Integrated: 8306075: Micro-optimize Enum.hashCode

[olivergillespie]

On Mon, 17 Apr 2023 10:59:34 GMT, olivergillespie <duke at openjdk.org> wrote:

> Improve the speed of Enum.hashCode by caching the identity hashcode on first use. I've seen an application where Enum.hashCode is a hot path, and this is fairly simple speedup. The memory overhead is low; in enums with no extra fields there is already a 4-byte space due to alignment so this new field can slot in 'for free'. In other cases, the singleton nature of enum values means that the number of total instances is typically very low, so a small per-instance overhead is not a concern.
> 
> Please see more discussion/explanation in the [original enhancement request](https://bugs.openjdk.org/browse/JDK-8306075). [Benchmark results and generated code analysis moved to comment]
> 
> Thanks @shipilev for help with the implementation and interpreting the generated code.

This pull request has now been integrated.

Changeset: 3da987ad
Author:    Oli Gillespie <ogillesp at amazon.com>
Committer: Aleksey Shipilev <shade at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/3da987adacc3acc120a2781ee9a2111e26356723
Stats:     73 lines in 2 files changed: 72 ins; 0 del; 1 mod

8306075: Micro-optimize Enum.hashCode

Co-authored-by: Aleksey Shipilev <shade at openjdk.org>
Reviewed-by: redestad, shade, rriggs, liach, apangin, jvernee

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PR: https://git.openjdk.org/jdk/pull/13491