1//===- ThinLTOBitcodeWriter.cpp - Bitcode writing pass for ThinLTO --------===//
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#include "llvm/Transforms/IPO/ThinLTOBitcodeWriter.h"
10#include "llvm/Analysis/BasicAliasAnalysis.h"
11#include "llvm/Analysis/ModuleSummaryAnalysis.h"
12#include "llvm/Analysis/ProfileSummaryInfo.h"
13#include "llvm/Analysis/TypeMetadataUtils.h"
14#include "llvm/Bitcode/BitcodeWriter.h"
15#include "llvm/IR/Constants.h"
16#include "llvm/IR/DebugInfo.h"
17#include "llvm/IR/Instructions.h"
18#include "llvm/IR/Intrinsics.h"
19#include "llvm/IR/Module.h"
20#include "llvm/IR/PassManager.h"
21#include "llvm/Object/ModuleSymbolTable.h"
22#include "llvm/Support/raw_ostream.h"
23#include "llvm/Transforms/IPO.h"
24#include "llvm/Transforms/IPO/FunctionAttrs.h"
25#include "llvm/Transforms/IPO/FunctionImport.h"
26#include "llvm/Transforms/IPO/LowerTypeTests.h"
27#include "llvm/Transforms/Utils/Cloning.h"
28#include "llvm/Transforms/Utils/ModuleUtils.h"
29using namespace llvm;
30
31namespace {
32
33// Determine if a promotion alias should be created for a symbol name.
34static bool allowPromotionAlias(const std::string &Name) {
35 // Promotion aliases are used only in inline assembly. It's safe to
36 // simply skip unusual names. Subset of MCAsmInfo::isAcceptableChar()
37 // and MCAsmInfoXCOFF::isAcceptableChar().
38 for (const char &C : Name) {
39 if (isAlnum(C) || C == '_' || C == '.')
40 continue;
41 return false;
42 }
43 return true;
44}
45
46// Promote each local-linkage entity defined by ExportM and used by ImportM by
47// changing visibility and appending the given ModuleId.
48void promoteInternals(Module &ExportM, Module &ImportM, StringRef ModuleId,
49 SetVector<GlobalValue *> &PromoteExtra) {
50 DenseMap<const Comdat *, Comdat *> RenamedComdats;
51 for (auto &ExportGV : ExportM.global_values()) {
52 if (!ExportGV.hasLocalLinkage())
53 continue;
54
55 auto Name = ExportGV.getName();
56 GlobalValue *ImportGV = nullptr;
57 if (!PromoteExtra.count(key: &ExportGV)) {
58 ImportGV = ImportM.getNamedValue(Name);
59 if (!ImportGV)
60 continue;
61 ImportGV->removeDeadConstantUsers();
62 if (ImportGV->use_empty()) {
63 ImportGV->eraseFromParent();
64 continue;
65 }
66 }
67
68 std::string OldName = Name.str();
69 std::string NewName = (Name + ModuleId).str();
70
71 if (const auto *C = ExportGV.getComdat())
72 if (C->getName() == Name)
73 RenamedComdats.try_emplace(Key: C, Args: ExportM.getOrInsertComdat(Name: NewName));
74
75 ExportGV.setName(NewName);
76 ExportGV.setLinkage(GlobalValue::ExternalLinkage);
77 ExportGV.setVisibility(GlobalValue::HiddenVisibility);
78
79 if (ImportGV) {
80 ImportGV->setName(NewName);
81 ImportGV->setVisibility(GlobalValue::HiddenVisibility);
82 }
83
84 if (isa<Function>(Val: &ExportGV) && allowPromotionAlias(Name: OldName)) {
85 // Create a local alias with the original name to avoid breaking
86 // references from inline assembly.
87 std::string Alias =
88 ".lto_set_conditional " + OldName + "," + NewName + "\n";
89 ExportM.appendModuleInlineAsm(Asm: Alias);
90 }
91 }
92
93 if (!RenamedComdats.empty())
94 for (auto &GO : ExportM.global_objects())
95 if (auto *C = GO.getComdat()) {
96 auto Replacement = RenamedComdats.find(Val: C);
97 if (Replacement != RenamedComdats.end())
98 GO.setComdat(Replacement->second);
99 }
100}
101
102// Promote all internal (i.e. distinct) type ids used by the module by replacing
103// them with external type ids formed using the module id.
