BranchProbabilityInfo.h revision 66dddd1da3e036d05f94df82221a97b7d26e3498 
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/Support/BranchProbability.h"
19#include "llvm/Analysis/LoopInfo.h"
20
21namespace llvm {
22
23class raw_ostream;
24
25class BranchProbabilityInfo : public FunctionPass {
26
27  // Default weight value. Used when we don't have information about the edge.
28  // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
29  // the successors have a weight yet. But it doesn't make sense when providing
30  // weight to an edge that may have siblings with non-zero weights. This can
31  // be handled various ways, but it's probably fine for an edge with unknown
32  // weight to just "inherit" the non-zero weight of an adjacent successor.
33  static const uint32_t DEFAULT_WEIGHT = 16;
34
35  typedef std::pair<BasicBlock *, BasicBlock *> Edge;
36
37  DenseMap<Edge, uint32_t> Weights;
38
39  // Get sum of the block successors' weights.
40  uint32_t getSumForBlock(BasicBlock *BB) const;
41
42public:
43  static char ID;
44
45  BranchProbabilityInfo() : FunctionPass(ID) {
46    initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
47  }
48
49  void getAnalysisUsage(AnalysisUsage &AU) const {
50    AU.addRequired<LoopInfo>();
51    AU.setPreservesAll();
52  }
53
54  bool runOnFunction(Function &F);
55
56  // Returned value is between 1 and UINT32_MAX. Look at
57  // BranchProbabilityInfo.cpp for details.
58  uint32_t getEdgeWeight(BasicBlock *Src, BasicBlock *Dst) const;
59
60  // Look at BranchProbabilityInfo.cpp for details. Use it with caution!
61  void setEdgeWeight(BasicBlock *Src, BasicBlock *Dst, uint32_t Weight);
62
63  // A 'Hot' edge is an edge which probability is >= 80%.
64  bool isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const;
65
66  // Return a hot successor for the block BB or null if there isn't one.
67  BasicBlock *getHotSucc(BasicBlock *BB) const;
68
69  // Return a probability as a fraction between 0 (0% probability) and
70  // 1 (100% probability), however the value is never equal to 0, and can be 1
71  // only iff SRC block has only one successor.
72  BranchProbability getEdgeProbability(BasicBlock *Src, BasicBlock *Dst) const;
73
74  // Print value between 0 (0% probability) and 1 (100% probability),
75  // however the value is never equal to 0, and can be 1 only iff SRC block
76  // has only one successor.
77  raw_ostream &printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
78                                    BasicBlock *Dst) const;
79};
80
81}
82
83#endif
84