1 //===--- CGCXX.cpp - Emit LLVM Code for declarations ----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This contains code dealing with C++ code generation.
12 //===----------------------------------------------------------------------===//
14 // We might split this into multiple files if it gets too unwieldy
16 #include "CodeGenModule.h"
18 #include "CodeGenFunction.h"
19 #include "clang/AST/ASTContext.h"
20 #include "clang/AST/Decl.h"
21 #include "clang/AST/DeclCXX.h"
22 #include "clang/AST/DeclObjC.h"
23 #include "clang/AST/Mangle.h"
24 #include "clang/AST/RecordLayout.h"
25 #include "clang/AST/StmtCXX.h"
26 #include "clang/Frontend/CodeGenOptions.h"
27 #include "llvm/ADT/StringExtras.h"
28 using namespace clang;
29 using namespace CodeGen;
32 /// Try to emit a base destructor as an alias to its primary
33 /// base-class destructor.
34 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
35 if (!getCodeGenOpts().CXXCtorDtorAliases)
38 // Producing an alias to a base class ctor/dtor can degrade debug quality
39 // as the debugger cannot tell them apart.
40 if (getCodeGenOpts().OptimizationLevel == 0)
43 // If sanitizing memory to check for use-after-dtor, do not emit as
44 // an alias, unless this class owns no members.
45 if (getCodeGenOpts().SanitizeMemoryUseAfterDtor &&
46 !D->getParent()->field_empty())
49 // If the destructor doesn't have a trivial body, we have to emit it
51 if (!D->hasTrivialBody())
54 const CXXRecordDecl *Class = D->getParent();
56 // We are going to instrument this destructor, so give up even if it is
58 if (Class->mayInsertExtraPadding())
61 // If we need to manipulate a VTT parameter, give up.
62 if (Class->getNumVBases()) {
63 // Extra Credit: passing extra parameters is perfectly safe
64 // in many calling conventions, so only bail out if the ctor's
65 // calling convention is nonstandard.
69 // If any field has a non-trivial destructor, we have to emit the
70 // destructor separately.
71 for (const auto *I : Class->fields())
72 if (I->getType().isDestructedType())
75 // Try to find a unique base class with a non-trivial destructor.
76 const CXXRecordDecl *UniqueBase = nullptr;
77 for (const auto &I : Class->bases()) {
79 // We're in the base destructor, so skip virtual bases.
80 if (I.isVirtual()) continue;
82 // Skip base classes with trivial destructors.
84 cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl());
85 if (Base->hasTrivialDestructor()) continue;
87 // If we've already found a base class with a non-trivial
88 // destructor, give up.
89 if (UniqueBase) return true;
93 // If we didn't find any bases with a non-trivial destructor, then
94 // the base destructor is actually effectively trivial, which can
95 // happen if it was needlessly user-defined or if there are virtual
96 // bases with non-trivial destructors.
100 // If the base is at a non-zero offset, give up.
101 const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
102 if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
105 // Give up if the calling conventions don't match. We could update the call,
106 // but it is probably not worth it.
107 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
108 if (BaseD->getType()->getAs<FunctionType>()->getCallConv() !=
109 D->getType()->getAs<FunctionType>()->getCallConv())
112 return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base),
113 GlobalDecl(BaseD, Dtor_Base));
116 /// Try to emit a definition as a global alias for another definition.
117 /// If \p InEveryTU is true, we know that an equivalent alias can be produced
118 /// in every translation unit.
119 bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
120 GlobalDecl TargetDecl) {
121 if (!getCodeGenOpts().CXXCtorDtorAliases)
124 // The alias will use the linkage of the referent. If we can't
125 // support aliases with that linkage, fail.
126 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
128 // We can't use an alias if the linkage is not valid for one.
129 if (!llvm::GlobalAlias::isValidLinkage(Linkage))
132 llvm::GlobalValue::LinkageTypes TargetLinkage =
133 getFunctionLinkage(TargetDecl);
135 // Check if we have it already.
136 StringRef MangledName = getMangledName(AliasDecl);
137 llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
138 if (Entry && !Entry->isDeclaration())
140 if (Replacements.count(MangledName))
143 // Derive the type for the alias.
144 llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
145 llvm::PointerType *AliasType = AliasValueType->getPointerTo();
147 // Find the referent. Some aliases might require a bitcast, in
148 // which case the caller is responsible for ensuring the soundness
149 // of these semantics.
150 auto *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
151 llvm::Constant *Aliasee = Ref;
152 if (Ref->getType() != AliasType)
153 Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
155 // Instead of creating as alias to a linkonce_odr, replace all of the uses
157 if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
158 !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&
159 TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
160 // FIXME: An extern template instantiation will create functions with
161 // linkage "AvailableExternally". In libc++, some classes also define
162 // members with attribute "AlwaysInline" and expect no reference to
163 // be generated. It is desirable to reenable this optimisation after
164 // corresponding LLVM changes.
