1 //===- lib/Linker/LinkModules.cpp - Module Linker Implementation ----------===//
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 LLVM module linker.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Linker.h"
15 #include "llvm/Constants.h"
16 #include "llvm/DerivedTypes.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/Module.h"
19 #include "llvm/ADT/DenseSet.h"
20 #include "llvm/ADT/Optional.h"
21 #include "llvm/ADT/SetVector.h"
22 #include "llvm/ADT/SmallPtrSet.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/Path.h"
25 #include "llvm/Support/raw_ostream.h"
26 #include "llvm/Transforms/Utils/Cloning.h"
27 #include "llvm/Transforms/Utils/ValueMapper.h"
31 //===----------------------------------------------------------------------===//
32 // TypeMap implementation.
33 //===----------------------------------------------------------------------===//
36 class TypeMapTy : public ValueMapTypeRemapper {
37 /// MappedTypes - This is a mapping from a source type to a destination type
39 DenseMap<Type*, Type*> MappedTypes;
41 /// SpeculativeTypes - When checking to see if two subgraphs are isomorphic,
42 /// we speculatively add types to MappedTypes, but keep track of them here in
43 /// case we need to roll back.
44 SmallVector<Type*, 16> SpeculativeTypes;
46 /// SrcDefinitionsToResolve - This is a list of non-opaque structs in the
47 /// source module that are mapped to an opaque struct in the destination
49 SmallVector<StructType*, 16> SrcDefinitionsToResolve;
51 /// DstResolvedOpaqueTypes - This is the set of opaque types in the
52 /// destination modules who are getting a body from the source module.
53 SmallPtrSet<StructType*, 16> DstResolvedOpaqueTypes;
56 /// addTypeMapping - Indicate that the specified type in the destination
57 /// module is conceptually equivalent to the specified type in the source
59 void addTypeMapping(Type *DstTy, Type *SrcTy);
61 /// linkDefinedTypeBodies - Produce a body for an opaque type in the dest
62 /// module from a type definition in the source module.
63 void linkDefinedTypeBodies();
65 /// get - Return the mapped type to use for the specified input type from the
67 Type *get(Type *SrcTy);
69 FunctionType *get(FunctionType *T) {return cast<FunctionType>(get((Type*)T));}
71 /// dump - Dump out the type map for debugging purposes.
73 for (DenseMap<Type*, Type*>::const_iterator
74 I = MappedTypes.begin(), E = MappedTypes.end(); I != E; ++I) {
75 dbgs() << "TypeMap: ";
84 Type *getImpl(Type *T);
85 /// remapType - Implement the ValueMapTypeRemapper interface.
86 Type *remapType(Type *SrcTy) {
90 bool areTypesIsomorphic(Type *DstTy, Type *SrcTy);
94 void TypeMapTy::addTypeMapping(Type *DstTy, Type *SrcTy) {
95 Type *&Entry = MappedTypes[SrcTy];
103 // Check to see if these types are recursively isomorphic and establish a
104 // mapping between them if so.
105 if (!areTypesIsomorphic(DstTy, SrcTy)) {
106 // Oops, they aren't isomorphic. Just discard this request by rolling out
107 // any speculative mappings we've established.
108 for (unsigned i = 0, e = SpeculativeTypes.size(); i != e; ++i)
109 MappedTypes.erase(SpeculativeTypes[i]);
111 SpeculativeTypes.clear();
114 /// areTypesIsomorphic - Recursively walk this pair of types, returning true
115 /// if they are isomorphic, false if they are not.
116 bool TypeMapTy::areTypesIsomorphic(Type *DstTy, Type *SrcTy) {
117 // Two types with differing kinds are clearly not isomorphic.
118 if (DstTy->getTypeID() != SrcTy->getTypeID()) return false;
120 // If we have an entry in the MappedTypes table, then we have our answer.
121 Type *&Entry = MappedTypes[SrcTy];
123 return Entry == DstTy;
125 // Two identical types are clearly isomorphic. Remember this
126 // non-speculatively.
127 if (DstTy == SrcTy) {
132 // Okay, we have two types with identical kinds that we haven't seen before.
134 // If this is an opaque struct type, special case it.
135 if (StructType *SSTy = dyn_cast<StructType>(SrcTy)) {
136 // Mapping an opaque type to any struct, just keep the dest struct.
137 if (SSTy->isOpaque()) {
139 SpeculativeTypes.push_back(SrcTy);
143 // Mapping a non-opaque source type to an opaque dest. If this is the first
144 // type that we're mapping onto this destination type then we succeed. Keep
145 // the dest, but fill it in later. This doesn't need to be speculative. If
146 // this is the second (different) type that we're trying to map onto the
147 // same opaque type then we fail.
148 if (cast<StructType>(DstTy)->isOpaque()) {
149 // We can only map one source type onto the opaque destination type.
150 if (!DstResolvedOpaqueTypes.insert(cast<StructType>(DstTy)))
152 SrcDefinitionsToResolve.push_back(SSTy);
158 // If the number of subtypes disagree between the two types, then we fail.
159 if (SrcTy->getNumContainedTypes() != DstTy->getNumContainedTypes())
162 // Fail if any of the extra properties (e.g. array size) of the type disagree.
163 if (isa<IntegerType>(DstTy))
164 return false; // bitwidth disagrees.
165 if (PointerType *PT = dyn_cast<PointerType>(DstTy)) {
166 if (PT->getAddressSpace() != cast<PointerType>(SrcTy)->getAddressSpace())
169 } else if (FunctionType *FT = dyn_cast<FunctionType>(DstTy)) {
170 if (FT->isVarArg() != cast<FunctionType>(SrcTy)->isVarArg())
172 } else if (StructType *DSTy = dyn_cast<StructType>(DstTy)) {
173 StructType *SSTy = cast<StructType>(SrcTy);
174 if (DSTy->isLiteral() != SSTy->isLiteral() ||
175 DSTy->isPacked() != SSTy->isPacked())
177 } else if (ArrayType *DATy = dyn_cast<ArrayType>(DstTy)) {
178 if (DATy->getNumElements() != cast<ArrayType>(SrcTy)->getNumElements())
180 } else if (VectorType *DVTy = dyn_cast<VectorType>(DstTy)) {
181 if (DVTy->getNumElements() != cast<ArrayType>(SrcTy)->getNumElements())
185 // Otherwise, we speculate that these two types will line up and recursively
186 // check the subelements.
