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));}
72 /// dump - Dump out the type map for debugging purposes.
74 for (DenseMap<Type*, Type*>::const_iterator
75 I = MappedTypes.begin(), E = MappedTypes.end(); I != E; ++I) {
76 dbgs() << "TypeMap: ";
86 Type *getImpl(Type *T);
87 /// remapType - Implement the ValueMapTypeRemapper interface.
88 Type *remapType(Type *SrcTy) {
92 bool areTypesIsomorphic(Type *DstTy, Type *SrcTy);
96 void TypeMapTy::addTypeMapping(Type *DstTy, Type *SrcTy) {
97 Type *&Entry = MappedTypes[SrcTy];
100 if (DstTy == SrcTy) {
105 // Check to see if these types are recursively isomorphic and establish a
106 // mapping between them if so.
107 if (!areTypesIsomorphic(DstTy, SrcTy)) {
108 // Oops, they aren't isomorphic. Just discard this request by rolling out
109 // any speculative mappings we've established.
110 for (unsigned i = 0, e = SpeculativeTypes.size(); i != e; ++i)
111 MappedTypes.erase(SpeculativeTypes[i]);
113 SpeculativeTypes.clear();
116 /// areTypesIsomorphic - Recursively walk this pair of types, returning true
117 /// if they are isomorphic, false if they are not.
118 bool TypeMapTy::areTypesIsomorphic(Type *DstTy, Type *SrcTy) {
119 // Two types with differing kinds are clearly not isomorphic.
120 if (DstTy->getTypeID() != SrcTy->getTypeID()) return false;
122 // If we have an entry in the MappedTypes table, then we have our answer.
123 Type *&Entry = MappedTypes[SrcTy];
125 return Entry == DstTy;
127 // Two identical types are clearly isomorphic. Remember this
128 // non-speculatively.
129 if (DstTy == SrcTy) {
134 // Okay, we have two types with identical kinds that we haven't seen before.
136 // If this is an opaque struct type, special case it.
137 if (StructType *SSTy = dyn_cast<StructType>(SrcTy)) {
138 // Mapping an opaque type to any struct, just keep the dest struct.
139 if (SSTy->isOpaque()) {
141 SpeculativeTypes.push_back(SrcTy);
145 // Mapping a non-opaque source type to an opaque dest. If this is the first
146 // type that we're mapping onto this destination type then we succeed. Keep
147 // the dest, but fill it in later. This doesn't need to be speculative. If
148 // this is the second (different) type that we're trying to map onto the
149 // same opaque type then we fail.
150 if (cast<StructType>(DstTy)->isOpaque()) {
151 // We can only map one source type onto the opaque destination type.
152 if (!DstResolvedOpaqueTypes.insert(cast<StructType>(DstTy)))
154 SrcDefinitionsToResolve.push_back(SSTy);
160 // If the number of subtypes disagree between the two types, then we fail.
161 if (SrcTy->getNumContainedTypes() != DstTy->getNumContainedTypes())
164 // Fail if any of the extra properties (e.g. array size) of the type disagree.
165 if (isa<IntegerType>(DstTy))
166 return false; // bitwidth disagrees.
167 if (PointerType *PT = dyn_cast<PointerType>(DstTy)) {
168 if (PT->getAddressSpace() != cast<PointerType>(SrcTy)->getAddressSpace())
171 } else if (FunctionType *FT = dyn_cast<FunctionType>(DstTy)) {
172 if (FT->isVarArg() != cast<FunctionType>(SrcTy)->isVarArg())
174 } else if (StructType *DSTy = dyn_cast<StructType>(DstTy)) {
175 StructType *SSTy = cast<StructType>(SrcTy);
176 if (DSTy->isLiteral() != SSTy->isLiteral() ||
177 DSTy->isPacked() != SSTy->isPacked())
179 } else if (ArrayType *DATy = dyn_cast<ArrayType>(DstTy)) {
180 if (DATy->getNumElements() != cast<ArrayType>(SrcTy)->getNumElements())
182 } else if (VectorType *DVTy = dyn_cast<VectorType>(DstTy)) {
183 if (DVTy->getNumElements() != cast<ArrayType>(SrcTy)->getNumElements())
187 // Otherwise, we speculate that these two types will line up and recursively
188 // check the subelements.
190 SpeculativeTypes.push_back(SrcTy);
192 for (unsigned i = 0, e = SrcTy->getNumContainedTypes(); i != e; ++i)
193 if (!areTypesIsomorphic(DstTy->getContainedType(i),
194 SrcTy->getContainedType(i)))
197 // If everything seems to have lined up, then everything is great.
201 /// linkDefinedTypeBodies - Produce a body for an opaque type in the dest
202 /// module from a type definition in the source module.
203 void TypeMapTy::linkDefinedTypeBodies() {
204 SmallVector<Type*, 16> Elements;
205 SmallString<16> TmpName;
207 // Note that processing entries in this loop (calling 'get') can add new
208 // entries to the SrcDefinitionsToResolve vector.
209 while (!SrcDefinitionsToResolve.empty()) {
210 StructType *SrcSTy = SrcDefinitionsToResolve.pop_back_val();
211 StructType *DstSTy = cast<StructType>(MappedTypes[SrcSTy]);
213 // TypeMap is a many-to-one mapping, if there were multiple types that
214 // provide a body for DstSTy then previous iterations of this loop may have
215 // already handled it. Just ignore this case.
216 if (!DstSTy->isOpaque()) continue;
217 assert(!SrcSTy->isOpaque() && "Not resolving a definition?");
219 // Map the body of the source type over to a new body for the dest type.
