RFR: 8342809: C2 hits "assert(is_If()) failed: invalid node class: Con" during IGVN due to unhandled top

[Christian Hagedorn]

`RegularPredicate::may_be_predicate_if()` is now called from the `AssertionPredicateWithHalt` class which is invoked during IGVN. We therefore need to be able to handle top as a possible input for an Assertion Predicate success projection. This patch fixes this.

Thanks,
Christian

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Commit messages:
 - 8342809: C2 hits "assert(is_If()) failed: invalid node class: Con" during IGVN due to unhandled top

Changes: https://git.openjdk.org/jdk/pull/21634/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21634&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342809
  Stats: 65 lines in 2 files changed: 64 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21634.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21634/head:pull/21634

PR: https://git.openjdk.org/jdk/pull/21634