RFR(S): 8224580: Matcher can cause oop field/array element to be reloaded

[Roland Westrelin]

> The change looks reasonable to me.
>
> I have run tests with the patch and can confirm that the original bug
> went away. I've also run a bunch of other tests and workloads and looks
> good too.

Thanks Roman. Anyone else for this?
Shenandoah needs this for a key change that's also out for review:

https://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2019-May/025931.html
(8224584: Shenandoah: Eliminate forwarding pointer word)

Roland.