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 Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified());
369 // Now emit our call.
370 llvm::CallBase *CallOrInvoke;
371 RValue RV = EmitCall(*CurFnInfo, CGCallee::forDirect(Callee, CurGD), Slot,
372 CallArgs, &CallOrInvoke);
374 // Consider return adjustment if we have ThunkInfo.
375 if (Thunk && !Thunk->Return.isEmpty())
376 RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
377 else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(CallOrInvoke))
378 Call->setTailCallKind(llvm::CallInst::TCK_Tail);
381 if (!ResultType->isVoidType() && Slot.isNull())
382 CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
384 // Disable the final ARC autorelease.
385 AutoreleaseResult = false;
390 void CodeGenFunction::EmitMustTailThunk(GlobalDecl GD,
391 llvm::Value *AdjustedThisPtr,
392 llvm::FunctionCallee Callee) {
393 // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
394 // to translate AST arguments into LLVM IR arguments. For thunks, we know
395 // that the caller prototype more or less matches the callee prototype with
396 // the exception of 'this'.
397 SmallVector<llvm::Value *, 8> Args;
398 for (llvm::Argument &A : CurFn->args())
401 // Set the adjusted 'this' pointer.
402 const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
403 if (ThisAI.isDirect()) {
404 const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
405 int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
406 llvm::Type *ThisType = Args[ThisArgNo]->getType();
407 if (ThisType != AdjustedThisPtr->getType())
408 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
409 Args[ThisArgNo] = AdjustedThisPtr;
411 assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
412 Address ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);
413 llvm::Type *ThisType = ThisAddr.getElementType();
414 if (ThisType != AdjustedThisPtr->getType())
415 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
416 Builder.CreateStore(AdjustedThisPtr, ThisAddr);
419 // Emit the musttail call manually. Even if the prologue pushed cleanups, we
420 // don't actually want to run them.
421 llvm::CallInst *Call = Builder.CreateCall(Callee, Args);
422 Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
424 // Apply the standard set of call attributes.
425 unsigned CallingConv;
426 llvm::AttributeList Attrs;
427 CGM.ConstructAttributeList(Callee.getCallee()->getName(), *CurFnInfo, GD,
428 Attrs, CallingConv, /*AttrOnCallSite=*/true);
429 Call->setAttributes(Attrs);
430 Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
432 if (Call->getType()->isVoidTy())
433 Builder.CreateRetVoid();
435 Builder.CreateRet(Call);
437 // Finish the function to maintain CodeGenFunction invariants.
438 // FIXME: Don't emit unreachable code.
439 EmitBlock(createBasicBlock());
444 void CodeGenFunction::generateThunk(llvm::Function *Fn,
445 const CGFunctionInfo &FnInfo, GlobalDecl GD,
446 const ThunkInfo &Thunk,
447 bool IsUnprototyped) {
448 StartThunk(Fn, GD, FnInfo, IsUnprototyped);
449 // Create a scope with an artificial location for the body of this function.
450 auto AL = ApplyDebugLocation::CreateArtificial(*this);
452 // Get our callee. Use a placeholder type if this method is unprototyped so
453 // that CodeGenModule doesn't try to set attributes.
456 Ty = llvm::StructType::get(getLLVMContext());
458 Ty = CGM.getTypes().GetFunctionType(FnInfo);
460 llvm::Constant *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
462 // Fix up the function type for an unprototyped musttail call.
464 Callee = llvm::ConstantExpr::getBitCast(Callee, Fn->getType());
466 // Make the call and return the result.
467 EmitCallAndReturnForThunk(llvm::FunctionCallee(Fn->getFunctionType(), Callee),
468 &Thunk, IsUnprototyped);
471 static bool shouldEmitVTableThunk(CodeGenModule &CGM, const CXXMethodDecl *MD,
472 bool IsUnprototyped, bool ForVTable) {
473 // Always emit thunks in the MS C++ ABI. We cannot rely on other TUs to
474 // provide thunks for us.