220 Elements.resize(SrcSTy->getNumElements());
221 for (unsigned i = 0, e = Elements.size(); i != e; ++i)
222 Elements[i] = getImpl(SrcSTy->getElementType(i));
224 DstSTy->setBody(Elements, SrcSTy->isPacked());
226 // If DstSTy has no name or has a longer name than STy, then viciously steal
228 if (!SrcSTy->hasName()) continue;
229 StringRef SrcName = SrcSTy->getName();
231 if (!DstSTy->hasName() || DstSTy->getName().size() > SrcName.size()) {
232 TmpName.insert(TmpName.end(), SrcName.begin(), SrcName.end());
234 DstSTy->setName(TmpName.str());
239 DstResolvedOpaqueTypes.clear();
243 /// get - Return the mapped type to use for the specified input type from the
245 Type *TypeMapTy::get(Type *Ty) {
246 Type *Result = getImpl(Ty);
248 // If this caused a reference to any struct type, resolve it before returning.
249 if (!SrcDefinitionsToResolve.empty())
250 linkDefinedTypeBodies();
254 /// getImpl - This is the recursive version of get().
255 Type *TypeMapTy::getImpl(Type *Ty) {
256 // If we already have an entry for this type, return it.
257 Type **Entry = &MappedTypes[Ty];
258 if (*Entry) return *Entry;
260 // If this is not a named struct type, then just map all of the elements and
261 // then rebuild the type from inside out.
262 if (!isa<StructType>(Ty) || cast<StructType>(Ty)->isLiteral()) {
263 // If there are no element types to map, then the type is itself. This is
264 // true for the anonymous {} struct, things like 'float', integers, etc.
265 if (Ty->getNumContainedTypes() == 0)
268 // Remap all of the elements, keeping track of whether any of them change.
269 bool AnyChange = false;
270 SmallVector<Type*, 4> ElementTypes;
271 ElementTypes.resize(Ty->getNumContainedTypes());
272 for (unsigned i = 0, e = Ty->getNumContainedTypes(); i != e; ++i) {
273 ElementTypes[i] = getImpl(Ty->getContainedType(i));
274 AnyChange |= ElementTypes[i] != Ty->getContainedType(i);
277 // If we found our type while recursively processing stuff, just use it.
278 Entry = &MappedTypes[Ty];
279 if (*Entry) return *Entry;
281 // If all of the element types mapped directly over, then the type is usable
286 // Otherwise, rebuild a modified type.
287 switch (Ty->getTypeID()) {
288 default: llvm_unreachable("unknown derived type to remap");
289 case Type::ArrayTyID:
290 return *Entry = ArrayType::get(ElementTypes[0],
291 cast<ArrayType>(Ty)->getNumElements());
292 case Type::VectorTyID:
293 return *Entry = VectorType::get(ElementTypes[0],
294 cast<VectorType>(Ty)->getNumElements());
295 case Type::PointerTyID:
296 return *Entry = PointerType::get(ElementTypes[0],
297 cast<PointerType>(Ty)->getAddressSpace());
298 case Type::FunctionTyID:
299 return *Entry = FunctionType::get(ElementTypes[0],
300 makeArrayRef(ElementTypes).slice(1),
301 cast<FunctionType>(Ty)->isVarArg());
302 case Type::StructTyID:
303 // Note that this is only reached for anonymous structs.
304 return *Entry = StructType::get(Ty->getContext(), ElementTypes,
305 cast<StructType>(Ty)->isPacked());
309 // Otherwise, this is an unmapped named struct. If the struct can be directly
310 // mapped over, just use it as-is. This happens in a case when the linked-in
311 // module has something like:
312 // %T = type {%T*, i32}
313 // @GV = global %T* null
314 // where T does not exist at all in the destination module.
316 // The other case we watch for is when the type is not in the destination
317 // module, but that it has to be rebuilt because it refers to something that
318 // is already mapped. For example, if the destination module has:
320 // and the source module has something like
321 // %A' = type { i32 }
322 // %B = type { %A'* }
323 // @GV = global %B* null
324 // then we want to create a new type: "%B = type { %A*}" and have it take the
325 // pristine "%B" name from the source module.
327 // To determine which case this is, we have to recursively walk the type graph
328 // speculating that we'll be able to reuse it unmodified. Only if this is
329 // safe would we map the entire thing over. Because this is an optimization,
330 // and is not required for the prettiness of the linked module, we just skip
331 // it and always rebuild a type here.
332 StructType *STy = cast<StructType>(Ty);
334 // If the type is opaque, we can just use it directly.
338 // Otherwise we create a new type and resolve its body later. This will be
339 // resolved by the top level of get().
340 SrcDefinitionsToResolve.push_back(STy);
341 StructType *DTy = StructType::create(STy->getContext());
342 DstResolvedOpaqueTypes.insert(DTy);
348 //===----------------------------------------------------------------------===//
349 // ModuleLinker implementation.
350 //===----------------------------------------------------------------------===//
353 /// ModuleLinker - This is an implementation class for the LinkModules
354 /// function, which is the entrypoint for this file.
360 /// ValueMap - Mapping of values from what they used to be in Src, to what
361 /// they are now in DstM. ValueToValueMapTy is a ValueMap, which involves
362 /// some overhead due to the use of Value handles which the Linker doesn't
363 /// actually need, but this allows us to reuse the ValueMapper code.
364 ValueToValueMapTy ValueMap;
366 struct AppendingVarInfo {
367 GlobalVariable *NewGV; // New aggregate global in dest module.
368 Constant *DstInit; // Old initializer from dest module.
369 Constant *SrcInit; // Old initializer from src module.
372 std::vector<AppendingVarInfo> AppendingVars;
374 unsigned Mode; // Mode to treat source module.
376 // Set of items not to link in from source.
377 SmallPtrSet<const Value*, 16> DoNotLinkFromSource;
379 // Vector of functions to lazily link in.
380 std::vector<Function*> LazilyLinkFunctions;
383 std::string ErrorMsg;
385 ModuleLinker(Module *dstM, Module *srcM, unsigned mode)
386 : DstM(dstM), SrcM(srcM), Mode(mode) { }
391 /// emitError - Helper method for setting a message and returning an error
393 bool emitError(const Twine &Message) {
394 ErrorMsg = Message.str();
398 /// getLinkageResult - This analyzes the two global values and determines
399 /// what the result will look like in the destination module.