188 SpeculativeTypes.push_back(SrcTy);
190 for (unsigned i = 0, e = SrcTy->getNumContainedTypes(); i != e; ++i)
191 if (!areTypesIsomorphic(DstTy->getContainedType(i),
192 SrcTy->getContainedType(i)))
195 // If everything seems to have lined up, then everything is great.
199 /// linkDefinedTypeBodies - Produce a body for an opaque type in the dest
200 /// module from a type definition in the source module.
201 void TypeMapTy::linkDefinedTypeBodies() {
202 SmallVector<Type*, 16> Elements;
203 SmallString<16> TmpName;
205 // Note that processing entries in this loop (calling 'get') can add new
206 // entries to the SrcDefinitionsToResolve vector.
207 while (!SrcDefinitionsToResolve.empty()) {
208 StructType *SrcSTy = SrcDefinitionsToResolve.pop_back_val();
209 StructType *DstSTy = cast<StructType>(MappedTypes[SrcSTy]);
211 // TypeMap is a many-to-one mapping, if there were multiple types that
212 // provide a body for DstSTy then previous iterations of this loop may have
213 // already handled it. Just ignore this case.
214 if (!DstSTy->isOpaque()) continue;
215 assert(!SrcSTy->isOpaque() && "Not resolving a definition?");
217 // Map the body of the source type over to a new body for the dest type.
218 Elements.resize(SrcSTy->getNumElements());
219 for (unsigned i = 0, e = Elements.size(); i != e; ++i)
220 Elements[i] = getImpl(SrcSTy->getElementType(i));
222 DstSTy->setBody(Elements, SrcSTy->isPacked());
224 // If DstSTy has no name or has a longer name than STy, then viciously steal
226 if (!SrcSTy->hasName()) continue;
227 StringRef SrcName = SrcSTy->getName();
229 if (!DstSTy->hasName() || DstSTy->getName().size() > SrcName.size()) {
230 TmpName.insert(TmpName.end(), SrcName.begin(), SrcName.end());
232 DstSTy->setName(TmpName.str());
237 DstResolvedOpaqueTypes.clear();
240 /// get - Return the mapped type to use for the specified input type from the
242 Type *TypeMapTy::get(Type *Ty) {
243 Type *Result = getImpl(Ty);
245 // If this caused a reference to any struct type, resolve it before returning.
246 if (!SrcDefinitionsToResolve.empty())
247 linkDefinedTypeBodies();
251 /// getImpl - This is the recursive version of get().
252 Type *TypeMapTy::getImpl(Type *Ty) {
253 // If we already have an entry for this type, return it.
254 Type **Entry = &MappedTypes[Ty];
255 if (*Entry) return *Entry;
257 // If this is not a named struct type, then just map all of the elements and
258 // then rebuild the type from inside out.
259 if (!isa<StructType>(Ty) || cast<StructType>(Ty)->isLiteral()) {
260 // If there are no element types to map, then the type is itself. This is
261 // true for the anonymous {} struct, things like 'float', integers, etc.
262 if (Ty->getNumContainedTypes() == 0)
265 // Remap all of the elements, keeping track of whether any of them change.
266 bool AnyChange = false;
267 SmallVector<Type*, 4> ElementTypes;
268 ElementTypes.resize(Ty->getNumContainedTypes());
269 for (unsigned i = 0, e = Ty->getNumContainedTypes(); i != e; ++i) {
270 ElementTypes[i] = getImpl(Ty->getContainedType(i));
271 AnyChange |= ElementTypes[i] != Ty->getContainedType(i);
274 // If we found our type while recursively processing stuff, just use it.
275 Entry = &MappedTypes[Ty];
276 if (*Entry) return *Entry;
278 // If all of the element types mapped directly over, then the type is usable
283 // Otherwise, rebuild a modified type.
284 switch (Ty->getTypeID()) {
285 default: llvm_unreachable("unknown derived type to remap");
286 case Type::ArrayTyID:
287 return *Entry = ArrayType::get(ElementTypes[0],
288 cast<ArrayType>(Ty)->getNumElements());
289 case Type::VectorTyID:
290 return *Entry = VectorType::get(ElementTypes[0],
291 cast<VectorType>(Ty)->getNumElements());
292 case Type::PointerTyID:
293 return *Entry = PointerType::get(ElementTypes[0],
294 cast<PointerType>(Ty)->getAddressSpace());
295 case Type::FunctionTyID:
296 return *Entry = FunctionType::get(ElementTypes[0],
297 makeArrayRef(ElementTypes).slice(1),
298 cast<FunctionType>(Ty)->isVarArg());
299 case Type::StructTyID:
300 // Note that this is only reached for anonymous structs.
301 return *Entry = StructType::get(Ty->getContext(), ElementTypes,
302 cast<StructType>(Ty)->isPacked());
306 // Otherwise, this is an unmapped named struct. If the struct can be directly
307 // mapped over, just use it as-is. This happens in a case when the linked-in
308 // module has something like:
309 // %T = type {%T*, i32}
310 // @GV = global %T* null
311 // where T does not exist at all in the destination module.
313 // The other case we watch for is when the type is not in the destination
314 // module, but that it has to be rebuilt because it refers to something that
315 // is already mapped. For example, if the destination module has:
317 // and the source module has something like
318 // %A' = type { i32 }
319 // %B = type { %A'* }
320 // @GV = global %B* null
321 // then we want to create a new type: "%B = type { %A*}" and have it take the
322 // pristine "%B" name from the source module.
324 // To determine which case this is, we have to recursively walk the type graph
325 // speculating that we'll be able to reuse it unmodified. Only if this is
326 // safe would we map the entire thing over. Because this is an optimization,
327 // and is not required for the prettiness of the linked module, we just skip
328 // it and always rebuild a type here.
329 StructType *STy = cast<StructType>(Ty);
331 // If the type is opaque, we can just use it directly.
335 // Otherwise we create a new type and resolve its body later. This will be
336 // resolved by the top level of get().
337 SrcDefinitionsToResolve.push_back(STy);
338 StructType *DTy = StructType::create(STy->getContext());
339 DstResolvedOpaqueTypes.insert(DTy);
343 //===----------------------------------------------------------------------===//
344 // ModuleLinker implementation.
