BranchProbabilityInfo.h revision 14edd314af99ccaad194d071f23e437a1371f176 
1//===--- BranchProbabilityInfo.h - Branch Probability Analysis --*- 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 is used to evaluate branch probabilties.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
15#define LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
16
17#include "llvm/InitializePasses.h"
18#include "llvm/Pass.h"
19#include "llvm/ADT/DenseMap.h"
20#include "llvm/Support/BranchProbability.h"
21
22namespace llvm {
23
24class raw_ostream;
25
26class BranchProbabilityInfo : public FunctionPass {
27
28  // Default weight value. Used when we don't have information about the edge.
29  // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
30  // the successors have a weight yet. But it doesn't make sense when providing
31  // weight to an edge that may have siblings with non-zero weights. This can
32  // be handled various ways, but it's probably fine for an edge with unknown
33  // weight to just "inherit" the non-zero weight of an adjacent successor.
34  static const uint32_t DEFAULT_WEIGHT = 16;
35
36  typedef std::pair<const BasicBlock *, const BasicBlock *> Edge;
37
38  DenseMap<Edge, uint32_t> Weights;
39
40  /// \brief Track the last function we run over for printing.
41  Function *LastF;
42
43  // Get sum of the block successors' weights.
44  uint32_t getSumForBlock(const BasicBlock *BB) const;
45
46public:
47  static char ID;
48
49  BranchProbabilityInfo() : FunctionPass(ID) {
50    initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
51  }
52
53  void getAnalysisUsage(AnalysisUsage &AU) const;
54  bool runOnFunction(Function &F);
55  void print(raw_ostream &OS, const Module *M = 0) const;
56
57  // Returned value is between 1 and UINT32_MAX. Look at
58  // BranchProbabilityInfo.cpp for details.
59  uint32_t getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const;
60
61  // Look at BranchProbabilityInfo.cpp for details. Use it with caution!
62  void setEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst,
63                     uint32_t Weight);
64
65  // A 'Hot' edge is an edge which probability is >= 80%.
66  bool isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const;
67
68  // Return a hot successor for the block BB or null if there isn't one.
69  BasicBlock *getHotSucc(BasicBlock *BB) const;
70
71  // Return a probability as a fraction between 0 (0% probability) and
72  // 1 (100% probability), however the value is never equal to 0, and can be 1
73  // only iff SRC block has only one successor.
74  BranchProbability getEdgeProbability(const BasicBlock *Src,
75                                       const BasicBlock *Dst) const;
76
77  // Print value between 0 (0% probability) and 1 (100% probability),
78  // however the value is never equal to 0, and can be 1 only iff SRC block
79  // has only one successor.
80  raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src,
81                                    const BasicBlock *Dst) const;
82};
83
84}
85
86#endif
87