[llvm] [RISCV] Fix missing scaling by LMUL in cost model (PR #73342)

[Luke Lau via llvm-commits]

================
@@ -1163,7 +1165,7 @@ RISCVTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
     auto LT = getTypeLegalizationCost(RetTy);
     if (const auto *Entry = CostTableLookup(VectorIntrinsicCostTable,
                                             ICA.getID(), LT.second))
-      return LT.first * Entry->Cost;
+      return LT.first * TLI->getLMULCost(LT.second) * Entry->Cost;
----------------
lukel97 wrote:

The entries in the cost table seem to be the same across various LMULs though, am I missing something here?
E.g. nxv1i64 is LMUL1, nxv2i64 is LMUL2 etc.
```c++
    {Intrinsic::bswap, MVT::nxv1i64, 31},
    {Intrinsic::bswap, MVT::nxv2i64, 31},
    {Intrinsic::bswap, MVT::nxv4i64, 31},
    {Intrinsic::bswap, MVT::nxv8i64, 31},
```

https://github.com/llvm/llvm-project/pull/73342