[llvm] [RISCV][NFC] Add helpers for RVV register classes (PR #84144)

[Wang Pengcheng via llvm-commits]

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@@ -112,11 +112,33 @@ struct RISCVRegisterInfo : public RISCVGenRegisterInfo {
 
   bool doesRegClassHavePseudoInitUndef(
       const TargetRegisterClass *RC) const override {
+    return isVRRegClass(RC);
+  }
+
+  bool isVRRegClass(const TargetRegisterClass *RC) const {
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wangpc-pp wrote:

in `RISCVRegisterInfo` class or a namespace?

https://github.com/llvm/llvm-project/pull/84144