1 //===- MachineBranchProbabilityInfo.cpp - Machine Branch Probability Info -===// 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 analysis uses probability info stored in Machine Basic Blocks. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h" 15 #include "llvm/CodeGen/MachineBasicBlock.h" 16 #include "llvm/IR/Instructions.h" 17 #include "llvm/Support/Debug.h" 18 #include "llvm/Support/raw_ostream.h" 19 20 using namespace llvm; 21 22 INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfo, "machine-branch-prob", 23 "Machine Branch Probability Analysis", false, true) 24 INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "machine-branch-prob", 25 "Machine Branch Probability Analysis", false, true) 26 27 cl::opt<unsigned> 28 StaticLikelyProb("static-likely-prob", 29 cl::desc("branch probability threshold in percentage" 30 "to be considered very likely"), 31 cl::init(80), cl::Hidden); 32 33 cl::opt<unsigned> ProfileLikelyProb( 34 "profile-likely-prob", 35 cl::desc("branch probability threshold in percentage to be considered" 36 " very likely when profile is available"), 37 cl::init(51), cl::Hidden); 38 39 char MachineBranchProbabilityInfo::ID = 0; 40 41 void MachineBranchProbabilityInfo::anchor() {} 42 43 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability( 44 const MachineBasicBlock *Src, 45 MachineBasicBlock::const_succ_iterator Dst) const { 46 return Src->getSuccProbability(Dst); 47 } 48 49 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability( 50 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const { 51 // This is a linear search. Try to use the const_succ_iterator version when 52 // possible. 53 return getEdgeProbability(Src, 54 std::find(Src->succ_begin(), Src->succ_end(), Dst)); 55 } 56 57 bool MachineBranchProbabilityInfo::isEdgeHot( 58 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const { 59 BranchProbability HotProb(StaticLikelyProb, 100); 60 return getEdgeProbability(Src, Dst) > HotProb; 61 } 62 63 MachineBasicBlock * 64 MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const { 65 auto MaxProb = BranchProbability::getZero(); 66 MachineBasicBlock *MaxSucc = nullptr; 67 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(), 68 E = MBB->succ_end(); I != E; ++I) { 69 auto Prob = getEdgeProbability(MBB, I); 70 if (Prob > MaxProb) { 71 MaxProb = Prob; 72 MaxSucc = *I; 73 } 74 } 75 76 BranchProbability HotProb(StaticLikelyProb, 100); 77 if (getEdgeProbability(MBB, MaxSucc) >= HotProb) 78 return MaxSucc; 79 80 return nullptr; 81 } 82 83 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability( 84 raw_ostream &OS, const MachineBasicBlock *Src, 85 const MachineBasicBlock *Dst) const { 86 87 const BranchProbability Prob = getEdgeProbability(Src, Dst); 88 OS << "edge MBB#" << Src->getNumber() << " -> MBB#" << Dst->getNumber() 89 << " probability is " << Prob 90 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n"); 91 92 return OS; 93 } 94
