[X86] Check MinMax has NaN and replace with NewX for minimumnum/maximumnum (llvm#164546)

It is incorrect to just check for NewX and return its ordered elements.

Author: phoebewang

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -29516,11 +29516,8 @@ static SDValue LowerFMINIMUM_FMAXIMUM(SDValue Op, const X86Subtarget &Subtarget,
   if (IgnoreNaN || DAG.isKnownNeverNaN(IsNum ? NewY : NewX))
     return MinMax;
 
-  if (DAG.isKnownNeverNaN(NewX))
-    NewX = NewY;
-
-  SDValue IsNaN =
-      DAG.getSetCC(DL, SetCCType, NewX, NewX, IsNum ? ISD::SETO : ISD::SETUO);
+  SDValue NaNSrc = IsNum ? MinMax : NewX;
+  SDValue IsNaN = DAG.getSetCC(DL, SetCCType, NaNSrc, NaNSrc, ISD::SETUO);
 
   return DAG.getSelect(DL, VT, IsNaN, NewX, MinMax);
 }