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

[Alexey Bataev via llvm-commits]

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@@ -10241,6 +10254,27 @@ InstructionCost BoUpSLP::getTreeCost(ArrayRef<Value *> VectorizedVals) {
 
     InstructionCost C = getEntryCost(&TE, VectorizedVals, CheckedExtracts);
     Cost += C;
+
+    // Calculate the cost difference of propagating a vector vs series of scalars
+    // across blocks. This may be nonzero in the case of illegal vectors.
+    Instruction *VL0 = TE.getMainOp();
+    if (VL0 && ((I + 1) < VectorizableTree.size())) {
+      Instruction *VL1 = VectorizableTree[I + 1]->getMainOp();
+      if (VL1 && (VL0->getParent() != VL1->getParent())) {
+        Type *ScalarTy = VL0->getType()->getScalarType();
+        if (ScalarTy && isValidElementType(ScalarTy)) {
+          InstructionCost ScalarDFlow =
+              TTI->getDataFlowCost(ScalarTy,
+                                 /*IsCallingConv=*/false) *
+              TE.getVectorFactor();
+          InstructionCost VectorDFlow = TTI->getDataFlowCost(
+              FixedVectorType::get(ScalarTy, TE.getVectorFactor()),
+              /*IsCallingConv=*/false);
+          Cost += (VectorDFlow - ScalarDFlow);
+        }
+      }
+    }
+
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alexey-bataev wrote:

1. It should not be here, it should be implemented in getEntryCost.
2. `vectorizableTree[I + 1]` does not always point to the operand of the previous node

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