[jdk20u] RFR: 8299179: ArrayFill with store on backedge needs to reduce length by 1

[Tobias Hartmann]

Backport of [JDK-8299179](https://bugs.openjdk.java.net/browse/JDK-8299179). Applies cleanly. Approval is pending.

Thanks,
Tobias

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Commit messages:
 - 8299179: ArrayFill with store on backedge needs to reduce length by 1

Changes: https://git.openjdk.org/jdk20u/pull/24/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk20u&pr=24&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299179
  Stats: 429 lines in 3 files changed: 429 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk20u/pull/24.diff
  Fetch: git fetch https://git.openjdk.org/jdk20u.git pull/24/head:pull/24

PR: https://git.openjdk.org/jdk20u/pull/24