[jdk21] RFR: 8310130: C2: assert(false) failed: scalar_input is neither phi nor a matchin reduction

[Tobias Hartmann]

Backport of [JDK-8310130](https://bugs.openjdk.java.net/browse/JDK-8310130). Applies cleanly.

Thanks,
Tobias

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Commit messages:
 - 8310130: C2: assert(false) failed: scalar_input is neither phi nor a matchin reduction

Changes: https://git.openjdk.org/jdk21/pull/77/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21&pr=77&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310130
  Stats: 145 lines in 3 files changed: 141 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21/pull/77.diff
  Fetch: git fetch https://git.openjdk.org/jdk21.git pull/77/head:pull/77

PR: https://git.openjdk.org/jdk21/pull/77