8339113: AccessFlags can be u2 in metadata #22246

coleenp · 2024-11-19T16:18:48Z

Please review this change that makes AccessFlags and modifier_flags u2 types and removes the last remnants of Hotspot adding internal access flags. This change moves AccessFlags and modifier_flags in Klass to alignment gaps saving 16 bytes. From pahole: so it's a bit better.

before:

        /* size: 216, cachelines: 4, members: 25, static members: 17 */
        /* sum members: 194, holes: 3, sum holes: 18 */

after:

        /* size: 200, cachelines: 4, members: 25, static members: 17 */
        /* sum members: 188, holes: 4, sum holes: 12 */

We may eventually move the modifiers to java.lang.Class but that's WIP.

Tested with tier1-7 on oracle platforms. Did test builds on other platforms (please try these changes ppc/arm32 and s390). Also requires minor Graal changes.

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Issue

JDK-8339113: AccessFlags can be u2 in metadata (Enhancement - P4)

Reviewers

David Holmes (@dholmes-ora - Reviewer) Review applies to d43b2fac
Serguei Spitsyn (@sspitsyn - Reviewer)
Vladimir Ivanov (@iwanowww - Reviewer)
Yudi Zheng (@mur47x111 - Committer)
Dean Long (@dean-long - Reviewer)

Contributors

Amit Kumar <[email protected]>

Reviewing

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bridgekeeper · 2024-11-19T16:19:25Z

👋 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 · 2024-11-19T16:20:27Z

@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:

8339113: AccessFlags can be u2 in metadata

Co-authored-by: Amit Kumar <[email protected]>
Reviewed-by: sspitsyn, vlivanov, yzheng, dlong, dholmes

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 67 new commits pushed to the master branch:

e413fc6: 8347127: CTW fails to build after JDK-8334733
9702acc: 8175709: DateTimeFormatterBuilder.appendZoneId() has misleading JavaDoc
030149f: 8334644: Automate javax/print/attribute/PageRangesException.java
c8a9dd3: 8346609: Improve MemorySegment.toString
4d8fb80: 8347038: [JMH] jdk.incubator.vector.SpiltReplicate fails NoClassDefFoundError
cf3e48e: 8346965: Multiple compiler/ciReplay test fails with -XX:+SegmentedCodeCache
e5f0c19: 8345041: IGV: Free Placement Mode in IGV Layout
8b22517: 8211851: (ch) java/nio/channels/AsynchronousSocketChannel/StressLoopback.java times out (aix)
5e6cda4: 8347000: Bug in com/sun/net/httpserver/bugs/B6361557.java test
3f7052e: 8346868: RISC-V: compiler/sharedstubs tests fail after JDK-8332689
... and 57 more: https://git.openjdk.org/jdk/compare/4d77dbad4e15c5392878e7bc91cd8eb7ce49a482...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 · 2024-11-19T16:21:24Z

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

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.

…sfile now.

mlbridge · 2024-12-17T21:28:46Z

Webrevs

bridgekeeper · 2024-12-17T23:52:38Z

@coleenp This pull request has been inactive for more than 4 weeks and will be automatically closed if another 4 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

coleenp · 2024-12-18T19:21:25Z

No, bot, this is a new PR.

dholmes-ora

Okay in principle but use of as_int() is very confusing.

src/hotspot/cpu/ppc/interp_masm_ppc_64.cpp

src/hotspot/cpu/ppc/templateInterpreterGenerator_ppc.cpp

src/hotspot/share/jfr/leakprofiler/chains/edgeUtils.cpp

src/hotspot/share/classfile/javaClasses.cpp

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

src/hotspot/share/oops/method.cpp

src/hotspot/share/opto/library_call.cpp

src/hotspot/share/prims/jvmtiClassFileReconstituter.cpp

src/hotspot/share/utilities/accessFlags.hpp

coleenp · 2024-12-19T12:47:19Z

The as_int() was because we are using the AccessFlags as an integral value. I was trying to minimize the effects of the change and the code uses AccessFlags as an integral value. as_int() returns u2 so I guess that's confusing. I don't want AccessFlags::get_flags() because that's implies the return is AccessFlags. I could change the name to as_unsigned_short(). Would that be less confusing?

Thank you David for looking through this change.

Co-authored-by: David Holmes <[email protected]>

src/hotspot/cpu/aarch64/templateInterpreterGenerator_aarch64.cpp

…method, field and class modifiers into AccessFlags. Change ciFlags to use AccessFlags.

src/hotspot/cpu/ppc/interp_masm_ppc_64.cpp

dholmes-ora · 2024-12-19T21:08:36Z

I could change the name to as_unsigned_short(). Would that be less confusing?