345 //===----------------------------------------------------------------------===//
348 /// ModuleLinker - This is an implementation class for the LinkModules
349 /// function, which is the entrypoint for this file.
355 /// ValueMap - Mapping of values from what they used to be in Src, to what
356 /// they are now in DstM. ValueToValueMapTy is a ValueMap, which involves
357 /// some overhead due to the use of Value handles which the Linker doesn't
358 /// actually need, but this allows us to reuse the ValueMapper code.
359 ValueToValueMapTy ValueMap;
361 struct AppendingVarInfo {
362 GlobalVariable *NewGV; // New aggregate global in dest module.
363 Constant *DstInit; // Old initializer from dest module.
364 Constant *SrcInit; // Old initializer from src module.
367 std::vector<AppendingVarInfo> AppendingVars;
369 unsigned Mode; // Mode to treat source module.
371 // Set of items not to link in from source.
372 SmallPtrSet<const Value*, 16> DoNotLinkFromSource;
374 // Vector of functions to lazily link in.
375 std::vector<Function*> LazilyLinkFunctions;
378 std::string ErrorMsg;
380 ModuleLinker(Module *dstM, Module *srcM, unsigned mode)
381 : DstM(dstM), SrcM(srcM), Mode(mode) { }
386 /// emitError - Helper method for setting a message and returning an error
388 bool emitError(const Twine &Message) {
389 ErrorMsg = Message.str();
393 /// getLinkageResult - This analyzes the two global values and determines
394 /// what the result will look like in the destination module.
395 bool getLinkageResult(GlobalValue *Dest, const GlobalValue *Src,
396 GlobalValue::LinkageTypes <,
397 GlobalValue::VisibilityTypes &Vis,
400 /// getLinkedToGlobal - Given a global in the source module, return the
401 /// global in the destination module that is being linked to, if any.
402 GlobalValue *getLinkedToGlobal(GlobalValue *SrcGV) {
403 // If the source has no name it can't link. If it has local linkage,
404 // there is no name match-up going on.
405 if (!SrcGV->hasName() || SrcGV->hasLocalLinkage())
408 // Otherwise see if we have a match in the destination module's symtab.
409 GlobalValue *DGV = DstM->getNamedValue(SrcGV->getName());
410 if (DGV == 0) return 0;
412 // If we found a global with the same name in the dest module, but it has
413 // internal linkage, we are really not doing any linkage here.
414 if (DGV->hasLocalLinkage())
417 // Otherwise, we do in fact link to the destination global.
421 void computeTypeMapping();
422 bool categorizeModuleFlagNodes(const NamedMDNode *ModFlags,
423 DenseMap<MDString*, MDNode*> &ErrorNode,
424 DenseMap<MDString*, MDNode*> &WarningNode,
425 DenseMap<MDString*, MDNode*> &OverrideNode,
427 SmallSetVector<MDNode*, 8> > &RequireNodes,
428 SmallSetVector<MDString*, 16> &SeenIDs);
430 bool linkAppendingVarProto(GlobalVariable *DstGV, GlobalVariable *SrcGV);
431 bool linkGlobalProto(GlobalVariable *SrcGV);
432 bool linkFunctionProto(Function *SrcF);
433 bool linkAliasProto(GlobalAlias *SrcA);
434 bool linkModuleFlagsMetadata();
436 void linkAppendingVarInit(const AppendingVarInfo &AVI);
437 void linkGlobalInits();
438 void linkFunctionBody(Function *Dst, Function *Src);
439 void linkAliasBodies();
440 void linkNamedMDNodes();
444 /// forceRenaming - The LLVM SymbolTable class autorenames globals that conflict
445 /// in the symbol table. This is good for all clients except for us. Go
446 /// through the trouble to force this back.
447 static void forceRenaming(GlobalValue *GV, StringRef Name) {
448 // If the global doesn't force its name or if it already has the right name,
449 // there is nothing for us to do.
450 if (GV->hasLocalLinkage() || GV->getName() == Name)
453 Module *M = GV->getParent();
455 // If there is a conflict, rename the conflict.
456 if (GlobalValue *ConflictGV = M->getNamedValue(Name)) {
457 GV->takeName(ConflictGV);
458 ConflictGV->setName(Name); // This will cause ConflictGV to get renamed
459 assert(ConflictGV->getName() != Name && "forceRenaming didn't work");
461 GV->setName(Name); // Force the name back
465 /// copyGVAttributes - copy additional attributes (those not needed to construct
466 /// a GlobalValue) from the SrcGV to the DestGV.
467 static void copyGVAttributes(GlobalValue *DestGV, const GlobalValue *SrcGV) {
468 // Use the maximum alignment, rather than just copying the alignment of SrcGV.
469 unsigned Alignment = std::max(DestGV->getAlignment(), SrcGV->getAlignment());
470 DestGV->copyAttributesFrom(SrcGV);
471 DestGV->setAlignment(Alignment);
473 forceRenaming(DestGV, SrcGV->getName());
476 static bool isLessConstraining(GlobalValue::VisibilityTypes a,
477 GlobalValue::VisibilityTypes b) {
478 if (a == GlobalValue::HiddenVisibility)
480 if (b == GlobalValue::HiddenVisibility)
482 if (a == GlobalValue::ProtectedVisibility)
484 if (b == GlobalValue::ProtectedVisibility)
489 /// getLinkageResult - This analyzes the two global values and determines what
490 /// the result will look like in the destination module. In particular, it
491 /// computes the resultant linkage type and visibility, computes whether the
492 /// global in the source should be copied over to the destination (replacing
493 /// the existing one), and computes whether this linkage is an error or not.
494 bool ModuleLinker::getLinkageResult(GlobalValue *Dest, const GlobalValue *Src,
495 GlobalValue::LinkageTypes <,
496 GlobalValue::VisibilityTypes &Vis,
498 assert(Dest && "Must have two globals being queried");
499 assert(!Src->hasLocalLinkage() &&
500 "If Src has internal linkage, Dest shouldn't be set!");
502 bool SrcIsDeclaration = Src->isDeclaration() && !Src->isMaterializable();
503 bool DestIsDeclaration = Dest->isDeclaration();
505 if (SrcIsDeclaration) {
506 // If Src is external or if both Src & Dest are external.. Just link the
507 // external globals, we aren't adding anything.
