BranchProbabilityInfo.h revision 12af93ae86cb4a517d1b67f9363fbf21f24f583b 
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<BasicBlock *, BasicBlock *> Edge;
37
38  DenseMap<Edge, uint32_t> Weights;
39
40  // Get sum of the block successors' weights.
41  uint32_t getSumForBlock(BasicBlock *BB) const;
42
43public:
44  static char ID;
45
46  BranchProbabilityInfo() : FunctionPass(ID) {
47    initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
48  }
49
50  void getAnalysisUsage(AnalysisUsage &AU) const;
51
52  bool runOnFunction(Function &F);
53
54  // Returned value is between 1 and UINT32_MAX. Look at
55  // BranchProbabilityInfo.cpp for details.
56  uint32_t getEdgeWeight(BasicBlock *Src, BasicBlock *Dst) const;
57
58  // Look at BranchProbabilityInfo.cpp for details. Use it with caution!
59  void setEdgeWeight(BasicBlock *Src, BasicBlock *Dst, uint32_t Weight);
60
61  // A 'Hot' edge is an edge which probability is >= 80%.
62  bool isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const;
63
64  // Return a hot successor for the block BB or null if there isn't one.
65  BasicBlock *getHotSucc(BasicBlock *BB) const;
66
67  // Return a probability as a fraction between 0 (0% probability) and
68  // 1 (100% probability), however the value is never equal to 0, and can be 1
69  // only iff SRC block has only one successor.
70  BranchProbability getEdgeProbability(BasicBlock *Src, BasicBlock *Dst) const;
71
72  // Print value between 0 (0% probability) and 1 (100% probability),
73  // however the value is never equal to 0, and can be 1 only iff SRC block
74  // has only one successor.
75  raw_ostream &printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
76                                    BasicBlock *Dst) const;
77};
78
79}
80
81#endif
82