104//
105// Note that this needs to be done before we clone the module because each clone
106// will receive its own set of distinct metadata nodes.
107void promoteTypeIds(Module &M, StringRef ModuleId) {
108 DenseMap<Metadata *, Metadata *> LocalToGlobal;
109 auto ExternalizeTypeId = [&](CallInst *CI, unsigned ArgNo) {
110 Metadata *MD =
111 cast<MetadataAsValue>(Val: CI->getArgOperand(i: ArgNo))->getMetadata();
112
113 if (isa<MDNode>(Val: MD) && cast<MDNode>(Val: MD)->isDistinct()) {
114 Metadata *&GlobalMD = LocalToGlobal[MD];
115 if (!GlobalMD) {
116 std::string NewName = (Twine(LocalToGlobal.size()) + ModuleId).str();
117 GlobalMD = MDString::get(Context&: M.getContext(), Str: NewName);
118 }
119
120 CI->setArgOperand(i: ArgNo,
121 v: MetadataAsValue::get(Context&: M.getContext(), MD: GlobalMD));
122 }
123 };
124
125 if (Function *TypeTestFunc =
126 M.getFunction(Name: Intrinsic::getName(id: Intrinsic::type_test))) {
127 for (const Use &U : TypeTestFunc->uses()) {
128 auto CI = cast<CallInst>(Val: U.getUser());
129 ExternalizeTypeId(CI, 1);
130 }
131 }
132
133 if (Function *PublicTypeTestFunc =
134 M.getFunction(Name: Intrinsic::getName(id: Intrinsic::public_type_test))) {
135 for (const Use &U : PublicTypeTestFunc->uses()) {
136 auto CI = cast<CallInst>(Val: U.getUser());
137 ExternalizeTypeId(CI, 1);
138 }
139 }
140
141 if (Function *TypeCheckedLoadFunc =
142 M.getFunction(Name: Intrinsic::getName(id: Intrinsic::type_checked_load))) {
143 for (const Use &U : TypeCheckedLoadFunc->uses()) {
144 auto CI = cast<CallInst>(Val: U.getUser());
145 ExternalizeTypeId(CI, 2);
146 }
147 }
148
149 if (Function *TypeCheckedLoadRelativeFunc = M.getFunction(
150 Name: Intrinsic::getName(id: Intrinsic::type_checked_load_relative))) {
151 for (const Use &U : TypeCheckedLoadRelativeFunc->uses()) {
152 auto CI = cast<CallInst>(Val: U.getUser());
153 ExternalizeTypeId(CI, 2);
154 }
155 }
156
157 for (GlobalObject &GO : M.global_objects()) {
158 SmallVector<MDNode *, 1> MDs;
159 GO.getMetadata(KindID: LLVMContext::MD_type, MDs);
160
161 GO.eraseMetadata(KindID: LLVMContext::MD_type);
162 for (auto *MD : MDs) {
163 auto I = LocalToGlobal.find(Val: MD->getOperand(I: 1));
164 if (I == LocalToGlobal.end()) {
165 GO.addMetadata(KindID: LLVMContext::MD_type, MD&: *MD);
166 continue;
167 }
168 GO.addMetadata(
169 KindID: LLVMContext::MD_type,
170 MD&: *MDNode::get(Context&: M.getContext(), MDs: {MD->getOperand(I: 0), I->second}));
171 }
172 }
173}
174
175// Drop unused globals, and drop type information from function declarations.
176// FIXME: If we made functions typeless then there would be no need to do this.
177void simplifyExternals(Module &M) {
178 FunctionType *EmptyFT =
179 FunctionType::get(Result: Type::getVoidTy(C&: M.getContext()), isVarArg: false);
180
181 for (Function &F : llvm::make_early_inc_range(Range&: M)) {
182 if (F.isDeclaration() && F.use_empty()) {
183 F.eraseFromParent();
184 continue;
185 }
186
187 if (!F.isDeclaration() || F.getFunctionType() == EmptyFT ||
188 // Changing the type of an intrinsic may invalidate the IR.
