[llvm] [SelectionDAG] Add expansion for llvm.modf intrinsic (PR #179434)

[Alex Wang via llvm-commits]

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@@ -2771,6 +2772,34 @@ SDValue SelectionDAGLegalize::expandFrexp(SDNode *Node) const {
   return DAG.getMergeValues({Result0, Result1}, dl);
 }
 
+SDValue SelectionDAGLegalize::expandModf(SDNode *Node) const {
+  SDLoc dl(Node);
+  SDValue Val = Node->getOperand(0);
+  EVT VT = Val.getValueType();
+  SDNodeFlags Flags = Node->getFlags();
+
+  SDValue IntPart = DAG.getNode(ISD::FTRUNC, dl, VT, Val, Flags);
+  SDValue FracPart = DAG.getNode(ISD::FSUB, dl, VT, Val, IntPart, Flags);
+
+  SDValue FracToUse;
+  if (Flags.hasNoInfs()) {
+    FracToUse = FracPart;
+  } else {
+    SDValue Abs = DAG.getNode(ISD::FABS, dl, VT, Val, Flags);
+    SDValue Inf =
+        DAG.getConstantFP(APFloat::getInf(VT.getFltSemantics()), dl, VT);
+    EVT SetCCVT =
+        TLI.getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(), VT);
+    SDValue IsInf = DAG.getSetCC(dl, SetCCVT, Abs, Inf, ISD::SETOEQ);
+    SDValue Zero = DAG.getConstantFP(0.0, dl, VT);
+    FracToUse = DAG.getNode(ISD::SELECT, dl, VT, IsInf, Zero, FracPart);
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aeft wrote:

Thanks! Updated.

https://github.com/llvm/llvm-project/pull/179434