How about as_u2() as that is what it is? (less typing :) ).

coleenp · 2024-12-19T22:17:02Z

I didn't really like that name since it's the name of the type rather than more of a description of the type returned. I was able to reduce the number of these by adding some helper functions in AccessFlags.

…or ppc.

dholmes-ora · 2024-12-20T05:02:57Z

Things become somewhat clearer once one realizes/recalls that AccessFlags do not specifically pertain to access, but to all class/method modifiers as per the various JVMS ACC_XXX constants. We need to restore the leading comment in accessFlags.hpp to read

// AccessFlags is an abstraction over Java ACC flags.

as it originally did.

src/hotspot/share/prims/jvmtiRedefineClasses.cpp

offamitkumar · 2025-01-03T07:47:16Z

Thanks for adding the patch Coleen :-)

I did another test-run and s390x looks fine now.

…rieval.

src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/oops/AccessFlags.java

src/hotspot/share/ci/ciFlags.cpp

src/hotspot/share/ci/ciFlags.hpp

src/hotspot/share/ci/ciKlass.cpp

src/hotspot/share/jvmci/jvmciCompilerToVM.cpp

src/hotspot/share/jvmci/jvmciEnv.cpp

sspitsyn

Thank you for update with this an unification!
I've posted a couple of comments with similar nits.

src/hotspot/share/interpreter/linkResolver.cpp

src/hotspot/share/prims/jvm.cpp

sspitsyn · 2025-01-06T17:00:47Z

src/hotspot/share/opto/memnode.cpp

    return TypeInt::make(klass->modifier_flags());
  }
  if (tkls->offset() == in_bytes(Klass::access_flags_offset())) {
    // The field is Klass::_access_flags.  Return its (constant) value.
    // (Folds up the 2nd indirection in Reflection.getClassAccessFlags(aClassConstant).)
-    assert(this->Opcode() == Op_LoadI, "must load an int from _access_flags");
+    assert(this->Opcode() == Op_LoadUS, "must load an unsigned short from _access_flags");


Nit: This can be unified with line 1979 and also get rid of this->.

1979 and 1985 are in different branches of an if statement (address of modifier flags vs access flags) so needs to be repeated. But I did remove the this->

dholmes-ora

I can't say that I really understand which API's are fine with flags-as-int and which need to care about the actual flag storage size. but I'll leave it at that. I will tick approve for the shared code portion of the change.

Thanks

…remove this->s.

coleenp · 2025-01-07T02:45:15Z

Thanks David. I'm hoping @iwanowww or @dean-long can review the compiler parts.

dean-long · 2025-01-07T03:17:32Z

Sure, I'll try to take a look at it tomorrow.

iwanowww

Looks good.

src/hotspot/share/ci/ciFlags.cpp

mur47x111

JVMCI changes look good to me!

sspitsyn

Thank you for one more unification update! Looks good.

dean-long · 2025-01-07T20:59:18Z

src/hotspot/share/classfile/vmIntrinsics.cpp

@@ -36,31 +36,31 @@
 #include "utilities/tribool.hpp"

 // These are flag-matching functions:
-inline bool match_F_R(jshort flags) {
+inline bool match_F_R(u2 flags) {


I wish more code could be size-agnostic. So instead of using u2 here, there could be a typedef in accessFlags.hpp that we could use that hides the size. However, it's not a big deal, because it seems unlikely this type will change much in the future without a JVM spec change. I'm tempted to suggesting using AccessFlags here, but it's a class. Since this is an end-point "consumer" of the type that doesn't store it or pass it along, we could even use something like uint here.

That seems like a good idea if this weren't so limited. I did chat with DanH. to see if access flags will ever grow in size from u2 and he was doubtful that would ever happen. uint would work here too, but this small use might prevent some future -Wconversion warnings and doesn't hurt anything.
Thank you for reviewing.

coleenp · 2025-01-07T22:02:07Z

IMO you could just call as_int() here. All other usages of ciFlags::as_int() are in printing code.
Ideally, ciField::print() could use ciFlags::print(), but such cleanup can be done separately.

