[llvm] [RISCV][CostModel][NFC] Add getRISCVInstructionCost() to TTI for Cost… (PR #73651)

[Wang Pengcheng via llvm-commits]

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@@ -48,6 +48,25 @@ class RISCVTTIImpl : public BasicTTIImplBase<RISCVTTIImpl> {
   /// actual target hardware.
   unsigned getEstimatedVLFor(VectorType *Ty);
 
+  enum class RISCVInstruction {
+    VRGATHER_VV,
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wangpc-pp wrote:

These are a lot like enums in `RISCV::XXX` namespace, which is generated by TableGen and defined in `RISCVMCTargetDesc.h` via `GET_INSTRINFO_ENUM`. I don't know if we can reuse them?

https://github.com/llvm/llvm-project/pull/73651