[DAG Combiner] Fix the native computation of the Newton series for reciprocals

The generic infrastructure to compute the Newton series for reciprocal and
reciprocal square root was conceived to allow a target to compute the series
itself.  However, the original code did not properly consider this condition
if returned by a target.  This patch addresses the issues to allow a target
to compute the series on its own.

Differential revision: https://reviews.llvm.org/D22975

llvm-svn: 286523
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index 2944e99..689a2e6 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -968,9 +968,9 @@
     SDValue DAGCombineTruncBoolExt(SDNode *N, DAGCombinerInfo &DCI) const;
     SDValue combineFPToIntToFP(SDNode *N, DAGCombinerInfo &DCI) const;
 
-    SDValue getRsqrtEstimate(SDValue Operand, SelectionDAG &DAG, int Enabled,
-                             int &RefinementSteps,
-                             bool &UseOneConstNR) const override;
+    SDValue getSqrtEstimate(SDValue Operand, SelectionDAG &DAG, int Enabled,
+                            int &RefinementSteps, bool &UseOneConstNR,
+                            bool Reciprocal) const override;
     SDValue getRecipEstimate(SDValue Operand, SelectionDAG &DAG, int Enabled,
                              int &RefinementSteps) const override;
     unsigned combineRepeatedFPDivisors() const override;