[jdk21] RFR: 8303279: C2: crash in SubTypeCheckNode::sub() at IGVN split if

[Tobias Hartmann]

Backport of [JDK-8303279](https://bugs.openjdk.java.net/browse/JDK-8303279). Applies cleanly.

Thanks,
Tobias

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Commit messages:
 - 8303279: C2: crash in SubTypeCheckNode::sub() at IGVN split if

Changes: https://git.openjdk.org/jdk21/pull/119/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21&pr=119&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303279
  Stats: 110 lines in 7 files changed: 94 ins; 4 del; 12 mod
  Patch: https://git.openjdk.org/jdk21/pull/119.diff
  Fetch: git fetch https://git.openjdk.org/jdk21.git pull/119/head:pull/119

PR: https://git.openjdk.org/jdk21/pull/119