[lworld] RFR: 8376135: [lworld] Add JIT support for NULLABLE_NON_ATOMIC_FLAT layout [v4]

[Tobias Hartmann]

On Tue, 27 Jan 2026 09:37:41 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> 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 substitutability test handling padding bytes incorrectly.
>> 
>> Please kindly review what there are for now, thanks a lot.
>
> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove unused variable

Good catch! Looks good to me but @fparain should also have a look at the runtime changes.

src/hotspot/share/opto/inlinetypenode.hpp line 71:

> 69: 
> 70:   // Initialize the inline type fields with the inputs or outputs of a MultiNode
> 71:   void initialize_fields(GraphKit* kit, MultiNode* multi, uint& base_input, bool in, bool no_null_marker, Node* null_check_region, GrowableArray<ciType*>& visited);

Any particular reason that you renamed this? If so, the corresponding argument of  `InlineTypeNode::make_from_multi` should be renamed as well. Could we use something like `has_null_marker` instead to avoid the double negation (`!no_null_marker`)?

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Marked as reviewed by thartmann (Committer).

PR Review: https://git.openjdk.org/valhalla/pull/1970#pullrequestreview-3715548989
PR Review Comment: https://git.openjdk.org/valhalla/pull/1970#discussion_r2735673707