Refactor the VectorTargetTransformInfo interface.

Add getCostXXX calls for different families of opcodes, such as casts, arithmetic, cmp, etc.

Port the LoopVectorizer to the new API.

The LoopVectorizer now finds instructions which will remain uniform after vectorization. It uses this information when calculating the cost of these instructions.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166836 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetLowering.h

@@ -411,6 +411,13 @@ public:
        getOperationAction(Op, VT) == Custom);
   }
 
+  /// isOperationExpand - Return true if the specified operation is illegal on
+  /// this target or unlikely to be made legal with custom lowering. This is
+  /// used to help guide high-level lowering decisions.
+  bool isOperationExpand(unsigned Op, EVT VT) const {
+    return (!isTypeLegal(VT) || getOperationAction(Op, VT) == Expand);
+  }
+
   /// isOperationLegal - Return true if the specified operation is legal on this
   /// target.
   bool isOperationLegal(unsigned Op, EVT VT) const {

include/llvm/Target/TargetTransformImpl.h

@@ -56,6 +56,10 @@ private:
   std::pair<unsigned, EVT>
   getTypeLegalizationCost(LLVMContext &C, EVT Ty) const;
 
+  /// Estimate the overhead of scalarizing an instruction. Insert and Extract
+  /// are set if the result needs to be inserted and/or extracted from vectors.
+  unsigned getScalarizationOverhead(Type *Ty, bool Insert, bool Extract) const;
+
 public:
   explicit VectorTargetTransformImpl(const TargetLowering *TL) : TLI(TL) {}
 
@@ -63,8 +67,21 @@ public:
 
   virtual unsigned getInstrCost(unsigned Opcode, Type *Ty1, Type *Ty2) const;
 
+  virtual unsigned getArithmeticInstrCost(unsigned Opcode, Type *Ty) const;
+
   virtual unsigned getBroadcastCost(Type *Tp) const;
 
+  virtual unsigned getCastInstrCost(unsigned Opcode, Type *Dst,
+                                    Type *Src) const;
+
+  virtual unsigned getCFInstrCost(unsigned Opcode) const;
+
+  virtual unsigned getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
+                                      Type *CondTy) const;
+
+  virtual unsigned getVectorInstrCost(unsigned Opcode, Type *Val,
+                                      unsigned Index) const;
+
   virtual unsigned getMemoryOpCost(unsigned Opcode, Type *Src,
                                    unsigned Alignment,
                                    unsigned AddressSpace) const;

include/llvm/TargetTransformInfo.h

@@ -143,12 +143,42 @@ public:
     return 1;
   }
 
+  /// Returns the expected cost of arithmetic ops, such as mul, xor, fsub, etc.
+  virtual unsigned getArithmeticInstrCost(unsigned Opcode, Type *Ty) const {
+    return 1;
+  }
+
   /// Returns the cost of a vector broadcast of a scalar at place zero to a
   /// vector of type 'Tp'.
   virtual unsigned getBroadcastCost(Type *Tp) const {
     return 1;
   }
 
+  /// Returns the expected cost of cast instructions, such as bitcast, trunc,
+  /// zext, etc.
+  virtual unsigned getCastInstrCost(unsigned Opcode, Type *Dst,
+                                    Type *Src) const {
+    return 1;
+  }
+
+  /// Returns the expected cost of control-flow related instrutctions such as
+  /// Phi, Ret, Br.
+  virtual unsigned getCFInstrCost(unsigned Opcode) const {
+    return 1;
+  }
+
+  /// Returns the expected cost of compare and select instructions.
+  virtual unsigned getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
+                                      Type *CondTy = 0) const {
+    return 1;
+  }
+
+  /// Returns the expected cost of vector Insert and Extract.
+  virtual unsigned getVectorInstrCost(unsigned Opcode, Type *Val,
+                                      unsigned Index = 0) const {
+    return 1;
+  }
+
   /// Returns the cost of Load and Store instructions.
   virtual unsigned getMemoryOpCost(unsigned Opcode, Type *Src,
                                    unsigned Alignment,

lib/Target/TargetTransformImpl.cpp

@@ -135,7 +135,7 @@ VectorTargetTransformImpl::getTypeLegalizationCost(LLVMContext &C,
     TargetLowering::LegalizeKind LK = TLI->getTypeConversion(C, Ty);
 
     if (LK.first == TargetLowering::TypeLegal)
-      return std::make_pair(Cost, LK.second);
+      return std::make_pair(Cost, Ty);
 
     if (LK.first == TargetLowering::TypeSplitVector)
       Cost *= 2;
@@ -146,44 +146,144 @@ VectorTargetTransformImpl::getTypeLegalizationCost(LLVMContext &C,
 }
 
 unsigned
-VectorTargetTransformImpl::getInstrCost(unsigned Opcode, Type *Ty1,
-                                        Type *Ty2) const {
-  // Check if any of the operands are vector operands.
-  int ISD = InstructionOpcodeToISD(Opcode);
+VectorTargetTransformImpl::getScalarizationOverhead(Type *Ty,
+                                                    bool Insert,
+                                                    bool Extract) const {
+  assert (Ty->isVectorTy() && "Can only scalarize vectors");
+   unsigned Cost = 0;
 
