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/Support/BranchProbability.h"
19 #include "llvm/Analysis/LoopInfo.h"
25 class BranchProbabilityInfo : public FunctionPass {
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;
35 typedef std::pair<BasicBlock *, BasicBlock *> Edge;
37 DenseMap<Edge, uint32_t> Weights;
39 // Get sum of the block successors' weights.
40 uint32_t getSumForBlock(BasicBlock *BB) const;
42 // Get sum of the edge weights going to the BB block.
43 uint32_t getBackSumForBlock(BasicBlock *BB) const;
48 BranchProbabilityInfo() : FunctionPass(ID) {
49 initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry());
52 void getAnalysisUsage(AnalysisUsage &AU) const {
53 AU.addRequired<LoopInfo>();
57 bool runOnFunction(Function &F);
59 // Returned value is between 1 and UINT32_MAX. Look at
60 // BranchProbabilityInfo.cpp for details.
61 uint32_t getEdgeWeight(BasicBlock *Src, BasicBlock *Dst) const;
63 // Look at BranchProbabilityInfo.cpp for details. Use it with caution!
64 void setEdgeWeight(BasicBlock *Src, BasicBlock *Dst, uint32_t Weight);
66 // A 'Hot' edge is an edge which probability is >= 80%.
67 bool isEdgeHot(BasicBlock *Src, BasicBlock *Dst) const;
69 // Return a hot successor for the block BB or null if there isn't one.
70 BasicBlock *getHotSucc(BasicBlock *BB) const;
72 // Return a probability as a fraction between 0 (0% probability) and
73 // 1 (100% probability), however the value is never equal to 0, and can be 1
74 // only iff SRC block has only one successor.
75 BranchProbability getEdgeProbability(BasicBlock *Src, BasicBlock *Dst) const;
77 // Return a probability of getting to the DST block through SRC->DST edge.
78 // Returned value is a fraction between 0 (0% probability) and
79 // 1 (100% probability), however the value is never equal to 0, and can be 1
80 // only iff DST block has only one predecesor.
81 BranchProbability getBackEdgeProbability(BasicBlock *Src,
82 BasicBlock *Dst) const;
84 // Print value between 0 (0% probability) and 1 (100% probability),
85 // however the value is never equal to 0, and can be 1 only iff SRC block
86 // has only one successor.
87 raw_ostream &printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
88 BasicBlock *Dst) const;