[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

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

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

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

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

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

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

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

[evandro]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14500

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

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

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

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

14669

@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

Sorry about that.

[evandro]

Addressed some comments.

[spatel]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

14669

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

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

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

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

@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

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/include/llvm/Target/TargetLowering.h

   /// Hooks for building estimates in place of slower divisions and square
   /// roots.
 
-  /// Return a reciprocal square root estimate value for the input operand.
-  /// The RefinementSteps output is the number of Newton-Raphson refinement
-  /// iterations required to generate a sufficient (though not necessarily
-  /// IEEE-754 compliant) estimate for the value type.
-  /// The boolean UseOneConstNR output is used to select a Newton-Raphson
-  /// algorithm implementation that uses one constant or two constants.
-  /// 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.
+  /// Return initial estimate of the reciprocal square root or an approximate
+  /// square root or its reciprocal for the input operand.
+  /// The target has the choice to use the generic approximation algorithm,
+  /// when it should return the initial estimate of the reciprocal square root
+  /// and the number of extra refinement iterations to generate a sufficient
+  /// (though not necessarily IEEE-754 compliant) approximation in
+  /// RefinementSteps, or to approximate square root or its reciprocal itself,
+  /// when it should return the approximation and '0' in RefinementSteps.
+  /// Reciprocal indicates whether the square root or its reciprocal is being
+  /// approximated, either by the target itself or by the generic algorithm.
+  /// The boolean UseOneConstNR output is used to select between the generic
+  /// Newton-Raphson algorithms for the refinement iterations that use one or
+  /// two constants, in case the target provides just the initial estimate.
   /// An empty SDValue return means no estimate sequence can be created.
-  virtual SDValue getRsqrtEstimate(SDValue Operand, DAGCombinerInfo &DCI,
-                                   unsigned &RefinementSteps,
-                                   bool &UseOneConstNR) const {
+  virtual SDValue getSqrtEstimate(SDValue Operand, DAGCombinerInfo &DCI,
+                                  bool &UseOneConstNR, bool Reciprocal) const {
     return SDValue();
   }
 

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

   return S;
 }
 
-SDValue DAGCombiner::BuildReciprocalEstimate(SDValue Op, SDNodeFlags *Flags) {
+/// 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 Arg, SDNodeFlags *Flags) {
   if (Level >= AfterLegalizeDAG)
     return SDValue();
 
   // Expose the DAG combiner to the target combiner implementations.
   TargetLowering::DAGCombinerInfo DCI(DAG, Level, false, this);
-
   unsigned Iterations = 0;
-  if (SDValue Est = TLI.getRecipEstimate(Op, DCI, Iterations)) {
+  if (SDValue Est = TLI.getRecipEstimate(Arg, DCI, Iterations)) {
     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);
+      EVT VT = Arg.getValueType();
+      SDLoc DL(Arg);
+      SDValue One = DAG.getConstantFP(1.0, DL, VT);
 
       AddToWorklist(Est.getNode());
 
       // Newton iterations: Est = Est + Est (1 - Arg * Est)
       for (unsigned i = 0; i < Iterations; ++i) {
-        SDValue NewEst = DAG.getNode(ISD::FMUL, DL, VT, Op, Est, Flags);
+        SDValue NewEst = DAG.getNode(ISD::FMUL, DL, VT, Arg, Est, Flags);
         AddToWorklist(NewEst.getNode());
 
-        NewEst = DAG.getNode(ISD::FSUB, DL, VT, FPOne, NewEst, Flags);
+        NewEst = DAG.getNode(ISD::FSUB, DL, VT, One, NewEst, Flags);
         AddToWorklist(NewEst.getNode());
 
         NewEst = DAG.getNode(ISD::FMUL, DL, VT, Est, NewEst, Flags);

