1 //===--- CGVTables.cpp - Emit LLVM Code for C++ vtables -------------------===//
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
7 //===----------------------------------------------------------------------===//
9 // This contains code dealing with C++ code generation of virtual tables.
11 //===----------------------------------------------------------------------===//
14 #include "CodeGenFunction.h"
15 #include "CodeGenModule.h"
16 #include "clang/AST/Attr.h"
17 #include "clang/AST/CXXInheritance.h"
18 #include "clang/AST/RecordLayout.h"
19 #include "clang/Basic/CodeGenOptions.h"
20 #include "clang/CodeGen/CGFunctionInfo.h"
21 #include "clang/CodeGen/ConstantInitBuilder.h"
22 #include "llvm/IR/IntrinsicInst.h"
23 #include "llvm/Support/Format.h"
24 #include "llvm/Transforms/Utils/Cloning.h"
28 using namespace clang;
29 using namespace CodeGen;
31 CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
32 : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
34 llvm::Constant *CodeGenModule::GetAddrOfThunk(StringRef Name, llvm::Type *FnTy,
36 return GetOrCreateLLVMFunction(Name, FnTy, GD, /*ForVTable=*/true,
37 /*DontDefer=*/true, /*IsThunk=*/true);
40 static void setThunkProperties(CodeGenModule &CGM, const ThunkInfo &Thunk,
41 llvm::Function *ThunkFn, bool ForVTable,
43 CGM.setFunctionLinkage(GD, ThunkFn);
44 CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
45 !Thunk.Return.isEmpty());
47 // Set the right visibility.
48 CGM.setGVProperties(ThunkFn, GD);
50 if (!CGM.getCXXABI().exportThunk()) {
51 ThunkFn->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
52 ThunkFn->setDSOLocal(true);
55 if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())
56 ThunkFn->setComdat(CGM.getModule().getOrInsertComdat(ThunkFn->getName()));
60 static bool similar(const ABIArgInfo &infoL, CanQualType typeL,
61 const ABIArgInfo &infoR, CanQualType typeR) {
62 return (infoL.getKind() == infoR.getKind() &&
64 (isa<PointerType>(typeL) && isa<PointerType>(typeR)) ||
65 (isa<ReferenceType>(typeL) && isa<ReferenceType>(typeR))));
69 static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
70 QualType ResultType, RValue RV,
71 const ThunkInfo &Thunk) {
72 // Emit the return adjustment.
73 bool NullCheckValue = !ResultType->isReferenceType();
75 llvm::BasicBlock *AdjustNull = nullptr;
76 llvm::BasicBlock *AdjustNotNull = nullptr;
77 llvm::BasicBlock *AdjustEnd = nullptr;
79 llvm::Value *ReturnValue = RV.getScalarVal();
82 AdjustNull = CGF.createBasicBlock("adjust.null");
83 AdjustNotNull = CGF.createBasicBlock("adjust.notnull");
84 AdjustEnd = CGF.createBasicBlock("adjust.end");
86 llvm::Value *IsNull = CGF.Builder.CreateIsNull(ReturnValue);
87 CGF.Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);
88 CGF.EmitBlock(AdjustNotNull);
91 auto ClassDecl = ResultType->getPointeeType()->getAsCXXRecordDecl();
92 auto ClassAlign = CGF.CGM.getClassPointerAlignment(ClassDecl);
93 ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(CGF,
94 Address(ReturnValue, ClassAlign),
98 CGF.Builder.CreateBr(AdjustEnd);
99 CGF.EmitBlock(AdjustNull);
100 CGF.Builder.CreateBr(AdjustEnd);
101 CGF.EmitBlock(AdjustEnd);
103 llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
104 PHI->addIncoming(ReturnValue, AdjustNotNull);
105 PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
110 return RValue::get(ReturnValue);
113 /// This function clones a function's DISubprogram node and enters it into
114 /// a value map with the intent that the map can be utilized by the cloner
115 /// to short-circuit Metadata node mapping.
116 /// Furthermore, the function resolves any DILocalVariable nodes referenced
117 /// by dbg.value intrinsics so they can be properly mapped during cloning.
118 static void resolveTopLevelMetadata(llvm::Function *Fn,
119 llvm::ValueToValueMapTy &VMap) {
120 // Clone the DISubprogram node and put it into the Value map.
121 auto *DIS = Fn->getSubprogram();
124 auto *NewDIS = DIS->replaceWithDistinct(DIS->clone());
125 VMap.MD()[DIS].reset(NewDIS);
127 // Find all llvm.dbg.declare intrinsics and resolve the DILocalVariable nodes
128 // they are referencing.
129 for (auto &BB : Fn->getBasicBlockList()) {
131 if (auto *DII = dyn_cast<llvm::DbgVariableIntrinsic>(&I)) {
132 auto *DILocal = DII->getVariable();
133 if (!DILocal->isResolved())
140 // This function does roughly the same thing as GenerateThunk, but in a
141 // very different way, so that va_start and va_end work correctly.
142 // FIXME: This function assumes "this" is the first non-sret LLVM argument of
143 // a function, and that there is an alloca built in the entry block
144 // for all accesses to "this".
145 // FIXME: This function assumes there is only one "ret" statement per function.
146 // FIXME: Cloning isn't correct in the presence of indirect goto!
147 // FIXME: This implementation of thunks bloats codesize by duplicating the
148 // function definition. There are alternatives:
149 // 1. Add some sort of stub support to LLVM for cases where we can
150 // do a this adjustment, then a sibcall.
151 // 2. We could transform the definition to take a va_list instead of an
152 // actual variable argument list, then have the thunks (including a
153 // no-op thunk for the regular definition) call va_start/va_end.
154 // There's a bit of per-call overhead for this solution, but it's
155 // better for codesize if the definition is long.
157 CodeGenFunction::GenerateVarArgsThunk(llvm::Function *Fn,
158 const CGFunctionInfo &FnInfo,
159 GlobalDecl GD, const ThunkInfo &Thunk) {
160 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
161 const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
162 QualType ResultType = FPT->getReturnType();
164 // Get the original function
165 assert(FnInfo.isVariadic());
166 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);
167 llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
168 llvm::Function *BaseFn = cast<llvm::Function>(Callee);
170 // Cloning can't work if we don't have a definition. The Microsoft ABI may
171 // require thunks when a definition is not available. Emit an error in these
173 if (!MD->isDefined()) {
174 CGM.ErrorUnsupported(MD, "return-adjusting thunk with variadic arguments");
177 assert(!BaseFn->isDeclaration() && "cannot clone undefined variadic method");
180 llvm::ValueToValueMapTy VMap;
182 // We are cloning a function while some Metadata nodes are still unresolved.
