RFR: 8323428: Shenandoah: Unused memory in regions compacted during a full GC should be mangled

[William Kemper]

Regions compacted by a full GC do not currently have the remaining unused memory mangled for debug builds. Mangling this memory will facilitate debugging.

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Commit messages:
 - 8323428: Shenandoah: Unused memory in regions compacted during a full GC should be mangled

Changes: https://git.openjdk.org/jdk/pull/17330/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17330&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323428
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17330.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17330/head:pull/17330

PR: https://git.openjdk.org/jdk/pull/17330