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/CXXInheritance.h"
17 #include "clang/AST/RecordLayout.h"
18 #include "clang/Basic/CodeGenOptions.h"
19 #include "clang/CodeGen/CGFunctionInfo.h"
20 #include "clang/CodeGen/ConstantInitBuilder.h"
21 #include "llvm/IR/IntrinsicInst.h"
22 #include "llvm/Support/Format.h"
23 #include "llvm/Transforms/Utils/Cloning.h"
27 using namespace clang;
28 using namespace CodeGen;
30 CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
31 : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
33 llvm::Constant *CodeGenModule::GetAddrOfThunk(StringRef Name, llvm::Type *FnTy,
35 return GetOrCreateLLVMFunction(Name, FnTy, GD, /*ForVTable=*/true,
36 /*DontDefer=*/true, /*IsThunk=*/true);
39 static void setThunkProperties(CodeGenModule &CGM, const ThunkInfo &Thunk,
40 llvm::Function *ThunkFn, bool ForVTable,
42 CGM.setFunctionLinkage(GD, ThunkFn);
43 CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
44 !Thunk.Return.isEmpty());
46 // Set the right visibility.
47 CGM.setGVProperties(ThunkFn, GD);
49 if (!CGM.getCXXABI().exportThunk()) {
50 ThunkFn->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
51 ThunkFn->setDSOLocal(true);
54 if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())
55 ThunkFn->setComdat(CGM.getModule().getOrInsertComdat(ThunkFn->getName()));
59 static bool similar(const ABIArgInfo &infoL, CanQualType typeL,
60 const ABIArgInfo &infoR, CanQualType typeR) {
61 return (infoL.getKind() == infoR.getKind() &&
63 (isa<PointerType>(typeL) && isa<PointerType>(typeR)) ||
64 (isa<ReferenceType>(typeL) && isa<ReferenceType>(typeR))));
68 static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
69 QualType ResultType, RValue RV,
70 const ThunkInfo &Thunk) {
71 // Emit the return adjustment.
72 bool NullCheckValue = !ResultType->isReferenceType();
74 llvm::BasicBlock *AdjustNull = nullptr;
75 llvm::BasicBlock *AdjustNotNull = nullptr;
76 llvm::BasicBlock *AdjustEnd = nullptr;
78 llvm::Value *ReturnValue = RV.getScalarVal();
81 AdjustNull = CGF.createBasicBlock("adjust.null");
82 AdjustNotNull = CGF.createBasicBlock("adjust.notnull");
83 AdjustEnd = CGF.createBasicBlock("adjust.end");
85 llvm::Value *IsNull = CGF.Builder.CreateIsNull(ReturnValue);
86 CGF.Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);
87 CGF.EmitBlock(AdjustNotNull);
90 auto ClassDecl = ResultType->getPointeeType()->getAsCXXRecordDecl();
91 auto ClassAlign = CGF.CGM.getClassPointerAlignment(ClassDecl);
92 ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(CGF,
93 Address(ReturnValue, ClassAlign),
97 CGF.Builder.CreateBr(AdjustEnd);
98 CGF.EmitBlock(AdjustNull);
99 CGF.Builder.CreateBr(AdjustEnd);
100 CGF.EmitBlock(AdjustEnd);
102 llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
103 PHI->addIncoming(ReturnValue, AdjustNotNull);
104 PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
109 return RValue::get(ReturnValue);
112 /// This function clones a function's DISubprogram node and enters it into
113 /// a value map with the intent that the map can be utilized by the cloner
114 /// to short-circuit Metadata node mapping.
115 /// Furthermore, the function resolves any DILocalVariable nodes referenced
116 /// by dbg.value intrinsics so they can be properly mapped during cloning.
117 static void resolveTopLevelMetadata(llvm::Function *Fn,
118 llvm::ValueToValueMapTy &VMap) {
119 // Clone the DISubprogram node and put it into the Value map.
120 auto *DIS = Fn->getSubprogram();
123 auto *NewDIS = DIS->replaceWithDistinct(DIS->clone());
124 VMap.MD()[DIS].reset(NewDIS);
126 // Find all llvm.dbg.declare intrinsics and resolve the DILocalVariable nodes
127 // they are referencing.
128 for (auto &BB : Fn->getBasicBlockList()) {
130 if (auto *DII = dyn_cast<llvm::DbgVariableIntrinsic>(&I)) {
131 auto *DILocal = DII->getVariable();
132 if (!DILocal->isResolved())
139 // This function does roughly the same thing as GenerateThunk, but in a
140 // very different way, so that va_start and va_end work correctly.
141 // FIXME: This function assumes "this" is the first non-sret LLVM argument of
142 // a function, and that there is an alloca built in the entry block
143 // for all accesses to "this".
144 // FIXME: This function assumes there is only one "ret" statement per function.
145 // FIXME: Cloning isn't correct in the presence of indirect goto!
146 // FIXME: This implementation of thunks bloats codesize by duplicating the
147 // function definition. There are alternatives:
148 // 1. Add some sort of stub support to LLVM for cases where we can
149 // do a this adjustment, then a sibcall.
