Reassociate.h revision 303231 
1//===- Reassociate.h - Reassociate binary expressions -----------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This pass reassociates commutative expressions in an order that is designed
11// to promote better constant propagation, GCSE, LICM, PRE, etc.
12//
13// For example: 4 + (x + 5) -> x + (4 + 5)
14//
15// In the implementation of this algorithm, constants are assigned rank = 0,
16// function arguments are rank = 1, and other values are assigned ranks
17// corresponding to the reverse post order traversal of current function
18// (starting at 2), which effectively gives values in deep loops higher rank
19// than values not in loops.
20//
21//===----------------------------------------------------------------------===//
22
23#ifndef LLVM_TRANSFORMS_SCALAR_REASSOCIATE_H
24#define LLVM_TRANSFORMS_SCALAR_REASSOCIATE_H
25
26#include "llvm/ADT/PostOrderIterator.h"
27#include "llvm/ADT/SetVector.h"
28#include "llvm/IR/IRBuilder.h"
29#include "llvm/IR/Operator.h"
30#include "llvm/IR/PassManager.h"
31
32namespace llvm {
33
34/// A private "module" namespace for types and utilities used by Reassociate.
35/// These are implementation details and should not be used by clients.
36namespace reassociate {
37struct ValueEntry {
38  unsigned Rank;
39  Value *Op;
40  ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
41};
42inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
43  return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start.
44}
45
46/// \brief Utility class representing a base and exponent pair which form one
47/// factor of some product.
48struct Factor {
49  Value *Base;
50  unsigned Power;
51  Factor(Value *Base, unsigned Power) : Base(Base), Power(Power) {}
52};
53
54class XorOpnd;
55}
56
57/// Reassociate commutative expressions.
58class ReassociatePass : public PassInfoMixin<ReassociatePass> {
59  DenseMap<BasicBlock *, unsigned> RankMap;
60  DenseMap<AssertingVH<Value>, unsigned> ValueRankMap;
61  SetVector<AssertingVH<Instruction>> RedoInsts;
62  bool MadeChange;
63
64public:
65  PreservedAnalyses run(Function &F, FunctionAnalysisManager &);
66
67private:
68  void BuildRankMap(Function &F, ReversePostOrderTraversal<Function *> &RPOT);
69  unsigned getRank(Value *V);
70  void canonicalizeOperands(Instruction *I);
71  void ReassociateExpression(BinaryOperator *I);
72  void RewriteExprTree(BinaryOperator *I,
73                       SmallVectorImpl<reassociate::ValueEntry> &Ops);
74  Value *OptimizeExpression(BinaryOperator *I,
75                            SmallVectorImpl<reassociate::ValueEntry> &Ops);
76  Value *OptimizeAdd(Instruction *I,
77                     SmallVectorImpl<reassociate::ValueEntry> &Ops);
78  Value *OptimizeXor(Instruction *I,
79                     SmallVectorImpl<reassociate::ValueEntry> &Ops);
80  bool CombineXorOpnd(Instruction *I, reassociate::XorOpnd *Opnd1,
81                      APInt &ConstOpnd, Value *&Res);
82  bool CombineXorOpnd(Instruction *I, reassociate::XorOpnd *Opnd1,
83                      reassociate::XorOpnd *Opnd2, APInt &ConstOpnd,
84                      Value *&Res);
85  bool collectMultiplyFactors(SmallVectorImpl<reassociate::ValueEntry> &Ops,
86                              SmallVectorImpl<reassociate::Factor> &Factors);
87  Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder,
88                                 SmallVectorImpl<reassociate::Factor> &Factors);
89  Value *OptimizeMul(BinaryOperator *I,
90                     SmallVectorImpl<reassociate::ValueEntry> &Ops);
91  Value *RemoveFactorFromExpression(Value *V, Value *Factor);
92  void EraseInst(Instruction *I);
93  void RecursivelyEraseDeadInsts(Instruction *I,
94                                 SetVector<AssertingVH<Instruction>> &Insts);
95  void OptimizeInst(Instruction *I);
96  Instruction *canonicalizeNegConstExpr(Instruction *I);
97};
98}
99
100#endif // LLVM_TRANSFORMS_SCALAR_REASSOCIATE_H
101