[SCEV] Construct SCEV iteratively.

This patch updates SCEV construction to work iteratively instead of recursively
in most cases. It resolves stack overflow issues when trying to construct SCEVs
for certain inputs, e.g. PR45201.

The basic approach is to to use a worklist to queue operands of V which
need to be created before V. To do so, the current patch adds a
getOperandsToCreate function which collects the operands SCEV
construction depends on for a given value. This is a slight duplication
with createSCEV.

At the moment, SCEVs for phis are still created recursively.

Fixes #32078, #42594, #44546, #49293, #49599,  #55333, #55511

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D114650

Author: fhahn

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -1575,9 +1575,17 @@ class ScalarEvolution {
   ConstantRange getRangeForUnknownRecurrence(const SCEVUnknown *U);
 
   /// We know that there is no SCEV for the specified value.  Analyze the
-  /// expression.
+  /// expression recursively.
   const SCEV *createSCEV(Value *V);
 
+  /// We know that there is no SCEV for the specified value. Create a new SCEV
+  /// for \p V iteratively.
+  const SCEV *createSCEVIter(Value *V);
+  /// Collect operands of \p V for which SCEV expressions should be constructed
+  /// first. Returns a SCEV directly if it can be constructed trivially for \p
+  /// V.
+  const SCEV *getOperandsToCreate(Value *V, SmallVectorImpl<Value *> &Ops);
+
   /// Provide the special handling we need to analyze PHI SCEVs.
   const SCEV *createNodeForPHI(PHINode *PN);
 

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -4406,18 +4406,9 @@ void ScalarEvolution::insertValueToMap(Value *V, const SCEV *S) {
 const SCEV *ScalarEvolution::getSCEV(Value *V) {
   assert(isSCEVable(V->getType()) && "Value is not SCEVable!");
 
-  const SCEV *S = getExistingSCEV(V);
-  if (S == nullptr) {
-    S = createSCEV(V);
-    // During PHI resolution, it is possible to create two SCEVs for the same
-    // V, so it is needed to double check whether V->S is inserted into
-    // ValueExprMap before insert S->{V, 0} into ExprValueMap.
-    std::pair<ValueExprMapType::iterator, bool> Pair =
-        ValueExprMap.insert({SCEVCallbackVH(V, this), S});
-    if (Pair.second)
-      ExprValueMap[S].insert(V);
-  }
-  return S;
+  if (const SCEV *S = getExistingSCEV(V))
+    return S;
+  return createSCEVIter(V);
 }
 
 const SCEV *ScalarEvolution::getExistingSCEV(Value *V) {
@@ -7185,6 +7176,211 @@ bool ScalarEvolution::loopIsFiniteByAssumption(const Loop *L) {
   return isFinite(L) || (isMustProgress(L) && loopHasNoSideEffects(L));
 }
 
