[jdk21u] RFR: 8303279: C2: crash in SubTypeCheckNode::sub() at IGVN split if

[Ben Taylor]

Backport is clean

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Commit messages:
 - Backport caadad4fdc78799dab2d492dba9b9f74b22d036e

Changes: https://git.openjdk.org/jdk21u/pull/9/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=9&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/jdk21u/pull/9.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/9/head:pull/9

PR: https://git.openjdk.org/jdk21u/pull/9