189 F.getName().starts_with(Prefix: "llvm."))
190 continue;
191
192 Function *NewF =
193 Function::Create(Ty: EmptyFT, Linkage: GlobalValue::ExternalLinkage,
194 AddrSpace: F.getAddressSpace(), N: "", M: &M);
195 NewF->copyAttributesFrom(Src: &F);
196 // Only copy function attribtues.
197 NewF->setAttributes(AttributeList::get(C&: M.getContext(),
198 Index: AttributeList::FunctionIndex,
199 Attrs: F.getAttributes().getFnAttrs()));
200 NewF->takeName(V: &F);
201 F.replaceAllUsesWith(V: NewF);
202 F.eraseFromParent();
203 }
204
205 for (GlobalIFunc &I : llvm::make_early_inc_range(Range: M.ifuncs())) {
206 if (I.use_empty())
207 I.eraseFromParent();
208 else
209 assert(I.getResolverFunction() && "ifunc misses its resolver function");
210 }
211
212 for (GlobalVariable &GV : llvm::make_early_inc_range(Range: M.globals())) {
213 if (GV.isDeclaration() && GV.use_empty()) {
214 GV.eraseFromParent();
215 continue;
216 }
217 }
218}
219
220static void
221filterModule(Module *M,
222 function_ref<bool(const GlobalValue *)> ShouldKeepDefinition) {
223 std::vector<GlobalValue *> V;
224 for (GlobalValue &GV : M->global_values())
225 if (!ShouldKeepDefinition(&GV))
226 V.push_back(x: &GV);
227
228 for (GlobalValue *GV : V)
229 if (!convertToDeclaration(GV&: *GV))
230 GV->eraseFromParent();
231}
232
233void forEachVirtualFunction(Constant *C, function_ref<void(Function *)> Fn) {
234 if (auto *F = dyn_cast<Function>(Val: C))
235 return Fn(F);
236 if (isa<GlobalValue>(Val: C))
237 return;
238 for (Value *Op : C->operands())
239 forEachVirtualFunction(C: cast<Constant>(Val: Op), Fn);
240}
241
242// Clone any @llvm[.compiler].used over to the new module and append
243// values whose defs were cloned into that module.
244static void cloneUsedGlobalVariables(const Module &SrcM, Module &DestM,
245 bool CompilerUsed) {
246 SmallVector<GlobalValue *, 4> Used, NewUsed;
247 // First collect those in the llvm[.compiler].used set.
248 collectUsedGlobalVariables(M: SrcM, Vec&: Used, CompilerUsed);
249 // Next build a set of the equivalent values defined in DestM.
250 for (auto *V : Used) {
251 auto *GV = DestM.getNamedValue(Name: V->getName());
252 if (GV && !GV->isDeclaration())
253 NewUsed.push_back(Elt: GV);
254 }
255 // Finally, add them to a llvm[.compiler].used variable in DestM.
256 if (CompilerUsed)
257 appendToCompilerUsed(M&: DestM, Values: NewUsed);
258 else
259 appendToUsed(M&: DestM, Values: NewUsed);
260}
261
262#ifndef NDEBUG
263static bool enableUnifiedLTO(Module &M) {
264 bool UnifiedLTO = false;
265 if (auto *MD =
266 mdconst::extract_or_null<ConstantInt>(M.getModuleFlag("UnifiedLTO")))
267 UnifiedLTO = MD->getZExtValue();
268 return UnifiedLTO;
269}
270#endif
271
272// If it's possible to split M into regular and thin LTO parts, do so and write
273// a multi-module bitcode file with the two parts to OS. Otherwise, write only a
274// regular LTO bitcode file to OS.
