[lworld] RFR: 8259230: [lworld] Several crashes with C2 stress options

[Tobias Hartmann]

This fixes several smaller C2 issues I've found when running testing with stress options like `StressReflectiveCode` and others enabled.

Thanks,
Tobias

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Commit messages:
 - 8259230: [lworld] Several crashes with C2 stress options

Changes: https://git.openjdk.java.net/valhalla/pull/305/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=305&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259230
  Stats: 38 lines in 9 files changed: 12 ins; 1 del; 25 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/305.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/305/head:pull/305

PR: https://git.openjdk.java.net/valhalla/pull/305