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 namespace llvm { 29 cl::opt<unsigned> 30 StaticLikelyProb("static-likely-prob", 31 cl::desc("branch probability threshold in percentage" 32 "to be considered very likely"), 33 cl::init(80), cl::Hidden); 34 35 cl::opt<unsigned> ProfileLikelyProb( 36 "profile-likely-prob", 37 cl::desc("branch probability threshold in percentage to be considered" 38 " very likely when profile is available"), 39 cl::init(51), cl::Hidden); 40 } // namespace llvm 41 42 char MachineBranchProbabilityInfo::ID = 0; 43 44 MachineBranchProbabilityInfo::MachineBranchProbabilityInfo() 45 : ImmutablePass(ID) { 46 PassRegistry &Registry = *PassRegistry::getPassRegistry(); 47 initializeMachineBranchProbabilityInfoPass(Registry); 48 } 49 50 void MachineBranchProbabilityInfo::anchor() {} 51 52 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability( 53 const MachineBasicBlock *Src, 54 MachineBasicBlock::const_succ_iterator Dst) const { 55 return Src->getSuccProbability(Dst); 56 } 57 58 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability( 59 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const { 60 // This is a linear search. Try to use the const_succ_iterator version when 61 // possible. 62 return getEdgeProbability(Src, find(Src->successors(), Dst)); 63 } 64 65 bool MachineBranchProbabilityInfo::isEdgeHot( 66 const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const { 67 BranchProbability HotProb(StaticLikelyProb, 100); 68 return getEdgeProbability(Src, Dst) > HotProb; 69 } 70 71 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability( 72 raw_ostream &OS, const MachineBasicBlock *Src, 73 const MachineBasicBlock *Dst) const { 74 75 const BranchProbability Prob = getEdgeProbability(Src, Dst); 76 OS << "edge " << printMBBReference(*Src) << " -> " << printMBBReference(*Dst) 77 << " probability is " << Prob 78 << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n"); 79 80 return OS; 81 } 82