508 if (Src->hasDLLImportLinkage()) {
509 // If one of GVs has DLLImport linkage, result should be dllimport'ed.
510 if (DestIsDeclaration) {
512 LT = Src->getLinkage();
514 } else if (Dest->hasExternalWeakLinkage()) {
515 // If the Dest is weak, use the source linkage.
517 LT = Src->getLinkage();
520 LT = Dest->getLinkage();
522 } else if (DestIsDeclaration && !Dest->hasDLLImportLinkage()) {
523 // If Dest is external but Src is not:
525 LT = Src->getLinkage();
526 } else if (Src->isWeakForLinker()) {
527 // At this point we know that Dest has LinkOnce, External*, Weak, Common,
529 if (Dest->hasExternalWeakLinkage() ||
530 Dest->hasAvailableExternallyLinkage() ||
531 (Dest->hasLinkOnceLinkage() &&
532 (Src->hasWeakLinkage() || Src->hasCommonLinkage()))) {
534 LT = Src->getLinkage();
537 LT = Dest->getLinkage();
539 } else if (Dest->isWeakForLinker()) {
540 // At this point we know that Src has External* or DLL* linkage.
541 if (Src->hasExternalWeakLinkage()) {
543 LT = Dest->getLinkage();
546 LT = GlobalValue::ExternalLinkage;
549 assert((Dest->hasExternalLinkage() || Dest->hasDLLImportLinkage() ||
550 Dest->hasDLLExportLinkage() || Dest->hasExternalWeakLinkage()) &&
551 (Src->hasExternalLinkage() || Src->hasDLLImportLinkage() ||
552 Src->hasDLLExportLinkage() || Src->hasExternalWeakLinkage()) &&
553 "Unexpected linkage type!");
554 return emitError("Linking globals named '" + Src->getName() +
555 "': symbol multiply defined!");
558 // Compute the visibility. We follow the rules in the System V Application
560 Vis = isLessConstraining(Src->getVisibility(), Dest->getVisibility()) ?
561 Dest->getVisibility() : Src->getVisibility();
565 /// computeTypeMapping - Loop over all of the linked values to compute type
566 /// mappings. For example, if we link "extern Foo *x" and "Foo *x = NULL", then
567 /// we have two struct types 'Foo' but one got renamed when the module was
568 /// loaded into the same LLVMContext.
569 void ModuleLinker::computeTypeMapping() {
570 // Incorporate globals.
571 for (Module::global_iterator I = SrcM->global_begin(),
572 E = SrcM->global_end(); I != E; ++I) {
573 GlobalValue *DGV = getLinkedToGlobal(I);
574 if (DGV == 0) continue;
576 if (!DGV->hasAppendingLinkage() || !I->hasAppendingLinkage()) {
577 TypeMap.addTypeMapping(DGV->getType(), I->getType());
581 // Unify the element type of appending arrays.
582 ArrayType *DAT = cast<ArrayType>(DGV->getType()->getElementType());
583 ArrayType *SAT = cast<ArrayType>(I->getType()->getElementType());
584 TypeMap.addTypeMapping(DAT->getElementType(), SAT->getElementType());
587 // Incorporate functions.
588 for (Module::iterator I = SrcM->begin(), E = SrcM->end(); I != E; ++I) {
589 if (GlobalValue *DGV = getLinkedToGlobal(I))
590 TypeMap.addTypeMapping(DGV->getType(), I->getType());
593 // Incorporate types by name, scanning all the types in the source module.
594 // At this point, the destination module may have a type "%foo = { i32 }" for
595 // example. When the source module got loaded into the same LLVMContext, if
596 // it had the same type, it would have been renamed to "%foo.42 = { i32 }".
597 std::vector<StructType*> SrcStructTypes;
598 SrcM->findUsedStructTypes(SrcStructTypes);
600 SmallPtrSet<StructType*, 32> SrcStructTypesSet(SrcStructTypes.begin(),
601 SrcStructTypes.end());
603 for (unsigned i = 0, e = SrcStructTypes.size(); i != e; ++i) {
604 StructType *ST = SrcStructTypes[i];
605 if (!ST->hasName()) continue;
607 // Check to see if there is a dot in the name followed by a digit.
608 size_t DotPos = ST->getName().rfind('.');
609 if (DotPos == 0 || DotPos == StringRef::npos ||
610 ST->getName().back() == '.' || !isdigit(ST->getName()[DotPos+1]))
613 // Check to see if the destination module has a struct with the prefix name.
614 if (StructType *DST = DstM->getTypeByName(ST->getName().substr(0, DotPos)))
615 // Don't use it if this actually came from the source module. They're in
616 // the same LLVMContext after all.
617 if (!SrcStructTypesSet.count(DST))
618 TypeMap.addTypeMapping(DST, ST);
621 // Don't bother incorporating aliases, they aren't generally typed well.
623 // Now that we have discovered all of the type equivalences, get a body for
624 // any 'opaque' types in the dest module that are now resolved.
625 TypeMap.linkDefinedTypeBodies();
628 /// linkAppendingVarProto - If there were any appending global variables, link
629 /// them together now. Return true on error.
630 bool ModuleLinker::linkAppendingVarProto(GlobalVariable *DstGV,
631 GlobalVariable *SrcGV) {
633 if (!SrcGV->hasAppendingLinkage() || !DstGV->hasAppendingLinkage())
634 return emitError("Linking globals named '" + SrcGV->getName() +
635 "': can only link appending global with another appending global!");
637 ArrayType *DstTy = cast<ArrayType>(DstGV->getType()->getElementType());
639 cast<ArrayType>(TypeMap.get(SrcGV->getType()->getElementType()));
640 Type *EltTy = DstTy->getElementType();
642 // Check to see that they two arrays agree on type.
643 if (EltTy != SrcTy->getElementType())
644 return emitError("Appending variables with different element types!");
645 if (DstGV->isConstant() != SrcGV->isConstant())
646 return emitError("Appending variables linked with different const'ness!");
648 if (DstGV->getAlignment() != SrcGV->getAlignment())
650 "Appending variables with different alignment need to be linked!");
652 if (DstGV->getVisibility() != SrcGV->getVisibility())
654 "Appending variables with different visibility need to be linked!");
656 if (DstGV->getSection() != SrcGV->getSection())
658 "Appending variables with different section name need to be linked!");
660 uint64_t NewSize = DstTy->getNumElements() + SrcTy->getNumElements();
661 ArrayType *NewType = ArrayType::get(EltTy, NewSize);
663 // Create the new global variable.
