8331264: Reduce java.lang.constant initialization overhead #18991

cl4es · 2024-04-29T08:11:06Z

I'm looking at ways at reducing/eliminating startup overheads the classfile API in preparation of #17108, and have pushed a series of enhancements to that effect already. This PR is a collection of minor improvements which add up to a 1.5% reduction in retired instructions - or a 5% reduction in executed bytecode - on a simple lambda startup test.

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Issue

JDK-8331264: Reduce java.lang.constant initialization overhead (Enhancement - P4)

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Chen Liang (@liach - Author)
Mandy Chung (@mlchung - Reviewer)

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$ git fetch https://git.openjdk.org/jdk.git pull/18991/head:pull/18991
$ git checkout pull/18991

Update a local copy of the PR:
$ git checkout pull/18991
$ git pull https://git.openjdk.org/jdk.git pull/18991/head

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Checkout this PR locally:
$ git pr checkout 18991

View PR using the GUI difftool:
$ git pr show -t 18991

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https://git.openjdk.org/jdk/pull/18991.diff

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bridgekeeper · 2024-04-29T08:11:41Z

👋 Welcome back redestad! 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 · 2024-04-29T08:12:05Z

@cl4es 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:

8331264: Reduce java.lang.constant initialization overhead

Reviewed-by: liach, mchung

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 17 new commits pushed to the master branch:

819f3d6: 8330748: ByteArrayOutputStream.writeTo(OutputStream) pins carrier
eb88343: 8331164: createJMHBundle.sh download jars fail when url needed to be redirected
9b423a8: 8330253: Remove verify_consistent_lock_order
4e42294: 8329004: Update Libpng to 1.6.43
bdcc240: 8331087: Move immutable nmethod data from CodeCache
8b8fb64: 8324776: runtime/os/TestTransparentHugePageUsage.java fails with The usage of THP is not enough
151ef5d: 8330677: Add Per-Compilation memory usage to JFR
7272939: 8331200: Serial: Remove unused methods in SerialHeap
70d3f22: 8331175: Parallel: Remove VerifyRememberedSets
549bc6a: 8330685: ZGC: share barrier spilling logic
... and 7 more: https://git.openjdk.org/jdk/compare/c3372c455542cef2aaf673d1f14be8759bb98e8d...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 · 2024-04-29T08:12:24Z

@cl4es The following label will be automatically applied to this pull request:

core-libs

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

mlbridge · 2024-04-29T08:15:27Z

Webrevs

…ith descriptorString().charAt(0) ==

liach · 2024-04-29T12:18:15Z

src/java.base/share/classes/java/lang/constant/MethodTypeDescImpl.java


        for (ClassDesc cd : trustedArgTypes)
-            if (cd.isPrimitive() && cd.descriptorString().charAt(0) == 'V') // implicit null check
+            if (cd.descriptorString().equals("V")) // implicit null check


Just curious, is equals faster than charAt(0) == for single-char strings?

I've not benchmarked this detail in JMH, only verified it does less work when interpreted. We could probably just drop cd.isPrimitive() &&, though, since a descriptor of length > 1 starting with V can't be created.

minborg · 2024-04-29T14:16:34Z

src/java.base/share/classes/java/lang/constant/ConstantDescs.java

-            ConstantDescs.CD_MethodHandles_Lookup,
-            ConstantDescs.CD_String,
-            ConstantDescs.CD_MethodType};
+            CD_MethodHandles_Lookup,


Can these fields be @stable?

I don't think it'd hurt, but I would be surprised if any of these would be hot enough to see a benefit from that.

I don't think this really helps; the array elements are not used directly via field reference.

mlchung

The changes look good to me but I wonder if the non-zero length check before calling arraycopy really needed? That seems to add some noise to the code.

cl4es · 2024-04-29T18:58:02Z

The changes look good to me but I wonder if the non-zero length check before calling arraycopy really needed? That seems to add some noise to the code.

I recall benchmarking similar code in MethodType extensively, and found that it had a small but significant impact, especially when adding or dropping parameters at the end or beginning of an argument list (which is the most common case). Adhoc JMH:

    @Benchmark
    public MethodTypeDesc dropFirstParameter() {
        return desc.dropParameterTypes(0, 1);
    }

Name                                                                   (descString) Cnt   Base   Error    Test   Error  Unit  Change
MethodTypeDescFactories.dropFirstParameter  (Ljava/lang/Object;Ljava/lang/String;)I   6 20,382 ± 0,635  16,116 ± 0,737 ns/op   1,26x (p = 0,000*)
MethodTypeDescFactories.dropFirstParameter ([IJLjava/lang/String;Z)Ljava/util/List;   6 26,875 ± 0,652  19,863 ± 0,749 ns/op   1,35x (p = 0,000*)
MethodTypeDescFactories.dropFirstParameter                                 (..IIJ)V   6 29,774 ± 0,983  20,747 ± 1,181 ns/op   1,44x (p = 0,000*)
MethodTypeDescFactories.dropFirstParameter                 (.....................).   6 33,224 ± 0,939  30,350 ± 1,739 ns/op   1,09x (p = 0,000*)
  * = significant

cl4es · 2024-04-30T08:26:50Z

/integrate

openjdk · 2024-04-30T08:27:39Z

Going to push as commit 0630bb0.
Since your change was applied there have been 19 commits pushed to the master branch:

60b61e5: 8331298: avoid alignment checks in UBSAN enabled build
b128bd7: 8331021: Deprecate and then obsolete the DontYieldALot flag
819f3d6: 8330748: ByteArrayOutputStream.writeTo(OutputStream) pins carrier
eb88343: 8331164: createJMHBundle.sh download jars fail when url needed to be redirected
9b423a8: 8330253: Remove verify_consistent_lock_order
4e42294: 8329004: Update Libpng to 1.6.43
bdcc240: 8331087: Move immutable nmethod data from CodeCache
8b8fb64: 8324776: runtime/os/TestTransparentHugePageUsage.java fails with The usage of THP is not enough
151ef5d: 8330677: Add Per-Compilation memory usage to JFR
7272939: 8331200: Serial: Remove unused methods in SerialHeap
... and 9 more: https://git.openjdk.org/jdk/compare/c3372c455542cef2aaf673d1f14be8759bb98e8d...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-04-30T08:27:45Z

@cl4es Pushed as commit 0630bb0.

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

cl4es added 2 commits April 29, 2024 09:35

Reduce java.lang.constant initialization overhead

a93bceb

Missed null-check on changeReturnType

c27d5ff

openjdk bot added the rfr Pull request is ready for review label Apr 29, 2024

openjdk bot added the core-libs core-libs-dev@openjdk.org label Apr 29, 2024

Descriptors can't be empty, optimize isArray and isClassOrInterface w…

7e7386e

…ith descriptorString().charAt(0) ==

liach reviewed Apr 29, 2024

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Simplified void check

40874ef

liach approved these changes Apr 29, 2024

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minborg reviewed Apr 29, 2024

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mlchung reviewed Apr 29, 2024

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mlchung approved these changes Apr 30, 2024

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openjdk bot added the ready Pull request is ready to be integrated label Apr 30, 2024

openjdk bot added the integrated Pull request has been integrated label Apr 30, 2024

openjdk bot closed this Apr 30, 2024

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Apr 30, 2024

8331264: Reduce java.lang.constant initialization overhead #18991

8331264: Reduce java.lang.constant initialization overhead #18991

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