RFR: 8372845: C2: Fold identity hash code if object is constant [v4]

[Quan Anh Mai]

On Tue, 13 Jan 2026 03:16:44 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> Chen Liang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision:
>> 
>>  - Move test, fix merge garbage
>>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/identity-hash-const
>>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/identity-hash-const
>>  - Typo
>>  - assert
>>  - refactorings
>>  - Typo
>>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/identity-hash-const
>>  - Cleanup
>>  - identity hash support in C2
>>  - ... and 2 more: https://git.openjdk.org/jdk/compare/91227712...67a3954f
>
> src/hotspot/share/ci/ciObject.hpp line 76:
> 
>> 74:   };
>> 75: 
>> 76:   const int IDENTITY_HASH_OFFSET = -1;
> 
> `const` is fine, but `constexpr` is often preferred. Also, is `static` needed here? Another nitpick is that constants are usually not in uppercase in C++, as macros are often in uppercase.

It is also useful to note what this value is. It is not clear at first glance why offset is -1 here.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28589#discussion_r2684658970