150 // 2. We could transform the definition to take a va_list instead of an
151 // actual variable argument list, then have the thunks (including a
152 // no-op thunk for the regular definition) call va_start/va_end.
153 // There's a bit of per-call overhead for this solution, but it's
154 // better for codesize if the definition is long.
156 CodeGenFunction::GenerateVarArgsThunk(llvm::Function *Fn,
157 const CGFunctionInfo &FnInfo,
158 GlobalDecl GD, const ThunkInfo &Thunk) {
159 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
160 const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
161 QualType ResultType = FPT->getReturnType();
163 // Get the original function
164 assert(FnInfo.isVariadic());
165 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);
166 llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
167 llvm::Function *BaseFn = cast<llvm::Function>(Callee);
169 // Cloning can't work if we don't have a definition. The Microsoft ABI may
170 // require thunks when a definition is not available. Emit an error in these
172 if (!MD->isDefined()) {
173 CGM.ErrorUnsupported(MD, "return-adjusting thunk with variadic arguments");
176 assert(!BaseFn->isDeclaration() && "cannot clone undefined variadic method");
179 llvm::ValueToValueMapTy VMap;
181 // We are cloning a function while some Metadata nodes are still unresolved.
182 // Ensure that the value mapper does not encounter any of them.
183 resolveTopLevelMetadata(BaseFn, VMap);
184 llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap);
185 Fn->replaceAllUsesWith(NewFn);
187 Fn->eraseFromParent();
190 // "Initialize" CGF (minimally).
193 // Get the "this" value
194 llvm::Function::arg_iterator AI = Fn->arg_begin();
195 if (CGM.ReturnTypeUsesSRet(FnInfo))
198 // Find the first store of "this", which will be to the alloca associated
200 Address ThisPtr(&*AI, CGM.getClassPointerAlignment(MD->getParent()));
201 llvm::BasicBlock *EntryBB = &Fn->front();
202 llvm::BasicBlock::iterator ThisStore =
203 std::find_if(EntryBB->begin(), EntryBB->end(), [&](llvm::Instruction &I) {
204 return isa<llvm::StoreInst>(I) &&
205 I.getOperand(0) == ThisPtr.getPointer();
207 assert(ThisStore != EntryBB->end() &&
208 "Store of this should be in entry block?");
209 // Adjust "this", if necessary.
210 Builder.SetInsertPoint(&*ThisStore);
211 llvm::Value *AdjustedThisPtr =
212 CGM.getCXXABI().performThisAdjustment(*this, ThisPtr, Thunk.This);
213 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr,
214 ThisStore->getOperand(0)->getType());
215 ThisStore->setOperand(0, AdjustedThisPtr);
217 if (!Thunk.Return.isEmpty()) {
218 // Fix up the returned value, if necessary.
219 for (llvm::BasicBlock &BB : *Fn) {
220 llvm::Instruction *T = BB.getTerminator();
221 if (isa<llvm::ReturnInst>(T)) {
222 RValue RV = RValue::get(T->getOperand(0));
223 T->eraseFromParent();
224 Builder.SetInsertPoint(&BB);
225 RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
226 Builder.CreateRet(RV.getScalarVal());
235 void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
236 const CGFunctionInfo &FnInfo,
237 bool IsUnprototyped) {
238 assert(!CurGD.getDecl() && "CurGD was already set!");
240 CurFuncIsThunk = true;
242 // Build FunctionArgs.
243 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
244 QualType ThisType = MD->getThisType();
247 ResultType = CGM.getContext().VoidTy;
248 else if (CGM.getCXXABI().HasThisReturn(GD))
249 ResultType = ThisType;
250 else if (CGM.getCXXABI().hasMostDerivedReturn(GD))
251 ResultType = CGM.getContext().VoidPtrTy;
253 ResultType = MD->getType()->castAs<FunctionProtoType>()->getReturnType();
254 FunctionArgList FunctionArgs;
256 // Create the implicit 'this' parameter declaration.
257 CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
259 // Add the rest of the parameters, if we have a prototype to work with.
260 if (!IsUnprototyped) {
261 FunctionArgs.append(MD->param_begin(), MD->param_end());
263 if (isa<CXXDestructorDecl>(MD))
264 CGM.getCXXABI().addImplicitStructorParams(*this, ResultType,
268 // Start defining the function.
269 auto NL = ApplyDebugLocation::CreateEmpty(*this);
270 StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
272 // Create a scope with an artificial location for the body of this function.
273 auto AL = ApplyDebugLocation::CreateArtificial(*this);
275 // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
276 CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
277 CXXThisValue = CXXABIThisValue;
282 void CodeGenFunction::FinishThunk() {
283 // Clear these to restore the invariants expected by
284 // StartFunction/FinishFunction.
