RFR: 8271925: ZGC: Arraycopy stub passes invalid oop to load barrier

[Tobias Hartmann]

The fix for [JDK-8270461](https://bugs.openjdk.java.net/browse/JDK-8270461), see [PR 252](https://git.openjdk.java.net/jdk17/pull/252), made sure that the arraycopy offset when cloning an oop array always points to the first element of the array. However, it missed to adjust the copy length as well, leading to reading/copying 8 bytes beyond the end of the array.

This only reproduces in Valhalla (probably because the mark word layout differs there) and only with  `-XX:-UseCompressedClassPointers`. I'll backport the fix to JDK 17u.

Thanks,
Tobias

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Commit messages:
 - 8271925: ZGC: Arraycopy stub passes invalid oop to load barrier

Changes: https://git.openjdk.java.net/jdk/pull/5014/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5014&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271925
  Stats: 9 lines in 1 file changed: 3 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5014.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5014/head:pull/5014

PR: https://git.openjdk.java.net/jdk/pull/5014