+const SCEV *ScalarEvolution::createSCEVIter(Value *V) {
+  // Worklist item with a Value and a bool indicating whether all operands have
+  // been visited already.
+  using PointerTy = PointerIntPair<Value *, 1, bool>;
+  SmallVector<PointerTy> Stack;
+
+  Stack.emplace_back(V, true);
+  Stack.emplace_back(V, false);
+  while (!Stack.empty()) {
+    auto E = Stack.pop_back_val();
+    Value *CurV = E.getPointer();
+
+    if (getExistingSCEV(CurV))
+      continue;
+
+    SmallVector<Value *> Ops;
+    const SCEV *CreatedSCEV = nullptr;
+    // If all operands have been visited already, create the SCEV.
+    if (E.getInt()) {
+      CreatedSCEV = createSCEV(CurV);
+    } else {
+      // Otherwise get the operands we need to create SCEV's for before creating
+      // the SCEV for CurV. If the SCEV for CurV can be constructed trivially,
+      // just use it.
+      CreatedSCEV = getOperandsToCreate(CurV, Ops);
+    }
+
+    if (CreatedSCEV) {
+      insertValueToMap(CurV, CreatedSCEV);
+    } else {
+      // Queue CurV for SCEV creation, followed by its's operands which need to
+      // be constructed first.
+      Stack.emplace_back(CurV, true);
+      for (Value *Op : Ops)
+        Stack.emplace_back(Op, false);
+    }
+  }
+
+  return getExistingSCEV(V);
+}
+
+const SCEV *
+ScalarEvolution::getOperandsToCreate(Value *V, SmallVectorImpl<Value *> &Ops) {
+  if (!isSCEVable(V->getType()))
+    return getUnknown(V);
+
+  if (Instruction *I = dyn_cast<Instruction>(V)) {
+    // Don't attempt to analyze instructions in blocks that aren't
+    // reachable. Such instructions don't matter, and they aren't required
+    // to obey basic rules for definitions dominating uses which this
+    // analysis depends on.
+    if (!DT.isReachableFromEntry(I->getParent()))
+      return getUnknown(PoisonValue::get(V->getType()));
+  } else if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
+    return getConstant(CI);
+  else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
+    if (!GA->isInterposable()) {
+      Ops.push_back(GA->getAliasee());
+      return nullptr;
+    }
+    return getUnknown(V);
+  } else if (!isa<ConstantExpr>(V))
+    return getUnknown(V);
+
+  Operator *U = cast<Operator>(V);
+  if (auto BO = MatchBinaryOp(U, DT)) {
+    bool IsConstArg = isa<ConstantInt>(BO->RHS);
+    switch (U->getOpcode()) {
+    case Instruction::Add: {
+      // For additions and multiplications, traverse add/mul chains for which we
+      // can potentially create a single SCEV, to reduce the number of
+      // get{Add,Mul}Expr calls.
+      do {
+        if (BO->Op) {
+          if (BO->Op != V && getExistingSCEV(BO->Op)) {
+            Ops.push_back(BO->Op);
+            break;
+          }
+        }
+        Ops.push_back(BO->RHS);
+        auto NewBO = MatchBinaryOp(BO->LHS, DT);
+        if (!NewBO || (NewBO->Opcode != Instruction::Add &&
+                       NewBO->Opcode != Instruction::Sub)) {
+          Ops.push_back(BO->LHS);
+          break;
+        }
+        BO = NewBO;
+      } while (true);
+      return nullptr;
+    }
+
+    case Instruction::Mul: {
+      do {
+        if (BO->Op) {
+          if (BO->Op != V && getExistingSCEV(BO->Op)) {
+            Ops.push_back(BO->Op);
+            break;
+          }
+        }
+        Ops.push_back(BO->RHS);
+        auto NewBO = MatchBinaryOp(BO->LHS, DT);
+        if (!NewBO || NewBO->Opcode != Instruction::Mul) {
+          Ops.push_back(BO->LHS);
+          break;
+        }
+        BO = NewBO;
+      } while (true);
+      return nullptr;
+    }
+
+    case Instruction::AShr:
+    case Instruction::Shl:
+    case Instruction::Xor:
+      if (!IsConstArg)
+        return nullptr;
+      break;
+    case Instruction::And:
+    case Instruction::Or:
+      if (!IsConstArg && BO->LHS->getType()->isIntegerTy(1))
+        return nullptr;
+      break;
+    default:
+      break;
+    }
+
+    Ops.push_back(BO->LHS);
+    Ops.push_back(BO->RHS);
+    return nullptr;
+  }
+
+  switch (U->getOpcode()) {
+  case Instruction::Trunc:
+  case Instruction::ZExt:
+  case Instruction::SExt:
+  case Instruction::PtrToInt:
+    Ops.push_back(U->getOperand(0));
+    return nullptr;
+
+  case Instruction::BitCast:
+    if (isSCEVable(U->getType()) && isSCEVable(U->getOperand(0)->getType())) {
+      Ops.push_back(U->getOperand(0));
+      return nullptr;
+    }
+    return getUnknown(V);
+
+  case Instruction::SDiv:
+  case Instruction::SRem:
+    Ops.push_back(U->getOperand(0));
+    Ops.push_back(U->getOperand(1));
+    return nullptr;
+
+  case Instruction::GetElementPtr:
+    assert(cast<GEPOperator>(U)->getSourceElementType()->isSized() &&
+           "GEP source element type must be sized");
+    for (Value *Index : U->operands())
+      Ops.push_back(Index);
+    return nullptr;
+
+  case Instruction::IntToPtr:
+    return getUnknown(V);
+
+  case Instruction::PHI:
+    // Keep constructing SCEVs' for phis recursively for now.
+    return nullptr;
+
+  case Instruction::Select:
+    for (Value *Inc : U->operands())
+      Ops.push_back(Inc);
+    return nullptr;
+    break;
+
+  case Instruction::Call:
+  case Instruction::Invoke:
+    if (Value *RV = cast<CallBase>(U)->getReturnedArgOperand()) {
+      Ops.push_back(RV);
+      return nullptr;
+    }
+
+    if (auto *II = dyn_cast<IntrinsicInst>(U)) {
+      switch (II->getIntrinsicID()) {
+      case Intrinsic::abs:
+        Ops.push_back(II->getArgOperand(0));
+        return nullptr;
+      case Intrinsic::umax:
+      case Intrinsic::umin:
+      case Intrinsic::smax:
+      case Intrinsic::smin:
+      case Intrinsic::usub_sat:
+      case Intrinsic::uadd_sat:
+        Ops.push_back(II->getArgOperand(0));
+        Ops.push_back(II->getArgOperand(1));
+        return nullptr;
+      case Intrinsic::start_loop_iterations:
+        Ops.push_back(II->getArgOperand(0));
+        return nullptr;
+      default:
+        break;
+      }
+    }
+    break;
+  }
+
+  return nullptr;
+}
+
 const SCEV *ScalarEvolution::createSCEV(Value *V) {
   if (!isSCEVable(V->getType()))
     return getUnknown(V);