Cost for Gather and Scatter operations.

[delena]

Summary

Implemented cost calculation for Gather/Scatter operations on X86.
Added a common interface.

Gather / scatter are expensive instructions on the current AVX-512 targets.
I calculate 2 scenarios - using GS machine instructions and full scalarization. The best cost is returned.
In order to give the right cost for intrinsic I should use argument values, argument types are not enough.
I added interface for intrinsic cost calculation based on values.
Added tests for intrinsics.

[Ayal]

../include/llvm/Analysis/TargetTransformInfo.h

464

poin[t]er

835

keep order of arguments "ID, RetTy, Args" similar to "ID, RetTy, Tys"?

../include/llvm/CodeGen/BasicTTIImpl.h

605

Maybe better call it ConstMasked or VarMasked instead of MaskedOp (throughout)

../lib/Target/X86/X86TargetTransformInfo.cpp

1306

Document the patterns that fold into 32bit indexed GS.

1308

May be better to first check if IndexSize < 64 or dyn_cast is null and return 32, to reduce subsequent indentation.

1312

check isVectorTy() instead?

1328

check this when bumping NumOfVarIndices. E.g., if (++NumOfVarIndices > 1)

1341–1342

Divide VF by SplitFactor instead of IdxsLT.first?

Else assert IdxsLT.first > 1? Otherwise recursion may spin.

1345–1347

Some explanation for the formula and overheads?

1349

space after *

1351

DataLT = SrcLT?

assert MaskLT.first == 1?

1404

Typos. Suggest: // Add the cost of inserting each scalar load into the vector.

1409

Suggest: // Add the cost of extracting each element out to a scalar store.

1424

Is 'cast' needed? See pattern used below in getGatherScatterOpCost, or use dyn_cast instead?

[delena]

../lib/Target/X86/X86TargetTransformInfo.cpp

1424

I removed this function

[delena]

Fixes according to Ayal's comments.

[Ayal]

../include/llvm/Analysis/TargetTransformInfo.h

465

... with a mask that is not a compile-time constant

../lib/Target/X86/X86TargetTransformInfo.cpp

572

this is independent of the rest of the patch, right?

1309

// operation will use 16 x 64 indices which do not fit in a zmm and needs to split. Also check that the base pointer is the same for all lanes, and that there's at most one variable index.

1313

this should be "if (IndexSize < 64 || !GEP)" to reverse your original condition.

1337–1338

Alternatively, pass VF to getIndexSizeInBits and fold this logic of checking for VF < 16 in it?

1352–1353

in[s]truction at a time

1357

no need for empty line

1364

VariableMask

1424

Mark as TODO?

../lib/Target/X86/X86TargetTransformInfo.h

80

VariableMask

[delena]

../lib/Target/X86/X86TargetTransformInfo.cpp

572

removed, it does not help with the current cost model algirithm

1352–1353

I don't know ho to add spell checker plug-in to kdevelop

1424

no

[delena]

Thanks Ayal,

The code is fixed according to your comments.

[Ayal]

This looks good to me. Thanks.

../include/llvm/Analysis/TargetTransformInfo.h

public:
   /// \return The cost of Load and Store instructions.
   int getMemoryOpCost(unsigned Opcode, Type *Src, unsigned Alignment,
                       unsigned AddressSpace) const;
 
   /// \return The cost of masked Load and Store instructions.
   int getMaskedMemoryOpCost(unsigned Opcode, Type *Src, unsigned Alignment,
                             unsigned AddressSpace) const;
 
+  /// \return The cost of Gather or Scatter operation
+  /// \p Opcode - is a type of memory access Load or Store
+  /// \p DataTy - a vector type of the data to be loaded or stored
+  /// \p Ptr - pointer [or vector of pointers] - address[es] in memory
+  /// \p VariableMask - true when the memory access is predicated with a mask
+  ///                   that is not a compile-time constant
+  /// \p Alignment - alignment of single element
+  int getGatherScatterOpCost(unsigned Opcode, Type *DataTy, Value *Ptr,
+                             bool VariableMask, unsigned Alignment) const;
+
   /// \return The cost of the interleaved memory operation.
   /// \p Opcode is the memory operation code
   /// \p VecTy is the vector type of the interleaved access.
   /// \p Factor is the interleave factor
   /// \p Indices is the indices for interleaved load members (as interleaved
   ///    load allows gaps)
   /// \p Alignment is the alignment of the memory operation
   /// \p AddressSpace is address space of the pointer.
public:
   /// Pairwise:
   ///  (v0, v1, v2, v3)
   ///  ((v0+v1), (v2, v3), undef, undef)
   /// Split:
   ///  (v0, v1, v2, v3)
   ///  ((v0+v2), (v1+v3), undef, undef)
   int getReductionCost(unsigned Opcode, Type *Ty, bool IsPairwiseForm) const;
 
-  /// \returns The cost of Intrinsic instructions.
+  /// \returns The cost of Intrinsic instructions. Types analysis only.
   int getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
                             ArrayRef<Type *> Tys) const;
 
+  /// \returns The cost of Intrinsic instructions. Analyses the real arguments.
+  int getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
+                            ArrayRef<Value *> Args) const;
+
   /// \returns The cost of Call instructions.
   int getCallInstrCost(Function *F, Type *RetTy, ArrayRef<Type *> Tys) const;
 
