[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286523 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 5 deletions

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index 823d91072fc..826b4d5a180 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -2986,21 +2986,24 @@ public:
   /// Hooks for building estimates in place of slower divisions and square
   /// roots.
 
-  /// Return a reciprocal square root estimate value for the input operand.
+  /// Return either a square root or its reciprocal estimate value for the input
+  /// operand.
   /// \p Enabled is a ReciprocalEstimate enum with value either 'Unspecified' or
   /// 'Enabled' as set by a potential default override attribute.
   /// If \p RefinementSteps is 'Unspecified', the number of Newton-Raphson
   /// refinement iterations required to generate a sufficient (though not
   /// necessarily IEEE-754 compliant) estimate is returned in that parameter.
   /// The boolean UseOneConstNR output is used to select a Newton-Raphson
-  /// algorithm implementation that uses one constant or two constants.
+  /// algorithm implementation that uses either one or two constants.
+  /// The boolean Reciprocal is used to select whether the estimate is for the
+  /// square root of the input operand or the reciprocal of its square root.
   /// A target may choose to implement its own refinement within this function.
   /// If that's true, then return '0' as the number of RefinementSteps to avoid
   /// any further refinement of the estimate.
   /// An empty SDValue return means no estimate sequence can be created.
-  virtual SDValue getRsqrtEstimate(SDValue Operand, SelectionDAG &DAG,
-                                   int Enabled, int &RefinementSteps,
-                                   bool &UseOneConstNR) const {
+  virtual SDValue getSqrtEstimate(SDValue Operand, SelectionDAG &DAG,
+                                  int Enabled, int &RefinementSteps,
+                                  bool &UseOneConstNR, bool Reciprocal) const {
     return SDValue();
   }