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/Constants.h" 24 #include "llvm/IR/Function.h" 25 #include "llvm/IR/GlobalAlias.h" 26 #include "llvm/IR/GlobalObject.h" 27 #include "llvm/IR/GlobalValue.h" 28 #include "llvm/IR/Module.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<GlobalIndirectSymbol>(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 // Adds all GlobalValue users of V to the same cluster as GV. 59 static void addAllGlobalValueUsers(ClusterMapType &GVtoClusterMap, 60 const GlobalValue *GV, const Value *V) { 61 for (auto *U : V->users()) { 62 SmallVector<const User *, 4> Worklist; 63 Worklist.push_back(U); 64 while (!Worklist.empty()) { 65 const User *UU = Worklist.pop_back_val(); 66 // For each constant that is not a GV (a pure const) recurse. 67 if (isa<Constant>(UU) && !isa<GlobalValue>(UU)) { 68 Worklist.append(UU->user_begin(), UU->user_end()); 69 continue; 70 } 71 addNonConstUser(GVtoClusterMap, GV, UU); 72 } 73 } 74 } 75 76 // Find partitions for module in the way that no locals need to be 77 // globalized. 78 // Try to balance pack those partitions into N files since this roughly equals 79 // thread balancing for the backend codegen step. 80 static void findPartitions(Module *M, ClusterIDMapType &ClusterIDMap, 81 unsigned N) { 82 // At this point module should have the proper mix of globals and locals. 83 // As we attempt to partition this module, we must not change any 84 // locals to globals. 85 DEBUG(dbgs() << "Partition module with (" << M->size() << ")functions\n"); 86 ClusterMapType GVtoClusterMap; 87 ComdatMembersType ComdatMembers; 88 89 auto recordGVSet = [&GVtoClusterMap, &ComdatMembers](GlobalValue &GV) { 90 if (GV.isDeclaration()) 91 return; 92 93 if (!GV.hasName()) 94 GV.setName("__llvmsplit_unnamed"); 95 96 // Comdat groups must not be partitioned. For comdat groups that contain 97 // locals, record all their members here so we can keep them together. 98 // Comdat groups that only contain external globals are already handled by 99 // the MD5-based partitioning. 100 if (const Comdat *C = GV.getComdat()) { 101 auto &Member = ComdatMembers[C]; 102 if (Member) 103 GVtoClusterMap.unionSets(Member, &GV); 104 else 105 Member = &GV; 106 } 107 108 // For aliases we should not separate them from their aliasees regardless 109 // of linkage. 110 if (auto *GIS = dyn_cast<GlobalIndirectSymbol>(&GV)) { 111 if (const GlobalObject *Base = GIS->getBaseObject()) 112 GVtoClusterMap.unionSets(&GV, Base); 113 } 114 115 if (const Function *F = dyn_cast<Function>(&GV)) { 116 for (const BasicBlock &BB : *F) { 117 BlockAddress *BA = BlockAddress::lookup(&BB); 118 if (!BA || !BA->isConstantUsed()) 119 continue; 120 addAllGlobalValueUsers(GVtoClusterMap, F, BA); 121 } 122 } 123 124 if (GV.hasLocalLinkage()) 125 addAllGlobalValueUsers(GVtoClusterMap, &GV, &GV); 126 }; 127 128 std::for_each(M->begin(), M->end(), recordGVSet); 129 std::for_each(M->global_begin(), M->global_end(), recordGVSet); 130 std::for_each(M->alias_begin(), M->alias_end(), recordGVSet); 131 132 // Assigned all GVs to merged clusters while balancing number of objects in 133 // each. 134 auto CompareClusters = [](const std::pair<unsigned, unsigned> &a, 135 const std::pair<unsigned, unsigned> &b) { 136 if (a.second || b.second) 137 return a.second > b.second; 138 else 139 return a.first > b.first; 140 }; 141 142 std::priority_queue<std::pair<unsigned, unsigned>, 143 std::vector<std::pair<unsigned, unsigned>>, 144 decltype(CompareClusters)> 145 BalancinQueue(CompareClusters); 146 // Pre-populate priority queue with N slot blanks. 