275void splitAndWriteThinLTOBitcode(
276 raw_ostream &OS, raw_ostream *ThinLinkOS,
277 function_ref<AAResults &(Function &)> AARGetter, Module &M) {
278 std::string ModuleId = getUniqueModuleId(M: &M);
279 if (ModuleId.empty()) {
280 assert(!enableUnifiedLTO(M));
281 // We couldn't generate a module ID for this module, write it out as a
282 // regular LTO module with an index for summary-based dead stripping.
283 ProfileSummaryInfo PSI(M);
284 M.addModuleFlag(Behavior: Module::Error, Key: "ThinLTO", Val: uint32_t(0));
285 ModuleSummaryIndex Index = buildModuleSummaryIndex(M, GetBFICallback: nullptr, PSI: &PSI);
286 WriteBitcodeToFile(M, Out&: OS, /*ShouldPreserveUseListOrder=*/false, Index: &Index,
287 /*UnifiedLTO=*/GenerateHash: false);
288
289 if (ThinLinkOS)
290 // We don't have a ThinLTO part, but still write the module to the
291 // ThinLinkOS if requested so that the expected output file is produced.
292 WriteBitcodeToFile(M, Out&: *ThinLinkOS, /*ShouldPreserveUseListOrder=*/false,
293 Index: &Index, /*UnifiedLTO=*/GenerateHash: false);
294
295 return;
296 }
297
298 promoteTypeIds(M, ModuleId);
299
300 // Returns whether a global or its associated global has attached type
301 // metadata. The former may participate in CFI or whole-program
302 // devirtualization, so they need to appear in the merged module instead of
303 // the thin LTO module. Similarly, globals that are associated with globals
304 // with type metadata need to appear in the merged module because they will
305 // reference the global's section directly.
306 auto HasTypeMetadata = [](const GlobalObject *GO) {
307 if (MDNode *MD = GO->getMetadata(KindID: LLVMContext::MD_associated))
308 if (auto *AssocVM = dyn_cast_or_null<ValueAsMetadata>(Val: MD->getOperand(I: 0)))
309 if (auto *AssocGO = dyn_cast<GlobalObject>(Val: AssocVM->getValue()))
310 if (AssocGO->hasMetadata(KindID: LLVMContext::MD_type))
311 return true;
312 return GO->hasMetadata(KindID: LLVMContext::MD_type);
313 };
314
315 // Collect the set of virtual functions that are eligible for virtual constant
316 // propagation. Each eligible function must not access memory, must return
317 // an integer of width <=64 bits, must take at least one argument, must not
318 // use its first argument (assumed to be "this") and all arguments other than
319 // the first one must be of <=64 bit integer type.
320 //
321 // Note that we test whether this copy of the function is readnone, rather
322 // than testing function attributes, which must hold for any copy of the
323 // function, even a less optimized version substituted at link time. This is
324 // sound because the virtual constant propagation optimizations effectively
325 // inline all implementations of the virtual function into each call site,
326 // rather than using function attributes to perform local optimization.
327 DenseSet<const Function *> EligibleVirtualFns;
328 // If any member of a comdat lives in MergedM, put all members of that
329 // comdat in MergedM to keep the comdat together.
330 DenseSet<const Comdat *> MergedMComdats;
331 for (GlobalVariable &GV : M.globals())
332 if (!GV.isDeclaration() && HasTypeMetadata(&GV)) {
333 if (const auto *C = GV.getComdat())
334 MergedMComdats.insert(V: C);
335 forEachVirtualFunction(C: GV.getInitializer(), Fn: [&](Function *F) {
336 auto *RT = dyn_cast<IntegerType>(Val: F->getReturnType());
337 if (!RT || RT->getBitWidth() > 64 || F->arg_empty() ||
338 !F->arg_begin()->use_empty())
339 return;
340 for (auto &Arg : drop_begin(RangeOrContainer: F->args())) {
341 auto *ArgT = dyn_cast<IntegerType>(Val: Arg.getType());
342 if (!ArgT || ArgT->getBitWidth() > 64)
343 return;
344 }
345 if (!F->isDeclaration() &&
346 computeFunctionBodyMemoryAccess(F&: *F, AAR&: AARGetter(*F))
347 .doesNotAccessMemory())
348 EligibleVirtualFns.insert(V: F);
349 });
350 }
351
352 ValueToValueMapTy VMap;
353 std::unique_ptr<Module> MergedM(
354 CloneModule(M, VMap, ShouldCloneDefinition: [&](const GlobalValue *GV) -> bool {
355 if (const auto *C = GV->getComdat())
356 if (MergedMComdats.count(V: C))
357 return true;
358 if (auto *F = dyn_cast<Function>(Val: GV))
359 return EligibleVirtualFns.count(V: F);
360 if (auto *GVar =
361 dyn_cast_or_null<GlobalVariable>(Val: GV->getAliaseeObject()))
362 return HasTypeMetadata(GVar);
363 return false;
364 }));
365 StripDebugInfo(M&: *MergedM);
366 MergedM->setModuleInlineAsm("");
367
368 // Clone any llvm.*used globals to ensure the included values are
369 // not deleted.
