8346194: Improve G1 pre-barrier C2 cost estimate

[tschatzl]

Hi all,

please review this change that modifies pre-barrier node costs for loop-unrolling to only consider the fast path. The reasoning is similar to zgc (and the new costs as well): only the part of the barrier inlined into the main code stream, as the slow path is laid out separately and does/should not directly affect performance (particularly if there is no marking going on).

There are no differences/impact in performance since the post barrier cost is still very large, which fill be fixed elsewhere.

Testing: gha, perf testing standalone (neither micros nor actual benchmarks give any difference outside of variance), testing with JDK-8342382

Hth,
Thomas

---

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-8346194: Improve G1 pre-barrier C2 cost estimate (Enhancement - P4)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/23862/head:pull/23862
$ git checkout pull/23862

Update a local copy of the PR:
$ git checkout pull/23862
$ git pull https://git.openjdk.org/jdk.git pull/23862/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 23862

View PR using the GUI difftool:
$ git pr show -t 23862

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/23862.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back tschatzl! 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]

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

• hotspot

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.

[mlbridge]

Webrevs

• 00: Full (429bc01b)