1 //===- lib/Transforms/Utils/FunctionImportUtils.cpp - Importing utilities -===//
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 implements the FunctionImportGlobalProcessing class, used
11 // to perform the necessary global value handling for function importing.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Utils/FunctionImportUtils.h"
16 #include "llvm/IR/InstIterator.h"
19 /// Checks if we should import SGV as a definition, otherwise import as a
21 bool FunctionImportGlobalProcessing::doImportAsDefinition(
22 const GlobalValue *SGV, SetVector<GlobalValue *> *GlobalsToImport) {
24 // Only import the globals requested for importing.
25 if (!GlobalsToImport->count(const_cast<GlobalValue *>(SGV)))
28 assert(!isa<GlobalAlias>(SGV) &&
29 "Unexpected global alias in the import list.");
35 bool FunctionImportGlobalProcessing::doImportAsDefinition(
36 const GlobalValue *SGV) {
37 if (!isPerformingImport())
39 return FunctionImportGlobalProcessing::doImportAsDefinition(SGV,
43 bool FunctionImportGlobalProcessing::shouldPromoteLocalToGlobal(
44 const GlobalValue *SGV) {
45 assert(SGV->hasLocalLinkage());
46 // Both the imported references and the original local variable must
48 if (!isPerformingImport() && !isModuleExporting())
51 if (isPerformingImport()) {
52 assert((!GlobalsToImport->count(const_cast<GlobalValue *>(SGV)) ||
53 !isNonRenamableLocal(*SGV)) &&
54 "Attempting to promote non-renamable local");
55 // We don't know for sure yet if we are importing this value (as either
56 // a reference or a def), since we are simply walking all values in the
57 // module. But by necessity if we end up importing it and it is local,
58 // it must be promoted, so unconditionally promote all values in the
63 // When exporting, consult the index. We can have more than one local
64 // with the same GUID, in the case of same-named locals in different but
65 // same-named source files that were compiled in their respective directories
66 // (so the source file name and resulting GUID is the same). Find the one
68 auto Summary = ImportIndex.findSummaryInModule(
69 SGV->getGUID(), SGV->getParent()->getModuleIdentifier());
70 assert(Summary && "Missing summary for global value when exporting");
71 auto Linkage = Summary->linkage();
72 if (!GlobalValue::isLocalLinkage(Linkage)) {
73 assert(!isNonRenamableLocal(*SGV) &&
74 "Attempting to promote non-renamable local");
82 bool FunctionImportGlobalProcessing::isNonRenamableLocal(
83 const GlobalValue &GV) const {
84 if (!GV.hasLocalLinkage())
86 // This needs to stay in sync with the logic in buildModuleSummaryIndex.
89 if (Used.count(const_cast<GlobalValue *>(&GV)))
95 std::string FunctionImportGlobalProcessing::getName(const GlobalValue *SGV,
97 // For locals that must be promoted to global scope, ensure that
98 // the promoted name uniquely identifies the copy in the original module,
99 // using the ID assigned during combined index creation. When importing,
100 // we rename all locals (not just those that are promoted) in order to
101 // avoid naming conflicts between locals imported from different modules.
102 if (SGV->hasLocalLinkage() && (DoPromote || isPerformingImport()))
103 return ModuleSummaryIndex::getGlobalNameForLocal(
105 ImportIndex.getModuleHash(SGV->getParent()->getModuleIdentifier()));
106 return SGV->getName();
109 GlobalValue::LinkageTypes
110 FunctionImportGlobalProcessing::getLinkage(const GlobalValue *SGV,
112 // Any local variable that is referenced by an exported function needs
113 // to be promoted to global scope. Since we don't currently know which
114 // functions reference which local variables/functions, we must treat
115 // all as potentially exported if this module is exporting anything.
116 if (isModuleExporting()) {
117 if (SGV->hasLocalLinkage() && DoPromote)
118 return GlobalValue::ExternalLinkage;
119 return SGV->getLinkage();
122 // Otherwise, if we aren't importing, no linkage change is needed.
123 if (!isPerformingImport())
124 return SGV->getLinkage();
126 switch (SGV->getLinkage()) {
127 case GlobalValue::LinkOnceAnyLinkage:
128 case GlobalValue::LinkOnceODRLinkage:
129 case GlobalValue::ExternalLinkage:
130 // External and linkonce definitions are converted to available_externally
131 // definitions upon import, so that they are available for inlining
132 // and/or optimization, but are turned into declarations later
133 // during the EliminateAvailableExternally pass.
134 if (doImportAsDefinition(SGV) && !dyn_cast<GlobalAlias>(SGV))
135 return GlobalValue::AvailableExternallyLinkage;
136 // An imported external declaration stays external.
137 return SGV->getLinkage();
139 case GlobalValue::AvailableExternallyLinkage:
140 // An imported available_externally definition converts
141 // to external if imported as a declaration.
142 if (!doImportAsDefinition(SGV))
143 return GlobalValue::ExternalLinkage;
144 // An imported available_externally declaration stays that way.
