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8277385: Zero: Enable CompactStrings support #6459



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@shipilev shipilev commented Nov 18, 2021

This enables CompactStrings for Zero. When we were doing original Compact Strings in JDK 9, we disabled the support on non-primary platforms, hoping relevant maintainers would follow up with platform-specific work. Here is me following up, as Zero maintainer :)

There is little to do on Zero side, as it is pure interpreter without String intrinsics. Other platforms had old-shaped String intrinsics, so for them enabling the feature would mean implementing Compact-String-shaped intrinsics too. But this is irrelevant for Zero. There is still benefit of doing less work with smaller Strings.

There are no regressions on the benchmarks I tried, and some benchmarks improve significantly. Notably, specjvm:{compiler,sunflow,derby,xmlvalidation} improve about 5%, specjvm:{serial,xmltransform} improve about 20% on x86_64.

Additional testing:

  • Linux x86_64 Zero benchmarks
  • Linux x86_64 Zero tier1


  • Change must not contain extraneous whitespace
  • Commit message must refer to an issue
  • Change must be properly reviewed




Using git

Checkout this PR locally:
$ git fetch pull/6459/head:pull/6459
$ git checkout pull/6459

Update a local copy of the PR:
$ git checkout pull/6459
$ git pull pull/6459/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 6459

View PR using the GUI difftool:
$ git pr show -t 6459

Using diff file

Download this PR as a diff file:

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@bridgekeeper bridgekeeper bot commented Nov 18, 2021

👋 Welcome back shade! 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 openjdk bot added the rfr label Nov 18, 2021
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@openjdk openjdk bot commented Nov 18, 2021

@shipilev 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.

@openjdk openjdk bot added the hotspot-compiler label Nov 18, 2021
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@mlbridge mlbridge bot commented Nov 18, 2021


cl4es approved these changes Nov 18, 2021
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@cl4es cl4es left a comment

Looks good and trivial.

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@openjdk openjdk bot commented Nov 18, 2021

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

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

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

8277385: Zero: Enable CompactStrings support

Reviewed-by: redestad, adinn

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 22 new commits pushed to the master branch:

  • b15e6f0: 8277449: compiler/vectorapi/ fails with release VMs
  • 11d819d: 8277439: G1: Correct include guard name in G1EvacFailureObjectsSet.hpp
  • 7a046e0: 8277371: Remove unnecessary DefNewGeneration::ref_processor_init()
  • 3a76d39: 8277324: C2 compilation fails with "bad AD file" on x86-32 after JDK-8276162 due to missing match rule
  • 2f20b0d: 8273039: JShell crashes when naming variable or method "abstract" or "strictfp"
  • f34f119: 8277213: CompileTask_lock is acquired out of order with MethodCompileQueue_lock
  • 47564ca: 8275643: C2's unaryOp vector intrinsic does not properly handle LongVector.neg
  • 2f0bde1: 8277102: Dubious PrintCompilation output
  • 839033b: 8276976: Rename LIR_OprDesc to LIR_Opr
  • 89b125f: 8275527: Refactor forward pointer access
  • ... and 12 more:

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.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

@openjdk openjdk bot added the ready label Nov 18, 2021
adinn approved these changes Nov 19, 2021
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@adinn adinn left a comment

That's a nice result for very little work :-)

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@shipilev shipilev commented Nov 22, 2021

Thanks! Extended Zero testing seems fine.


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@openjdk openjdk bot commented Nov 22, 2021

Going to push as commit 3f847fe.
Since your change was applied there have been 42 commits pushed to the master branch:

  • ca31ed5: 8275448: [REDO] AArch64: Implement string_compare intrinsic in SVE
  • 4ff4301: 8224922: Access JavaFileObject from Element(s)
  • 0a9e76c: 8277485: Zero: Fix fast{i,f}access_0 bytecodes handling
  • 1c215f3: 8272773: Configurable card table card size
  • 1d7cef3: 8276662: Scalability bottleneck in SymbolTable::lookup_common()
  • c79a485: 8277494: [BACKOUT] JDK-8276150 Quarantined jpackage apps are labeled as "damaged"
  • 2ab43ec: 8273544: Increase test coverage for snippets
  • 2d4af22: 8277370: configure script cannot distinguish WSL version
  • a3406a1: 8277092: fails with "RuntimeException: Committed seems high: NNNN expected at most MMMM"
  • e47cc81: 8275386: Change nested classes in jdk.jlink to static nested classes
  • ... and 32 more:

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot closed this Nov 22, 2021
@openjdk openjdk bot added integrated and removed ready rfr labels Nov 22, 2021
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@openjdk openjdk bot commented Nov 22, 2021

@shipilev Pushed as commit 3f847fe.

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

@shipilev shipilev deleted the JDK-8277385-zero-compactstrings branch Nov 22, 2021
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