[DAGCombiner] Use FoldConstantArithmetic instead of dyn_cast in visitFP_ROUND.

[Jimerlife]

Summary

Use FoldConstantArithmetic instead of dyn_cast in visitFP_ROUND.

[RKSimon]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

15863–15864

Might this be better as just a constant fold attempt?

if (SDValue C = DAG.FoldConstantArithmetic(ISD::FP_ROUND, SDLoc(N), VT, {N0, N1}))
  return C;

[Jimerlife]

address comment

[Jimerlife]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

15863–15864

Thank you. Good suggestion.

[RKSimon]

Thanks - please can you update the title and summary

[Jimerlife]

In D132439#3745305, @RKSimon wrote:

Thanks - please can you update the title and summary

I updated the title and summary. Thanks for your careful review.

[RKSimon]

LGTM - cheers

[RKSimon]

(please drop the NFC as it probably has different behaviour now - vector support etc)

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

if (DAG.isConstantFPBuildVectorOrConstantFP(N0))
     return DAG.getNode(ISD::FP_TO_UINT, SDLoc(N), VT, N0);
 
   return FoldIntToFPToInt(N, DAG);
 }
 
 SDValue DAGCombiner::visitFP_ROUND(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
-  ConstantFPSDNode *N0CFP = dyn_cast<ConstantFPSDNode>(N0);
   EVT VT = N->getValueType(0);
 
   // fold (fp_round c1fp) -> c1fp
-  if (N0CFP)
-    return DAG.getNode(ISD::FP_ROUND, SDLoc(N), VT, N0, N1);
+  if (SDValue C =
+          DAG.FoldConstantArithmetic(ISD::FP_ROUND, SDLoc(N), VT, {N0, N1}))
+    return C;
 
   // fold (fp_round (fp_extend x)) -> x
   if (N0.getOpcode() == ISD::FP_EXTEND && VT == N0.getOperand(0).getValueType())
     return N0.getOperand(0);
 
   // fold (fp_round (fp_round x)) -> (fp_round x)
   if (N0.getOpcode() == ISD::FP_ROUND) {
     const bool NIsTrunc = N->getConstantOperandVal(1) == 1;