8341893: AArch64: Micro-optimize compressed ptr decoding

[shipilev]

See the bug for full description. I think there is an accidental inefficiency in decoding: we don't have to shift when shift is zero, but we are tripped by d != s check. Other architectures seem to do this right. This fix surgically fixes the decoding. I have a variant of a more comprehensive MacroAssembler fix that could cover this shift-to-mov translation wholesale, but that fix is riskier.

Additional testing:

• Linux AArch64 server fastdebug, tier{1,2,3}

---

Progress

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Issue

• JDK-8341893: AArch64: Micro-optimize compressed ptr decoding (Enhancement - P4)

Reviewers

• Andrew Haley (@theRealAph - Reviewer)
• Fei Yang (@RealFYang - Reviewer)

Reviewing

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$ git pull https://git.openjdk.org/jdk.git pull/21443/head

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$ git pr checkout 21443

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[openjdk]

@shipilev 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:

8341893: AArch64: Micro-optimize compressed ptr decoding

Reviewed-by: aph, fyang

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 71 new commits pushed to the master branch:

• 037f11b: 8341708: Optimize safepoint poll encoding with smaller poll data offset
• 8d0975a: 8336726: C2: assert(!do_asserts || projs->fallthrough_ioproj != nullptr) failed: must be found
• fe98f86: 8226938: [TEST_BUG]GTK L&F: There is no Details button in FileChooser Dialog
• 5c4f1ef: 8226933: [TEST_BUG]GTK L&F: There is no swatches or RGB tab in JColorChooser
• 41ee582: 8341138: Rename jtreg property docker.support as container.support
• 2e1c193: 8342003: ProblemList sun/security/tools/keytool/GenKeyPairSigner.java
• 2db3397: 8341797: Fix ExceptionOccurred in jdk.jdi
• c4965d9: 8341794: Fix ExceptionOccurred in jdk.attach
• 3f53d57: 8340327: A common framework to support public key algorithms with standard parameter sets
• 0a57fe1: 8341178: TypeRawPtr::add_offset may be "miscompiled" due to UB
• ... and 61 more: https://git.openjdk.org/jdk/compare/580eb62dc097efeb51c76b095c1404106859b673...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]

@shipilev 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 (f500a3d9)

[shipilev]

Thanks!

I think I need another Reviewer for this Hotspot patch.

[RealFYang]

LGTM. Seems riscv bears a similar issue. Will check and propose a seperate fix.

[shipilev]

Thanks! Yes, I think RISC-V would enjoy a similar fix.

/integrate

[openjdk]

Going to push as commit e3f6503.
Since your change was applied there have been 71 commits pushed to the master branch:

• 037f11b: 8341708: Optimize safepoint poll encoding with smaller poll data offset
• 8d0975a: 8336726: C2: assert(!do_asserts || projs->fallthrough_ioproj != nullptr) failed: must be found
• fe98f86: 8226938: [TEST_BUG]GTK L&F: There is no Details button in FileChooser Dialog
• 5c4f1ef: 8226933: [TEST_BUG]GTK L&F: There is no swatches or RGB tab in JColorChooser
• 41ee582: 8341138: Rename jtreg property docker.support as container.support
• 2e1c193: 8342003: ProblemList sun/security/tools/keytool/GenKeyPairSigner.java
• 2db3397: 8341797: Fix ExceptionOccurred in jdk.jdi
• c4965d9: 8341794: Fix ExceptionOccurred in jdk.attach
• 3f53d57: 8340327: A common framework to support public key algorithms with standard parameter sets
• 0a57fe1: 8341178: TypeRawPtr::add_offset may be "miscompiled" due to UB
• ... and 61 more: https://git.openjdk.org/jdk/compare/580eb62dc097efeb51c76b095c1404106859b673...master

Your commit was automatically rebased without conflicts.

[openjdk]

@shipilev Pushed as commit e3f6503.

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