RFR: 8326638: Crash in PhaseIdealLoop::remix_address_expressions due to unexpected Region instead of Loop [v2]

[Vladimir Kozlov]

On Tue, 27 Feb 2024 08:59:29 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> Adds a missing `_head->is_Loop()` check to handle the case when the loop head is not a `LoopNode` but a `RegionNode` because the loop is irreducible:
>> 
>> 
>> (rr) p n_loop->_head->dump(1)
>>   412 IfTrue === 411 [[ 345 ]] #1 !jvms: Test$Class1::Class1_method0 @ bci:286 (line 119)
>>   339 SafePoint === 336 1 340 1 1 344 290 1 1 1 1 291 1 1 293 294 295 1 320 297 1 298 299 300 301 302 1 303 1 [[ 345 ]] SafePoint !jvms: Test$Class1::Class1_method0 @ bci:307 (line 122)
>>   345 Region === 345 339 412 [[ 345 456 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 1861 1863 1865 1867 1882 1888 ]] #irreducible !jvms: Test$Class1::Class1_method0 @ bci:138 (line 101)
>> 
>> 
>> We then crash when invoking `LoopNode::skip_strip_mined` on a RegionNode or assert in debug. Unfortunately, I was not able to simply the test any further.
>> 
>> This is a regression from [JDK-8303511](https://bugs.openjdk.org/browse/JDK-8303511) in JDK 21 b13
>> 
>> Thanks,
>> Tobias
>
> Tobias Hartmann has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Skip optimization for irreducible loops

Good.

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Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18002#pullrequestreview-1904137031