JDK-8330795 : C2: assert((uint)type <= T_CONFLICT && _zero_type[type] != nullptr) failed: bad type with -XX:-UseCompressedClassPointers

[JohnTortugo]

The assert((uint)type <= T_CONFLICT && _zero_type[type] != nullptr) failed: bad type failure was caused by the fact that we didn't have a "zero value" for the type T_METADATA. The RAM patch uses that data when it creates a Phi node merging Klass loads and UseCompressedClassPointers is disabled.

Tested with JTREG tier1-4 on Linux x86_64 & ARM64.

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Issue

• JDK-8330795: C2: assert((uint)type <= T_CONFLICT && _zero_type[type] != nullptr) failed: bad type with -XX:-UseCompressedClassPointers (Bug - P3)

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[openjdk[bot]]

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

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

8330795: C2: assert((uint)type <= T_CONFLICT && _zero_type[type] != nullptr) failed: bad type with -XX:-UseCompressedClassPointers

Reviewed-by: 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 61 new commits pushed to the master branch:

• 95a601316de06b4b0fbf6e3c7777be5d2a1ca978: 8332042: Move MEMFLAGS to its own include file
• 5a4415a6bddb25cbd5b87ff8ad1a06179c2e452e: 8331858: [nmt] VM.native_memory statistics should work in summary mode
• 4ba74475d44831c1fe49359458163cd1567e9619: 8326957: Implement JEP 474: ZGC: Generational Mode by Default
• 7ce4a13c0a891e606480e138f4025ffa328a18b3: 8332130: RISC-V: remove wrong instructions of Vector Crypto Extension
• ea5eb74a65f20ce28fa0a94ea851915d4a6f83da: 8326404: Assertion error when trying to compile switch with fallthrough with pattern
• beea5305b071820e2b128a55c5ca384caf470fdd: 8331907: BigInteger and BigDecimal should use optimized division
• 440782e0160f867f08afbec0abf48d557a522c72: 8331466: Problemlist serviceability/dcmd/gc/RunFinalizationTest.java on generic-all
• 5ded8da676d62158d0011086d7f80ff2c9096e13: 8332085: Remove 10 year old transition check in GenerateCurrencyData tool
• 7c2c24fc0511b36132952c96be46eea5904a53c5: 8261433: Better pkcs11 performance for libpkcs11:C_EncryptInit/libpkcs11:C_DecryptInit
• ff4bf1cf9f18547cff8f484433c3c55b4c288aaa: 8332102: Add @since to package-info of jdk.security.jarsigner
• ... and 51 more: https://git.openjdk.org/jdk/compare/ad78b7fa67ba30cab2e8f496e4c765be15deeca6...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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[openjdk[bot]]

@JohnTortugo The following label will be automatically applied to this pull request:

• hotspot-compiler

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[mlbridge[bot]]

Webrevs

• 02: Full - Incremental (bb632c27)
• 01: Full - Incremental (91fc61de)
• 00: Full (ea64c880)

[vnkozlov]

New test failed in GHA with 32-bit VM because:

Unrecognized VM option 'UseCompressedClassPointers'

You can add -XX:+IgnoreUnrecognizedVMOptions to run test on all platforms.

[vnkozlov]

@JohnTortugo, thank you for adding new test. But it would be nice also add additional run with -XX:+IgnoreUnrecognizedVMOptions -XX:-UseCompressedClassPointers to failed test test/hotspot/jtreg/compiler/c2/irTests/scalarReplacement/AllocationMergesTests.java

Also why you require to run test only with compressed oops on?:

* @requires vm.debug == true & vm.bits == 64 & vm.compiler2.enabled & vm.opt.final.UseCompressedOops & vm.opt.final.EliminateAllocations

[vnkozlov]

@JohnTortugo, thank you for adding new test. But it would be nice also add additional run with -XX:+IgnoreUnrecognizedVMOptions -XX:-UseCompressedClassPointers to failed test test/hotspot/jtreg/compiler/c2/irTests/scalarReplacement/AllocationMergesTests.java

Actually -XX:+IgnoreUnrecognizedVMOptions is not needed because you require vm.bits == 64 in the test.