   /// \returns The number of pieces into which the provided type must be
   /// split during legalization. Zero is returned when the answer is unknown.
   unsigned getNumberOfParts(Type *Tp) const;
 
   /// \returns The cost of the address computation. For most targets this can be
virtual int getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
                                  Type *CondTy) = 0;
   virtual int getVectorInstrCost(unsigned Opcode, Type *Val,
                                  unsigned Index) = 0;
   virtual int getMemoryOpCost(unsigned Opcode, Type *Src, unsigned Alignment,
                               unsigned AddressSpace) = 0;
   virtual int getMaskedMemoryOpCost(unsigned Opcode, Type *Src,
                                     unsigned Alignment,
                                     unsigned AddressSpace) = 0;
+  virtual int getGatherScatterOpCost(unsigned Opcode, Type *DataTy,
+                                     Value *Ptr, bool VariableMask,
+                                     unsigned Alignment) = 0;
   virtual int getInterleavedMemoryOpCost(unsigned Opcode, Type *VecTy,
                                          unsigned Factor,
                                          ArrayRef<unsigned> Indices,
                                          unsigned Alignment,
                                          unsigned AddressSpace) = 0;
   virtual int getReductionCost(unsigned Opcode, Type *Ty,
                                bool IsPairwiseForm) = 0;
   virtual int getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
                                     ArrayRef<Type *> Tys) = 0;
+  virtual int getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
+                                    ArrayRef<Value *> Args) = 0;
   virtual int getCallInstrCost(Function *F, Type *RetTy,
                                ArrayRef<Type *> Tys) = 0;
   virtual unsigned getNumberOfParts(Type *Tp) = 0;
   virtual int getAddressComputationCost(Type *Ty, bool IsComplex) = 0;
   virtual unsigned getCostOfKeepingLiveOverCall(ArrayRef<Type *> Tys) = 0;
   virtual bool getTgtMemIntrinsic(IntrinsicInst *Inst,
                                   MemIntrinsicInfo &Info) = 0;
   virtual Value *getOrCreateResultFromMemIntrinsic(IntrinsicInst *Inst,
public:
   int getMemoryOpCost(unsigned Opcode, Type *Src, unsigned Alignment,
                       unsigned AddressSpace) override {
     return Impl.getMemoryOpCost(Opcode, Src, Alignment, AddressSpace);
   }
   int getMaskedMemoryOpCost(unsigned Opcode, Type *Src, unsigned Alignment,
                             unsigned AddressSpace) override {
     return Impl.getMaskedMemoryOpCost(Opcode, Src, Alignment, AddressSpace);
   }
+  int getGatherScatterOpCost(unsigned Opcode, Type *DataTy,
+                             Value *Ptr, bool VariableMask,
+                             unsigned Alignment) override {
+    return Impl.getGatherScatterOpCost(Opcode, DataTy, Ptr, VariableMask,
+                                       Alignment);
+  }
   int getInterleavedMemoryOpCost(unsigned Opcode, Type *VecTy, unsigned Factor,
                                  ArrayRef<unsigned> Indices, unsigned Alignment,
                                  unsigned AddressSpace) override {
     return Impl.getInterleavedMemoryOpCost(Opcode, VecTy, Factor, Indices,
                                            Alignment, AddressSpace);
   }
   int getReductionCost(unsigned Opcode, Type *Ty,
                        bool IsPairwiseForm) override {
     return Impl.getReductionCost(Opcode, Ty, IsPairwiseForm);
   }
   int getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
                             ArrayRef<Type *> Tys) override {
     return Impl.getIntrinsicInstrCost(ID, RetTy, Tys);
   }
+  int getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
+                            ArrayRef<Value *> Args) override {
+    return Impl.getIntrinsicInstrCost(ID, RetTy, Args);
+  }
   int getCallInstrCost(Function *F, Type *RetTy,
                        ArrayRef<Type *> Tys) override {
     return Impl.getCallInstrCost(F, RetTy, Tys);
   }
   unsigned getNumberOfParts(Type *Tp) override {
     return Impl.getNumberOfParts(Tp);
   }
   int getAddressComputationCost(Type *Ty, bool IsComplex) override {

../include/llvm/Analysis/TargetTransformInfoImpl.h

unsigned getMemoryOpCost(unsigned Opcode, Type *Src, unsigned Alignment,
     return 1;
   }
 
   unsigned getMaskedMemoryOpCost(unsigned Opcode, Type *Src, unsigned Alignment,
                                  unsigned AddressSpace) {
     return 1;
   }
 
