[llvm] [SLP]: Introduce and use getDataFlowCost (PR #112999)

[Alexey Bataev via llvm-commits]

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@@ -9222,6 +9223,18 @@ BoUpSLP::getEntryCost(const TreeEntry *E, ArrayRef<Value *> VectorizedVals,
                                             OpTE->Scalars.size());
     }
 
+    // Calculate the cost difference of propagating a vector vs series of
+    // scalars across blocks. This may be nonzero in the case of illegal
+    // vectors.
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alexey-bataev wrote:

The comment talks about illegal vector types but the code affects only legal vector types

https://github.com/llvm/llvm-project/pull/112999