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

[Emanuel Peter]

On Thu, 1 Jun 2023 15:48:02 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> 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. Passed.
>
> Marked as reviewed by kvn (Reviewer).

Thanks @vnkozlov @chhagedorn for the reviews!

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PR Comment: https://git.openjdk.org/jdk/pull/14178#issuecomment-1586759492