[RISCV] Lower fixed-length {insert,extract}_vector_elt on zvfhmin/zvfbfmin

RISCVTargetLowering::lower{INSERT,EXTRACT}_VECTOR_ELT already handles f16 and bf16 scalable vectors after llvm#110221, so we can reuse it for fixed-length vectors.

Author: lukel97

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -1333,7 +1333,8 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
         // expansion to a build_vector of 0s.
         setOperationAction(ISD::UNDEF, VT, Custom);
 
-        setOperationAction({ISD::CONCAT_VECTORS, ISD::INSERT_SUBVECTOR,
+        setOperationAction({ISD::INSERT_VECTOR_ELT, ISD::EXTRACT_VECTOR_ELT,
+                            ISD::CONCAT_VECTORS, ISD::INSERT_SUBVECTOR,
                             ISD::EXTRACT_SUBVECTOR, ISD::VECTOR_REVERSE,
                             ISD::VECTOR_SHUFFLE, ISD::VECTOR_COMPRESS},
                            VT, Custom);
@@ -1404,10 +1405,8 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
           continue;
         }
 
-        setOperationAction({ISD::BUILD_VECTOR,
-                            ISD::INSERT_VECTOR_ELT, ISD::EXTRACT_VECTOR_ELT,
-                            ISD::SCALAR_TO_VECTOR},
-                           VT, Custom);
+        setOperationAction({ISD::BUILD_VECTOR, ISD::SCALAR_TO_VECTOR}, VT,
+                           Custom);
 
         setOperationAction(
             {ISD::MLOAD, ISD::MSTORE, ISD::MGATHER, ISD::MSCATTER}, VT, Custom);