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

[evandro]

Summary

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.

[t.p.northover]

llvm/include/llvm/CodeGen/ISDOpcodes.h

540–542 ↗

(On Diff #66169)

You should probably mention the argument order and precision requirements here (specifically that multiple rounding steps may occur).

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14522 ↗

(On Diff #66169)

Isn't this more a question of legality?

llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp

203–204 ↗

(On Diff #66169)

Probably should be all lower-case looking at the surrounding entries.

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

7832–7833 ↗

(On Diff #66169)

Isn't this really just a pattern? It looks like we could mark FRECPI as legal (which is more what the DAGCombiner should be asking anyway) and write:

def : Pat<(f32 (frecpi f32:$arg, f32:$est),
          (FMULSrr (FRECPS32 $arg, $est) $est>;

Similarly for the sqrt case.

llvm/test/CodeGen/AArch64/recp-fastmath.ll

16 ↗

(On Diff #66169)

We should be checking data-flow too in these tests. It's not enough to know that LLVM managed to cobble together an frecps instruction.

[n.bozhenov]

llvm/include/llvm/CodeGen/ISDOpcodes.h

546 ↗

(On Diff #66169)

I don't quite understand why do you need to introduce new ARM specific nodes into the ISD namespace. As an alternative, you could ask the target to directly build ARMISD::FRSQRTI instructions from buildSqrtNRNative function.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14695 ↗

(On Diff #66169)

A more consistent way to choose a refinement method would be to replace the boolean UseOneConstNR value with some enum, let the target set this enum and choose the refinement method based on the enum value.

Yet another option would be to return an already refined value from ARMTargetLowering::getRsqrtEstimate and set Iterations to 0. In this case we wouldn't need the buildSqrtNRNative function.

[evandro]

Thank you.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14695 ↗

(On Diff #66169)

I like this suggestion. I'll explore it and get back to y'all.

[evandro]

Refactored the previous patch extensively to implement the series in the AArch64 backend.

[evandro]

Harden the test cases.

[t.p.northover]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14500 ↗

(On Diff #66540)

All of the changes in this file appear to be refactoring, is that right?

Mostly they look OK (though should be committed separately). But I'm not convinced moving the sqrt(0) handling into BuildReciprocalEstimate is an improvement.

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

4598 ↗

(On Diff #66540)

A for loop would probably be better. People expect while loops to do crazy things.

[evandro]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14500 ↗

(On Diff #66540)

It's actually necessary to inform getRsqrtEstimate() if the estimate is for sqrt() so that, if the target prefers to generate the whole sequence, it has to know if it's for sqrt() or its reciprocal, since the final product, in case of sqrt(), is currently done inside buildSqrtNR{One,Two}Const().

[t.p.northover]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14500 ↗

(On Diff #66719)

OK, I see that change now. But what about the block of 0-handling code moved from buildSqrtEstimate to buildSqrtEstimateImpl? I still don't see how that's an improvement.

[spatel]

llvm/test/CodeGen/X86/sqrt-fastmath.ll

42–45 ↗

(On Diff #66719)

vblendvps is a regression vs. the vandnps that we had. Do you know what caused that?

Also, why did the "-NEXT" part of the assertions disappear? For any x86 codegen test changes, please use the script that is noted on the first line of the test file to avoid that problem.

[evandro]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14500 ↗

(On Diff #66719)

For now it does improve grouping, IMO. But I'm mulling whether the handling code could be profitably moved inside getSqrtEstimate.

14669 ↗

(On Diff #66719)

@spatel I changed Zero for Op here, since Op is then known to be 0. The motivation was that since AArch64 has an immediate version that implements SETEQ and materializing a 0 can be expensive. This probably caused the side effect of changing andnps for vblendvps in X86.

llvm/test/CodeGen/X86/sqrt-fastmath.ll

42–45 ↗

(On Diff #66719)

Sorry about that.

[evandro]

Addressed some comments.

