1//===- lib/Transforms/Utils/FunctionImportUtils.cpp - Importing utilities -===//
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 implements the FunctionImportGlobalProcessing class, used
10// to perform the necessary global value handling for function importing.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Transforms/Utils/FunctionImportUtils.h"
15#include "llvm/Support/CommandLine.h"
16using namespace llvm;
17
18/// Uses the "source_filename" instead of a Module hash ID for the suffix of
19/// promoted locals during LTO. NOTE: This requires that the source filename
20/// has a unique name / path to avoid name collisions.
21static cl::opt<bool> UseSourceFilenameForPromotedLocals(
22 "use-source-filename-for-promoted-locals", cl::Hidden,
23 cl::desc("Uses the source file name instead of the Module hash. "
24 "This requires that the source filename has a unique name / "
25 "path to avoid name collisions."));
26
27/// Checks if we should import SGV as a definition, otherwise import as a
28/// declaration.
29bool FunctionImportGlobalProcessing::doImportAsDefinition(
30 const GlobalValue *SGV) {
31 if (!isPerformingImport())
32 return false;
33
34 // Only import the globals requested for importing.
35 if (!GlobalsToImport->count(key: const_cast<GlobalValue *>(SGV)))
36 return false;
37
38 assert(!isa<GlobalAlias>(SGV) &&
39 "Unexpected global alias in the import list.");
40
41 // Otherwise yes.
42 return true;
43}
44
45bool FunctionImportGlobalProcessing::shouldPromoteLocalToGlobal(
46 const GlobalValue *SGV, ValueInfo VI) {
47 assert(SGV->hasLocalLinkage());
48
49 // Ifuncs and ifunc alias does not have summary.
50 if (isa<GlobalIFunc>(Val: SGV) ||
51 (isa<GlobalAlias>(Val: SGV) &&
52 isa<GlobalIFunc>(Val: cast<GlobalAlias>(Val: SGV)->getAliaseeObject())))
53 return false;
54
55 // Both the imported references and the original local variable must
56 // be promoted.
57 if (!isPerformingImport() && !isModuleExporting())
58 return false;
59
60 if (isPerformingImport()) {
61 assert((!GlobalsToImport->count(const_cast<GlobalValue *>(SGV)) ||
62 !isNonRenamableLocal(*SGV)) &&
63 "Attempting to promote non-renamable local");
64 // We don't know for sure yet if we are importing this value (as either
65 // a reference or a def), since we are simply walking all values in the
66 // module. But by necessity if we end up importing it and it is local,
67 // it must be promoted, so unconditionally promote all values in the
68 // importing module.
69 return true;
70 }
71
72 // When exporting, consult the index. We can have more than one local
73 // with the same GUID, in the case of same-named locals in different but
74 // same-named source files that were compiled in their respective directories
75 // (so the source file name and resulting GUID is the same). Find the one
76 // in this module.
77 auto Summary = ImportIndex.findSummaryInModule(
78 VI, ModuleId: SGV->getParent()->getModuleIdentifier());
79 assert(Summary && "Missing summary for global value when exporting");
80 auto Linkage = Summary->linkage();
81 if (!GlobalValue::isLocalLinkage(Linkage)) {
82 assert(!isNonRenamableLocal(*SGV) &&
83 "Attempting to promote non-renamable local");
84 return true;
85 }
86
87 return false;
88}
89
90#ifndef NDEBUG
91bool FunctionImportGlobalProcessing::isNonRenamableLocal(
92 const GlobalValue &GV) const {
93 if (!GV.hasLocalLinkage())
94 return false;
95 // This needs to stay in sync with the logic in buildModuleSummaryIndex.
96 if (GV.hasSection())
97 return true;
98 if (Used.count(const_cast<GlobalValue *>(&GV)))
99 return true;
100 return false;
101}
102#endif
103
104std::string
105FunctionImportGlobalProcessing::getPromotedName(const GlobalValue *SGV) {
106 assert(SGV->hasLocalLinkage());
107
108 // For locals that must be promoted to global scope, ensure that
109 // the promoted name uniquely identifies the copy in the original module,
110 // using the ID assigned during combined index creation.