400 bool getLinkageResult(GlobalValue *Dest, const GlobalValue *Src,
401 GlobalValue::LinkageTypes <,
402 GlobalValue::VisibilityTypes &Vis,
405 /// getLinkedToGlobal - Given a global in the source module, return the
406 /// global in the destination module that is being linked to, if any.
407 GlobalValue *getLinkedToGlobal(GlobalValue *SrcGV) {
408 // If the source has no name it can't link. If it has local linkage,
409 // there is no name match-up going on.
410 if (!SrcGV->hasName() || SrcGV->hasLocalLinkage())
413 // Otherwise see if we have a match in the destination module's symtab.
414 GlobalValue *DGV = DstM->getNamedValue(SrcGV->getName());
415 if (DGV == 0) return 0;
417 // If we found a global with the same name in the dest module, but it has
418 // internal linkage, we are really not doing any linkage here.
419 if (DGV->hasLocalLinkage())
422 // Otherwise, we do in fact link to the destination global.
426 void computeTypeMapping();
427 bool categorizeModuleFlagNodes(const NamedMDNode *ModFlags,
428 DenseMap<MDString*, MDNode*> &ErrorNode,
429 DenseMap<MDString*, MDNode*> &WarningNode,
430 DenseMap<MDString*, MDNode*> &OverrideNode,
432 SmallSetVector<MDNode*, 8> > &RequireNodes,
433 SmallSetVector<MDString*, 16> &SeenIDs);
435 bool linkAppendingVarProto(GlobalVariable *DstGV, GlobalVariable *SrcGV);
436 bool linkGlobalProto(GlobalVariable *SrcGV);
437 bool linkFunctionProto(Function *SrcF);
438 bool linkAliasProto(GlobalAlias *SrcA);
439 bool linkModuleFlagsMetadata();
441 void linkAppendingVarInit(const AppendingVarInfo &AVI);
442 void linkGlobalInits();
443 void linkFunctionBody(Function *Dst, Function *Src);
444 void linkAliasBodies();
445 void linkNamedMDNodes();
449 /// forceRenaming - The LLVM SymbolTable class autorenames globals that conflict
450 /// in the symbol table. This is good for all clients except for us. Go
451 /// through the trouble to force this back.
452 static void forceRenaming(GlobalValue *GV, StringRef Name) {
453 // If the global doesn't force its name or if it already has the right name,
454 // there is nothing for us to do.
455 if (GV->hasLocalLinkage() || GV->getName() == Name)
458 Module *M = GV->getParent();
460 // If there is a conflict, rename the conflict.
461 if (GlobalValue *ConflictGV = M->getNamedValue(Name)) {
462 GV->takeName(ConflictGV);
463 ConflictGV->setName(Name); // This will cause ConflictGV to get renamed
464 assert(ConflictGV->getName() != Name && "forceRenaming didn't work");
466 GV->setName(Name); // Force the name back
470 /// copyGVAttributes - copy additional attributes (those not needed to construct
471 /// a GlobalValue) from the SrcGV to the DestGV.
472 static void copyGVAttributes(GlobalValue *DestGV, const GlobalValue *SrcGV) {
473 // Use the maximum alignment, rather than just copying the alignment of SrcGV.
474 unsigned Alignment = std::max(DestGV->getAlignment(), SrcGV->getAlignment());
475 DestGV->copyAttributesFrom(SrcGV);
476 DestGV->setAlignment(Alignment);
478 forceRenaming(DestGV, SrcGV->getName());
481 static bool isLessConstraining(GlobalValue::VisibilityTypes a,
482 GlobalValue::VisibilityTypes b) {
483 if (a == GlobalValue::HiddenVisibility)
485 if (b == GlobalValue::HiddenVisibility)
487 if (a == GlobalValue::ProtectedVisibility)
489 if (b == GlobalValue::ProtectedVisibility)
494 /// getLinkageResult - This analyzes the two global values and determines what
495 /// the result will look like in the destination module. In particular, it
496 /// computes the resultant linkage type and visibility, computes whether the
497 /// global in the source should be copied over to the destination (replacing
498 /// the existing one), and computes whether this linkage is an error or not.
499 bool ModuleLinker::getLinkageResult(GlobalValue *Dest, const GlobalValue *Src,
500 GlobalValue::LinkageTypes <,
501 GlobalValue::VisibilityTypes &Vis,
503 assert(Dest && "Must have two globals being queried");
504 assert(!Src->hasLocalLinkage() &&
505 "If Src has internal linkage, Dest shouldn't be set!");
507 bool SrcIsDeclaration = Src->isDeclaration() && !Src->isMaterializable();
508 bool DestIsDeclaration = Dest->isDeclaration();
510 if (SrcIsDeclaration) {
511 // If Src is external or if both Src & Dest are external.. Just link the
512 // external globals, we aren't adding anything.
513 if (Src->hasDLLImportLinkage()) {
514 // If one of GVs has DLLImport linkage, result should be dllimport'ed.
515 if (DestIsDeclaration) {
517 LT = Src->getLinkage();
519 } else if (Dest->hasExternalWeakLinkage()) {
520 // If the Dest is weak, use the source linkage.
522 LT = Src->getLinkage();
525 LT = Dest->getLinkage();
527 } else if (DestIsDeclaration && !Dest->hasDLLImportLinkage()) {
528 // If Dest is external but Src is not:
530 LT = Src->getLinkage();
531 } else if (Src->isWeakForLinker()) {
532 // At this point we know that Dest has LinkOnce, External*, Weak, Common,
534 if (Dest->hasExternalWeakLinkage() ||
535 Dest->hasAvailableExternallyLinkage() ||
536 (Dest->hasLinkOnceLinkage() &&
537 (Src->hasWeakLinkage() || Src->hasCommonLinkage()))) {
539 LT = Src->getLinkage();
542 LT = Dest->getLinkage();
544 } else if (Dest->isWeakForLinker()) {
545 // At this point we know that Src has External* or DLL* linkage.