+  unsigned getGatherScatterOpCost(unsigned Opcode, Type *DataTy, Value *Ptr,
+                                  bool VariableMask,
+                                  unsigned Alignment) {
+    return 1;
+  }
+
   unsigned getInterleavedMemoryOpCost(unsigned Opcode, Type *VecTy,
                                       unsigned Factor,
                                       ArrayRef<unsigned> Indices,
                                       unsigned Alignment,
                                       unsigned AddressSpace) {
     return 1;
   }
 
   unsigned getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
                                  ArrayRef<Type *> Tys) {
     return 1;
   }
+  unsigned getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
+                                 ArrayRef<Value *> Args) {
+    return 1;
+  }
 
   unsigned getCallInstrCost(Function *F, Type *RetTy, ArrayRef<Type *> Tys) {
     return 1;
   }
 
   unsigned getNumberOfParts(Type *Tp) { return 0; }
 
   unsigned getAddressComputationCost(Type *Tp, bool) { return 0; }

../include/llvm/CodeGen/BasicTTIImpl.h

if (Opcode == Instruction::Load) {
       for (unsigned i = 0; i < NumElts; i++)
         Cost += static_cast<T *>(this)
                     ->getVectorInstrCost(Instruction::InsertElement, VT, i);
     }
 
     return Cost;
   }
 
+  /// Get intrinsic cost based on arguments  
+  unsigned getIntrinsicInstrCost(Intrinsic::ID IID, Type *RetTy,
+                                 ArrayRef<Value *> Args) {
+    switch (IID) {
+    default: {
+      SmallVector<Type *, 4> Types;
+      for (Value *Op : Args)
+        Types.push_back(Op->getType());
+      return getIntrinsicInstrCost(IID, RetTy, Types);
+    }
+    case Intrinsic::masked_scatter: {
+      Value *Mask = Args[3];
+      bool VarMask = !isa<Constant>(Mask);
+      unsigned Alignment = cast<ConstantInt>(Args[2])->getZExtValue();
+      return
+        static_cast<T *>(this)->getGatherScatterOpCost(Instruction::Store,
+                                                       Args[0]->getType(),
+                                                       Args[1], VarMask,
+                                                       Alignment);
+    }
+    case Intrinsic::masked_gather: {
+      Value *Mask = Args[2];
+      bool VarMask = !isa<Constant>(Mask);
+      unsigned Alignment = cast<ConstantInt>(Args[1])->getZExtValue();
+      return
+        static_cast<T *>(this)->getGatherScatterOpCost(Instruction::Load,
+                                                       RetTy, Args[0], VarMask,
+                                                       Alignment);
+    }
+    }
+  }
+  
+  /// Get intrinsic cost based on argument types
   unsigned getIntrinsicInstrCost(Intrinsic::ID IID, Type *RetTy,
                                  ArrayRef<Type *> Tys) {
     unsigned ISD = 0;
     switch (IID) {
     default: {
       // Assume that we need to scalarize this intrinsic.
       unsigned ScalarizationCost = 0;
       unsigned ScalarCalls = 1;

../lib/Analysis/CostModel.cpp

if (NumVecElems == Mask.size()) {
         return TTI->getShuffleCost(TargetTransformInfo::SK_Alternate,
                                    VecTypOp0, 0, nullptr);
     }
 
     return -1;
   }
   case Instruction::Call:
     if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
-      SmallVector<Type*, 4> Tys;
+      SmallVector<Value *, 4> Args;
       for (unsigned J = 0, JE = II->getNumArgOperands(); J != JE; ++J)
-        Tys.push_back(II->getArgOperand(J)->getType());
+        Args.push_back(II->getArgOperand(J));
 
       return TTI->getIntrinsicInstrCost(II->getIntrinsicID(), II->getType(),
-                                        Tys);
+                                        Args);
     }
     return -1;
   default:
     // We don't have any information on this instruction.
     return -1;
   }
 }
 

../lib/Analysis/TargetTransformInfo.cpp

int TargetTransformInfo::getMaskedMemoryOpCost(unsigned Opcode, Type *Src,
                                                unsigned Alignment,
                                                unsigned AddressSpace) const {
   int Cost =
       TTIImpl->getMaskedMemoryOpCost(Opcode, Src, Alignment, AddressSpace);
   assert(Cost >= 0 && "TTI should not produce negative costs!");
   return Cost;
 }
 
+int TargetTransformInfo::getGatherScatterOpCost(unsigned Opcode, Type *DataTy,
+                                                Value *Ptr, bool VariableMask,
+                                                unsigned Alignment) const {
+  int Cost = TTIImpl->getGatherScatterOpCost(Opcode, DataTy, Ptr, VariableMask,
+                                             Alignment);
+  assert(Cost >= 0 && "TTI should not produce negative costs!");
+  return Cost;
+}
+
 int TargetTransformInfo::getInterleavedMemoryOpCost(
     unsigned Opcode, Type *VecTy, unsigned Factor, ArrayRef<unsigned> Indices,
     unsigned Alignment, unsigned AddressSpace) const {
   int Cost = TTIImpl->getInterleavedMemoryOpCost(Opcode, VecTy, Factor, Indices,
                                                  Alignment, AddressSpace);
   assert(Cost >= 0 && "TTI should not produce negative costs!");
   return Cost;
 }
 
 int TargetTransformInfo::getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
                                                ArrayRef<Type *> Tys) const {
   int Cost = TTIImpl->getIntrinsicInstrCost(ID, RetTy, Tys);
   assert(Cost >= 0 && "TTI should not produce negative costs!");
   return Cost;
 }
 
