8379148: [lworld] Wrapper class caches should not be used when --enable-preview

[Arraying]

Hi all,

This contributes @xmas92's previously disregarded patch to disable the boxed primitive cache entirely when using preview mode.

Testing: tiers 1-4, Oracle tiers 5-7 with --enable-preview only.

---

Progress

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Issue

• JDK-8379148: [lworld] Wrapper class caches should not be used when --enable-preview (Bug - P3)

Contributors

• Axel Boldt-Christmas <aboldtch@openjdk.org>

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/valhalla.git pull/2249/head:pull/2249
$ git checkout pull/2249

Update a local copy of the PR:
$ git checkout pull/2249
$ git pull https://git.openjdk.org/valhalla.git pull/2249/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 2249

View PR using the GUI difftool:
$ git pr show -t 2249

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/valhalla/pull/2249.diff

[Arraying]

/contributor add @xmas92

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[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@Arraying
Contributor Axel Boldt-Christmas <aboldtch@openjdk.org> successfully added.

[liach]

What does this really solve? This doesn't identify the sites that incorrectly initialized these caches. This doesn't remove the C2 recognition of special wrapper arrays. Why do we need this?

[Arraying]

Thanks for your comments @liach.

What does this really solve?

The purpose of this PR is to clean up the remaining box cache changes that are necessary. Once the scope of this task is finalized and the PR goes out of draft, I will update the description to be more representative.

This doesn't identify the sites that incorrectly initialized these caches.

There are likely other usage sites that I have not overhauled. This is still a draft.

This doesn't remove the C2 recognition of special wrapper arrays.

We cannot remove C2's recognition of these arrays. The box caches are VM symbols, we can only restrict their usages from the VM's side by ensuring control flow does not use them and verifying this through assertions. One prominent usage is during deoptimization. Axel has already changed the VM code for this in JDK-8378531.

We still had underlying test failures, for instance JDK-8379863, which was a missing piece for this PR. Now that this has been integrated, things will look a lot clearer.

Why do we need this?

When it comes to boxed caches, we should not initialize from (nor write to) the CDS archives.

[iklam]

Overall it looks good to me, but is it possible to do this:

 static boolean isEnabled() {
     return cache != null;

That way you don't need the unused anymore.

[matias9927]

So far, the design makes sense to me! The caches will still exist in the CDS archive because they will be in the default classlist, but minimizing their use in preview mode will help transition to its deprecation.

[matias9927]

I would assert that archivedCache is null here so we know it does not get loaded by CDS at all.