[RISCV] Use CONCAT_VECTORS instead of INSERT_SUBVECTOR. NFC. (llvm#164226)

Author: tclin914

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -12649,10 +12649,7 @@ SDValue RISCVTargetLowering::lowerVECTOR_REVERSE(SDValue Op,
       Lo = DAG.getNode(ISD::VECTOR_REVERSE, DL, LoVT, Lo);
       Hi = DAG.getNode(ISD::VECTOR_REVERSE, DL, HiVT, Hi);
       // Reassemble the low and high pieces reversed.
-      // FIXME: This is a CONCAT_VECTORS.
-      SDValue Res = DAG.getInsertSubvector(DL, DAG.getUNDEF(VecVT), Hi, 0);
-      return DAG.getInsertSubvector(DL, Res, Lo,
-                                    LoVT.getVectorMinNumElements());
+      return DAG.getNode(ISD::CONCAT_VECTORS, DL, VecVT, Hi, Lo);
     }
 
     // Just promote the int type to i16 which will double the LMUL.