183 // Ensure that the value mapper does not encounter any of them.
184 resolveTopLevelMetadata(BaseFn, VMap);
185 llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap);
186 Fn->replaceAllUsesWith(NewFn);
188 Fn->eraseFromParent();
191 // "Initialize" CGF (minimally).
194 // Get the "this" value
195 llvm::Function::arg_iterator AI = Fn->arg_begin();
196 if (CGM.ReturnTypeUsesSRet(FnInfo))
199 // Find the first store of "this", which will be to the alloca associated
201 Address ThisPtr(&*AI, CGM.getClassPointerAlignment(MD->getParent()));
202 llvm::BasicBlock *EntryBB = &Fn->front();
203 llvm::BasicBlock::iterator ThisStore =
204 std::find_if(EntryBB->begin(), EntryBB->end(), [&](llvm::Instruction &I) {
205 return isa<llvm::StoreInst>(I) &&
206 I.getOperand(0) == ThisPtr.getPointer();
208 assert(ThisStore != EntryBB->end() &&
209 "Store of this should be in entry block?");
210 // Adjust "this", if necessary.
211 Builder.SetInsertPoint(&*ThisStore);
212 llvm::Value *AdjustedThisPtr =
213 CGM.getCXXABI().performThisAdjustment(*this, ThisPtr, Thunk.This);
214 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr,
215 ThisStore->getOperand(0)->getType());
216 ThisStore->setOperand(0, AdjustedThisPtr);
218 if (!Thunk.Return.isEmpty()) {
219 // Fix up the returned value, if necessary.
220 for (llvm::BasicBlock &BB : *Fn) {
221 llvm::Instruction *T = BB.getTerminator();
222 if (isa<llvm::ReturnInst>(T)) {
223 RValue RV = RValue::get(T->getOperand(0));
224 T->eraseFromParent();
225 Builder.SetInsertPoint(&BB);
226 RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
227 Builder.CreateRet(RV.getScalarVal());
236 void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
237 const CGFunctionInfo &FnInfo,
238 bool IsUnprototyped) {
239 assert(!CurGD.getDecl() && "CurGD was already set!");
241 CurFuncIsThunk = true;
243 // Build FunctionArgs.
244 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
245 QualType ThisType = MD->getThisType();
248 ResultType = CGM.getContext().VoidTy;
249 else if (CGM.getCXXABI().HasThisReturn(GD))
250 ResultType = ThisType;
251 else if (CGM.getCXXABI().hasMostDerivedReturn(GD))
252 ResultType = CGM.getContext().VoidPtrTy;
254 ResultType = MD->getType()->castAs<FunctionProtoType>()->getReturnType();
255 FunctionArgList FunctionArgs;
257 // Create the implicit 'this' parameter declaration.
258 CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
260 // Add the rest of the parameters, if we have a prototype to work with.
261 if (!IsUnprototyped) {
262 FunctionArgs.append(MD->param_begin(), MD->param_end());
264 if (isa<CXXDestructorDecl>(MD))
265 CGM.getCXXABI().addImplicitStructorParams(*this, ResultType,
269 // Start defining the function.
270 auto NL = ApplyDebugLocation::CreateEmpty(*this);
271 StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
273 // Create a scope with an artificial location for the body of this function.
274 auto AL = ApplyDebugLocation::CreateArtificial(*this);
276 // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
277 CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
278 CXXThisValue = CXXABIThisValue;
283 void CodeGenFunction::FinishThunk() {
284 // Clear these to restore the invariants expected by
285 // StartFunction/FinishFunction.
286 CurCodeDecl = nullptr;
287 CurFuncDecl = nullptr;
292 void CodeGenFunction::EmitCallAndReturnForThunk(llvm::FunctionCallee Callee,
293 const ThunkInfo *Thunk,
294 bool IsUnprototyped) {
295 assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
296 "Please use a new CGF for this thunk");
297 const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurGD.getDecl());
299 // Adjust the 'this' pointer if necessary
300 llvm::Value *AdjustedThisPtr =
301 Thunk ? CGM.getCXXABI().performThisAdjustment(
302 *this, LoadCXXThisAddress(), Thunk->This)
305 // If perfect forwarding is required a variadic method, a method using
306 // inalloca, or an unprototyped thunk, use musttail. Emit an error if this
307 // thunk requires a return adjustment, since that is impossible with musttail.
308 if (CurFnInfo->usesInAlloca() || CurFnInfo->isVariadic() || IsUnprototyped) {
309 if (Thunk && !Thunk->Return.isEmpty()) {
311 CGM.ErrorUnsupported(
312 MD, "return-adjusting thunk with incomplete parameter type");
313 else if (CurFnInfo->isVariadic())
314 llvm_unreachable("shouldn't try to emit musttail return-adjusting "
315 "thunks for variadic functions");
317 CGM.ErrorUnsupported(
318 MD, "non-trivial argument copy for return-adjusting thunk");
320 EmitMustTailThunk(CurGD, AdjustedThisPtr, Callee);
324 // Start building CallArgs.
325 CallArgList CallArgs;
326 QualType ThisType = MD->getThisType();
327 CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
329 if (isa<CXXDestructorDecl>(MD))
330 CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);
333 unsigned PrefixArgs = CallArgs.size() - 1;
335 // Add the rest of the arguments.
336 for (const ParmVarDecl *PD : MD->parameters())
337 EmitDelegateCallArg(CallArgs, PD, SourceLocation());
339 const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
342 const CGFunctionInfo &CallFnInfo = CGM.getTypes().arrangeCXXMethodCall(
343 CallArgs, FPT, RequiredArgs::forPrototypePlus(FPT, 1), PrefixArgs);
344 assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
345 CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
346 CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
347 assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
348 similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
349 CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
350 assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
351 for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
352 assert(similar(CallFnInfo.arg_begin()[i].info,
353 CallFnInfo.arg_begin()[i].type,
354 CurFnInfo->arg_begin()[i].info,
355 CurFnInfo->arg_begin()[i].type));
358 // Determine whether we have a return value slot to use.
359 QualType ResultType = CGM.getCXXABI().HasThisReturn(CurGD)
361 : CGM.getCXXABI().hasMostDerivedReturn(CurGD)
362 ? CGM.getContext().VoidPtrTy
363 : FPT->getReturnType();
364 ReturnValueSlot Slot;
365 if (!ResultType->isVoidType() &&
366 (CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect ||
367 hasAggregateEvaluationKind(ResultType)))
368 Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified(),
369 /*IsUnused=*/false, /*IsExternallyDestructed=*/true);
371 // Now emit our call.