-  // If we don't have any information about this instruction assume it costs 1.
-  if (ISD == 0)
-    return 1;
-
-  // Selects on vectors are actually vector selects.
-  if (ISD == ISD::SELECT) {
-    assert(Ty2 && "Ty2 must hold the condition type");
-    if (Ty2->isVectorTy())
-    ISD = ISD::VSELECT;
+  for (int i = 0, e = Ty->getVectorNumElements(); i < e; ++i) {
+    if (Insert)
+      Cost += getVectorInstrCost(Instruction::InsertElement, Ty, i);
+    if (Extract)
+      Cost += getVectorInstrCost(Instruction::ExtractElement, Ty, i);
   }
 
-  assert(Ty1 && "We need to have at least one type");
+  return Cost;
+}
+
+unsigned VectorTargetTransformImpl::getArithmeticInstrCost(unsigned Opcode,
+                                                           Type *Ty) const {
+  // Check if any of the operands are vector operands.
+  int ISD = InstructionOpcodeToISD(Opcode);
+  assert(ISD && "Invalid opcode");
 
-  // From this stage we look at the legalized type.
   std::pair<unsigned, EVT> LT =
-  getTypeLegalizationCost(Ty1->getContext(), TLI->getValueType(Ty1));
+  getTypeLegalizationCost(Ty->getContext(), TLI->getValueType(Ty));
 
-  if (TLI->isOperationLegalOrCustom(ISD, LT.second)) {
+  if (!TLI->isOperationExpand(ISD, LT.second)) {
     // The operation is legal. Assume it costs 1. Multiply
     // by the type-legalization overhead.
     return LT.first * 1;
   }
 
-  unsigned NumElem =
-    (LT.second.isVector() ? LT.second.getVectorNumElements() : 1);
+  // Else, assume that we need to scalarize this op.
+  if (Ty->isVectorTy()) {
+    unsigned Num = Ty->getVectorNumElements();
+    unsigned Cost = getArithmeticInstrCost(Opcode, Ty->getScalarType());
+    // return the cost of multiple scalar invocation plus the cost of inserting
+    // and extracting the values.
+    return getScalarizationOverhead(Ty, true, true) + Num * Cost;
+  }
 
