[jdk11u-dev] RFR: 8283408: Fix a C2 crash when filling arrays with unsafe

[Goetz Lindenmaier]

I backport this for parity with 11.0.16-oracle.

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Commit messages:
 - Backport a6740c010b7d37f991c8547be6ea72b198e9094f

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/1015/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=1015&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/jdk11u-dev/pull/1015.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/1015/head:pull/1015

PR: https://git.openjdk.java.net/jdk11u-dev/pull/1015