RFR: 8372845: C2: Fold identity hash code if object is constant [v6]

[Emanuel Peter]

On Mon, 26 Jan 2026 19:37:06 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Folding identity hash as constant if the incoming argument is constant would be useful for quick map lookups, such as for the [Classifier proposal](https://openjdk.org/jeps/8357674). Currently, identity hash is not constant because it loads the object header/mark word. We can add an explicit bypass to load an existing hash eagerly instead.
>
> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use UpperCamelCase

test/hotspot/jtreg/compiler/intrinsics/object/IdentityHashCodeFold.java line 37:

> 35:  * @summary Verify constant folding is possible for identity hash code
> 36:  * @library /test/lib /
> 37:  * @requires vm.compiler2.enabled

Drive-by comment:
Do you really need this restriction? IR rules are only executed if C2 is available anyway.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28589#discussion_r2730518926