8339303: C2: dead node after failing to match cloned address expression #21829

robcasloz · 2024-11-01T13:53:33Z

This changeset prevents the x86 platform-specific logic from cloning address expressions consisting of two chained AddP nodes with a small constant offset each, such as in the following example:

Such patterns cannot be fully subsumed into x86 complex addressing modes, and cloning them can cause the matcher to introduce dead nodes that trigger a segmentation fault in the subsequent global code motion phase. See a detailed analysis of the failure in the JBS issue description.

The changeset additionally extends the post-matching verification logic to check that no old node is reachable by travesing both node inputs and outputs. This extension would have caused the original test case to fail directly after matching with an informative assertion message rather than an opaque segmentation fault in an unrelated code generation phase.

Note that the pattern causing the failure should be in general optimized by AddPNode::Ideal into a single AddP node with the constant sum of the offsets. While JDK-8343067 should address the missing optimization, this changeset proposes a complementary solution that is easily backportable and avoids relying on specific optimizations for correctness.

Testing

Functionality

tier1-5 (linux-x64, windows-x64, macosx-x64, linux-aarch64, macosx-aarch64; release and debug mode).

Performance

Tested performance on a set of standard benchmark suites (DaCapo, SPECjbb2015, SPECjvm2008). No significant change was observed.

Progress

Change must be properly reviewed (1 review required, with at least 1 Reviewer)
Change must not contain extraneous whitespace
Commit message must refer to an issue

Issue

JDK-8339303: C2: dead node after failing to match cloned address expression (Bug - P2)

Reviewers

Vladimir Kozlov (@vnkozlov - Reviewer) Review applies to e85ba7cb
Vladimir Ivanov (@iwanowww - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/21829/head:pull/21829
$ git checkout pull/21829

Update a local copy of the PR:
$ git checkout pull/21829
$ git pull https://git.openjdk.org/jdk.git pull/21829/head

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Checkout this PR locally:
$ git pr checkout 21829

View PR using the GUI difftool:
$ git pr show -t 21829

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/21829.diff

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bridgekeeper · 2024-11-01T13:54:15Z

👋 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.

openjdk · 2024-11-01T13:54:40Z

@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:

8339303: C2: dead node after failing to match cloned address expression

Reviewed-by: vlivanov, kvn

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 86 new commits pushed to the master branch:

d4d9831: 8340454: C2 EA asserts with "previous reducible Phi is no longer reducible before SUT"
2a1ae0f: 8331008: Implement JEP 478: Key Derivation Function API (Preview)
847cc5e: 8343173: Remove ZGC-specific non-JVMCI test groups
3fab8e3: 8341903: Implementation of Scoped Values (Fourth Preview)
839de82: 8332744: [REDO] 'internal proprietary API' diagnostics if --system is configured to an earlier JDK version
8cb1221: 8343532: Test test/hotspot/jtreg/runtime/cds/appcds/jigsaw/addmods/AddmodsOption.java fails on Linux ppc64le after JDK-8319343
fbf9b96: 8343480: Remove unnecessary @SuppressWarnings annotations (javadoc)
f95097c: 8343482: Remove unnecessary @SuppressWarnings annotations (net)
c799cad: 8343486: Remove unnecessary @SuppressWarnings annotations and -Xlint:-foo options
0b733e9: 8336874: WhiteBoxAPI: assert(!method->is_abstract() && (osr_bci == InvocationEntryBci || !method->is_native())) failed: cannot compile abstract/native methods
... and 76 more: https://git.openjdk.org/jdk/compare/388d44fbf0126f253860edc88c2efd57f86e5a2b...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 · 2024-11-01T13:55:20Z

@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.

mlbridge · 2024-11-04T09:44:50Z

Webrevs

01: Full - Incremental (b0aa39fc)
00: Full (e85ba7cb)

vnkozlov

Looks good. Yes, it looks like code expect LShift here instead of constant.

iwanowww

Looks good.

iwanowww · 2024-11-04T22:58:47Z

src/hotspot/share/opto/matcher.cpp

      }
    }
+    for (uint j = 0; j < n->outcnt(); j++) {


Why don't you use DU iterator instead (e.g., DUIterator_Fast)?

Right, done in commit b0aa39f, thanks. Please re-review.

robcasloz · 2024-11-06T09:16:13Z

Thanks for reviewing, @vnkozlov and @iwanowww!

robcasloz · 2024-11-06T09:16:20Z

/integrate

openjdk · 2024-11-06T09:17:26Z

Going to push as commit 83f3d42.
Since your change was applied there have been 93 commits pushed to the master branch:

ead0116: 8331341: secondary_super_cache does not scale well: C1 and interpreter
06d8216: 8318442: java/net/httpclient/ManyRequests2.java fails intermittently on Linux
bdd6816: 8343502: RISC-V: SIGBUS in updateBytesCRC32 after JDK-8339738
4431852: 8342943: Replace predicate walking and cloning code for main/post loops with a predicate visitor
1b0281d: 8333427: langtools/tools/javac/newlines/NewLineTest.java is failing on Japanese Windows
471f112: 8342577: Clean up JVMTI breakpoint support
69bc088: 8343071: Broken anchors to restricted method page and some redundant ids
d4d9831: 8340454: C2 EA asserts with "previous reducible Phi is no longer reducible before SUT"
2a1ae0f: 8331008: Implement JEP 478: Key Derivation Function API (Preview)
847cc5e: 8343173: Remove ZGC-specific non-JVMCI test groups
... and 83 more: https://git.openjdk.org/jdk/compare/388d44fbf0126f253860edc88c2efd57f86e5a2b...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-11-06T09:17:35Z

@robcasloz Pushed as commit 83f3d42.

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

robcasloz added 4 commits November 1, 2024 10:26

Do not clone two pointer adds using each an immediate on x86

4a71924

Verify that there are no out references to dead nodes after matching

cfecbc9

Add regression test

2902993

Remove fix condition

e85ba7c

openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Nov 1, 2024

robcasloz marked this pull request as ready for review November 4, 2024 09:40

openjdk bot added the rfr Pull request is ready for review label Nov 4, 2024

vnkozlov approved these changes Nov 4, 2024

View reviewed changes

openjdk bot added the ready Pull request is ready to be integrated label Nov 4, 2024

iwanowww approved these changes Nov 4, 2024

View reviewed changes

Use DUIterator_Fast to traverse node outputs

b0aa39f

openjdk bot removed the ready Pull request is ready to be integrated label Nov 5, 2024

robcasloz requested a review from iwanowww November 5, 2024 17:03

iwanowww approved these changes Nov 5, 2024

View reviewed changes

openjdk bot added the ready Pull request is ready to be integrated label Nov 5, 2024

openjdk bot added the integrated Pull request has been integrated label Nov 6, 2024

openjdk bot closed this Nov 6, 2024

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Nov 6, 2024

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8339303: C2: dead node after failing to match cloned address expression #21829

8339303: C2: dead node after failing to match cloned address expression #21829

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8339303: C2: dead node after failing to match cloned address expression #21829

8339303: C2: dead node after failing to match cloned address expression #21829

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