RFR: 8363996: Obsolete UseCompressedClassPointers [v5]

[Thomas Stuefe]

On Tue, 10 Feb 2026 05:39:07 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 62 commits:
>> 
>>  - Replace Klass::_metadata union with narrowKlass member
>>  - Ivan: fix various instances of ObjLayout::undefined should assert
>>  - Ivan: Update src/hotspot/share/oops/instanceKlass.cpp
>>    
>>    Co-authored-by: Ivan Walulya <ivan.walulya at oracle.com>
>>  - David: reduce diff in ObjectCountEventVerifier.java
>>  - David: minimize change in GetObjectSizeIntrinsicsTest.java
>>  - David: minimize diffs in TestZGCWithCDS.java
>>  - David: minimize diffs for runtime/ErrorHandling/TestVMConfigInHsErrFile.java
>>  - David: revert type change in arguments.cpp
>>  - David: fix comment in metaspace
>>  - Merge branch 'master' into JDK-8363996-Obsolete-UseCompressedClassPointers
>>  - ... and 52 more: https://git.openjdk.org/jdk/compare/ffb6279c...642604ac
>
> test/jdk/jdk/jfr/event/gc/objectcount/ObjectCountEventVerifier.java line 73:
> 
>> 71:         boolean runsOn32Bit = System.getProperty("sun.arch.data.model").equals("32");
>> 72:         int bytesPerWord = runsOn32Bit ? 4 : 8;
>> 73:         int objectHeaderSize = runsOn32Bit ? 12 : 16;
> 
> This seems a separate bug fix. ??

See comment here: https://github.com/openjdk/jdk/pull/28366#discussion_r2781992992

The old test did run with explicit uncompressed class pointers. I want to reuse the test, so I had to fix it to be able to run with compressed class pointers. With -UCCP, array headers for object arrays are 24 bytes; for +UCCP, array headers are 16 byte.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28366#discussion_r2786317490