145 return SGV->getLinkage();
147 case GlobalValue::WeakAnyLinkage:
148 // Can't import weak_any definitions correctly, or we might change the
149 // program semantics, since the linker will pick the first weak_any
150 // definition and importing would change the order they are seen by the
151 // linker. The module linking caller needs to enforce this.
152 assert(!doImportAsDefinition(SGV));
153 // If imported as a declaration, it becomes external_weak.
154 return SGV->getLinkage();
156 case GlobalValue::WeakODRLinkage:
157 // For weak_odr linkage, there is a guarantee that all copies will be
158 // equivalent, so the issue described above for weak_any does not exist,
159 // and the definition can be imported. It can be treated similarly
160 // to an imported externally visible global value.
161 if (doImportAsDefinition(SGV) && !dyn_cast<GlobalAlias>(SGV))
162 return GlobalValue::AvailableExternallyLinkage;
164 return GlobalValue::ExternalLinkage;
166 case GlobalValue::AppendingLinkage:
167 // It would be incorrect to import an appending linkage variable,
168 // since it would cause global constructors/destructors to be
169 // executed multiple times. This should have already been handled
170 // by linkIfNeeded, and we will assert in shouldLinkFromSource
171 // if we try to import, so we simply return AppendingLinkage.
172 return GlobalValue::AppendingLinkage;
174 case GlobalValue::InternalLinkage:
175 case GlobalValue::PrivateLinkage:
176 // If we are promoting the local to global scope, it is handled
177 // similarly to a normal externally visible global.
179 if (doImportAsDefinition(SGV) && !dyn_cast<GlobalAlias>(SGV))
180 return GlobalValue::AvailableExternallyLinkage;
182 return GlobalValue::ExternalLinkage;
184 // A non-promoted imported local definition stays local.
185 // The ThinLTO pass will eventually force-import their definitions.
186 return SGV->getLinkage();
188 case GlobalValue::ExternalWeakLinkage:
189 // External weak doesn't apply to definitions, must be a declaration.
190 assert(!doImportAsDefinition(SGV));
191 // Linkage stays external_weak.
192 return SGV->getLinkage();
194 case GlobalValue::CommonLinkage:
195 // Linkage stays common on definitions.
196 // The ThinLTO pass will eventually force-import their definitions.
197 return SGV->getLinkage();
200 llvm_unreachable("unknown linkage type");
203 void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
205 // Check the summaries to see if the symbol gets resolved to a known local
208 ValueInfo VI = ImportIndex.getValueInfo(GV.getGUID());
209 if (VI && VI.isDSOLocal()) {
210 GV.setDSOLocal(true);
211 if (GV.hasDLLImportStorageClass())
212 GV.setDLLStorageClass(GlobalValue::DefaultStorageClass);
216 bool DoPromote = false;
217 if (GV.hasLocalLinkage() &&
218 ((DoPromote = shouldPromoteLocalToGlobal(&GV)) || isPerformingImport())) {
219 // Once we change the name or linkage it is difficult to determine
220 // again whether we should promote since shouldPromoteLocalToGlobal needs
221 // to locate the summary (based on GUID from name and linkage). Therefore,
222 // use DoPromote result saved above.
223 GV.setName(getName(&GV, DoPromote));
224 GV.setLinkage(getLinkage(&GV, DoPromote));
225 if (!GV.hasLocalLinkage())
226 GV.setVisibility(GlobalValue::HiddenVisibility);
228 GV.setLinkage(getLinkage(&GV, /* DoPromote */ false));
230 // Remove functions imported as available externally defs from comdats,
231 // as this is a declaration for the linker, and will be dropped eventually.
232 // It is illegal for comdats to contain declarations.
233 auto *GO = dyn_cast_or_null<GlobalObject>(&GV);
234 if (GO && GO->isDeclarationForLinker() && GO->hasComdat()) {
235 // The IRMover should not have placed any imported declarations in
236 // a comdat, so the only declaration that should be in a comdat
237 // at this point would be a definition imported as available_externally.
238 assert(GO->hasAvailableExternallyLinkage() &&
239 "Expected comdat on definition (possibly available external)");
240 GO->setComdat(nullptr);
244 void FunctionImportGlobalProcessing::processGlobalsForThinLTO() {
245 for (GlobalVariable &GV : M.globals())
246 processGlobalForThinLTO(GV);
247 for (Function &SF : M)
248 processGlobalForThinLTO(SF);
249 for (GlobalAlias &GA : M.aliases())
250 processGlobalForThinLTO(GA);
253 bool FunctionImportGlobalProcessing::run() {
254 processGlobalsForThinLTO();
258 bool llvm::renameModuleForThinLTO(Module &M, const ModuleSummaryIndex &Index,
259 SetVector<GlobalValue *> *GlobalsToImport) {
260 FunctionImportGlobalProcessing ThinLTOProcessing(M, Index, GlobalsToImport);
261 return ThinLTOProcessing.run();