RFR: 8160821: VarHandle accesses are penalized when argument conversion is required [v9]

[Christian Hagedorn]

On Mon, 8 Dec 2025 19:10:48 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Since access descriptor is created for each VH operation site, we can optimistically cache the adapted method handle in a site if the site operates on a constant VH.  Used a C2 IR test to verify such a setup through an inexact VarHandle invocation can be constant folded through (previously, it was blocked by `asType`)
>
> 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 17 additional commits since the last revision:
> 
>  - Review
>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/vh-adapt-cache
>  - Bugs and verify loader leak
>  - Try to avoid loader leak
>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/vh-adapt-cache
>  - Revert void special case removal due to C2 shortage causing TestZGCBarrierElision::testAtomicThenAtomicAnotherField failure
>  - Test from Jorn
>  - Copyright years
>  - Fix problem identified by Jorn
>  - Rollback getAndAdd for now
>  - ... and 7 more: https://git.openjdk.org/jdk/compare/45fb0e07...d734e8a6

test/hotspot/jtreg/compiler/c2/irTests/constantFold/VarHandleMismatchedTypeFold.java line 70:

> 68: 
> 69:     @Check(test = "testSum")
> 70:     public void runTestSum() {

Drive-by comment: From the method name, it seems that you want to have a runner method. For that, you need to switch to `@Run`. But you can also do result verification with `@Check`. In the latter case, you do not need to call `testSum()` again but you can just add a `long result` as parameter. The IR framework will then call this `@Check` method with the result of `testSum()`.

Example:
https://github.com/openjdk/jdk/blob/1bbbce75c5e68429c2a32519eb3c36d964dcdf57/test/hotspot/jtreg/testlibrary_tests/ir_framework/examples/CheckedTestExample.java#L94-L102

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PR Review Comment: https://git.openjdk.org/jdk/pull/28585#discussion_r2605606400