372 llvm::CallBase *CallOrInvoke;
373 RValue RV = EmitCall(*CurFnInfo, CGCallee::forDirect(Callee, CurGD), Slot,
374 CallArgs, &CallOrInvoke);
376 // Consider return adjustment if we have ThunkInfo.
377 if (Thunk && !Thunk->Return.isEmpty())
378 RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
379 else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(CallOrInvoke))
380 Call->setTailCallKind(llvm::CallInst::TCK_Tail);
383 if (!ResultType->isVoidType() && Slot.isNull())
384 CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
386 // Disable the final ARC autorelease.
387 AutoreleaseResult = false;
392 void CodeGenFunction::EmitMustTailThunk(GlobalDecl GD,
393 llvm::Value *AdjustedThisPtr,
394 llvm::FunctionCallee Callee) {
395 // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
396 // to translate AST arguments into LLVM IR arguments. For thunks, we know
397 // that the caller prototype more or less matches the callee prototype with
398 // the exception of 'this'.
399 SmallVector<llvm::Value *, 8> Args;
400 for (llvm::Argument &A : CurFn->args())
403 // Set the adjusted 'this' pointer.
404 const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
405 if (ThisAI.isDirect()) {
406 const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
407 int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
408 llvm::Type *ThisType = Args[ThisArgNo]->getType();
409 if (ThisType != AdjustedThisPtr->getType())
410 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
411 Args[ThisArgNo] = AdjustedThisPtr;
413 assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
414 Address ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);
415 llvm::Type *ThisType = ThisAddr.getElementType();
416 if (ThisType != AdjustedThisPtr->getType())
417 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
418 Builder.CreateStore(AdjustedThisPtr, ThisAddr);
421 // Emit the musttail call manually. Even if the prologue pushed cleanups, we
422 // don't actually want to run them.
423 llvm::CallInst *Call = Builder.CreateCall(Callee, Args);
424 Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
426 // Apply the standard set of call attributes.
427 unsigned CallingConv;
428 llvm::AttributeList Attrs;
429 CGM.ConstructAttributeList(Callee.getCallee()->getName(), *CurFnInfo, GD,
430 Attrs, CallingConv, /*AttrOnCallSite=*/true);
431 Call->setAttributes(Attrs);
432 Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
434 if (Call->getType()->isVoidTy())
435 Builder.CreateRetVoid();
437 Builder.CreateRet(Call);
439 // Finish the function to maintain CodeGenFunction invariants.
440 // FIXME: Don't emit unreachable code.
441 EmitBlock(createBasicBlock());
446 void CodeGenFunction::generateThunk(llvm::Function *Fn,
447 const CGFunctionInfo &FnInfo, GlobalDecl GD,
448 const ThunkInfo &Thunk,
449 bool IsUnprototyped) {
450 StartThunk(Fn, GD, FnInfo, IsUnprototyped);
451 // Create a scope with an artificial location for the body of this function.
452 auto AL = ApplyDebugLocation::CreateArtificial(*this);
454 // Get our callee. Use a placeholder type if this method is unprototyped so
455 // that CodeGenModule doesn't try to set attributes.
458 Ty = llvm::StructType::get(getLLVMContext());
460 Ty = CGM.getTypes().GetFunctionType(FnInfo);
462 llvm::Constant *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
464 // Fix up the function type for an unprototyped musttail call.
466 Callee = llvm::ConstantExpr::getBitCast(Callee, Fn->getType());
468 // Make the call and return the result.
469 EmitCallAndReturnForThunk(llvm::FunctionCallee(Fn->getFunctionType(), Callee),
470 &Thunk, IsUnprototyped);
473 static bool shouldEmitVTableThunk(CodeGenModule &CGM, const CXXMethodDecl *MD,
474 bool IsUnprototyped, bool ForVTable) {
475 // Always emit thunks in the MS C++ ABI. We cannot rely on other TUs to
476 // provide thunks for us.
477 if (CGM.getTarget().getCXXABI().isMicrosoft())
480 // In the Itanium C++ ABI, vtable thunks are provided by TUs that provide
481 // definitions of the main method. Therefore, emitting thunks with the vtable
482 // is purely an optimization. Emit the thunk if optimizations are enabled and
483 // all of the parameter types are complete.
485 return CGM.getCodeGenOpts().OptimizationLevel && !IsUnprototyped;
487 // Always emit thunks along with the method definition.
491 llvm::Constant *CodeGenVTables::maybeEmitThunk(GlobalDecl GD,
494 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
496 // First, get a declaration. Compute the mangled name. Don't worry about
497 // getting the function prototype right, since we may only need this
498 // declaration to fill in a vtable slot.
499 SmallString<256> Name;
500 MangleContext &MCtx = CGM.getCXXABI().getMangleContext();
501 llvm::raw_svector_ostream Out(Name);
502 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))
503 MCtx.mangleCXXDtorThunk(DD, GD.getDtorType(), TI.This, Out);
505 MCtx.mangleThunk(MD, TI, Out);
506 llvm::Type *ThunkVTableTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
507 llvm::Constant *Thunk = CGM.GetAddrOfThunk(Name, ThunkVTableTy, GD);
509 // If we don't need to emit a definition, return this declaration as is.
510 bool IsUnprototyped = !CGM.getTypes().isFuncTypeConvertible(
511 MD->getType()->castAs<FunctionType>());
512 if (!shouldEmitVTableThunk(CGM, MD, IsUnprototyped, ForVTable))
515 // Arrange a function prototype appropriate for a function definition. In some
516 // cases in the MS ABI, we may need to build an unprototyped musttail thunk.
517 const CGFunctionInfo &FnInfo =
518 IsUnprototyped ? CGM.getTypes().arrangeUnprototypedMustTailThunk(MD)
519 : CGM.getTypes().arrangeGlobalDeclaration(GD);
520 llvm::FunctionType *ThunkFnTy = CGM.getTypes().GetFunctionType(FnInfo);
522 // If the type of the underlying GlobalValue is wrong, we'll have to replace
523 // it. It should be a declaration.
524 llvm::Function *ThunkFn = cast<llvm::Function>(Thunk->stripPointerCasts());
525 if (ThunkFn->getFunctionType() != ThunkFnTy) {
526 llvm::GlobalValue *OldThunkFn = ThunkFn;
528 assert(OldThunkFn->isDeclaration() && "Shouldn't replace non-declaration");
530 // Remove the name from the old thunk function and get a new thunk.
