RFR: 8372451: C2 SuperWord: "endless loop" assert. Need to implement proper worklist mechanism [v2]

[Emanuel Peter]

On Thu, 27 Nov 2025 14:15:16 GMT, Manuel Hässig <mhaessig at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   limit steps of optimize, for Manuel
>
> Thank you for fixing this, @eme64!
> 
> The optimization mechanism you are replacing had a mechanism to detect when too many passes had been done. Now there is no such mechanism. How can you detect a condition where we take way too long to reach a fixpoint apart from a timeout?
> 
> What do implementations of `VTransform::optimize` have to guarantee to ensure that we reach a fixpoint?

@mhaessig Good point! I had intended to do that, but then somehow forgot 🙈 

I now just limit it to `100 * number_of_initial_nodes`. Maybe that won't be good enough forever, but for now it should be good.

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PR Comment: https://git.openjdk.org/jdk/pull/28512#issuecomment-3586493314