-  // We will probably scalarize this instruction. Assume that the cost is the
-  // number of the vector elements.
-  return LT.first * NumElem * 1;
+  // We don't know anything about this scalar instruction.
+  return 1;
+}
+
+unsigned VectorTargetTransformImpl::getBroadcastCost(Type *Tp) const {
+  return 1;
+}
+
+unsigned VectorTargetTransformImpl::getCastInstrCost(unsigned Opcode, Type *Dst,
+                                  Type *Src) const {
+  assert(Src->isVectorTy() == Dst->isVectorTy() && "Invalid input types");
+  int ISD = InstructionOpcodeToISD(Opcode);
+  assert(ISD && "Invalid opcode");
+
+  std::pair<unsigned, EVT> SrcLT =
+  getTypeLegalizationCost(Src->getContext(), TLI->getValueType(Src));
+
+  std::pair<unsigned, EVT> DstLT =
+  getTypeLegalizationCost(Dst->getContext(), TLI->getValueType(Dst));
+
+  // If the cast is between same-sized registers, then the check is simple.
+  if (SrcLT.first == DstLT.first &&
+      SrcLT.second.getSizeInBits() == DstLT.second.getSizeInBits()) {
+    // Just check the op cost:
+    if (!TLI->isOperationExpand(ISD, DstLT.second)) {
+      // The operation is legal. Assume it costs 1. Multiply
+      // by the type-legalization overhead.
+      return SrcLT.first * 1;
+    }
+  }
+
+  // Otherwise, assume that the cast is scalarized.
+  if (Dst->isVectorTy()) {
+    unsigned Num = Dst->getVectorNumElements();
+    unsigned Cost = getCastInstrCost(Opcode, Src->getScalarType(),
+                                     Dst->getScalarType());
+    // return the cost of multiple scalar invocation plus the cost of inserting
+    // and extracting the values.
+    return getScalarizationOverhead(Dst, true, true) + Num * Cost;
+  }
+
+  // Unknown scalar opcode.
+  return 1;
+}
+
+unsigned VectorTargetTransformImpl::getCFInstrCost(unsigned Opcode) const {
+  return 1;
+}
+
+unsigned VectorTargetTransformImpl::getCmpSelInstrCost(unsigned Opcode,
+                                                       Type *ValTy,
+                                                       Type *CondTy) const {
+  int ISD = InstructionOpcodeToISD(Opcode);
+  assert(ISD && "Invalid opcode");
+  
+  // Selects on vectors are actually vector selects.
+  if (ISD == ISD::SELECT) {
+    assert(CondTy && "CondTy must exist");
+    if (CondTy->isVectorTy())
+      ISD = ISD::VSELECT;
+  }
+
+  std::pair<unsigned, EVT> LT =
+  getTypeLegalizationCost(ValTy->getContext(), TLI->getValueType(ValTy));
+
+  if (!TLI->isOperationExpand(ISD, LT.second)) {
+    // The operation is legal. Assume it costs 1. Multiply
+    // by the type-legalization overhead.
+    return LT.first * 1;
+  }
+
+  // Otherwise, assume that the cast is scalarized.
+  if (ValTy->isVectorTy()) {
+    unsigned Num = ValTy->getVectorNumElements();
+    if (CondTy)
+      CondTy = CondTy->getScalarType();
+    unsigned Cost = getCmpSelInstrCost(Opcode, ValTy->getScalarType(),
+                                       CondTy);
+
+    // return the cost of multiple scalar invocation plus the cost of inserting
+    // and extracting the values.
+    return getScalarizationOverhead(ValTy, true, false) + Num * Cost;
+  }
+
+  // Unknown scalar opcode. 
+  return 1;
+}
+
+/// Returns the expected cost of Vector Insert and Extract.
+unsigned VectorTargetTransformImpl::getVectorInstrCost(unsigned Opcode,
+                                                       Type *Val,
+                                                       unsigned Index) const {
+  return 1;
 }
 
 unsigned
-VectorTargetTransformImpl::getBroadcastCost(Type *Tp) const {
+VectorTargetTransformImpl::getInstrCost(unsigned Opcode, Type *Ty1,
+                                        Type *Ty2) const {
   return 1;
 }
 
@@ -191,17 +291,15 @@ unsigned
 VectorTargetTransformImpl::getMemoryOpCost(unsigned Opcode, Type *Src,
                                            unsigned Alignment,
                                            unsigned AddressSpace) const {
-  // From this stage we look at the legalized type.
   std::pair<unsigned, EVT> LT =
   getTypeLegalizationCost(Src->getContext(), TLI->getValueType(Src));
+
   // Assume that all loads of legal types cost 1.
   return LT.first;
 }
 
 unsigned
 VectorTargetTransformImpl::getNumberOfParts(Type *Tp) const {
-  std::pair<unsigned, EVT>  LT =
-  getTypeLegalizationCost(Tp->getContext(), TLI->getValueType(Tp));
-  return LT.first;
+  return TLI->getNumRegisters(Tp->getContext(), TLI->getValueType(Tp));
 }
 

lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -254,6 +254,9 @@ public:
   /// This check allows us to vectorize A[idx] into a wide load/store.
   bool isConsecutiveGep(Value *Ptr);
 
+  /// Returns true if this instruction will remain scalar after vectorization.
+  bool isUniformAfterVectorization(Instruction* I) {return Uniforms.count(I);}
+
 private:
   /// Check if a single basic block loop is vectorizable.
   /// At this point we know that this is a loop with a constant trip count
@@ -291,6 +294,9 @@ private:
   /// Allowed outside users. This holds the reduction
   /// vars which can be accessed from outside the loop.
   SmallPtrSet<Value*, 4> AllowedExit;
+  /// This set holds the variables which are known to be uniform after
+  /// vectorization.
+  SmallPtrSet<Instruction*, 4> Uniforms;
 };
 
 /// LoopVectorizationCostModel - estimates the expected speedups due to
@@ -1177,9 +1183,40 @@ bool LoopVectorizationLegality::canVectorizeBlock(BasicBlock &BB) {
       return false;
   }
 
