[DAG] visitSINT_TO_FP/UINT_TO_FP - use FoldConstantArithmetic to attempt to constant fold

Don't rely on isConstantIntBuildVectorOrConstantInt 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

@@ -18002,10 +18002,10 @@ SDValue DAGCombiner::visitSINT_TO_FP(SDNode *N) {
     return DAG.getConstantFP(0.0, DL, VT);
 
   // fold (sint_to_fp c1) -> c1fp
-  if (DAG.isConstantIntBuildVectorOrConstantInt(N0) &&
-      // ...but only if the target supports immediate floating-point values
-      (!LegalOperations || TLI.isOperationLegalOrCustom(ISD::ConstantFP, VT)))
-    return DAG.getNode(ISD::SINT_TO_FP, DL, VT, N0);
+  // ...but only if the target supports immediate floating-point values
+  if ((!LegalOperations || TLI.isOperationLegalOrCustom(ISD::ConstantFP, VT)))
+    if (SDValue C = DAG.FoldConstantArithmetic(ISD::SINT_TO_FP, DL, VT, {N0}))
+      return C;
 
   // If the input is a legal type, and SINT_TO_FP is not legal on this target,
   // but UINT_TO_FP is legal on this target, try to convert.
@@ -18050,10 +18050,10 @@ SDValue DAGCombiner::visitUINT_TO_FP(SDNode *N) {
     return DAG.getConstantFP(0.0, DL, VT);
 
   // fold (uint_to_fp c1) -> c1fp
-  if (DAG.isConstantIntBuildVectorOrConstantInt(N0) &&
-      // ...but only if the target supports immediate floating-point values
-      (!LegalOperations || TLI.isOperationLegalOrCustom(ISD::ConstantFP, VT)))
-    return DAG.getNode(ISD::UINT_TO_FP, DL, VT, N0);
+  // ...but only if the target supports immediate floating-point values
+  if ((!LegalOperations || TLI.isOperationLegalOrCustom(ISD::ConstantFP, VT)))
+    if (SDValue C = DAG.FoldConstantArithmetic(ISD::UINT_TO_FP, DL, VT, {N0}))
+      return C;
 
   // If the input is a legal type, and UINT_TO_FP is not legal on this target,
   // but SINT_TO_FP is legal on this target, try to convert.