[jdk21u-dev] RFR: 8320807: [PPC64][ZGC] C1 generates wrong code for atomics

[Martin Doerr]

Backport of [JDK-8320807](https://bugs.openjdk.org/browse/JDK-8320807).

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Commit messages:
 - Backport 3087e14cde9257680f0406b11942f9cb7739cb7b

Changes: https://git.openjdk.org/jdk21u-dev/pull/4/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=4&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320807
  Stats: 121 lines in 4 files changed: 42 ins; 70 del; 9 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/4.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/4/head:pull/4

PR: https://git.openjdk.org/jdk21u-dev/pull/4