[jdk11u-dev] RFR: 8223923: C2: Missing interference with mismatched unsafe accesses

[Aleksey Shipilev]

Clean backport to fix C2 bug.

Additional testing:
 - [x] New test fails without the C2 fix, passes with it
 - [x] Linux x86_64 tier1 passes with the fix

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Commit messages:
 - Backport 86add21a85ec57de00aecb0a18bc99567a91d0d8

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/276/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=276&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8223923
  Stats: 84 lines in 2 files changed: 76 ins; 2 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/276.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/276/head:pull/276

PR: https://git.openjdk.java.net/jdk11u-dev/pull/276