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

[Emanuel Peter]

On Sat, 27 Jan 2024 05:10:56 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

src/hotspot/share/opto/superword.cpp line 1110:

> 1108: }
> 1109: 
> 1110: // Are all nodes in nodes mutually independent?

Suggestion:

// Are all nodes in nodes list mutually independent?

src/hotspot/share/opto/superword.hpp line 452:

> 450:   // Is there no data path from s1 to s2 or s2 to s1?
> 451:   bool independent(Node* s1, Node* s2);
> 452:   // Are all nodes in nodes mutually independent?

Suggestion:

  // Are all nodes in nodes list mutually independent?

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PR Review Comment: https://git.openjdk.org/jdk/pull/17594#discussion_r1468344947
PR Review Comment: https://git.openjdk.org/jdk/pull/17594#discussion_r1468344729