475 if (CGM.getTarget().getCXXABI().isMicrosoft())
478 // In the Itanium C++ ABI, vtable thunks are provided by TUs that provide
479 // definitions of the main method. Therefore, emitting thunks with the vtable
480 // is purely an optimization. Emit the thunk if optimizations are enabled and
481 // all of the parameter types are complete.
483 return CGM.getCodeGenOpts().OptimizationLevel && !IsUnprototyped;
485 // Always emit thunks along with the method definition.
489 llvm::Constant *CodeGenVTables::maybeEmitThunk(GlobalDecl GD,
492 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
494 // First, get a declaration. Compute the mangled name. Don't worry about
495 // getting the function prototype right, since we may only need this
496 // declaration to fill in a vtable slot.
497 SmallString<256> Name;
498 MangleContext &MCtx = CGM.getCXXABI().getMangleContext();
499 llvm::raw_svector_ostream Out(Name);
500 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))
501 MCtx.mangleCXXDtorThunk(DD, GD.getDtorType(), TI.This, Out);
503 MCtx.mangleThunk(MD, TI, Out);
504 llvm::Type *ThunkVTableTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
505 llvm::Constant *Thunk = CGM.GetAddrOfThunk(Name, ThunkVTableTy, GD);
507 // If we don't need to emit a definition, return this declaration as is.
508 bool IsUnprototyped = !CGM.getTypes().isFuncTypeConvertible(
509 MD->getType()->castAs<FunctionType>());
510 if (!shouldEmitVTableThunk(CGM, MD, IsUnprototyped, ForVTable))
513 // Arrange a function prototype appropriate for a function definition. In some
514 // cases in the MS ABI, we may need to build an unprototyped musttail thunk.
515 const CGFunctionInfo &FnInfo =
516 IsUnprototyped ? CGM.getTypes().arrangeUnprototypedMustTailThunk(MD)
517 : CGM.getTypes().arrangeGlobalDeclaration(GD);
518 llvm::FunctionType *ThunkFnTy = CGM.getTypes().GetFunctionType(FnInfo);
520 // If the type of the underlying GlobalValue is wrong, we'll have to replace
521 // it. It should be a declaration.
522 llvm::Function *ThunkFn = cast<llvm::Function>(Thunk->stripPointerCasts());
523 if (ThunkFn->getFunctionType() != ThunkFnTy) {
524 llvm::GlobalValue *OldThunkFn = ThunkFn;
526 assert(OldThunkFn->isDeclaration() && "Shouldn't replace non-declaration");
528 // Remove the name from the old thunk function and get a new thunk.
529 OldThunkFn->setName(StringRef());
530 ThunkFn = llvm::Function::Create(ThunkFnTy, llvm::Function::ExternalLinkage,
531 Name.str(), &CGM.getModule());
532 CGM.SetLLVMFunctionAttributes(MD, FnInfo, ThunkFn);
534 // If needed, replace the old thunk with a bitcast.
535 if (!OldThunkFn->use_empty()) {
536 llvm::Constant *NewPtrForOldDecl =
537 llvm::ConstantExpr::getBitCast(ThunkFn, OldThunkFn->getType());
538 OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
541 // Remove the old thunk.
542 OldThunkFn->eraseFromParent();
545 bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
546 bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
548 if (!ThunkFn->isDeclaration()) {
549 if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
550 // There is already a thunk emitted for this function, do nothing.
554 setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
558 // If this will be unprototyped, add the "thunk" attribute so that LLVM knows
559 // that the return type is meaningless. These thunks can be used to call
560 // functions with differing return types, and the caller is required to cast
561 // the prototype appropriately to extract the correct value.
563 ThunkFn->addFnAttr("thunk");
565 CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
567 // Thunks for variadic methods are special because in general variadic
568 // arguments cannot be perfectly forwarded. In the general case, clang
569 // implements such thunks by cloning the original function body. However, for
570 // thunks with no return adjustment on targets that support musttail, we can
571 // use musttail to perfectly forward the variadic arguments.