[spatel]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14669 ↗

(On Diff #66840)

Ah, I see the diff now. But this is a target-independent transform, so isn't using 'Zero' in the select the more specific, and therefore the better, construct? This suggests that AArch64 is missing a fold that checks if an operand of a select is a zero; x86 must have this somewhere to allow the transform from blendv to andn?

llvm/test/CodeGen/X86/sqrt-fastmath.ll

42–45 ↗

(On Diff #66840)

No worries. Note that I've used a modified version of that script to generate checks for targets besides x86 - in case anyone would like to enhance the script and make test generation easier for AArch64. :)

[t.p.northover]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14669 ↗

(On Diff #66840)

Using Op also gets the correct value for -0. I'm not entirely sure how much that matters though given that we're in fast-math anyway.

[evandro]

Cleaned up comments that no longer apply.

[RKSimon]

Please can you recreate the diff with context? svn diff --diff-cmd=diff -x -U999999

llvm/test/CodeGen/X86/sqrt-fastmath.ll

42–45 ↗

(On Diff #66840)

As Sanjay said, the use of vblendvps over vandnps is a regression that could affect throughput quite badly.

[evandro]

llvm/test/CodeGen/X86/sqrt-fastmath.ll

42–45 ↗

(On Diff #66840)

@t.p.northover, is Sanjay onto something that AArch64 could use a folding instead? Otherwise, I could move the check for 0.0 inside getSqrtEstimate().

[t.p.northover]

llvm/test/CodeGen/X86/sqrt-fastmath.ll

42–45 ↗

(On Diff #66840)

We seem to catch the simple cases, based on:

define <4 x float> @foo(<4 x float> %lhs, <4 x float> %rhs, <4 x float> %val) {
  %tst = fcmp oeq <4 x float> %lhs, %rhs
  %res = select <4 x i1> %tst, <4 x float> %val, <4 x float> zeroinitializer
  ret <4 x float> %res
}

(I haven't checked but suspect it's actually the generic DAG combiner that's doing it). I'm not sure why we don't get this one, but fixing it would improve performance, probably beyond using Op.

[spatel]

Side note regarding select folding with -1/0: inspired by this patch, I filed PR28895 ( https://llvm.org/bugs/show_bug.cgi?id=28895 ).
There are a few different paths and optimizations for this in x86. Some of it (eg, D23337 ) could be lifted to generic DAG combiner I think.

When I looked at how AArch64 handled the case in PR28895, I noticed that the select always get cracked into and/andn/or and then re-matched into a vbsl. That seems like better general policy than what x86 is doing (matching to ISD::VSELECT early).

Regardless of all that, we really do want to avoid vblendv on x86 in this patch. As Simon hinted, some cores suffer greatly because vblendv is cracked into the base logic ops (and/andn/or) by the HW, and so that instruction has 3 times worse latency/throughput than a simple op.

[evandro]

I folded the checking when the argument is zero into getSqrtEstimate(). I think that it makes sense when it returns no iterations, allowing the target to handle everything as is more optimal for it.

[evandro]

It's better to use VSELECT also for scalar types. How do I go about to stuff scalars into vectors and then out around VSELECT?

Thank you.

[evandro]

Ping^1

[evandro]

Ping^2

[evandro]

Ahem, update the patch with full context.

[evandro]

Rebase patch from D25291.

[evandro]

Rebase patch from D25291.

[evandro]

Ping^1

[spatel]

The generic combiner parts look alright to me, and since there are no test changes for PPC or x86, I assume that those changes are only enabling the AArch64 diffs. Someone with AArch experience should confirm that that part of the patch looks good.

[evandro]

Thanks, @spatel!

[evandro]

It makes sense to split the fix of this issue from the native implementation using it in AArch64.

This part retains the target-independent changes as before. The part with the AArch64 specific changes will be followed up in another patch.