665 new GlobalVariable(*DstGV->getParent(), NewType, SrcGV->isConstant(),
666 DstGV->getLinkage(), /*init*/0, /*name*/"", DstGV,
667 DstGV->isThreadLocal(),
668 DstGV->getType()->getAddressSpace());
670 // Propagate alignment, visibility and section info.
671 copyGVAttributes(NG, DstGV);
673 AppendingVarInfo AVI;
675 AVI.DstInit = DstGV->getInitializer();
676 AVI.SrcInit = SrcGV->getInitializer();
677 AppendingVars.push_back(AVI);
679 // Replace any uses of the two global variables with uses of the new
681 ValueMap[SrcGV] = ConstantExpr::getBitCast(NG, TypeMap.get(SrcGV->getType()));
683 DstGV->replaceAllUsesWith(ConstantExpr::getBitCast(NG, DstGV->getType()));
684 DstGV->eraseFromParent();
686 // Track the source variable so we don't try to link it.
687 DoNotLinkFromSource.insert(SrcGV);
692 /// linkGlobalProto - Loop through the global variables in the src module and
693 /// merge them into the dest module.
694 bool ModuleLinker::linkGlobalProto(GlobalVariable *SGV) {
695 GlobalValue *DGV = getLinkedToGlobal(SGV);
696 llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;
699 // Concatenation of appending linkage variables is magic and handled later.
700 if (DGV->hasAppendingLinkage() || SGV->hasAppendingLinkage())
701 return linkAppendingVarProto(cast<GlobalVariable>(DGV), SGV);
703 // Determine whether linkage of these two globals follows the source
704 // module's definition or the destination module's definition.
705 GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
706 GlobalValue::VisibilityTypes NV;
707 bool LinkFromSrc = false;
708 if (getLinkageResult(DGV, SGV, NewLinkage, NV, LinkFromSrc))
712 // If we're not linking from the source, then keep the definition that we
715 // Special case for const propagation.
716 if (GlobalVariable *DGVar = dyn_cast<GlobalVariable>(DGV))
717 if (DGVar->isDeclaration() && SGV->isConstant() && !DGVar->isConstant())
718 DGVar->setConstant(true);
720 // Set calculated linkage and visibility.
721 DGV->setLinkage(NewLinkage);
722 DGV->setVisibility(*NewVisibility);
724 // Make sure to remember this mapping.
725 ValueMap[SGV] = ConstantExpr::getBitCast(DGV,TypeMap.get(SGV->getType()));
727 // Track the source global so that we don't attempt to copy it over when
728 // processing global initializers.
729 DoNotLinkFromSource.insert(SGV);
735 // No linking to be performed or linking from the source: simply create an
736 // identical version of the symbol over in the dest module... the
737 // initializer will be filled in later by LinkGlobalInits.
738 GlobalVariable *NewDGV =
739 new GlobalVariable(*DstM, TypeMap.get(SGV->getType()->getElementType()),
740 SGV->isConstant(), SGV->getLinkage(), /*init*/0,
741 SGV->getName(), /*insertbefore*/0,
742 SGV->isThreadLocal(),
743 SGV->getType()->getAddressSpace());
744 // Propagate alignment, visibility and section info.
745 copyGVAttributes(NewDGV, SGV);
747 NewDGV->setVisibility(*NewVisibility);
750 DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDGV, DGV->getType()));
751 DGV->eraseFromParent();
754 // Make sure to remember this mapping.
755 ValueMap[SGV] = NewDGV;
759 /// linkFunctionProto - Link the function in the source module into the
760 /// destination module if needed, setting up mapping information.
761 bool ModuleLinker::linkFunctionProto(Function *SF) {
762 GlobalValue *DGV = getLinkedToGlobal(SF);
763 llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;
766 GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
767 bool LinkFromSrc = false;
768 GlobalValue::VisibilityTypes NV;
769 if (getLinkageResult(DGV, SF, NewLinkage, NV, LinkFromSrc))
774 // Set calculated linkage
775 DGV->setLinkage(NewLinkage);
776 DGV->setVisibility(*NewVisibility);
778 // Make sure to remember this mapping.
779 ValueMap[SF] = ConstantExpr::getBitCast(DGV, TypeMap.get(SF->getType()));
781 // Track the function from the source module so we don't attempt to remap
783 DoNotLinkFromSource.insert(SF);
789 // If there is no linkage to be performed or we are linking from the source,
791 Function *NewDF = Function::Create(TypeMap.get(SF->getFunctionType()),
792 SF->getLinkage(), SF->getName(), DstM);
793 copyGVAttributes(NewDF, SF);
795 NewDF->setVisibility(*NewVisibility);
798 // Any uses of DF need to change to NewDF, with cast.
799 DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDF, DGV->getType()));
800 DGV->eraseFromParent();
802 // Internal, LO_ODR, or LO linkage - stick in set to ignore and lazily link.
803 if (SF->hasLocalLinkage() || SF->hasLinkOnceLinkage() ||
804 SF->hasAvailableExternallyLinkage()) {
805 DoNotLinkFromSource.insert(SF);
806 LazilyLinkFunctions.push_back(SF);
810 ValueMap[SF] = NewDF;
814 /// LinkAliasProto - Set up prototypes for any aliases that come over from the
816 bool ModuleLinker::linkAliasProto(GlobalAlias *SGA) {
817 GlobalValue *DGV = getLinkedToGlobal(SGA);
818 llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;
821 GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
822 GlobalValue::VisibilityTypes NV;
823 bool LinkFromSrc = false;
824 if (getLinkageResult(DGV, SGA, NewLinkage, NV, LinkFromSrc))
829 // Set calculated linkage.
830 DGV->setLinkage(NewLinkage);
831 DGV->setVisibility(*NewVisibility);
833 // Make sure to remember this mapping.
834 ValueMap[SGA] = ConstantExpr::getBitCast(DGV,TypeMap.get(SGA->getType()));
836 // Track the alias from the source module so we don't attempt to remap it.
