[SCEV] Add SCEVType to represent vscale.

This is part of an effort to remove ConstantExpr based
representations of `vscale` so that its LangRef definiton can
be relaxed to accommodate a less strict definition of constant.

Differential Revision: https://reviews.llvm.org/D144891

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -566,6 +566,7 @@ class ScalarEvolution {
   const SCEV *getLosslessPtrToIntExpr(const SCEV *Op, unsigned Depth = 0);
   const SCEV *getPtrToIntExpr(const SCEV *Op, Type *Ty);
   const SCEV *getTruncateExpr(const SCEV *Op, Type *Ty, unsigned Depth = 0);
+  const SCEV *getVScale(Type *Ty);
   const SCEV *getZeroExtendExpr(const SCEV *Op, Type *Ty, unsigned Depth = 0);
   const SCEV *getZeroExtendExprImpl(const SCEV *Op, Type *Ty,
                                     unsigned Depth = 0);

llvm/include/llvm/Analysis/ScalarEvolutionDivision.h

@@ -48,6 +48,8 @@ struct SCEVDivision : public SCEVVisitor<SCEVDivision, void> {
 
   void visitConstant(const SCEVConstant *Numerator);
 
+  void visitVScale(const SCEVVScale *Numerator);
+
   void visitAddRecExpr(const SCEVAddRecExpr *Numerator);
 
   void visitAddExpr(const SCEVAddExpr *Numerator);

llvm/include/llvm/Analysis/ScalarEvolutionExpressions.h

@@ -39,6 +39,7 @@ enum SCEVTypes : unsigned short {
   // These should be ordered in terms of increasing complexity to make the
   // folders simpler.
   scConstant,
+  scVScale,
   scTruncate,
   scZeroExtend,
   scSignExtend,
@@ -75,6 +76,23 @@ class SCEVConstant : public SCEV {
   static bool classof(const SCEV *S) { return S->getSCEVType() == scConstant; }
 };
 
+/// This class represents the value of vscale, as used when defining the length
+/// of a scalable vector or returned by the llvm.vscale() intrinsic.
+class SCEVVScale : public SCEV {
+  friend class ScalarEvolution;
+
+  SCEVVScale(const FoldingSetNodeIDRef ID, Type *ty)
+      : SCEV(ID, scVScale, 0), Ty(ty) {}
+
+  Type *Ty;
+
+public:
+  Type *getType() const { return Ty; }
+
+  /// Methods for support type inquiry through isa, cast, and dyn_cast:
+  static bool classof(const SCEV *S) { return S->getSCEVType() == scVScale; }
+};
+
 inline unsigned short computeExpressionSize(ArrayRef<const SCEV *> Args) {
   APInt Size(16, 1);
   for (const auto *Arg : Args)
@@ -579,9 +597,6 @@ class SCEVUnknown final : public SCEV, private CallbackVH {
 public:
   Value *getValue() const { return getValPtr(); }
 
-  /// Check whether this represents vscale.
-  bool isVScale() const;
-
   Type *getType() const { return getValPtr()->getType(); }
 
   /// Methods for support type inquiry through isa, cast, and dyn_cast:
@@ -595,6 +610,8 @@ template <typename SC, typename RetVal = void> struct SCEVVisitor {
     switch (S->getSCEVType()) {
     case scConstant:
       return ((SC *)this)->visitConstant((const SCEVConstant *)S);
+    case scVScale:
+      return ((SC *)this)->visitVScale((const SCEVVScale *)S);
     case scPtrToInt:
       return ((SC *)this)->visitPtrToIntExpr((const SCEVPtrToIntExpr *)S);
     case scTruncate:
@@ -662,6 +679,7 @@ template <typename SV> class SCEVTraversal {
 
       switch (S->getSCEVType()) {
       case scConstant:
+      case scVScale:
       case scUnknown:
         continue;
       case scPtrToInt:
@@ -751,6 +769,8 @@ class SCEVRewriteVisitor : public SCEVVisitor<SC, const SCEV *> {
 
   const SCEV *visitConstant(const SCEVConstant *Constant) { return Constant; }
 
+  const SCEV *visitVScale(const SCEVVScale *VScale) { return VScale; }
+
   const SCEV *visitPtrToIntExpr(const SCEVPtrToIntExpr *Expr) {
     const SCEV *Operand = ((SC *)this)->visit(Expr->getOperand());
     return Operand == Expr->getOperand()

llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h

@@ -457,6 +457,8 @@ class SCEVExpander : public SCEVVisitor<SCEVExpander, Value *> {
 