370 cloneUsedGlobalVariables(SrcM: M, DestM&: *MergedM, /*CompilerUsed*/ false);
371 cloneUsedGlobalVariables(SrcM: M, DestM&: *MergedM, /*CompilerUsed*/ true);
372
373 for (Function &F : *MergedM)
374 if (!F.isDeclaration()) {
375 // Reset the linkage of all functions eligible for virtual constant
376 // propagation. The canonical definitions live in the thin LTO module so
377 // that they can be imported.
378 F.setLinkage(GlobalValue::AvailableExternallyLinkage);
379 F.setComdat(nullptr);
380 }
381
382 SetVector<GlobalValue *> CfiFunctions;
383 for (auto &F : M)
384 if ((!F.hasLocalLinkage() || F.hasAddressTaken()) && HasTypeMetadata(&F))
385 CfiFunctions.insert(X: &F);
386
387 // Remove all globals with type metadata, globals with comdats that live in
388 // MergedM, and aliases pointing to such globals from the thin LTO module.
389 filterModule(M: &M, ShouldKeepDefinition: [&](const GlobalValue *GV) {
390 if (auto *GVar = dyn_cast_or_null<GlobalVariable>(Val: GV->getAliaseeObject()))
391 if (HasTypeMetadata(GVar))
392 return false;
393 if (const auto *C = GV->getComdat())
394 if (MergedMComdats.count(V: C))
395 return false;
396 return true;
397 });
398
399 promoteInternals(ExportM&: *MergedM, ImportM&: M, ModuleId, PromoteExtra&: CfiFunctions);
400 promoteInternals(ExportM&: M, ImportM&: *MergedM, ModuleId, PromoteExtra&: CfiFunctions);
401
402 auto &Ctx = MergedM->getContext();
403 SmallVector<MDNode *, 8> CfiFunctionMDs;
404 for (auto *V : CfiFunctions) {
405 Function &F = *cast<Function>(Val: V);
406 SmallVector<MDNode *, 2> Types;
407 F.getMetadata(KindID: LLVMContext::MD_type, MDs&: Types);
408
409 SmallVector<Metadata *, 4> Elts;
410 Elts.push_back(Elt: MDString::get(Context&: Ctx, Str: F.getName()));
411 CfiFunctionLinkage Linkage;
412 if (lowertypetests::isJumpTableCanonical(F: &F))
413 Linkage = CFL_Definition;
414 else if (F.hasExternalWeakLinkage())
415 Linkage = CFL_WeakDeclaration;
416 else
417 Linkage = CFL_Declaration;
418 Elts.push_back(Elt: ConstantAsMetadata::get(
419 C: llvm::ConstantInt::get(Ty: Type::getInt8Ty(C&: Ctx), V: Linkage)));
420 append_range(C&: Elts, R&: Types);
421 CfiFunctionMDs.push_back(Elt: MDTuple::get(Context&: Ctx, MDs: Elts));
422 }
423
424 if(!CfiFunctionMDs.empty()) {
425 NamedMDNode *NMD = MergedM->getOrInsertNamedMetadata(Name: "cfi.functions");
426 for (auto *MD : CfiFunctionMDs)
427 NMD->addOperand(M: MD);
428 }
429
430 SmallVector<MDNode *, 8> FunctionAliases;
431 for (auto &A : M.aliases()) {
432 if (!isa<Function>(Val: A.getAliasee()))
433 continue;
434
435 auto *F = cast<Function>(Val: A.getAliasee());
436
437 Metadata *Elts[] = {
438 MDString::get(Context&: Ctx, Str: A.getName()),
439 MDString::get(Context&: Ctx, Str: F->getName()),
440 ConstantAsMetadata::get(
