RFR: JDK-8223244: Fix usage of ARRAYCOPY_DISJOINT decorator

[Erik Österlund]

Hi Roman,

This looks good to me.

/Erik

On 2019-05-02 17:19, 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).
>
> 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