   Value *visitConstant(const SCEVConstant *S) { return S->getValue(); }
 
+  Value *visitVScale(const SCEVVScale *S);
+
   Value *visitPtrToIntExpr(const SCEVPtrToIntExpr *S);
 
   Value *visitTruncateExpr(const SCEVTruncateExpr *S);

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -271,6 +271,9 @@ void SCEV::print(raw_ostream &OS) const {
   case scConstant:
     cast<SCEVConstant>(this)->getValue()->printAsOperand(OS, false);
     return;
+  case scVScale:
+    OS << "vscale";
+    return;
   case scPtrToInt: {
     const SCEVPtrToIntExpr *PtrToInt = cast<SCEVPtrToIntExpr>(this);
     const SCEV *Op = PtrToInt->getOperand();
@@ -366,17 +369,9 @@ void SCEV::print(raw_ostream &OS) const {
     OS << "(" << *UDiv->getLHS() << " /u " << *UDiv->getRHS() << ")";
     return;
   }
-  case scUnknown: {
-    const SCEVUnknown *U = cast<SCEVUnknown>(this);
-    if (U->isVScale()) {
-      OS << "vscale";
-      return;
-    }
-
-    // Otherwise just print it normally.
-    U->getValue()->printAsOperand(OS, false);
+  case scUnknown:
+    cast<SCEVUnknown>(this)->getValue()->printAsOperand(OS, false);
     return;
-  }
   case scCouldNotCompute:
     OS << "***COULDNOTCOMPUTE***";
     return;
@@ -388,6 +383,8 @@ Type *SCEV::getType() const {
   switch (getSCEVType()) {
   case scConstant:
     return cast<SCEVConstant>(this)->getType();
+  case scVScale:
+    return cast<SCEVVScale>(this)->getType();
   case scPtrToInt:
   case scTruncate:
   case scZeroExtend:
@@ -419,6 +416,7 @@ Type *SCEV::getType() const {
 ArrayRef<const SCEV *> SCEV::operands() const {
   switch (getSCEVType()) {
   case scConstant:
+  case scVScale:
   case scUnknown:
     return {};
   case scPtrToInt:
@@ -501,6 +499,18 @@ ScalarEvolution::getConstant(Type *Ty, uint64_t V, bool isSigned) {
   return getConstant(ConstantInt::get(ITy, V, isSigned));
 }
 
+const SCEV *ScalarEvolution::getVScale(Type *Ty) {
+  FoldingSetNodeID ID;
+  ID.AddInteger(scVScale);
+  ID.AddPointer(Ty);
+  void *IP = nullptr;
+  if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP))
+    return S;
+  SCEV *S = new (SCEVAllocator) SCEVVScale(ID.Intern(SCEVAllocator), Ty);
+  UniqueSCEVs.InsertNode(S, IP);
+  return S;
+}
+
 SCEVCastExpr::SCEVCastExpr(const FoldingSetNodeIDRef ID, SCEVTypes SCEVTy,
                            const SCEV *op, Type *ty)
     : SCEV(ID, SCEVTy, computeExpressionSize(op)), Op(op), Ty(ty) {}
@@ -560,10 +570,6 @@ void SCEVUnknown::allUsesReplacedWith(Value *New) {
   setValPtr(New);
 }
 
-bool SCEVUnknown::isVScale() const {
-  return match(getValue(), m_VScale());
-}
-
 //===----------------------------------------------------------------------===//
 //                               SCEV Utilities
 //===----------------------------------------------------------------------===//
@@ -714,6 +720,12 @@ CompareSCEVComplexity(EquivalenceClasses<const SCEV *> &EqCacheSCEV,
     return LA.ult(RA) ? -1 : 1;
   }
 
+  case scVScale: {
+    const auto *LTy = cast<IntegerType>(cast<SCEVVScale>(LHS)->getType());
+    const auto *RTy = cast<IntegerType>(cast<SCEVVScale>(RHS)->getType());
+    return LTy->getBitWidth() - RTy->getBitWidth();
+  }
+
   case scAddRecExpr: {
     const SCEVAddRecExpr *LA = cast<SCEVAddRecExpr>(LHS);
     const SCEVAddRecExpr *RA = cast<SCEVAddRecExpr>(RHS);
@@ -4015,6 +4027,8 @@ class SCEVSequentialMinMaxDeduplicatingVisitor final
 
