RFR: 8354300: Fields in String are not trusted

Mon Apr 14 15:00:00 UTC 2025

This PR proposes to add the `@Stable` annotation to `j.l.String.hash` and `j.l.String.hashIsZero`. This means the VM can trust these fields to never change which enables constant folding optimizations.

This PR is tested in tier1, tier2, and tier3 which all pass.

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Commit messages:
 - Update copyright year
 - Annotate fields with @Stable

Changes: https://git.openjdk.org/jdk/pull/24625/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24625&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8354300
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24625.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24625/head:pull/24625

PR: https://git.openjdk.org/jdk/pull/24625