Can you add a comment somewhere documenting the fact that the 
checkcast_arraycopy is always disjoint, as in other cases "disjoint" 
forms part of the name.

Thanks,
David
-----

> Unfortunately, the fix is less trivial than it sounds. 
> ModRefBarrierSetAssembler's prologue implicitely assumes that 
> checkcast->!disjoint and gets the register shuffling wrong. Same for 
> ShenandoahBarrierSetAssembler. Hence the re-shuffling of that code. It 
> should be clearer/more explicit now, and equivalent to what we had before.
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8223244
> Webrev:
> http://cr.openjdk.java.net/~rkennke/8223244/webrev.00/
> 
> Testing: hotspot/tier1, hotspot_gc_shenandoah both x86 and aarch64. 
> Intend to do jdk-submit before push.
> 
> Can I please get a review?
> 
> Thanks,
> Roman