1 //===- SplitModule.cpp - Split a module into partitions -------------------===// 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 file defines the function llvm::SplitModule, which splits a module 11 // into multiple linkable partitions. It can be used to implement parallel code 12 // generation for link-time optimization. 13 // 14 //===----------------------------------------------------------------------===// 15 16 #define DEBUG_TYPE "split-module" 17 18 #include "llvm/Transforms/Utils/SplitModule.h" 19 #include "llvm/ADT/EquivalenceClasses.h" 20 #include "llvm/ADT/Hashing.h" 21 #include "llvm/ADT/MapVector.h" 22 #include "llvm/ADT/SetVector.h" 23 #include "llvm/IR/Function.h" 24 #include "llvm/IR/GlobalAlias.h" 25 #include "llvm/IR/GlobalObject.h" 26 #include "llvm/IR/GlobalValue.h" 27 #include "llvm/IR/Module.h" 28 #include "llvm/Support/CommandLine.h" 29 #include "llvm/Support/Debug.h" 30 #include "llvm/Support/MD5.h" 31 #include "llvm/Support/raw_ostream.h" 32 #include "llvm/Transforms/Utils/Cloning.h" 33 #include <queue> 34 35 using namespace llvm; 36 37 namespace { 38 typedef EquivalenceClasses<const GlobalValue *> ClusterMapType; 39 typedef DenseMap<const Comdat *, const GlobalValue *> ComdatMembersType; 40 typedef DenseMap<const GlobalValue *, unsigned> ClusterIDMapType; 41 } 42 43 static void addNonConstUser(ClusterMapType &GVtoClusterMap, 44 const GlobalValue *GV, const User *U) { 45 assert((!isa<Constant>(U) || isa<GlobalValue>(U)) && "Bad user"); 46 47 if (const Instruction *I = dyn_cast<Instruction>(U)) { 48 const GlobalValue *F = I->getParent()->getParent(); 49 GVtoClusterMap.unionSets(GV, F); 50 } else if (isa<GlobalAlias>(U) || isa<Function>(U) || 51 isa<GlobalVariable>(U)) { 52 GVtoClusterMap.unionSets(GV, cast<GlobalValue>(U)); 53 } else { 54 llvm_unreachable("Underimplemented use case"); 55 } 56 } 57 58 // Find partitions for module in the way that no locals need to be 59 // globalized. 60 // Try to balance pack those partitions into N files since this roughly equals 61 // thread balancing for the backend codegen step. 62 static void findPartitions(Module *M, ClusterIDMapType &ClusterIDMap, 63 unsigned N) { 64 // At this point module should have the proper mix of globals and locals. 65 // As we attempt to partition this module, we must not change any 66 // locals to globals. 67 68 DEBUG(dbgs() << "Partition module with (" << M->size() << ")functions\n"); 69 ClusterMapType GVtoClusterMap; 70 ComdatMembersType ComdatMembers; 71 72 auto recordGVSet = [&GVtoClusterMap, &ComdatMembers](GlobalValue &GV) { 73 if (GV.isDeclaration()) 74 return; 75 76 if (!GV.hasName()) 77 GV.setName("__llvmsplit_unnamed"); 78 79 // Comdat groups must not be partitioned. For comdat groups that contain 80 // locals, record all their members here so we can keep them together. 81 // Comdat groups that only contain external globals are already handled by 82 // the MD5-based partitioning. 83 if (const Comdat *C = GV.getComdat()) { 84 auto &Member = ComdatMembers[C]; 85 if (Member) 86 GVtoClusterMap.unionSets(Member, &GV); 87 else 88 Member = &GV; 89 } 90 91 // Further only iterate over local GVs. 92 if (!GV.hasLocalLinkage()) 93 return; 94 95 for (auto *U : GV.users()) { 96 SmallVector<const User *, 4> Worklist; 97 Worklist.push_back(U); 98 while (!Worklist.empty()) { 99 const User *UU = Worklist.pop_back_val(); 100 // For each constant that is not a GV (a pure const) recurse. 101 if (isa<Constant>(UU) && !isa<GlobalValue>(UU)) { 102 Worklist.append(UU->user_begin(), UU->user_end()); 103 continue; 104 } 105 addNonConstUser(GVtoClusterMap, &GV, UU); 106 } 107 } 108 }; 109 110 std::for_each(M->begin(), M->end(), recordGVSet); 111 std::for_each(M->global_begin(), M->global_end(), recordGVSet); 112 std::for_each(M->alias_begin(), M->alias_end(), recordGVSet); 113 114 // Assigned all GVs to merged clusters while balancing number of objects in 115 // each. 116 auto CompareClusters = [](const std::pair<unsigned, unsigned> &a, 117 const std::pair<unsigned, unsigned> &b) { 118 if (a.second || b.second) 119 return a.second > b.second; 120 else 121 return a.first > b.first; 122 }; 123 124 std::priority_queue<std::pair<unsigned, unsigned>, 125 std::vector<std::pair<unsigned, unsigned>>, 126 decltype(CompareClusters)> 127 BalancinQueue(CompareClusters); 128 // Pre-populate priority queue with N slot blanks. 