[JohnTortugo]

@JohnTortugo, thank you for adding new test. But it would be nice also add additional run with -XX:+IgnoreUnrecognizedVMOptions -XX:-UseCompressedClassPointers to failed test test/hotspot/jtreg/compiler/c2/irTests/scalarReplacement/AllocationMergesTests.java

Thank you @vnkozlov , I'll work on that.

[JohnTortugo]

@vnkozlov - I updated the patch by adding new tests with CompressedOops/CompressedClassPointers enabled and disabled.

[vnkozlov]

@JohnTortugo This looks reasonable. Can you explain more why having klass field load is bad for your code?

Is it because you need klass as constant for deoptimization?

Is it possible to handle such case (loading klass) as separate RFE later?

[JohnTortugo]

Can you explain more why having klass field load is bad for your code?

The issue involves LoadNKlass, DecodeNKlass and NULL NKlass. It happens when splitting a LoadNKlass through a nullable Phi. In that process another "nullable" Phi of type TypeNarrowKlass may be created merging the "Klass'es" of the original Phi inputs. A NULL NarrowKlass seems to be something not quite well defined: for instance, there is no definition of "_zero_type" for T_METADATA which is the basic type of TypeNarrowKlass. The first commit in this PR was to add this definition.

However, I think a better approach - than the one from first commit - maybe to instead of creating a Phi of type NarrowKlass create a Phi of type TypePtr that merges DecodeNKlass. By doing so I won't need to create a Phi with a NULL NKlass so the original patch isn't necessary. However, in my opinion, doing that is better left for a separate RFE + PR.

Is it possible to handle such case (loading klass) as separate RFE later?

Yes, I think we can do it as a separate RFE. However, in my experiments klass field loading doesn't appear very often in the benchmarks and therefore may not be much worth the added complication.

[vnkozlov]

However, in my experiments klass field loading doesn't appear very often in the benchmarks and therefore may not be much worth the added complication.

It may be true for code with new allocations but in general case when an object is passed as argument or loaded from field klass loading is common case.

[vnkozlov]

Thank you for explaining issue you have with klass loading. I will run our testing with you current version.

[JohnTortugo]

Thank you for reviewing and testing @vnkozlov !

[JohnTortugo]

/integrate

[openjdk[bot]]

@JohnTortugo Your change (at version bb632c27f17d1377106c1788051ab0f7d96cd503) is now ready to be sponsored by a Committer.

[vnkozlov]

/sponsor

[openjdk[bot]]

Going to push as commit 4e77cf881d031e5b0320915b3eabd7702e560291. Since your change was applied there have been 65 commits pushed to the master branch:

• 7b4ba7f90ab9ea5e1070c79534c587dad17d1bdd: 8325932: Replace ATTRIBUTE_NORETURN with direct [[noreturn]]
• 0bb5ae645165b97527ecccf02308df6072c363d8: 8332248: (fc) java/nio/channels/FileChannel/BlockDeviceSize.java failed with RuntimeException
• 4d32c607a4b496bf2bb09e54167ecbbab5569a0c: 8322008: Exclude some CDS tests from running with -Xshare:off
• e91492ab4333c61f39b50eb428fa932131a5b908: 8313674: (fc) java/nio/channels/FileChannel/BlockDeviceSize.java should test for more block devices
• 95a601316de06b4b0fbf6e3c7777be5d2a1ca978: 8332042: Move MEMFLAGS to its own include file
• 5a4415a6bddb25cbd5b87ff8ad1a06179c2e452e: 8331858: [nmt] VM.native_memory statistics should work in summary mode
• 4ba74475d44831c1fe49359458163cd1567e9619: 8326957: Implement JEP 474: ZGC: Generational Mode by Default
• 7ce4a13c0a891e606480e138f4025ffa328a18b3: 8332130: RISC-V: remove wrong instructions of Vector Crypto Extension
• ea5eb74a65f20ce28fa0a94ea851915d4a6f83da: 8326404: Assertion error when trying to compile switch with fallthrough with pattern
• beea5305b071820e2b128a55c5ca384caf470fdd: 8331907: BigInteger and BigDecimal should use optimized division
• ... and 55 more: https://git.openjdk.org/jdk/compare/ad78b7fa67ba30cab2e8f496e4c765be15deeca6...master

Your commit was automatically rebased without conflicts.

[openjdk[bot]]

@vnkozlov @JohnTortugo Pushed as commit 4e77cf881d031e5b0320915b3eabd7702e560291.

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