531 OldThunkFn->setName(StringRef());
532 ThunkFn = llvm::Function::Create(ThunkFnTy, llvm::Function::ExternalLinkage,
533 Name.str(), &CGM.getModule());
534 CGM.SetLLVMFunctionAttributes(MD, FnInfo, ThunkFn);
536 // If needed, replace the old thunk with a bitcast.
537 if (!OldThunkFn->use_empty()) {
538 llvm::Constant *NewPtrForOldDecl =
539 llvm::ConstantExpr::getBitCast(ThunkFn, OldThunkFn->getType());
540 OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
543 // Remove the old thunk.
544 OldThunkFn->eraseFromParent();
547 bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
548 bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
550 if (!ThunkFn->isDeclaration()) {
551 if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
552 // There is already a thunk emitted for this function, do nothing.
556 setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
560 // If this will be unprototyped, add the "thunk" attribute so that LLVM knows
561 // that the return type is meaningless. These thunks can be used to call
562 // functions with differing return types, and the caller is required to cast
563 // the prototype appropriately to extract the correct value.
565 ThunkFn->addFnAttr("thunk");
567 CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
569 // Thunks for variadic methods are special because in general variadic
570 // arguments cannot be perfectly forwarded. In the general case, clang
571 // implements such thunks by cloning the original function body. However, for
572 // thunks with no return adjustment on targets that support musttail, we can
573 // use musttail to perfectly forward the variadic arguments.
574 bool ShouldCloneVarArgs = false;
575 if (!IsUnprototyped && ThunkFn->isVarArg()) {
576 ShouldCloneVarArgs = true;
577 if (TI.Return.isEmpty()) {
578 switch (CGM.getTriple().getArch()) {
579 case llvm::Triple::x86_64:
580 case llvm::Triple::x86:
581 case llvm::Triple::aarch64:
582 ShouldCloneVarArgs = false;
590 if (ShouldCloneVarArgs) {
591 if (UseAvailableExternallyLinkage)
594 CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, TI);
596 // Normal thunk body generation.
597 CodeGenFunction(CGM).generateThunk(ThunkFn, FnInfo, GD, TI, IsUnprototyped);
600 setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
604 void CodeGenVTables::EmitThunks(GlobalDecl GD) {
605 const CXXMethodDecl *MD =
606 cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
608 // We don't need to generate thunks for the base destructor.
609 if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
612 const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
613 VTContext->getThunkInfo(GD);
615 if (!ThunkInfoVector)
618 for (const ThunkInfo& Thunk : *ThunkInfoVector)
619 maybeEmitThunk(GD, Thunk, /*ForVTable=*/false);
622 void CodeGenVTables::addRelativeComponent(ConstantArrayBuilder &builder,
623 llvm::Constant *component,
624 unsigned vtableAddressPoint,
625 bool vtableHasLocalLinkage,
626 bool isCompleteDtor) const {
627 // No need to get the offset of a nullptr.
628 if (component->isNullValue())
629 return builder.add(llvm::ConstantInt::get(CGM.Int32Ty, 0));
632 cast<llvm::GlobalValue>(component->stripPointerCastsAndAliases());
633 llvm::Module &module = CGM.getModule();
635 // We don't want to copy the linkage of the vtable exactly because we still
636 // want the stub/proxy to be emitted for properly calculating the offset.
637 // Examples where there would be no symbol emitted are available_externally
638 // and private linkages.
639 auto stubLinkage = vtableHasLocalLinkage ? llvm::GlobalValue::InternalLinkage
640 : llvm::GlobalValue::ExternalLinkage;
642 llvm::Constant *target;
643 if (auto *func = dyn_cast<llvm::Function>(globalVal)) {
644 target = getOrCreateRelativeStub(func, stubLinkage, isCompleteDtor);
646 llvm::SmallString<16> rttiProxyName(globalVal->getName());
647 rttiProxyName.append(".rtti_proxy");
649 // The RTTI component may not always be emitted in the same linkage unit as
650 // the vtable. As a general case, we can make a dso_local proxy to the RTTI
651 // that points to the actual RTTI struct somewhere. This will result in a
652 // GOTPCREL relocation when taking the relative offset to the proxy.
653 llvm::GlobalVariable *proxy = module.getNamedGlobal(rttiProxyName);
655 proxy = new llvm::GlobalVariable(module, globalVal->getType(),
656 /*isConstant=*/true, stubLinkage,
657 globalVal, rttiProxyName);
658 proxy->setDSOLocal(true);
659 proxy->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
660 if (!proxy->hasLocalLinkage()) {
661 proxy->setVisibility(llvm::GlobalValue::HiddenVisibility);
662 proxy->setComdat(module.getOrInsertComdat(rttiProxyName));
668 builder.addRelativeOffsetToPosition(CGM.Int32Ty, target,
669 /*position=*/vtableAddressPoint);
672 llvm::Function *CodeGenVTables::getOrCreateRelativeStub(
673 llvm::Function *func, llvm::GlobalValue::LinkageTypes stubLinkage,
674 bool isCompleteDtor) const {
675 // A complete object destructor can later be substituted in the vtable for an
676 // appropriate base object destructor when optimizations are enabled. This can
677 // happen for child classes that don't have their own destructor. In the case
678 // where a parent virtual destructor is not guaranteed to be in the same
679 // linkage unit as the child vtable, it's possible for an external reference
680 // for this destructor to be substituted into the child vtable, preventing it
681 // from being in rodata. If this function is a complete virtual destructor, we
682 // can just force a stub to be emitted for it.
683 if (func->isDSOLocal() && !isCompleteDtor)
686 llvm::SmallString<16> stubName(func->getName());
687 stubName.append(".stub");
689 // Instead of taking the offset between the vtable and virtual function
690 // directly, we emit a dso_local stub that just contains a tail call to the
691 // original virtual function and take the offset between that and the
692 // vtable. We do this because there are some cases where the original
693 // function that would've been inserted into the vtable is not dso_local
694 // which may require some kind of dynamic relocation which prevents the
695 // vtable from being readonly. On x86_64, taking the offset between the
696 // function and the vtable gets lowered to the offset between the PLT entry
697 // for the function and the vtable which gives us a PLT32 reloc. On AArch64,
698 // right now only CALL26 and JUMP26 instructions generate PLT relocations,
699 // so we manifest them with stubs that are just jumps to the original
701 auto &module = CGM.getModule();
702 llvm::Function *stub = module.getFunction(stubName);
704 assert(stub->isDSOLocal() &&
705 "The previous definition of this stub should've been dso_local.");
709 stub = llvm::Function::Create(func->getFunctionType(), stubLinkage, stubName,
712 // Propogate function attributes.
