JDK-8075816: Deprecate AliasLevel flag since it is broken #8140

tobiasholenstein · 2022-04-07T08:29:07Z

Deprecate the AliasLevel flag. AliasLevel can have the following values:

"0 - for no aliasing, "
"1 - for oop/field/static/array split, "
"2 - for class split, "
"3 - for unique instances"

Deprecate AliasLevel in JDK 19.
Obsolete it in JDK 20
Expire it in JDK 21.

Users will now get the following message when running:
java -XX:AliasLevel= Java HotSpot(TM) 64-Bit Server VM warning: Option AliasLevel was deprecated in version 19.0 and will likely be removed in a future release.

Progress

Change must not contain extraneous whitespace
Commit message must refer to an issue
Change must be properly reviewed
Change requires a CSR request to be approved

Issues

JDK-8075816: Deprecate AliasLevel flag since it is broken
JDK-8284515: Deprecate AliasLevel flag (CSR)

Reviewers

Tobias Hartmann (@TobiHartmann - Reviewer)
Vladimir Kozlov (@vnkozlov - Reviewer)

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jdk pull/8140/head:pull/8140
$ git checkout pull/8140

Update a local copy of the PR:
$ git checkout pull/8140
$ git pull https://git.openjdk.java.net/jdk pull/8140/head

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Checkout this PR locally:
$ git pr checkout 8140

View PR using the GUI difftool:
$ git pr show -t 8140

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https://git.openjdk.java.net/jdk/pull/8140.diff

bridgekeeper · 2022-04-07T08:30:45Z

👋 Welcome back tobiasholenstein! 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 · 2022-04-07T08:32:46Z

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

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tobiasholenstein · 2022-04-07T08:54:10Z

/csr needed

openjdk · 2022-04-07T08:56:11Z

@tobiasholenstein this pull request will not be integrated until the CSR request JDK-8284515 for issue JDK-8075816 has been approved.

TobiHartmann

Looks good to me.

mlbridge · 2022-04-07T09:01:04Z

Webrevs

vnkozlov

I would like to have full description about the issue. The flags has values range [0-3]. Which values are broken? Which default value will be after flags removal and why?

vnkozlov · 2022-04-11T16:10:38Z

src/hotspot/share/opto/compile.cpp

-  if (!do_escape_analysis() && aliaslevel == 3) {
-    aliaslevel = 2;  // No unique types without escape analysis
-  }
-  _AliasLevel = aliaslevel;


Please, test with EA switched off -XX:-DoEscapeAnalysis
There are tests which switch it off. Also it is off in tier7 and tier8 for compiler tests. So I am puzzled that bug say that it crash with aliasLevel=2.
Also update subject of PR to match new bug's subject.

You are right: the statement in the bug report that AliasLevel<3 is broken is wrong. The VM crashes for AliasLevel=0 and AliasLevel=1 but not for AliasLevel=2. So with -XX:-DoEscapeAnalysis it is always automatically set toAliasLevel=2.
But when -XX:+DoEscapeAnalysis -XX:+EliminateAllocations there is ONE use-case for AliasLevel :
https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/escape.cpp#L336-L341

for -XX:AliasLevel=3 split_unique_types(alloc_worklist, arraycopy_worklist, mergemem_worklist); is called

for -XX:AliasLevel=2 split_unique_types(alloc_worklist, arraycopy_worklist, mergemem_worklist); is NOT called

So does the use case -XX:+DoEscapeAnalysis -XX:+EliminateAllocations -XX:AliasLevel=2 make sense and is it something that is used?

Since AliasLevel is not completely broken the question is if we should deprecated instead of making it obsolete?

I don't think there is a real use case for -XX:AliasLevel=2 given that one can get similar behavior with -XX:-EliminateAllocations (or -XX:-DoEscapeAnalysis). I would therefore vote for deprecating AliasLevel.

Yes, I agree with Tobias. Lets treat -XX:AliasLevel=2 as -XX:-EliminateAllocations. There are tests which use this flags.
And yes, we should deprecate AliasLevel but correcting bug's and CSR's text with this new information about -XX:AliasLevel=2.

The CSR request (JDK-8284515) is now updated for deprecating AliasLevel

TobiHartmann · 2022-04-12T05:42:52Z

From looking at the code and history, it seems that AliasLevel values 0 and 1 are currently disabled due to issues. The VM will print:

AliasLevel (1) is not compatible with -Xcomp or -Xmixed
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

But 2 seems to work fine. 3 is the default. @tobiasholenstein did you find any issues with AliasLevel=2?

This reverts commit 6a1bed2.

