[DAG] visitFCEIL/FTRUNC/FFLOOR/FNEG - use FoldConstantArithmetic to attempt to constant fold

Don't rely on isConstantFPBuildVectorOrConstantFP followed by getNode() will constant fold - FoldConstantArithmetic will do all of this for us.

Cleanup for #112682

Author: RKSimon

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -18291,8 +18291,8 @@ SDValue DAGCombiner::visitFCEIL(SDNode *N) {
   EVT VT = N->getValueType(0);
 
   // fold (fceil c1) -> fceil(c1)
-  if (DAG.isConstantFPBuildVectorOrConstantFP(N0))
-    return DAG.getNode(ISD::FCEIL, SDLoc(N), VT, N0);
+  if (SDValue C = DAG.FoldConstantArithmetic(ISD::FCEIL, SDLoc(N), VT, {N0}))
+    return C;
 
   return SDValue();
 }
@@ -18302,8 +18302,8 @@ SDValue DAGCombiner::visitFTRUNC(SDNode *N) {
   EVT VT = N->getValueType(0);
 
   // fold (ftrunc c1) -> ftrunc(c1)
-  if (DAG.isConstantFPBuildVectorOrConstantFP(N0))
-    return DAG.getNode(ISD::FTRUNC, SDLoc(N), VT, N0);
+  if (SDValue C = DAG.FoldConstantArithmetic(ISD::FTRUNC, SDLoc(N), VT, {N0}))
+    return C;
 
   // fold ftrunc (known rounded int x) -> x
   // ftrunc is a part of fptosi/fptoui expansion on some targets, so this is
@@ -18336,8 +18336,8 @@ SDValue DAGCombiner::visitFFLOOR(SDNode *N) {
   EVT VT = N->getValueType(0);
 
   // fold (ffloor c1) -> ffloor(c1)
-  if (DAG.isConstantFPBuildVectorOrConstantFP(N0))
-    return DAG.getNode(ISD::FFLOOR, SDLoc(N), VT, N0);
+  if (SDValue C = DAG.FoldConstantArithmetic(ISD::FFLOOR, SDLoc(N), VT, {N0}))
+    return C;
 
   return SDValue();
 }
@@ -18348,8 +18348,8 @@ SDValue DAGCombiner::visitFNEG(SDNode *N) {
   SelectionDAG::FlagInserter FlagsInserter(DAG, N);
 
   // Constant fold FNEG.
-  if (DAG.isConstantFPBuildVectorOrConstantFP(N0))
-    return DAG.getNode(ISD::FNEG, SDLoc(N), VT, N0);
+  if (SDValue C = DAG.FoldConstantArithmetic(ISD::FNEG, SDLoc(N), VT, {N0}))
+    return C;
 
   if (SDValue NegN0 =
           TLI.getNegatedExpression(N0, DAG, LegalOperations, ForCodeSize))