+int TargetTransformInfo::getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
+                                               ArrayRef<Value *> Args) const {
+  int Cost = TTIImpl->getIntrinsicInstrCost(ID, RetTy, Args);
+  assert(Cost >= 0 && "TTI should not produce negative costs!");
+  return Cost;
+}
+
 int TargetTransformInfo::getCallInstrCost(Function *F, Type *RetTy,
                                           ArrayRef<Type *> Tys) const {
   int Cost = TTIImpl->getCallInstrCost(F, RetTy, Tys);
   assert(Cost >= 0 && "TTI should not produce negative costs!");
   return Cost;
 }
 
 unsigned TargetTransformInfo::getNumberOfParts(Type *Tp) const {

../lib/Target/X86/X86TargetTransformInfo.h

public:
   int getShuffleCost(TTI::ShuffleKind Kind, Type *Tp, int Index, Type *SubTp);
   int getCastInstrCost(unsigned Opcode, Type *Dst, Type *Src);
   int getCmpSelInstrCost(unsigned Opcode, Type *ValTy, Type *CondTy);
   int getVectorInstrCost(unsigned Opcode, Type *Val, unsigned Index);
   int getMemoryOpCost(unsigned Opcode, Type *Src, unsigned Alignment,
                       unsigned AddressSpace);
   int getMaskedMemoryOpCost(unsigned Opcode, Type *Src, unsigned Alignment,
                             unsigned AddressSpace);
-
+  int getGatherScatterOpCost(unsigned Opcode, Type *DataTy, Value *Ptr,
+                             bool VariableMask, unsigned Alignment);
   int getAddressComputationCost(Type *PtrTy, bool IsComplex);
 
   int getReductionCost(unsigned Opcode, Type *Ty, bool IsPairwiseForm);
 
   int getIntImmCost(int64_t);
 
   int getIntImmCost(const APInt &Imm, Type *Ty);
 
   int getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm, Type *Ty);
   int getIntImmCost(Intrinsic::ID IID, unsigned Idx, const APInt &Imm,
                     Type *Ty);
   bool isLegalMaskedLoad(Type *DataType);
   bool isLegalMaskedStore(Type *DataType);
   bool isLegalMaskedGather(Type *DataType);
   bool isLegalMaskedScatter(Type *DataType);
   bool areInlineCompatible(const Function *Caller,
                            const Function *Callee) const;
+private:
+  int getGSScalarCost(unsigned Opcode, Type *DataTy, bool VariableMask,
+                      unsigned Alignment, unsigned AddressSpace);
+  int getGSVectorCost(unsigned Opcode, Type *DataTy, Value *Ptr,
+                      unsigned Alignment, unsigned AddressSpace);
 
   /// @}
 };
 
 } // end namespace llvm
 
 #endif

../lib/Target/X86/X86TargetTransformInfo.cpp

static const TypeConversionCostTblEntry AVX512FConversionTbl[] = {
     { ISD::SIGN_EXTEND, MVT::v16i32, MVT::v16i8,  1 },
     { ISD::ZERO_EXTEND, MVT::v16i32, MVT::v16i8,  1 },
     { ISD::SIGN_EXTEND, MVT::v16i32, MVT::v16i16, 1 },
     { ISD::ZERO_EXTEND, MVT::v16i32, MVT::v16i16, 1 },
     { ISD::SIGN_EXTEND, MVT::v8i64,  MVT::v8i32,  1 },
     { ISD::ZERO_EXTEND, MVT::v8i64,  MVT::v8i32,  1 },
     { ISD::ZERO_EXTEND, MVT::v8i64,  MVT::v8i16,  1 },
     { ISD::SIGN_EXTEND, MVT::v8i64,  MVT::v8i16,  1 },
 
     { ISD::SINT_TO_FP,  MVT::v16f32, MVT::v16i1,  3 },
     { ISD::SINT_TO_FP,  MVT::v16f32, MVT::v16i8,  2 },
     { ISD::SINT_TO_FP,  MVT::v16f32, MVT::v16i16, 2 },
     { ISD::SINT_TO_FP,  MVT::v16f32, MVT::v16i32, 1 },
     { ISD::SINT_TO_FP,  MVT::v8f64,  MVT::v8i1,   4 },
     { ISD::SINT_TO_FP,  MVT::v8f64,  MVT::v8i8,   2 },
     { ISD::SINT_TO_FP,  MVT::v8f64,  MVT::v8i16,  2 },
     { ISD::SINT_TO_FP,  MVT::v8f64,  MVT::v8i32,  1 },
int X86TTIImpl::getIntImmCost(Intrinsic::ID IID, unsigned Idx, const APInt &Imm,
   case Intrinsic::experimental_patchpoint_i64:
     if ((Idx < 4) || (Imm.getBitWidth() <= 64 && isInt<64>(Imm.getSExtValue())))
       return TTI::TCC_Free;
     break;
   }
   return X86TTIImpl::getIntImmCost(Imm, Ty);
 }
 
