Revert "[SelectionDAG] Remove unused FP constant in getNegatedExpression"

2508ef0 doesn't totally fix the issue since we did not handle the case
when unused temporary negated result is the same with the result, which
is found by address sanitizer.

Author: ecnelises

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -5773,10 +5773,8 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
 
     // If we already have the use of the negated floating constant, it is free
     // to negate it even it has multiple uses.
-    if (!Op.hasOneUse() && CFP.use_empty()) {
-      RemoveDeadNode(CFP);
+    if (!Op.hasOneUse() && CFP.use_empty())
       break;
-    }
     Cost = NegatibleCost::Neutral;
     return CFP;
   }