[jdk16u] RFR: 8259706: C2 compilation fails with assert(vtable_index == Method::invalid_vtable_index) failed: correct sentinel value

[Tobias Hartmann]

Backport of [JDK-8259706](https://bugs.openjdk.java.net/browse/JDK-8259706). Applies cleanly.

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Commit messages:
 - 8259706: C2 compilation fails with assert(vtable_index == Method::invalid_vtable_index) failed: correct sentinel value

Changes: https://git.openjdk.java.net/jdk16u/pull/19/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=19&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259706
  Stats: 7 lines in 1 file changed: 5 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk16u/pull/19.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/19/head:pull/19

PR: https://git.openjdk.java.net/jdk16u/pull/19