[jdk16u] RFR: 8267652: c2 loop unrolling by 8 results in reading memory past array

[Vladimir Kempik]

This fixes a p2 issue in jdk16.
the issue is intermitent. Happens when array object located at the very end of a mapped heap region
Backport applies cleanly

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Commit messages:
 - Backport dc12cb78b81f56e9d4b282cf7cad5faa9a9886bf

Changes: https://git.openjdk.java.net/jdk16u/pull/129/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=129&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267652
  Stats: 49 lines in 1 file changed: 27 ins; 0 del; 22 mod
  Patch: https://git.openjdk.java.net/jdk16u/pull/129.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/129/head:pull/129

PR: https://git.openjdk.java.net/jdk16u/pull/129