285 CurCodeDecl = nullptr;
286 CurFuncDecl = nullptr;
291 void CodeGenFunction::EmitCallAndReturnForThunk(llvm::FunctionCallee Callee,
292 const ThunkInfo *Thunk,
293 bool IsUnprototyped) {
294 assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
295 "Please use a new CGF for this thunk");
296 const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurGD.getDecl());
298 // Adjust the 'this' pointer if necessary
299 llvm::Value *AdjustedThisPtr =
300 Thunk ? CGM.getCXXABI().performThisAdjustment(
301 *this, LoadCXXThisAddress(), Thunk->This)
304 // If perfect forwarding is required a variadic method, a method using
305 // inalloca, or an unprototyped thunk, use musttail. Emit an error if this
306 // thunk requires a return adjustment, since that is impossible with musttail.
307 if (CurFnInfo->usesInAlloca() || CurFnInfo->isVariadic() || IsUnprototyped) {
308 if (Thunk && !Thunk->Return.isEmpty()) {
310 CGM.ErrorUnsupported(
311 MD, "return-adjusting thunk with incomplete parameter type");
312 else if (CurFnInfo->isVariadic())
313 llvm_unreachable("shouldn't try to emit musttail return-adjusting "
314 "thunks for variadic functions");
316 CGM.ErrorUnsupported(
317 MD, "non-trivial argument copy for return-adjusting thunk");
319 EmitMustTailThunk(CurGD, AdjustedThisPtr, Callee);
323 // Start building CallArgs.
324 CallArgList CallArgs;
325 QualType ThisType = MD->getThisType();
326 CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
328 if (isa<CXXDestructorDecl>(MD))
329 CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);
332 unsigned PrefixArgs = CallArgs.size() - 1;
334 // Add the rest of the arguments.
335 for (const ParmVarDecl *PD : MD->parameters())
336 EmitDelegateCallArg(CallArgs, PD, SourceLocation());
338 const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
341 const CGFunctionInfo &CallFnInfo = CGM.getTypes().arrangeCXXMethodCall(
342 CallArgs, FPT, RequiredArgs::forPrototypePlus(FPT, 1), PrefixArgs);
343 assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
344 CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
345 CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
346 assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
347 similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
348 CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
349 assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
350 for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
351 assert(similar(CallFnInfo.arg_begin()[i].info,
352 CallFnInfo.arg_begin()[i].type,
353 CurFnInfo->arg_begin()[i].info,
354 CurFnInfo->arg_begin()[i].type));
357 // Determine whether we have a return value slot to use.
358 QualType ResultType = CGM.getCXXABI().HasThisReturn(CurGD)
360 : CGM.getCXXABI().hasMostDerivedReturn(CurGD)
361 ? CGM.getContext().VoidPtrTy
362 : FPT->getReturnType();
363 ReturnValueSlot Slot;
364 if (!ResultType->isVoidType() &&
365 CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect)
366 Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified());
368 // Now emit our call.
369 llvm::CallBase *CallOrInvoke;
370 RValue RV = EmitCall(*CurFnInfo, CGCallee::forDirect(Callee, CurGD), Slot,
371 CallArgs, &CallOrInvoke);
373 // Consider return adjustment if we have ThunkInfo.
374 if (Thunk && !Thunk->Return.isEmpty())
375 RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
376 else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(CallOrInvoke))
377 Call->setTailCallKind(llvm::CallInst::TCK_Tail);
380 if (!ResultType->isVoidType() && Slot.isNull())
381 CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
383 // Disable the final ARC autorelease.
384 AutoreleaseResult = false;
389 void CodeGenFunction::EmitMustTailThunk(GlobalDecl GD,
390 llvm::Value *AdjustedThisPtr,
391 llvm::FunctionCallee Callee) {
392 // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
393 // to translate AST arguments into LLVM IR arguments. For thunks, we know
394 // that the caller prototype more or less matches the callee prototype with
395 // the exception of 'this'.
396 SmallVector<llvm::Value *, 8> Args;
397 for (llvm::Argument &A : CurFn->args())
400 // Set the adjusted 'this' pointer.
401 const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
402 if (ThisAI.isDirect()) {
403 const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
404 int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
405 llvm::Type *ThisType = Args[ThisArgNo]->getType();
406 if (ThisType != AdjustedThisPtr->getType())
407 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
408 Args[ThisArgNo] = AdjustedThisPtr;
410 assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
411 Address ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);
412 llvm::Type *ThisType = ThisAddr.getElementType();
413 if (ThisType != AdjustedThisPtr->getType())
414 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
415 Builder.CreateStore(AdjustedThisPtr, ThisAddr);
418 // Emit the musttail call manually. Even if the prologue pushed cleanups, we
419 // don't actually want to run them.
420 llvm::CallInst *Call = Builder.CreateCall(Callee, Args);
421 Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
423 // Apply the standard set of call attributes.
424 unsigned CallingConv;
425 llvm::AttributeList Attrs;
426 CGM.ConstructAttributeList(Callee.getCallee()->getName(), *CurFnInfo, GD,
427 Attrs, CallingConv, /*AttrOnCallSite=*/true);
428 Call->setAttributes(Attrs);
429 Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
431 if (Call->getType()->isVoidTy())
432 Builder.CreateRetVoid();
434 Builder.CreateRet(Call);
436 // Finish the function to maintain CodeGenFunction invariants.