   TargetLowering::DAGCombinerInfo DCI(DAG, Level, false, this);
   unsigned Iterations = 0;
   bool UseOneConstNR = false;
-  if (SDValue Est = TLI.getRsqrtEstimate(Op, DCI, Iterations, UseOneConstNR)) {
+  if (SDValue Est = TLI.getSqrtEstimate(Op, DCI, Iterations, UseOneConstNR,
+                                        Reciprocal)) {
     AddToWorklist(Est.getNode());
-    if (Iterations) {
+
+    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.
+      // Select out this case and force the answer to 0.
+      EVT VT = Op.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, Op, Est);
+      AddToWorklist(Est.getNode());
     }
+
     return Est;
   }
 

 }
 
 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

llvm/lib/Target/AArch64/AArch64ISelLowering.h

   SMULL,
   UMULL,
 
-  // Reciprocal estimates.
-  FRECPE,
-  FRSQRTE,
+  // Reciprocal estimates and steps.
+  FRECPE, FRECPS,
+  FRSQRTE, FRSQRTS,
 
   // NEON Load/Store with post-increment base updates
   LD2post = ISD::FIRST_TARGET_MEMORY_OPCODE,

 
   SDValue BuildSDIVPow2(SDNode *N, const APInt &Divisor, SelectionDAG &DAG,
                         std::vector<SDNode *> *Created) const override;
-  SDValue getRsqrtEstimate(SDValue Operand, DAGCombinerInfo &DCI,
-                           unsigned &RefinementSteps,
-                           bool &UseOneConstNR) const override;
+  SDValue getSqrtEstimate(SDValue Operand, DAGCombinerInfo &DCI,
+                          unsigned &RefinementSteps, bool &UseOneConstNR,
+                          bool Reciprocal) const override;
   SDValue getRecipEstimate(SDValue Operand, DAGCombinerInfo &DCI,
                            unsigned &RefinementSteps) const override;
   unsigned combineRepeatedFPDivisors() const override;

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

   case AArch64ISD::ST4LANEpost:       return "AArch64ISD::ST4LANEpost";
   case AArch64ISD::SMULL:             return "AArch64ISD::SMULL";
   case AArch64ISD::UMULL:             return "AArch64ISD::UMULL";
-  case AArch64ISD::FRSQRTE:           return "AArch64ISD::FRSQRTE";
   case AArch64ISD::FRECPE:            return "AArch64ISD::FRECPE";
+  case AArch64ISD::FRECPS:            return "AArch64ISD::FRECPS";
+  case AArch64ISD::FRSQRTE:           return "AArch64ISD::FRSQRTE";
+  case AArch64ISD::FRSQRTS:           return "AArch64ISD::FRSQRTS";
   }
   return nullptr;
 }

   return DCI.DAG.getNode(Opcode, SDLoc(Operand), VT, Operand);
 }
 
-SDValue AArch64TargetLowering::getRecipEstimate(SDValue Operand,
+SDValue AArch64TargetLowering::getRecipEstimate(SDValue Arg,
   DAGCombinerInfo &DCI, unsigned &ExtraSteps) const {
-  return getEstimate(*Subtarget, DCI, AArch64ISD::FRECPE, Operand, ExtraSteps);
+  if (SDValue Est = getEstimate(*Subtarget, DCI, AArch64ISD::FRECPE, Arg,
+                                ExtraSteps)) {
+    SDLoc DL(Arg);
+    EVT VT = Arg.getValueType();
+
+    SDNodeFlags Flags;
+    Flags.setUnsafeAlgebra(true);
+
+    // Newton reciprocal iteration: Est * (2 - Arg * Est)
+    // AArch64 reciprocal iteration instruction: (2 - M * N)
+    while (ExtraSteps > 0) {
+      SDValue Step = DCI.DAG.getNode(AArch64ISD::FRECPS, DL, VT, Arg, Est,
+                                     &Flags);
+      Est = DCI.DAG.getNode(ISD::FMUL, DL, VT, Est, Step, &Flags);
+
+      --ExtraSteps;
+    }
+
+    return Est;
+  }
+
+  return SDValue();
 }
 
