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 {
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;
36 typedef std::pair<BasicBlock *, BasicBlock *> Edge;
38 DenseMap<Edge, uint32_t> Weights;
40 // Get sum of the block successors' weights.
41 uint32_t getSumForBlock(BasicBlock *BB) const;
46 BranchProbabilityInfo() : FunctionPass(ID) {
47 initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
50 void getAnalysisUsage(AnalysisUsage &AU) const;
52 bool runOnFunction(Function &F);
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;
58 // Look at BranchProbabilityInfo.cpp for details. Use it with caution!
59 void setEdgeWeight(BasicBlock *Src, BasicBlock *Dst, uint32_t Weight);
61 // A 'Hot' edge is an edge which probability is >= 80%.
62 bool isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const;
64 // Return a hot successor for the block BB or null if there isn't one.
65 BasicBlock *getHotSucc(BasicBlock *BB) const;
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;
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;