8309902: C2: assert(false) failed: Bad graph detected in build_loop_late after JDK-8305189

[rwestrel]

The crash happens after the following steps:

1- pre/main/post loops are created with assert predicates above the main loop.

2- the main loop is peeled

3- as a consequence, the OpaqueZeroTripGuard for the main loop is removed

4- That allows narrowing of the type of the CastII that was added right
after the zero trip guard during pre/main/post loops creation

5- The CastII feeds into a range check CastII for the peeled iteration
that becomes top because the narrowed type of the first CastII
conflicts with the type recorded in the range check CastII.

6- The assert predicate that should fold to protect the range check
CastII doesn't because of the fix for JDK-8282592: on assert
predicate updates, the CastII at the zero trip guard is skipped. So
the range check CastII sees the narrowing of the type of the CastII
at the zero trip guard but the assert predicate doesn't.

The fix I propose is to revert that part of the change from
JDK-8282592 so both the range check CastII and the assert predicate
have the CastII at the zero trip guard as input and observe its type
updates. I went back to that bug and tried to reproduce the failure
again but couldn't. Reverting JDK-8281429 causes the bug to reproduce
again. I tried tweaking the test so the crash reproduces with
JDK-8281429 applied but couldn't.

This is caused by JDK-8305189 because step 3- happens because of
it. Before JDK-8305189, 3- happened after loop opts are over. I think
what happened then was that a template assertion predicate that was in
the process of having its OpaqueLoopInit and OpaqueLoopStride
removed constant folded so the crash wouldn't reproduce.

---

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Issue

• JDK-8309902: C2: assert(false) failed: Bad graph detected in build_loop_late after JDK-8305189 (Bug - P3)

Reviewers

• Vladimir Kozlov (@vnkozlov - Reviewer)
• Christian Hagedorn (@chhagedorn - Reviewer)

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[vnkozlov]

Looks good.

[openjdk]

@rwestrel This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8309902: C2: assert(false) failed: Bad graph detected in build_loop_late after JDK-8305189

Reviewed-by: kvn, chagedorn

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At the time when this comment was updated there had been 88 new commits pushed to the master branch:

• 690d626: 8307927: C2: "malformed control flow" with irreducible loop
• be64d3a: 8310299: C2: 8275201 broke constant folding of array store check in some cases
• b2eae16: 8295191: IR framework timeout options expect ms instead of s
• af319d9: 8311064: Windows builds fail without precompiled headers after JDK-8310728
• cbf418a: 8311020: Typo cleanup in Classfile API
• f4b900b: 8310902: (fc) FileChannel.transferXXX async close and interrupt issues
• cf8d706: 8308463: Refactor regenerated class handling in lambdaFormInvokers.cpp
• 6f58ab2: 8301569: jmod list option and jimage list --help not interpreted correctly on turkish locale
• 8f5a384: 8311032: Empty value for java.protocol.handler.pkgs system property can lead to unnecessary classloading attempts of protocol handlers
• ded1370: 8309811: BytecodePrinter cannot handle unlinked classes
• ... and 78 more: https://git.openjdk.org/jdk/compare/7628da200833d0d26215a91afdd1bf7fc110da1d...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.

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[chhagedorn]

Looks reasonable. I will also remove any skipping of cast nodes in my patch for JDK-8288981.

[rwestrel]

@vnkozlov @chhagedorn thanks for the reviews

[rwestrel]

/integrate

[openjdk]

Going to push as commit 26efff7.
Since your change was applied there have been 94 commits pushed to the master branch:

• 05c2b6c: 8309979: BootstrapMethods attribute is missing in class files recreated by SA
• 20f7d05: 8310502: Optimization for j.l.Long.fastUUID()
• 07734f6: 8310848: Convert ClassDesc and MethodTypeDesc to be stored in static final fields
• e5744b8: 8310919: runtime/ErrorHandling/TestAbortVmOnException.java times out due to core dumps taking a long time on OSX
• 98a954e: 8308286: Fix clang warnings in linux code
• f842ec4: 8305667: Some fonts installed in user directory are not detected on Windows
• 690d626: 8307927: C2: "malformed control flow" with irreducible loop
• be64d3a: 8310299: C2: 8275201 broke constant folding of array store check in some cases
• b2eae16: 8295191: IR framework timeout options expect ms instead of s
• af319d9: 8311064: Windows builds fail without precompiled headers after JDK-8310728
• ... and 84 more: https://git.openjdk.org/jdk/compare/7628da200833d0d26215a91afdd1bf7fc110da1d...master

Your commit was automatically rebased without conflicts.

[openjdk]

@rwestrel Pushed as commit 26efff7.

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