8342498: Add test for Allocation elimination after use as alignment reference by SuperWord

[eme64]

There used to be a bug where this happens:

• SuperWord vectorizes, and picks a field-store as he alignment reference, using a CastP2X on he object pointer.
• Later, all field loads disappear, and the Allocation of the object is eliminated.
• The GC code then thinks the CastP2X is part of the GC barrier code... and crashes with wrong assumptions about that part of the IR.

We should obviously not use field-accesses as alignment references for SuperWord. A few other changes have fixed this issue:

• JDK-8328544: it disallows any non-array accesses that do not have an int-index. This code was backported and so should on its own fix the issue everywhere. But maybe somebody has the idea and wants to be more smart... allowing such memory accesses without int-indices. For that we should add this regression test.

// We did not find the int_index. Just to be safe, reject this VPointer.
if (!_has_int_index_after_convI2L) {
  return false;
}

• Recently, we now only allow memory access to be alignment references if they are actually vectorized... which cannot happen with field stores.
• Roberto's change with GC barriers also removed the asserting/crashing code. Though I'm not sure if that means the IR is then ok.

At any rate: the bug seems fixed, but we should add and possibly backport this regression test anyway.

---

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Issue

• JDK-8342498: Add test for Allocation elimination after use as alignment reference by SuperWord (Enhancement - P2)

Reviewers

• Tobias Hartmann (@TobiHartmann - Reviewer)
• Vladimir Kozlov (@vnkozlov - Reviewer)

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8342498: Add test for Allocation elimination after use as alignment reference by SuperWord

Reviewed-by: thartmann, kvn

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At the time when this comment was updated there had been 5 new commits pushed to the master branch:

• 7f8450c: 8343473: Update copyright year of AddmodsOption.java
• b74652b: 8343167: Unnecessary define checks in InterpreterRuntime after JDK-8199809
• 646d64e: 8340307: Add explanation around MemorySegment:reinterpret regarding arenas
• 8d6cfba: 8336267: Method and Constructor signature parsing can be shared on the root object
• 1f7d524: 8343437: ClassDesc.of incorrectly permitting empty names

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• 01: Full - Incremental (4ff0aa27)
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[TobiHartmann]

Great job extracting this test, Emanuel. Looks good to me!

[vnkozlov]

Good.

[eme64]

Thanks @vnkozlov for the approval.
Thanks @TobiHartmann for the review and all the helpful suggestions along the way!

/integrate

[openjdk]

Going to push as commit f62fc48.
Since your change was applied there have been 21 commits pushed to the master branch:

• f3671be: 8335392: C2 MergeStores: enhanced pointer parsing
• 4fc6d41: 8341194: [REDO] Implement C2 VectorizedHashCode on AArch64
• abf2dc7: 8343298: Improve stability of runtime/cds/DeterministicDump.java test
• dafa2e5: 8343124: Tests fails with java.lang.IllegalAccessException: class com.sun.javatest.regtest.agent.MainWrapper$MainTask cannot access
• 0f7dd98: 8251926: PPC: Remove an unused variable in assembler_ppc.cpp
• cd91a44: 8343549: SeededSecureRandomTest needn't be in a package
• 20f3aaf: 8343471: RISC-V: compiler/cpuflags/TestAESIntrinsicsOnUnsupportedConfig.java fails after JDK-8334999
• 67907d5: 8343500: Optimize ArrayClassDescImpl computeDescriptor
• 714472d: 8341798: Fix ExceptionOccurred in jdk.jdwp.agent
• 825ceb1: 8341796: Fix ExceptionOccurred in jdk.hotspot.agent
• ... and 11 more: https://git.openjdk.org/jdk/compare/895a7b64f01dec7248549b127875edcf006457cf...master

Your commit was automatically rebased without conflicts.

[openjdk]

@eme64 Pushed as commit f62fc48.

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