837 DoNotLinkFromSource.insert(SGA);
843 // If there is no linkage to be performed or we're linking from the source,
845 GlobalAlias *NewDA = new GlobalAlias(TypeMap.get(SGA->getType()),
846 SGA->getLinkage(), SGA->getName(),
848 copyGVAttributes(NewDA, SGA);
850 NewDA->setVisibility(*NewVisibility);
853 // Any uses of DGV need to change to NewDA, with cast.
854 DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDA, DGV->getType()));
855 DGV->eraseFromParent();
858 ValueMap[SGA] = NewDA;
862 static void getArrayElements(Constant *C, SmallVectorImpl<Constant*> &Dest) {
863 unsigned NumElements = cast<ArrayType>(C->getType())->getNumElements();
865 for (unsigned i = 0; i != NumElements; ++i)
866 Dest.push_back(C->getAggregateElement(i));
869 void ModuleLinker::linkAppendingVarInit(const AppendingVarInfo &AVI) {
870 // Merge the initializer.
871 SmallVector<Constant*, 16> Elements;
872 getArrayElements(AVI.DstInit, Elements);
874 Constant *SrcInit = MapValue(AVI.SrcInit, ValueMap, RF_None, &TypeMap);
875 getArrayElements(SrcInit, Elements);
877 ArrayType *NewType = cast<ArrayType>(AVI.NewGV->getType()->getElementType());
878 AVI.NewGV->setInitializer(ConstantArray::get(NewType, Elements));
881 /// linkGlobalInits - Update the initializers in the Dest module now that all
882 /// globals that may be referenced are in Dest.
883 void ModuleLinker::linkGlobalInits() {
884 // Loop over all of the globals in the src module, mapping them over as we go
885 for (Module::const_global_iterator I = SrcM->global_begin(),
886 E = SrcM->global_end(); I != E; ++I) {
888 // Only process initialized GV's or ones not already in dest.
889 if (!I->hasInitializer() || DoNotLinkFromSource.count(I)) continue;
891 // Grab destination global variable.
892 GlobalVariable *DGV = cast<GlobalVariable>(ValueMap[I]);
893 // Figure out what the initializer looks like in the dest module.
894 DGV->setInitializer(MapValue(I->getInitializer(), ValueMap,
899 /// linkFunctionBody - Copy the source function over into the dest function and
900 /// fix up references to values. At this point we know that Dest is an external
901 /// function, and that Src is not.
902 void ModuleLinker::linkFunctionBody(Function *Dst, Function *Src) {
903 assert(Src && Dst && Dst->isDeclaration() && !Src->isDeclaration());
905 // Go through and convert function arguments over, remembering the mapping.
906 Function::arg_iterator DI = Dst->arg_begin();
907 for (Function::arg_iterator I = Src->arg_begin(), E = Src->arg_end();
909 DI->setName(I->getName()); // Copy the name over.
911 // Add a mapping to our mapping.
915 if (Mode == Linker::DestroySource) {
916 // Splice the body of the source function into the dest function.
917 Dst->getBasicBlockList().splice(Dst->end(), Src->getBasicBlockList());
919 // At this point, all of the instructions and values of the function are now
920 // copied over. The only problem is that they are still referencing values in
921 // the Source function as operands. Loop through all of the operands of the
922 // functions and patch them up to point to the local versions.
923 for (Function::iterator BB = Dst->begin(), BE = Dst->end(); BB != BE; ++BB)
924 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
925 RemapInstruction(I, ValueMap, RF_IgnoreMissingEntries, &TypeMap);
928 // Clone the body of the function into the dest function.
929 SmallVector<ReturnInst*, 8> Returns; // Ignore returns.
930 CloneFunctionInto(Dst, Src, ValueMap, false, Returns, "", NULL, &TypeMap);
933 // There is no need to map the arguments anymore.
934 for (Function::arg_iterator I = Src->arg_begin(), E = Src->arg_end();
940 /// linkAliasBodies - Insert all of the aliases in Src into the Dest module.
941 void ModuleLinker::linkAliasBodies() {
942 for (Module::alias_iterator I = SrcM->alias_begin(), E = SrcM->alias_end();
944 if (DoNotLinkFromSource.count(I))
946 if (Constant *Aliasee = I->getAliasee()) {
947 GlobalAlias *DA = cast<GlobalAlias>(ValueMap[I]);
948 DA->setAliasee(MapValue(Aliasee, ValueMap, RF_None, &TypeMap));
953 /// linkNamedMDNodes - Insert all of the named MDNodes in Src into the Dest
955 void ModuleLinker::linkNamedMDNodes() {
956 const NamedMDNode *SrcModFlags = SrcM->getModuleFlagsMetadata();
957 for (Module::const_named_metadata_iterator I = SrcM->named_metadata_begin(),
958 E = SrcM->named_metadata_end(); I != E; ++I) {
959 // Don't link module flags here. Do them separately.
960 if (&*I == SrcModFlags) continue;
961 NamedMDNode *DestNMD = DstM->getOrInsertNamedMetadata(I->getName());
962 // Add Src elements into Dest node.
963 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
964 DestNMD->addOperand(MapValue(I->getOperand(i), ValueMap,
969 /// categorizeModuleFlagNodes - Categorize the module flags according to their
970 /// type: Error, Warning, Override, and Require.