[spatel]

LGTM.

llvm/trunk/include/llvm/Target/TargetLowering.h

public:
   /// that must exist.
   virtual unsigned combineRepeatedFPDivisors() const {
     return 0;
   }
 
   /// 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,
+                                  bool &UseOneConstNR, bool Reciprocal) const {
     return SDValue();
   }
 
   /// Return a 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

llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

SDValue DAGCombiner::BuildUDIV(SDNode *N) {
   SDValue S =
       TLI.BuildUDIV(N, C->getAPIntValue(), DAG, LegalOperations, &Built);
 
   for (SDNode *N : Built)
     AddToWorklist(N);
   return S;
 }
 
+/// Newton iteration for a function: F(X) is X_{i+1} = X_i - F(X_i)/F'(X_i)
+/// For the reciprocal, we need to find the zero of the function:
+///   F(X) = A X - 1 [which has a zero at X = 1/A]
+///     =>
+///   X_{i+1} = X_i (2 - A X_i) = X_i + X_i (1 - A X_i) [this second form
+///     does not require additional intermediate precision]
 SDValue DAGCombiner::BuildReciprocalEstimate(SDValue Op, SDNodeFlags *Flags) {
   if (Level >= AfterLegalizeDAG)
     return SDValue();
 
   // TODO: Handle half and/or extended types?
   EVT VT = Op.getValueType();
   if (VT.getScalarType() != MVT::f32 && VT.getScalarType() != MVT::f64)
     return SDValue();
 
   // If estimates are explicitly disabled for this function, we're done.
   MachineFunction &MF = DAG.getMachineFunction();
   int Enabled = TLI.getRecipEstimateDivEnabled(VT, MF);
   if (Enabled == TLI.ReciprocalEstimate::Disabled)
     return SDValue();
 
   // Estimates may be explicitly enabled for this type with a custom number of
   // refinement steps.
   int Iterations = TLI.getDivRefinementSteps(VT, MF);
   if (SDValue Est = TLI.getRecipEstimate(Op, DAG, Enabled, Iterations)) {
+    AddToWorklist(Est.getNode());
+
     if (Iterations) {
-      // Newton iteration for a function: F(X) is X_{i+1} = X_i - F(X_i)/F'(X_i)
-      // For the reciprocal, we need to find the zero of the function:
-      //   F(X) = A X - 1 [which has a zero at X = 1/A]
-      //     =>
-      //   X_{i+1} = X_i (2 - A X_i) = X_i + X_i (1 - A X_i) [this second form
-      //     does not require additional intermediate precision]
       EVT VT = Op.getValueType();
       SDLoc DL(Op);
       SDValue FPOne = DAG.getConstantFP(1.0, DL, VT);
 
-      AddToWorklist(Est.getNode());
-
       // Newton iterations: Est = Est + Est (1 - Arg * Est)
       for (int i = 0; i < Iterations; ++i) {
         SDValue NewEst = DAG.getNode(ISD::FMUL, DL, VT, Op, Est, Flags);
         AddToWorklist(NewEst.getNode());
 
         NewEst = DAG.getNode(ISD::FSUB, DL, VT, FPOne, NewEst, Flags);
         AddToWorklist(NewEst.getNode());
 
if (Enabled == TLI.ReciprocalEstimate::Disabled)
     return SDValue();
 
   // Estimates may be explicitly enabled for this type with a custom number of
   // refinement steps.
   int Iterations = TLI.getSqrtRefinementSteps(VT, MF);
 
