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

[Alexey Bataev via llvm-commits]

================
@@ -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.
+    Type *ScalarTy = VL0->getType()->getScalarType();
+    if (ScalarTy && isValidElementType(ScalarTy)) {
+      ScalarCost += TTI->getDataFlowCost(ScalarTy,
+                                         /*IsCallingConv=*/false) *
+                    EntryVF;
+      CommonCost += TTI->getDataFlowCost(
+          FixedVectorType::get(ScalarTy, EntryVF), /*IsCallingConv=*/false);
----------------
alexey-bataev wrote:

```suggestion
      ScalarCost += TTI->getDataFlowCost(ScalarTy,
                                         /*IsCallingConv=*/false) *
                    EntryVF;
      CommonCost += TTI->getDataFlowCost(
          VecTy, /*IsCallingConv=*/false);
```

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