111 if (UseSourceFilenameForPromotedLocals &&
112 !SGV->getParent()->getSourceFileName().empty()) {
113 SmallString<256> Suffix(SGV->getParent()->getSourceFileName());
114 std::replace_if(first: std::begin(cont&: Suffix), last: std::end(cont&: Suffix),
115 pred: [&](char ch) { return !isAlnum(C: ch); }, new_value: '_');
116 return ModuleSummaryIndex::getGlobalNameForLocal(
117 Name: SGV->getName(), Suffix);
118 }
119
120 return ModuleSummaryIndex::getGlobalNameForLocal(
121 Name: SGV->getName(),
122 ModHash: ImportIndex.getModuleHash(ModPath: SGV->getParent()->getModuleIdentifier()));
123}
124
125GlobalValue::LinkageTypes
126FunctionImportGlobalProcessing::getLinkage(const GlobalValue *SGV,
127 bool DoPromote) {
128 // Any local variable that is referenced by an exported function needs
129 // to be promoted to global scope. Since we don't currently know which
130 // functions reference which local variables/functions, we must treat
131 // all as potentially exported if this module is exporting anything.
132 if (isModuleExporting()) {
133 if (SGV->hasLocalLinkage() && DoPromote)
134 return GlobalValue::ExternalLinkage;
135 return SGV->getLinkage();
136 }
137
138 // Otherwise, if we aren't importing, no linkage change is needed.
139 if (!isPerformingImport())
140 return SGV->getLinkage();
141
142 switch (SGV->getLinkage()) {
143 case GlobalValue::LinkOnceODRLinkage:
144 case GlobalValue::ExternalLinkage:
145 // External and linkonce definitions are converted to available_externally
146 // definitions upon import, so that they are available for inlining
147 // and/or optimization, but are turned into declarations later
148 // during the EliminateAvailableExternally pass.
149 if (doImportAsDefinition(SGV) && !isa<GlobalAlias>(Val: SGV))
150 return GlobalValue::AvailableExternallyLinkage;
151 // An imported external declaration stays external.
152 return SGV->getLinkage();
153
154 case GlobalValue::AvailableExternallyLinkage:
155 // An imported available_externally definition converts
156 // to external if imported as a declaration.
157 if (!doImportAsDefinition(SGV))
158 return GlobalValue::ExternalLinkage;
159 // An imported available_externally declaration stays that way.
160 return SGV->getLinkage();
161
162 case GlobalValue::LinkOnceAnyLinkage:
163 case GlobalValue::WeakAnyLinkage:
164 // Can't import linkonce_any/weak_any definitions correctly, or we might
165 // change the program semantics, since the linker will pick the first
166 // linkonce_any/weak_any definition and importing would change the order
167 // they are seen by the linker. The module linking caller needs to enforce
168 // this.
169 assert(!doImportAsDefinition(SGV));
170 // If imported as a declaration, it becomes external_weak.
171 return SGV->getLinkage();
172
173 case GlobalValue::WeakODRLinkage:
174 // For weak_odr linkage, there is a guarantee that all copies will be
175 // equivalent, so the issue described above for weak_any does not exist,
176 // and the definition can be imported. It can be treated similarly
177 // to an imported externally visible global value.
178 if (doImportAsDefinition(SGV) && !isa<GlobalAlias>(Val: SGV))
179 return GlobalValue::AvailableExternallyLinkage;
180 else
181 return GlobalValue::ExternalLinkage;
182
183 case GlobalValue::AppendingLinkage:
184 // It would be incorrect to import an appending linkage variable,
185 // since it would cause global constructors/destructors to be
186 // executed multiple times. This should have already been handled
187 // by linkIfNeeded, and we will assert in shouldLinkFromSource
188 // if we try to import, so we simply return AppendingLinkage.
189 return GlobalValue::AppendingLinkage;
190
191 case GlobalValue::InternalLinkage:
192 case GlobalValue::PrivateLinkage:
193 // If we are promoting the local to global scope, it is handled
194 // similarly to a normal externally visible global.