This does seem like a good future cleanup. Thanks for reviewing Vladimir.

coleenp · 2025-01-07T22:02:50Z

Thanks for reviewing David, Yudi and Serguei. I reran tiers 1-7 on this change.
/integrate

openjdk · 2025-01-07T22:03:39Z

Going to push as commit 098afc8.
Since your change was applied there have been 67 commits pushed to the master branch:

e413fc6: 8347127: CTW fails to build after JDK-8334733
9702acc: 8175709: DateTimeFormatterBuilder.appendZoneId() has misleading JavaDoc
030149f: 8334644: Automate javax/print/attribute/PageRangesException.java
c8a9dd3: 8346609: Improve MemorySegment.toString
4d8fb80: 8347038: [JMH] jdk.incubator.vector.SpiltReplicate fails NoClassDefFoundError
cf3e48e: 8346965: Multiple compiler/ciReplay test fails with -XX:+SegmentedCodeCache
e5f0c19: 8345041: IGV: Free Placement Mode in IGV Layout
8b22517: 8211851: (ch) java/nio/channels/AsynchronousSocketChannel/StressLoopback.java times out (aix)
5e6cda4: 8347000: Bug in com/sun/net/httpserver/bugs/B6361557.java test
3f7052e: 8346868: RISC-V: compiler/sharedstubs tests fail after JDK-8332689
... and 57 more: https://git.openjdk.org/jdk/compare/4d77dbad4e15c5392878e7bc91cd8eb7ce49a482...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-01-07T22:03:48Z

@coleenp Pushed as commit 098afc8.

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

openjdk bot added graal [email protected] serviceability [email protected] hotspot [email protected] labels Nov 19, 2024

graalvmbot mentioned this pull request Dec 9, 2024

[JDK-8345428] Adapt JDK-8347147: [REDO] AccessFlags can be u2 in metadata oracle/graal#10271

Merged

coleenp added 2 commits December 17, 2024 13:02

8339113: AccessFlags can be u2 in metadata

5e8fee6

Remove JVM_ACC_WRITTEN_FLAGS because they are all written in the clas…

3106bdd

…sfile now.

coleenp force-pushed the access-flags branch from 5d7ae0a to 3106bdd Compare December 17, 2024 20:54

coleenp marked this pull request as ready for review December 17, 2024 21:24

openjdk bot added the rfr Pull request is ready for review label Dec 17, 2024

dholmes-ora suggested changes Dec 19, 2024

View reviewed changes

coleenp and others added 2 commits December 19, 2024 07:48

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

3ec96d5

Co-authored-by: David Holmes <[email protected]>

Update src/hotspot/cpu/ppc/templateInterpreterGenerator_ppc.cpp

cc69a3f

Co-authored-by: David Holmes <[email protected]>

theRealAph reviewed Dec 19, 2024

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src/hotspot/cpu/aarch64/templateInterpreterGenerator_aarch64.cpp Outdated Show resolved Hide resolved

coleenp added 2 commits December 19, 2024 14:20

Renamed AccessFlags.as_int() to as_unsigned_short(), moved masks for …

fbe8331

…method, field and class modifiers into AccessFlags. Change ciFlags to use AccessFlags.

Merge branch 'master' into access-flags

428a043

dean-long reviewed Dec 19, 2024

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src/hotspot/cpu/ppc/interp_masm_ppc_64.cpp Outdated Show resolved Hide resolved

coleenp added 2 commits December 19, 2024 19:58

Fix merge and compilation errors.

aa2887d

Fixed bug.

522ade8

Use ldrh rather than load_unsigned_short for aarch64, use testbitdi f…

828e483

…or ppc.

Restore ACC in comment.

4faf19b

sspitsyn reviewed Jan 2, 2025

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src/hotspot/share/prims/jvmtiRedefineClasses.cpp Outdated Show resolved Hide resolved

coleenp added 2 commits January 3, 2025 21:50

Adopt @sspitsyn suggestion and strengthen field/method/class flag ret…

8682a77

…rieval.

Fix more copyrights.

82bd1a2

dholmes-ora reviewed Jan 6, 2025

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Remove unused SA function.

d43b2fa

sspitsyn reviewed Jan 6, 2025

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dholmes-ora approved these changes Jan 7, 2025

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openjdk bot added the ready Pull request is ready to be integrated label Jan 7, 2025

Make more AccessFlags fetches more specific and remove an assert and …

35784c7

…remove this->s.

openjdk bot removed the ready Pull request is ready to be integrated label Jan 7, 2025

iwanowww approved these changes Jan 7, 2025

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coleenp deleted the access-flags branch January 7, 2025 22:04

coleenp mentioned this pull request Jan 8, 2025

8347147: [REDO] AccessFlags can be u2 in metadata #22968

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8344232: [PPC64] secondary_super_cache does not scale well: C1 and interpreter #22881

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8339113: AccessFlags can be u2 in metadata #22246

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