[llvm-branch-commits] [llvm] [LoopInterchange] Improve profitability check for vectorization (PR #133672)

[Ryotaro Kasuga via llvm-branch-commits]

================
@@ -80,6 +80,21 @@ enum class RuleTy {
   ForVectorization,
 };
 
+/// Store the information about if corresponding direction vector was negated
----------------
kasuga-fj wrote:

> But I now guess that the complication here is the unique entries in the dependency matrix, is that right?

Yes. (But holding two boolean values is a bit redundant. What is actually needed are three states. If both of them are false, it is an illegal state.)

> I am wondering if it isn't easier to keep all the entries and don't make them unique?

I think it would be simpler. Also, there is no need to stop making entries unique altogether. If duplicate direction vectors are allowed, I think the simplest implementation would be to keep pairs of a direction vector and a boolean value indicating whether the corresponding vector is negated. However, I'm not sure how effective it is to make direction vectors unique. In the worst case, holding pairs of a vector and a boolean value instead of a single vector doubles the number of entries. Is this allowed?

https://github.com/llvm/llvm-project/pull/133672