TobiHartmann

Looks good to me.

vnkozlov

Good.

openjdk · 2022-04-19T16:44:41Z

@tobiasholenstein 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:

8075816: Deprecate AliasLevel flag since it is broken

Reviewed-by: thartmann, kvn

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 164 new commits pushed to the master branch:

1b71621: 8042381: Test javax/swing/JRootPane/4670486/bug4670486.java fails with Action has not been received
0f81d8f: 8284933: Improve debug in jdk.crypto.cryptoki
72726c4: 8284563: AArch64: bitperm feature detection for SVE2 on Linux
98d54e8: 8282397: createTempFile method of java.io.File is failing when called with suffix of spaces character
8d456ac: 8282300: Throws NamingException instead of InvalidNameException after JDK-8278972
f61d121: 8281388: Change wrapping of EncryptedPrivateKeyInfo
9e051d5: 8278972: Improve URL supports
395bb5b: 8278356: Improve file creation
ee07438: 8277672: Better invocation handler handling
9ce2d75: 8278449: Improve keychain support
... and 154 more: https://git.openjdk.java.net/jdk/compare/ec205f68a883cef6b98f26a06baf675f7da26928...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, @vnkozlov) 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).

tobiasholenstein · 2022-04-20T08:22:15Z

thanks @TobiHartmann and @vnkozlov for the reviews!

tobiasholenstein · 2022-04-20T08:22:25Z

/integrate

openjdk · 2022-04-20T09:39:49Z

@tobiasholenstein
Your change (at version 782fb37) is now ready to be sponsored by a Committer.

TobiHartmann · 2022-04-20T09:40:05Z

/sponsor

openjdk · 2022-04-20T09:42:04Z

Going to push as commit 46b2e54.
Since your change was applied there have been 164 commits pushed to the master branch:

1b71621: 8042381: Test javax/swing/JRootPane/4670486/bug4670486.java fails with Action has not been received
0f81d8f: 8284933: Improve debug in jdk.crypto.cryptoki
72726c4: 8284563: AArch64: bitperm feature detection for SVE2 on Linux
98d54e8: 8282397: createTempFile method of java.io.File is failing when called with suffix of spaces character
8d456ac: 8282300: Throws NamingException instead of InvalidNameException after JDK-8278972
f61d121: 8281388: Change wrapping of EncryptedPrivateKeyInfo
9e051d5: 8278972: Improve URL supports
395bb5b: 8278356: Improve file creation
ee07438: 8277672: Better invocation handler handling
9ce2d75: 8278449: Improve keychain support
... and 154 more: https://git.openjdk.java.net/jdk/compare/ec205f68a883cef6b98f26a06baf675f7da26928...master

Your commit was automatically rebased without conflicts.

openjdk · 2022-04-20T09:42:25Z

@TobiHartmann @tobiasholenstein Pushed as commit 46b2e54.

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

JDK-8075816: AliasLevel is broken and should be deprecated

84412b8

openjdk bot added the hotspot hotspot-dev@openjdk.org label Apr 7, 2022

tobiasholenstein marked this pull request as ready for review April 7, 2022 08:54

openjdk bot added rfr Pull request is ready for review csr Pull request needs approved CSR before integration labels Apr 7, 2022

TobiHartmann approved these changes Apr 7, 2022

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vnkozlov reviewed Apr 7, 2022

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Obsolete AliasLevel flag

6a1bed2

vnkozlov reviewed Apr 11, 2022

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tobiasholenstein changed the title ~~JDK-8075816: AliasLevel is broken and should be deprecated~~ JDK-8075816: Deprecate AliasLevel flag since it is broken Apr 14, 2022

Revert "Obsolete AliasLevel flag"

782fb37

This reverts commit 6a1bed2.

TobiHartmann approved these changes Apr 19, 2022

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vnkozlov approved these changes Apr 19, 2022

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openjdk bot removed the csr Pull request needs approved CSR before integration label Apr 19, 2022

openjdk bot added the ready Pull request is ready to be integrated label Apr 19, 2022

openjdk bot added the sponsor Pull request is ready to be sponsored label Apr 20, 2022

openjdk bot added the integrated Pull request has been integrated label Apr 20, 2022

openjdk bot closed this Apr 20, 2022

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review sponsor Pull request is ready to be sponsored labels Apr 20, 2022

tobiasholenstein deleted the JDK-8075816 branch August 29, 2022 07:43

JDK-8075816: Deprecate AliasLevel flag since it is broken #8140

JDK-8075816: Deprecate AliasLevel flag since it is broken #8140

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