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 LLVM_DEBUG(dbgs() << "Partition module with (" << M->size() 105 << ")functions\n"); 106 ClusterMapType GVtoClusterMap; 107 ComdatMembersType ComdatMembers; 108 109 auto recordGVSet = [&GVtoClusterMap, &ComdatMembers](GlobalValue &GV) { 110 if (GV.isDeclaration()) 111 return; 112 113 if (!GV.hasName()) 114 GV.setName("__llvmsplit_unnamed"); 115 116 // Comdat groups must not be partitioned. For comdat groups that contain 117 // locals, record all their members here so we can keep them together. 118 // Comdat groups that only contain external globals are already handled by 119 // the MD5-based partitioning. 120 if (const Comdat *C = GV.getComdat()) { 121 auto &Member = ComdatMembers[C]; 122 if (Member) 123 GVtoClusterMap.unionSets(Member, &GV); 124 else 125 Member = &GV; 126 } 127 128 // For aliases we should not separate them from their aliasees regardless 129 // of linkage. 130 if (auto *GIS = dyn_cast<GlobalIndirectSymbol>(&GV)) { 131 if (const GlobalObject *Base = GIS->getBaseObject()) 132 GVtoClusterMap.unionSets(&GV, Base); 133 } 134 135 if (const Function *F = dyn_cast<Function>(&GV)) { 136 for (const BasicBlock &BB : *F) { 137 BlockAddress *BA = BlockAddress::lookup(&BB); 138 if (!BA || !BA->isConstantUsed()) 139 continue; 140 addAllGlobalValueUsers(GVtoClusterMap, F, BA); 141 } 142 } 143 144 if (GV.hasLocalLinkage()) 145 addAllGlobalValueUsers(GVtoClusterMap, &GV, &GV); 146 }; 147 148 llvm::for_each(M->functions(), recordGVSet); 149 llvm::for_each(M->globals(), recordGVSet); 150 llvm::for_each(M->aliases(), recordGVSet); 151 152 // Assigned all GVs to merged clusters while balancing number of objects in 153 // each. 154 auto CompareClusters = [](const std::pair<unsigned, unsigned> &a, 155 const std::pair<unsigned, unsigned> &b) { 156 if (a.second || b.second) 157 return a.second > b.second; 158 else 159 return a.first > b.first; 160 }; 161 162 std::priority_queue<std::pair<unsigned, unsigned>, 163 std::vector<std::pair<unsigned, unsigned>>, 164 decltype(CompareClusters)> 165 BalancinQueue(CompareClusters); 166 // Pre-populate priority queue with N slot blanks. 167 for (unsigned i = 0; i < N; ++i) 168 BalancinQueue.push(std::make_pair(i, 0)); 169 170 using SortType = std::pair<unsigned, ClusterMapType::iterator>; 171 172 SmallVector<SortType, 64> Sets; 173 SmallPtrSet<const GlobalValue *, 32> Visited; 174 175 // To guarantee determinism, we have to sort SCC according to size. 176 // When size is the same, use leader's name. 177 for (ClusterMapType::iterator I = GVtoClusterMap.begin(), 178 E = GVtoClusterMap.end(); I != E; ++I) 179 if (I->isLeader()) 180 Sets.push_back( 181 std::make_pair(std::distance(GVtoClusterMap.member_begin(I), 182 GVtoClusterMap.member_end()), I)); 183 184 llvm::sort(Sets, [](const SortType &a, const SortType &b) { 185 if (a.first == b.first) 186 return a.second->getData()->getName() > b.second->getData()->getName(); 187 else 188 return a.first > b.first; 189 }); 190 191 for (auto &I : Sets) { 192 unsigned CurrentClusterID = BalancinQueue.top().first; 193 unsigned CurrentClusterSize = BalancinQueue.top().second; 194 BalancinQueue.pop(); 195 196 LLVM_DEBUG(dbgs() << "Root[" << CurrentClusterID << "] cluster_size(" 197 << I.first << ") ----> " << I.second->getData()->getName() 198 << "\n"); 199 200 for (ClusterMapType::member_iterator MI = 201 GVtoClusterMap.findLeader(I.second); 202 MI != GVtoClusterMap.member_end(); ++MI) { 203 if (!Visited.insert(*MI).second) 204 continue; 205 LLVM_DEBUG(dbgs() << "----> " << (*MI)->getName() 206 << ((*MI)->hasLocalLinkage() ? " l " : " e ") << "\n"); 207 Visited.insert(*MI); 208 ClusterIDMap[*MI] = CurrentClusterID; 209 CurrentClusterSize++; 210 } 211 // Add this set size to the number of entries in this cluster. 212 BalancinQueue.push(std::make_pair(CurrentClusterID, CurrentClusterSize)); 213 } 214 } 215 216 static void externalize(GlobalValue *GV) { 217 if (GV->hasLocalLinkage()) { 218 GV->setLinkage(GlobalValue::ExternalLinkage); 219 GV->setVisibility(GlobalValue::HiddenVisibility); 220 } 221 222 // Unnamed entities must be named consistently between modules. setName will 223 // give a distinct name to each such entity. 224 if (!GV->hasName()) 225 GV->setName("__llvmsplit_unnamed"); 226 } 227 228 // Returns whether GV should be in partition (0-based) I of N. 229 static bool isInPartition(const GlobalValue *GV, unsigned I, unsigned N) { 230 if (auto *GIS = dyn_cast<GlobalIndirectSymbol>(GV)) 231 if (const GlobalObject *Base = GIS->getBaseObject()) 232 GV = Base; 233 234 StringRef Name; 235 if (const Comdat *C = GV->getComdat()) 236 Name = C->getName(); 237 else 238 Name = GV->getName(); 239 240 // Partition by MD5 hash. We only need a few bits for evenness as the number 241 // of partitions will generally be in the 1-2 figure range; the low 16 bits 242 // are enough. 243 MD5 H; 244 MD5::MD5Result R; 245 H.update(Name); 246 H.final(R); 247 return (R[0] | (R[1] << 8)) % N == I; 248 } 249 250 void llvm::SplitModule( 251 std::unique_ptr<Module> M, unsigned N, 252 function_ref<void(std::unique_ptr<Module> MPart)> ModuleCallback, 253 bool PreserveLocals) { 254 if (!PreserveLocals) { 255 for (Function &F : *M) 256 externalize(&F); 257 for (GlobalVariable &GV : M->globals()) 258 externalize(&GV); 259 for (GlobalAlias &GA : M->aliases()) 260 externalize(&GA); 261 for (GlobalIFunc &GIF : M->ifuncs()) 262 externalize(&GIF); 263 } 264 265 // This performs splitting without a need for externalization, which might not 266 // always be possible. 267 ClusterIDMapType ClusterIDMap; 268 findPartitions(M.get(), ClusterIDMap, N); 269 270 // FIXME: We should be able to reuse M as the last partition instead of 271 // cloning it. 272 for (unsigned I = 0; I < N; ++I) { 273 ValueToValueMapTy VMap; 274 std::unique_ptr<Module> MPart( 275 CloneModule(*M, VMap, [&](const GlobalValue *GV) { 276 if (ClusterIDMap.count(GV)) 277 return (ClusterIDMap[GV] == I); 278 else 279 return isInPartition(GV, I, N); 280 })); 281 if (I != 0) 282 MPart->setModuleInlineAsm(""); 283 ModuleCallback(std::move(MPart)); 284 } 285 } 286