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

[Manuel Hässig]

On Thu, 27 Nov 2025 15:42:25 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> **Context**: `VTransform::optimize`. Works a bit like IGVN, it allows each node to perform optimizations. Recently introduced during JDK26.
>> 
>> **Problem**: I made the assumption that we don't need a worklist mechanism, we can just do multiple passes over all nodes. The assumption was that there would not be any "trickling" of updates over the graph. But that is wrong: for example we can have a long chain of dead nodes, and we need to progressively remove the last node and mark it as dead.
>> 
>> **Solution**: Implement proper worklist mechanism, so that updates can trickle over the graph.
>
> 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 addressing my comment. It would be good to get another testing run with the limit. Otherwise, this looks good to me.

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Marked as reviewed by mhaessig (Committer).

PR Review: https://git.openjdk.org/jdk/pull/28512#pullrequestreview-3516292071