1 //===- SplitModule.cpp - Split a module into partitions -------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
14 //===----------------------------------------------------------------------===//
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"
52 #define DEBUG_TYPE "split-module"
56 using ClusterMapType = EquivalenceClasses<const GlobalValue *>;
57 using ComdatMembersType = DenseMap<const Comdat *, const GlobalValue *>;
58 using ClusterIDMapType = DenseMap<const GlobalValue *, unsigned>;
60 } // end anonymous namespace
62 static void addNonConstUser(ClusterMapType &GVtoClusterMap,
63 const GlobalValue *GV, const User *U) {
64 assert((!isa<Constant>(U) || isa<GlobalValue>(U)) && "Bad user");
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));
73 llvm_unreachable("Underimplemented use case");
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());
90 addNonConstUser(GVtoClusterMap, GV, UU);
95 // Find partitions for module in the way that no locals need to be
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,
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;
108 auto recordGVSet = [&GVtoClusterMap, &ComdatMembers](GlobalValue &GV) {
109 if (GV.isDeclaration())
113 GV.setName("__llvmsplit_unnamed");
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];
122 GVtoClusterMap.unionSets(Member, &GV);
127 // For aliases we should not separate them from their aliasees regardless
129 if (auto *GIS = dyn_cast<GlobalIndirectSymbol>(&GV)) {
130 if (const GlobalObject *Base = GIS->getBaseObject())
131 GVtoClusterMap.unionSets(&GV, Base);
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())
139 addAllGlobalValueUsers(GVtoClusterMap, F, BA);
143 if (GV.hasLocalLinkage())
144 addAllGlobalValueUsers(GVtoClusterMap, &GV, &GV);
147 llvm::for_each(M->functions(), recordGVSet);
148 llvm::for_each(M->globals(), recordGVSet);
149 llvm::for_each(M->aliases(), recordGVSet);
151 // Assigned all GVs to merged clusters while balancing number of objects in
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;
158 return a.first > b.first;
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));
169 using SortType = std::pair<unsigned, ClusterMapType::iterator>;
171 SmallVector<SortType, 64> Sets;
172 SmallPtrSet<const GlobalValue *, 32> Visited;
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)
180 std::make_pair(std::distance(GVtoClusterMap.member_begin(I),
181 GVtoClusterMap.member_end()), I));
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();
187 return a.first > b.first;
190 for (auto &I : Sets) {
191 unsigned CurrentClusterID = BalancinQueue.top().first;
192 unsigned CurrentClusterSize = BalancinQueue.top().second;
195 DEBUG(dbgs() << "Root[" << CurrentClusterID << "] cluster_size(" << I.first
196 << ") ----> " << I.second->getData()->getName() << "\n");
198 for (ClusterMapType::member_iterator MI =
199 GVtoClusterMap.findLeader(I.second);
200 MI != GVtoClusterMap.member_end(); ++MI) {
201 if (!Visited.insert(*MI).second)
203 DEBUG(dbgs() << "----> " << (*MI)->getName()
204 << ((*MI)->hasLocalLinkage() ? " l " : " e ") << "\n");
206 ClusterIDMap[*MI] = CurrentClusterID;
207 CurrentClusterSize++;
209 // Add this set size to the number of entries in this cluster.
210 BalancinQueue.push(std::make_pair(CurrentClusterID, CurrentClusterSize));
214 static void externalize(GlobalValue *GV) {
215 if (GV->hasLocalLinkage()) {
216 GV->setLinkage(GlobalValue::ExternalLinkage);
217 GV->setVisibility(GlobalValue::HiddenVisibility);
220 // Unnamed entities must be named consistently between modules. setName will
221 // give a distinct name to each such entity.
223 GV->setName("__llvmsplit_unnamed");
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())
233 if (const Comdat *C = GV->getComdat())
236 Name = GV->getName();
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
245 return (R[0] | (R[1] << 8)) % N == I;
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)
255 for (GlobalVariable &GV : M->globals())
257 for (GlobalAlias &GA : M->aliases())
259 for (GlobalIFunc &GIF : M->ifuncs())
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);
268 // FIXME: We should be able to reuse M as the last partition instead of
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);
277 return isInPartition(GV, I, N);
280 MPart->setModuleInlineAsm("");
281 ModuleCallback(std::move(MPart));