[lworld] RFR: 8370450: [lworld] Alternate implementation of the substitutability test method [v2]

[Frederic Parain]

On Wed, 22 Oct 2025 21:50:59 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Frederic Parain has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
>> 
>>  - Merge remote-tracking branch 'upstream/lworld' into new_acmp
>>  - Add alternate version of the substitutability method
>
> src/java.base/share/classes/java/lang/runtime/ValueObjectMethods.java line 1417:
> 
>> 1415:         int size = map[i * 2 + 2];
>> 1416:         int nlong = size / 8;
>> 1417:         for (int j = 0; j < nlong; j++) {
> 
> Are we sure that for all value objects with `size >= 8`, they are always 8-byte aligned?

There's a processing during the map generation that ensures this property (see last loop in FieldLayoutBuilder::generate_acmp_maps().

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1695#discussion_r2454916414