546 if (Src->hasExternalWeakLinkage()) {
548 LT = Dest->getLinkage();
551 LT = GlobalValue::ExternalLinkage;
554 assert((Dest->hasExternalLinkage() || Dest->hasDLLImportLinkage() ||
555 Dest->hasDLLExportLinkage() || Dest->hasExternalWeakLinkage()) &&
556 (Src->hasExternalLinkage() || Src->hasDLLImportLinkage() ||
557 Src->hasDLLExportLinkage() || Src->hasExternalWeakLinkage()) &&
558 "Unexpected linkage type!");
559 return emitError("Linking globals named '" + Src->getName() +
560 "': symbol multiply defined!");
563 // Compute the visibility. We follow the rules in the System V Application
565 Vis = isLessConstraining(Src->getVisibility(), Dest->getVisibility()) ?
566 Dest->getVisibility() : Src->getVisibility();
570 /// computeTypeMapping - Loop over all of the linked values to compute type
571 /// mappings. For example, if we link "extern Foo *x" and "Foo *x = NULL", then
572 /// we have two struct types 'Foo' but one got renamed when the module was
573 /// loaded into the same LLVMContext.
574 void ModuleLinker::computeTypeMapping() {
575 // Incorporate globals.
576 for (Module::global_iterator I = SrcM->global_begin(),
577 E = SrcM->global_end(); I != E; ++I) {
578 GlobalValue *DGV = getLinkedToGlobal(I);
579 if (DGV == 0) continue;
581 if (!DGV->hasAppendingLinkage() || !I->hasAppendingLinkage()) {
582 TypeMap.addTypeMapping(DGV->getType(), I->getType());
586 // Unify the element type of appending arrays.
587 ArrayType *DAT = cast<ArrayType>(DGV->getType()->getElementType());
588 ArrayType *SAT = cast<ArrayType>(I->getType()->getElementType());
589 TypeMap.addTypeMapping(DAT->getElementType(), SAT->getElementType());
592 // Incorporate functions.
593 for (Module::iterator I = SrcM->begin(), E = SrcM->end(); I != E; ++I) {
594 if (GlobalValue *DGV = getLinkedToGlobal(I))
595 TypeMap.addTypeMapping(DGV->getType(), I->getType());
598 // Incorporate types by name, scanning all the types in the source module.
599 // At this point, the destination module may have a type "%foo = { i32 }" for
600 // example. When the source module got loaded into the same LLVMContext, if
601 // it had the same type, it would have been renamed to "%foo.42 = { i32 }".
602 // Though it isn't required for correctness, attempt to link these up to clean
604 std::vector<StructType*> SrcStructTypes;
605 SrcM->findUsedStructTypes(SrcStructTypes);
607 SmallPtrSet<StructType*, 32> SrcStructTypesSet(SrcStructTypes.begin(),
608 SrcStructTypes.end());
610 for (unsigned i = 0, e = SrcStructTypes.size(); i != e; ++i) {
611 StructType *ST = SrcStructTypes[i];
612 if (!ST->hasName()) continue;
614 // Check to see if there is a dot in the name followed by a digit.
615 size_t DotPos = ST->getName().rfind('.');
616 if (DotPos == 0 || DotPos == StringRef::npos ||
617 ST->getName().back() == '.' || !isdigit(ST->getName()[DotPos+1]))
620 // Check to see if the destination module has a struct with the prefix name.
621 if (StructType *DST = DstM->getTypeByName(ST->getName().substr(0, DotPos)))
622 // Don't use it if this actually came from the source module. They're in
623 // the same LLVMContext after all.
624 if (!SrcStructTypesSet.count(DST))
625 TypeMap.addTypeMapping(DST, ST);
628 // Don't bother incorporating aliases, they aren't generally typed well.
630 // Now that we have discovered all of the type equivalences, get a body for
631 // any 'opaque' types in the dest module that are now resolved.
632 TypeMap.linkDefinedTypeBodies();
635 /// linkAppendingVarProto - If there were any appending global variables, link
636 /// them together now. Return true on error.
637 bool ModuleLinker::linkAppendingVarProto(GlobalVariable *DstGV,
638 GlobalVariable *SrcGV) {
640 if (!SrcGV->hasAppendingLinkage() || !DstGV->hasAppendingLinkage())
641 return emitError("Linking globals named '" + SrcGV->getName() +
642 "': can only link appending global with another appending global!");
644 ArrayType *DstTy = cast<ArrayType>(DstGV->getType()->getElementType());
646 cast<ArrayType>(TypeMap.get(SrcGV->getType()->getElementType()));
647 Type *EltTy = DstTy->getElementType();
649 // Check to see that they two arrays agree on type.
650 if (EltTy != SrcTy->getElementType())
651 return emitError("Appending variables with different element types!");
652 if (DstGV->isConstant() != SrcGV->isConstant())
653 return emitError("Appending variables linked with different const'ness!");
655 if (DstGV->getAlignment() != SrcGV->getAlignment())
657 "Appending variables with different alignment need to be linked!");
659 if (DstGV->getVisibility() != SrcGV->getVisibility())
661 "Appending variables with different visibility need to be linked!");
663 if (DstGV->getSection() != SrcGV->getSection())
665 "Appending variables with different section name need to be linked!");
667 uint64_t NewSize = DstTy->getNumElements() + SrcTy->getNumElements();
668 ArrayType *NewType = ArrayType::get(EltTy, NewSize);
670 // Create the new global variable.
672 new GlobalVariable(*DstGV->getParent(), NewType, SrcGV->isConstant(),
673 DstGV->getLinkage(), /*init*/0, /*name*/"", DstGV,
674 DstGV->isThreadLocal(),
675 DstGV->getType()->getAddressSpace());
677 // Propagate alignment, visibility and section info.
678 copyGVAttributes(NG, DstGV);
680 AppendingVarInfo AVI;
682 AVI.DstInit = DstGV->getInitializer();
683 AVI.SrcInit = SrcGV->getInitializer();
684 AppendingVars.push_back(AVI);
686 // Replace any uses of the two global variables with uses of the new
688 ValueMap[SrcGV] = ConstantExpr::getBitCast(NG, TypeMap.get(SrcGV->getType()));
690 DstGV->replaceAllUsesWith(ConstantExpr::getBitCast(NG, DstGV->getType()));
691 DstGV->eraseFromParent();
693 // Track the source variable so we don't try to link it.