713 stub->setAttributes(func->getAttributes());
715 stub->setDSOLocal(true);
716 stub->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
717 if (!stub->hasLocalLinkage()) {
718 stub->setVisibility(llvm::GlobalValue::HiddenVisibility);
719 stub->setComdat(module.getOrInsertComdat(stubName));
722 // Fill the stub with a tail call that will be optimized.
723 llvm::BasicBlock *block =
724 llvm::BasicBlock::Create(module.getContext(), "entry", stub);
725 llvm::IRBuilder<> block_builder(block);
726 llvm::SmallVector<llvm::Value *, 8> args;
727 for (auto &arg : stub->args())
728 args.push_back(&arg);
729 llvm::CallInst *call = block_builder.CreateCall(func, args);
730 call->setAttributes(func->getAttributes());
732 if (call->getType()->isVoidTy())
733 block_builder.CreateRetVoid();
735 block_builder.CreateRet(call);
740 bool CodeGenVTables::useRelativeLayout() const {
741 return CGM.getTarget().getCXXABI().isItaniumFamily() &&
742 CGM.getItaniumVTableContext().isRelativeLayout();
745 llvm::Type *CodeGenVTables::getVTableComponentType() const {
746 if (useRelativeLayout())
748 return CGM.Int8PtrTy;
751 static void AddPointerLayoutOffset(const CodeGenModule &CGM,
752 ConstantArrayBuilder &builder,
754 builder.add(llvm::ConstantExpr::getIntToPtr(
755 llvm::ConstantInt::get(CGM.PtrDiffTy, offset.getQuantity()),
759 static void AddRelativeLayoutOffset(const CodeGenModule &CGM,
760 ConstantArrayBuilder &builder,
762 builder.add(llvm::ConstantInt::get(CGM.Int32Ty, offset.getQuantity()));
765 void CodeGenVTables::addVTableComponent(ConstantArrayBuilder &builder,
766 const VTableLayout &layout,
767 unsigned componentIndex,
768 llvm::Constant *rtti,
769 unsigned &nextVTableThunkIndex,
770 unsigned vtableAddressPoint,
771 bool vtableHasLocalLinkage) {
772 auto &component = layout.vtable_components()[componentIndex];
774 auto addOffsetConstant =
775 useRelativeLayout() ? AddRelativeLayoutOffset : AddPointerLayoutOffset;
777 switch (component.getKind()) {
778 case VTableComponent::CK_VCallOffset:
779 return addOffsetConstant(CGM, builder, component.getVCallOffset());
781 case VTableComponent::CK_VBaseOffset:
782 return addOffsetConstant(CGM, builder, component.getVBaseOffset());
784 case VTableComponent::CK_OffsetToTop:
785 return addOffsetConstant(CGM, builder, component.getOffsetToTop());
787 case VTableComponent::CK_RTTI:
788 if (useRelativeLayout())
789 return addRelativeComponent(builder, rtti, vtableAddressPoint,
790 vtableHasLocalLinkage,
791 /*isCompleteDtor=*/false);
793 return builder.add(llvm::ConstantExpr::getBitCast(rtti, CGM.Int8PtrTy));
795 case VTableComponent::CK_FunctionPointer:
796 case VTableComponent::CK_CompleteDtorPointer:
797 case VTableComponent::CK_DeletingDtorPointer: {
800 // Get the right global decl.
801 switch (component.getKind()) {
803 llvm_unreachable("Unexpected vtable component kind");
804 case VTableComponent::CK_FunctionPointer:
805 GD = component.getFunctionDecl();
807 case VTableComponent::CK_CompleteDtorPointer:
808 GD = GlobalDecl(component.getDestructorDecl(), Dtor_Complete);
810 case VTableComponent::CK_DeletingDtorPointer:
811 GD = GlobalDecl(component.getDestructorDecl(), Dtor_Deleting);
815 if (CGM.getLangOpts().CUDA) {
816 // Emit NULL for methods we can't codegen on this
817 // side. Otherwise we'd end up with vtable with unresolved
819 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
820 // OK on device side: functions w/ __device__ attribute
821 // OK on host side: anything except __device__-only functions.
823 CGM.getLangOpts().CUDAIsDevice
824 ? MD->hasAttr<CUDADeviceAttr>()
825 : (MD->hasAttr<CUDAHostAttr>() || !MD->hasAttr<CUDADeviceAttr>());
827 return builder.add(llvm::ConstantExpr::getNullValue(CGM.Int8PtrTy));
828 // Method is acceptable, continue processing as usual.
831 auto getSpecialVirtualFn = [&](StringRef name) -> llvm::Constant * {
832 // FIXME(PR43094): When merging comdat groups, lld can select a local
833 // symbol as the signature symbol even though it cannot be accessed
834 // outside that symbol's TU. The relative vtables ABI would make
835 // __cxa_pure_virtual and __cxa_deleted_virtual local symbols, and
836 // depending on link order, the comdat groups could resolve to the one
837 // with the local symbol. As a temporary solution, fill these components
838 // with zero. We shouldn't be calling these in the first place anyway.
839 if (useRelativeLayout())
840 return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
842 // For NVPTX devices in OpenMP emit special functon as null pointers,
843 // otherwise linking ends up with unresolved references.
844 if (CGM.getLangOpts().OpenMP && CGM.getLangOpts().OpenMPIsDevice &&
845 CGM.getTriple().isNVPTX())
846 return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
847 llvm::FunctionType *fnTy =
848 llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
849 llvm::Constant *fn = cast<llvm::Constant>(
850 CGM.CreateRuntimeFunction(fnTy, name).getCallee());
851 if (auto f = dyn_cast<llvm::Function>(fn))
852 f->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
853 return llvm::ConstantExpr::getBitCast(fn, CGM.Int8PtrTy);
856 llvm::Constant *fnPtr;
858 // Pure virtual member functions.
859 if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
862 getSpecialVirtualFn(CGM.getCXXABI().GetPureVirtualCallName());
863 fnPtr = PureVirtualFn;
865 // Deleted virtual member functions.
