[llvm] [RISCV] Add cost for @llvm.experimental.vp.splat (PR #117313)

[Luke Lau via llvm-commits]

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@@ -1155,6 +1155,11 @@ RISCVTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
     return getCmpSelInstrCost(Instruction::Select, ICA.getReturnType(),
                               ICA.getArgTypes()[0], CmpInst::BAD_ICMP_PREDICATE,
                               CostKind);
+  case Intrinsic::experimental_vp_splat: {
+    auto LT = getTypeLegalizationCost(RetTy);
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lukel97 wrote:

If there's no V instructions then `getTypeLegalizationCost` will return an invalid type legalization cost for scalable vectors, or a scalar legalized type for fixed vectors, both of which will end up in invalid cost. We could be more explicit about this though?

https://github.com/llvm/llvm-project/pull/117313