RFR: 8312424: 80% throughput decrease in Arrays.hashCode(Object[]) after JDK-8312164

[Glavo]

On Thu, 20 Jul 2023 02:04:53 GMT, Chen Liang <liach at openjdk.org> wrote:

>>> A similar performance decrease have been discussed here: [#14752 (comment)](https://github.com/openjdk/jdk/pull/14752#discussion_r1250888931)
>>> 
>>> Can you check whether adding `@ForceInline` on `Objects.equals` help with JIT? If it helps, then I think adding `@ForceInline` might be a better solution.
>> 
>> I added `@ForceInline` on `Objects.hashCode(Object)`, but the JMH results did not change.
>
> @Glavo I have created a test case with polymorphic objects in an array: https://github.com/liachmodded/jdk/tree/explore/arrays-hash-poly
> Can you see if you can produce the same outcome on your patch, and how the existing `Objects.equals` behave on the polymorphicObjects case?
> 
> 
> Benchmark               (size)  Mode  Cnt     Score    Error  Units
> ArraysHashCode.objects       1  avgt   15     0.770 ±  0.011  ns/op
> ArraysHashCode.objects      10  avgt   15     4.704 ±  0.059  ns/op
> ArraysHashCode.objects     100  avgt   15    54.610 ±  0.384  ns/op
> ArraysHashCode.objects   10000  avgt   15  6053.742 ± 35.244  ns/op
> 
> 
> 
> Benchmark                          (size)  Mode  Cnt      Score      Error  Units
> ArraysHashCode.polymorphicObjects       1  avgt   15      0.921 ±    0.069  ns/op
> ArraysHashCode.polymorphicObjects      10  avgt   15     23.322 ±    1.076  ns/op
> ArraysHashCode.polymorphicObjects     100  avgt   15    211.325 ±    2.200  ns/op
> ArraysHashCode.polymorphicObjects   10000  avgt   15  81850.916 ± 2427.661  ns/op

@liach 

JMH Result:


                                                           (JDK-8312164)                  (This PR)
Benchmark                    (size)   Mode  Cnt       Score    Error   Units         Score      Error   Units
HashCode.polymorphicObjects       1  thrpt    5  148056.877 ±  8.046  ops/ms    546370.781 ± 2682.146  ops/ms
HashCode.polymorphicObjects      10  thrpt    5   21207.629 ± 39.585  ops/ms     21491.320 ±   66.698  ops/ms
HashCode.polymorphicObjects     100  thrpt    5    1467.886 ± 21.025  ops/ms      1509.838 ±   11.098  ops/ms
HashCode.polymorphicObjects   10000  thrpt    5       9.037 ±  0.006  ops/ms         9.123 ±    0.022  ops/ms


It looks like calling `Objects.hashCode(Object)` is preventing the JIT from monomorphizing.

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PR Comment: https://git.openjdk.org/jdk/pull/14944#issuecomment-1643016889