437 // FIXME: Don't emit unreachable code.
438 EmitBlock(createBasicBlock());
442 void CodeGenFunction::generateThunk(llvm::Function *Fn,
443 const CGFunctionInfo &FnInfo, GlobalDecl GD,
444 const ThunkInfo &Thunk,
445 bool IsUnprototyped) {
446 StartThunk(Fn, GD, FnInfo, IsUnprototyped);
447 // Create a scope with an artificial location for the body of this function.
448 auto AL = ApplyDebugLocation::CreateArtificial(*this);
450 // Get our callee. Use a placeholder type if this method is unprototyped so
451 // that CodeGenModule doesn't try to set attributes.
454 Ty = llvm::StructType::get(getLLVMContext());
456 Ty = CGM.getTypes().GetFunctionType(FnInfo);
458 llvm::Constant *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
460 // Fix up the function type for an unprototyped musttail call.
462 Callee = llvm::ConstantExpr::getBitCast(Callee, Fn->getType());
464 // Make the call and return the result.
465 EmitCallAndReturnForThunk(llvm::FunctionCallee(Fn->getFunctionType(), Callee),
466 &Thunk, IsUnprototyped);
469 static bool shouldEmitVTableThunk(CodeGenModule &CGM, const CXXMethodDecl *MD,
470 bool IsUnprototyped, bool ForVTable) {
471 // Always emit thunks in the MS C++ ABI. We cannot rely on other TUs to
472 // provide thunks for us.
473 if (CGM.getTarget().getCXXABI().isMicrosoft())
476 // In the Itanium C++ ABI, vtable thunks are provided by TUs that provide
477 // definitions of the main method. Therefore, emitting thunks with the vtable
478 // is purely an optimization. Emit the thunk if optimizations are enabled and
479 // all of the parameter types are complete.
481 return CGM.getCodeGenOpts().OptimizationLevel && !IsUnprototyped;
483 // Always emit thunks along with the method definition.
487 llvm::Constant *CodeGenVTables::maybeEmitThunk(GlobalDecl GD,
490 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
492 // First, get a declaration. Compute the mangled name. Don't worry about
493 // getting the function prototype right, since we may only need this
494 // declaration to fill in a vtable slot.
495 SmallString<256> Name;
496 MangleContext &MCtx = CGM.getCXXABI().getMangleContext();
497 llvm::raw_svector_ostream Out(Name);
498 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))
499 MCtx.mangleCXXDtorThunk(DD, GD.getDtorType(), TI.This, Out);
501 MCtx.mangleThunk(MD, TI, Out);
502 llvm::Type *ThunkVTableTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
503 llvm::Constant *Thunk = CGM.GetAddrOfThunk(Name, ThunkVTableTy, GD);
505 // If we don't need to emit a definition, return this declaration as is.
506 bool IsUnprototyped = !CGM.getTypes().isFuncTypeConvertible(
507 MD->getType()->castAs<FunctionType>());
508 if (!shouldEmitVTableThunk(CGM, MD, IsUnprototyped, ForVTable))
511 // Arrange a function prototype appropriate for a function definition. In some
512 // cases in the MS ABI, we may need to build an unprototyped musttail thunk.
513 const CGFunctionInfo &FnInfo =
514 IsUnprototyped ? CGM.getTypes().arrangeUnprototypedMustTailThunk(MD)
515 : CGM.getTypes().arrangeGlobalDeclaration(GD);
516 llvm::FunctionType *ThunkFnTy = CGM.getTypes().GetFunctionType(FnInfo);
518 // If the type of the underlying GlobalValue is wrong, we'll have to replace
519 // it. It should be a declaration.
520 llvm::Function *ThunkFn = cast<llvm::Function>(Thunk->stripPointerCasts());
521 if (ThunkFn->getFunctionType() != ThunkFnTy) {
522 llvm::GlobalValue *OldThunkFn = ThunkFn;
524 assert(OldThunkFn->isDeclaration() && "Shouldn't replace non-declaration");
526 // Remove the name from the old thunk function and get a new thunk.
527 OldThunkFn->setName(StringRef());
528 ThunkFn = llvm::Function::Create(ThunkFnTy, llvm::Function::ExternalLinkage,
529 Name.str(), &CGM.getModule());
530 CGM.SetLLVMFunctionAttributes(MD, FnInfo, ThunkFn);
532 // If needed, replace the old thunk with a bitcast.
533 if (!OldThunkFn->use_empty()) {
534 llvm::Constant *NewPtrForOldDecl =
535 llvm::ConstantExpr::getBitCast(ThunkFn, OldThunkFn->getType());
536 OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
539 // Remove the old thunk.
540 OldThunkFn->eraseFromParent();
543 bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
544 bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
546 if (!ThunkFn->isDeclaration()) {
547 if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
548 // There is already a thunk emitted for this function, do nothing.