866 } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
867 if (!DeletedVirtualFn)
869 getSpecialVirtualFn(CGM.getCXXABI().GetDeletedVirtualCallName());
870 fnPtr = DeletedVirtualFn;
873 } else if (nextVTableThunkIndex < layout.vtable_thunks().size() &&
874 layout.vtable_thunks()[nextVTableThunkIndex].first ==
876 auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;
878 nextVTableThunkIndex++;
879 fnPtr = maybeEmitThunk(GD, thunkInfo, /*ForVTable=*/true);
881 // Otherwise we can use the method definition directly.
883 llvm::Type *fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
884 fnPtr = CGM.GetAddrOfFunction(GD, fnTy, /*ForVTable=*/true);
887 if (useRelativeLayout()) {
888 return addRelativeComponent(
889 builder, fnPtr, vtableAddressPoint, vtableHasLocalLinkage,
890 component.getKind() == VTableComponent::CK_CompleteDtorPointer);
892 return builder.add(llvm::ConstantExpr::getBitCast(fnPtr, CGM.Int8PtrTy));
895 case VTableComponent::CK_UnusedFunctionPointer:
896 if (useRelativeLayout())
897 return builder.add(llvm::ConstantExpr::getNullValue(CGM.Int32Ty));
899 return builder.addNullPointer(CGM.Int8PtrTy);
902 llvm_unreachable("Unexpected vtable component kind");
905 llvm::Type *CodeGenVTables::getVTableType(const VTableLayout &layout) {
906 SmallVector<llvm::Type *, 4> tys;
907 llvm::Type *componentType = getVTableComponentType();
908 for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i)
909 tys.push_back(llvm::ArrayType::get(componentType, layout.getVTableSize(i)));
911 return llvm::StructType::get(CGM.getLLVMContext(), tys);
914 void CodeGenVTables::createVTableInitializer(ConstantStructBuilder &builder,
915 const VTableLayout &layout,
916 llvm::Constant *rtti,
917 bool vtableHasLocalLinkage) {
918 llvm::Type *componentType = getVTableComponentType();
920 const auto &addressPoints = layout.getAddressPointIndices();
921 unsigned nextVTableThunkIndex = 0;
922 for (unsigned vtableIndex = 0, endIndex = layout.getNumVTables();
923 vtableIndex != endIndex; ++vtableIndex) {
924 auto vtableElem = builder.beginArray(componentType);
926 size_t vtableStart = layout.getVTableOffset(vtableIndex);
927 size_t vtableEnd = vtableStart + layout.getVTableSize(vtableIndex);
928 for (size_t componentIndex = vtableStart; componentIndex < vtableEnd;
930 addVTableComponent(vtableElem, layout, componentIndex, rtti,
931 nextVTableThunkIndex, addressPoints[vtableIndex],
932 vtableHasLocalLinkage);
934 vtableElem.finishAndAddTo(builder);
938 llvm::GlobalVariable *CodeGenVTables::GenerateConstructionVTable(
939 const CXXRecordDecl *RD, const BaseSubobject &Base, bool BaseIsVirtual,
940 llvm::GlobalVariable::LinkageTypes Linkage,
941 VTableAddressPointsMapTy &AddressPoints) {
942 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
943 DI->completeClassData(Base.getBase());
945 std::unique_ptr<VTableLayout> VTLayout(
946 getItaniumVTableContext().createConstructionVTableLayout(
947 Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
949 // Add the address points.
950 AddressPoints = VTLayout->getAddressPoints();
952 // Get the mangled construction vtable name.
953 SmallString<256> OutName;
954 llvm::raw_svector_ostream Out(OutName);
955 cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
956 .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
957 Base.getBase(), Out);
958 SmallString<256> Name(OutName);
960 bool UsingRelativeLayout = getItaniumVTableContext().isRelativeLayout();
961 bool VTableAliasExists =
962 UsingRelativeLayout && CGM.getModule().getNamedAlias(Name);
963 if (VTableAliasExists) {
964 // We previously made the vtable hidden and changed its name.
965 Name.append(".local");
968 llvm::Type *VTType = getVTableType(*VTLayout);
970 // Construction vtable symbols are not part of the Itanium ABI, so we cannot
971 // guarantee that they actually will be available externally. Instead, when
972 // emitting an available_externally VTT, we provide references to an internal
973 // linkage construction vtable. The ABI only requires complete-object vtables
974 // to be the same for all instances of a type, not construction vtables.
975 if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
976 Linkage = llvm::GlobalVariable::InternalLinkage;
978 unsigned Align = CGM.getDataLayout().getABITypeAlignment(VTType);
980 // Create the variable that will hold the construction vtable.
981 llvm::GlobalVariable *VTable =
982 CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage, Align);
984 // V-tables are always unnamed_addr.
985 VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
987 llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
988 CGM.getContext().getTagDeclType(Base.getBase()));
990 // Create and set the initializer.
991 ConstantInitBuilder builder(CGM);
992 auto components = builder.beginStruct();
993 createVTableInitializer(components, *VTLayout, RTTI,
994 VTable->hasLocalLinkage());
995 components.finishAndSetAsInitializer(VTable);
997 // Set properties only after the initializer has been set to ensure that the
998 // GV is treated as definition and not declaration.
999 assert(!VTable->isDeclaration() && "Shouldn't set properties on declaration");
1000 CGM.setGVProperties(VTable, RD);
1002 CGM.EmitVTableTypeMetadata(RD, VTable, *VTLayout.get());
1004 if (UsingRelativeLayout && !VTable->isDSOLocal())
1005 GenerateRelativeVTableAlias(VTable, OutName);
1010 // If the VTable is not dso_local, then we will not be able to indicate that
1011 // the VTable does not need a relocation and move into rodata. A frequent
1012 // time this can occur is for classes that should be made public from a DSO
1013 // (like in libc++). For cases like these, we can make the vtable hidden or
1014 // private and create a public alias with the same visibility and linkage as
1015 // the original vtable type.
1016 void CodeGenVTables::GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
1017 llvm::StringRef AliasNameRef) {
1018 assert(getItaniumVTableContext().isRelativeLayout() &&
1019 "Can only use this if the relative vtable ABI is used");
1020 assert(!VTable->isDSOLocal() && "This should be called only if the vtable is "
1021 "not guaranteed to be dso_local");
1023 // If the vtable is available_externally, we shouldn't (or need to) generate
1024 // an alias for it in the first place since the vtable won't actually by
1025 // emitted in this compilation unit.
1026 if (VTable->hasAvailableExternallyLinkage())
1029 // Create a new string in the event the alias is already the name of the
1030 // vtable. Using the reference directly could lead to use of an inititialized
1031 // value in the module's StringMap.