972 categorizeModuleFlagNodes(const NamedMDNode *ModFlags,
973 DenseMap<MDString*, MDNode*> &ErrorNode,
974 DenseMap<MDString*, MDNode*> &WarningNode,
975 DenseMap<MDString*, MDNode*> &OverrideNode,
977 SmallSetVector<MDNode*, 8> > &RequireNodes,
978 SmallSetVector<MDString*, 16> &SeenIDs) {
981 for (unsigned I = 0, E = ModFlags->getNumOperands(); I != E; ++I) {
982 MDNode *Op = ModFlags->getOperand(I);
983 assert(Op->getNumOperands() == 3 && "Invalid module flag metadata!");
984 assert(isa<ConstantInt>(Op->getOperand(0)) &&
985 "Module flag's first operand must be an integer!");
986 assert(isa<MDString>(Op->getOperand(1)) &&
987 "Module flag's second operand must be an MDString!");
989 ConstantInt *Behavior = cast<ConstantInt>(Op->getOperand(0));
990 MDString *ID = cast<MDString>(Op->getOperand(1));
991 Value *Val = Op->getOperand(2);
992 switch (Behavior->getZExtValue()) {
994 assert(false && "Invalid behavior in module flag metadata!");
996 case Module::Error: {
997 MDNode *&ErrNode = ErrorNode[ID];
998 if (!ErrNode) ErrNode = Op;
999 if (ErrNode->getOperand(2) != Val)
1000 HasErr = emitError("linking module flags '" + ID->getString() +
1001 "': IDs have conflicting values");
1004 case Module::Warning: {
1005 MDNode *&WarnNode = WarningNode[ID];
1006 if (!WarnNode) WarnNode = Op;
1007 if (WarnNode->getOperand(2) != Val)
1008 errs() << "WARNING: linking module flags '" << ID->getString()
1009 << "': IDs have conflicting values";
1012 case Module::Require: RequireNodes[ID].insert(Op); break;
1013 case Module::Override: {
1014 MDNode *&OvrNode = OverrideNode[ID];
1015 if (!OvrNode) OvrNode = Op;
1016 if (OvrNode->getOperand(2) != Val)
1017 HasErr = emitError("linking module flags '" + ID->getString() +
1018 "': IDs have conflicting override values");
1029 /// linkModuleFlagsMetadata - Merge the linker flags in Src into the Dest
1031 bool ModuleLinker::linkModuleFlagsMetadata() {
1032 const NamedMDNode *SrcModFlags = SrcM->getModuleFlagsMetadata();
1033 if (!SrcModFlags) return false;
1035 NamedMDNode *DstModFlags = DstM->getOrInsertModuleFlagsMetadata();
1037 // If the destination module doesn't have module flags yet, then just copy
1038 // over the source module's flags.
1039 if (DstModFlags->getNumOperands() == 0) {
1040 for (unsigned I = 0, E = SrcModFlags->getNumOperands(); I != E; ++I)
1041 DstModFlags->addOperand(SrcModFlags->getOperand(I));
1046 bool HasErr = false;
1048 // Otherwise, we have to merge them based on their behaviors. First,
1049 // categorize all of the nodes in the modules' module flags. If an error or
1050 // warning occurs, then emit the appropriate message(s).
1051 DenseMap<MDString*, MDNode*> ErrorNode;
1052 DenseMap<MDString*, MDNode*> WarningNode;
1053 DenseMap<MDString*, MDNode*> OverrideNode;
1054 DenseMap<MDString*, SmallSetVector<MDNode*, 8> > RequireNodes;
1055 SmallSetVector<MDString*, 16> SeenIDs;
1057 HasErr |= categorizeModuleFlagNodes(SrcModFlags, ErrorNode, WarningNode,
1058 OverrideNode, RequireNodes, SeenIDs);
1059 HasErr |= categorizeModuleFlagNodes(DstModFlags, ErrorNode, WarningNode,
1060 OverrideNode, RequireNodes, SeenIDs);
1062 // Check that there isn't both an error and warning node for a flag.
1063 for (SmallSetVector<MDString*, 16>::iterator
1064 I = SeenIDs.begin(), E = SeenIDs.end(); I != E; ++I) {
1066 if (ErrorNode[ID] && WarningNode[ID])
1067 HasErr = emitError("linking module flags '" + ID->getString() +
1068 "': IDs have conflicting behaviors");
1071 // Early exit if we had an error.
1072 if (HasErr) return true;
1074 // Get the destination's module flags ready for new operands.
1075 DstModFlags->dropAllReferences();
1077 // Add all of the module flags to the destination module.
1078 DenseMap<MDString*, SmallVector<MDNode*, 4> > AddedNodes;
1079 for (SmallSetVector<MDString*, 16>::iterator
1080 I = SeenIDs.begin(), E = SeenIDs.end(); I != E; ++I) {
1082 if (OverrideNode[ID]) {
1083 DstModFlags->addOperand(OverrideNode[ID]);
1084 AddedNodes[ID].push_back(OverrideNode[ID]);
1085 } else if (ErrorNode[ID]) {
1086 DstModFlags->addOperand(ErrorNode[ID]);
1087 AddedNodes[ID].push_back(ErrorNode[ID]);
1088 } else if (WarningNode[ID]) {
1089 DstModFlags->addOperand(WarningNode[ID]);
1090 AddedNodes[ID].push_back(WarningNode[ID]);
1093 for (SmallSetVector<MDNode*, 8>::iterator
1094 II = RequireNodes[ID].begin(), IE = RequireNodes[ID].end();
1096 DstModFlags->addOperand(*II);
1099 // Now check that all of the requirements have been satisfied.
1100 for (SmallSetVector<MDString*, 16>::iterator
1101 I = SeenIDs.begin(), E = SeenIDs.end(); I != E; ++I) {
1103 SmallSetVector<MDNode*, 8> &Set = RequireNodes[ID];
1105 for (SmallSetVector<MDNode*, 8>::iterator
1106 II = Set.begin(), IE = Set.end(); II != IE; ++II) {
1108 assert(isa<MDNode>(Node->getOperand(2)) &&
1109 "Module flag's third operand must be an MDNode!");
1110 MDNode *Val = cast<MDNode>(Node->getOperand(2));
1112 MDString *ReqID = cast<MDString>(Val->getOperand(0));
1113 Value *ReqVal = Val->getOperand(1);
1115 bool HasValue = false;
1116 for (SmallVectorImpl<MDNode*>::iterator
1117 RI = AddedNodes[ReqID].begin(), RE = AddedNodes[ReqID].end();
1119 MDNode *ReqNode = *RI;
1120 if (ReqNode->getOperand(2) == ReqVal) {
1127 HasErr = emitError("linking module flags '" + ReqID->getString() +
1128 "': does not have the required value");
1135 bool ModuleLinker::run() {
1136 assert(DstM && "Null destination module");
1137 assert(SrcM && "Null source module");
1139 // Inherit the target data from the source module if the destination module
1140 // doesn't have one already.
1141 if (DstM->getDataLayout().empty() && !SrcM->getDataLayout().empty())
1142 DstM->setDataLayout(SrcM->getDataLayout());
1144 // Copy the target triple from the source to dest if the dest's is empty.
