RFR: Always copy forward for disjoint arrays

[Aleksey Shipilev]

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? Note these are the "disjoint" cases, you can just change them to "should only copy forward,
because types may mismatch":

  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?

-Aleksey