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8264020: Optimize double negation elimination #3231

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@theRealELiu theRealELiu commented Mar 28, 2021

For the double negation '-(-x)', c2 could reduce the redundant 'sub'
through SubNode::Ideal. But every time when 'sub' is removed, there
would generate two useless nodes SubNode(x, 0)[1] and AddNode(x, -0)[2],
which would be removed by later phases but should have optimized better
to 'x' itself without generating those new stuffs.

This patch is a small fix for SubNode's Ideal, by leaving this special
case to 'Identity' which handled double negation already[3].

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/subnode.cpp#L238
[2] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/subnode.cpp#L181
[3] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/subnode.cpp#L55


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Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jdk pull/3231/head:pull/3231
$ git checkout pull/3231

Update a local copy of the PR:
$ git checkout pull/3231
$ git pull https://git.openjdk.java.net/jdk pull/3231/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 3231

View PR using the GUI difftool:
$ git pr show -t 3231

Using diff file

Download this PR as a diff file:
https://git.openjdk.java.net/jdk/pull/3231.diff

For the double negation '-(-x)', c2 could reduce the redundant 'sub'
through SubNode::Ideal. But every time when 'sub' is removed, there
would generate two useless nodes SubNode(x, 0)[1] and AddNode(x, -0)[2],
which would be removed by later phases but should have optimized better
to 'x' itself without generating those new stuffs.

This patch is a small fix for SubNode's Ideal, by leaving this special
case to 'Identity' which handled double negation already[3].

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/subnode.cpp#L238
[2] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/subnode.cpp#L181
[3] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/subnode.cpp#L55

Change-Id: I5597e43001a4593b32b1bb25d4a4bef0ba1bcc09
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@bridgekeeper bridgekeeper bot commented Mar 28, 2021

👋 Welcome back theRealELiu! 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.

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@openjdk openjdk bot added the rfr label Mar 28, 2021
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@openjdk openjdk bot commented Mar 28, 2021

@theRealELiu 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.

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@mlbridge mlbridge bot commented Mar 28, 2021

Webrevs

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@TobiHartmann TobiHartmann left a comment

Otherwise, looks good to me.

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src/hotspot/share/opto/subnode.cpp Outdated Show resolved Hide resolved
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@openjdk openjdk bot commented Mar 29, 2021

@theRealELiu 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:

8264020: Optimize double negation elimination

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 125 new commits pushed to the master branch:

  • 1a681fa: 8263560: Remove needless wrapping with BufferedInputStream
  • 182b11c: 8264016: [JVMCI] add some thread local fields for use by JVMCI
  • 8cf1c62: 8263754: HexFormat 'fromHex' methods should be static
  • a5d7de2: 8263404: RsaPrivateKeySpec is always recognized as RSAPrivateCrtKeySpec in RSAKeyFactory.engineGetKeySpec
  • 128c0c9: 8248418: jpackage fails to extract main class and version from app module linked in external runtime
  • fd45694: 8264344: Outdated links in JavaComponentAccessibility.m
  • f17ea9e: 8262899: TestRedirectLinks fails
  • 963f1fc: 8264309: JFR: Improve .jfc parser
  • 364cce1: 8264332: Use the blessed modifier order in jdk.charsets
  • fbbd98b: 8264029: Replace uses of StringBuffer with StringBuilder in java.base
  • ... and 115 more: https://git.openjdk.java.net/jdk/compare/a5e7a890fe7c7845cd06cfd3770e32f21d8d0573...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).

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@openjdk openjdk bot added the ready label Mar 29, 2021
Change-Id: I4c8f67f6277ded894af2572ff89b6b08f9187e11
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@TobiHartmann TobiHartmann left a comment

Thanks for updating! Looks good to me.

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@chhagedorn chhagedorn left a comment

Looks good!

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@theRealELiu theRealELiu commented Mar 30, 2021

/integrate

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@openjdk openjdk bot added the sponsor label Mar 30, 2021
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@openjdk openjdk bot commented Mar 30, 2021

@theRealELiu
Your change (at version d553a68) is now ready to be sponsored by a Committer.

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@nsjian nsjian commented Mar 30, 2021

/sponsor

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@openjdk openjdk bot commented Mar 30, 2021

@nsjian @theRealELiu Since your change was applied there have been 131 commits pushed to the master branch:

  • 4ffa41c: 8263615: Cleanup tightly_coupled_allocation
  • 4ea6abf: 8264324: Simplify allocation list management in OopStorage::reduce_deferred_updates
  • 8735259: 8264333: Use the blessed modifier order in jdk.jshell
  • d2a63f2: 8264360: Loop strip mining verification fails with "should be on the backedge"
  • 8100a20: 8263971: C2 crashes with SIGFPE with -XX:+StressGCM and -XX:+StressIGVN
  • bcdf469: 8264337: VM crashed when -XX:+VerifySharedSpaces
  • 1a681fa: 8263560: Remove needless wrapping with BufferedInputStream
  • 182b11c: 8264016: [JVMCI] add some thread local fields for use by JVMCI
  • 8cf1c62: 8263754: HexFormat 'fromHex' methods should be static
  • a5d7de2: 8263404: RsaPrivateKeySpec is always recognized as RSAPrivateCrtKeySpec in RSAKeyFactory.engineGetKeySpec
  • ... and 121 more: https://git.openjdk.java.net/jdk/compare/a5e7a890fe7c7845cd06cfd3770e32f21d8d0573...master

Your commit was automatically rebased without conflicts.

Pushed as commit f3726a8.

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

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@theRealELiu theRealELiu deleted the neg branch Jun 9, 2021
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