1145 if (DstM->getTargetTriple().empty() && !SrcM->getTargetTriple().empty())
1146 DstM->setTargetTriple(SrcM->getTargetTriple());
1148 if (!SrcM->getDataLayout().empty() && !DstM->getDataLayout().empty() &&
1149 SrcM->getDataLayout() != DstM->getDataLayout())
1150 errs() << "WARNING: Linking two modules of different data layouts!\n";
1151 if (!SrcM->getTargetTriple().empty() &&
1152 DstM->getTargetTriple() != SrcM->getTargetTriple()) {
1153 errs() << "WARNING: Linking two modules of different target triples: ";
1154 if (!SrcM->getModuleIdentifier().empty())
1155 errs() << SrcM->getModuleIdentifier() << ": ";
1156 errs() << "'" << SrcM->getTargetTriple() << "' and '"
1157 << DstM->getTargetTriple() << "'\n";
1160 // Append the module inline asm string.
1161 if (!SrcM->getModuleInlineAsm().empty()) {
1162 if (DstM->getModuleInlineAsm().empty())
1163 DstM->setModuleInlineAsm(SrcM->getModuleInlineAsm());
1165 DstM->setModuleInlineAsm(DstM->getModuleInlineAsm()+"\n"+
1166 SrcM->getModuleInlineAsm());
1169 // Update the destination module's dependent libraries list with the libraries
1170 // from the source module. There's no opportunity for duplicates here as the
1171 // Module ensures that duplicate insertions are discarded.
1172 for (Module::lib_iterator SI = SrcM->lib_begin(), SE = SrcM->lib_end();
1174 DstM->addLibrary(*SI);
1176 // If the source library's module id is in the dependent library list of the
1177 // destination library, remove it since that module is now linked in.
1178 StringRef ModuleId = SrcM->getModuleIdentifier();
1179 if (!ModuleId.empty())
1180 DstM->removeLibrary(sys::path::stem(ModuleId));
1182 // Loop over all of the linked values to compute type mappings.
1183 computeTypeMapping();
1185 // Insert all of the globals in src into the DstM module... without linking
1186 // initializers (which could refer to functions not yet mapped over).
1187 for (Module::global_iterator I = SrcM->global_begin(),
1188 E = SrcM->global_end(); I != E; ++I)
1189 if (linkGlobalProto(I))
1192 // Link the functions together between the two modules, without doing function
1193 // bodies... this just adds external function prototypes to the DstM
1194 // function... We do this so that when we begin processing function bodies,
1195 // all of the global values that may be referenced are available in our
1197 for (Module::iterator I = SrcM->begin(), E = SrcM->end(); I != E; ++I)
1198 if (linkFunctionProto(I))
1201 // If there were any aliases, link them now.
1202 for (Module::alias_iterator I = SrcM->alias_begin(),
1203 E = SrcM->alias_end(); I != E; ++I)
1204 if (linkAliasProto(I))
1207 for (unsigned i = 0, e = AppendingVars.size(); i != e; ++i)
1208 linkAppendingVarInit(AppendingVars[i]);
1210 // Update the initializers in the DstM module now that all globals that may
1211 // be referenced are in DstM.
1214 // Link in the function bodies that are defined in the source module into
1216 for (Module::iterator SF = SrcM->begin(), E = SrcM->end(); SF != E; ++SF) {
1217 // Skip if not linking from source.
1218 if (DoNotLinkFromSource.count(SF)) continue;
1220 // Skip if no body (function is external) or materialize.
1221 if (SF->isDeclaration()) {
1222 if (!SF->isMaterializable())
1224 if (SF->Materialize(&ErrorMsg))
1228 linkFunctionBody(cast<Function>(ValueMap[SF]), SF);
1231 // Resolve all uses of aliases with aliasees.
1234 // Remap all of the named MDNodes in Src into the DstM module. We do this
1235 // after linking GlobalValues so that MDNodes that reference GlobalValues
1236 // are properly remapped.
1239 // Merge the module flags into the DstM module.
1240 if (linkModuleFlagsMetadata())
1243 // Process vector of lazily linked in functions.
1244 bool LinkedInAnyFunctions;
1246 LinkedInAnyFunctions = false;
1248 for(std::vector<Function*>::iterator I = LazilyLinkFunctions.begin(),
1249 E = LazilyLinkFunctions.end(); I != E; ++I) {
1254 Function *DF = cast<Function>(ValueMap[SF]);
1256 if (!DF->use_empty()) {
1258 // Materialize if necessary.
1259 if (SF->isDeclaration()) {
1260 if (!SF->isMaterializable())
1262 if (SF->Materialize(&ErrorMsg))
1266 // Link in function body.
1267 linkFunctionBody(DF, SF);
1269 // "Remove" from vector by setting the element to 0.
1272 // Set flag to indicate we may have more functions to lazily link in
1273 // since we linked in a function.
1274 LinkedInAnyFunctions = true;
1277 } while (LinkedInAnyFunctions);
1279 // Remove any prototypes of functions that were not actually linked in.
1280 for(std::vector<Function*>::iterator I = LazilyLinkFunctions.begin(),
1281 E = LazilyLinkFunctions.end(); I != E; ++I) {
1286 Function *DF = cast<Function>(ValueMap[SF]);
1287 if (DF->use_empty())
1288 DF->eraseFromParent();
1291 // Now that all of the types from the source are used, resolve any structs
1292 // copied over to the dest that didn't exist there.
1293 TypeMap.linkDefinedTypeBodies();
1298 //===----------------------------------------------------------------------===//
1299 // LinkModules entrypoint.
1300 //===----------------------------------------------------------------------===//
1302 /// LinkModules - This function links two modules together, with the resulting
1303 /// left module modified to be the composite of the two input modules. If an
1304 /// error occurs, true is returned and ErrorMsg (if not null) is set to indicate
1305 /// the problem. Upon failure, the Dest module could be in a modified state,
1306 /// and shouldn't be relied on to be consistent.
1307 bool Linker::LinkModules(Module *Dest, Module *Src, unsigned Mode,
1308 std::string *ErrorMsg) {
1309 ModuleLinker TheLinker(Dest, Src, Mode);
1310 if (TheLinker.run()) {
1311 if (ErrorMsg) *ErrorMsg = TheLinker.ErrorMsg;