8332455: Improve G1 tasks to not override array lengths

[rkennke]

In order to not cause excessive traffic on task queues when scanning large object arrays, G1 uses a way of slicing those arrays into smaller pieces. It overrides the from-space array's length field to track the array slices.

We should improve the tasks such that array slices can be fully encoded in the task and does not require overriding the array length.

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8332455: Improve G1 tasks to not override array lengths (Enhancement - P4)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/19282/head:pull/19282
$ git checkout pull/19282

Update a local copy of the PR:
$ git checkout pull/19282
$ git pull https://git.openjdk.org/jdk.git pull/19282/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 19282

View PR using the GUI difftool:
$ git pr show -t 19282

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/19282.diff

[bridgekeeper]

👋 Welcome back rkennke! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

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

[openjdk]

@rkennke The following label will be automatically applied to this pull request:

• hotspot-gc

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

[openjdk]

@rkennke this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout JDK-8332455
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push