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 #include "llvm/Transforms/Utils/SplitModule.h" 17 #include "llvm/ADT/DenseMap.h" 18 #include "llvm/ADT/EquivalenceClasses.h" 19 #include "llvm/ADT/SmallPtrSet.h" 20 #include "llvm/ADT/SmallVector.h" 21 #include "llvm/ADT/StringRef.h" 22 #include "llvm/IR/Comdat.h" 23 #include "llvm/IR/Constant.h" 24 #include "llvm/IR/Constants.h" 25 #include "llvm/IR/Function.h" 26 #include "llvm/IR/GlobalAlias.h" 27 #include "llvm/IR/GlobalObject.h" 28 #include "llvm/IR/GlobalIndirectSymbol.h" 29 #include "llvm/IR/GlobalValue.h" 30 #include "llvm/IR/GlobalVariable.h" 31 #include "llvm/IR/Instruction.h" 32 #include "llvm/IR/Module.h" 33 #include "llvm/IR/User.h" 34 #include "llvm/IR/Value.h" 35 #include "llvm/Support/Casting.h" 36 #include "llvm/Support/Debug.h" 37 #include "llvm/Support/ErrorHandling.h" 38 #include "llvm/Support/MD5.h" 39 #include "llvm/Support/raw_ostream.h" 40 #include "llvm/Transforms/Utils/Cloning.h" 41 #include "llvm/Transforms/Utils/ValueMapper.h" 42 #include <algorithm> 43 #include <cassert> 44 #include <iterator> 45 #include <memory> 46 #include <queue> 47 #include <utility> 48 #include <vector> 49 50 using namespace llvm; 51 52 #define DEBUG_TYPE "split-module" 53 54 namespace { 55 56 using ClusterMapType = EquivalenceClasses<const GlobalValue *>; 57 using ComdatMembersType = DenseMap<const Comdat *, const GlobalValue *>; 58 using ClusterIDMapType = DenseMap<const GlobalValue *, unsigned>; 59 60 } // end anonymous namespace 61 62 static void addNonConstUser(ClusterMapType &GVtoClusterMap, 63 const GlobalValue *GV, const User *U) { 64 assert((!isa<Constant>(U) || isa<GlobalValue>(U)) && "Bad user"); 65 66 if (const Instruction *I = dyn_cast<Instruction>(U)) { 67 const GlobalValue *F = I->getParent()->getParent(); 68 GVtoClusterMap.unionSets(GV, F); 69 } else if (isa<GlobalIndirectSymbol>(U) || isa<Function>(U) || 70 isa<GlobalVariable>(U)) { 71 GVtoClusterMap.unionSets(GV, cast<GlobalValue>(U)); 72 } else { 73 llvm_unreachable("Underimplemented use case"); 74 } 75 } 76 77 // Adds all GlobalValue users of V to the same cluster as GV. 78 static void addAllGlobalValueUsers(ClusterMapType &GVtoClusterMap, 79 const GlobalValue *GV, const Value *V) { 80 for (auto *U : V->users()) { 81 SmallVector<const User *, 4> Worklist; 82 Worklist.push_back(U); 83 while (!Worklist.empty()) { 84 const User *UU = Worklist.pop_back_val(); 85 // For each constant that is not a GV (a pure const) recurse. 86 if (isa<Constant>(UU) && !isa<GlobalValue>(UU)) { 87 Worklist.append(UU->user_begin(), UU->user_end()); 88 continue; 89 } 90 addNonConstUser(GVtoClusterMap, GV, UU); 91 } 92 } 93 } 94 95 // Find partitions for module in the way that no locals need to be 96 // globalized. 97 // Try to balance pack those partitions into N files since this roughly equals 98 // thread balancing for the backend codegen step. 99 static void findPartitions(Module *M, ClusterIDMapType &ClusterIDMap, 100 unsigned N) { 101 // At this point module should have the proper mix of globals and locals. 102 // As we attempt to partition this module, we must not change any 103 // locals to globals. 104 DEBUG(dbgs() << "Partition module with (" << M->size() << ")functions\n"); 105 ClusterMapType GVtoClusterMap; 106 ComdatMembersType ComdatMembers; 107 108 auto recordGVSet = [&GVtoClusterMap, &ComdatMembers](GlobalValue &GV) { 109 if (GV.isDeclaration()) 110 return; 111 112 if (!GV.hasName()) 113 GV.setName("__llvmsplit_unnamed"); 114 115 // Comdat groups must not be partitioned. For comdat groups that contain 116 // locals, record all their members here so we can keep them together. 117 // Comdat groups that only contain external globals are already handled by 118 // the MD5-based partitioning. 119 if (const Comdat *C = GV.getComdat()) { 120 auto &Member = ComdatMembers[C]; 121 if (Member) 122 GVtoClusterMap.unionSets(Member, &GV); 123 else 124 Member = &GV; 125 } 126 127 // For aliases we should not separate them from their aliasees regardless 128 // of linkage. 