1032 llvm::SmallString<256> AliasName(AliasNameRef);
1033 VTable->setName(AliasName + ".local");
1035 auto Linkage = VTable->getLinkage();
1036 assert(llvm::GlobalAlias::isValidLinkage(Linkage) &&
1037 "Invalid vtable alias linkage");
1039 llvm::GlobalAlias *VTableAlias = CGM.getModule().getNamedAlias(AliasName);
1041 VTableAlias = llvm::GlobalAlias::create(VTable->getValueType(),
1042 VTable->getAddressSpace(), Linkage,
1043 AliasName, &CGM.getModule());
1045 assert(VTableAlias->getValueType() == VTable->getValueType());
1046 assert(VTableAlias->getLinkage() == Linkage);
1048 VTableAlias->setVisibility(VTable->getVisibility());
1049 VTableAlias->setUnnamedAddr(VTable->getUnnamedAddr());
1051 // Both of these imply dso_local for the vtable.
1052 if (!VTable->hasComdat()) {
1053 // If this is in a comdat, then we shouldn't make the linkage private due to
1054 // an issue in lld where private symbols can be used as the key symbol when
1055 // choosing the prevelant group. This leads to "relocation refers to a
1056 // symbol in a discarded section".
1057 VTable->setLinkage(llvm::GlobalValue::PrivateLinkage);
1059 // We should at least make this hidden since we don't want to expose it.
1060 VTable->setVisibility(llvm::GlobalValue::HiddenVisibility);
1063 VTableAlias->setAliasee(VTable);
1066 static bool shouldEmitAvailableExternallyVTable(const CodeGenModule &CGM,
1067 const CXXRecordDecl *RD) {
1068 return CGM.getCodeGenOpts().OptimizationLevel > 0 &&
1069 CGM.getCXXABI().canSpeculativelyEmitVTable(RD);
1072 /// Compute the required linkage of the vtable for the given class.
1074 /// Note that we only call this at the end of the translation unit.
1075 llvm::GlobalVariable::LinkageTypes
1076 CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
1077 if (!RD->isExternallyVisible())
1078 return llvm::GlobalVariable::InternalLinkage;
1080 // We're at the end of the translation unit, so the current key
1081 // function is fully correct.
1082 const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
1083 if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
1084 // If this class has a key function, use that to determine the
1085 // linkage of the vtable.
1086 const FunctionDecl *def = nullptr;
1087 if (keyFunction->hasBody(def))
1088 keyFunction = cast<CXXMethodDecl>(def);
1090 switch (keyFunction->getTemplateSpecializationKind()) {
1091 case TSK_Undeclared:
1092 case TSK_ExplicitSpecialization:
1093 assert((def || CodeGenOpts.OptimizationLevel > 0 ||
1094 CodeGenOpts.getDebugInfo() != codegenoptions::NoDebugInfo) &&
1095 "Shouldn't query vtable linkage without key function, "
1096 "optimizations, or debug info");
1097 if (!def && CodeGenOpts.OptimizationLevel > 0)
1098 return llvm::GlobalVariable::AvailableExternallyLinkage;
1100 if (keyFunction->isInlined())
1101 return !Context.getLangOpts().AppleKext ?
1102 llvm::GlobalVariable::LinkOnceODRLinkage :
1103 llvm::Function::InternalLinkage;
1105 return llvm::GlobalVariable::ExternalLinkage;
1107 case TSK_ImplicitInstantiation:
1108 return !Context.getLangOpts().AppleKext ?
1109 llvm::GlobalVariable::LinkOnceODRLinkage :
1110 llvm::Function::InternalLinkage;
1112 case TSK_ExplicitInstantiationDefinition:
1113 return !Context.getLangOpts().AppleKext ?
1114 llvm::GlobalVariable::WeakODRLinkage :
1115 llvm::Function::InternalLinkage;
1117 case TSK_ExplicitInstantiationDeclaration:
1118 llvm_unreachable("Should not have been asked to emit this");
1122 // -fapple-kext mode does not support weak linkage, so we must use
1123 // internal linkage.
1124 if (Context.getLangOpts().AppleKext)
1125 return llvm::Function::InternalLinkage;
1127 llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
1128 llvm::GlobalValue::LinkOnceODRLinkage;
1129 llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
1130 llvm::GlobalValue::WeakODRLinkage;
1131 if (RD->hasAttr<DLLExportAttr>()) {
1132 // Cannot discard exported vtables.
1133 DiscardableODRLinkage = NonDiscardableODRLinkage;
1134 } else if (RD->hasAttr<DLLImportAttr>()) {
1135 // Imported vtables are available externally.
1136 DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
1137 NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
1140 switch (RD->getTemplateSpecializationKind()) {
1141 case TSK_Undeclared:
1142 case TSK_ExplicitSpecialization:
1143 case TSK_ImplicitInstantiation:
1144 return DiscardableODRLinkage;
1146 case TSK_ExplicitInstantiationDeclaration:
1147 // Explicit instantiations in MSVC do not provide vtables, so we must emit
1149 if (getTarget().getCXXABI().isMicrosoft())
1150 return DiscardableODRLinkage;
1151 return shouldEmitAvailableExternallyVTable(*this, RD)
1152 ? llvm::GlobalVariable::AvailableExternallyLinkage
1153 : llvm::GlobalVariable::ExternalLinkage;
1155 case TSK_ExplicitInstantiationDefinition:
1156 return NonDiscardableODRLinkage;
1159 llvm_unreachable("Invalid TemplateSpecializationKind!");
1162 /// This is a callback from Sema to tell us that a particular vtable is
1163 /// required to be emitted in this translation unit.
1165 /// This is only called for vtables that _must_ be emitted (mainly due to key
1166 /// functions). For weak vtables, CodeGen tracks when they are needed and
1167 /// emits them as-needed.
1168 void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
1169 VTables.GenerateClassData(theClass);
1173 CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
1174 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
1175 DI->completeClassData(RD);
1177 if (RD->getNumVBases())
1178 CGM.getCXXABI().emitVirtualInheritanceTables(RD);
1180 CGM.getCXXABI().emitVTableDefinitions(*this, RD);
1183 /// At this point in the translation unit, does it appear that can we
1184 /// rely on the vtable being defined elsewhere in the program?
1186 /// The response is really only definitive when called at the end of
1187 /// the translation unit.