572 bool ShouldCloneVarArgs = false;
573 if (!IsUnprototyped && ThunkFn->isVarArg()) {
574 ShouldCloneVarArgs = true;
575 if (TI.Return.isEmpty()) {
576 switch (CGM.getTriple().getArch()) {
577 case llvm::Triple::x86_64:
578 case llvm::Triple::x86:
579 case llvm::Triple::aarch64:
580 ShouldCloneVarArgs = false;
588 if (ShouldCloneVarArgs) {
589 if (UseAvailableExternallyLinkage)
592 CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, TI);
594 // Normal thunk body generation.
595 CodeGenFunction(CGM).generateThunk(ThunkFn, FnInfo, GD, TI, IsUnprototyped);
598 setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
602 void CodeGenVTables::EmitThunks(GlobalDecl GD) {
603 const CXXMethodDecl *MD =
604 cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
606 // We don't need to generate thunks for the base destructor.
607 if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
610 const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
611 VTContext->getThunkInfo(GD);
613 if (!ThunkInfoVector)
616 for (const ThunkInfo& Thunk : *ThunkInfoVector)
617 maybeEmitThunk(GD, Thunk, /*ForVTable=*/false);
620 void CodeGenVTables::addVTableComponent(
621 ConstantArrayBuilder &builder, const VTableLayout &layout,
622 unsigned idx, llvm::Constant *rtti, unsigned &nextVTableThunkIndex) {
623 auto &component = layout.vtable_components()[idx];
625 auto addOffsetConstant = [&](CharUnits offset) {
626 builder.add(llvm::ConstantExpr::getIntToPtr(
627 llvm::ConstantInt::get(CGM.PtrDiffTy, offset.getQuantity()),
631 switch (component.getKind()) {
632 case VTableComponent::CK_VCallOffset:
633 return addOffsetConstant(component.getVCallOffset());
635 case VTableComponent::CK_VBaseOffset:
636 return addOffsetConstant(component.getVBaseOffset());
638 case VTableComponent::CK_OffsetToTop:
639 return addOffsetConstant(component.getOffsetToTop());
641 case VTableComponent::CK_RTTI:
642 return builder.add(llvm::ConstantExpr::getBitCast(rtti, CGM.Int8PtrTy));
644 case VTableComponent::CK_FunctionPointer:
645 case VTableComponent::CK_CompleteDtorPointer:
646 case VTableComponent::CK_DeletingDtorPointer: {
649 // Get the right global decl.
650 switch (component.getKind()) {
652 llvm_unreachable("Unexpected vtable component kind");
653 case VTableComponent::CK_FunctionPointer:
654 GD = component.getFunctionDecl();
656 case VTableComponent::CK_CompleteDtorPointer:
657 GD = GlobalDecl(component.getDestructorDecl(), Dtor_Complete);
659 case VTableComponent::CK_DeletingDtorPointer:
660 GD = GlobalDecl(component.getDestructorDecl(), Dtor_Deleting);
664 if (CGM.getLangOpts().CUDA) {
665 // Emit NULL for methods we can't codegen on this
666 // side. Otherwise we'd end up with vtable with unresolved
668 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
669 // OK on device side: functions w/ __device__ attribute
670 // OK on host side: anything except __device__-only functions.
672 CGM.getLangOpts().CUDAIsDevice
673 ? MD->hasAttr<CUDADeviceAttr>()
674 : (MD->hasAttr<CUDAHostAttr>() || !MD->hasAttr<CUDADeviceAttr>());
676 return builder.addNullPointer(CGM.Int8PtrTy);
677 // Method is acceptable, continue processing as usual.
680 auto getSpecialVirtualFn = [&](StringRef name) -> llvm::Constant * {
681 // For NVPTX devices in OpenMP emit special functon as null pointers,
682 // otherwise linking ends up with unresolved references.
683 if (CGM.getLangOpts().OpenMP && CGM.getLangOpts().OpenMPIsDevice &&
684 CGM.getTriple().isNVPTX())
685 return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
686 llvm::FunctionType *fnTy =
687 llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
688 llvm::Constant *fn = cast<llvm::Constant>(
689 CGM.CreateRuntimeFunction(fnTy, name).getCallee());
690 if (auto f = dyn_cast<llvm::Function>(fn))
691 f->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
692 return llvm::ConstantExpr::getBitCast(fn, CGM.Int8PtrTy);
695 llvm::Constant *fnPtr;
697 // Pure virtual member functions.
698 if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
701 getSpecialVirtualFn(CGM.getCXXABI().GetPureVirtualCallName());
702 fnPtr = PureVirtualFn;
704 // Deleted virtual member functions.
705 } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
706 if (!DeletedVirtualFn)
708 getSpecialVirtualFn(CGM.getCXXABI().GetDeletedVirtualCallName());
709 fnPtr = DeletedVirtualFn;
712 } else if (nextVTableThunkIndex < layout.vtable_thunks().size() &&
713 layout.vtable_thunks()[nextVTableThunkIndex].first == idx) {
714 auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;
716 nextVTableThunkIndex++;
717 fnPtr = maybeEmitThunk(GD, thunkInfo, /*ForVTable=*/true);
719 // Otherwise we can use the method definition directly.
721 llvm::Type *fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
722 fnPtr = CGM.GetAddrOfFunction(GD, fnTy, /*ForVTable=*/true);
725 fnPtr = llvm::ConstantExpr::getBitCast(fnPtr, CGM.Int8PtrTy);
730 case VTableComponent::CK_UnusedFunctionPointer:
731 return builder.addNullPointer(CGM.Int8PtrTy);
734 llvm_unreachable("Unexpected vtable component kind");
737 llvm::Type *CodeGenVTables::getVTableType(const VTableLayout &layout) {
738 SmallVector<llvm::Type *, 4> tys;
739 for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i) {
740 tys.push_back(llvm::ArrayType::get(CGM.Int8PtrTy, layout.getVTableSize(i)));
743 return llvm::StructType::get(CGM.getLLVMContext(), tys);
746 void CodeGenVTables::createVTableInitializer(ConstantStructBuilder &builder,
747 const VTableLayout &layout,
748 llvm::Constant *rtti) {
749 unsigned nextVTableThunkIndex = 0;
750 for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i) {
751 auto vtableElem = builder.beginArray(CGM.Int8PtrTy);
752 size_t thisIndex = layout.getVTableOffset(i);
753 size_t nextIndex = thisIndex + layout.getVTableSize(i);
754 for (unsigned i = thisIndex; i != nextIndex; ++i) {
755 addVTableComponent(vtableElem, layout, i, rtti, nextVTableThunkIndex);
757 vtableElem.finishAndAddTo(builder);
761 llvm::GlobalVariable *
762 CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
763 const BaseSubobject &Base,
765 llvm::GlobalVariable::LinkageTypes Linkage,
766 VTableAddressPointsMapTy& AddressPoints) {
767 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
768 DI->completeClassData(Base.getBase());
770 std::unique_ptr<VTableLayout> VTLayout(
771 getItaniumVTableContext().createConstructionVTableLayout(
772 Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
774 // Add the address points.
775 AddressPoints = VTLayout->getAddressPoints();
777 // Get the mangled construction vtable name.
778 SmallString<256> OutName;
779 llvm::raw_svector_ostream Out(OutName);
780 cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
781 .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
782 Base.getBase(), Out);
783 StringRef Name = OutName.str();
785 llvm::Type *VTType = getVTableType(*VTLayout);
787 // Construction vtable symbols are not part of the Itanium ABI, so we cannot
788 // guarantee that they actually will be available externally. Instead, when
789 // emitting an available_externally VTT, we provide references to an internal
790 // linkage construction vtable. The ABI only requires complete-object vtables
791 // to be the same for all instances of a type, not construction vtables.
792 if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
793 Linkage = llvm::GlobalVariable::InternalLinkage;
795 unsigned Align = CGM.getDataLayout().getABITypeAlignment(VTType);
797 // Create the variable that will hold the construction vtable.
798 llvm::GlobalVariable *VTable =
799 CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage, Align);
801 // V-tables are always unnamed_addr.
802 VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
804 llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
805 CGM.getContext().getTagDeclType(Base.getBase()));
807 // Create and set the initializer.
808 ConstantInitBuilder builder(CGM);
809 auto components = builder.beginStruct();
810 createVTableInitializer(components, *VTLayout, RTTI);
811 components.finishAndSetAsInitializer(VTable);
813 // Set properties only after the initializer has been set to ensure that the
814 // GV is treated as definition and not declaration.
815 assert(!VTable->isDeclaration() && "Shouldn't set properties on declaration");
816 CGM.setGVProperties(VTable, RD);
818 CGM.EmitVTableTypeMetadata(RD, VTable, *VTLayout.get());
823 static bool shouldEmitAvailableExternallyVTable(const CodeGenModule &CGM,
824 const CXXRecordDecl *RD) {
825 return CGM.getCodeGenOpts().OptimizationLevel > 0 &&
826 CGM.getCXXABI().canSpeculativelyEmitVTable(RD);
829 /// Compute the required linkage of the vtable for the given class.
831 /// Note that we only call this at the end of the translation unit.
832 llvm::GlobalVariable::LinkageTypes
833 CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
834 if (!RD->isExternallyVisible())
835 return llvm::GlobalVariable::InternalLinkage;
837 // We're at the end of the translation unit, so the current key
838 // function is fully correct.
839 const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
840 if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
841 // If this class has a key function, use that to determine the
842 // linkage of the vtable.
843 const FunctionDecl *def = nullptr;
844 if (keyFunction->hasBody(def))
845 keyFunction = cast<CXXMethodDecl>(def);
847 switch (keyFunction->getTemplateSpecializationKind()) {
849 case TSK_ExplicitSpecialization:
850 assert((def || CodeGenOpts.OptimizationLevel > 0 ||
851 CodeGenOpts.getDebugInfo() != codegenoptions::NoDebugInfo) &&
852 "Shouldn't query vtable linkage without key function, "
853 "optimizations, or debug info");
854 if (!def && CodeGenOpts.OptimizationLevel > 0)
855 return llvm::GlobalVariable::AvailableExternallyLinkage;
857 if (keyFunction->isInlined())
858 return !Context.getLangOpts().AppleKext ?
859 llvm::GlobalVariable::LinkOnceODRLinkage :
860 llvm::Function::InternalLinkage;
862 return llvm::GlobalVariable::ExternalLinkage;
864 case TSK_ImplicitInstantiation:
865 return !Context.getLangOpts().AppleKext ?
866 llvm::GlobalVariable::LinkOnceODRLinkage :
867 llvm::Function::InternalLinkage;
869 case TSK_ExplicitInstantiationDefinition:
870 return !Context.getLangOpts().AppleKext ?
871 llvm::GlobalVariable::WeakODRLinkage :
872 llvm::Function::InternalLinkage;
874 case TSK_ExplicitInstantiationDeclaration:
875 llvm_unreachable("Should not have been asked to emit this");
879 // -fapple-kext mode does not support weak linkage, so we must use
881 if (Context.getLangOpts().AppleKext)
882 return llvm::Function::InternalLinkage;
884 llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
885 llvm::GlobalValue::LinkOnceODRLinkage;
886 llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
887 llvm::GlobalValue::WeakODRLinkage;
888 if (RD->hasAttr<DLLExportAttr>()) {
889 // Cannot discard exported vtables.
890 DiscardableODRLinkage = NonDiscardableODRLinkage;
891 } else if (RD->hasAttr<DLLImportAttr>()) {
892 // Imported vtables are available externally.