-SDValue AArch64TargetLowering::getRsqrtEstimate(SDValue Operand,
-  DAGCombinerInfo &DCI, unsigned &ExtraSteps, bool &UseOneConst) const {
-  UseOneConst = true;
-  return getEstimate(*Subtarget, DCI, AArch64ISD::FRSQRTE, Operand, ExtraSteps);
+SDValue AArch64TargetLowering::getSqrtEstimate
+  (SDValue Arg, DAGCombinerInfo &DCI, unsigned &ExtraSteps, bool &UseOneConst,
+   bool Reciprocal) const {
+  if (SDValue Est = getEstimate(*Subtarget, DCI, AArch64ISD::FRSQRTE, Arg,
+                                ExtraSteps)) {
+    SDLoc DL(Arg);
+    EVT VT = Arg.getValueType();
+
+    SDNodeFlags Flags;
+    Flags.setUnsafeAlgebra(true);
+
+    // Newton reciprocal square root iteration: Est * 0.5 * (3 - Arg * Est^2)
+    // AArch64 reciprocal square root iteration instruction: 0.5 * (3 - M * N)
+    for (unsigned i = ExtraSteps; i > 0; --i) {
+      SDValue Step = DCI.DAG.getNode(ISD::FMUL, DL, VT, Est, Est, &Flags);
+      Step = DCI.DAG.getNode(AArch64ISD::FRSQRTS, DL, VT, Arg, Step, &Flags);
+      Est = DCI.DAG.getNode(ISD::FMUL, DL, VT, Est, Step, &Flags);
+    }
+
+    if (!Reciprocal)
+      Est = DCI.DAG.getNode(ISD::FMUL, DL, VT, Arg, Est, &Flags);
+
+    ExtraSteps = 0;
+    return Est;
+  }
+
+  return SDValue();
 }
 
 //===----------------------------------------------------------------------===//

llvm/lib/Target/AArch64/AArch64InstrInfo.td

 def AArch64umull    : SDNode<"AArch64ISD::UMULL", SDT_AArch64mull>;
 
 def AArch64frecpe   : SDNode<"AArch64ISD::FRECPE", SDTFPUnaryOp>;
+def AArch64frecps   : SDNode<"AArch64ISD::FRECPS", SDTFPBinOp>;
 def AArch64frsqrte  : SDNode<"AArch64ISD::FRSQRTE", SDTFPUnaryOp>;
+def AArch64frsqrts  : SDNode<"AArch64ISD::FRSQRTS", SDTFPBinOp>;
 
 def AArch64saddv    : SDNode<"AArch64ISD::SADDV", SDT_AArch64UnaryVec>;
 def AArch64uaddv    : SDNode<"AArch64ISD::UADDV", SDT_AArch64UnaryVec>;

 def : Pat<(v2f64 (AArch64frecpe (v2f64 FPR128:$Rn))),
           (FRECPEv2f64 FPR128:$Rn)>;
 
+def : Pat<(f32 (AArch64frecps (f32 FPR32:$Rn), (f32 FPR32:$Rm))),
+          (FRECPS32 FPR32:$Rn, FPR32:$Rm)>;
+def : Pat<(v2f32 (AArch64frecps (v2f32 V64:$Rn), (v2f32 V64:$Rm))),
+          (FRECPSv2f32 V64:$Rn, V64:$Rm)>;
+def : Pat<(v4f32 (AArch64frecps (v4f32 FPR128:$Rn), (v4f32 FPR128:$Rm))),
+          (FRECPSv4f32 FPR128:$Rn, FPR128:$Rm)>;
+def : Pat<(f64 (AArch64frecps (f64 FPR64:$Rn), (f64 FPR64:$Rm))),
+          (FRECPS64 FPR64:$Rn, FPR64:$Rm)>;
+def : Pat<(v2f64 (AArch64frecps (v2f64 FPR128:$Rn), (v2f64 FPR128:$Rm))),
+          (FRECPSv2f64 FPR128:$Rn, FPR128:$Rm)>;
+
 def : Pat<(f32 (int_aarch64_neon_frecpx (f32 FPR32:$Rn))),
           (FRECPXv1i32 FPR32:$Rn)>;
 def : Pat<(f64 (int_aarch64_neon_frecpx (f64 FPR64:$Rn))),

