RFR: 8237821: 8237637 Broke Shenandoah

[Stefan Karlsson]

Hi all,

I broke Shenandoah release builds with 8237821.

During the review I was asked to do some simplification and get rid of 
redundant casts. I did the same for Shenandoah, but the patch wasn't 
complete.

So, to fix the current build I've reverted all the Shenandoah changes 
from 8237821:
https://cr.openjdk.java.net/~stefank/8237821/webrev.01.revert/

Then I only do the simple change of casting with (HeapWord*) to using 
cast_from_oop<HeapWord>:
https://cr.openjdk.java.net/~stefank/8237821/webrev.01.fix/

Both these combined gives this final patch:
https://cr.openjdk.java.net/~stefank/8237821/webrev.01.combined/

I've compiled Shenandoah with both fastdebug and release builds, and am 
currently testing this locally.

Thanks,
StefanK