   RetVal visitConstant(const SCEVConstant *Constant) { return Constant; }
 
+  RetVal visitVScale(const SCEVVScale *VScale) { return VScale; }
+
   RetVal visitPtrToIntExpr(const SCEVPtrToIntExpr *Expr) { return Expr; }
 
   RetVal visitTruncateExpr(const SCEVTruncateExpr *Expr) { return Expr; }
@@ -4061,6 +4075,7 @@ class SCEVSequentialMinMaxDeduplicatingVisitor final
 static bool scevUnconditionallyPropagatesPoisonFromOperands(SCEVTypes Kind) {
   switch (Kind) {
   case scConstant:
+  case scVScale:
   case scTruncate:
   case scZeroExtend:
   case scSignExtend:
@@ -4104,6 +4119,7 @@ static bool impliesPoison(const SCEV *AssumedPoison, const SCEV *S) {
       if (!scevUnconditionallyPropagatesPoisonFromOperands(S->getSCEVType())) {
         switch (S->getSCEVType()) {
         case scConstant:
+        case scVScale:
         case scTruncate:
         case scZeroExtend:
         case scSignExtend:
@@ -4315,15 +4331,8 @@ const SCEV *ScalarEvolution::getUMinExpr(SmallVectorImpl<const SCEV *> &Ops,
 const SCEV *
 ScalarEvolution::getSizeOfExpr(Type *IntTy, TypeSize Size) {
   const SCEV *Res = getConstant(IntTy, Size.getKnownMinValue());
-  if (Size.isScalable()) {
-    // TODO: Why is there no ConstantExpr::getVScale()?
-    Type *SrcElemTy = ScalableVectorType::get(Type::getInt8Ty(getContext()), 1);
-    Constant *NullPtr = Constant::getNullValue(SrcElemTy->getPointerTo());
-    Constant *One = ConstantInt::get(IntTy, 1);
-    Constant *GEP = ConstantExpr::getGetElementPtr(SrcElemTy, NullPtr, One);
-    Constant *VScale = ConstantExpr::getPtrToInt(GEP, IntTy);
-    Res = getMulExpr(Res, getUnknown(VScale));
-  }
+  if (Size.isScalable())
+    Res = getMulExpr(Res, getVScale(IntTy));
   return Res;
 }
 
@@ -5887,6 +5896,7 @@ static bool IsAvailableOnEntry(const Loop *L, DominatorTree &DT, const SCEV *S,
     bool follow(const SCEV *S) {
       switch (S->getSCEVType()) {
       case scConstant:
+      case scVScale:
       case scPtrToInt:
       case scTruncate:
       case scZeroExtend:
@@ -6274,6 +6284,8 @@ uint32_t ScalarEvolution::GetMinTrailingZerosImpl(const SCEV *S) {
   switch (S->getSCEVType()) {
   case scConstant:
     return cast<SCEVConstant>(S)->getAPInt().countr_zero();
+  case scVScale:
+    return 0;
   case scTruncate: {
     const SCEVTruncateExpr *T = cast<SCEVTruncateExpr>(S);
     return std::min(GetMinTrailingZeros(T->getOperand()),
@@ -6504,6 +6516,7 @@ ScalarEvolution::getRangeRefIter(const SCEV *S,
         break;
       [[fallthrough]];
     case scConstant:
+    case scVScale:
     case scTruncate:
     case scZeroExtend:
     case scSignExtend:
@@ -6607,6 +6620,8 @@ const ConstantRange &ScalarEvolution::getRangeRef(
   switch (S->getSCEVType()) {
   case scConstant:
     llvm_unreachable("Already handled above.");
+  case scVScale:
+    return setRange(S, SignHint, std::move(ConservativeResult));
   case scTruncate: {
     const SCEVTruncateExpr *Trunc = cast<SCEVTruncateExpr>(S);
     ConstantRange X = getRangeRef(Trunc->getOperand(), SignHint, Depth + 1);
@@ -9711,6 +9726,7 @@ static Constant *BuildConstantFromSCEV(const SCEV *V) {
   switch (V->getSCEVType()) {
   case scCouldNotCompute:
   case scAddRecExpr:
+  case scVScale:
     return nullptr;
   case scConstant:
     return cast<SCEVConstant>(V)->getValue();
@@ -9794,6 +9810,7 @@ static Constant *BuildConstantFromSCEV(const SCEV *V) {
 const SCEV *ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) {
   switch (V->getSCEVType()) {
   case scConstant:
+  case scVScale:
     return V;
   case scAddRecExpr: {
     // If this is a loop recurrence for a loop that does not contain L, then we
@@ -9892,6 +9909,7 @@ const SCEV *ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) {
         case scSequentialUMinExpr:
           return getSequentialMinMaxExpr(V->getSCEVType(), NewOps);
         case scConstant:
+        case scVScale:
         case scAddRecExpr:
         case scUnknown:
         case scCouldNotCompute:
@@ -13677,6 +13695,7 @@ ScalarEvolution::LoopDisposition
 ScalarEvolution::computeLoopDisposition(const SCEV *S, const Loop *L) {
   switch (S->getSCEVType()) {
   case scConstant:
+  case scVScale:
     return LoopInvariant;
   case scAddRecExpr: {
     const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(S);
@@ -13775,6 +13794,7 @@ ScalarEvolution::BlockDisposition
 ScalarEvolution::computeBlockDisposition(const SCEV *S, const BasicBlock *BB) {
   switch (S->getSCEVType()) {
   case scConstant:
+  case scVScale:
     return ProperlyDominatesBlock;
   case scAddRecExpr: {
     // This uses a "dominates" query instead of "properly dominates" query