+// Return an average cost of Gather / Scatter instruction, maybe improved later
+int X86TTIImpl::getGSVectorCost(unsigned Opcode, Type *SrcVTy, Value *Ptr,
+                                unsigned Alignment, unsigned AddressSpace) {
+
+  assert(isa<VectorType>(SrcVTy) && "Unexpected type in getGSVectorCost");
+  unsigned VF = SrcVTy->getVectorNumElements();
+
+  // Try to reduce index size from 64 bit (default for GEP)
+  // to 32. It is essential for VF 16. If the index can't be reduced to 32, the
+  // operation will use 16 x 64 indices which do not fit in a zmm and needs
+  // to split. Also check that the base pointer is the same for all lanes,
+  // and that there's at most one variable index.
+  auto getIndexSizeInBits = [](Value *Ptr, const DataLayout& DL) {
+    unsigned IndexSize = DL.getPointerSizeInBits();
+    GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr);
+    if (IndexSize < 64 || !GEP)
+      return IndexSize;
+ 
+    unsigned NumOfVarIndices = 0;
+    Value *Ptrs = GEP->getPointerOperand();
+    if (Ptrs->getType()->isVectorTy() && !getSplatValue(Ptrs))
+      return IndexSize;
+    for (unsigned i = 1; i < GEP->getNumOperands(); ++i) {
+      if (isa<Constant>(GEP->getOperand(i)))
+        continue;
+      Type *IndxTy = GEP->getOperand(i)->getType();
+      if (IndxTy->isVectorTy())
+        IndxTy = IndxTy->getVectorElementType();
+      if ((IndxTy->getPrimitiveSizeInBits() == 64 &&
+          !isa<SExtInst>(GEP->getOperand(i))) ||
+         ++NumOfVarIndices > 1)
+        return IndexSize; // 64
+    }
+    return (unsigned)32;
+  };
+
+
+  // Trying to reduce IndexSize to 32 bits for vector 16.
+  // By default the IndexSize is equal to pointer size.
+  unsigned IndexSize = (VF >= 16) ? getIndexSizeInBits(Ptr, DL) :
+    DL.getPointerSizeInBits();
+
+  Type *IndexVTy = VectorType::get(IntegerType::get(getGlobalContext(),
+                                                    IndexSize), VF);
+  std::pair<int, MVT> IdxsLT = TLI->getTypeLegalizationCost(DL, IndexVTy);
+  std::pair<int, MVT> SrcLT = TLI->getTypeLegalizationCost(DL, SrcVTy);
+  int SplitFactor = std::max(IdxsLT.first, SrcLT.first);
+  if (SplitFactor > 1) {
+    // Handle splitting of vector of pointers
+    Type *SplitSrcTy = VectorType::get(SrcVTy->getScalarType(), VF / SplitFactor);
+    return SplitFactor * getGSVectorCost(Opcode, SplitSrcTy, Ptr, Alignment,
+                                         AddressSpace);
+  }
+
+  // The gather / scatter cost is given by Intel architects. It is a rough
+  // number since we are looking at one instruction in a time.
+  const int GSOverhead = 2;
+  return GSOverhead + VF * getMemoryOpCost(Opcode, SrcVTy->getScalarType(),
+                                           Alignment, AddressSpace);
+}
+
+/// Return the cost of full scalarization of gather / scatter operation.
+///
+/// Opcode - Load or Store instruction.
+/// SrcVTy - The type of the data vector that should be gathered or scattered.
+/// VariableMask - The mask is non-constant at compile time.
+/// Alignment - Alignment for one element.
+/// AddressSpace - pointer[s] address space.
+///
+int X86TTIImpl::getGSScalarCost(unsigned Opcode, Type *SrcVTy,
+                                bool VariableMask, unsigned Alignment,
+                                unsigned AddressSpace) {
+  unsigned VF = SrcVTy->getVectorNumElements();
+
+  int MaskUnpackCost = 0;
+  if (VariableMask) {
+    VectorType *MaskTy =
+      VectorType::get(Type::getInt1Ty(getGlobalContext()), VF);
+    MaskUnpackCost = getScalarizationOverhead(MaskTy, false, true);
+    int ScalarCompareCost =
+      getCmpSelInstrCost(Instruction::ICmp, Type::getInt1Ty(getGlobalContext()),
+                         nullptr);
+    int BranchCost = getCFInstrCost(Instruction::Br);
+    MaskUnpackCost += VF * (BranchCost + ScalarCompareCost);
+  }
+
+  // The cost of the scalar loads/stores.
+  int MemoryOpCost = VF * getMemoryOpCost(Opcode, SrcVTy->getScalarType(),
+                                          Alignment, AddressSpace);
+
+  int InsertExtractCost = 0;
+  if (Opcode == Instruction::Load)
+    for (unsigned i = 0; i < VF; ++i)
+      // Add the cost of inserting each scalar load into the vector
+      InsertExtractCost +=
+        getVectorInstrCost(Instruction::InsertElement, SrcVTy, i);
+  else
+    for (unsigned i = 0; i < VF; ++i)
+      // Add the cost of extracting each element out of the data vector
+      InsertExtractCost +=
+        getVectorInstrCost(Instruction::ExtractElement, SrcVTy, i);
+
+  return MemoryOpCost + MaskUnpackCost + InsertExtractCost;
+}
+
+/// Calculate the cost of Gather / Scatter operation
+int X86TTIImpl::getGatherScatterOpCost(unsigned Opcode, Type *SrcVTy,
+                                       Value *Ptr, bool VariableMask,
+                                       unsigned Alignment) {
+  assert(SrcVTy->isVectorTy() && "Unexpected data type for Gather/Scatter");
+  unsigned VF = SrcVTy->getVectorNumElements();
+  PointerType *PtrTy = dyn_cast<PointerType>(Ptr->getType());
+  if (!PtrTy && Ptr->getType()->isVectorTy())
+    PtrTy = dyn_cast<PointerType>(Ptr->getType()->getVectorElementType());
+  assert(PtrTy && "Unexpected type for Ptr argument");
+  unsigned AddressSpace = PtrTy->getAddressSpace();
+
+  bool Scalarize = false;
+  if ((Opcode == Instruction::Load && !isLegalMaskedGather(SrcVTy)) ||
+      (Opcode == Instruction::Store && !isLegalMaskedScatter(SrcVTy)))
+    Scalarize = true;
+  // Gather / Scatter for vector 2 is not profitable on KNL / SKX
+  // Vector 4 gather/scatter instruction does not exist on KNL.
+  // We can extend it to 8 elements, but zeroing upper bits of
+  // the mask vector will add more instructions. Right now we decide
+  // to scalarize vector-4 for KNL.
+  if (VF == 2 || (VF == 4 && !ST->hasVLX()))
+    Scalarize = true;
+
+  if (Scalarize)
+    return getGSScalarCost(Opcode, SrcVTy, VariableMask, Alignment, AddressSpace);
+
+  return getGSVectorCost(Opcode, SrcVTy, Ptr, Alignment, AddressSpace);
+}
+
 bool X86TTIImpl::isLegalMaskedLoad(Type *DataTy) {
   Type *ScalarTy = DataTy->getScalarType();
   int DataWidth = isa<PointerType>(ScalarTy) ?
     DL.getPointerSizeInBits() : ScalarTy->getPrimitiveSizeInBits();
 