1189 /// The only semantic restriction here is that the object file should
1190 /// not contain a vtable definition when that vtable is defined
1191 /// strongly elsewhere. Otherwise, we'd just like to avoid emitting
1192 /// vtables when unnecessary.
1193 bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
1194 assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
1196 // We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't
1197 // emit them even if there is an explicit template instantiation.
1198 if (CGM.getTarget().getCXXABI().isMicrosoft())
1201 // If we have an explicit instantiation declaration (and not a
1202 // definition), the vtable is defined elsewhere.
1203 TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
1204 if (TSK == TSK_ExplicitInstantiationDeclaration)
1207 // Otherwise, if the class is an instantiated template, the
1208 // vtable must be defined here.
1209 if (TSK == TSK_ImplicitInstantiation ||
1210 TSK == TSK_ExplicitInstantiationDefinition)
1213 // Otherwise, if the class doesn't have a key function (possibly
1214 // anymore), the vtable must be defined here.
1215 const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
1219 // Otherwise, if we don't have a definition of the key function, the
1220 // vtable must be defined somewhere else.
1221 return !keyFunction->hasBody();
1224 /// Given that we're currently at the end of the translation unit, and
1225 /// we've emitted a reference to the vtable for this class, should
1226 /// we define that vtable?
1227 static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
1228 const CXXRecordDecl *RD) {
1229 // If vtable is internal then it has to be done.
1230 if (!CGM.getVTables().isVTableExternal(RD))
1233 // If it's external then maybe we will need it as available_externally.
1234 return shouldEmitAvailableExternallyVTable(CGM, RD);
1237 /// Given that at some point we emitted a reference to one or more
1238 /// vtables, and that we are now at the end of the translation unit,
1239 /// decide whether we should emit them.
1240 void CodeGenModule::EmitDeferredVTables() {
1242 // Remember the size of DeferredVTables, because we're going to assume
1243 // that this entire operation doesn't modify it.
1244 size_t savedSize = DeferredVTables.size();
1247 for (const CXXRecordDecl *RD : DeferredVTables)
1248 if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
1249 VTables.GenerateClassData(RD);
1250 else if (shouldOpportunisticallyEmitVTables())
1251 OpportunisticVTables.push_back(RD);
1253 assert(savedSize == DeferredVTables.size() &&
1254 "deferred extra vtables during vtable emission?");
1255 DeferredVTables.clear();
1258 bool CodeGenModule::HasLTOVisibilityPublicStd(const CXXRecordDecl *RD) {
1259 if (!getCodeGenOpts().LTOVisibilityPublicStd)
1262 const DeclContext *DC = RD;
1264 auto *D = cast<Decl>(DC);
1265 DC = DC->getParent();
1266 if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {
1267 if (auto *ND = dyn_cast<NamespaceDecl>(D))
1268 if (const IdentifierInfo *II = ND->getIdentifier())
1269 if (II->isStr("std") || II->isStr("stdext"))
1278 bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
1279 LinkageInfo LV = RD->getLinkageAndVisibility();
1280 if (!isExternallyVisible(LV.getLinkage()))
1283 if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>())
1286 if (getTriple().isOSBinFormatCOFF()) {
1287 if (RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())
1290 if (LV.getVisibility() != HiddenVisibility)
1294 return !HasLTOVisibilityPublicStd(RD);
1297 llvm::GlobalObject::VCallVisibility
1298 CodeGenModule::GetVCallVisibilityLevel(const CXXRecordDecl *RD) {
1299 LinkageInfo LV = RD->getLinkageAndVisibility();
1300 llvm::GlobalObject::VCallVisibility TypeVis;
1301 if (!isExternallyVisible(LV.getLinkage()))
1302 TypeVis = llvm::GlobalObject::VCallVisibilityTranslationUnit;
1303 else if (HasHiddenLTOVisibility(RD))
1304 TypeVis = llvm::GlobalObject::VCallVisibilityLinkageUnit;
1306 TypeVis = llvm::GlobalObject::VCallVisibilityPublic;
1308 for (auto B : RD->bases())
1309 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1310 TypeVis = std::min(TypeVis,
1311 GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl()));
1313 for (auto B : RD->vbases())
1314 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1315 TypeVis = std::min(TypeVis,
1316 GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl()));
1321 void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
1322 llvm::GlobalVariable *VTable,
1323 const VTableLayout &VTLayout) {
1324 if (!getCodeGenOpts().LTOUnit)
1327 CharUnits PointerWidth =
1328 Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
1330 typedef std::pair<const CXXRecordDecl *, unsigned> AddressPoint;
1331 std::vector<AddressPoint> AddressPoints;
1332 for (auto &&AP : VTLayout.getAddressPoints())
1333 AddressPoints.push_back(std::make_pair(
1334 AP.first.getBase(), VTLayout.getVTableOffset(AP.second.VTableIndex) +
1335 AP.second.AddressPointIndex));
1337 // Sort the address points for determinism.
1338 llvm::sort(AddressPoints, [this](const AddressPoint &AP1,
1339 const AddressPoint &AP2) {
1344 llvm::raw_string_ostream O1(S1);
1345 getCXXABI().getMangleContext().mangleTypeName(
1346 QualType(AP1.first->getTypeForDecl(), 0), O1);
1350 llvm::raw_string_ostream O2(S2);
1351 getCXXABI().getMangleContext().mangleTypeName(
1352 QualType(AP2.first->getTypeForDecl(), 0), O2);
1360 return AP1.second < AP2.second;
1363 ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();
1364 for (auto AP : AddressPoints) {
1365 // Create type metadata for the address point.
1366 AddVTableTypeMetadata(VTable, PointerWidth * AP.second, AP.first);
1368 // The class associated with each address point could also potentially be
1369 // used for indirect calls via a member function pointer, so we need to
1370 // annotate the address of each function pointer with the appropriate member
1371 // function pointer type.
1372 for (unsigned I = 0; I != Comps.size(); ++I) {
1373 if (Comps[I].getKind() != VTableComponent::CK_FunctionPointer)
1375 llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(
1376 Context.getMemberPointerType(
1377 Comps[I].getFunctionDecl()->getType(),
1378 Context.getRecordType(AP.first).getTypePtr()));
1379 VTable->addTypeMetadata((PointerWidth * I).getQuantity(), MD);
1383 if (getCodeGenOpts().VirtualFunctionElimination ||
1384 getCodeGenOpts().WholeProgramVTables) {
1385 llvm::GlobalObject::VCallVisibility TypeVis = GetVCallVisibilityLevel(RD);
1386 if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)
1387 VTable->setVCallVisibilityMetadata(TypeVis);