RFR: 8363998: Implement Compressed Class Pointers for 32-bit [v3]

[Thomas Stuefe]

On Mon, 28 Jul 2025 20:39:25 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove stray include
>
> src/hotspot/share/oops/compressedKlass.cpp line 67:
> 
>> 65:     _max_shift = max_shift_coh;
>> 66:   } else {
>> 67: #ifdef _LP64
> 
> It's a bit confusing when we need NEEDS_CLASS_SPACE vs. LP64.  Like here.

@coleenp I modified the patch, removed the NEEDS_CLASS_SPACE macro, since most of the sections can be compiled just fine on arm. There is the basic question of whether one wants to exclude anything related to 32-bit on 64-bit from builds or not. If one does, 32-bit will bitrot even easier, if not (this seems e.g. the strategy Ioi is following in most of his CDS code) one sees errors in 32-bit more easily and reduces ifdef sections. I opted for the latter here, but it won't make much difference in practice I assume.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26491#discussion_r2244534430