[lworld] RFR: 8353202: [lworld] TestArrays.java crashes with -XX:+UseNullableValueFlattening [v2]

[Tobias Hartmann]

> Nullable, atomic, flat arrays and fields of an empty value class should be treated as atomic by C2. Currently, C2 treats them as naturally atomic because they only have one field (the null marker).
> 
> The changes in `src/hotspot/share/c1/c1_LIRGenerator.cpp` are unrelated to this and serve as a temporary workaround for [JDK-8353851](https://bugs.openjdk.org/browse/JDK-8353851) which I found with my new tests.
> 
> Best regards,
> Tobias

Tobias Hartmann has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Workaround for JDK-8353851
 - Merge branch 'lworld' into JDK-8353202
 - 8353202: [lworld] TestArrays.java crashes with -XX:+UseNullableValueFlattening

-------------

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1418/files
  - new: https://git.openjdk.org/valhalla/pull/1418/files/9f65ab2b..98f0e550

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1418&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1418&range=00-01

  Stats: 47733 lines in 796 files changed: 21709 ins; 16580 del; 9444 mod
  Patch: https://git.openjdk.org/valhalla/pull/1418.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1418/head:pull/1418

PR: https://git.openjdk.org/valhalla/pull/1418