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

[Ryan Buchner via llvm-commits]

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@@ -1143,6 +1153,10 @@ class LLVM_ABI TargetTransformInfoImplBase {
     return true;
   }
 
+  virtual bool canSplatOperand(unsigned Opcode, int Operand) const {
+    return false;
+  }
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bababuck wrote:

We don't have information about the user within `getShuffleCost` and `getVectorInstCost` so I think we need another TTI hook.

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