[lilliput-jdk21u:lilliput] RFR: 8316126: [Lilliput/JDK21] Cherry-pick: 8305895: Implementation: JEP 450: Compact Object Headers (Experimental) [v3]

[Aleksey Shipilev]

On Tue, 12 Sep 2023 15:46:05 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> Let's cherry-pick the current state of upstream https://github.com/openjdk/jdk/pull/13961 into Lilliput/JDK21u.
>> 
>> Testing:
>>  - [ ] tier1 +UCOH
>>  - [ ] tier1 -UCOH
>
> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove misplaced assert

I basically have an only question about `TypeOopPtr` constants. It does not seem to match lilliput-jdk17u. 

Also, we probably miss the `Problemlist-Lilliput` support. We can do it later.

src/hotspot/share/opto/compile.cpp line 1353:

> 1351:         // range is OK as-is.
> 1352:         tj = ta = TypeAryPtr::RANGE;
> 1353:       } else if( offset == TypeOopPtr::klass_offset_in_bytes() ) {

Here and everywhere. Not sure why this is here. Why not in `oopDesc::`?

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PR Review: https://git.openjdk.org/lilliput-jdk21u/pull/5#pullrequestreview-1622716297
PR Review Comment: https://git.openjdk.org/lilliput-jdk21u/pull/5#discussion_r1323320150