   return (DataWidth >= 32 && ST->hasAVX2());
 }
 

../test/Analysis/CostModel/X86/masked-intrinsic-cost.ll

-; RUN: opt -S -mtriple=x86_64-apple-darwin -mcpu=core-avx2 -cost-model -analyze < %s | FileCheck %s -check-prefix=AVX2
+; RUN: opt -S -mtriple=x86_64-apple-darwin -mcpu=core-avx2 -cost-model -analyze < %s | FileCheck %s --check-prefix=AVX2
+; RUN: opt -S -mtriple=x86_64-apple-darwin -mcpu=knl -cost-model -analyze < %s | FileCheck %s --check-prefix=KNL
+; RUN: opt -S -mtriple=x86_64-apple-darwin -mcpu=skx -cost-model -analyze < %s | FileCheck %s --check-prefix=SKX
 
 
 ; AVX2-LABEL: test1
 ; AVX2: Found an estimated cost of 4 {{.*}}.masked
 define <2 x double> @test1(<2 x i64> %trigger, <2 x double>* %addr, <2 x double> %dst) {
   %mask = icmp eq <2 x i64> %trigger, zeroinitializer
   %res = call <2 x double> @llvm.masked.load.v2f64(<2 x double>* %addr, i32 4, <2 x i1>%mask, <2 x double>%dst)
   ret <2 x double> %res

 ; AVX2-LABEL: test8
 ; AVX2: Found an estimated cost of 6 {{.*}}.masked
 define <2 x i32> @test8(<2 x i32> %trigger, <2 x i32>* %addr, <2 x i32> %dst) {
   %mask = icmp eq <2 x i32> %trigger, zeroinitializer
   %res = call <2 x i32> @llvm.masked.load.v2i32(<2 x i32>* %addr, i32 4, <2 x i1>%mask, <2 x i32>%dst)
   ret <2 x i32> %res
 }
 
