[jdk20u] RFR: 8296412: Special case infinite loops with unmerged backedges in IdealLoopTree::check_safepts [v2]

[Tobias Hartmann]

> Backport of [JDK-8296412](https://bugs.openjdk.java.net/browse/JDK-8296412). Applies cleanly. Approval is pending.
> 
> Thanks,
> Tobias

Tobias Hartmann has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into backport_8296412_rev1
 - 8296412: Special case infinite loops with unmerged backedges in IdealLoopTree::check_safepts
   
   Reviewed-by: chagedorn, kvn, thartmann

-------------

Changes:
  - all: https://git.openjdk.org/jdk20u/pull/49/files
  - new: https://git.openjdk.org/jdk20u/pull/49/files/51569a84..f6ddb23f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk20u&pr=49&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk20u&pr=49&range=00-01

  Stats: 141 lines in 7 files changed: 115 ins; 23 del; 3 mod
  Patch: https://git.openjdk.org/jdk20u/pull/49.diff
  Fetch: git fetch https://git.openjdk.org/jdk20u.git pull/49/head:pull/49

PR: https://git.openjdk.org/jdk20u/pull/49