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8259984: IGV: Crash when drawing control flow before GCM #2607

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@robcasloz robcasloz commented Feb 17, 2021

The block formation algorithm applied by IGV to schedule graphs without associated CFG information traverses the graph backwards. This makes it difficult to deal with block projection nodes, leading in some cases to double addition of block nodes and block edges, and ultimately causing assertion failures.

This fix replaces the backward traversal by a forward traversal that relies on node category information (introduced in 8261336) to identify control successors. The forward traversal is arguably simpler and, besides avoiding the reported assertion failure, has two advantages:

  • it places block projection nodes in the same block as their predecessors, and
  • it numbers basic blocks more naturally.

The following screenshots illustrate the improvements (before the fix to the left, after the fix to the right):

cfgs-before-after

Tested automatically on tens of thousands of graphs by running java -Xcomp -XX:-TieredCompilation -XX:PrintIdealGraphLevel=4 ... on an instrumented version of IGV that schedules graphs eagerly. Checked manually that the CFGs of a few selected graphs (included the reported one) are well-formed. Also checked that the overall IGV graph scheduling time is not affected by the changes.

Thanks to Christian Hagedorn for checking the fix independently.


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  • JDK-8259984: IGV: Crash when drawing control flow before GCM

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$ git fetch https://git.openjdk.java.net/jdk pull/2607/head:pull/2607
$ git checkout pull/2607

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@bridgekeeper bridgekeeper bot commented Feb 17, 2021

👋 Welcome back rcastanedalo! 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 commented Feb 17, 2021

@robcasloz 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.

@robcasloz robcasloz marked this pull request as ready for review Feb 17, 2021
@openjdk openjdk bot added the rfr label Feb 17, 2021
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@mlbridge mlbridge bot commented Feb 17, 2021

Webrevs

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@chhagedorn chhagedorn left a comment

Looks good to me! I played around with it in the IGV. I regularly got some assertion failure messages before - now they are gone now 👍

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@openjdk openjdk bot commented Feb 18, 2021

@robcasloz 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:

8259984: IGV: Crash when drawing control flow before GCM

Replace backward traversal in the IGV block formation algorithm by forward
traversal guided by node category information. This change addresses the
reported assertion failures, places block projection nodes together with their
predecessors, and gives a more natural block numbering.

Reviewed-by: chagedorn, neliasso

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 45 new commits pushed to the master branch:

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 Feb 18, 2021
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@neliasso neliasso left a comment

Excellent!

@robcasloz
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@robcasloz robcasloz commented Feb 18, 2021

Thanks Christian and Nils for reviewing! Christian, I refactored the code as per your suggestion, please have a look again.

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@chhagedorn chhagedorn left a comment

Looks good!

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@robcasloz robcasloz commented Feb 19, 2021

/summary
Replace backward traversal in the IGV block formation algorithm by forward
traversal guided by node category information. This change addresses the
reported assertion failures, places block projection nodes together with their
predecessors, and gives a more natural block numbering.

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@openjdk openjdk bot commented Feb 19, 2021

@robcasloz Setting summary to:

Replace backward traversal in the IGV block formation algorithm by forward
traversal guided by node category information. This change addresses the
reported assertion failures, places block projection nodes together with their
predecessors, and gives a more natural block numbering.

@robcasloz
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@robcasloz robcasloz commented Feb 19, 2021

Looks good!

Thanks again, Christian.

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@robcasloz robcasloz commented Feb 19, 2021

/integrate

@openjdk openjdk bot closed this Feb 19, 2021
@openjdk openjdk bot added integrated and removed ready rfr labels Feb 19, 2021
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@openjdk openjdk bot commented Feb 19, 2021

@robcasloz Since your change was applied there have been 45 commits pushed to the master branch:

Your commit was automatically rebased without conflicts.

Pushed as commit 61820b7.

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

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