[aarch64-port-dev ] RFR (XS) 8252366: Shenandoah: revert/cleanup changes in graphKit.cpp

[Aleksey Shipilev]

Hi,

This is aarch64-port/jdk8u-shenandoah specific issue:
   https://bugs.openjdk.java.net/browse/JDK-8252366

The assert seems to fail on ppc64. Also, we might inline g1_write_barrier_pre_helper for clarity.

8u webrev:
   https://cr.openjdk.java.net/~shade/8252366/webrev.01/

Testing: x86_64 hotspot_gc_shenandoah

-- 
Thanks,
-Aleksey