129 for (unsigned i = 0; i < N; ++i) 130 BalancinQueue.push(std::make_pair(i, 0)); 131 132 typedef std::pair<unsigned, ClusterMapType::iterator> SortType; 133 SmallVector<SortType, 64> Sets; 134 SmallPtrSet<const GlobalValue *, 64> Visited; 135 136 // To guarantee determinism, we have to sort SCC according to size. 137 // When size is the same, use leader's name. 138 for (ClusterMapType::iterator I = GVtoClusterMap.begin(), 139 E = GVtoClusterMap.end(); I != E; ++I) 140 if (I->isLeader()) 141 Sets.push_back( 142 std::make_pair(std::distance(GVtoClusterMap.member_begin(I), 143 GVtoClusterMap.member_end()), I)); 144 145 std::sort(Sets.begin(), Sets.end(), [](const SortType &a, const SortType &b) { 146 if (a.first == b.first) 147 return a.second->getData()->getName() > b.second->getData()->getName(); 148 else 149 return a.first > b.first; 150 }); 151 152 for (auto &I : Sets) { 153 unsigned CurrentClusterID = BalancinQueue.top().first; 154 unsigned CurrentClusterSize = BalancinQueue.top().second; 155 BalancinQueue.pop(); 156 157 DEBUG(dbgs() << "Root[" << CurrentClusterID << "] cluster_size(" << I.first 158 << ") ----> " << I.second->getData()->getName() << "\n"); 159 160 for (ClusterMapType::member_iterator MI = 161 GVtoClusterMap.findLeader(I.second); 162 MI != GVtoClusterMap.member_end(); ++MI) { 163 if (!Visited.insert(*MI).second) 164 continue; 165 DEBUG(dbgs() << "----> " << (*MI)->getName() 166 << ((*MI)->hasLocalLinkage() ? " l " : " e ") << "\n"); 167 Visited.insert(*MI); 168 ClusterIDMap[*MI] = CurrentClusterID; 169 CurrentClusterSize++; 170 } 171 // Add this set size to the number of entries in this cluster. 172 BalancinQueue.push(std::make_pair(CurrentClusterID, CurrentClusterSize)); 173 } 174 } 175 176 static void externalize(GlobalValue *GV) { 177 if (GV->hasLocalLinkage()) { 178 GV->setLinkage(GlobalValue::ExternalLinkage); 179 GV->setVisibility(GlobalValue::HiddenVisibility); 180 } 181 182 // Unnamed entities must be named consistently between modules. setName will 183 // give a distinct name to each such entity. 184 if (!GV->hasName()) 185 GV->setName("__llvmsplit_unnamed"); 186 } 187 188 // Returns whether GV should be in partition (0-based) I of N. 189 static bool isInPartition(const GlobalValue *GV, unsigned I, unsigned N) { 190 if (auto GA = dyn_cast<GlobalAlias>(GV)) 191 if (const GlobalObject *Base = GA->getBaseObject()) 192 GV = Base; 193 194 StringRef Name; 195 if (const Comdat *C = GV->getComdat()) 196 Name = C->getName(); 197 else 198 Name = GV->getName(); 199 200 // Partition by MD5 hash. We only need a few bits for evenness as the number 201 // of partitions will generally be in the 1-2 figure range; the low 16 bits 202 // are enough. 203 MD5 H; 204 MD5::MD5Result R; 205 H.update(Name); 206 H.final(R); 207 return (R[0] | (R[1] << 8)) % N == I; 208 } 209 210 void llvm::SplitModule( 211 std::unique_ptr<Module> M, unsigned N, 212 std::function<void(std::unique_ptr<Module> MPart)> ModuleCallback, 213 bool PreserveLocals) { 214 if (!PreserveLocals) { 215 for (Function &F : *M) 216 externalize(&F); 217 for (GlobalVariable &GV : M->globals()) 218 externalize(&GV); 219 for (GlobalAlias &GA : M->aliases()) 220 externalize(&GA); 221 222 // FIXME: We should be able to reuse M as the last partition instead of 223 // cloning it. 224 for (unsigned I = 0; I != N; ++I) { 225 ValueToValueMapTy VMap; 226 std::unique_ptr<Module> MPart( 227 CloneModule(M.get(), VMap, [=](const GlobalValue *GV) { 228 return isInPartition(GV, I, N); 229 })); 230 if (I != 0) 231 MPart->setModuleInlineAsm(""); 232 ModuleCallback(std::move(MPart)); 233 } 234 } else { 235 // This performs splitting without a need for externalization, which might not 236 // always be possible. 237 ClusterIDMapType ClusterIDMap; 238 findPartitions(M.get(), ClusterIDMap, N); 239 240 for (unsigned I = 0; I < N; ++I) { 241 ValueToValueMapTy VMap; 242 std::unique_ptr<Module> MPart( 243 CloneModule(M.get(), VMap, [&](const GlobalValue *GV) { 244 if (ClusterIDMap.count(GV)) 245 return (ClusterIDMap[GV] == I); 246 else 247 return isInPartition(GV, I, N); 248 })); 249 if (I != 0) 250 MPart->setModuleInlineAsm(""); 251 ModuleCallback(std::move(MPart)); 252 } 253 } 254 } 255