165 addReplacement(MangledName, Aliasee);
169 // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
170 // template instantiation or a dllexported class, avoid forming it on COFF.
171 // A COFF weak external alias cannot satisfy a normal undefined symbol
172 // reference from another TU. The other TU must also mark the referenced
173 // symbol as weak, which we cannot rely on.
174 if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
175 getTriple().isOSBinFormatCOFF()) {
179 // If we don't have a definition for the destructor yet or the definition is
180 // avaialable_externally, don't emit an alias. We can't emit aliases to
181 // declarations; that's just not how aliases work.
182 if (Ref->isDeclarationForLinker())
185 // Don't create an alias to a linker weak symbol. This avoids producing
186 // different COMDATs in different TUs. Another option would be to
187 // output the alias both for weak_odr and linkonce_odr, but that
188 // requires explicit comdat support in the IL.
189 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
192 // Create the alias with no name.
193 auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
194 Aliasee, &getModule());
196 // Switch any previous uses to the alias.
198 assert(Entry->getType() == AliasType &&
199 "declaration exists with different type");
200 Alias->takeName(Entry);
201 Entry->replaceAllUsesWith(Alias);
202 Entry->eraseFromParent();
204 Alias->setName(MangledName);
207 // Finally, set up the alias with its proper name and attributes.
208 setAliasAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias);
213 llvm::Function *CodeGenModule::codegenCXXStructor(const CXXMethodDecl *MD,
215 const CGFunctionInfo &FnInfo =
216 getTypes().arrangeCXXStructorDeclaration(MD, Type);
217 auto *Fn = cast<llvm::Function>(
218 getAddrOfCXXStructor(MD, Type, &FnInfo, /*FnType=*/nullptr,
219 /*DontDefer=*/true, ForDefinition));
222 if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD)) {
223 GD = GlobalDecl(DD, toCXXDtorType(Type));
225 const auto *CD = cast<CXXConstructorDecl>(MD);
226 GD = GlobalDecl(CD, toCXXCtorType(Type));
229 setFunctionLinkage(GD, Fn);
230 setFunctionDLLStorageClass(GD, Fn);
232 CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
233 setFunctionDefinitionAttributes(MD, Fn);
234 SetLLVMFunctionAttributesForDefinition(MD, Fn);
238 llvm::Constant *CodeGenModule::getAddrOfCXXStructor(
239 const CXXMethodDecl *MD, StructorType Type, const CGFunctionInfo *FnInfo,
240 llvm::FunctionType *FnType, bool DontDefer,
241 ForDefinition_t IsForDefinition) {
243 if (auto *CD = dyn_cast<CXXConstructorDecl>(MD)) {
244 GD = GlobalDecl(CD, toCXXCtorType(Type));
246 GD = GlobalDecl(cast<CXXDestructorDecl>(MD), toCXXDtorType(Type));
251 FnInfo = &getTypes().arrangeCXXStructorDeclaration(MD, Type);
252 FnType = getTypes().GetFunctionType(*FnInfo);
255 return GetOrCreateLLVMFunction(
256 getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,
257 /*isThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);
260 static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,
263 const CXXRecordDecl *RD) {
264 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
265 "No kext in Microsoft ABI");
266 GD = GD.getCanonicalDecl();
267 CodeGenModule &CGM = CGF.CGM;
268 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
269 Ty = Ty->getPointerTo()->getPointerTo();
270 VTable = CGF.Builder.CreateBitCast(VTable, Ty);
271 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
272 uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
273 const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);
274 VTableLayout::AddressPointLocation AddressPoint =
275 VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
276 VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +
277 AddressPoint.AddressPointIndex;
278 llvm::Value *VFuncPtr =
279 CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt");
281 CGF.Builder.CreateAlignedLoad(VFuncPtr, CGF.PointerAlignInBytes);
282 CGCallee Callee(GD.getDecl(), VFunc);
286 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
287 /// indirect call to virtual functions. It makes the call through indexing
290 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
291 NestedNameSpecifier *Qual,
293 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
294 "BuildAppleKextVirtualCall - bad Qual kind");
296 const Type *QTy = Qual->getAsType();
297 QualType T = QualType(QTy, 0);
298 const RecordType *RT = T->getAs<RecordType>();
299 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
300 const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
302 if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
303 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
305 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
308 /// BuildVirtualCall - This routine makes indirect vtable call for
309 /// call to virtual destructors. It returns 0 if it could not do it.
311 CodeGenFunction::BuildAppleKextVirtualDestructorCall(
312 const CXXDestructorDecl *DD,
314 const CXXRecordDecl *RD) {
315 assert(DD->isVirtual() && Type != Dtor_Base);
316 // Compute the function type we're calling.
317 const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
318 DD, StructorType::Complete);
319 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
320 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);