-  // If the memory dependencies do not prevent us from
-  // vectorizing, then vectorize.
-  return canVectorizeMemory(BB);
+  // Don't vectorize if the memory dependencies do not allow vectorization.
+  if (!canVectorizeMemory(BB))
+    return false;
+
+  // We now know that the loop is vectorizable!
+  // Collect variables that will remain uniform after vectorization.
+  std::vector<Value*> Worklist;
+
+  // Start with the conditional branch and walk up the block.
+  Worklist.push_back(BB.getTerminator()->getOperand(0));
+
+  while (Worklist.size()) {
+    Instruction *I = dyn_cast<Instruction>(Worklist.back());
+    Worklist.pop_back();
+    // Look at instructions inside this block.
+    if (!I) continue;
+    if (I->getParent() != &BB) continue;
+
+    // Stop when reaching PHI nodes.
+    if (isa<PHINode>(I)) {
+      assert(I == Induction && "Found a uniform PHI that is not the induction");
+      break;
+    }
+
+    // This is a known uniform.
+    Uniforms.insert(I);
+
+    // Insert all operands.
+    for (int i=0, Op = I->getNumOperands(); i < Op; ++i) {
+      Worklist.push_back(I->getOperand(i));
+    }
+  }
+
+  return true;
 }
 
 bool LoopVectorizationLegality::canVectorizeMemory(BasicBlock &BB) {
@@ -1484,9 +1521,15 @@ unsigned
 LoopVectorizationCostModel::getInstructionCost(Instruction *I, unsigned VF) {
   assert(VTTI && "Invalid vector target transformation info");
 
+  // If we know that this instruction will remain uniform, check the cost of
+  // the scalar version.
+  if (Legal->isUniformAfterVectorization(I))
+    VF = 1;
+
   Type *RetTy = I->getType();
   Type *VectorTy = ToVectorTy(RetTy, VF);
 
+
   // TODO: We need to estimate the cost of intrinsic calls.
   switch (I->getOpcode()) {
     case Instruction::GetElementPtr:
@@ -1495,7 +1538,7 @@ LoopVectorizationCostModel::getInstructionCost(Instruction *I, unsigned VF) {
       // generate vector geps.
       return 0;
     case Instruction::Br: {
-      return VTTI->getInstrCost(I->getOpcode());
+      return VTTI->getCFInstrCost(I->getOpcode());
     }
     case Instruction::PHI:
       return 0;
@@ -1517,7 +1560,7 @@ LoopVectorizationCostModel::getInstructionCost(Instruction *I, unsigned VF) {
     case Instruction::And:
     case Instruction::Or:
     case Instruction::Xor: {
-      return VTTI->getInstrCost(I->getOpcode(), VectorTy);
+      return VTTI->getArithmeticInstrCost(I->getOpcode(), VectorTy);
     }
     case Instruction::Select: {
       SelectInst *SI = cast<SelectInst>(I);
@@ -1527,13 +1570,13 @@ LoopVectorizationCostModel::getInstructionCost(Instruction *I, unsigned VF) {
       if (ScalarCond)
         CondTy = VectorType::get(CondTy, VF);
 
-      return VTTI->getInstrCost(I->getOpcode(), VectorTy, CondTy);
+      return VTTI->getCmpSelInstrCost(I->getOpcode(), VectorTy, CondTy);
     }
     case Instruction::ICmp:
     case Instruction::FCmp: {
       Type *ValTy = I->getOperand(0)->getType();
       VectorTy = ToVectorTy(ValTy, VF);
-      return VTTI->getInstrCost(I->getOpcode(), VectorTy);
+      return VTTI->getCmpSelInstrCost(I->getOpcode(), VectorTy);
     }
     case Instruction::Store: {
       StoreInst *SI = cast<StoreInst>(I);
@@ -1602,7 +1645,7 @@ LoopVectorizationCostModel::getInstructionCost(Instruction *I, unsigned VF) {
     case Instruction::FPTrunc:
     case Instruction::BitCast: {
       Type *SrcVecTy = ToVectorTy(I->getOperand(0)->getType(), VF);
-      return VTTI->getInstrCost(I->getOpcode(), VectorTy, SrcVecTy);
+      return VTTI->getCastInstrCost(I->getOpcode(), VectorTy, SrcVecTy);
     }
     default: {
       // We are scalarizing the instruction. Return the cost of the scalar

test/Transforms/LoopVectorize/X86/cost-model.ll

@@ -9,7 +9,7 @@ target triple = "x86_64-apple-macosx10.8.0"
 @a = common global [2048 x i32] zeroinitializer, align 16
 
 ;CHECK: cost_model_1
-;CHECK: <4 x i32>
+;CHECK-NOT: <4 x i32>
 ;CHECK: ret void
 define void @cost_model_1() nounwind uwtable noinline ssp {
 entry: