1 //===- SplitModule.cpp - Split a module into partitions -------------------===// 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 file defines the function llvm::SplitModule, which splits a module 10 // into multiple linkable partitions. It can be used to implement parallel code 11 // generation for link-time optimization. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/Transforms/Utils/SplitModule.h" 16 #include "llvm/ADT/DenseMap.h" 17 #include "llvm/ADT/EquivalenceClasses.h" 18 #include "llvm/ADT/SmallPtrSet.h" 19 #include "llvm/ADT/SmallVector.h" 20 #include "llvm/ADT/StringRef.h" 21 #include "llvm/IR/Comdat.h" 22 #include "llvm/IR/Constant.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/GlobalVariable.h" 29 #include "llvm/IR/Instruction.h" 30 #include "llvm/IR/Module.h" 31 #include "llvm/IR/User.h" 32 #include "llvm/IR/Value.h" 33 #include "llvm/Support/Casting.h" 34 #include "llvm/Support/Debug.h" 35 #include "llvm/Support/ErrorHandling.h" 36 #include "llvm/Support/MD5.h" 37 #include "llvm/Support/raw_ostream.h" 38 #include "llvm/Transforms/Utils/Cloning.h" 39 #include "llvm/Transforms/Utils/ValueMapper.h" 40 #include <algorithm> 41 #include <cassert> 42 #include <iterator> 43 #include <memory> 44 #include <queue> 45 #include <utility> 46 #include <vector> 47 48 using namespace llvm; 49 50 #define DEBUG_TYPE "split-module" 51 52 namespace { 53 54 using ClusterMapType = EquivalenceClasses<const GlobalValue *>; 55 using ComdatMembersType = DenseMap<const Comdat *, const GlobalValue *>; 56 using ClusterIDMapType = DenseMap<const GlobalValue *, unsigned>; 57 58 } // end anonymous namespace 59 60 static void addNonConstUser(ClusterMapType &GVtoClusterMap, 61 const GlobalValue *GV, const User *U) { 62 assert((!isa<Constant>(U) || isa<GlobalValue>(U)) && "Bad user"); 63 64 if (const Instruction *I = dyn_cast<Instruction>(U)) { 65 const GlobalValue *F = I->getParent()->getParent(); 66 GVtoClusterMap.unionSets(GV, F); 67 } else if (const GlobalValue *GVU = dyn_cast<GlobalValue>(U)) { 68 GVtoClusterMap.unionSets(GV, GVU); 69 } else { 70 llvm_unreachable("Underimplemented use case"); 71 } 72 } 73 74 // Adds all GlobalValue users of V to the same cluster as GV. 75 static void addAllGlobalValueUsers(ClusterMapType &GVtoClusterMap, 76 const GlobalValue *GV, const Value *V) { 77 for (auto *U : V->users()) { 78 SmallVector<const User *, 4> Worklist; 79 Worklist.push_back(U); 80 while (!Worklist.empty()) { 81 const User *UU = Worklist.pop_back_val(); 82 // For each constant that is not a GV (a pure const) recurse. 83 if (isa<Constant>(UU) && !isa<GlobalValue>(UU)) { 84 Worklist.append(UU->user_begin(), UU->user_end()); 85 continue; 86 } 87 addNonConstUser(GVtoClusterMap, GV, UU); 88 } 89 } 90 } 91 92 static const GlobalObject *getGVPartitioningRoot(const GlobalValue *GV) { 93 const GlobalObject *GO = GV->getAliaseeObject(); 94 if (const auto *GI = dyn_cast_or_null<GlobalIFunc>(GO)) 95 GO = GI->getResolverFunction(); 96 return GO; 97 } 98 99 // Find partitions for module in the way that no locals need to be 100 // globalized. 101 // Try to balance pack those partitions into N files since this roughly equals 102 // thread balancing for the backend codegen step. 103 static void findPartitions(Module &M, ClusterIDMapType &ClusterIDMap, 104 unsigned N) { 105 // At this point module should have the proper mix of globals and locals. 106 // As we attempt to partition this module, we must not change any 107 // locals to globals. 108 LLVM_DEBUG(dbgs() << "Partition module with (" << M.size() << ")functions\n"); 109 ClusterMapType GVtoClusterMap; 110 ComdatMembersType ComdatMembers; 111 112 auto recordGVSet = [&GVtoClusterMap, &ComdatMembers](GlobalValue &GV) { 113 if (GV.isDeclaration()) 114 return; 115 116 if (!GV.hasName()) 117 GV.setName("__llvmsplit_unnamed"); 118 119 // Comdat groups must not be partitioned. For comdat groups that contain 120 // locals, record all their members here so we can keep them together. 121 // Comdat groups that only contain external globals are already handled by 122 // the MD5-based partitioning. 123 if (const Comdat *C = GV.getComdat()) { 124 auto &Member = ComdatMembers[C]; 125 if (Member) 126 GVtoClusterMap.unionSets(Member, &GV); 127 else 128 Member = &GV; 129 } 130 131 // Aliases should not be separated from their aliasees and ifuncs should 132 // not be separated from their resolvers regardless of linkage. 133 if (const GlobalObject *Root = getGVPartitioningRoot(&GV)) 134 if (&GV != Root) 135 GVtoClusterMap.unionSets(&GV, Root); 136 137 if (const Function *F = dyn_cast<Function>(&GV)) { 138 for (const BasicBlock &BB : *F) { 139 BlockAddress *BA = BlockAddress::lookup(&BB); 140 if (!BA || !BA->isConstantUsed()) 141 continue; 142 addAllGlobalValueUsers(GVtoClusterMap, F, BA); 143 } 144 } 145 146 if (GV.hasLocalLinkage()) 147 addAllGlobalValueUsers(GVtoClusterMap, &GV, &GV); 148 }; 149 150 llvm::for_each(M.functions(), recordGVSet); 151 llvm::for_each(M.globals(), recordGVSet); 152 llvm::for_each(M.aliases(), recordGVSet); 153 154 // Assigned all GVs to merged clusters while balancing number of objects in 155 // each. 156 auto CompareClusters = [](const std::pair<unsigned, unsigned> &a, 157 const std::pair<unsigned, unsigned> &b) { 158 if (a.second || b.second) 159 return a.second > b.second; 160 else 161 return a.first > b.first; 162 }; 163 164 std::priority_queue<std::pair<unsigned, unsigned>, 165 std::vector<std::pair<unsigned, unsigned>>, 166 decltype(CompareClusters)> 167 BalancinQueue(CompareClusters); 168 // Pre-populate priority queue with N slot blanks. 169 for (unsigned i = 0; i < N; ++i) 170 BalancinQueue.push(std::make_pair(i, 0)); 171 172 using SortType = std::pair<unsigned, ClusterMapType::iterator>; 173 174 SmallVector<SortType, 64> Sets; 175 SmallPtrSet<const GlobalValue *, 32> Visited; 176 177 // To guarantee determinism, we have to sort SCC according to size. 178 // When size is the same, use leader's name. 179 for (ClusterMapType::iterator I = GVtoClusterMap.begin(), 180 E = GVtoClusterMap.end(); I != E; ++I) 181 if (I->isLeader()) 182 Sets.push_back( 183 std::make_pair(std::distance(GVtoClusterMap.member_begin(I), 184 GVtoClusterMap.member_end()), I)); 185 186 llvm::sort(Sets, [](const SortType &a, const SortType &b) { 187 if (a.first == b.first) 188 return a.second->getData()->getName() > b.second->getData()->getName(); 189 else 190 return a.first > b.first; 191 }); 192 193 for (auto &I : Sets) { 194 unsigned CurrentClusterID = BalancinQueue.top().first; 195 unsigned CurrentClusterSize = BalancinQueue.top().second; 196 BalancinQueue.pop(); 197 198 LLVM_DEBUG(dbgs() << "Root[" << CurrentClusterID << "] cluster_size(" 199 << I.first << ") ----> " << I.second->getData()->getName() 200 << "\n"); 201 202 for (ClusterMapType::member_iterator MI = 203 GVtoClusterMap.findLeader(I.second); 204 MI != GVtoClusterMap.member_end(); ++MI) { 205 if (!Visited.insert(*MI).second) 206 continue; 207 LLVM_DEBUG(dbgs() << "----> " << (*MI)->getName() 208 << ((*MI)->hasLocalLinkage() ? " l " : " e ") << "\n"); 209 Visited.insert(*MI); 210 ClusterIDMap[*MI] = CurrentClusterID; 211 CurrentClusterSize++; 212 } 213 // Add this set size to the number of entries in this cluster. 214 BalancinQueue.push(std::make_pair(CurrentClusterID, CurrentClusterSize)); 215 } 216 } 217 218 static void externalize(GlobalValue *GV) { 219 if (GV->hasLocalLinkage()) { 220 GV->setLinkage(GlobalValue::ExternalLinkage); 221 GV->setVisibility(GlobalValue::HiddenVisibility); 222 } 223 224 // Unnamed entities must be named consistently between modules. setName will 225 // give a distinct name to each such entity. 226 if (!GV->hasName()) 227 GV->setName("__llvmsplit_unnamed"); 228 } 229 230 // Returns whether GV should be in partition (0-based) I of N. 231 static bool isInPartition(const GlobalValue *GV, unsigned I, unsigned N) { 232 if (const GlobalObject *Root = getGVPartitioningRoot(GV)) 233 GV = Root; 234 235 StringRef Name; 236 if (const Comdat *C = GV->getComdat()) 237 Name = C->getName(); 238 else 239 Name = GV->getName(); 240 241 // Partition by MD5 hash. We only need a few bits for evenness as the number 242 // of partitions will generally be in the 1-2 figure range; the low 16 bits 243 // are enough. 244 MD5 H; 245 MD5::MD5Result R; 246 H.update(Name); 247 H.final(R); 248 return (R[0] | (R[1] << 8)) % N == I; 249 } 250 251 void llvm::SplitModule( 252 Module &M, unsigned N, 253 function_ref<void(std::unique_ptr<Module> MPart)> ModuleCallback, 254 bool PreserveLocals) { 255 if (!PreserveLocals) { 256 for (Function &F : M) 257 externalize(&F); 258 for (GlobalVariable &GV : M.globals()) 259 externalize(&GV); 260 for (GlobalAlias &GA : M.aliases()) 261 externalize(&GA); 262 for (GlobalIFunc &GIF : M.ifuncs()) 263 externalize(&GIF); 264 } 265 266 // This performs splitting without a need for externalization, which might not 267 // always be possible. 268 ClusterIDMapType ClusterIDMap; 269 findPartitions(M, ClusterIDMap, N); 270 271 // FIXME: We should be able to reuse M as the last partition instead of 272 // cloning it. Note that the callers at the moment expect the module to 273 // be preserved, so will need some adjustments as well. 274 for (unsigned I = 0; I < N; ++I) { 275 ValueToValueMapTy VMap; 276 std::unique_ptr<Module> MPart( 277 CloneModule(M, VMap, [&](const GlobalValue *GV) { 278 if (ClusterIDMap.count(GV)) 279 return (ClusterIDMap[GV] == I); 280 else 281 return isInPartition(GV, I, N); 282 })); 283 if (I != 0) 284 MPart->setModuleInlineAsm(""); 285 ModuleCallback(std::move(MPart)); 286 } 287 } 288