129 if (auto *GIS = dyn_cast<GlobalIndirectSymbol>(&GV)) { 130 if (const GlobalObject *Base = GIS->getBaseObject()) 131 GVtoClusterMap.unionSets(&GV, Base); 132 } 133 134 if (const Function *F = dyn_cast<Function>(&GV)) { 135 for (const BasicBlock &BB : *F) { 136 BlockAddress *BA = BlockAddress::lookup(&BB); 137 if (!BA || !BA->isConstantUsed()) 138 continue; 139 addAllGlobalValueUsers(GVtoClusterMap, F, BA); 140 } 141 } 142 143 if (GV.hasLocalLinkage()) 144 addAllGlobalValueUsers(GVtoClusterMap, &GV, &GV); 145 }; 146 147 llvm::for_each(M->functions(), recordGVSet); 148 llvm::for_each(M->globals(), recordGVSet); 149 llvm::for_each(M->aliases(), recordGVSet); 150 151 // Assigned all GVs to merged clusters while balancing number of objects in 152 // each. 153 auto CompareClusters = [](const std::pair<unsigned, unsigned> &a, 154 const std::pair<unsigned, unsigned> &b) { 155 if (a.second || b.second) 156 return a.second > b.second; 157 else 158 return a.first > b.first; 159 }; 160 161 std::priority_queue<std::pair<unsigned, unsigned>, 162 std::vector<std::pair<unsigned, unsigned>>, 163 decltype(CompareClusters)> 164 BalancinQueue(CompareClusters); 165 // Pre-populate priority queue with N slot blanks. 166 for (unsigned i = 0; i < N; ++i) 167 BalancinQueue.push(std::make_pair(i, 0)); 168 169 using SortType = std::pair<unsigned, ClusterMapType::iterator>; 170 171 SmallVector<SortType, 64> Sets; 172 SmallPtrSet<const GlobalValue *, 32> Visited; 173 174 // To guarantee determinism, we have to sort SCC according to size. 175 // When size is the same, use leader's name. 176 for (ClusterMapType::iterator I = GVtoClusterMap.begin(), 177 E = GVtoClusterMap.end(); I != E; ++I) 178 if (I->isLeader()) 179 Sets.push_back( 180 std::make_pair(std::distance(GVtoClusterMap.member_begin(I), 181 GVtoClusterMap.member_end()), I)); 182 183 std::sort(Sets.begin(), Sets.end(), [](const SortType &a, const SortType &b) { 184 if (a.first == b.first) 185 return a.second->getData()->getName() > b.second->getData()->getName(); 186 else 187 return a.first > b.first; 188 }); 189 190 for (auto &I : Sets) { 191 unsigned CurrentClusterID = BalancinQueue.top().first; 192 unsigned CurrentClusterSize = BalancinQueue.top().second; 193 BalancinQueue.pop(); 194 195 DEBUG(dbgs() << "Root[" << CurrentClusterID << "] cluster_size(" << I.first 196 << ") ----> " << I.second->getData()->getName() << "\n"); 197 198 for (ClusterMapType::member_iterator MI = 199 GVtoClusterMap.findLeader(I.second); 200 MI != GVtoClusterMap.member_end(); ++MI) { 201 if (!Visited.insert(*MI).second) 202 continue; 203 DEBUG(dbgs() << "----> " << (*MI)->getName() 204 << ((*MI)->hasLocalLinkage() ? " l " : " e ") << "\n"); 205 Visited.insert(*MI); 206 ClusterIDMap[*MI] = CurrentClusterID; 207 CurrentClusterSize++; 208 } 209 // Add this set size to the number of entries in this cluster. 210 BalancinQueue.push(std::make_pair(CurrentClusterID, CurrentClusterSize)); 211 } 212 } 213 214 static void externalize(GlobalValue *GV) { 215 if (GV->hasLocalLinkage()) { 216 GV->setLinkage(GlobalValue::ExternalLinkage); 217 GV->setVisibility(GlobalValue::HiddenVisibility); 218 } 219 220 // Unnamed entities must be named consistently between modules. setName will 221 // give a distinct name to each such entity. 222 if (!GV->hasName()) 223 GV->setName("__llvmsplit_unnamed"); 224 } 225 226 // Returns whether GV should be in partition (0-based) I of N. 227 static bool isInPartition(const GlobalValue *GV, unsigned I, unsigned N) { 228 if (auto *GIS = dyn_cast<GlobalIndirectSymbol>(GV)) 229 if (const GlobalObject *Base = GIS->getBaseObject()) 230 GV = Base; 231 232 StringRef Name; 233 if (const Comdat *C = GV->getComdat()) 234 Name = C->getName(); 235 else 236 Name = GV->getName(); 237 238 // Partition by MD5 hash. We only need a few bits for evenness as the number 239 // of partitions will generally be in the 1-2 figure range; the low 16 bits 240 // are enough. 241 MD5 H; 242 MD5::MD5Result R; 243 H.update(Name); 244 H.final(R); 245 return (R[0] | (R[1] << 8)) % N == I; 246 } 247 248 void llvm::SplitModule( 249 std::unique_ptr<Module> M, unsigned N, 250 function_ref<void(std::unique_ptr<Module> MPart)> ModuleCallback, 251 bool PreserveLocals) { 252 if (!PreserveLocals) { 253 for (Function &F : *M) 254 externalize(&F); 255 for (GlobalVariable &GV : M->globals()) 256 externalize(&GV); 257 for (GlobalAlias &GA : M->aliases()) 258 externalize(&GA); 259 for (GlobalIFunc &GIF : M->ifuncs()) 260 externalize(&GIF); 261 } 262 263 // This performs splitting without a need for externalization, which might not 264 // always be possible. 265 ClusterIDMapType ClusterIDMap; 266 findPartitions(M.get(), ClusterIDMap, N); 267 268 // FIXME: We should be able to reuse M as the last partition instead of 269 // cloning it. 270 for (unsigned I = 0; I < N; ++I) { 271 ValueToValueMapTy VMap; 272 std::unique_ptr<Module> MPart( 273 CloneModule(M.get(), VMap, [&](const GlobalValue *GV) { 274 if (ClusterIDMap.count(GV)) 275 return (ClusterIDMap[GV] == I); 276 else 277 return isInPartition(GV, I, N); 278 })); 279 if (I != 0) 280 MPart->setModuleInlineAsm(""); 281 ModuleCallback(std::move(MPart)); 282 } 283 } 284