147 for (unsigned i = 0; i < N; ++i) 148 BalancinQueue.push(std::make_pair(i, 0)); 149 150 typedef std::pair<unsigned, ClusterMapType::iterator> SortType; 151 SmallVector<SortType, 64> Sets; 152 SmallPtrSet<const GlobalValue *, 32> Visited; 153 154 // To guarantee determinism, we have to sort SCC according to size. 155 // When size is the same, use leader's name. 156 for (ClusterMapType::iterator I = GVtoClusterMap.begin(), 157 E = GVtoClusterMap.end(); I != E; ++I) 158 if (I->isLeader()) 159 Sets.push_back( 160 std::make_pair(std::distance(GVtoClusterMap.member_begin(I), 161 GVtoClusterMap.member_end()), I)); 162 163 std::sort(Sets.begin(), Sets.end(), [](const SortType &a, const SortType &b) { 164 if (a.first == b.first) 165 return a.second->getData()->getName() > b.second->getData()->getName(); 166 else 167 return a.first > b.first; 168 }); 169 170 for (auto &I : Sets) { 171 unsigned CurrentClusterID = BalancinQueue.top().first; 172 unsigned CurrentClusterSize = BalancinQueue.top().second; 173 BalancinQueue.pop(); 174 175 DEBUG(dbgs() << "Root[" << CurrentClusterID << "] cluster_size(" << I.first 176 << ") ----> " << I.second->getData()->getName() << "\n"); 177 178 for (ClusterMapType::member_iterator MI = 179 GVtoClusterMap.findLeader(I.second); 180 MI != GVtoClusterMap.member_end(); ++MI) { 181 if (!Visited.insert(*MI).second) 182 continue; 183 DEBUG(dbgs() << "----> " << (*MI)->getName() 184 << ((*MI)->hasLocalLinkage() ? " l " : " e ") << "\n"); 185 Visited.insert(*MI); 186 ClusterIDMap[*MI] = CurrentClusterID; 187 CurrentClusterSize++; 188 } 189 // Add this set size to the number of entries in this cluster. 190 BalancinQueue.push(std::make_pair(CurrentClusterID, CurrentClusterSize)); 191 } 192 } 193 194 static void externalize(GlobalValue *GV) { 195 if (GV->hasLocalLinkage()) { 196 GV->setLinkage(GlobalValue::ExternalLinkage); 197 GV->setVisibility(GlobalValue::HiddenVisibility); 198 } 199 200 // Unnamed entities must be named consistently between modules. setName will 201 // give a distinct name to each such entity. 202 if (!GV->hasName()) 203 GV->setName("__llvmsplit_unnamed"); 204 } 205 206 // Returns whether GV should be in partition (0-based) I of N. 207 static bool isInPartition(const GlobalValue *GV, unsigned I, unsigned N) { 208 if (auto *GIS = dyn_cast<GlobalIndirectSymbol>(GV)) 209 if (const GlobalObject *Base = GIS->getBaseObject()) 210 GV = Base; 211 212 StringRef Name; 213 if (const Comdat *C = GV->getComdat()) 214 Name = C->getName(); 215 else 216 Name = GV->getName(); 217 218 // Partition by MD5 hash. We only need a few bits for evenness as the number 219 // of partitions will generally be in the 1-2 figure range; the low 16 bits 220 // are enough. 221 MD5 H; 222 MD5::MD5Result R; 223 H.update(Name); 224 H.final(R); 225 return (R[0] | (R[1] << 8)) % N == I; 226 } 227 228 void llvm::SplitModule( 229 std::unique_ptr<Module> M, unsigned N, 230 function_ref<void(std::unique_ptr<Module> MPart)> ModuleCallback, 231 bool PreserveLocals) { 232 if (!PreserveLocals) { 233 for (Function &F : *M) 234 externalize(&F); 235 for (GlobalVariable &GV : M->globals()) 236 externalize(&GV); 237 for (GlobalAlias &GA : M->aliases()) 238 externalize(&GA); 239 for (GlobalIFunc &GIF : M->ifuncs()) 240 externalize(&GIF); 241 } 242 243 // This performs splitting without a need for externalization, which might not 244 // always be possible. 245 ClusterIDMapType ClusterIDMap; 246 findPartitions(M.get(), ClusterIDMap, N); 247 248 // FIXME: We should be able to reuse M as the last partition instead of 249 // cloning it. 250 for (unsigned I = 0; I < N; ++I) { 251 ValueToValueMapTy VMap; 252 std::unique_ptr<Module> MPart( 253 CloneModule(M.get(), VMap, [&](const GlobalValue *GV) { 254 if (ClusterIDMap.count(GV)) 255 return (ClusterIDMap[GV] == I); 256 else 257 return isInPartition(GV, I, N); 258 })); 259 if (I != 0) 260 MPart->setModuleInlineAsm(""); 261 ModuleCallback(std::move(MPart)); 262 } 263 } 264