552 setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
556 // If this will be unprototyped, add the "thunk" attribute so that LLVM knows
557 // that the return type is meaningless. These thunks can be used to call
558 // functions with differing return types, and the caller is required to cast
559 // the prototype appropriately to extract the correct value.
561 ThunkFn->addFnAttr("thunk");
563 CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
565 // Thunks for variadic methods are special because in general variadic
566 // arguments cannot be perferctly forwarded. In the general case, clang
567 // implements such thunks by cloning the original function body. However, for
568 // thunks with no return adjustment on targets that support musttail, we can
569 // use musttail to perfectly forward the variadic arguments.
570 bool ShouldCloneVarArgs = false;
571 if (!IsUnprototyped && ThunkFn->isVarArg()) {
572 ShouldCloneVarArgs = true;
573 if (TI.Return.isEmpty()) {
574 switch (CGM.getTriple().getArch()) {
575 case llvm::Triple::x86_64:
576 case llvm::Triple::x86:
577 case llvm::Triple::aarch64:
578 ShouldCloneVarArgs = false;
586 if (ShouldCloneVarArgs) {
587 if (UseAvailableExternallyLinkage)
590 CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, TI);
592 // Normal thunk body generation.
593 CodeGenFunction(CGM).generateThunk(ThunkFn, FnInfo, GD, TI, IsUnprototyped);
596 setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
600 void CodeGenVTables::EmitThunks(GlobalDecl GD) {
601 const CXXMethodDecl *MD =
602 cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
604 // We don't need to generate thunks for the base destructor.
605 if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
608 const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
609 VTContext->getThunkInfo(GD);
611 if (!ThunkInfoVector)
614 for (const ThunkInfo& Thunk : *ThunkInfoVector)
615 maybeEmitThunk(GD, Thunk, /*ForVTable=*/false);
618 void CodeGenVTables::addVTableComponent(
619 ConstantArrayBuilder &builder, const VTableLayout &layout,
620 unsigned idx, llvm::Constant *rtti, unsigned &nextVTableThunkIndex) {
621 auto &component = layout.vtable_components()[idx];
623 auto addOffsetConstant = [&](CharUnits offset) {
624 builder.add(llvm::ConstantExpr::getIntToPtr(
625 llvm::ConstantInt::get(CGM.PtrDiffTy, offset.getQuantity()),
629 switch (component.getKind()) {
630 case VTableComponent::CK_VCallOffset:
631 return addOffsetConstant(component.getVCallOffset());
633 case VTableComponent::CK_VBaseOffset:
634 return addOffsetConstant(component.getVBaseOffset());
636 case VTableComponent::CK_OffsetToTop:
637 return addOffsetConstant(component.getOffsetToTop());
639 case VTableComponent::CK_RTTI:
640 return builder.add(llvm::ConstantExpr::getBitCast(rtti, CGM.Int8PtrTy));
642 case VTableComponent::CK_FunctionPointer:
643 case VTableComponent::CK_CompleteDtorPointer:
644 case VTableComponent::CK_DeletingDtorPointer: {
647 // Get the right global decl.
648 switch (component.getKind()) {
650 llvm_unreachable("Unexpected vtable component kind");
651 case VTableComponent::CK_FunctionPointer:
652 GD = component.getFunctionDecl();
654 case VTableComponent::CK_CompleteDtorPointer:
655 GD = GlobalDecl(component.getDestructorDecl(), Dtor_Complete);
657 case VTableComponent::CK_DeletingDtorPointer:
658 GD = GlobalDecl(component.getDestructorDecl(), Dtor_Deleting);
662 if (CGM.getLangOpts().CUDA) {
663 // Emit NULL for methods we can't codegen on this
664 // side. Otherwise we'd end up with vtable with unresolved
666 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
667 // OK on device side: functions w/ __device__ attribute
668 // OK on host side: anything except __device__-only functions.
670 CGM.getLangOpts().CUDAIsDevice
671 ? MD->hasAttr<CUDADeviceAttr>()
672 : (MD->hasAttr<CUDAHostAttr>() || !MD->hasAttr<CUDADeviceAttr>());
674 return builder.addNullPointer(CGM.Int8PtrTy);
675 // Method is acceptable, continue processing as usual.
678 auto getSpecialVirtualFn = [&](StringRef name) {
679 llvm::FunctionType *fnTy =
680 llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
681 llvm::Constant *fn = cast<llvm::Constant>(
682 CGM.CreateRuntimeFunction(fnTy, name).getCallee());
683 if (auto f = dyn_cast<llvm::Function>(fn))
684 f->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
685 return llvm::ConstantExpr::getBitCast(fn, CGM.Int8PtrTy);
688 llvm::Constant *fnPtr;
690 // Pure virtual member functions.
691 if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
694 getSpecialVirtualFn(CGM.getCXXABI().GetPureVirtualCallName());
695 fnPtr = PureVirtualFn;
697 // Deleted virtual member functions.
