[llvm] [AArch64][CostModel] Improve cost estimate of scalarizing a vector di… (PR #118055)

[Alexey Bataev via llvm-commits]

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@@ -3572,6 +3573,40 @@ InstructionCost AArch64TTIImpl::getArithmeticInstrCost(
           Cost *= 4;
         return Cost;
       } else {
+        // If the information about individual scalars being vectorized is
+        // available, this yeilds better cost estimation.
+        if (auto *VTy = dyn_cast<FixedVectorType>(Ty); VTy && !Args.empty()) {
+          assert(Args.size() % 2 == 0 && "Args size should be even");
+          InstructionCost InsertExtractCost =
+              ST->getVectorInsertExtractBaseCost();
+          // If the cost of single sdiv is inquired through the cost-model.
+          // FIXME: remove the isa checks once the PR 122236 lands.
+          if (Args.size() == 2 &&
+              !(isa<ConstantVector>(Args[1]) ||
+                isa<ConstantDataVector>(Args[1]) ||
+                isa<ConstantExpr>(Args[1])) &&
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alexey-bataev wrote:

Why?

https://github.com/llvm/llvm-project/pull/118055