[lworld] RFR: 8376135: [lworld] Add JIT support for NULLABLE_NON_ATOMIC_FLAT layout

Mon Jan 26 14:08:56 UTC 2026

Hi,

This PR implements the support of `NULLABLE_NON_ATOMIC_FLAT` layout in the JITs. There is nothing to do in C2. In C1, I need to implement loading/storing nullable value of a non-atomic field.

The test `TestValueClasses` is failing with `-XX:-TieredCompilation`, which I suspect is due to the sustitutability test handling padding bytes incorrectly.

Please kindly review what there are for now, thanks a lot.

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Commit messages:
 - Support NULLABLE_NON_ATOMIC in the JITs

Changes: https://git.openjdk.org/valhalla/pull/1970/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1970&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376135
  Stats: 151 lines in 11 files changed: 83 ins; 22 del; 46 mod
  Patch: https://git.openjdk.org/valhalla/pull/1970.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1970/head:pull/1970

PR: https://git.openjdk.org/valhalla/pull/1970