[jdk18u] RFR: 8283408: Fix a C2 crash when filling arrays with unsafe

[Tobias Hartmann]

Backport of [JDK-8283408](https://bugs.openjdk.java.net/browse/JDK-8283408). Applies cleanly. Approval is pending.

Thanks,
Tobias

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Commit messages:
 - 8283408: Fix a C2 crash when filling arrays with unsafe

Changes: https://git.openjdk.java.net/jdk18u/pull/58/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=58&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283408
  Stats: 75 lines in 2 files changed: 72 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk18u/pull/58.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18u pull/58/head:pull/58

PR: https://git.openjdk.java.net/jdk18u/pull/58