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/Analysis/ModuleSummaryAnalysis.h"
17 #include "llvm/IR/InstIterator.h"
18 #include "llvm/IR/Instructions.h"
21 /// Checks if we should import SGV as a definition, otherwise import as a
23 bool FunctionImportGlobalProcessing::doImportAsDefinition(
24 const GlobalValue *SGV, SetVector<GlobalValue *> *GlobalsToImport) {
26 // For alias, we tie the definition to the base object. Extract it and recurse
27 if (auto *GA = dyn_cast<GlobalAlias>(SGV)) {
28 if (GA->isInterposable())
30 const GlobalObject *GO = GA->getBaseObject();
31 if (!GO->hasLinkOnceODRLinkage())
33 return FunctionImportGlobalProcessing::doImportAsDefinition(
36 // Only import the globals requested for importing.
37 if (GlobalsToImport->count(const_cast<GlobalValue *>(SGV)))
43 bool FunctionImportGlobalProcessing::doImportAsDefinition(
44 const GlobalValue *SGV) {
45 if (!isPerformingImport())
47 return FunctionImportGlobalProcessing::doImportAsDefinition(SGV,
51 bool FunctionImportGlobalProcessing::shouldPromoteLocalToGlobal(
52 const GlobalValue *SGV) {
53 assert(SGV->hasLocalLinkage());
54 // Both the imported references and the original local variable must
56 if (!isPerformingImport() && !isModuleExporting())
59 if (isPerformingImport()) {
60 assert((!GlobalsToImport->count(const_cast<GlobalValue *>(SGV)) ||
61 !isNonRenamableLocal(*SGV)) &&
62 "Attempting to promote non-renamable local");
63 // We don't know for sure yet if we are importing this value (as either
64 // a reference or a def), since we are simply walking all values in the
65 // module. But by necessity if we end up importing it and it is local,
66 // it must be promoted, so unconditionally promote all values in the
71 // When exporting, consult the index. We can have more than one local
72 // with the same GUID, in the case of same-named locals in different but
73 // same-named source files that were compiled in their respective directories
74 // (so the source file name and resulting GUID is the same). Find the one
76 auto Summary = ImportIndex.findSummaryInModule(
77 SGV->getGUID(), SGV->getParent()->getModuleIdentifier());
78 assert(Summary && "Missing summary for global value when exporting");
79 auto Linkage = Summary->linkage();
80 if (!GlobalValue::isLocalLinkage(Linkage)) {
81 assert(!isNonRenamableLocal(*SGV) &&
82 "Attempting to promote non-renamable local");
90 bool FunctionImportGlobalProcessing::isNonRenamableLocal(
91 const GlobalValue &GV) const {
92 if (!GV.hasLocalLinkage())
94 // This needs to stay in sync with the logic in buildModuleSummaryIndex.
97 if (Used.count(const_cast<GlobalValue *>(&GV)))
103 std::string FunctionImportGlobalProcessing::getName(const GlobalValue *SGV,
105 // For locals that must be promoted to global scope, ensure that
106 // the promoted name uniquely identifies the copy in the original module,
107 // using the ID assigned during combined index creation. When importing,
108 // we rename all locals (not just those that are promoted) in order to
109 // avoid naming conflicts between locals imported from different modules.
110 if (SGV->hasLocalLinkage() && (DoPromote || isPerformingImport()))
111 return ModuleSummaryIndex::getGlobalNameForLocal(
113 ImportIndex.getModuleHash(SGV->getParent()->getModuleIdentifier()));
114 return SGV->getName();
117 GlobalValue::LinkageTypes
118 FunctionImportGlobalProcessing::getLinkage(const GlobalValue *SGV,
120 // Any local variable that is referenced by an exported function needs
121 // to be promoted to global scope. Since we don't currently know which
122 // functions reference which local variables/functions, we must treat
123 // all as potentially exported if this module is exporting anything.
124 if (isModuleExporting()) {
125 if (SGV->hasLocalLinkage() && DoPromote)
126 return GlobalValue::ExternalLinkage;
127 return SGV->getLinkage();
130 // Otherwise, if we aren't importing, no linkage change is needed.
131 if (!isPerformingImport())
132 return SGV->getLinkage();
134 switch (SGV->getLinkage()) {
135 case GlobalValue::ExternalLinkage:
136 // External defnitions are converted to available_externally
137 // definitions upon import, so that they are available for inlining
138 // and/or optimization, but are turned into declarations later
139 // during the EliminateAvailableExternally pass.
140 if (doImportAsDefinition(SGV) && !dyn_cast<GlobalAlias>(SGV))
141 return GlobalValue::AvailableExternallyLinkage;
142 // An imported external declaration stays external.
143 return SGV->getLinkage();
145 case GlobalValue::AvailableExternallyLinkage:
146 // An imported available_externally definition converts
147 // to external if imported as a declaration.
148 if (!doImportAsDefinition(SGV))
149 return GlobalValue::ExternalLinkage;
150 // An imported available_externally declaration stays that way.
151 return SGV->getLinkage();
153 case GlobalValue::LinkOnceAnyLinkage:
154 case GlobalValue::LinkOnceODRLinkage:
155 // These both stay the same when importing the definition.
156 // The ThinLTO pass will eventually force-import their definitions.
157 return SGV->getLinkage();
159 case GlobalValue::WeakAnyLinkage:
160 // Can't import weak_any definitions correctly, or we might change the
161 // program semantics, since the linker will pick the first weak_any
162 // definition and importing would change the order they are seen by the
163 // linker. The module linking caller needs to enforce this.
164 assert(!doImportAsDefinition(SGV));
165 // If imported as a declaration, it becomes external_weak.
166 return SGV->getLinkage();
168 case GlobalValue::WeakODRLinkage:
169 // For weak_odr linkage, there is a guarantee that all copies will be
170 // equivalent, so the issue described above for weak_any does not exist,
171 // and the definition can be imported. It can be treated similarly
172 // to an imported externally visible global value.
173 if (doImportAsDefinition(SGV) && !dyn_cast<GlobalAlias>(SGV))
174 return GlobalValue::AvailableExternallyLinkage;
176 return GlobalValue::ExternalLinkage;
178 case GlobalValue::AppendingLinkage:
179 // It would be incorrect to import an appending linkage variable,
180 // since it would cause global constructors/destructors to be
181 // executed multiple times. This should have already been handled
182 // by linkIfNeeded, and we will assert in shouldLinkFromSource
183 // if we try to import, so we simply return AppendingLinkage.
184 return GlobalValue::AppendingLinkage;
186 case GlobalValue::InternalLinkage:
187 case GlobalValue::PrivateLinkage:
188 // If we are promoting the local to global scope, it is handled
189 // similarly to a normal externally visible global.
191 if (doImportAsDefinition(SGV) && !dyn_cast<GlobalAlias>(SGV))
192 return GlobalValue::AvailableExternallyLinkage;
194 return GlobalValue::ExternalLinkage;
196 // A non-promoted imported local definition stays local.
197 // The ThinLTO pass will eventually force-import their definitions.
198 return SGV->getLinkage();
200 case GlobalValue::ExternalWeakLinkage:
201 // External weak doesn't apply to definitions, must be a declaration.
202 assert(!doImportAsDefinition(SGV));
203 // Linkage stays external_weak.
204 return SGV->getLinkage();
206 case GlobalValue::CommonLinkage:
207 // Linkage stays common on definitions.
208 // The ThinLTO pass will eventually force-import their definitions.
209 return SGV->getLinkage();
212 llvm_unreachable("unknown linkage type");
215 void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
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();