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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 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.
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SetVector.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 IRBuilderBase;
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> {
using OrderedSet =
SetVector<AssertingVH<Instruction>, std::deque<AssertingVH<Instruction>>>;
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;
struct PairMapValue {
WeakVH Value1;
WeakVH Value2;
unsigned Score;
bool isValid() const { return Value1 && Value2; }
DenseMap<std::pair<Value *, Value *>, PairMapValue> PairMap[NumBinaryOps];
bool MadeChange;
PreservedAnalyses run(Function &F, FunctionAnalysisManager &);
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(IRBuilderBase &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 *canonicalizeNegFPConstantsForOp(Instruction *I, Instruction *Op,
Value *OtherOp);
Instruction *canonicalizeNegFPConstants(Instruction *I);
void BuildPairMap(ReversePostOrderTraversal<Function *> &RPOT);
} // end namespace llvm