Integrated: 8345465: Fix performance regression on x64 after JDK-8345120

[Per Minborg]

On Wed, 4 Dec 2024 08:40:31 GMT, Per Minborg <pminborg at openjdk.org> wrote:

> This PR proposes to fix a performance regression (on x64 platforms) for 32-bit strings introduced by [JDK-8345120](https://bugs.openjdk.org/browse/JDK-8345120).
> 
> The PR also fixes a performance regression in the benchmarks caused by using the wrong type for `MemorySegment`.
> 
> Regrettably, this PR uses different code paths for various architectures. This gives optimum performance for all platforms at the expense of slightly more code complexity. More specifically, the PR gives a ~15% performance improvement on x64 platforms for longer 32-bit strings.
> 
> Passes tier1-tier3.

This pull request has now been integrated.

Changeset: 06c44dd5
Author:    Per Minborg <pminborg at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/06c44dd568d91e1bd68f60fd3e57abcbe97e5dca
Stats:     31 lines in 2 files changed: 7 ins; 2 del; 22 mod

8345465: Fix performance regression on x64 after JDK-8345120

Reviewed-by: mcimadamore

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PR: https://git.openjdk.org/jdk/pull/22539