441 C: ConstantInt::get(Ty: Type::getInt8Ty(C&: Ctx), V: A.getVisibility())),
442 ConstantAsMetadata::get(
443 C: ConstantInt::get(Ty: Type::getInt8Ty(C&: Ctx), V: A.isWeakForLinker())),
444 };
445
446 FunctionAliases.push_back(Elt: MDTuple::get(Context&: Ctx, MDs: Elts));
447 }
448
449 if (!FunctionAliases.empty()) {
450 NamedMDNode *NMD = MergedM->getOrInsertNamedMetadata(Name: "aliases");
451 for (auto *MD : FunctionAliases)
452 NMD->addOperand(M: MD);
453 }
454
455 SmallVector<MDNode *, 8> Symvers;
456 ModuleSymbolTable::CollectAsmSymvers(M, AsmSymver: [&](StringRef Name, StringRef Alias) {
457 Function *F = M.getFunction(Name);
458 if (!F || F->use_empty())
459 return;
460
461 Symvers.push_back(Elt: MDTuple::get(
462 Context&: Ctx, MDs: {MDString::get(Context&: Ctx, Str: Name), MDString::get(Context&: Ctx, Str: Alias)}));
463 });
464
465 if (!Symvers.empty()) {
466 NamedMDNode *NMD = MergedM->getOrInsertNamedMetadata(Name: "symvers");
467 for (auto *MD : Symvers)
468 NMD->addOperand(M: MD);
469 }
470
471 simplifyExternals(M&: *MergedM);
472
473 // FIXME: Try to re-use BSI and PFI from the original module here.
474 ProfileSummaryInfo PSI(M);
475 ModuleSummaryIndex Index = buildModuleSummaryIndex(M, GetBFICallback: nullptr, PSI: &PSI);
476
477 // Mark the merged module as requiring full LTO. We still want an index for
478 // it though, so that it can participate in summary-based dead stripping.
479 MergedM->addModuleFlag(Behavior: Module::Error, Key: "ThinLTO", Val: uint32_t(0));
480 ModuleSummaryIndex MergedMIndex =
481 buildModuleSummaryIndex(M: *MergedM, GetBFICallback: nullptr, PSI: &PSI);
482
483 SmallVector<char, 0> Buffer;
484
485 BitcodeWriter W(Buffer);
486 // Save the module hash produced for the full bitcode, which will
487 // be used in the backends, and use that in the minimized bitcode
488 // produced for the full link.
489 ModuleHash ModHash = {._M_elems: {0}};
490 W.writeModule(M, /*ShouldPreserveUseListOrder=*/false, Index: &Index,
491 /*GenerateHash=*/true, ModHash: &ModHash);
492 W.writeModule(M: *MergedM, /*ShouldPreserveUseListOrder=*/false, Index: &MergedMIndex);
493 W.writeSymtab();
494 W.writeStrtab();
495 OS << Buffer;
496
497 // If a minimized bitcode module was requested for the thin link, only
498 // the information that is needed by thin link will be written in the
499 // given OS (the merged module will be written as usual).
500 if (ThinLinkOS) {
501 Buffer.clear();
502 BitcodeWriter W2(Buffer);
503 StripDebugInfo(M);
504 W2.writeThinLinkBitcode(M, Index, ModHash);
505 W2.writeModule(M: *MergedM, /*ShouldPreserveUseListOrder=*/false,
506 Index: &MergedMIndex);
507 W2.writeSymtab();
508 W2.writeStrtab();
509 *ThinLinkOS << Buffer;
510 }
511}
512
513// Check if the LTO Unit splitting has been enabled.
