[lworld] RFR: 8378862: [lworld] flatArrayKlass::copy_array is missing a memory barrier when copying from flat array to non-flat array

[Frederic Parain]

Small patch fixing a missing memory barrier in FlatArrayKlass::copy_array.
The unit test covers more scenario where a flat value has to be buffered before to be written to another heap variable. So far, these tests haven't shown any other issue (they were run repeatedly 50 times using Mach5).

However, the unit test is quite heavy, testing 5 different scenarios, and running each for 3 minutes, using all detected cores of the machine each time. This might qualify this unit test as a "resourcehog" test, it then should be moved to test/hotspot/jtreg/resourcehogs/

Fred

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Commit messages:
 - Add missing memory barrier in FlatArrayKlass::copy_array

Changes: https://git.openjdk.org/valhalla/pull/2183/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2183&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378862
  Stats: 367 lines in 2 files changed: 367 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/2183.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2183/head:pull/2183

PR: https://git.openjdk.org/valhalla/pull/2183