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

[Luke Lau via llvm-commits]

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@@ -191,6 +191,7 @@ enum class VectorInstrContext : uint8_t {
   Load,  ///< The value being inserted comes from a load (InsertElement only).
   Store, ///< The extracted value is stored (ExtractElement only).
   BinaryOp, ///< One of the operands is a binary op.
+  SplatOpFolded,  ///< The value's user supports a scalar splat operand
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lukel97 wrote:

Nit
```suggestion
  SplatOpFolded,  ///< All of the value's users support splatting the value.
```

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