893 DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
894 NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
897 switch (RD->getTemplateSpecializationKind()) {
899 case TSK_ExplicitSpecialization:
900 case TSK_ImplicitInstantiation:
901 return DiscardableODRLinkage;
903 case TSK_ExplicitInstantiationDeclaration:
904 // Explicit instantiations in MSVC do not provide vtables, so we must emit
906 if (getTarget().getCXXABI().isMicrosoft())
907 return DiscardableODRLinkage;
908 return shouldEmitAvailableExternallyVTable(*this, RD)
909 ? llvm::GlobalVariable::AvailableExternallyLinkage
910 : llvm::GlobalVariable::ExternalLinkage;
912 case TSK_ExplicitInstantiationDefinition:
913 return NonDiscardableODRLinkage;
916 llvm_unreachable("Invalid TemplateSpecializationKind!");
919 /// This is a callback from Sema to tell us that a particular vtable is
920 /// required to be emitted in this translation unit.
922 /// This is only called for vtables that _must_ be emitted (mainly due to key
923 /// functions). For weak vtables, CodeGen tracks when they are needed and
924 /// emits them as-needed.
925 void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
926 VTables.GenerateClassData(theClass);
930 CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
931 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
932 DI->completeClassData(RD);
934 if (RD->getNumVBases())
935 CGM.getCXXABI().emitVirtualInheritanceTables(RD);
937 CGM.getCXXABI().emitVTableDefinitions(*this, RD);
940 /// At this point in the translation unit, does it appear that can we
941 /// rely on the vtable being defined elsewhere in the program?
943 /// The response is really only definitive when called at the end of
944 /// the translation unit.
946 /// The only semantic restriction here is that the object file should
947 /// not contain a vtable definition when that vtable is defined
948 /// strongly elsewhere. Otherwise, we'd just like to avoid emitting
949 /// vtables when unnecessary.
950 bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
951 assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
953 // We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't
954 // emit them even if there is an explicit template instantiation.
955 if (CGM.getTarget().getCXXABI().isMicrosoft())
958 // If we have an explicit instantiation declaration (and not a
959 // definition), the vtable is defined elsewhere.
960 TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
961 if (TSK == TSK_ExplicitInstantiationDeclaration)
964 // Otherwise, if the class is an instantiated template, the
965 // vtable must be defined here.
966 if (TSK == TSK_ImplicitInstantiation ||
967 TSK == TSK_ExplicitInstantiationDefinition)
970 // Otherwise, if the class doesn't have a key function (possibly
971 // anymore), the vtable must be defined here.
972 const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
976 // Otherwise, if we don't have a definition of the key function, the
977 // vtable must be defined somewhere else.
978 return !keyFunction->hasBody();
981 /// Given that we're currently at the end of the translation unit, and
982 /// we've emitted a reference to the vtable for this class, should
983 /// we define that vtable?
984 static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
985 const CXXRecordDecl *RD) {
986 // If vtable is internal then it has to be done.
987 if (!CGM.getVTables().isVTableExternal(RD))
990 // If it's external then maybe we will need it as available_externally.
991 return shouldEmitAvailableExternallyVTable(CGM, RD);
994 /// Given that at some point we emitted a reference to one or more
995 /// vtables, and that we are now at the end of the translation unit,
996 /// decide whether we should emit them.
997 void CodeGenModule::EmitDeferredVTables() {
999 // Remember the size of DeferredVTables, because we're going to assume
1000 // that this entire operation doesn't modify it.
