[llvm] [RISCV][CostModel] Updates reduction and shuffle cost (PR #77342)

[Philip Reames via llvm-commits]

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@@ -482,11 +481,10 @@ InstructionCost RISCVTTIImpl::getShuffleCost(TTI::ShuffleKind Kind,
       //   vmsne.vi  v0, v8, 0
 
       return LT.first *
-             (TLI->getLMULCost(LT.second) + // FIXME: this should be 1 for andi
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preames wrote:

If the index is non-zero, then there's a vslide needed in the current sequence which does scale with LMUL.

So, this change is wrong for non-zero index.  

https://github.com/llvm/llvm-project/pull/77342