195 if (DoPromote) {
196 if (doImportAsDefinition(SGV) && !isa<GlobalAlias>(Val: SGV))
197 return GlobalValue::AvailableExternallyLinkage;
198 else
199 return GlobalValue::ExternalLinkage;
200 }
201 // A non-promoted imported local definition stays local.
202 // The ThinLTO pass will eventually force-import their definitions.
203 return SGV->getLinkage();
204
205 case GlobalValue::ExternalWeakLinkage:
206 // External weak doesn't apply to definitions, must be a declaration.
207 assert(!doImportAsDefinition(SGV));
208 // Linkage stays external_weak.
209 return SGV->getLinkage();
210
211 case GlobalValue::CommonLinkage:
212 // Linkage stays common on definitions.
213 // The ThinLTO pass will eventually force-import their definitions.
214 return SGV->getLinkage();
215 }
216
217 llvm_unreachable("unknown linkage type");
218}
219
220void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
221
222 ValueInfo VI;
223 if (GV.hasName()) {
224 VI = ImportIndex.getValueInfo(GUID: GV.getGUID());
225 // Set synthetic function entry counts.
226 if (VI && ImportIndex.hasSyntheticEntryCounts()) {
227 if (Function *F = dyn_cast<Function>(Val: &GV)) {
228 if (!F->isDeclaration()) {
229 for (const auto &S : VI.getSummaryList()) {
230 auto *FS = cast<FunctionSummary>(Val: S->getBaseObject());
231 if (FS->modulePath() == M.getModuleIdentifier()) {
232 F->setEntryCount(Count: Function::ProfileCount(FS->entryCount(),
233 Function::PCT_Synthetic));
234 break;
235 }
236 }
237 }
238 }
239 }
240 }
241
242 // We should always have a ValueInfo (i.e. GV in index) for definitions when
243 // we are exporting, and also when importing that value.
244 assert(VI || GV.isDeclaration() ||
245 (isPerformingImport() && !doImportAsDefinition(&GV)));
246
247 // Mark read/write-only variables which can be imported with specific
248 // attribute. We can't internalize them now because IRMover will fail
249 // to link variable definitions to their external declarations during
250 // ThinLTO import. We'll internalize read-only variables later, after
251 // import is finished. See internalizeGVsAfterImport.
252 //
253 // If global value dead stripping is not enabled in summary then
254 // propagateConstants hasn't been run. We can't internalize GV
255 // in such case.
256 if (!GV.isDeclaration() && VI && ImportIndex.withAttributePropagation()) {
257 if (GlobalVariable *V = dyn_cast<GlobalVariable>(Val: &GV)) {
258 // We can have more than one local with the same GUID, in the case of
259 // same-named locals in different but same-named source files that were
260 // compiled in their respective directories (so the source file name
261 // and resulting GUID is the same). Find the one in this module.
262 // Handle the case where there is no summary found in this module. That
263 // can happen in the distributed ThinLTO backend, because the index only
264 // contains summaries from the source modules if they are being imported.
265 // We might have a non-null VI and get here even in that case if the name
266 // matches one in this module (e.g. weak or appending linkage).
267 auto *GVS = dyn_cast_or_null<GlobalVarSummary>(
268 Val: ImportIndex.findSummaryInModule(VI, ModuleId: M.getModuleIdentifier()));
269 if (GVS &&
270 (ImportIndex.isReadOnly(GVS) || ImportIndex.isWriteOnly(GVS))) {
271 V->addAttribute(Kind: "thinlto-internalize");
272 // Objects referenced by writeonly GV initializer should not be
273 // promoted, because there is no any kind of read access to them
274 // on behalf of this writeonly GV. To avoid promotion we convert
275 // GV initializer to 'zeroinitializer'. This effectively drops
276 // references in IR module (not in combined index), so we can
277 // ignore them when computing import. We do not export references
278 // of writeonly object. See computeImportForReferencedGlobals
279 if (ImportIndex.isWriteOnly(GVS))
280 V->setInitializer(Constant::getNullValue(Ty: V->getValueType()));
281 }
282 }
283 }
284
285 if (GV.hasLocalLinkage() && shouldPromoteLocalToGlobal(SGV: &GV, VI)) {
286 // Save the original name string before we rename GV below.
