[master] RFR: Relax array elements alignment [v8]

[Thomas Stuefe]

On Tue, 26 Apr 2022 17:32:29 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> PR #40 eliminated the Klass* word. A whole class of objects would not benefit from it, though: array elements are aligned at 8-byte-boundaries, even for element types where this is not necessary (byte, bool, char, short, int, float, compressed-objs). This means that array elements would still start at byte#16, after 8 bytes header and 4 bytes length and another 4 bytes unused gap.
>> 
>> This change improves the array element alignment and relaxes it such that elements can align at 4-byte boundaries.
>> 
>> Note about C2 changes: the code that extracts the state field (either byte, int or long array) assumed that all arrays would be equal, and asks for header size of T_INT. This would give wrong offset for T_LONG arrays.
>> 
>> I'm adding a test that checks correct array elements base offsets.
>> 
>> Testing:
>>  - [x] tier1 (x86_64)
>>  - [x] tier1 (x86_32)
>>  - [x] tier1 (aarch64)
>>  - [x] tier2 (x86_64)
>>  - [x] tier2 (x86_32)
>>  - [x] tier2 (aarch64)
>>  - [x] tier3 (x86_64)
>>  - [x] tier3 (x86_32)
>>  - [x] tier3 (aarch64)
>
> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix Z array initialization: initialize at byte granularity instead of words

I looked through this again, good work. I could not find anything wrong beyond my first remark. Thanks for renaming the header size method, new name is much clearer.

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Marked as reviewed by stuefe (Committer).

PR: https://git.openjdk.java.net/lilliput/pull/41