RFR: 8324775: C2 SuperWord: refactor visited sets

[Christian Hagedorn]

On Fri, 26 Jan 2024 16:53:46 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> Subtask of https://github.com/openjdk/jdk/pull/16620
> 
> Currently, the visited set is a "global" set that is reused all through SuperWord:
> `_visited`, `_post_visited`, and also `_stk`.
> 
> This makes other refactorings difficult. I am refactoring all related code to make the visited sets local, with use of ResourceMark.
> 
> I am also refactoring the `independent` queries: from using recursive function calls to iterative. This is necessary, unless we want to pass the visited set around into the recursive calls (I think not!)
> 
> At the same time, I wanted the code of `find_dependence` to become easier, and closer to `independent`, hence I re-defined it to `mutually_independent`, and had to slightly adapt also its usages.

Looks good!

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Marked as reviewed by chagedorn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17594#pullrequestreview-1846572613