[jdk18u] RFR: 8283187: C2: loop candidate for superword not always unrolled fully if superword fails

[Tobias Hartmann]

Backport of [JDK-8283187](https://bugs.openjdk.java.net/browse/JDK-8283187). Did not apply cleanly due to changes to surrounding code in `test/hotspot/jtreg/compiler/lib/ir_framework/IRNode.java`. Approval is pending.

Thanks,
Tobias

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Commit messages:
 - 8283187: C2: loop candidate for superword not always unrolled fully if superword fails

Changes: https://git.openjdk.java.net/jdk18u/pull/84/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=84&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283187
  Stats: 135 lines in 5 files changed: 90 ins; 6 del; 39 mod
  Patch: https://git.openjdk.java.net/jdk18u/pull/84.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18u pull/84/head:pull/84

PR: https://git.openjdk.java.net/jdk18u/pull/84