llvm/lib/Analysis/ScalarEvolutionDivision.cpp

@@ -126,6 +126,10 @@ void SCEVDivision::visitConstant(const SCEVConstant *Numerator) {
   }
 }
 
+void SCEVDivision::visitVScale(const SCEVVScale *Numerator) {
+  return cannotDivide(Numerator);
+}
+
 void SCEVDivision::visitAddRecExpr(const SCEVAddRecExpr *Numerator) {
   const SCEV *StartQ, *StartR, *StepQ, *StepR;
   if (!Numerator->isAffine())

llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

@@ -976,6 +976,7 @@ static bool isHighCostExpansion(const SCEV *S,
   switch (S->getSCEVType()) {
   case scUnknown:
   case scConstant:
+  case scVScale:
     return false;
   case scTruncate:
     return isHighCostExpansion(cast<SCEVTruncateExpr>(S)->getOperand(),
@@ -2812,9 +2813,10 @@ static bool isCompatibleIVType(Value *LVal, Value *RVal) {
 /// SCEVUnknown, we simply return the rightmost SCEV operand.
 static const SCEV *getExprBase(const SCEV *S) {
   switch (S->getSCEVType()) {
-  default: // uncluding scUnknown.
+  default: // including scUnknown.
     return S;
   case scConstant:
+  case scVScale:
     return nullptr;
   case scTruncate:
     return getExprBase(cast<SCEVTruncateExpr>(S)->getOperand());

llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp

@@ -680,6 +680,7 @@ const Loop *SCEVExpander::getRelevantLoop(const SCEV *S) {
 
   switch (S->getSCEVType()) {
   case scConstant:
+  case scVScale:
     return nullptr; // A constant has no relevant loops.
   case scTruncate:
   case scZeroExtend:
@@ -1744,6 +1745,10 @@ Value *SCEVExpander::visitSequentialUMinExpr(const SCEVSequentialUMinExpr *S) {
   return expandMinMaxExpr(S, Intrinsic::umin, "umin", /*IsSequential*/true);
 }
 
+Value *SCEVExpander::visitVScale(const SCEVVScale *S) {
+  return Builder.CreateVScale(ConstantInt::get(S->getType(), 1));
+}
+
 Value *SCEVExpander::expandCodeForImpl(const SCEV *SH, Type *Ty,
                                        Instruction *IP) {
   setInsertPoint(IP);
@@ -2124,6 +2129,7 @@ template<typename T> static InstructionCost costAndCollectOperands(
     llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
   case scUnknown:
   case scConstant:
+  case scVScale:
     return 0;
   case scPtrToInt:
     Cost = CastCost(Instruction::PtrToInt);
@@ -2260,6 +2266,7 @@ bool SCEVExpander::isHighCostExpansionHelper(
   case scCouldNotCompute:
     llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
   case scUnknown:
+  case scVScale:
     // Assume to be zero-cost.
     return false;
   case scConstant: {