 def : Pat<(v2f64 (AArch64frsqrte (v2f64 FPR128:$Rn))),
           (FRSQRTEv2f64 FPR128:$Rn)>;
 
+def : Pat<(f32 (AArch64frsqrts (f32 FPR32:$Rn), (f32 FPR32:$Rm))),
+          (FRSQRTS32 FPR32:$Rn, FPR32:$Rm)>;
+def : Pat<(v2f32 (AArch64frsqrts (v2f32 V64:$Rn), (v2f32 V64:$Rm))),
+          (FRSQRTSv2f32 V64:$Rn, V64:$Rm)>;
+def : Pat<(v4f32 (AArch64frsqrts (v4f32 FPR128:$Rn), (v4f32 FPR128:$Rm))),
+          (FRSQRTSv4f32 FPR128:$Rn, FPR128:$Rm)>;
+def : Pat<(f64 (AArch64frsqrts (f64 FPR64:$Rn), (f64 FPR64:$Rm))),
+          (FRSQRTS64 FPR64:$Rn, FPR64:$Rm)>;
+def : Pat<(v2f64 (AArch64frsqrts (v2f64 FPR128:$Rn), (v2f64 FPR128:$Rm))),
+          (FRSQRTSv2f64 FPR128:$Rn, FPR128:$Rm)>;
+
 // If an integer is about to be converted to a floating point value,
 // just load it on the floating point unit.
 // Here are the patterns for 8 and 16-bits to float.

llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h

 
   const char* getTargetNodeName(unsigned Opcode) const override;
 
-  SDValue getRsqrtEstimate(SDValue Operand,
-                           DAGCombinerInfo &DCI,
-                           unsigned &RefinementSteps,
-                           bool &UseOneConstNR) const override;
+  SDValue getSqrtEstimate(SDValue Operand,
+                          bool &UseOneConstNR,
+                          bool Reciprocal) const override;
   SDValue getRecipEstimate(SDValue Operand,
                            DAGCombinerInfo &DCI,
                            unsigned &RefinementSteps) const override;

llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp

   return nullptr;
 }
 
-SDValue AMDGPUTargetLowering::getRsqrtEstimate(SDValue Operand,
-                                               DAGCombinerInfo &DCI,
-                                               unsigned &RefinementSteps,
-                                               bool &UseOneConstNR) const {
+SDValue AMDGPUTargetLowering::getSqrtEstimate(SDValue Operand,
+                                              bool &UseOneConstNR,
+                                              bool Reciprocal) const {
   SelectionDAG &DAG = DCI.DAG;
   EVT VT = Operand.getValueType();
 

llvm/lib/Target/PowerPC/PPCISelLowering.h

     SDValue DAGCombineTruncBoolExt(SDNode *N, DAGCombinerInfo &DCI) const;
     SDValue combineFPToIntToFP(SDNode *N, DAGCombinerInfo &DCI) const;
 
-    SDValue getRsqrtEstimate(SDValue Operand, DAGCombinerInfo &DCI,
-                             unsigned &RefinementSteps,
-                             bool &UseOneConstNR) const override;
+    SDValue getSqrtEstimate(SDValue Operand, DAGCombinerInfo &DCI,
+                            unsigned &RefinementSteps, bool &UseOneConstNR,
+                            bool Reciprocal) const override;
     SDValue getRecipEstimate(SDValue Operand, DAGCombinerInfo &DCI,
                              unsigned &RefinementSteps) const override;
     unsigned combineRepeatedFPDivisors() const override;

