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 
32 namespace 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.
36 namespace reassociate {
37 struct ValueEntry {
38   unsigned Rank;
39   Value *Op;
ValueEntryValueEntry40   ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
41 };
42 inline 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.
48 struct Factor {
49   Value *Base;
50   unsigned Power;
FactorFactor51   Factor(Value *Base, unsigned Power) : Base(Base), Power(Power) {}
52 };
53 
54 class XorOpnd;
55 }
56 
57 /// Reassociate commutative expressions.
58 class ReassociatePass : public PassInfoMixin<ReassociatePass> {
59   DenseMap<BasicBlock *, unsigned> RankMap;
60   DenseMap<AssertingVH<Value>, unsigned> ValueRankMap;
61   SetVector<AssertingVH<Instruction>> RedoInsts;
62   bool MadeChange;
63 
64 public:
65   PreservedAnalyses run(Function &F, FunctionAnalysisManager &);
66 
67 private:
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