RFR: 8324775: C2 SuperWord: refactor visited sets [v2]

[Vladimir Kozlov]

On Sat, 27 Jan 2024 05:13:35 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.
>
> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   comment improvement by Vladimir

Good.

-------------

Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17594#pullrequestreview-1847259410