[SelectionDAG] Add MVT::bf16 to getConstantFP()

[asmith]

Summary

This was probably overlooked in recent bfloat patches.
Needed to handle bf16 constants in SelectionDAG.

ConstantFP:bf16<APFloat(0)>

[stuij]

LGTM. Thanks :)

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

 SDValue SelectionDAG::getConstantFP(double Val, const SDLoc &DL, EVT VT,
                                     bool isTarget) {
   EVT EltVT = VT.getScalarType();
   if (EltVT == MVT::f32)
     return getConstantFP(APFloat((float)Val), DL, VT, isTarget);
   else if (EltVT == MVT::f64)
     return getConstantFP(APFloat(Val), DL, VT, isTarget);
   else if (EltVT == MVT::f80 || EltVT == MVT::f128 || EltVT == MVT::ppcf128 ||
-           EltVT == MVT::f16) {
+           EltVT == MVT::f16 || EltVT == MVT::bf16) {
     bool Ignored;
     APFloat APF = APFloat(Val);
     APF.convert(EVTToAPFloatSemantics(EltVT), APFloat::rmNearestTiesToEven,
                 &Ignored);
     return getConstantFP(APF, DL, VT, isTarget);
   } else
     llvm_unreachable("Unsupported type in getConstantFP");
 }