514bool enableSplitLTOUnit(Module &M) {
515 bool EnableSplitLTOUnit = false;
516 if (auto *MD = mdconst::extract_or_null<ConstantInt>(
517 MD: M.getModuleFlag(Key: "EnableSplitLTOUnit")))
518 EnableSplitLTOUnit = MD->getZExtValue();
519 return EnableSplitLTOUnit;
520}
521
522// Returns whether this module needs to be split because it uses type metadata.
523bool hasTypeMetadata(Module &M) {
524 for (auto &GO : M.global_objects()) {
525 if (GO.hasMetadata(KindID: LLVMContext::MD_type))
526 return true;
527 }
528 return false;
529}
530
531bool writeThinLTOBitcode(raw_ostream &OS, raw_ostream *ThinLinkOS,
532 function_ref<AAResults &(Function &)> AARGetter,
533 Module &M, const ModuleSummaryIndex *Index) {
534 std::unique_ptr<ModuleSummaryIndex> NewIndex = nullptr;
535 // See if this module has any type metadata. If so, we try to split it
536 // or at least promote type ids to enable WPD.
537 if (hasTypeMetadata(M)) {
538 if (enableSplitLTOUnit(M)) {
539 splitAndWriteThinLTOBitcode(OS, ThinLinkOS, AARGetter, M);
540 return true;
541 }
542 // Promote type ids as needed for index-based WPD.
543 std::string ModuleId = getUniqueModuleId(M: &M);
544 if (!ModuleId.empty()) {
545 promoteTypeIds(M, ModuleId);
546 // Need to rebuild the index so that it contains type metadata
547 // for the newly promoted type ids.
548 // FIXME: Probably should not bother building the index at all
549 // in the caller of writeThinLTOBitcode (which does so via the
550 // ModuleSummaryIndexAnalysis pass), since we have to rebuild it
551 // anyway whenever there is type metadata (here or in
552 // splitAndWriteThinLTOBitcode). Just always build it once via the
553 // buildModuleSummaryIndex when Module(s) are ready.
554 ProfileSummaryInfo PSI(M);
555 NewIndex = std::make_unique<ModuleSummaryIndex>(
556 args: buildModuleSummaryIndex(M, GetBFICallback: nullptr, PSI: &PSI));
557 Index = NewIndex.get();
558 }
559 }
560
561 // Write it out as an unsplit ThinLTO module.
562
563 // Save the module hash produced for the full bitcode, which will
564 // be used in the backends, and use that in the minimized bitcode
565 // produced for the full link.
566 ModuleHash ModHash = {._M_elems: {0}};
567 WriteBitcodeToFile(M, Out&: OS, /*ShouldPreserveUseListOrder=*/false, Index,
568 /*GenerateHash=*/true, ModHash: &ModHash);
569 // If a minimized bitcode module was requested for the thin link, only
570 // the information that is needed by thin link will be written in the
571 // given OS.
572 if (ThinLinkOS && Index)
573 writeThinLinkBitcodeToFile(M, Out&: *ThinLinkOS, Index: *Index, ModHash);
574 return false;
575}
576
577} // anonymous namespace
578extern bool WriteNewDbgInfoFormatToBitcode;
579PreservedAnalyses
580llvm::ThinLTOBitcodeWriterPass::run(Module &M, ModuleAnalysisManager &AM) {
581 FunctionAnalysisManager &FAM =
582 AM.getResult<FunctionAnalysisManagerModuleProxy>(IR&: M).getManager();
583
584 ScopedDbgInfoFormatSetter FormatSetter(M, M.IsNewDbgInfoFormat &&
585 WriteNewDbgInfoFormatToBitcode);
586 if (M.IsNewDbgInfoFormat)
587 M.removeDebugIntrinsicDeclarations();
588
589 bool Changed = writeThinLTOBitcode(
590 OS, ThinLinkOS,
591 AARGetter: [&FAM](Function &F) -> AAResults & {
592 return FAM.getResult<AAManager>(IR&: F);
593 },
594 M, Index: &AM.getResult<ModuleSummaryIndexAnalysis>(IR&: M));
595
596 return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
597}
598