1 //===- MachineBranchProbabilityInfo.cpp - Machine Branch Probability Info -===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This analysis uses probability info stored in Machine Basic Blocks. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h" 14 #include "llvm/CodeGen/MachineBasicBlock.h" 15 #include "llvm/IR/Instructions.h" 16 #include "llvm/Support/Debug.h" 17 #include "llvm/Support/raw_ostream.h" 18 19 using namespace llvm; 20 21 INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfo, "machine-branch-prob", 22 "Machine Branch Probability Analysis", false, true) 23 INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "machine-branch-prob", 24 "Machine Branch Probability Analysis", false, true) 25 26 cl::opt<unsigned> 27 StaticLikelyProb("static-likely-prob", 28 cl::desc("branch probability threshold in percentage" 29 "to be considered very likely"), 30 cl::init(80), cl::Hidden); 31 32 cl::opt<unsigned> ProfileLikelyProb( 33 "profile-likely-prob", 34 cl::desc("branch probability threshold in percentage to be considered" 35 " very likely when profile is available"), 36 cl::init(51), cl::Hidden); 37 38 char MachineBranchProbabilityInfo::ID = 0; 39 40 void MachineBranchProbabilityInfo::anchor() {} 41 42 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability( 43 const MachineBasicBlock *Src, 44 MachineBasicBlock::const_succ_iterator Dst) const { 45 return Src->getSuccProbability(Dst); 46 } 47 48 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability( 49 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const { 50 // This is a linear search. Try to use the const_succ_iterator version when 51 // possible. 52 return getEdgeProbability(Src, find(Src->successors(), Dst)); 53 } 54 55 bool MachineBranchProbabilityInfo::isEdgeHot( 56 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const { 57 BranchProbability HotProb(StaticLikelyProb, 100); 58 return getEdgeProbability(Src, Dst) > HotProb; 59 } 60 61 MachineBasicBlock * 62 MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const { 63 auto MaxProb = BranchProbability::getZero(); 64 MachineBasicBlock *MaxSucc = nullptr; 65 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(), 66 E = MBB->succ_end(); I != E; ++I) { 67 auto Prob = getEdgeProbability(MBB, I); 68 if (Prob > MaxProb) { 69 MaxProb = Prob; 70 MaxSucc = *I; 71 } 72 } 73 74 BranchProbability HotProb(StaticLikelyProb, 100); 75 if (getEdgeProbability(MBB, MaxSucc) >= HotProb) 76 return MaxSucc; 77 78 return nullptr; 79 } 80 81 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability( 82 raw_ostream &OS, const MachineBasicBlock *Src, 83 const MachineBasicBlock *Dst) const { 84 85 const BranchProbability Prob = getEdgeProbability(Src, Dst); 86 OS << "edge " << printMBBReference(*Src) << " -> " << printMBBReference(*Dst) 87 << " probability is " << Prob 88 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n"); 89 90 return OS; 91 } 92