694 DoNotLinkFromSource.insert(SrcGV);
699 /// linkGlobalProto - Loop through the global variables in the src module and
700 /// merge them into the dest module.
701 bool ModuleLinker::linkGlobalProto(GlobalVariable *SGV) {
702 GlobalValue *DGV = getLinkedToGlobal(SGV);
703 llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;
706 // Concatenation of appending linkage variables is magic and handled later.
707 if (DGV->hasAppendingLinkage() || SGV->hasAppendingLinkage())
708 return linkAppendingVarProto(cast<GlobalVariable>(DGV), SGV);
710 // Determine whether linkage of these two globals follows the source
711 // module's definition or the destination module's definition.
712 GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
713 GlobalValue::VisibilityTypes NV;
714 bool LinkFromSrc = false;
715 if (getLinkageResult(DGV, SGV, NewLinkage, NV, LinkFromSrc))
719 // If we're not linking from the source, then keep the definition that we
722 // Special case for const propagation.
723 if (GlobalVariable *DGVar = dyn_cast<GlobalVariable>(DGV))
724 if (DGVar->isDeclaration() && SGV->isConstant() && !DGVar->isConstant())
725 DGVar->setConstant(true);
727 // Set calculated linkage and visibility.
728 DGV->setLinkage(NewLinkage);
729 DGV->setVisibility(*NewVisibility);
731 // Make sure to remember this mapping.
732 ValueMap[SGV] = ConstantExpr::getBitCast(DGV,TypeMap.get(SGV->getType()));
734 // Track the source global so that we don't attempt to copy it over when
735 // processing global initializers.
736 DoNotLinkFromSource.insert(SGV);
742 // No linking to be performed or linking from the source: simply create an
743 // identical version of the symbol over in the dest module... the
744 // initializer will be filled in later by LinkGlobalInits.
745 GlobalVariable *NewDGV =
746 new GlobalVariable(*DstM, TypeMap.get(SGV->getType()->getElementType()),
747 SGV->isConstant(), SGV->getLinkage(), /*init*/0,
748 SGV->getName(), /*insertbefore*/0,
749 SGV->isThreadLocal(),
750 SGV->getType()->getAddressSpace());
751 // Propagate alignment, visibility and section info.
752 copyGVAttributes(NewDGV, SGV);
754 NewDGV->setVisibility(*NewVisibility);
757 DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDGV, DGV->getType()));
758 DGV->eraseFromParent();
761 // Make sure to remember this mapping.
762 ValueMap[SGV] = NewDGV;
766 /// linkFunctionProto - Link the function in the source module into the
767 /// destination module if needed, setting up mapping information.
768 bool ModuleLinker::linkFunctionProto(Function *SF) {
769 GlobalValue *DGV = getLinkedToGlobal(SF);
770 llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;
773 GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
774 bool LinkFromSrc = false;
775 GlobalValue::VisibilityTypes NV;
776 if (getLinkageResult(DGV, SF, NewLinkage, NV, LinkFromSrc))
781 // Set calculated linkage
782 DGV->setLinkage(NewLinkage);
783 DGV->setVisibility(*NewVisibility);
785 // Make sure to remember this mapping.
786 ValueMap[SF] = ConstantExpr::getBitCast(DGV, TypeMap.get(SF->getType()));
788 // Track the function from the source module so we don't attempt to remap
790 DoNotLinkFromSource.insert(SF);
796 // If there is no linkage to be performed or we are linking from the source,
798 Function *NewDF = Function::Create(TypeMap.get(SF->getFunctionType()),
799 SF->getLinkage(), SF->getName(), DstM);
800 copyGVAttributes(NewDF, SF);
802 NewDF->setVisibility(*NewVisibility);
805 // Any uses of DF need to change to NewDF, with cast.
806 DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDF, DGV->getType()));
807 DGV->eraseFromParent();
809 // Internal, LO_ODR, or LO linkage - stick in set to ignore and lazily link.
810 if (SF->hasLocalLinkage() || SF->hasLinkOnceLinkage() ||
811 SF->hasAvailableExternallyLinkage()) {
812 DoNotLinkFromSource.insert(SF);
813 LazilyLinkFunctions.push_back(SF);
817 ValueMap[SF] = NewDF;
821 /// LinkAliasProto - Set up prototypes for any aliases that come over from the
823 bool ModuleLinker::linkAliasProto(GlobalAlias *SGA) {
824 GlobalValue *DGV = getLinkedToGlobal(SGA);
825 llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;
828 GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
829 GlobalValue::VisibilityTypes NV;
830 bool LinkFromSrc = false;
831 if (getLinkageResult(DGV, SGA, NewLinkage, NV, LinkFromSrc))
836 // Set calculated linkage.
837 DGV->setLinkage(NewLinkage);
838 DGV->setVisibility(*NewVisibility);
840 // Make sure to remember this mapping.
841 ValueMap[SGA] = ConstantExpr::getBitCast(DGV,TypeMap.get(SGA->getType()));
843 // Track the alias from the source module so we don't attempt to remap it.
844 DoNotLinkFromSource.insert(SGA);
850 // If there is no linkage to be performed or we're linking from the source,
852 GlobalAlias *NewDA = new GlobalAlias(TypeMap.get(SGA->getType()),
853 SGA->getLinkage(), SGA->getName(),
855 copyGVAttributes(NewDA, SGA);
857 NewDA->setVisibility(*NewVisibility);
860 // Any uses of DGV need to change to NewDA, with cast.
861 DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDA, DGV->getType()));
862 DGV->eraseFromParent();
865 ValueMap[SGA] = NewDA;
869 static void getArrayElements(Constant *C, SmallVectorImpl<Constant*> &Dest) {
870 unsigned NumElements = cast<ArrayType>(C->getType())->getNumElements();
872 for (unsigned i = 0; i != NumElements; ++i)
873 Dest.push_back(C->getAggregateElement(i));
876 void ModuleLinker::linkAppendingVarInit(const AppendingVarInfo &AVI) {
877 // Merge the initializer.