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

   return RecipOp;
 }
 
-SDValue PPCTargetLowering::getRsqrtEstimate(SDValue Operand,
-                                            DAGCombinerInfo &DCI,
-                                            unsigned &RefinementSteps,
-                                            bool &UseOneConstNR) const {
+SDValue PPCTargetLowering::getSqrtEstimate(SDValue Operand,
+                                           bool &UseOneConstNR,
+                                           bool Reciprocal) const {
   EVT VT = Operand.getValueType();
   if ((VT == MVT::f32 && Subtarget.hasFRSQRTES()) ||
       (VT == MVT::f64 && Subtarget.hasFRSQRTE()) ||

llvm/lib/Target/X86/X86ISelLowering.h

     SDValue ConvertCmpIfNecessary(SDValue Cmp, SelectionDAG &DAG) const;
 
     /// Use rsqrt* to speed up sqrt calculations.
-    SDValue getRsqrtEstimate(SDValue Operand, DAGCombinerInfo &DCI,
-                             unsigned &RefinementSteps,
-                             bool &UseOneConstNR) const override;
+    SDValue getSqrtEstimate(SDValue Operand, DAGCombinerInfo &DCI,
+                            unsigned &RefinementSteps, bool &UseOneConstNR,
+                            bool Reciprocal) const override;
 
     /// Use rcp* to speed up fdiv calculations.
     SDValue getRecipEstimate(SDValue Operand, DAGCombinerInfo &DCI,

llvm/lib/Target/X86/X86ISelLowering.cpp

 
 /// 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,
-                                            DAGCombinerInfo &DCI,
-                                            unsigned &RefinementSteps,
-                                            bool &UseOneConstNR) const {
+SDValue X86TargetLowering::getSqrtEstimate(SDValue Op,
+                                           bool &UseOneConstNR,
+                                           bool Reciprocal) const {
   EVT VT = Op.getValueType();
   const char *RecipOp;
 

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

 
 ; CHECK-LABEL: frecp:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: frecpe
-; CHECK-NEXT: fmov
+; CHECK-NEXT: frecpe{{[[:space:]]+}}[[R:s[0-7]]]
+; CHECK-NEXT: frecps{{[[:space:]]+s[0-7](, s[0-7])?}}, [[R]]
 }
 
 define <2 x float> @f2recp(<2 x float> %x) #0 {

 
 ; CHECK-LABEL: f2recp:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frecpe
+; CHECK-NEXT: frecpe{{[[:space:]]+}}[[R:v[0-7]\.2s]]
+; CHECK-NEXT: frecps{{[[:space:]]+v[0-7]\.2s(, v[0-7].2s)?}}, [[R]]
 }
 
 define <4 x float> @f4recp(<4 x float> %x) #0 {

 
 ; CHECK-LABEL: f4recp:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frecpe
+; CHECK-NEXT: frecpe{{[[:space:]]+}}[[R:v[0-7]\.4s]]
+; CHECK-NEXT: frecps{{[[:space:]]+v[0-7]\.4s(, v[0-7].4s)?}}, [[R]]
 }
 
 define <8 x float> @f8recp(<8 x float> %x) #0 {

 
 ; CHECK-LABEL: f8recp:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frecpe
-; CHECK: frecpe
+; CHECK-NEXT: frecpe{{[[:space:]]+}}[[RA:v[0-7]\.4s]]
+; CHECK-NEXT: frecpe{{[[:space:]]+}}[[RB:v[0-7]\.4s]]
+; CHECK-NEXT: frecps{{[[:space:]]+v[0-7]\.4s(, v[0-7].4s)?}}, [[RA]]
+; CHECK: frecps{{[[:space:]]+v[0-7]\.4s(, v[0-7].4s)?}}, [[RB]]
 }
 