+define <2 x double> @test_gather_2f64(<2 x double*> %ptrs, <2 x i1> %mask, <2 x double> %src0)  {
+
+; AVX2-LABEL: test_gather_2f64
+; AVX2: Found an estimated cost of 7 {{.*}}.gather
+
+; KNL-LABEL: test_gather_2f64
+; KNL: Found an estimated cost of 7 {{.*}}.gather
+
+; SKX-LABEL: test_gather_2f64
+; SKX: Found an estimated cost of 7 {{.*}}.gather
+
+%res = call <2 x double> @llvm.masked.gather.v2f64(<2 x double*> %ptrs, i32 4, <2 x i1> %mask, <2 x double> %src0)
+  ret <2 x double> %res
+}
+declare <2 x double> @llvm.masked.gather.v2f64(<2 x double*> %ptrs, i32, <2 x i1> %mask, <2 x double> %src0)
+
+define <4 x i32> @test_gather_4i32(<4 x i32*> %ptrs, <4 x i1> %mask, <4 x i32> %src0)  {
+
+; AVX2-LABEL: test_gather_4i32
+; AVX2: Found an estimated cost of 16 {{.*}}.gather
+
+; KNL-LABEL: test_gather_4i32
+; KNL: Found an estimated cost of 16 {{.*}}.gather
+
+; SKX-LABEL: test_gather_4i32
+; SKX: Found an estimated cost of 6 {{.*}}.gather
+
+%res = call <4 x i32> @llvm.masked.gather.v4i32(<4 x i32*> %ptrs, i32 4, <4 x i1> %mask, <4 x i32> %src0)
+  ret <4 x i32> %res
+}
+
+define <4 x i32> @test_gather_4i32_const_mask(<4 x i32*> %ptrs, <4 x i32> %src0)  {
+
+; AVX2-LABEL: test_gather_4i32_const_mask
+; AVX2: Found an estimated cost of 8 {{.*}}.gather
+
+; KNL-LABEL: test_gather_4i32_const_mask
+; KNL: Found an estimated cost of 8 {{.*}}.gather
+
+; SKX-LABEL: test_gather_4i32_const_mask
+; SKX: Found an estimated cost of 6 {{.*}}.gather
+
+%res = call <4 x i32> @llvm.masked.gather.v4i32(<4 x i32*> %ptrs, i32 4, <4 x i1> <i1 true, i1 true, i1 true, i1 true>, <4 x i32> %src0)
+  ret <4 x i32> %res
+}
+declare <4 x i32> @llvm.masked.gather.v4i32(<4 x i32*> %ptrs, i32, <4 x i1> %mask, <4 x i32> %src0)
+
+define <16 x float> @test_gather_16f32_const_mask(float* %base, <16 x i32> %ind) {
+
+; AVX2-LABEL: test_gather_16f32_const_mask
+; AVX2: Found an estimated cost of 30 {{.*}}.gather
+
+; KNL-LABEL: test_gather_16f32_const_mask
+; KNL: Found an estimated cost of 18 {{.*}}.gather
+
+; SKX-LABEL: test_gather_16f32_const_mask
+; SKX: Found an estimated cost of 18 {{.*}}.gather
+
+  %sext_ind = sext <16 x i32> %ind to <16 x i64>
+  %gep.v = getelementptr float, float* %base, <16 x i64> %sext_ind
+
+  %res = call <16 x float> @llvm.masked.gather.v16f32(<16 x float*> %gep.v, i32 4, <16 x i1> <i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true>, <16 x float> undef)
+  ret <16 x float>%res
+}
+
+define <16 x float> @test_gather_16f32_var_mask(float* %base, <16 x i32> %ind, <16 x i1>%mask) {
+
+; AVX2-LABEL: test_gather_16f32_var_mask
+; AVX2: Found an estimated cost of 62 {{.*}}.gather
+
+; KNL-LABEL: test_gather_16f32_var_mask
+; KNL: Found an estimated cost of 18 {{.*}}.gather
+
+; SKX-LABEL: test_gather_16f32_var_mask
+; SKX: Found an estimated cost of 18 {{.*}}.gather
+
+  %sext_ind = sext <16 x i32> %ind to <16 x i64>
+  %gep.v = getelementptr float, float* %base, <16 x i64> %sext_ind
+
+  %res = call <16 x float> @llvm.masked.gather.v16f32(<16 x float*> %gep.v, i32 4, <16 x i1> %mask, <16 x float> undef)
+  ret <16 x float>%res
+}
+
+define <16 x float> @test_gather_16f32_ra_var_mask(<16 x float*> %ptrs, <16 x i32> %ind, <16 x i1>%mask) {
+
+; AVX2-LABEL: test_gather_16f32_ra_var_mask
+; AVX2: Found an estimated cost of 62 {{.*}}.gather
+
+; KNL-LABEL: test_gather_16f32_ra_var_mask
+; KNL: Found an estimated cost of 20 {{.*}}.gather
+
+; SKX-LABEL: test_gather_16f32_ra_var_mask
+; SKX: Found an estimated cost of 20 {{.*}}.gather
+
+  %sext_ind = sext <16 x i32> %ind to <16 x i64>
+  %gep.v = getelementptr float, <16 x float*> %ptrs, <16 x i64> %sext_ind
+
+  %res = call <16 x float> @llvm.masked.gather.v16f32(<16 x float*> %gep.v, i32 4, <16 x i1> %mask, <16 x float> undef)
+  ret <16 x float>%res
+}
+
+define <16 x float> @test_gather_16f32_const_mask2(float* %base, <16 x i32> %ind) {
+
+; AVX2-LABEL: test_gather_16f32_const_mask2
+; AVX2: Found an estimated cost of 30 {{.*}}.gather
+
+; KNL-LABEL: test_gather_16f32_const_mask2
+; KNL: Found an estimated cost of 18 {{.*}}.gather
+
+; SKX-LABEL: test_gather_16f32_const_mask2
+; SKX: Found an estimated cost of 18 {{.*}}.gather
+
+  %broadcast.splatinsert = insertelement <16 x float*> undef, float* %base, i32 0
+  %broadcast.splat = shufflevector <16 x float*> %broadcast.splatinsert, <16 x float*> undef, <16 x i32> zeroinitializer
+
