[lworld] RFR: 8244975: [lworld] Investigate if VM can implement Object::hashCode by calling ValueBootstrapMethods for inline types

[Mandy Chung]

On Wed, 5 Aug 2020 11:32:15 GMT, David Simms <dsimms at openjdk.org> wrote:

> Use ValueBootstrapMethods for Object::hashCode()

src/java.base/share/classes/java/lang/invoke/ValueBootstrapMethods.java line 486:

> 485:         @Override protected MethodHandle computeValue(Class<?> type) {
> 486:             return MethodHandleBuilder.hashCodeForType(type);
> 487:         }

@MrSimms thanks for working on this.

I expect this to call the existing `hashCodeInvoker` if the type is an inline type.   `hashCodeForType` is the method
handle invoking `java.util.Objects::hashCode`.   The existing `hashCodeInvoker` should be changed to take `Class<?>
type` once javac no longer generates `equals` and `hashCode` method for inline type.

Maybe I should take this patch and make the coordinated changes??

src/hotspot/share/runtime/globals.hpp line 2474:

> 2473:                                                                             \
> 2474:   product(bool, InlineTypeIHashCodeViaMethod, true,                         \
> 2475:          "Use generated hashCode for identity hash code")                   \

Do you anticipate this VM flag is needed?

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PR: https://git.openjdk.java.net/valhalla/pull/136