1//===- Reassociate.h - Reassociate binary expressions -----------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This pass reassociates commutative expressions in an order that is designed
10// to promote better constant propagation, GCSE, LICM, PRE, etc.
11//
12// For example: 4 + (x + 5) -> x + (4 + 5)
13//
14// In the implementation of this algorithm, constants are assigned rank = 0,
15// function arguments are rank = 1, and other values are assigned ranks
16// corresponding to the reverse post order traversal of current function
17// (starting at 2), which effectively gives values in deep loops higher rank
18// than values not in loops.
19//
20//===----------------------------------------------------------------------===//
21
22#ifndef LLVM_TRANSFORMS_SCALAR_REASSOCIATE_H
23#define LLVM_TRANSFORMS_SCALAR_REASSOCIATE_H
24
25#include "llvm/ADT/DenseMap.h"
26#include "llvm/ADT/PostOrderIterator.h"
27#include "llvm/ADT/SetVector.h"
28#include "llvm/IR/IRBuilder.h"
29#include "llvm/IR/PassManager.h"
30#include "llvm/IR/ValueHandle.h"
31#include <deque>
32
33namespace llvm {
34
35class APInt;
36class BasicBlock;
37class BinaryOperator;
38class Function;
39class Instruction;
40class Value;
41
42/// A private "module" namespace for types and utilities used by Reassociate.
43/// These are implementation details and should not be used by clients.
44namespace reassociate {
45
46struct ValueEntry {
47  unsigned Rank;
48  Value *Op;
49
50  ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
51};
52
53inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
54  return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
55}
56
57/// Utility class representing a base and exponent pair which form one
58/// factor of some product.
59struct Factor {
60  Value *Base;
61  unsigned Power;
62
63  Factor(Value *Base, unsigned Power) : Base(Base), Power(Power) {}
64};
65
66class XorOpnd;
67
68} // end namespace reassociate
69
70/// Reassociate commutative expressions.
71class ReassociatePass : public PassInfoMixin<ReassociatePass> {
72public:
73  using OrderedSet =
74      SetVector<AssertingVH<Instruction>, std::deque<AssertingVH<Instruction>>>;
75
76protected:
77  DenseMap<BasicBlock *, unsigned> RankMap;
78  DenseMap<AssertingVH<Value>, unsigned> ValueRankMap;
79  OrderedSet RedoInsts;
80
81  // Arbitrary, but prevents quadratic behavior.
82  static const unsigned GlobalReassociateLimit = 10;
83  static const unsigned NumBinaryOps =
84      Instruction::BinaryOpsEnd - Instruction::BinaryOpsBegin;
85
86  struct PairMapValue {
87    WeakVH Value1;
88    WeakVH Value2;
89    unsigned Score;
90    bool isValid() const { return Value1 && Value2; }
91  };
92  DenseMap<std::pair<Value *, Value *>, PairMapValue> PairMap[NumBinaryOps];
93
94  bool MadeChange;
95
96public:
97  PreservedAnalyses run(Function &F, FunctionAnalysisManager &);
98
99private:
100  void BuildRankMap(Function &F, ReversePostOrderTraversal<Function *> &RPOT);
101  unsigned getRank(Value *V);
102  void canonicalizeOperands(Instruction *I);
103  void ReassociateExpression(BinaryOperator *I);
104  void RewriteExprTree(BinaryOperator *I,
105                       SmallVectorImpl<reassociate::ValueEntry> &Ops);
106  Value *OptimizeExpression(BinaryOperator *I,
107                            SmallVectorImpl<reassociate::ValueEntry> &Ops);
108  Value *OptimizeAdd(Instruction *I,
109                     SmallVectorImpl<reassociate::ValueEntry> &Ops);
110  Value *OptimizeXor(Instruction *I,
111                     SmallVectorImpl<reassociate::ValueEntry> &Ops);
112  bool CombineXorOpnd(Instruction *I, reassociate::XorOpnd *Opnd1,
113                      APInt &ConstOpnd, Value *&Res);
114  bool CombineXorOpnd(Instruction *I, reassociate::XorOpnd *Opnd1,
115                      reassociate::XorOpnd *Opnd2, APInt &ConstOpnd,
116                      Value *&Res);
117  Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder,
118                                 SmallVectorImpl<reassociate::Factor> &Factors);
119  Value *OptimizeMul(BinaryOperator *I,
120                     SmallVectorImpl<reassociate::ValueEntry> &Ops);
121  Value *RemoveFactorFromExpression(Value *V, Value *Factor);
122  void EraseInst(Instruction *I);
123  void RecursivelyEraseDeadInsts(Instruction *I, OrderedSet &Insts);
124  void OptimizeInst(Instruction *I);
125  Instruction *canonicalizeNegFPConstantsForOp(Instruction *I, Instruction *Op,
126                                               Value *OtherOp);
127  Instruction *canonicalizeNegFPConstants(Instruction *I);
128  void BuildPairMap(ReversePostOrderTraversal<Function *> &RPOT);
129};
130
131} // end namespace llvm
132
133#endif // LLVM_TRANSFORMS_SCALAR_REASSOCIATE_H
134