   bool UseOneConstNR = false;
   if (SDValue Est =
-      TLI.getRsqrtEstimate(Op, DAG, Enabled, Iterations, UseOneConstNR)) {
+      TLI.getSqrtEstimate(Op, DAG, Enabled, Iterations, UseOneConstNR,
+                          Reciprocal)) {
     AddToWorklist(Est.getNode());
+
     if (Iterations) {
       Est = UseOneConstNR
             ? buildSqrtNROneConst(Op, Est, Iterations, Flags, Reciprocal)
             : buildSqrtNRTwoConst(Op, Est, Iterations, Flags, Reciprocal);
+
+      if (!Reciprocal) {
+        // Unfortunately, Est is now NaN if the input was exactly 0.0.
+        // Select out this case and force the answer to 0.0.
+        EVT VT = Op.getValueType();
+        SDLoc DL(Op);
+
+        SDValue FPZero = DAG.getConstantFP(0.0, DL, VT);
+        EVT CCVT = getSetCCResultType(VT);
+        SDValue ZeroCmp = DAG.getSetCC(DL, CCVT, Op, FPZero, ISD::SETEQ);
+        AddToWorklist(ZeroCmp.getNode());
+
+        Est = DAG.getNode(VT.isVector() ? ISD::VSELECT : ISD::SELECT, DL, VT,
+                          ZeroCmp, FPZero, Est);
+        AddToWorklist(Est.getNode());
+      }
     }
     return Est;
   }
 
   return SDValue();
 }
 
 SDValue DAGCombiner::buildRsqrtEstimate(SDValue Op, SDNodeFlags *Flags) {
   return buildSqrtEstimateImpl(Op, Flags, true);
 }
 
 SDValue DAGCombiner::buildSqrtEstimate(SDValue Op, SDNodeFlags *Flags) {
-  SDValue Est = buildSqrtEstimateImpl(Op, Flags, false);
-  if (!Est)
-    return SDValue();
-
-  // Unfortunately, Est is now NaN if the input was exactly 0.
-  // Select out this case and force the answer to 0.
-  EVT VT = Est.getValueType();
-  SDLoc DL(Op);
-  SDValue Zero = DAG.getConstantFP(0.0, DL, VT);
-  EVT CCVT = getSetCCResultType(VT);
-  SDValue ZeroCmp = DAG.getSetCC(DL, CCVT, Op, Zero, ISD::SETEQ);
-  AddToWorklist(ZeroCmp.getNode());
-
-  Est = DAG.getNode(VT.isVector() ? ISD::VSELECT : ISD::SELECT, DL, VT, ZeroCmp,
-                    Zero, Est);
-  AddToWorklist(Est.getNode());
-  return Est;
+  return buildSqrtEstimateImpl(Op, Flags, false);
 }
 
 /// Return true if base is a frame index, which is known not to alias with
 /// anything but itself.  Provides base object and offset as results.
 static bool FindBaseOffset(SDValue Ptr, SDValue &Base, int64_t &Offset,
                            const GlobalValue *&GV, const void *&CV) {
   // Assume it is a primitive operation.
   Base = Ptr; Offset = 0; GV = nullptr; CV = nullptr;

llvm/trunk/lib/Target/AArch64/AArch64ISelLowering.h

private:
   SDValue LowerINT_TO_FP(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerVectorAND(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerVectorOR(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerCONCAT_VECTORS(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerFSINCOS(SDValue Op, SelectionDAG &DAG) const;
 
   SDValue BuildSDIVPow2(SDNode *N, const APInt &Divisor, SelectionDAG &DAG,
                         std::vector<SDNode *> *Created) const override;
-  SDValue getRsqrtEstimate(SDValue Operand, SelectionDAG &DAG, int Enabled,
-                           int &ExtraSteps, bool &UseOneConst) const override;
+  SDValue getSqrtEstimate(SDValue Operand, SelectionDAG &DAG, int Enabled,
+                          int &ExtraSteps, bool &UseOneConst,
+                          bool Reciprocal) const override;
   SDValue getRecipEstimate(SDValue Operand, SelectionDAG &DAG, int Enabled,
                            int &ExtraSteps) const override;
   unsigned combineRepeatedFPDivisors() const override;
 
