8355387: [jittester] Disable downcasts by default

[lepestock]

Currently, JITTester's love to downcast often produces something like this:

ArrayList someVar = (TreeSet)(Object)(List)(new ArrayList());

... which is possible because it goes up to Object and then starts downcasting to some totally unrelated class / type.

Considering the JITTester's love to casts (they are more-or-less 'safe' expressions), it means a high probability (30-50%) of a gentest to fail compilation. Even worse is the situation for ByteCode tests - that they're faulty is only recognized during the run phase.

I suggest to disable the downcasts for now.
Testing: 50-100 generated tests in different combinations (default, with the flag set to 'false' or 'true') with artificially increased chance to casts.

---

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-8355387: [jittester] Disable downcasts by default (Bug - P4)

Reviewers

• Tobias Hartmann (@TobiHartmann - Reviewer)
• Christian Hagedorn (@chhagedorn - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/24840/head:pull/24840
$ git checkout pull/24840

Update a local copy of the PR:
$ git checkout pull/24840
$ git pull https://git.openjdk.org/jdk.git pull/24840/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 24840

View PR using the GUI difftool:
$ git pr show -t 24840

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/24840.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back enikitin! 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]

@lepestock This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8355387: [jittester] Disable downcasts by default

Reviewed-by: thartmann, chagedorn

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 33 new commits pushed to the master branch:

• 290d24d: 8355400: Better git detection in update_copyright_year.sh
• 84e9264: 8346552: C2: Add IR tests to check that Predicate cloning in Loop Unswitching works as expected
• 953eef4: 8347337: ZGC: String dedups short-lived strings
• ... and 30 more: https://git.openjdk.org/jdk/compare/82c249446f2bd6f3b0e612c5ef3e6bfcab388c3b...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

As you do not have Committer status in this project an existing Committer must agree to sponsor your change. Possible candidates are the reviewers of this PR (@TobiHartmann, @chhagedorn) but any other Committer may sponsor as well.

➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

[openjdk]

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

• hotspot-compiler

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 (5f1e46c1)

[TobiHartmann]

Looks good and trivial.

[lepestock]

/integrate

[openjdk]

@lepestock
Your change (at version 5f1e46c) is now ready to be sponsored by a Committer.

[TobiHartmann]

/sponsor

[openjdk]

Going to push as commit b41e0b1.
Since your change was applied there have been 55 commits pushed to the master branch:

• dbd2fb0: 8355473: Clean up x86 globals/VM_Version after 32-bit x86 removal
• 70030ba: 8354803: ALL_64_BITS is the same across platforms
• f27fc01: 8355576: Problem list compiler/c2/TestVerifyConstraintCasts.java until JDK-8355574 is fixed
• ... and 52 more: https://git.openjdk.org/jdk/compare/82c249446f2bd6f3b0e612c5ef3e6bfcab388c3b...master

Your commit was automatically rebased without conflicts.

[openjdk]

@TobiHartmann @lepestock Pushed as commit b41e0b1.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.