1001 size_t savedSize = DeferredVTables.size();
1004 for (const CXXRecordDecl *RD : DeferredVTables)
1005 if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
1006 VTables.GenerateClassData(RD);
1007 else if (shouldOpportunisticallyEmitVTables())
1008 OpportunisticVTables.push_back(RD);
1010 assert(savedSize == DeferredVTables.size() &&
1011 "deferred extra vtables during vtable emission?");
1012 DeferredVTables.clear();
1015 bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
1016 LinkageInfo LV = RD->getLinkageAndVisibility();
1017 if (!isExternallyVisible(LV.getLinkage()))
1020 if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>())
1023 if (getTriple().isOSBinFormatCOFF()) {
1024 if (RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())
1027 if (LV.getVisibility() != HiddenVisibility)
1031 if (getCodeGenOpts().LTOVisibilityPublicStd) {
1032 const DeclContext *DC = RD;
1034 auto *D = cast<Decl>(DC);
1035 DC = DC->getParent();
1036 if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {
1037 if (auto *ND = dyn_cast<NamespaceDecl>(D))
1038 if (const IdentifierInfo *II = ND->getIdentifier())
1039 if (II->isStr("std") || II->isStr("stdext"))
1049 llvm::GlobalObject::VCallVisibility
1050 CodeGenModule::GetVCallVisibilityLevel(const CXXRecordDecl *RD) {
1051 LinkageInfo LV = RD->getLinkageAndVisibility();
1052 llvm::GlobalObject::VCallVisibility TypeVis;
1053 if (!isExternallyVisible(LV.getLinkage()))
1054 TypeVis = llvm::GlobalObject::VCallVisibilityTranslationUnit;
1055 else if (HasHiddenLTOVisibility(RD))
1056 TypeVis = llvm::GlobalObject::VCallVisibilityLinkageUnit;
1058 TypeVis = llvm::GlobalObject::VCallVisibilityPublic;
1060 for (auto B : RD->bases())
1061 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1062 TypeVis = std::min(TypeVis,
1063 GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl()));
1065 for (auto B : RD->vbases())
1066 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1067 TypeVis = std::min(TypeVis,
1068 GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl()));
1073 void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
1074 llvm::GlobalVariable *VTable,
1075 const VTableLayout &VTLayout) {
1076 if (!getCodeGenOpts().LTOUnit)
1079 CharUnits PointerWidth =
1080 Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
1082 typedef std::pair<const CXXRecordDecl *, unsigned> AddressPoint;
1083 std::vector<AddressPoint> AddressPoints;
1084 for (auto &&AP : VTLayout.getAddressPoints())
1085 AddressPoints.push_back(std::make_pair(
1086 AP.first.getBase(), VTLayout.getVTableOffset(AP.second.VTableIndex) +
1087 AP.second.AddressPointIndex));
1089 // Sort the address points for determinism.
1090 llvm::sort(AddressPoints, [this](const AddressPoint &AP1,
1091 const AddressPoint &AP2) {
1096 llvm::raw_string_ostream O1(S1);
1097 getCXXABI().getMangleContext().mangleTypeName(
1098 QualType(AP1.first->getTypeForDecl(), 0), O1);
1102 llvm::raw_string_ostream O2(S2);
1103 getCXXABI().getMangleContext().mangleTypeName(
1104 QualType(AP2.first->getTypeForDecl(), 0), O2);
1112 return AP1.second < AP2.second;
1115 ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();
1116 for (auto AP : AddressPoints) {
1117 // Create type metadata for the address point.
1118 AddVTableTypeMetadata(VTable, PointerWidth * AP.second, AP.first);
1120 // The class associated with each address point could also potentially be
1121 // used for indirect calls via a member function pointer, so we need to
1122 // annotate the address of each function pointer with the appropriate member
1123 // function pointer type.
1124 for (unsigned I = 0; I != Comps.size(); ++I) {
1125 if (Comps[I].getKind() != VTableComponent::CK_FunctionPointer)
1127 llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(
1128 Context.getMemberPointerType(
1129 Comps[I].getFunctionDecl()->getType(),
1130 Context.getRecordType(AP.first).getTypePtr()));
1131 VTable->addTypeMetadata((PointerWidth * I).getQuantity(), MD);
1135 if (getCodeGenOpts().VirtualFunctionElimination) {
1136 llvm::GlobalObject::VCallVisibility TypeVis = GetVCallVisibilityLevel(RD);
1137 if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)
1138 VTable->addVCallVisibilityMetadata(TypeVis);