878 SmallVector<Constant*, 16> Elements;
879 getArrayElements(AVI.DstInit, Elements);
881 Constant *SrcInit = MapValue(AVI.SrcInit, ValueMap, RF_None, &TypeMap);
882 getArrayElements(SrcInit, Elements);
884 ArrayType *NewType = cast<ArrayType>(AVI.NewGV->getType()->getElementType());
885 AVI.NewGV->setInitializer(ConstantArray::get(NewType, Elements));
888 /// linkGlobalInits - Update the initializers in the Dest module now that all
889 /// globals that may be referenced are in Dest.
890 void ModuleLinker::linkGlobalInits() {
891 // Loop over all of the globals in the src module, mapping them over as we go
892 for (Module::const_global_iterator I = SrcM->global_begin(),
893 E = SrcM->global_end(); I != E; ++I) {
895 // Only process initialized GV's or ones not already in dest.
896 if (!I->hasInitializer() || DoNotLinkFromSource.count(I)) continue;
898 // Grab destination global variable.
899 GlobalVariable *DGV = cast<GlobalVariable>(ValueMap[I]);
900 // Figure out what the initializer looks like in the dest module.
901 DGV->setInitializer(MapValue(I->getInitializer(), ValueMap,
906 /// linkFunctionBody - Copy the source function over into the dest function and
907 /// fix up references to values. At this point we know that Dest is an external
908 /// function, and that Src is not.
909 void ModuleLinker::linkFunctionBody(Function *Dst, Function *Src) {
910 assert(Src && Dst && Dst->isDeclaration() && !Src->isDeclaration());
912 // Go through and convert function arguments over, remembering the mapping.
913 Function::arg_iterator DI = Dst->arg_begin();
914 for (Function::arg_iterator I = Src->arg_begin(), E = Src->arg_end();
916 DI->setName(I->getName()); // Copy the name over.
918 // Add a mapping to our mapping.
922 if (Mode == Linker::DestroySource) {
923 // Splice the body of the source function into the dest function.
924 Dst->getBasicBlockList().splice(Dst->end(), Src->getBasicBlockList());
926 // At this point, all of the instructions and values of the function are now
927 // copied over. The only problem is that they are still referencing values in
928 // the Source function as operands. Loop through all of the operands of the
929 // functions and patch them up to point to the local versions.
930 for (Function::iterator BB = Dst->begin(), BE = Dst->end(); BB != BE; ++BB)
931 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
932 RemapInstruction(I, ValueMap, RF_IgnoreMissingEntries, &TypeMap);
935 // Clone the body of the function into the dest function.
936 SmallVector<ReturnInst*, 8> Returns; // Ignore returns.
937 CloneFunctionInto(Dst, Src, ValueMap, false, Returns, "", NULL, &TypeMap);
940 // There is no need to map the arguments anymore.
941 for (Function::arg_iterator I = Src->arg_begin(), E = Src->arg_end();
947 /// linkAliasBodies - Insert all of the aliases in Src into the Dest module.
948 void ModuleLinker::linkAliasBodies() {
949 for (Module::alias_iterator I = SrcM->alias_begin(), E = SrcM->alias_end();
951 if (DoNotLinkFromSource.count(I))
953 if (Constant *Aliasee = I->getAliasee()) {
954 GlobalAlias *DA = cast<GlobalAlias>(ValueMap[I]);
955 DA->setAliasee(MapValue(Aliasee, ValueMap, RF_None, &TypeMap));
960 /// linkNamedMDNodes - Insert all of the named MDNodes in Src into the Dest
962 void ModuleLinker::linkNamedMDNodes() {
963 const NamedMDNode *SrcModFlags = SrcM->getModuleFlagsMetadata();
964 for (Module::const_named_metadata_iterator I = SrcM->named_metadata_begin(),
965 E = SrcM->named_metadata_end(); I != E; ++I) {
966 // Don't link module flags here. Do them separately.
967 if (&*I == SrcModFlags) continue;
968 NamedMDNode *DestNMD = DstM->getOrInsertNamedMetadata(I->getName());
969 // Add Src elements into Dest node.
970 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
971 DestNMD->addOperand(MapValue(I->getOperand(i), ValueMap,
976 /// categorizeModuleFlagNodes - Categorize the module flags according to their
977 /// type: Error, Warning, Override, and Require.
979 categorizeModuleFlagNodes(const NamedMDNode *ModFlags,
980 DenseMap<MDString*, MDNode*> &ErrorNode,
981 DenseMap<MDString*, MDNode*> &WarningNode,
982 DenseMap<MDString*, MDNode*> &OverrideNode,
984 SmallSetVector<MDNode*, 8> > &RequireNodes,
985 SmallSetVector<MDString*, 16> &SeenIDs) {
988 for (unsigned I = 0, E = ModFlags->getNumOperands(); I != E; ++I) {
989 MDNode *Op = ModFlags->getOperand(I);
990 assert(Op->getNumOperands() == 3 && "Invalid module flag metadata!");
991 assert(isa<ConstantInt>(Op->getOperand(0)) &&
992 "Module flag's first operand must be an integer!");
993 assert(isa<MDString>(Op->getOperand(1)) &&
994 "Module flag's second operand must be an MDString!");
996 ConstantInt *Behavior = cast<ConstantInt>(Op->getOperand(0));
997 MDString *ID = cast<MDString>(Op->getOperand(1));
998 Value *Val = Op->getOperand(2);
999 switch (Behavior->getZExtValue()) {
1001 assert(false && "Invalid behavior in module flag metadata!");
1003 case Module::Error: {
1004 MDNode *&ErrNode = ErrorNode[ID];
1005 if (!ErrNode) ErrNode = Op;
1006 if (ErrNode->getOperand(2) != Val)
1007 HasErr = emitError("linking module flags '" + ID->getString() +
1008 "': IDs have conflicting values");
1011 case Module::Warning: {
1012 MDNode *&WarnNode = WarningNode[ID];
1013 if (!WarnNode) WarnNode = Op;
1014 if (WarnNode->getOperand(2) != Val)
1015 errs() << "WARNING: linking module flags '" << ID->getString()
1016 << "': IDs have conflicting values";
1019 case Module::Require: RequireNodes[ID].insert(Op); break;
1020 case Module::Override: {
1021 MDNode *&OvrNode = OverrideNode[ID];
1022 if (!OvrNode) OvrNode = Op;
1023 if (OvrNode->getOperand(2) != Val)
1024 HasErr = emitError("linking module flags '" + ID->getString() +
1025 "': IDs have conflicting override values");
1036 /// linkModuleFlagsMetadata - Merge the linker flags in Src into the Dest
1038 bool ModuleLinker::linkModuleFlagsMetadata() {
1039 const NamedMDNode *SrcModFlags = SrcM->getModuleFlagsMetadata();
1040 if (!SrcModFlags) return false;
1042 NamedMDNode *DstModFlags = DstM->getOrInsertModuleFlagsMetadata();
1044 // If the destination module doesn't have module flags yet, then just copy
1045 // over the source module's flags.
