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8292203: AArch64: Represent Registers as values #9826

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iwanowww
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@iwanowww iwanowww commented Aug 10, 2022

(It's a PR dependent on #9815.)

Along with x86 (JDK-8292153), I propose to refactor Register classes on AArch64 and migrate away from pointer-based representation.

The motivation is the same: improve compile-time checks and avoid ambiguities between overloads due to implicit conversions between pointers and integral types.

Proposed change hides pointer representation behind value class.

Pointer-based representation is kept to avoid massive migration of users (from -> to .) and to enable incremental migration on per-platform basis (pointer-based representation is assumed in shared code).

Code quality improves:
GCC: https://godbolt.org/z/r6G36facj
Clang: https://godbolt.org/z/x5oPdYEPM

(I noticed one downside: slowdebug builds become slower, because operator-> isn't inlined there. If it becomes a problem, migrating performance-sensitive places from -> to . should solve the problem.)

Testing: hs-tier1 - hs-tier5

PS: a number of cleanups are incorporated. In particular, I decided to expand all macros from register.hpp because IMO they add confusion rather than improve readability.


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@iwanowww iwanowww marked this pull request as ready for review August 10, 2022 21:51
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bridgekeeper bot commented Aug 11, 2022

👋 Welcome back vlivanov! 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 Pull request is ready for review label Aug 11, 2022
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@iwanowww The following labels will be automatically applied to this pull request:

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

@openjdk openjdk bot added hotspot hotspot-dev@openjdk.org shenandoah shenandoah-dev@openjdk.org labels Aug 11, 2022
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Webrevs

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I looked on aarch64 changes. Looks fine.
The rest come from #9815 as I understand.

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openjdk bot commented Aug 11, 2022

@iwanowww 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:

8292203: AArch64: Represent Registers as values

Reviewed-by: kvn, aph

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 16 new commits pushed to the master branch:

  • 5a20bc4: 8292715: Cleanup Problemlist
  • 7b81a9c: 8289764: gc/lock tests failed with "OutOfMemoryError: Java heap space: failed reallocation of scalar replaced objects"
  • 76ee549: 8292329: Enable CDS shared heap for zero builds
  • 14623c6: 8292739: Invalid legacy entries may be returned by Provider.getServices() call
  • 568be58: 8290469: Add new positioning options to PassFailJFrame test framework
  • 69448f9: 8292679: Simplify thread creation in gtest and port 2 tests to new way
  • 3c2289d: 8215916: The failure reason of an optional JAAS LoginModule is not logged
  • 71ab5c9: 8292816: GPL Classpath exception missing from assemblyprefix.h
  • c062397: 8292713: Unsafe.allocateInstance should be intrinsified without UseUnalignedAccesses
  • a45a4b9: 8292194: G1 nmethod entry barrier disarm value wraps around too early
  • ... and 6 more: https://git.openjdk.org/jdk/compare/fe0544f8a7db5bf0e93313e16b54b31bcdff946a...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.

➡️ 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 Pull request is ready to be integrated label Aug 11, 2022

inline constexpr Register as_Register(int encoding);
constexpr Register(int encoding, bool unused) : _encoding(encoding) {}
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Why do we need unused here? If the intention is to prevent implicit conversion from int to Register then you can mark the constructor as explicit. Thanks.

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Good point. Fixed.

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Pointer-based representation is kept to avoid massive migration of users (from -> to .) and to enable incremental migration on per-platform basis (pointer-based representation is assumed in shared code).

I don't really understand this part. Can we overload the -> operator instead? I believe this works:

Register* operator->() {
    return this;
}

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Pointer-based representation is kept to avoid massive migration of users (from -> to .) and to enable incremental migration on per-platform basis (pointer-based representation is assumed in shared code).

I don't really understand this part. Can we overload the -> operator instead? I believe this works:

Register* operator->() {
    return this;
}

I tried something like that before, and got poor code quality.

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openjdk bot commented Aug 17, 2022

@iwanowww 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 rwrapper.aarch64
git fetch https://git.openjdk.org/jdk master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

@openjdk openjdk bot added merge-conflict Pull request has merge conflict with target branch and removed ready Pull request is ready to be integrated labels Aug 17, 2022
@openjdk openjdk bot added ready Pull request is ready to be integrated and removed merge-conflict Pull request has merge conflict with target branch labels Aug 17, 2022
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Thanks for the review, Vladimir.

Anybody else planning to review? Otherwise, I'll push it tomorrow.

@iwanowww
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Thanks for the review, Andrew.

/integrate

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openjdk bot commented Aug 25, 2022

Going to push as commit 2fe0ce0.
Since your change was applied there have been 22 commits pushed to the master branch:

  • 251bff6: 8292877: java/util/concurrent/atomic/Serial.java uses {Double,Long}Accumulator incorrectly
  • f57d342: 8292867: RISC-V: Simplify weak CAS return value handling
  • 88af204: 8292494: Ensure SystemDictionary::set_platform_loader and set_system_loader are called only once
  • 8d3d439: 8292903: enhance round_up_power_of_2 assertion output
  • 054c23f: 8290025: Remove the Sweeper
  • dc7e256: 8290376: G1: Refactor G1MMUTracker::when_sec
  • 5a20bc4: 8292715: Cleanup Problemlist
  • 7b81a9c: 8289764: gc/lock tests failed with "OutOfMemoryError: Java heap space: failed reallocation of scalar replaced objects"
  • 76ee549: 8292329: Enable CDS shared heap for zero builds
  • 14623c6: 8292739: Invalid legacy entries may be returned by Provider.getServices() call
  • ... and 12 more: https://git.openjdk.org/jdk/compare/fe0544f8a7db5bf0e93313e16b54b31bcdff946a...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Aug 25, 2022
@openjdk openjdk bot closed this Aug 25, 2022
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Aug 25, 2022
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openjdk bot commented Aug 25, 2022

@iwanowww Pushed as commit 2fe0ce0.

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

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