[PATCH] D136277: [LoopInterchange] Simplify DepMatrix to a dependency vector.

[Congzhe Cao via Phabricator via llvm-commits]

congzhe added a comment.

Just one more question on the summary: when combining the two dependencies [<,=] and [=,<] that generated [<=,<=], I think we could still interchange the combined dependency? `[<=,<=]` is non-negative and swapping the two elements `<=` and `<=` gives a non-negative dependency. Thus we are not converting a positive dependency to a negative dependency, hence not violating the dependency rules for a valid interchange. Perhaps with the current `validDepInterchange()` we cannot interchange [<=,<=], but like I mentioned in the past meetings I'm rewriting `validDepInterchange()` to make the legality decisions be purely based on the signs of the dependence vectors before/after interchange. With the rewritten `validDepInterchange()` I think we can interchange [<=,<=].

My apologies for not being able to post the patch that rewrites `validDepInterchange()` sooner. We are actively working on it recently and now it seems there is a real need for this patch. We'll post the patch as soon as we can.


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