1046 if (DstModFlags->getNumOperands() == 0) {
1047 for (unsigned I = 0, E = SrcModFlags->getNumOperands(); I != E; ++I)
1048 DstModFlags->addOperand(SrcModFlags->getOperand(I));
1053 bool HasErr = false;
1055 // Otherwise, we have to merge them based on their behaviors. First,
1056 // categorize all of the nodes in the modules' module flags. If an error or
1057 // warning occurs, then emit the appropriate message(s).
1058 DenseMap<MDString*, MDNode*> ErrorNode;
1059 DenseMap<MDString*, MDNode*> WarningNode;
1060 DenseMap<MDString*, MDNode*> OverrideNode;
1061 DenseMap<MDString*, SmallSetVector<MDNode*, 8> > RequireNodes;
1062 SmallSetVector<MDString*, 16> SeenIDs;
1064 HasErr |= categorizeModuleFlagNodes(SrcModFlags, ErrorNode, WarningNode,
1065 OverrideNode, RequireNodes, SeenIDs);
1066 HasErr |= categorizeModuleFlagNodes(DstModFlags, ErrorNode, WarningNode,
1067 OverrideNode, RequireNodes, SeenIDs);
1069 // Check that there isn't both an error and warning node for a flag.
1070 for (SmallSetVector<MDString*, 16>::iterator
1071 I = SeenIDs.begin(), E = SeenIDs.end(); I != E; ++I) {
1073 if (ErrorNode[ID] && WarningNode[ID])
1074 HasErr = emitError("linking module flags '" + ID->getString() +
1075 "': IDs have conflicting behaviors");
1078 // Early exit if we had an error.
1079 if (HasErr) return true;
1081 // Get the destination's module flags ready for new operands.
1082 DstModFlags->dropAllReferences();
1084 // Add all of the module flags to the destination module.
1085 DenseMap<MDString*, SmallVector<MDNode*, 4> > AddedNodes;
1086 for (SmallSetVector<MDString*, 16>::iterator
1087 I = SeenIDs.begin(), E = SeenIDs.end(); I != E; ++I) {
1089 if (OverrideNode[ID]) {
1090 DstModFlags->addOperand(OverrideNode[ID]);
1091 AddedNodes[ID].push_back(OverrideNode[ID]);
1092 } else if (ErrorNode[ID]) {
1093 DstModFlags->addOperand(ErrorNode[ID]);
1094 AddedNodes[ID].push_back(ErrorNode[ID]);
1095 } else if (WarningNode[ID]) {
1096 DstModFlags->addOperand(WarningNode[ID]);
1097 AddedNodes[ID].push_back(WarningNode[ID]);
1100 for (SmallSetVector<MDNode*, 8>::iterator
1101 II = RequireNodes[ID].begin(), IE = RequireNodes[ID].end();
1103 DstModFlags->addOperand(*II);
1106 // Now check that all of the requirements have been satisfied.
1107 for (SmallSetVector<MDString*, 16>::iterator
1108 I = SeenIDs.begin(), E = SeenIDs.end(); I != E; ++I) {
1110 SmallSetVector<MDNode*, 8> &Set = RequireNodes[ID];
1112 for (SmallSetVector<MDNode*, 8>::iterator
1113 II = Set.begin(), IE = Set.end(); II != IE; ++II) {
1115 assert(isa<MDNode>(Node->getOperand(2)) &&
1116 "Module flag's third operand must be an MDNode!");
1117 MDNode *Val = cast<MDNode>(Node->getOperand(2));
1119 MDString *ReqID = cast<MDString>(Val->getOperand(0));
1120 Value *ReqVal = Val->getOperand(1);
1122 bool HasValue = false;
1123 for (SmallVectorImpl<MDNode*>::iterator
1124 RI = AddedNodes[ReqID].begin(), RE = AddedNodes[ReqID].end();
1126 MDNode *ReqNode = *RI;
1127 if (ReqNode->getOperand(2) == ReqVal) {
1134 HasErr = emitError("linking module flags '" + ReqID->getString() +
1135 "': does not have the required value");
1142 bool ModuleLinker::run() {
1143 assert(DstM && "Null destination module");
1144 assert(SrcM && "Null source module");
1146 // Inherit the target data from the source module if the destination module
1147 // doesn't have one already.
1148 if (DstM->getDataLayout().empty() && !SrcM->getDataLayout().empty())
1149 DstM->setDataLayout(SrcM->getDataLayout());
1151 // Copy the target triple from the source to dest if the dest's is empty.