   ConstraintType getConstraintType(StringRef Constraint) const override;
   unsigned getRegisterByName(const char* RegName, EVT VT,
                              SelectionDAG &DAG) const override;
 

llvm/trunk/lib/Target/AArch64/AArch64ISelLowering.cpp

if (ExtraSteps == TargetLoweringBase::ReciprocalEstimate::Unspecified)
       ExtraSteps = VT == MVT::f64 ? 3 : 2;
 
     return DAG.getNode(Opcode, SDLoc(Operand), VT, Operand);
   }
 
   return SDValue();
 }
 
-SDValue AArch64TargetLowering::getRsqrtEstimate(SDValue Operand,
-                                                SelectionDAG &DAG, int Enabled,
-                                                int &ExtraSteps,
-                                                bool &UseOneConst) const {
+SDValue AArch64TargetLowering::getSqrtEstimate(SDValue Operand,
+                                               bool &UseOneConst,
+                                               bool Reciprocal) const {
   if (Enabled == ReciprocalEstimate::Enabled ||
       (Enabled == ReciprocalEstimate::Unspecified && Subtarget->useRSqrt()))
     if (SDValue Estimate = getEstimate(Subtarget, AArch64ISD::FRSQRTE, Operand,
                                        DAG, ExtraSteps)) {
       UseOneConst = true;
       return Estimate;
     }
 

llvm/trunk/lib/Target/AMDGPU/AMDGPUISelLowering.h

SDValue CombineFMinMaxLegacy(const SDLoc &DL, EVT VT, SDValue LHS,
                                SDValue RHS, SDValue True, SDValue False,
                                SDValue CC, DAGCombinerInfo &DCI) const;
 
   const char* getTargetNodeName(unsigned Opcode) const override;
 
   bool isFsqrtCheap(SDValue Operand, SelectionDAG &DAG) const override {
     return true;
   }
-  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;
 
   virtual SDNode *PostISelFolding(MachineSDNode *N,
                                   SelectionDAG &DAG) const = 0;
 
   /// \brief Determine which of the bits specified in \p Mask are known to be
   /// either zero or one and return them in the \p KnownZero and \p KnownOne

llvm/trunk/lib/Target/AMDGPU/AMDGPUISelLowering.cpp

const char* AMDGPUTargetLowering::getTargetNodeName(unsigned Opcode) const {
   NODE_NAME_CASE(ATOMIC_CMP_SWAP)
   NODE_NAME_CASE(ATOMIC_INC)
   NODE_NAME_CASE(ATOMIC_DEC)
   case AMDGPUISD::LAST_AMDGPU_ISD_NUMBER: break;
   }
   return nullptr;
 }
 
-SDValue AMDGPUTargetLowering::getRsqrtEstimate(SDValue Operand,
-                                               SelectionDAG &DAG, int Enabled,
-                                               int &RefinementSteps,
-                                               bool &UseOneConstNR) const {
+SDValue AMDGPUTargetLowering::getSqrtEstimate(SDValue Operand,
+                                              bool &UseOneConstNR,
+                                              bool Reciprocal) const {
   EVT VT = Operand.getValueType();
 
   if (VT == MVT::f32) {
     RefinementSteps = 0;
     return DAG.getNode(AMDGPUISD::RSQ, SDLoc(Operand), VT, Operand);
   }
 
   // TODO: There is also f64 rsq instruction, but the documentation is less

llvm/trunk/lib/Target/PowerPC/PPCISelLowering.h

private:
     SDValue lowerEH_SJLJ_SETJMP(SDValue Op, SelectionDAG &DAG) const;
     SDValue lowerEH_SJLJ_LONGJMP(SDValue Op, SelectionDAG &DAG) const;
 
     SDValue DAGCombineExtBoolTrunc(SDNode *N, DAGCombinerInfo &DCI) const;
     SDValue DAGCombineBuildVector(SDNode *N, DAGCombinerInfo &DCI) const;
     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;
 
