[jdk16] RFR: 8258619: -XX:CompileCommand=blackhole, * should only accept empty static methods

[Aleksey Shipilev]

In JDK-8257827 CSR, a further comment was raised about changing the semantics of the method. This allegedly introduces the conformance problem. While it is still an open question where the conformance problem is real, we can sidestep the entire issue by allowing only empty static methods to be blackholed. This eliminates any behavioral difference: empty methods have no side effects, and static methods do not need any null checks.

This change eliminates a lot of new code added by original JDK-8252505 push, mostly now-useless testing code. It adds two more tests that verify that non-empty and non-static methods are properly rejected.

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Commit messages:
 - Amend assertion messages
 - 8258619: -XX:CompileCommand=blackhole,* should only accept empty static methods

Changes: https://git.openjdk.java.net/jdk16/pull/45/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16&pr=45&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258619
  Stats: 1180 lines in 11 files changed: 203 ins; 914 del; 63 mod
  Patch: https://git.openjdk.java.net/jdk16/pull/45.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16 pull/45/head:pull/45

PR: https://git.openjdk.java.net/jdk16/pull/45