698 } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
699 if (!DeletedVirtualFn)
701 getSpecialVirtualFn(CGM.getCXXABI().GetDeletedVirtualCallName());
702 fnPtr = DeletedVirtualFn;
705 } else if (nextVTableThunkIndex < layout.vtable_thunks().size() &&
706 layout.vtable_thunks()[nextVTableThunkIndex].first == idx) {
707 auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;
709 nextVTableThunkIndex++;
710 fnPtr = maybeEmitThunk(GD, thunkInfo, /*ForVTable=*/true);
712 // Otherwise we can use the method definition directly.
714 llvm::Type *fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
715 fnPtr = CGM.GetAddrOfFunction(GD, fnTy, /*ForVTable=*/true);
718 fnPtr = llvm::ConstantExpr::getBitCast(fnPtr, CGM.Int8PtrTy);
723 case VTableComponent::CK_UnusedFunctionPointer:
724 return builder.addNullPointer(CGM.Int8PtrTy);
727 llvm_unreachable("Unexpected vtable component kind");
730 llvm::Type *CodeGenVTables::getVTableType(const VTableLayout &layout) {
731 SmallVector<llvm::Type *, 4> tys;
732 for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i) {
733 tys.push_back(llvm::ArrayType::get(CGM.Int8PtrTy, layout.getVTableSize(i)));
736 return llvm::StructType::get(CGM.getLLVMContext(), tys);
739 void CodeGenVTables::createVTableInitializer(ConstantStructBuilder &builder,
740 const VTableLayout &layout,
741 llvm::Constant *rtti) {
742 unsigned nextVTableThunkIndex = 0;
743 for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i) {
744 auto vtableElem = builder.beginArray(CGM.Int8PtrTy);
745 size_t thisIndex = layout.getVTableOffset(i);
746 size_t nextIndex = thisIndex + layout.getVTableSize(i);
747 for (unsigned i = thisIndex; i != nextIndex; ++i) {
748 addVTableComponent(vtableElem, layout, i, rtti, nextVTableThunkIndex);
750 vtableElem.finishAndAddTo(builder);
754 llvm::GlobalVariable *
755 CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
756 const BaseSubobject &Base,
758 llvm::GlobalVariable::LinkageTypes Linkage,
759 VTableAddressPointsMapTy& AddressPoints) {
760 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
761 DI->completeClassData(Base.getBase());
763 std::unique_ptr<VTableLayout> VTLayout(
764 getItaniumVTableContext().createConstructionVTableLayout(
765 Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
767 // Add the address points.
768 AddressPoints = VTLayout->getAddressPoints();
770 // Get the mangled construction vtable name.
771 SmallString<256> OutName;
772 llvm::raw_svector_ostream Out(OutName);
773 cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
774 .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
775 Base.getBase(), Out);
776 StringRef Name = OutName.str();
778 llvm::Type *VTType = getVTableType(*VTLayout);
780 // Construction vtable symbols are not part of the Itanium ABI, so we cannot
781 // guarantee that they actually will be available externally. Instead, when
782 // emitting an available_externally VTT, we provide references to an internal
783 // linkage construction vtable. The ABI only requires complete-object vtables
784 // to be the same for all instances of a type, not construction vtables.
785 if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
786 Linkage = llvm::GlobalVariable::InternalLinkage;
788 unsigned Align = CGM.getDataLayout().getABITypeAlignment(VTType);
790 // Create the variable that will hold the construction vtable.
791 llvm::GlobalVariable *VTable =
792 CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage, Align);
794 // V-tables are always unnamed_addr.
795 VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
797 llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
798 CGM.getContext().getTagDeclType(Base.getBase()));
800 // Create and set the initializer.
801 ConstantInitBuilder builder(CGM);
802 auto components = builder.beginStruct();
803 createVTableInitializer(components, *VTLayout, RTTI);
804 components.finishAndSetAsInitializer(VTable);
806 // Set properties only after the initializer has been set to ensure that the
807 // GV is treated as definition and not declaration.
808 assert(!VTable->isDeclaration() && "Shouldn't set properties on declaration");
809 CGM.setGVProperties(VTable, RD);
811 CGM.EmitVTableTypeMetadata(RD, VTable, *VTLayout.get());
816 static bool shouldEmitAvailableExternallyVTable(const CodeGenModule &CGM,
817 const CXXRecordDecl *RD) {
818 return CGM.getCodeGenOpts().OptimizationLevel > 0 &&
819 CGM.getCXXABI().canSpeculativelyEmitVTable(RD);
822 /// Compute the required linkage of the vtable for the given class.
824 /// Note that we only call this at the end of the translation unit.
825 llvm::GlobalVariable::LinkageTypes
826 CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
827 if (!RD->isExternallyVisible())
828 return llvm::GlobalVariable::InternalLinkage;
830 // We're at the end of the translation unit, so the current key
831 // function is fully correct.
832 const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
833 if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
834 // If this class has a key function, use that to determine the
835 // linkage of the vtable.