 define double @drecp(double %x) #0 {

 
 ; CHECK-LABEL: drecp:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: frecpe
-; CHECK-NEXT: fmov
+; CHECK-NEXT: frecpe{{[[:space:]]+}}[[R:d[0-7]]]
+; CHECK-NEXT: frecps{{[[:space:]]+d[0-7](, d[0-7])?}}, [[R]]
 }
 
 define <2 x double> @d2recp(<2 x double> %x) #0 {

 
 ; CHECK-LABEL: d2recp:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frecpe
+; CHECK-NEXT: frecpe{{[[:space:]]+}}[[R:v[0-7]\.2d]]
+; CHECK-NEXT: frecps{{[[:space:]]+v[0-7]\.2d(, v[0-7].2d)?}}, [[R]]
 }
 
 define <4 x double> @d4recp(<4 x double> %x) #0 {

 
 ; CHECK-LABEL: d4recp:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frecpe
-; CHECK: frecpe
+; CHECK-NEXT: frecpe{{[[:space:]]+}}[[RA:v[0-7]\.2d]]
+; CHECK-NEXT: frecpe{{[[:space:]]+}}[[RB:v[0-7]\.2d]]
+; CHECK-NEXT: frecps{{[[:space:]]+v[0-7]\.2d(, v[0-7].2d)?}}, [[RA]]
+; CHECK: frecps{{[[:space:]]+v[0-7]\.2d(, v[0-7].2d)?}}, [[RB]]
 }
 
 attributes #0 = { nounwind "unsafe-fp-math"="true" }

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

 
 ; CHECK-LABEL: fsqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:s[0-7]]]
+; CHECK-NEXT: fmul{{[[:space:]]+}}[[RB:s[0-7]]], [[RA]], [[RA]]
+; CHECK-NEXT: frsqrts{{[[:space:]]+s[0-7](, s[0-7])?}}, [[RB]]
+; CHECK: fcmp{{[[:space:]]+}}s0, #0
 }
 
 define <2 x float> @f2sqrt(<2 x float> %a) #0 {

 
 ; CHECK-LABEL: f2sqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: mov
-; CHECK-NEXT: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:v[0-7]\.2s]]
+; CHECK-NEXT: fmul{{[[:space:]]+}}[[RB:v[0-7]\.2s]], [[RA]], [[RA]]
+; CHECK-NEXT: frsqrts{{[[:space:]]+v[0-7]\.2s(, v[0-7]\.2s)?}}, [[RB]]
+; CHECK: fcmeq{{[[:space:]]+v[0-7]\.2s, v0\.2s}}, #0
 }
 
 define <4 x float> @f4sqrt(<4 x float> %a) #0 {

 
 ; CHECK-LABEL: f4sqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: mov
-; CHECK-NEXT: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:v[0-7]\.4s]]
+; CHECK-NEXT: fmul{{[[:space:]]+}}[[RB:v[0-7]\.4s]], [[RA]], [[RA]]
+; CHECK-NEXT: frsqrts{{[[:space:]]+v[0-7]\.4s(, v[0-7]\.4s)?}}, [[RB]]
+; CHECK: fcmeq{{[[:space:]]+v[0-7]\.4s, v0\.4s}}, #0
 }
 
 define <8 x float> @f8sqrt(<8 x float> %a) #0 {

 
 ; CHECK-LABEL: f8sqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: mov
-; CHECK-NEXT: frsqrte
-; CHECK: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:v[0-7]\.4s]]
+; CHECK: fmul{{[[:space:]]+}}[[RB:v[0-7]\.4s]], [[RA]], [[RA]]
+; CHECK: frsqrts{{[[:space:]]+v[0-7]\.4s(, v[0-7]\.4s)?}}, [[RB]]
+; CHECK: fcmeq{{[[:space:]]+v[0-7]\.4s, v[0-1]\.4s}}, #0
 }
 
