RFR: 8308749: C2 failed: regular loops only (counted loop inside infinite loop)

[Emanuel Peter]

I found this failure with my jasm fuzzer. Have not tried to reproduce it with plain java.

I added the code above the assert, the comments explain why:

https://github.com/openjdk/jdk/blob/1fd6699e44f8caea9a1c7a8b1e946b2d1ebc0f82/src/hotspot/share/opto/loopnode.cpp#L1749-L1763

Here the graph just before the assert:
![image](https://github.com/openjdk/jdk/assets/32593061/7f11875d-49fb-49df-a3d8-6d4102711b01)

`120 Loop` -> need it to kick of `beautify_loop` and a second `build_loop_tree`
`71 Region` -> inifinite loop, `NeverBranch` is inserted on first `build_loop_tree` pass. Only attached to loop tree after second `build_loop_tree`.
`x = 81 Region` -> looks like a counted loop, but is only attached to the loop tree after `beautify_loop` in the second `build_loop_tree`.

Testing up to tier6 and stress testing. TODO

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Commit messages:
 - 8308749: failed: regular loops only (counted loop inside infinite loop

Changes: https://git.openjdk.org/jdk/pull/14178/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14178&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308749
  Stats: 114 lines in 3 files changed: 114 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14178.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14178/head:pull/14178

PR: https://git.openjdk.org/jdk/pull/14178