BranchProbabilityInfo.h revision 9e76422b963a65f243fdbee0abed61068b82dd98 
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/Analysis/LoopInfo.h"
19#include "llvm/Support/Debug.h"
20
21namespace llvm {
22
23class BranchProbabilityInfo : public FunctionPass {
24
25  // Default weight value. Used when we don't have information about the edge.
26  static const unsigned int DEFAULT_WEIGHT = 16;
27
28  typedef std::pair<BasicBlock *, BasicBlock *> Edge;
29
30  DenseMap<Edge, unsigned> Weights;
31
32public:
33  static char ID;
34
35  BranchProbabilityInfo() : FunctionPass(ID) {
36    initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
37  }
38
39  void getAnalysisUsage(AnalysisUsage &AU) const {
40    AU.addRequired<LoopInfo>();
41    AU.setPreservesAll();
42  }
43
44  bool runOnFunction(Function &F);
45
46  // Returned value is between 1 and UINT_MAX. Look at BranchProbabilityInfo.cpp
47  // for details.
48  unsigned getEdgeWeight(BasicBlock *Src, BasicBlock *Dst) const;
49
50  // Look at BranchProbabilityInfo.cpp for details. Use it with caution!
51  void setEdgeWeight(BasicBlock *Src, BasicBlock *Dst, unsigned Weight);
52
53  // A 'Hot' edge is an edge which probability is >= 80%.
54  bool isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const;
55
56  // Return a hot successor for the block BB or null if there isn't one.
57  BasicBlock *getHotSucc(BasicBlock *BB) const;
58
59  // Print value between 0 (0% probability) and 1 (100% probability),
60  // however the value is never equal to 0, and can be 1 only iff SRC block
61  // has only one successor.
62  raw_ostream &printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
63                                   BasicBlock *Dst) const;
64};
65
66}
67
68#endif
69