+  %sext_ind = sext <16 x i32> %ind to <16 x i64>
+  %gep.random = getelementptr float, <16 x float*> %broadcast.splat, <16 x i64> %sext_ind
+
+  %res = call <16 x float> @llvm.masked.gather.v16f32(<16 x float*> %gep.random, i32 4, <16 x i1> <i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true>, <16 x float> undef)
+  ret <16 x float>%res
+}
+
+define void @test_scatter_16i32(i32* %base, <16 x i32> %ind, i16 %mask, <16 x i32>%val) {
+; AVX2-LABEL: test_scatter_16i32
+; AVX2: Found an estimated cost of 64 {{.*}}.scatter
+
+; KNL-LABEL: test_scatter_16i32
+; KNL: Found an estimated cost of 18 {{.*}}.scatter
+
+; SKX-LABEL: test_scatter_16i32
+; SKX: Found an estimated cost of 18 {{.*}}.scatter
+
+  %broadcast.splatinsert = insertelement <16 x i32*> undef, i32* %base, i32 0
+  %broadcast.splat = shufflevector <16 x i32*> %broadcast.splatinsert, <16 x i32*> undef, <16 x i32> zeroinitializer
+
+  %gep.random = getelementptr i32, <16 x i32*> %broadcast.splat, <16 x i32> %ind
+  %imask = bitcast i16 %mask to <16 x i1>
+  call void @llvm.masked.scatter.v16i32(<16 x i32>%val, <16 x i32*> %gep.random, i32 4, <16 x i1> %imask)
+  ret void
+}
+
+define void @test_scatter_8i32(<8 x i32>%a1, <8 x i32*> %ptr, <8 x i1>%mask) {
+; AVX2-LABEL: test_scatter_8i32
+; AVX2: Found an estimated cost of 32 {{.*}}.scatter
+
+; KNL-LABEL: test_scatter_8i32
+; KNL: Found an estimated cost of 10 {{.*}}.scatter
+
+; SKX-LABEL: test_scatter_8i32
+; SKX: Found an estimated cost of 10 {{.*}}.scatter
+
+  call void @llvm.masked.scatter.v8i32(<8 x i32> %a1, <8 x i32*> %ptr, i32 4, <8 x i1> %mask)
+  ret void
+}
+
+declare void @llvm.masked.scatter.v8i32(<8 x i32> %a1, <8 x i32*> %ptr, i32, <8 x i1> %mask)
+
+define void @test_scatter_4i32(<4 x i32>%a1, <4 x i32*> %ptr, <4 x i1>%mask) {
+; AVX2-LABEL: test_scatter_4i32
+; AVX2: Found an estimated cost of 16 {{.*}}.scatter
+
+; KNL-LABEL: test_scatter_4i32
+; KNL: Found an estimated cost of 16 {{.*}}.scatter
+
+; SKX-LABEL: test_scatter_4i32
+; SKX: Found an estimated cost of 6 {{.*}}.scatter
+
+  call void @llvm.masked.scatter.v4i32(<4 x i32> %a1, <4 x i32*> %ptr, i32 4, <4 x i1> %mask)
+  ret void
+}
+
+define <4 x float> @test_gather_4f32(float* %ptr, <4 x i32> %ind, <4 x i1>%mask) {
+
+; AVX2-LABEL: test_gather_4f32
+; AVX2: Found an estimated cost of 15 {{.*}}.gather
+
+; KNL-LABEL: test_gather_4f32
+; KNL: Found an estimated cost of 15 {{.*}}.gather
+
+; SKX-LABEL: test_gather_4f32
+; SKX: Found an estimated cost of 6 {{.*}}.gather
+
+  %sext_ind = sext <4 x i32> %ind to <4 x i64>
+  %gep.v = getelementptr float, float* %ptr, <4 x i64> %sext_ind
+
+  %res = call <4 x float> @llvm.masked.gather.v4f32(<4 x float*> %gep.v, i32 4, <4 x i1> %mask, <4 x float> undef)
+  ret <4 x float>%res
+}
+
+define <4 x float> @test_gather_4f32_const_mask(float* %ptr, <4 x i32> %ind) {
+
+; AVX2-LABEL: test_gather_4f32_const_mask
+; AVX2: Found an estimated cost of 7 {{.*}}.gather
+
+; KNL-LABEL: test_gather_4f32_const_mask
+; KNL: Found an estimated cost of 7 {{.*}}.gather
+
+; SKX-LABEL: test_gather_4f32_const_mask
+; SKX: Found an estimated cost of 6 {{.*}}.gather
+
+  %sext_ind = sext <4 x i32> %ind to <4 x i64>
+  %gep.v = getelementptr float, float* %ptr, <4 x i64> %sext_ind
+
+  %res = call <4 x float> @llvm.masked.gather.v4f32(<4 x float*> %gep.v, i32 4, <4 x i1> <i1 true, i1 true, i1 true, i1 true>, <4 x float> undef)
+  ret <4 x float>%res
+}
+
+declare <4 x float> @llvm.masked.gather.v4f32(<4 x float*> %gep.v, i32, <4 x i1> %mask, <4 x float> )
+declare void @llvm.masked.scatter.v4i32(<4 x i32> %a1, <4 x i32*> %ptr, i32, <4 x i1> %mask)
+declare void @llvm.masked.scatter.v16i32(<16 x i32>%val, <16 x i32*> %gep.random, i32, <16 x i1> %imask)
+declare <16 x float> @llvm.masked.gather.v16f32(<16 x float*> %gep.v, i32, <16 x i1> %mask, <16 x float>)
 
 declare <16 x i32> @llvm.masked.load.v16i32(<16 x i32>*, i32, <16 x i1>, <16 x i32>)
 declare <4 x i32> @llvm.masked.load.v4i32(<4 x i32>*, i32, <4 x i1>, <4 x i32>)
 declare <2 x i32> @llvm.masked.load.v2i32(<2 x i32>*, i32, <2 x i1>, <2 x i32>)
 declare void @llvm.masked.store.v16i32(<16 x i32>, <16 x i32>*, i32, <16 x i1>)
 declare void @llvm.masked.store.v8i32(<8 x i32>, <8 x i32>*, i32, <8 x i1>)
 declare void @llvm.masked.store.v4i32(<4 x i32>, <4 x i32>*, i32, <4 x i1>)
 declare void @llvm.masked.store.v2f32(<2 x float>, <2 x float>*, i32, <2 x i1>)