[jdk21u] RFR: 8303737: C2: Load can bypass subtype check that enforces it's from the right object type

Wed Oct 25 10:17:02 UTC 2023

Clean backport to fix old C2 bug.

Additional testing:
 - [x] New tests fail without the patch, pass with it
 - [ ] Linux aarch64 server fastdebug, `tier1 tier2 tier3`

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Commit messages:
 - Backport 52983ed529182901db4e33857bfeab2727e235df

Changes: https://git.openjdk.org/jdk21u/pull/291/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=291&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303737
  Stats: 499 lines in 8 files changed: 450 ins; 3 del; 46 mod
  Patch: https://git.openjdk.org/jdk21u/pull/291.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/291/head:pull/291

PR: https://git.openjdk.org/jdk21u/pull/291