8346567: Make Class.getModifiers() non-native #22652

coleenp · 2024-12-09T19:26:53Z

The Class.getModifiers() method is implemented as a native method in java.lang.Class to access a field that we've calculated when creating the mirror. The field is final after that point. The VM doesn't need it anymore, so there's no real need for the jdk code to call into the VM to get it. This moves the field to Java and removes the intrinsic code. I promoted the compute_modifiers() functions to return int since that's how java.lang.Class uses the value. It should really be an unsigned short though.

There's a couple of JMH benchmarks added with this change. One does show that for array classes for non-bootstrap class loader, this results in one extra load which in a long loop of just that, is observable. I don't think this is real life code. The other benchmarks added show no regression.

Tested with tier1-8.

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Issue

JDK-8346567: Make Class.getModifiers() non-native (Enhancement - P4)

Reviewers

Alan Bateman (@AlanBateman - Reviewer)
Dean Long (@dean-long - Reviewer) Review applies to ff693418
Vladimir Ivanov (@iwanowww - Reviewer)
Yudi Zheng (@mur47x111 - Committer)

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bridgekeeper · 2024-12-09T19:27:33Z

👋 Welcome back coleenp! 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 · 2024-12-09T19:27:38Z

@coleenp 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:

8346567: Make Class.getModifiers() non-native

Reviewed-by: alanb, vlivanov, yzheng, dlong

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 98 new commits pushed to the master branch:

8f6ccde: 8349554: [UBSAN] os::attempt_reserve_memory_between reported applying non-zero offset to non-null pointer produced null pointer
7d52f1e: 8349525: RBTree: provide leftmost, rightmost, and a simple way to print trees
e9278de: 8348411: C2: Remove the control input of LoadKlassNode and LoadNKlassNode
5395ffa: 8327378: XMLStreamReader throws EOFException instead of XMLStreamException
1ed9ef1: 8349559: Compiler interface doesn't need to store protection domain
f0ea38b: 8349509: [macos] Clean up macOS dead code in jpackage
7f6c687: 8349374: [JVMCI] concurrent use of HotSpotSpeculationLog can crash
bd9b24c: 8349512: Duplicate PermittedSubclasses entries with doclint enabled
b40f8ee: 8337251: C1: Improve Class.isInstance intrinsic
88a8483: 8349121: SSLParameters.setApplicationProtocols() ALPN example could be clarified
... and 88 more: https://git.openjdk.org/jdk/compare/f05c53c2c4adec4c4e875d8b84ec7682bbe356f8...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 · 2024-12-09T19:28:18Z

@coleenp The following labels will be automatically applied to this pull request:

core-libs
graal
hotspot
serviceability

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing lists. If you would like to change these labels, use the /label pull request command.

src/java.base/share/classes/java/lang/Class.java

src/hotspot/share/classfile/javaClasses.cpp

liach

The change to java.lang.Class looks good.

src/java.base/share/classes/java/lang/Class.java

openjdk · 2024-12-16T17:49:44Z

@coleenp this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout modifiers2
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

src/java.base/share/classes/java/lang/Class.java

test/micro/org/openjdk/bench/java/lang/reflect/Clazz.java

coleenp · 2025-02-03T17:41:56Z

/assign @iwanowww

liach · 2025-02-03T17:41:58Z

Looking at #23396, we might need to filter this field too.

openjdk · 2025-02-03T17:43:40Z

@coleenp Unknown command assign - for a list of valid commands use /help.

coleenp · 2025-02-03T17:43:43Z

Looking at #23396, we might need to filter this field too.

Yes, I agree. This patch is a follow on to that one, so I'll add it to the same places when that one is merged in here.

mlbridge · 2025-02-03T17:49:19Z

Webrevs

src/hotspot/share/oops/arrayKlass.hpp

dean-long

Overall looks good to me. Please ask @iwanowww to review compiler changes.

coleenp

Thank you for the detailed comments.

coleenp · 2025-02-06T12:29:15Z

src/hotspot/share/jfr/recorder/checkpoint/types/jfrTypeSet.cpp

  writer->write(mark_symbol(klass, leakp));
  writer->write(package_id(klass, leakp));
-  writer->write(klass->modifier_flags());
+  writer->write(klass->compute_modifier_flags());


I was trying not to add a Klass::modifier_flags function, but now I have.

coleenp · 2025-02-06T12:37:50Z

src/hotspot/share/compiler/compileLog.cpp

        print(" unloaded='1'");
      } else {
-        print(" flags='%d'", klass->modifier_flags());
+        print(" flags='%d'", klass->access_flags());


Okay, I wanted to remove the one use of ciKlass::modifier_flags() and the field with this change, but I'll add it back since I added a Klass::modifier_flags() function.

coleenp · 2025-02-06T13:08:31Z

test/micro/org/openjdk/bench/java/lang/reflect/Clazz.java

+    @Benchmark
+    public int getAppArrayModifiers() {
+        return clazzArray.getClass().getModifiers();
+    }


Yes. Yes it does.

Co-authored-by: Dean Long <17332032+dean-long@users.noreply.github.com>

…ifier_flags, add benchmark.

iwanowww

Looks good. (Except a left-over ??? in a comment.)

I very much like this cleanup. Migrating from Klass to Class simplifies compiler logic since there's no need to care about primitives at runtime anymore.

