RFR: Always copy forward for disjoint arrays

[Zhengyu Gu]

On 11/9/18 3:34 PM, Aleksey Shipilev wrote:
> On 11/09/2018 09:24 PM, Zhengyu Gu wrote:
>> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/disjoint_arraycopy/webrev.00/index.html
> 
> Awww. So conjoint copies do not run into this problem, because their types are guaranteed to match,
> right?

Right! Also made me wonder if you can bypass checkcast for conjoint copies.

Note these are the "disjoint" cases, you can just change them to "should 
only copy forward,
> because types may mismatch":
Fixed.
> 
>    b) src < dst, non-intersecting, can copy forward/backward
>    d) src > dst, non-intersecting, can copy forward/backward

> 
> Otherwise looks good.
> 
> Any chance for a quick regression test that triggers it?

Yep, added Jiri's reproducer.

Updated webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/disjoint_arraycopy/webrev.01/

Okay?

Thanks,

-Zhengyu

> 
> -Aleksey
>