     CCAssignFn *useFastISelCCs(unsigned Flag) const;
   };
 
   namespace PPC {

llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp

static int getEstimateRefinementSteps(EVT VT, const PPCSubtarget &Subtarget) {
   // the minimum architected relative accuracy is 2^-5. When hasRecipPrec(),
   // this is 2^-14. IEEE float has 23 digits and double has 52 digits.
   int RefinementSteps = Subtarget.hasRecipPrec() ? 1 : 3;
   if (VT.getScalarType() == MVT::f64)
     RefinementSteps++;
   return RefinementSteps;
 }
 
-SDValue PPCTargetLowering::getRsqrtEstimate(SDValue Operand, SelectionDAG &DAG,
-                                            int Enabled, int &RefinementSteps,
-                                            bool &UseOneConstNR) const {
+SDValue PPCTargetLowering::getSqrtEstimate(SDValue Operand, SelectionDAG &DAG,
+                                           bool &UseOneConstNR,
+                                           bool Reciprocal) const {
   EVT VT = Operand.getValueType();
   if ((VT == MVT::f32 && Subtarget.hasFRSQRTES()) ||
       (VT == MVT::f64 && Subtarget.hasFRSQRTE()) ||
       (VT == MVT::v4f32 && Subtarget.hasAltivec()) ||
       (VT == MVT::v2f64 && Subtarget.hasVSX()) ||
       (VT == MVT::v4f32 && Subtarget.hasQPX()) ||
       (VT == MVT::v4f64 && Subtarget.hasQPX())) {
     if (RefinementSteps == ReciprocalEstimate::Unspecified)

llvm/trunk/lib/Target/X86/X86ISelLowering.h

private:
 
     /// Convert a comparison if required by the subtarget.
     SDValue ConvertCmpIfNecessary(SDValue Cmp, SelectionDAG &DAG) const;
 
     /// Check if replacement of SQRT with RSQRT should be disabled.
     bool isFsqrtCheap(SDValue Operand, SelectionDAG &DAG) const override;
 
     /// Use rsqrt* to speed up sqrt calculations.
-    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;
 
     /// Use rcp* to speed up fdiv calculations.
     SDValue getRecipEstimate(SDValue Operand, SelectionDAG &DAG, int Enabled,
                              int &RefinementSteps) const override;
 
     /// Reassociate floating point divisions into multiply by reciprocal.
     unsigned combineRepeatedFPDivisors() const override;
   };
 
   namespace X86 {
     FastISel *createFastISel(FunctionLoweringInfo &funcInfo,
                              const TargetLibraryInfo *libInfo);
   } // end namespace X86
 } // end namespace llvm
 
 #endif // LLVM_LIB_TARGET_X86_X86ISELLOWERING_H

llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

bool X86TargetLowering::isFsqrtCheap(SDValue Op, SelectionDAG &DAG) const {
 
   if (VT.isVector())
     return Subtarget.hasFastVectorFSQRT();
   return Subtarget.hasFastScalarFSQRT();
 }
 
 /// The minimum architected relative accuracy is 2^-12. We need one
 /// Newton-Raphson step to have a good float result (24 bits of precision).
-SDValue X86TargetLowering::getRsqrtEstimate(SDValue Op,
-                                            SelectionDAG &DAG, int Enabled,
-                                            int &RefinementSteps,
-                                            bool &UseOneConstNR) const {
+SDValue X86TargetLowering::getSqrtEstimate(SDValue Op,
+                                           bool &UseOneConstNR,
+                                           bool Reciprocal) const {
   EVT VT = Op.getValueType();
 
   // SSE1 has rsqrtss and rsqrtps. AVX adds a 256-bit variant for rsqrtps.
   // TODO: Add support for AVX512 (v16f32).
   // It is likely not profitable to do this for f64 because a double-precision
   // rsqrt estimate with refinement on x86 prior to FMA requires at least 16
   // instructions: convert to single, rsqrtss, convert back to double, refine
   // (3 steps = at least 13 insts). If an 'rsqrtsd' variant was added to the ISA