[lworld] RFR: 8377451: [lworld] Add ValuePayload abstraction [v14]

Axel Boldt-Christmas aboldtch at openjdk.org
Wed Feb 18 07:12:34 UTC 2026


> Create a wrapper class which represents the payload of an InlineKlass object.
> 
> The current convention is to use a `void*` representing where the payload starts, the `InlineKlass*` (as we do not always have a header when flattened) and a `LayoutKind` (describing the payloads layout). 
> 
> I suggest we introduce something like a `ValuePayload` which encapsulate these properties. As well as a hierarchy built upon these, with the proper interfaces implemented.
> * ValuePayload (Any payload)
>   * ~RawValuePayload (Payload with holder erased)~ (Removed in favour of using a static function)
>   * BufferedValuePayload (Payload of normal heap object)
>   * FlatValuePayload (Payload of flattened value)
>     * FlatFieldPayload (Payload of flattened field)
>     * FlatArrayPayload (Payload of flattened array element)
>    
> The goal is to both make interfaces clearer, and easier to understand. As well as consolidating the implementation in one place rather than spread across different subsystems. 
> 
> Each type (except RawValuePayload) also allows for the creation of a Handle, (thread local, or in an OopStorage) for keeping the payload as a thread or global root.
> 
> The ValuePayload class is also the interface for interacting with the Access API for InlineKlass objects.
> 
> * Testing
>   * Running tier 1-4 with preview enabled
>   * Running app tests with preview enabled
>   * Running normal tier 1-5 
> 
> #### _Extra Notes:_
>  * The `OopHandle` type is there so that we can migrate the JVMTI payload abstraction implementation to using this instead. (Future RFE)
>  * Some interfaces got cleaned up. Some are unused. Like the `null_payload` which was superseded by the `Access::value_store_null`. C1 still uses the `.null_reset` but if that dependency is removed we should be able to remove that weird object all together.
>  * Simply adding the Java to VM transition deep inside the payload code created a circular include dependency here. So rather than fixing that, I implemented the relevant bytecodes in the BytecodeInterpreter.

Axel Boldt-Christmas 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 72 additional commits since the last revision:

 - Merge remote-tracking branch 'upstream_valhalla/lworld' into lworld-payload-rebase
 - Destructor is a CHECK_UNHANDLED_OOPS property
 - @shipilev formatted table
 - Revert "Fix BytecodeInterpreter dispatch table"
   
   This reverts commit 59c1fc2e7dedd079a61dced4401267dace7c642d.
 - Revert "Avoid having to align label entires"
   
   This reverts commit 342cd358eec59e1798ef62d03bbbd3a0e0f79d9d.
 - Missed header guard rename
 - Rename inlineKlassPayload files to valuePayload
 - Add missing inline keywords
 - Fix typo in suggested fix
 - Update src/hotspot/share/oops/inlineKlassPayload.hpp
   
   Co-authored-by: Stefan Karlsson <stefan.karlsson at oracle.com>
 - ... and 62 more: https://git.openjdk.org/valhalla/compare/eb80ccf7...e1834ba5

-------------

Changes:
  - all: https://git.openjdk.org/valhalla/pull/2068/files
  - new: https://git.openjdk.org/valhalla/pull/2068/files/f5fb80fd..e1834ba5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=2068&range=13
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=2068&range=12-13

  Stats: 1444 lines in 73 files changed: 948 ins; 299 del; 197 mod
  Patch: https://git.openjdk.org/valhalla/pull/2068.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2068/head:pull/2068

PR: https://git.openjdk.org/valhalla/pull/2068


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