8330681: Explicit hashCode and equals for java.lang.runtime.SwitchBootstraps$TypePairs #18865

cl4es · 2024-04-19T13:23:53Z

We can reduce overhead of first use of a switch bootstrap by moving typePairToName into TypePairs and by explicitly overriding hashCode and equals. The first change avoids loading and initializing the TypePairs class in actual cases, the second remove some excess code generation from happening on first use.

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JDK-8330681: Explicit hashCode and equals for java.lang.runtime.SwitchBootstraps$TypePairs (Enhancement - P4)

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Jan Lahoda (@lahodaj - Reviewer)
Mandy Chung (@mlchung - Reviewer)

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bridgekeeper · 2024-04-19T13:24:36Z

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openjdk · 2024-04-19T13:25:03Z

@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:

8330681: Explicit hashCode and equals for java.lang.runtime.SwitchBootstraps$TypePairs

Reviewed-by: jlahoda, 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 13 new commits pushed to the master branch:

5313dcc: 8330733: Generational ZGC: Remove ZBarrier::verify_old_object_live_slow_path
5394f57: 8330621: Make 5 compiler tests use ProcessTools.executeProcess
20546c1: 8330004: Refactor cloning down code in Split If for Template Assertion Predicates
bd67ac6: 8329331: Intrinsify Unsafe::setMemory
185e711: 8318650: Optimized subword gather for x86 targets.
6d56996: 8330540: Rename the enum type CompileCommand to CompileCommandEnum
f6feeb0: 8330703: Improve link syntax in javax.lang.model.util
df04358: 8330179: Clean up non-standard use of /** comments in jdk.compiler
c1dd82b: 8329644: Discuss expected visitor evolution patterns in javax.lang.model.util
b704e91: 8329433: Reduce nmethod header size
... and 3 more: https://git.openjdk.org/jdk/compare/177092b952c2135c6f6872c6b64d1e210452d35a...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 · 2024-04-19T13:25:27Z

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

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lahodaj

Looks good to me.

mlbridge · 2024-04-19T13:30:26Z

Webrevs

mlchung

LGTM

ExE-Boss · 2024-04-19T23:56:00Z

src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java

+        }
+
+        public boolean equals(Object other) {
+            if (other instanceof TypePairs otherPair) {


To match the behaviour of the equals method body generated by java.lang.runtime.ObjectMethods::bootstrap, this should include a fast path check for this == other:

Suggested change

if (other instanceof TypePairs otherPair) {

if (this == other) {

return true;

}

if (other instanceof TypePairs otherPair) {

No, see https://www.youtube.com/watch?v=kuzjX_efuDs; this fast path is faster for == matching case but significantly slows down all other branches.

ExE-Boss · 2024-04-20T00:00:54Z

src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java

@@ -684,13 +681,27 @@ else if (selectorType.equals(targetType) ||

    // TypePairs should be in sync with the corresponding record in Lower
    record TypePairs(Class<?> from, Class<?> to) {
+
+        private static final Map<TypePairs, String> typePairToName = initialize();


If TypePairs.typePairToName is never modified after initialisation, then it should probably be made immutable:

Suggested change

private static final Map<TypePairs, String> typePairToName = initialize();

private static final Map<TypePairs, String> typePairToName = Map.copyOf(initialize());

If you really think about it, the initialize method itself is somewhat problematic, as it's initializing with byte/short/char on the left, all of which are already converted to int in the of() factory. This should be done in a separate issue.

Yes, the "redirected" mappings can simply be removed in the current implementation.

Using Map.copyOf should be ok to nail down the read-only intent.

cl4es · 2024-04-22T08:54:03Z

/integrate

openjdk · 2024-04-22T08:54:31Z

Going to push as commit 3d62bbf.
Since your change was applied there have been 13 commits pushed to the master branch:

5313dcc: 8330733: Generational ZGC: Remove ZBarrier::verify_old_object_live_slow_path
5394f57: 8330621: Make 5 compiler tests use ProcessTools.executeProcess
20546c1: 8330004: Refactor cloning down code in Split If for Template Assertion Predicates
bd67ac6: 8329331: Intrinsify Unsafe::setMemory
185e711: 8318650: Optimized subword gather for x86 targets.
6d56996: 8330540: Rename the enum type CompileCommand to CompileCommandEnum
f6feeb0: 8330703: Improve link syntax in javax.lang.model.util
df04358: 8330179: Clean up non-standard use of /** comments in jdk.compiler
c1dd82b: 8329644: Discuss expected visitor evolution patterns in javax.lang.model.util
b704e91: 8329433: Reduce nmethod header size
... and 3 more: https://git.openjdk.org/jdk/compare/177092b952c2135c6f6872c6b64d1e210452d35a...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-04-22T08:54:36Z

@cl4es Pushed as commit 3d62bbf.

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

cl4es added 2 commits April 19, 2024 14:36

Explicit hashCode and equals for SwitchBootstraps

3b0131e

Move typePairToName to TypePairs to make this lazy loaded

57d5084

openjdk bot added the rfr Pull request is ready for review label Apr 19, 2024

openjdk bot added the core-libs core-libs-dev@openjdk.org label Apr 19, 2024

lahodaj approved these changes Apr 19, 2024

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openjdk bot added the ready Pull request is ready to be integrated label Apr 19, 2024

mlchung approved these changes Apr 19, 2024

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ExE-Boss reviewed Apr 20, 2024

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cl4es added 2 commits April 22, 2024 10:47

Remove redundant mappings; store an immutable copy

b6d29f2

Revert changes, splitting these out to a separate PR

6226f1b

openjdk bot added the integrated Pull request has been integrated label Apr 22, 2024

openjdk bot closed this Apr 22, 2024

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Apr 22, 2024

cl4es mentioned this pull request Apr 22, 2024

8330802: Desugar switch in Locale::createLocale #18882

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8330681: Explicit hashCode and equals for java.lang.runtime.SwitchBootstraps$TypePairs #18865

8330681: Explicit hashCode and equals for java.lang.runtime.SwitchBootstraps$TypePairs #18865

cl4es commented Apr 19, 2024 •

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cl4es commented Apr 22, 2024

openjdk bot commented Apr 22, 2024

openjdk bot commented Apr 22, 2024

	private static final Map<TypePairs, String> typePairToName = initialize();
	private static final Map<TypePairs, String> typePairToName = Map.copyOf(initialize());

8330681: Explicit hashCode and equals for java.lang.runtime.SwitchBootstraps$TypePairs #18865

8330681: Explicit hashCode and equals for java.lang.runtime.SwitchBootstraps$TypePairs #18865

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