RFR: 8285595: Assert frame anchor doesn't change in safepoints/handshakes

[Ron Pressler]

Hi.
Please review this change that asserts that the frame anchor is not changed by safepoints/handshakes.

— Ron

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Commit messages:
 - 8285595: Assert frame anchor doesn't change in safepoints/handshakes

Changes: https://git.openjdk.java.net/jdk/pull/8402/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8402&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285595
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8402.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8402/head:pull/8402

PR: https://git.openjdk.java.net/jdk/pull/8402