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/InitializePasses.h" 17 #include "llvm/Support/CommandLine.h" 18 #include "llvm/Support/Debug.h" 19 #include "llvm/Support/raw_ostream.h" 20 21 using namespace llvm; 22 23 INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfo, "machine-branch-prob", 24 "Machine Branch Probability Analysis", false, true) 25 INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "machine-branch-prob", 26 "Machine Branch Probability Analysis", false, true) 27 28 cl::opt<unsigned> 29 StaticLikelyProb("static-likely-prob", 30 cl::desc("branch probability threshold in percentage" 31 "to be considered very likely"), 32 cl::init(80), cl::Hidden); 33 34 cl::opt<unsigned> ProfileLikelyProb( 35 "profile-likely-prob", 36 cl::desc("branch probability threshold in percentage to be considered" 37 " very likely when profile is available"), 38 cl::init(51), cl::Hidden); 39 40 char MachineBranchProbabilityInfo::ID = 0; 41 42 MachineBranchProbabilityInfo::MachineBranchProbabilityInfo() 43 : ImmutablePass(ID) { 44 PassRegistry &Registry = *PassRegistry::getPassRegistry(); 45 initializeMachineBranchProbabilityInfoPass(Registry); 46 } 47 48 void MachineBranchProbabilityInfo::anchor() {} 49 50 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability( 51 const MachineBasicBlock *Src, 52 MachineBasicBlock::const_succ_iterator Dst) const { 53 return Src->getSuccProbability(Dst); 54 } 55 56 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability( 57 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const { 58 // This is a linear search. Try to use the const_succ_iterator version when 59 // possible. 60 return getEdgeProbability(Src, find(Src->successors(), Dst)); 61 } 62 63 bool MachineBranchProbabilityInfo::isEdgeHot( 64 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const { 65 BranchProbability HotProb(StaticLikelyProb, 100); 66 return getEdgeProbability(Src, Dst) > HotProb; 67 } 68 69 MachineBasicBlock * 70 MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const { 71 auto MaxProb = BranchProbability::getZero(); 72 MachineBasicBlock *MaxSucc = nullptr; 73 for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(), 74 E = MBB->succ_end(); I != E; ++I) { 75 auto Prob = getEdgeProbability(MBB, I); 76 if (Prob > MaxProb) { 77 MaxProb = Prob; 78 MaxSucc = *I; 79 } 80 } 81 82 BranchProbability HotProb(StaticLikelyProb, 100); 83 if (getEdgeProbability(MBB, MaxSucc) >= HotProb) 84 return MaxSucc; 85 86 return nullptr; 87 } 88 89 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability( 90 raw_ostream &OS, const MachineBasicBlock *Src, 91 const MachineBasicBlock *Dst) const { 92 93 const BranchProbability Prob = getEdgeProbability(Src, Dst); 94 OS << "edge " << printMBBReference(*Src) << " -> " << printMBBReference(*Dst) 95 << " probability is " << Prob 96 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n"); 97 98 return OS; 99 } 100