1152 if (DstM->getTargetTriple().empty() && !SrcM->getTargetTriple().empty())
1153 DstM->setTargetTriple(SrcM->getTargetTriple());
1155 if (!SrcM->getDataLayout().empty() && !DstM->getDataLayout().empty() &&
1156 SrcM->getDataLayout() != DstM->getDataLayout())
1157 errs() << "WARNING: Linking two modules of different data layouts!\n";
1158 if (!SrcM->getTargetTriple().empty() &&
1159 DstM->getTargetTriple() != SrcM->getTargetTriple()) {
1160 errs() << "WARNING: Linking two modules of different target triples: ";
1161 if (!SrcM->getModuleIdentifier().empty())
1162 errs() << SrcM->getModuleIdentifier() << ": ";
1163 errs() << "'" << SrcM->getTargetTriple() << "' and '"
1164 << DstM->getTargetTriple() << "'\n";
1167 // Append the module inline asm string.
1168 if (!SrcM->getModuleInlineAsm().empty()) {
1169 if (DstM->getModuleInlineAsm().empty())
1170 DstM->setModuleInlineAsm(SrcM->getModuleInlineAsm());
1172 DstM->setModuleInlineAsm(DstM->getModuleInlineAsm()+"\n"+
1173 SrcM->getModuleInlineAsm());
1176 // Update the destination module's dependent libraries list with the libraries
1177 // from the source module. There's no opportunity for duplicates here as the
1178 // Module ensures that duplicate insertions are discarded.
1179 for (Module::lib_iterator SI = SrcM->lib_begin(), SE = SrcM->lib_end();
1181 DstM->addLibrary(*SI);
1183 // If the source library's module id is in the dependent library list of the
1184 // destination library, remove it since that module is now linked in.
1185 StringRef ModuleId = SrcM->getModuleIdentifier();
1186 if (!ModuleId.empty())
1187 DstM->removeLibrary(sys::path::stem(ModuleId));
1189 // Loop over all of the linked values to compute type mappings.
1190 computeTypeMapping();
1192 // Insert all of the globals in src into the DstM module... without linking
1193 // initializers (which could refer to functions not yet mapped over).
1194 for (Module::global_iterator I = SrcM->global_begin(),
1195 E = SrcM->global_end(); I != E; ++I)
1196 if (linkGlobalProto(I))
1199 // Link the functions together between the two modules, without doing function
1200 // bodies... this just adds external function prototypes to the DstM
1201 // function... We do this so that when we begin processing function bodies,
1202 // all of the global values that may be referenced are available in our
1204 for (Module::iterator I = SrcM->begin(), E = SrcM->end(); I != E; ++I)
1205 if (linkFunctionProto(I))
1208 // If there were any aliases, link them now.
1209 for (Module::alias_iterator I = SrcM->alias_begin(),
1210 E = SrcM->alias_end(); I != E; ++I)
1211 if (linkAliasProto(I))
1214 for (unsigned i = 0, e = AppendingVars.size(); i != e; ++i)
1215 linkAppendingVarInit(AppendingVars[i]);
1217 // Update the initializers in the DstM module now that all globals that may
1218 // be referenced are in DstM.
1221 // Link in the function bodies that are defined in the source module into
1223 for (Module::iterator SF = SrcM->begin(), E = SrcM->end(); SF != E; ++SF) {
1224 // Skip if not linking from source.
1225 if (DoNotLinkFromSource.count(SF)) continue;
1227 // Skip if no body (function is external) or materialize.
1228 if (SF->isDeclaration()) {
1229 if (!SF->isMaterializable())
1231 if (SF->Materialize(&ErrorMsg))
1235 linkFunctionBody(cast<Function>(ValueMap[SF]), SF);
1238 // Resolve all uses of aliases with aliasees.
1241 // Remap all of the named MDNodes in Src into the DstM module. We do this
1242 // after linking GlobalValues so that MDNodes that reference GlobalValues
1243 // are properly remapped.
1246 // Merge the module flags into the DstM module.
1247 if (linkModuleFlagsMetadata())
1250 // Process vector of lazily linked in functions.
1251 bool LinkedInAnyFunctions;
1253 LinkedInAnyFunctions = false;
1255 for(std::vector<Function*>::iterator I = LazilyLinkFunctions.begin(),
1256 E = LazilyLinkFunctions.end(); I != E; ++I) {
1261 Function *DF = cast<Function>(ValueMap[SF]);
1263 if (!DF->use_empty()) {
1265 // Materialize if necessary.
1266 if (SF->isDeclaration()) {
1267 if (!SF->isMaterializable())
1269 if (SF->Materialize(&ErrorMsg))
1273 // Link in function body.
1274 linkFunctionBody(DF, SF);
1276 // "Remove" from vector by setting the element to 0.
1279 // Set flag to indicate we may have more functions to lazily link in
1280 // since we linked in a function.
1281 LinkedInAnyFunctions = true;
1284 } while (LinkedInAnyFunctions);
1286 // Remove any prototypes of functions that were not actually linked in.
1287 for(std::vector<Function*>::iterator I = LazilyLinkFunctions.begin(),
1288 E = LazilyLinkFunctions.end(); I != E; ++I) {
1293 Function *DF = cast<Function>(ValueMap[SF]);
1294 if (DF->use_empty())
1295 DF->eraseFromParent();
1298 // Now that all of the types from the source are used, resolve any structs
1299 // copied over to the dest that didn't exist there.
1300 TypeMap.linkDefinedTypeBodies();
1305 //===----------------------------------------------------------------------===//
1306 // LinkModules entrypoint.
1307 //===----------------------------------------------------------------------===//
1309 /// LinkModules - This function links two modules together, with the resulting
1310 /// left module modified to be the composite of the two input modules. If an
1311 /// error occurs, true is returned and ErrorMsg (if not null) is set to indicate
1312 /// the problem. Upon failure, the Dest module could be in a modified state,
1313 /// and shouldn't be relied on to be consistent.
1314 bool Linker::LinkModules(Module *Dest, Module *Src, unsigned Mode,
1315 std::string *ErrorMsg) {
1316 ModuleLinker TheLinker(Dest, Src, Mode);
1317 if (TheLinker.run()) {
1318 if (ErrorMsg) *ErrorMsg = TheLinker.ErrorMsg;