[lworld] RFR: 8353432: [lworld] Deoptimization needs to handle nullable, flat fields in non-value class holders

[Quan Anh Mai]

Hi,

This patch adds handling of nullable flat fields in non-value class holder. Currently, we add all the fields to the safepoint, then add all the null markers. I decide to change this to adding the null marker of a flat field right after all the subfields of it. It makes the shape similar to how we pass nullable flat fields in the ABI, as well as simplifies the implementation since we do not have to keep track of all null markers when traversing the object payload.

Please take a look and leave your reviews, thanks a lot.

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

Commit messages:
 - handle nullable flat fields in safepoint

Changes: https://git.openjdk.org/valhalla/pull/1478/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1478&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8353432
  Stats: 317 lines in 8 files changed: 141 ins; 112 del; 64 mod
  Patch: https://git.openjdk.org/valhalla/pull/1478.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1478/head:pull/1478

PR: https://git.openjdk.org/valhalla/pull/1478