836 const FunctionDecl *def = nullptr;
837 if (keyFunction->hasBody(def))
838 keyFunction = cast<CXXMethodDecl>(def);
840 switch (keyFunction->getTemplateSpecializationKind()) {
842 case TSK_ExplicitSpecialization:
843 assert((def || CodeGenOpts.OptimizationLevel > 0 ||
844 CodeGenOpts.getDebugInfo() != codegenoptions::NoDebugInfo) &&
845 "Shouldn't query vtable linkage without key function, "
846 "optimizations, or debug info");
847 if (!def && CodeGenOpts.OptimizationLevel > 0)
848 return llvm::GlobalVariable::AvailableExternallyLinkage;
850 if (keyFunction->isInlined())
851 return !Context.getLangOpts().AppleKext ?
852 llvm::GlobalVariable::LinkOnceODRLinkage :
853 llvm::Function::InternalLinkage;
855 return llvm::GlobalVariable::ExternalLinkage;
857 case TSK_ImplicitInstantiation:
858 return !Context.getLangOpts().AppleKext ?
859 llvm::GlobalVariable::LinkOnceODRLinkage :
860 llvm::Function::InternalLinkage;
862 case TSK_ExplicitInstantiationDefinition:
863 return !Context.getLangOpts().AppleKext ?
864 llvm::GlobalVariable::WeakODRLinkage :
865 llvm::Function::InternalLinkage;
867 case TSK_ExplicitInstantiationDeclaration:
868 llvm_unreachable("Should not have been asked to emit this");
872 // -fapple-kext mode does not support weak linkage, so we must use
874 if (Context.getLangOpts().AppleKext)
875 return llvm::Function::InternalLinkage;
877 llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
878 llvm::GlobalValue::LinkOnceODRLinkage;
879 llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
880 llvm::GlobalValue::WeakODRLinkage;
881 if (RD->hasAttr<DLLExportAttr>()) {
882 // Cannot discard exported vtables.
883 DiscardableODRLinkage = NonDiscardableODRLinkage;
884 } else if (RD->hasAttr<DLLImportAttr>()) {
885 // Imported vtables are available externally.
886 DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
887 NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
890 switch (RD->getTemplateSpecializationKind()) {
892 case TSK_ExplicitSpecialization:
893 case TSK_ImplicitInstantiation:
894 return DiscardableODRLinkage;
896 case TSK_ExplicitInstantiationDeclaration:
897 // Explicit instantiations in MSVC do not provide vtables, so we must emit
899 if (getTarget().getCXXABI().isMicrosoft())
900 return DiscardableODRLinkage;
901 return shouldEmitAvailableExternallyVTable(*this, RD)
902 ? llvm::GlobalVariable::AvailableExternallyLinkage
903 : llvm::GlobalVariable::ExternalLinkage;
905 case TSK_ExplicitInstantiationDefinition:
906 return NonDiscardableODRLinkage;
909 llvm_unreachable("Invalid TemplateSpecializationKind!");
912 /// This is a callback from Sema to tell us that a particular vtable is
913 /// required to be emitted in this translation unit.
915 /// This is only called for vtables that _must_ be emitted (mainly due to key
916 /// functions). For weak vtables, CodeGen tracks when they are needed and
917 /// emits them as-needed.
918 void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
919 VTables.GenerateClassData(theClass);
923 CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
924 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
925 DI->completeClassData(RD);
927 if (RD->getNumVBases())
928 CGM.getCXXABI().emitVirtualInheritanceTables(RD);
930 CGM.getCXXABI().emitVTableDefinitions(*this, RD);
933 /// At this point in the translation unit, does it appear that can we
934 /// rely on the vtable being defined elsewhere in the program?
936 /// The response is really only definitive when called at the end of
937 /// the translation unit.
939 /// The only semantic restriction here is that the object file should
940 /// not contain a vtable definition when that vtable is defined
941 /// strongly elsewhere. Otherwise, we'd just like to avoid emitting
942 /// vtables when unnecessary.
943 bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
944 assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
946 // We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't
947 // emit them even if there is an explicit template instantiation.
948 if (CGM.getTarget().getCXXABI().isMicrosoft())
951 // If we have an explicit instantiation declaration (and not a
952 // definition), the vtable is defined elsewhere.
953 TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
954 if (TSK == TSK_ExplicitInstantiationDeclaration)
957 // Otherwise, if the class is an instantiated template, the
958 // vtable must be defined here.
959 if (TSK == TSK_ImplicitInstantiation ||
960 TSK == TSK_ExplicitInstantiationDefinition)
963 // Otherwise, if the class doesn't have a key function (possibly
964 // anymore), the vtable must be defined here.
965 const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
969 // Otherwise, if we don't have a definition of the key function, the
970 // vtable must be defined somewhere else.
971 return !keyFunction->hasBody();
974 /// Given that we're currently at the end of the translation unit, and
975 /// we've emitted a reference to the vtable for this class, should
976 /// we define that vtable?
977 static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
978 const CXXRecordDecl *RD) {
979 // If vtable is internal then it has to be done.