 define double @dsqrt(double %a) #0 {

 
 ; CHECK-LABEL: dsqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:d[0-7]]]
+; CHECK-NEXT: fmul{{[[:space:]]+}}[[RB:d[0-7]]], [[RA]], [[RA]]
+; CHECK-NEXT: frsqrts{{[[:space:]]+d[0-7](, d[0-7])?}}, [[RB]]
+; CHECK: fcmp{{[[:space:]]+}}d0, #0
 }
 
 define <2 x double> @d2sqrt(<2 x double> %a) #0 {

 
 ; CHECK-LABEL: d2sqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: mov
-; CHECK-NEXT: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:v[0-7]\.2d]]
+; CHECK-NEXT: fmul{{[[:space:]]+}}[[RB:v[0-7]\.2d]], [[RA]], [[RA]]
+; CHECK-NEXT: frsqrts{{[[:space:]]+v[0-7]\.2d(, v[0-7]\.2d)?}}, [[RB]]
+; CHECK: fcmeq{{[[:space:]]+v[0-7]\.2d, v0\.2d}}, #0
 }
 
 define <4 x double> @d4sqrt(<4 x double> %a) #0 {

 
 ; CHECK-LABEL: d4sqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: mov
-; CHECK-NEXT: frsqrte
-; CHECK: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:v[0-7]\.2d]]
+; CHECK: fmul{{[[:space:]]+}}[[RB:v[0-7]\.2d]], [[RA]], [[RA]]
+; CHECK: frsqrts{{[[:space:]]+v[0-7]\.2d(, v[0-7]\.2d)?}}, [[RB]]
+; CHECK: fcmeq{{[[:space:]]+v[0-7]\.2d, v[0-1]\.2d}}, #0
 }
 
 define float @frsqrt(float %a) #0 {

 
 ; CHECK-LABEL: frsqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:s[0-7]]]
+; CHECK-NEXT: fmul{{[[:space:]]+}}[[RB:s[0-7]]], [[RA]], [[RA]]
+; CHECK-NEXT: frsqrts{{[[:space:]]+s[0-7](, s[0-7])?}}, [[RB]]
+; CHECK-NOT: fcmp{{[[:space:]]+s[0-7]}}, #0
 }
 
 define <2 x float> @f2rsqrt(<2 x float> %a) #0 {

 
 ; CHECK-LABEL: f2rsqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:v[0-7]\.2s]]
+; CHECK-NEXT: fmul{{[[:space:]]+}}[[RB:v[0-7]\.2s]], [[RA]], [[RA]]
+; CHECK-NEXT: frsqrts{{[[:space:]]+v[0-7]\.2s(, v[0-7]\.2s)?}}, [[RB]]
+; CHECK-NOT: fcmeq{{[[:space:]]+v[0-7]\.2s, v0\.2s}}, #0
 }
 
 define <4 x float> @f4rsqrt(<4 x float> %a) #0 {

 
 ; CHECK-LABEL: f4rsqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:v[0-7]\.4s]]
+; CHECK-NEXT: fmul{{[[:space:]]+}}[[RB:v[0-7]\.4s]], [[RA]], [[RA]]
+; CHECK-NEXT: frsqrts{{[[:space:]]+v[0-7]\.4s(, v[0-7]\.4s)?}}, [[RB]]
+; CHECK-NOT: fcmeq{{[[:space:]]+v[0-7]\.4s, v0\.4s}}, #0
 }
 
 define <8 x float> @f8rsqrt(<8 x float> %a) #0 {

 
 ; CHECK-LABEL: f8rsqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frsqrte
-; CHECK: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:v[0-7]\.4s]]
+; CHECK: fmul{{[[:space:]]+}}[[RB:v[0-7]\.4s]], [[RA]], [[RA]]
+; CHECK: frsqrts{{[[:space:]]+v[0-7]\.4s(, v[0-7]\.4s)?}}, [[RB]]
+; CHECK-NOT: fcmeq{{[[:space:]]+v[0-7]\.4s, v0\.4s}}, #0
 }
 
