[X86] getConstVector - remove raw bits -> fp handling and leave it to getNode/FoldConstantArithmetic (#135337)

getConstVector could only handle f32/f64 vector element types from raw APInt bit data - instead of trying to add all supported fp types, just bitcast the integer equivalent and leave it to getNode/FoldConstantArithmetic to perform the constant bitcast conversion

Tentative fix for a regression reported after #133913

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -4014,6 +4014,7 @@ static SDValue getConstVector(ArrayRef<APInt> Bits, const APInt &Undefs,
   }
 
   MVT EltVT = ConstVecVT.getVectorElementType();
+  MVT EltIntVT = EltVT.changeTypeToInteger();
   for (unsigned i = 0, e = Bits.size(); i != e; ++i) {
     if (Undefs[i]) {
       Ops.append(Split ? 2 : 1, DAG.getUNDEF(EltVT));
@@ -4024,14 +4025,8 @@ static SDValue getConstVector(ArrayRef<APInt> Bits, const APInt &Undefs,
     if (Split) {
       Ops.push_back(DAG.getConstant(V.extractBits(32, 0), dl, EltVT));
       Ops.push_back(DAG.getConstant(V.extractBits(32, 32), dl, EltVT));
-    } else if (EltVT == MVT::f32) {
-      APFloat FV(APFloat::IEEEsingle(), V);
-      Ops.push_back(DAG.getConstantFP(FV, dl, EltVT));
-    } else if (EltVT == MVT::f64) {
-      APFloat FV(APFloat::IEEEdouble(), V);
-      Ops.push_back(DAG.getConstantFP(FV, dl, EltVT));
     } else {
-      Ops.push_back(DAG.getConstant(V, dl, EltVT));
+      Ops.push_back(DAG.getBitcast(EltVT, DAG.getConstant(V, dl, EltIntVT)));
     }
   }