[ISel/RISCV] Custom-promote [b]f16 in [l]lrint (#146507)

Extend lowerVectorXRINT to also do a FP_EXTEND_VL when the source
element type is [b]f16, and wire up this custom-promote. Updating the
cost-model to not give these an invalid cost is left to a companion
patch.

Author: artagnon

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -1150,6 +1150,7 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
       setOperationAction({ISD::STRICT_FP_ROUND, ISD::STRICT_FP_EXTEND}, VT,
                          Custom);
       setOperationAction({ISD::VP_FP_ROUND, ISD::VP_FP_EXTEND}, VT, Custom);
+      setOperationAction({ISD::LRINT, ISD::LLRINT}, VT, Custom);
       setOperationAction({ISD::VP_MERGE, ISD::VP_SELECT, ISD::SELECT}, VT,
                          Custom);
       setOperationAction(ISD::SELECT_CC, VT, Expand);
@@ -1451,6 +1452,7 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
               Custom);
           setOperationAction({ISD::VP_SINT_TO_FP, ISD::VP_UINT_TO_FP}, VT,
                              Custom);
+          setOperationAction({ISD::LRINT, ISD::LLRINT}, VT, Custom);
           if (Subtarget.hasStdExtZfhmin()) {
             setOperationAction(ISD::BUILD_VECTOR, VT, Custom);
           } else {
@@ -1475,6 +1477,7 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
         if (VT.getVectorElementType() == MVT::bf16) {
           setOperationAction(ISD::BITCAST, VT, Custom);
           setOperationAction({ISD::VP_FP_ROUND, ISD::VP_FP_EXTEND}, VT, Custom);
+          setOperationAction({ISD::LRINT, ISD::LLRINT}, VT, Custom);
           if (Subtarget.hasStdExtZfbfmin()) {
             setOperationAction(ISD::BUILD_VECTOR, VT, Custom);
           } else {
@@ -3487,6 +3490,14 @@ static SDValue lowerVectorXRINT(SDValue Op, SelectionDAG &DAG,
   }
 
   auto [Mask, VL] = getDefaultVLOps(SrcVT, SrcContainerVT, DL, DAG, Subtarget);
+
+  // [b]f16 -> f32
+  MVT SrcElemType = SrcVT.getVectorElementType();
+  if (SrcElemType == MVT::f16 || SrcElemType == MVT::bf16) {
+    MVT F32VT = SrcContainerVT.changeVectorElementType(MVT::f32);
+    Src = DAG.getNode(RISCVISD::FP_EXTEND_VL, DL, F32VT, Src, Mask, VL);
+  }
+
   SDValue Res =
       DAG.getNode(RISCVISD::VFCVT_RM_X_F_VL, DL, DstContainerVT, Src, Mask,
                   DAG.getTargetConstant(matchRoundingOp(Op.getOpcode()), DL,