1 //===--- BranchProbabilityInfo.h - Branch Probability Analysis --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass is used to evaluate branch probabilties.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
15 #define LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
17 #include "llvm/InitializePasses.h"
18 #include "llvm/Pass.h"
19 #include "llvm/ADT/DenseMap.h"
20 #include "llvm/Support/BranchProbability.h"
26 class BranchProbabilityInfo : public FunctionPass {
30 BranchProbabilityInfo() : FunctionPass(ID) {
31 initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
34 void getAnalysisUsage(AnalysisUsage &AU) const;
35 bool runOnFunction(Function &F);
36 void print(raw_ostream &OS, const Module *M = 0) const;
38 // Returned value is between 1 and UINT32_MAX. Look at
39 // BranchProbabilityInfo.cpp for details.
40 uint32_t getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const;
42 // Look at BranchProbabilityInfo.cpp for details. Use it with caution!
43 void setEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst,
46 // A 'Hot' edge is an edge which probability is >= 80%.
47 bool isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const;
49 // Return a hot successor for the block BB or null if there isn't one.
50 BasicBlock *getHotSucc(BasicBlock *BB) const;
52 // Return a probability as a fraction between 0 (0% probability) and
53 // 1 (100% probability), however the value is never equal to 0, and can be 1
54 // only iff SRC block has only one successor.
55 BranchProbability getEdgeProbability(const BasicBlock *Src,
56 const BasicBlock *Dst) const;
58 // Print value between 0 (0% probability) and 1 (100% probability),
59 // however the value is never equal to 0, and can be 1 only iff SRC block
60 // has only one successor.
61 raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src,
62 const BasicBlock *Dst) const;
65 typedef std::pair<const BasicBlock *, const BasicBlock *> Edge;
67 // Default weight value. Used when we don't have information about the edge.
68 // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
69 // the successors have a weight yet. But it doesn't make sense when providing
70 // weight to an edge that may have siblings with non-zero weights. This can
71 // be handled various ways, but it's probably fine for an edge with unknown
72 // weight to just "inherit" the non-zero weight of an adjacent successor.
73 static const uint32_t DEFAULT_WEIGHT = 16;
75 DenseMap<Edge, uint32_t> Weights;
77 /// \brief Handle to the LoopInfo analysis.
80 /// \brief Track the last function we run over for printing.
83 /// \brief Get sum of the block successors' weights.
84 uint32_t getSumForBlock(const BasicBlock *BB) const;
86 bool calcMetadataWeights(BasicBlock *BB);
87 bool calcReturnHeuristics(BasicBlock *BB);
88 bool calcPointerHeuristics(BasicBlock *BB);
89 bool calcLoopBranchHeuristics(BasicBlock *BB);
90 bool calcZeroHeuristics(BasicBlock *BB);
91 bool calcFloatingPointHeuristics(BasicBlock *BB);