[llvm] [SLP] More accurately cost RISCV scalar splats (PR #213104)

[Alexey Bataev via llvm-commits]

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@@ -2561,6 +2563,12 @@ InstructionCost RISCVTTIImpl::getVectorInstrCost(
     return BaseT::getVectorInstrCost(Opcode, Val, CostKind, Index, Op0, Op1,
                                      VIC);
 
+  // Scalar splat operand can be folded for vector ops that support splatting
+  // the scalar operand, so the explicit insertelement is free in this context.
+  if (Opcode == Instruction::InsertElement &&
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alexey-bataev wrote:

Add a check/assertion that insert index is zero

https://github.com/llvm/llvm-project/pull/213104