287 auto Name = GV.getName().str();
288 GV.setName(getPromotedName(SGV: &GV));
289 GV.setLinkage(getLinkage(SGV: &GV, /* DoPromote */ true));
290 assert(!GV.hasLocalLinkage());
291 GV.setVisibility(GlobalValue::HiddenVisibility);
292
293 // If we are renaming a COMDAT leader, ensure that we record the COMDAT
294 // for later renaming as well. This is required for COFF.
295 if (const auto *C = GV.getComdat())
296 if (C->getName() == Name)
297 RenamedComdats.try_emplace(Key: C, Args: M.getOrInsertComdat(Name: GV.getName()));
298 } else
299 GV.setLinkage(getLinkage(SGV: &GV, /* DoPromote */ false));
300
301 // When ClearDSOLocalOnDeclarations is true, clear dso_local if GV is
302 // converted to a declaration, to disable direct access. Don't do this if GV
303 // is implicitly dso_local due to a non-default visibility.
304 if (ClearDSOLocalOnDeclarations &&
305 (GV.isDeclarationForLinker() ||
306 (isPerformingImport() && !doImportAsDefinition(SGV: &GV))) &&
307 !GV.isImplicitDSOLocal()) {
308 GV.setDSOLocal(false);
309 } else if (VI && VI.isDSOLocal(WithDSOLocalPropagation: ImportIndex.withDSOLocalPropagation())) {
310 // If all summaries are dso_local, symbol gets resolved to a known local
311 // definition.
312 GV.setDSOLocal(true);
313 if (GV.hasDLLImportStorageClass())
314 GV.setDLLStorageClass(GlobalValue::DefaultStorageClass);
315 }
316
317 // Remove functions imported as available externally defs from comdats,
318 // as this is a declaration for the linker, and will be dropped eventually.
319 // It is illegal for comdats to contain declarations.
320 auto *GO = dyn_cast<GlobalObject>(Val: &GV);
321 if (GO && GO->isDeclarationForLinker() && GO->hasComdat()) {
322 // The IRMover should not have placed any imported declarations in
323 // a comdat, so the only declaration that should be in a comdat
324 // at this point would be a definition imported as available_externally.
325 assert(GO->hasAvailableExternallyLinkage() &&
326 "Expected comdat on definition (possibly available external)");
327 GO->setComdat(nullptr);
328 }
329}
330
331void FunctionImportGlobalProcessing::processGlobalsForThinLTO() {
332 for (GlobalVariable &GV : M.globals())
333 processGlobalForThinLTO(GV);
334 for (Function &SF : M)
335 processGlobalForThinLTO(GV&: SF);
336 for (GlobalAlias &GA : M.aliases())
337 processGlobalForThinLTO(GV&: GA);
338
339 // Replace any COMDATS that required renaming (because the COMDAT leader was
340 // promoted and renamed).
341 if (!RenamedComdats.empty())
342 for (auto &GO : M.global_objects())
343 if (auto *C = GO.getComdat()) {
344 auto Replacement = RenamedComdats.find(Val: C);
345 if (Replacement != RenamedComdats.end())
346 GO.setComdat(Replacement->second);
347 }
348}
349
350bool FunctionImportGlobalProcessing::run() {
351 processGlobalsForThinLTO();
352 return false;
353}
354
355bool llvm::renameModuleForThinLTO(Module &M, const ModuleSummaryIndex &Index,
356 bool ClearDSOLocalOnDeclarations,
357 SetVector<GlobalValue *> *GlobalsToImport) {
358 FunctionImportGlobalProcessing ThinLTOProcessing(M, Index, GlobalsToImport,
359 ClearDSOLocalOnDeclarations);
360 return ThinLTOProcessing.run();
361}
362