git: openjdk/jdk16: 8259271: gc/parallel/TestDynShrinkHeap.java still fails "assert(covered_region.contains(new_memregion)) failed: new region is not in covered_region"

[Kim Barrett]

Changeset: 685c03dc
Author:    Kim Barrett <kbarrett at openjdk.org>
Date:      2021-01-22 11:20:52 +0000
URL:       https://git.openjdk.java.net/jdk16/commit/685c03dc

8259271: gc/parallel/TestDynShrinkHeap.java still fails "assert(covered_region.contains(new_memregion)) failed: new region is not in covered_region"

Use load_acquire to order reads of top and end.

Reviewed-by: tschatzl, iwalulya, eosterlund

! src/hotspot/share/gc/parallel/mutableSpace.cpp