include/llvm/Analysis/BranchProbabilityInfo.h

   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
  21 namespace llvm {
  22
  23 class 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
  32 public:
  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