[jdk18u] RFR: 8287432: C2: assert(tn->in(0) != __null) failed: must have live top node

[Tobias Hartmann]

Backport of [JDK-8287432](https://bugs.openjdk.java.net/browse/JDK-8287432). Applies cleanly. Approval is pending.

Thanks,
Tobias

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Commit messages:
 - 8287432: C2: assert(tn->in(0) != __null) failed: must have live top node

Changes: https://git.openjdk.org/jdk18u/pull/165/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk18u&pr=165&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8287432
  Stats: 56 lines in 2 files changed: 55 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk18u/pull/165.diff
  Fetch: git fetch https://git.openjdk.org/jdk18u pull/165/head:pull/165

PR: https://git.openjdk.org/jdk18u/pull/165