RFR: 8286104: use aggressive liveness for unstable_if traps

[Xin Liu]

8286104: use aggressive liveness for unstable_if traps

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Commit messages:
 - 8286104: use aggressive liveness for unstable_if traps

Changes: https://git.openjdk.java.net/jdk/pull/8545/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8545&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286104
  Stats: 119 lines in 6 files changed: 103 ins; 3 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8545.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8545/head:pull/8545

PR: https://git.openjdk.java.net/jdk/pull/8545