[jdk25u-dev] RFR: 8362979: C2 fails with unexpected node in SuperWord truncation: CmpLTMask, RoundF

[Vishal Chand]

Clean backport of [8362979](https://github.com/openjdk/jdk/pull/26494): C2 fails with unexpected node in SuperWord truncation: CmpLTMask, RoundF

This backport fixes a debug assert failure discovered by CTW. The fix adds CmpLTMask, RoundF, and RoundD nodes to the SuperWord truncation switch statement and includes reduced test cases.

Additional Testing:
- [x] New regression test fails without the fix, passes with it.
- [x] Linux x86_64 server fastebug `compiler tests`.

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Commit messages:
 - Backport ea0b49c36db7dce508aec7e72e73c7274d65bc15

Changes: https://git.openjdk.org/jdk25u-dev/pull/232/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u-dev&pr=232&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8362979
  Stats: 57 lines in 3 files changed: 57 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk25u-dev/pull/232.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u-dev.git pull/232/head:pull/232

PR: https://git.openjdk.org/jdk25u-dev/pull/232