[RISCV] Lower f16/bf16 splat_vector by bitcasting to i16 instead of promoting to f32. (#108298)

If f16/bf16 scalar types are not legal we also need to custom legalize
to prevent a crash. We do similar lowering for build_vector.

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -1080,6 +1080,8 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
                            VT, Custom);
         if (Subtarget.hasStdExtZfhmin())
           setOperationAction(ISD::SPLAT_VECTOR, VT, Custom);
+        else
+          setOperationAction(ISD::SPLAT_VECTOR, MVT::f16, Custom);
         // load/store
         setOperationAction({ISD::LOAD, ISD::STORE}, VT, Custom);
 
@@ -1117,6 +1119,8 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
                            VT, Custom);
         if (Subtarget.hasStdExtZfbfmin())
           setOperationAction(ISD::SPLAT_VECTOR, VT, Custom);
+        else
+          setOperationAction(ISD::SPLAT_VECTOR, MVT::bf16, Custom);
         setOperationAction({ISD::LOAD, ISD::STORE}, VT, Custom);
 
         setOperationAction(ISD::FNEG, VT, Expand);
@@ -6988,30 +6992,28 @@ SDValue RISCVTargetLowering::LowerOperation(SDValue Op,
     return lowerVECTOR_SPLICE(Op, DAG);
   case ISD::BUILD_VECTOR:
     return lowerBUILD_VECTOR(Op, DAG, Subtarget);
-  case ISD::SPLAT_VECTOR:
-    if ((Op.getValueType().getScalarType() == MVT::f16 &&
-         (Subtarget.hasVInstructionsF16Minimal() &&
-          Subtarget.hasStdExtZfhminOrZhinxmin() &&
-          !Subtarget.hasVInstructionsF16())) ||
-        (Op.getValueType().getScalarType() == MVT::bf16 &&
-         (Subtarget.hasVInstructionsBF16Minimal() &&
-          Subtarget.hasStdExtZfbfmin()))) {
-      if (Op.getValueType() == MVT::nxv32f16 ||
-          Op.getValueType() == MVT::nxv32bf16)
-        return SplitVectorOp(Op, DAG);
+  case ISD::SPLAT_VECTOR: {
+    MVT VT = Op.getSimpleValueType();
+    MVT EltVT = VT.getVectorElementType();
+    if ((EltVT == MVT::f16 && !Subtarget.hasStdExtZvfh()) ||
+        EltVT == MVT::bf16) {
       SDLoc DL(Op);
-      SDValue NewScalar =
-          DAG.getNode(ISD::FP_EXTEND, DL, MVT::f32, Op.getOperand(0));
-      SDValue NewSplat = DAG.getNode(
-          ISD::SPLAT_VECTOR, DL,
-          MVT::getVectorVT(MVT::f32, Op.getValueType().getVectorElementCount()),
-          NewScalar);
-      return DAG.getNode(ISD::FP_ROUND, DL, Op.getValueType(), NewSplat,
-                         DAG.getIntPtrConstant(0, DL, /*isTarget=*/true));
+      SDValue Elt;
+      if ((EltVT == MVT::bf16 && Subtarget.hasStdExtZfbfmin()) ||
+          (EltVT == MVT::f16 && Subtarget.hasStdExtZfhmin()))
+        Elt = DAG.getNode(RISCVISD::FMV_X_ANYEXTH, DL, Subtarget.getXLenVT(),
+                          Op.getOperand(0));
+      else
+        Elt = DAG.getNode(ISD::BITCAST, DL, MVT::i16, Op.getOperand(0));
+      MVT IVT = VT.changeVectorElementType(MVT::i16);
+      return DAG.getNode(ISD::BITCAST, DL, VT,
+                         DAG.getNode(ISD::SPLAT_VECTOR, DL, IVT, Elt));
     }
-    if (Op.getValueType().getVectorElementType() == MVT::i1)
+
+    if (EltVT == MVT::i1)
       return lowerVectorMaskSplat(Op, DAG);
     return SDValue();
+  }
   case ISD::VECTOR_SHUFFLE:
     return lowerVECTOR_SHUFFLE(Op, DAG, Subtarget);
   case ISD::CONCAT_VECTORS: {