1 //===-- BranchFolding.h - Fold machine code branch instructions -*- 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 #ifndef LLVM_LIB_CODEGEN_BRANCHFOLDING_H
11 #define LLVM_LIB_CODEGEN_BRANCHFOLDING_H
12 
13 #include "llvm/ADT/SmallPtrSet.h"
14 #include "llvm/CodeGen/MachineBasicBlock.h"
15 #include "llvm/Support/BlockFrequency.h"
16 #include <vector>
17 
18 namespace llvm {
19   class MachineBlockFrequencyInfo;
20   class MachineBranchProbabilityInfo;
21   class MachineFunction;
22   class MachineModuleInfo;
23   class RegScavenger;
24   class TargetInstrInfo;
25   class TargetRegisterInfo;
26 
27   class BranchFolder {
28   public:
29     explicit BranchFolder(bool defaultEnableTailMerge, bool CommonHoist,
30                           const MachineBlockFrequencyInfo &MBFI,
31                           const MachineBranchProbabilityInfo &MBPI);
32 
33     bool OptimizeFunction(MachineFunction &MF,
34                           const TargetInstrInfo *tii,
35                           const TargetRegisterInfo *tri,
36                           MachineModuleInfo *mmi);
37   private:
38     class MergePotentialsElt {
39       unsigned Hash;
40       MachineBasicBlock *Block;
41     public:
MergePotentialsElt(unsigned h,MachineBasicBlock * b)42       MergePotentialsElt(unsigned h, MachineBasicBlock *b)
43         : Hash(h), Block(b) {}
44 
getHash()45       unsigned getHash() const { return Hash; }
getBlock()46       MachineBasicBlock *getBlock() const { return Block; }
47 
setBlock(MachineBasicBlock * MBB)48       void setBlock(MachineBasicBlock *MBB) {
49         Block = MBB;
50       }
51 
52       bool operator<(const MergePotentialsElt &) const;
53     };
54     typedef std::vector<MergePotentialsElt>::iterator MPIterator;
55     std::vector<MergePotentialsElt> MergePotentials;
56     SmallPtrSet<const MachineBasicBlock*, 2> TriedMerging;
57 
58     class SameTailElt {
59       MPIterator MPIter;
60       MachineBasicBlock::iterator TailStartPos;
61     public:
SameTailElt(MPIterator mp,MachineBasicBlock::iterator tsp)62       SameTailElt(MPIterator mp, MachineBasicBlock::iterator tsp)
63         : MPIter(mp), TailStartPos(tsp) {}
64 
getMPIter()65       MPIterator getMPIter() const {
66         return MPIter;
67       }
getMergePotentialsElt()68       MergePotentialsElt &getMergePotentialsElt() const {
69         return *getMPIter();
70       }
getTailStartPos()71       MachineBasicBlock::iterator getTailStartPos() const {
72         return TailStartPos;
73       }
getHash()74       unsigned getHash() const {
75         return getMergePotentialsElt().getHash();
76       }
getBlock()77       MachineBasicBlock *getBlock() const {
78         return getMergePotentialsElt().getBlock();
79       }
tailIsWholeBlock()80       bool tailIsWholeBlock() const {
81         return TailStartPos == getBlock()->begin();
82       }
83 
setBlock(MachineBasicBlock * MBB)84       void setBlock(MachineBasicBlock *MBB) {
85         getMergePotentialsElt().setBlock(MBB);
86       }
setTailStartPos(MachineBasicBlock::iterator Pos)87       void setTailStartPos(MachineBasicBlock::iterator Pos) {
88         TailStartPos = Pos;
89       }
90     };
91     std::vector<SameTailElt> SameTails;
92 
93     bool EnableTailMerge;
94     bool EnableHoistCommonCode;
95     const TargetInstrInfo *TII;
96     const TargetRegisterInfo *TRI;
97     MachineModuleInfo *MMI;
98     RegScavenger *RS;
99 
100     /// \brief This class keeps track of branch frequencies of newly created
101     /// blocks and tail-merged blocks.
102     class MBFIWrapper {
103     public:
MBFIWrapper(const MachineBlockFrequencyInfo & I)104       MBFIWrapper(const MachineBlockFrequencyInfo &I) : MBFI(I) {}
105       BlockFrequency getBlockFreq(const MachineBasicBlock *MBB) const;
106       void setBlockFreq(const MachineBasicBlock *MBB, BlockFrequency F);
107 
108     private:
109       const MachineBlockFrequencyInfo &MBFI;
110       DenseMap<const MachineBasicBlock *, BlockFrequency> MergedBBFreq;
111     };
112 
113     MBFIWrapper MBBFreqInfo;
114     const MachineBranchProbabilityInfo &MBPI;
115 
116     bool TailMergeBlocks(MachineFunction &MF);
117     bool TryTailMergeBlocks(MachineBasicBlock* SuccBB,
118                        MachineBasicBlock* PredBB);
119     void setCommonTailEdgeWeights(MachineBasicBlock &TailMBB);
120     void MaintainLiveIns(MachineBasicBlock *CurMBB,
121                          MachineBasicBlock *NewMBB);
122     void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
123                                  MachineBasicBlock *NewDest);
124     MachineBasicBlock *SplitMBBAt(MachineBasicBlock &CurMBB,
125                                   MachineBasicBlock::iterator BBI1,
126                                   const BasicBlock *BB);
127     unsigned ComputeSameTails(unsigned CurHash, unsigned minCommonTailLength,
128                               MachineBasicBlock *SuccBB,
129                               MachineBasicBlock *PredBB);
130     void RemoveBlocksWithHash(unsigned CurHash, MachineBasicBlock* SuccBB,
131                                                 MachineBasicBlock* PredBB);
132     bool CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
133                                    MachineBasicBlock *SuccBB,
134                                    unsigned maxCommonTailLength,
135                                    unsigned &commonTailIndex);
136 
137     bool OptimizeBranches(MachineFunction &MF);
138     bool OptimizeBlock(MachineBasicBlock *MBB);
139     void RemoveDeadBlock(MachineBasicBlock *MBB);
140     bool OptimizeImpDefsBlock(MachineBasicBlock *MBB);
141 
142     bool HoistCommonCode(MachineFunction &MF);
143     bool HoistCommonCodeInSuccs(MachineBasicBlock *MBB);
144   };
145 }
146 
147 #endif /* LLVM_CODEGEN_BRANCHFOLDING_HPP */
148