[SelectionDAG] also deduce nnan from users

Author: paperchalice

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -6715,6 +6715,9 @@ static SDValue foldAndOrOfSETCC(SDNode *LogicOp, SelectionDAG &DAG) {
                                  DAG, isFMAXNUMFMINNUM_IEEE, isFMAXNUMFMINNUM);
 
       if (NewOpcode != ISD::DELETED_NODE) {
+        // Propagate fast-math flags from setcc.
+        SelectionDAG::FlagInserter FlagInserter(DAG, LHS->getFlags() &
+                                                         RHS->getFlags());
         SDValue MinMaxValue =
             DAG.getNode(NewOpcode, DL, OpVT, Operand1, Operand2);
         return DAG.getSetCC(DL, VT, MinMaxValue, CommonValue, CC);

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -5869,6 +5869,12 @@ bool SelectionDAG::isKnownNeverNaN(SDValue Op, bool SNaN,
                            ? APInt::getAllOnes(VT.getVectorNumElements())
                            : APInt(1, 1);
 
+  // If all users of this operand is annotated with nnan, we can assume
+  // it self is not NaN, since nnan also affects inputs.
+  if (llvm::all_of(Op->users(),
+                   [](const SDNode *N) { return N->getFlags().hasNoNaNs(); }))
+    return true;
+
   return isKnownNeverNaN(Op, DemandedElts, SNaN, Depth);
 }