[llvm] [RISCV][TTI] Scale the cost of intrinsic stepvector with LMUL (PR #87301)

[Luke Lau via llvm-commits]

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@@ -860,11 +860,13 @@ RISCVTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
     break;
   }
   // TODO: add more intrinsic
-  case Intrinsic::experimental_stepvector: {
-    unsigned Cost = 1; // vid
-    auto LT = getTypeLegalizationCost(RetTy);
-    return Cost + (LT.first - 1);
-  }
+  case Intrinsic::experimental_stepvector:
+    if (ST->hasVInstructions()) {
+      auto LT = getTypeLegalizationCost(RetTy);
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lukel97 wrote:

Do we ever reach here without `+v` and need to return the scalarized cost?

https://github.com/llvm/llvm-project/pull/87301