[jdk11u-dev] RFR: 8268347: C2: nested locks optimization may create unbalanced monitor enter/exit code

[Roland Westrelin]

Original patch does not apply cleanly to 11u because of context is
different in several places. 11u patch is otherwise identical to the
original patch.
 
Testing: x86_64 build, tier1. Included test case doesn't fail with 11u.

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Commit messages:
 - Backport 4d8b5c70dff51470210a0ca93b932af1b27c9f27

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/115/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=115&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268347
  Stats: 384 lines in 11 files changed: 345 ins; 16 del; 23 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/115.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/115/head:pull/115

PR: https://git.openjdk.java.net/jdk11u-dev/pull/115