RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v6]

[Coleen Phillimore]

On Mon, 9 Sep 2024 10:02:53 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix bit counts in GCForwarding
>
> src/hotspot/share/oops/compressedKlass.hpp line 43:
> 
>> 41: 
>> 42:   // Tiny-class-pointer mode
>> 43:   static int _tiny_cp; // -1, 0=true, 1=false
> 
> Suggestion:
> 
>   static int _tiny_cp; // -1 = uninitialized, 0 = true, 1 = false
> 
> In addition to that, I am not sure if introducing a new term ("tiny") for compact class header related changes (and just here) makes the code more clear; I would have expected a "_compact_" prefix. Also all other members use "k"-klass and spell out "klass pointer", so I would prefer to keep that style.

I agree with this.  'cp' reads as ConstantPool for me even though this is a different context.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1750531167