[jdk17u-dev] RFR: 8358334: C2/Shenandoah: incorrect execution with Unsafe

[Roland Westrelin]

21u patch doesn't apply cleanly but only because some code that's
replaced still uses `NULL` instead of `nullptr`. Otherwise, patch is
identical to 21u patch.

Tested with hotspot_gc_shenandoah + tier1 with -XX:+UseShenandoahGC

-------------

Commit messages:
 - Backport 23069e9163c4d416aa9861bc0c7beb37a71dbfa7

Changes: https://git.openjdk.org/jdk17u-dev/pull/3770/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=3770&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358334
  Stats: 154 lines in 3 files changed: 117 ins; 26 del; 11 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/3770.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/3770/head:pull/3770

PR: https://git.openjdk.org/jdk17u-dev/pull/3770