Speaking of missing optimization opportunities (demonstrated by one microbenchmark), it looks like a corner case and can be addressed later.

coleenp · 2025-02-06T23:23:11Z

Thank you Vladimir for encouraging me to continue this change. I removed the ??? and hid the modifiers field for reflection as suggested in this PR.

coleenp · 2025-02-07T19:13:07Z

I added some code to hide the Class.modifiers field and fixed the JVMCI test. Please re-review.

Also @iwanowww I think the intrinsic for isInterface can be removed and just be Java code like:

public boolean isInterface()  {
  return getModifiers().isInterface();
}

iwanowww · 2025-02-07T19:58:12Z

I think the intrinsic for isInterface can be removed

Good point. Moreover, it seems most of intrinsics on Class queries can be replaced with a flag bit check on the mirror. (Do we have 16 unused bits in Class::modifiers after this change?)

coleenp · 2025-02-07T21:11:56Z

Good point. Moreover, it seems most of intrinsics on Class queries can be replaced with a flag bit check on the mirror. (Do we have 16 unused bits in Class::modifiers after this change?)

Yes, I think so. isArray and isPrimitive definitely. We could first change the modifiers field to "char" because that's its size and then have a booleans for each of these.

liach · 2025-02-07T21:34:59Z

Making isArray and isPrimitive Java-based is going to be helpful for the interpreter performance of these methods in early bootstrap. 👍

AlanBateman

No more comments from me.

mur47x111

JVMCI change looks good to me

coleenp · 2025-02-10T12:43:35Z

Thank you for the reviews Yudi, Alan, Chen, Vladimir and Dean, and the help and comments with the various pieces of this.
/integrate

openjdk · 2025-02-10T12:44:30Z

Going to push as commit c9cadbd.
Since your change was applied there have been 101 commits pushed to the master branch:

5589892: 8343074: test/jdk/com/sun/net/httpserver/docs/test1/largefile.txt could be generated
d104deb: 8349556: RISC-V: improve the performance when -COH and -AvoidUnalignedAccesses for UL and LU string comparison
4a83ca1: 8349666: RISC-V: enable superwords tests for vector reductions
8f6ccde: 8349554: [UBSAN] os::attempt_reserve_memory_between reported applying non-zero offset to non-null pointer produced null pointer
7d52f1e: 8349525: RBTree: provide leftmost, rightmost, and a simple way to print trees
e9278de: 8348411: C2: Remove the control input of LoadKlassNode and LoadNKlassNode
5395ffa: 8327378: XMLStreamReader throws EOFException instead of XMLStreamException
1ed9ef1: 8349559: Compiler interface doesn't need to store protection domain
f0ea38b: 8349509: [macos] Clean up macOS dead code in jpackage
7f6c687: 8349374: [JVMCI] concurrent use of HotSpotSpeculationLog can crash
... and 91 more: https://git.openjdk.org/jdk/compare/f05c53c2c4adec4c4e875d8b84ec7682bbe356f8...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-02-10T12:44:42Z

@coleenp Pushed as commit c9cadbd.

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

openjdk bot added graal graal-dev@openjdk.org serviceability serviceability-dev@openjdk.org hotspot hotspot-dev@openjdk.org core-libs core-libs-dev@openjdk.org labels Dec 9, 2024

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coleenp changed the title ~~8345678: Make Class.getModifiers() non-native.~~ 8346567: Make Class.getModifiers() non-native Dec 18, 2024

graalvmbot mentioned this pull request Jan 9, 2025

[JDK-8347328] Adapt JDK-8346567: Make Class.getModifiers() non-native oracle/graal#10440

Merged

coleenp force-pushed the modifiers2 branch from 9965d2e to c74bfc0 Compare January 9, 2025 18:41

coleenp added 2 commits January 30, 2025 20:43

8345678: Make Class.getModifiers() non-native.

ec546ae

Fix JFR bug.

86bc216

coleenp force-pushed the modifiers2 branch from 0b25791 to 86bc216 Compare February 3, 2025 17:26

Removed @stable.

8854fcc

coleenp marked this pull request as ready for review February 3, 2025 17:41

openjdk bot added the rfr Pull request is ready for review label Feb 3, 2025

AlanBateman reviewed Feb 4, 2025

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coleenp commented Feb 6, 2025

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Update src/hotspot/share/opto/memnode.cpp

f92620e

Co-authored-by: Dean Long <17332032+dean-long@users.noreply.github.com>

openjdk bot removed the ready Pull request is ready to be integrated label Feb 6, 2025

coleenp added 2 commits February 6, 2025 13:19

Add Klass::modifier_flags to look in the mirror, restore ciKlass::mod…

8502636

…ifier_flags, add benchmark.

Make compute_modifiers return u2.

146e255

iwanowww approved these changes Feb 6, 2025

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openjdk bot added the ready Pull request is ready to be integrated label Feb 6, 2025

Hide Class.modifiers field.

2ea6664

openjdk bot removed the ready Pull request is ready to be integrated label Feb 6, 2025

Remove ??? in the code.

304a17e

Fix jvmci test.

37a8cf8

iwanowww approved these changes Feb 7, 2025

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coleenp deleted the modifiers2 branch February 10, 2025 12:47

8346567: Make Class.getModifiers() non-native #22652

8346567: Make Class.getModifiers() non-native #22652

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