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 #define DEBUG_TYPE "split-module"
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"
38 typedef EquivalenceClasses<const GlobalValue *> ClusterMapType;
39 typedef DenseMap<const Comdat *, const GlobalValue *> ComdatMembersType;
40 typedef DenseMap<const GlobalValue *, unsigned> ClusterIDMapType;
43 static void addNonConstUser(ClusterMapType &GVtoClusterMap,
44 const GlobalValue *GV, const User *U) {
45 assert((!isa<Constant>(U) || isa<GlobalValue>(U)) && "Bad user");
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));
54 llvm_unreachable("Underimplemented use case");
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());
71 addNonConstUser(GVtoClusterMap, GV, UU);
76 // Find partitions for module in the way that no locals need to be
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,
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
85 DEBUG(dbgs() << "Partition module with (" << M->size() << ")functions\n");
86 ClusterMapType GVtoClusterMap;
87 ComdatMembersType ComdatMembers;
89 auto recordGVSet = [&GVtoClusterMap, &ComdatMembers](GlobalValue &GV) {
90 if (GV.isDeclaration())
94 GV.setName("__llvmsplit_unnamed");
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];
103 GVtoClusterMap.unionSets(Member, &GV);
108 // For aliases we should not separate them from their aliasees regardless
110 if (auto *GIS = dyn_cast<GlobalIndirectSymbol>(&GV)) {
111 if (const GlobalObject *Base = GIS->getBaseObject())
112 GVtoClusterMap.unionSets(&GV, Base);
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())
120 addAllGlobalValueUsers(GVtoClusterMap, F, BA);
124 if (GV.hasLocalLinkage())
125 addAllGlobalValueUsers(GVtoClusterMap, &GV, &GV);
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);
132 // Assigned all GVs to merged clusters while balancing number of objects in
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;
139 return a.first > b.first;
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));
150 typedef std::pair<unsigned, ClusterMapType::iterator> SortType;
151 SmallVector<SortType, 64> Sets;
152 SmallPtrSet<const GlobalValue *, 32> Visited;
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)
160 std::make_pair(std::distance(GVtoClusterMap.member_begin(I),
161 GVtoClusterMap.member_end()), I));
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();
167 return a.first > b.first;
170 for (auto &I : Sets) {
171 unsigned CurrentClusterID = BalancinQueue.top().first;
172 unsigned CurrentClusterSize = BalancinQueue.top().second;
175 DEBUG(dbgs() << "Root[" << CurrentClusterID << "] cluster_size(" << I.first
176 << ") ----> " << I.second->getData()->getName() << "\n");
178 for (ClusterMapType::member_iterator MI =
179 GVtoClusterMap.findLeader(I.second);
180 MI != GVtoClusterMap.member_end(); ++MI) {
181 if (!Visited.insert(*MI).second)
183 DEBUG(dbgs() << "----> " << (*MI)->getName()
184 << ((*MI)->hasLocalLinkage() ? " l " : " e ") << "\n");
186 ClusterIDMap[*MI] = CurrentClusterID;
187 CurrentClusterSize++;
189 // Add this set size to the number of entries in this cluster.
190 BalancinQueue.push(std::make_pair(CurrentClusterID, CurrentClusterSize));
194 static void externalize(GlobalValue *GV) {
195 if (GV->hasLocalLinkage()) {
196 GV->setLinkage(GlobalValue::ExternalLinkage);
197 GV->setVisibility(GlobalValue::HiddenVisibility);
200 // Unnamed entities must be named consistently between modules. setName will
201 // give a distinct name to each such entity.
203 GV->setName("__llvmsplit_unnamed");
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())
213 if (const Comdat *C = GV->getComdat())
216 Name = GV->getName();
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
225 return (R[0] | (R[1] << 8)) % N == I;
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)
235 for (GlobalVariable &GV : M->globals())
237 for (GlobalAlias &GA : M->aliases())
239 for (GlobalIFunc &GIF : M->ifuncs())
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);
248 // FIXME: We should be able to reuse M as the last partition instead of
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);
257 return isInPartition(GV, I, N);
260 MPart->setModuleInlineAsm("");
261 ModuleCallback(std::move(MPart));