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+//===- Reassociate.h - Reassociate binary expressions -----------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass reassociates commutative expressions in an order that is designed
+// to promote better constant propagation, GCSE, LICM, PRE, etc.
+//
+// For example: 4 + (x + 5) -> x + (4 + 5)
+//
+// In the implementation of this algorithm, constants are assigned rank = 0,
+// function arguments are rank = 1, and other values are assigned ranks
+// corresponding to the reverse post order traversal of current function
+// (starting at 2), which effectively gives values in deep loops higher rank
+// than values not in loops.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_SCALAR_REASSOCIATE_H
+#define LLVM_TRANSFORMS_SCALAR_REASSOCIATE_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/ValueHandle.h"
+#include <deque>
+
+namespace llvm {
+
+class APInt;
+class BasicBlock;
+class BinaryOperator;
+class Function;
+class Instruction;
+class Value;
+
+/// A private "module" namespace for types and utilities used by Reassociate.
+/// These are implementation details and should not be used by clients.
+namespace reassociate {
+
+struct ValueEntry {
+  unsigned Rank;
+  Value *Op;
+
+  ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
+};
+
+inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
+  return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
+}
+
+/// Utility class representing a base and exponent pair which form one
+/// factor of some product.
+struct Factor {
+  Value *Base;
+  unsigned Power;
+
+  Factor(Value *Base, unsigned Power) : Base(Base), Power(Power) {}
+};
+
+class XorOpnd;
+
+} // end namespace reassociate
+
+/// Reassociate commutative expressions.
+class ReassociatePass : public PassInfoMixin<ReassociatePass> {
+public:
+  using OrderedSet =
+      SetVector<AssertingVH<Instruction>, std::deque<AssertingVH<Instruction>>>;
+
+protected:
+  DenseMap<BasicBlock *, unsigned> RankMap;
+  DenseMap<AssertingVH<Value>, unsigned> ValueRankMap;
+  OrderedSet RedoInsts;
+
+  // Arbitrary, but prevents quadratic behavior.
+  static const unsigned GlobalReassociateLimit = 10;
+  static const unsigned NumBinaryOps =
+      Instruction::BinaryOpsEnd - Instruction::BinaryOpsBegin;
+  DenseMap<std::pair<Value *, Value *>, unsigned> PairMap[NumBinaryOps];
+
+  bool MadeChange;
+
+public:
+  PreservedAnalyses run(Function &F, FunctionAnalysisManager &);
+
+private:
+  void BuildRankMap(Function &F, ReversePostOrderTraversal<Function *> &RPOT);
+  unsigned getRank(Value *V);
+  void canonicalizeOperands(Instruction *I);
+  void ReassociateExpression(BinaryOperator *I);
+  void RewriteExprTree(BinaryOperator *I,
+                       SmallVectorImpl<reassociate::ValueEntry> &Ops);
+  Value *OptimizeExpression(BinaryOperator *I,
+                            SmallVectorImpl<reassociate::ValueEntry> &Ops);
+  Value *OptimizeAdd(Instruction *I,
+                     SmallVectorImpl<reassociate::ValueEntry> &Ops);
+  Value *OptimizeXor(Instruction *I,
+                     SmallVectorImpl<reassociate::ValueEntry> &Ops);
+  bool CombineXorOpnd(Instruction *I, reassociate::XorOpnd *Opnd1,
+                      APInt &ConstOpnd, Value *&Res);
+  bool CombineXorOpnd(Instruction *I, reassociate::XorOpnd *Opnd1,
+                      reassociate::XorOpnd *Opnd2, APInt &ConstOpnd,
+                      Value *&Res);
+  Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder,
+                                 SmallVectorImpl<reassociate::Factor> &Factors);
+  Value *OptimizeMul(BinaryOperator *I,
+                     SmallVectorImpl<reassociate::ValueEntry> &Ops);
+  Value *RemoveFactorFromExpression(Value *V, Value *Factor);
+  void EraseInst(Instruction *I);
+  void RecursivelyEraseDeadInsts(Instruction *I, OrderedSet &Insts);
+  void OptimizeInst(Instruction *I);
+  Instruction *canonicalizeNegConstExpr(Instruction *I);
+  void BuildPairMap(ReversePostOrderTraversal<Function *> &RPOT);
+};
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_SCALAR_REASSOCIATE_H