980 if (!CGM.getVTables().isVTableExternal(RD))
983 // If it's external then maybe we will need it as available_externally.
984 return shouldEmitAvailableExternallyVTable(CGM, RD);
987 /// Given that at some point we emitted a reference to one or more
988 /// vtables, and that we are now at the end of the translation unit,
989 /// decide whether we should emit them.
990 void CodeGenModule::EmitDeferredVTables() {
992 // Remember the size of DeferredVTables, because we're going to assume
993 // that this entire operation doesn't modify it.
994 size_t savedSize = DeferredVTables.size();
997 for (const CXXRecordDecl *RD : DeferredVTables)
998 if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
999 VTables.GenerateClassData(RD);
1000 else if (shouldOpportunisticallyEmitVTables())
1001 OpportunisticVTables.push_back(RD);
1003 assert(savedSize == DeferredVTables.size() &&
1004 "deferred extra vtables during vtable emission?");
1005 DeferredVTables.clear();
1008 bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
1009 LinkageInfo LV = RD->getLinkageAndVisibility();
1010 if (!isExternallyVisible(LV.getLinkage()))
1013 if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>())
1016 if (getTriple().isOSBinFormatCOFF()) {
1017 if (RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())
1020 if (LV.getVisibility() != HiddenVisibility)
1024 if (getCodeGenOpts().LTOVisibilityPublicStd) {
1025 const DeclContext *DC = RD;
1027 auto *D = cast<Decl>(DC);
1028 DC = DC->getParent();
1029 if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {
1030 if (auto *ND = dyn_cast<NamespaceDecl>(D))
1031 if (const IdentifierInfo *II = ND->getIdentifier())
1032 if (II->isStr("std") || II->isStr("stdext"))
1042 llvm::GlobalObject::VCallVisibility
1043 CodeGenModule::GetVCallVisibilityLevel(const CXXRecordDecl *RD) {
1044 LinkageInfo LV = RD->getLinkageAndVisibility();
1045 llvm::GlobalObject::VCallVisibility TypeVis;
1046 if (!isExternallyVisible(LV.getLinkage()))
1047 TypeVis = llvm::GlobalObject::VCallVisibilityTranslationUnit;
1048 else if (HasHiddenLTOVisibility(RD))
1049 TypeVis = llvm::GlobalObject::VCallVisibilityLinkageUnit;
1051 TypeVis = llvm::GlobalObject::VCallVisibilityPublic;
1053 for (auto B : RD->bases())
1054 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1055 TypeVis = std::min(TypeVis,
1056 GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl()));
1058 for (auto B : RD->vbases())
1059 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1060 TypeVis = std::min(TypeVis,
1061 GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl()));
1066 void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
1067 llvm::GlobalVariable *VTable,
1068 const VTableLayout &VTLayout) {
1069 if (!getCodeGenOpts().LTOUnit)
1072 CharUnits PointerWidth =
1073 Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
1075 typedef std::pair<const CXXRecordDecl *, unsigned> AddressPoint;
1076 std::vector<AddressPoint> AddressPoints;
1077 for (auto &&AP : VTLayout.getAddressPoints())
1078 AddressPoints.push_back(std::make_pair(
1079 AP.first.getBase(), VTLayout.getVTableOffset(AP.second.VTableIndex) +
1080 AP.second.AddressPointIndex));
1082 // Sort the address points for determinism.
1083 llvm::sort(AddressPoints, [this](const AddressPoint &AP1,
1084 const AddressPoint &AP2) {
1089 llvm::raw_string_ostream O1(S1);
1090 getCXXABI().getMangleContext().mangleTypeName(
1091 QualType(AP1.first->getTypeForDecl(), 0), O1);
1095 llvm::raw_string_ostream O2(S2);
1096 getCXXABI().getMangleContext().mangleTypeName(
1097 QualType(AP2.first->getTypeForDecl(), 0), O2);
1105 return AP1.second < AP2.second;
1108 ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();
1109 for (auto AP : AddressPoints) {
1110 // Create type metadata for the address point.
1111 AddVTableTypeMetadata(VTable, PointerWidth * AP.second, AP.first);
1113 // The class associated with each address point could also potentially be
1114 // used for indirect calls via a member function pointer, so we need to
1115 // annotate the address of each function pointer with the appropriate member
1116 // function pointer type.
1117 for (unsigned I = 0; I != Comps.size(); ++I) {
1118 if (Comps[I].getKind() != VTableComponent::CK_FunctionPointer)
1120 llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(
1121 Context.getMemberPointerType(
1122 Comps[I].getFunctionDecl()->getType(),
1123 Context.getRecordType(AP.first).getTypePtr()));
1124 VTable->addTypeMetadata((PointerWidth * I).getQuantity(), MD);
1128 if (getCodeGenOpts().VirtualFunctionElimination) {
1129 llvm::GlobalObject::VCallVisibility TypeVis = GetVCallVisibilityLevel(RD);
1130 if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)
1131 VTable->addVCallVisibilityMetadata(TypeVis);