 define double @drsqrt(double %a) #0 {

 
 ; CHECK-LABEL: drsqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:d[0-7]]]
+; CHECK-NEXT: fmul{{[[:space:]]+}}[[RB:d[0-7]]], [[RA]], [[RA]]
+; CHECK-NEXT: frsqrts{{[[:space:]]+d[0-7](, d[0-7])?}}, [[RB]]
+; CHECK-NOT: fcmp{{[[:space:]]+}}d0, #0
 }
 
 define <2 x double> @d2rsqrt(<2 x double> %a) #0 {

 
 ; CHECK-LABEL: d2rsqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:v[0-7]\.2d]]
+; CHECK-NEXT: fmul{{[[:space:]]+}}[[RB:v[0-7]\.2d]], [[RA]], [[RA]]
+; CHECK-NEXT: frsqrts{{[[:space:]]+v[0-7]\.2d(, v[0-7]\.2d)?}}, [[RB]]
+; CHECK-NOT: fcmeq{{[[:space:]]+v[0-7]\.2d, v0\.2d}}, #0
 }
 
 define <4 x double> @d4rsqrt(<4 x double> %a) #0 {

 
 ; CHECK-LABEL: d4rsqrt:
 ; CHECK-NEXT: BB#0
-; CHECK-NEXT: fmov
-; CHECK-NEXT: frsqrte
-; CHECK: frsqrte
+; CHECK-NEXT: frsqrte{{[[:space:]]+}}[[RA:v[0-7]\.2d]]
+; CHECK: fmul{{[[:space:]]+}}[[RB:v[0-7]\.2d]], [[RA]], [[RA]]
+; CHECK: frsqrts{{[[:space:]]+v[0-7]\.2d(, v[0-7]\.2d)?}}, [[RB]]
+; CHECK-NOT: fcmeq{{[[:space:]]+v[0-7]\.2d, v0\.2d}}, #0
 }
 
 attributes #0 = { nounwind "unsafe-fp-math"="true" }

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

 ; CHECK:     %10 = VFMADDSSr213r %8, %9, %4
 ; CHECK:     %11 = VMULSSrr %9, %6
 ; CHECK:     %12 = VMULSSrr killed %11, killed %10
-; CHECK:     %13 = FsFLD0SS
-; CHECK:     %14 = VCMPSSrr %0, killed %13, 0
-; CHECK:     %15 = VFsANDNPSrr killed %14, killed %12
-; CHECK:     %xmm0 = COPY %15
+; CHECK:     %13 = COPY %12
+; CHECK:     %14 = FsFLD0SS
+; CHECK:     %15 = VCMPSSrr %0, killed %14, 0
+; CHECK:     %16 = COPY %15
+; CHECK:     %xmm0 = COPY %19
 ; CHECK:     RET 0, %xmm0
   %call = tail call float @llvm.sqrt.f32(float %f) #1
   ret float %call

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

 ; ESTIMATE-NEXT:    vaddss {{.*}}(%rip), %xmm1, %xmm1
 ; ESTIMATE-NEXT:    vmulss {{.*}}(%rip), %xmm2, %xmm2
 ; ESTIMATE-NEXT:    vmulss %xmm1, %xmm2, %xmm1
-; ESTIMATE-NEXT:    vxorps %xmm2, %xmm2, %xmm2
-; ESTIMATE-NEXT:    vcmpeqss %xmm2, %xmm0, %xmm0
-; ESTIMATE-NEXT:    vandnps %xmm1, %xmm0, %xmm0
-; ESTIMATE-NEXT:    retq
+; ESTIMATE:         vxorps %xmm2, %xmm2, %xmm2
+; ESTIMATE:         vcmpeqss %xmm2, %xmm0, %xmm2
+; ESTIMATE:         vblendvps %xmm2, %xmm0, %xmm1, %xmm0
+; ESTIMATE:         retq
   %call = tail call float @__sqrtf_finite(float %f) #1
   ret float %call
 }