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;
31 /// Try to emit a base destructor as an alias to its primary
32 /// base-class destructor.
33 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
34 if (!getCodeGenOpts().CXXCtorDtorAliases)
37 // Producing an alias to a base class ctor/dtor can degrade debug quality
38 // as the debugger cannot tell them appart.
39 if (getCodeGenOpts().OptimizationLevel == 0)
42 // If the destructor doesn't have a trivial body, we have to emit it
44 if (!D->hasTrivialBody())
47 const CXXRecordDecl *Class = D->getParent();
49 // If we need to manipulate a VTT parameter, give up.
50 if (Class->getNumVBases()) {
51 // Extra Credit: passing extra parameters is perfectly safe
52 // in many calling conventions, so only bail out if the ctor's
53 // calling convention is nonstandard.
57 // If any field has a non-trivial destructor, we have to emit the
58 // destructor separately.
59 for (CXXRecordDecl::field_iterator I = Class->field_begin(),
60 E = Class->field_end(); I != E; ++I)
61 if (I->getType().isDestructedType())
64 // Try to find a unique base class with a non-trivial destructor.
65 const CXXRecordDecl *UniqueBase = 0;
66 for (CXXRecordDecl::base_class_const_iterator I = Class->bases_begin(),
67 E = Class->bases_end(); I != E; ++I) {
69 // We're in the base destructor, so skip virtual bases.
70 if (I->isVirtual()) continue;
72 // Skip base classes with trivial destructors.
73 const CXXRecordDecl *Base
74 = cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
75 if (Base->hasTrivialDestructor()) continue;
77 // If we've already found a base class with a non-trivial
78 // destructor, give up.
79 if (UniqueBase) return true;
83 // If we didn't find any bases with a non-trivial destructor, then
84 // the base destructor is actually effectively trivial, which can
85 // happen if it was needlessly user-defined or if there are virtual
86 // bases with non-trivial destructors.
90 // If the base is at a non-zero offset, give up.
91 const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
92 if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
95 // Give up if the calling conventions don't match. We could update the call,
96 // but it is probably not worth it.
97 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
98 if (BaseD->getType()->getAs<FunctionType>()->getCallConv() !=
99 D->getType()->getAs<FunctionType>()->getCallConv())
102 return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base),
103 GlobalDecl(BaseD, Dtor_Base),
107 /// Try to emit a definition as a global alias for another definition.
108 /// If \p InEveryTU is true, we know that an equivalent alias can be produced
109 /// in every translation unit.
110 bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
111 GlobalDecl TargetDecl,
113 if (!getCodeGenOpts().CXXCtorDtorAliases)
116 // The alias will use the linkage of the referrent. If we can't
117 // support aliases with that linkage, fail.
118 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
120 // We can't use an alias if the linkage is not valid for one.
121 if (!llvm::GlobalAlias::isValidLinkage(Linkage))
124 llvm::GlobalValue::LinkageTypes TargetLinkage =
125 getFunctionLinkage(TargetDecl);
127 // Check if we have it already.
128 StringRef MangledName = getMangledName(AliasDecl);
129 llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
130 if (Entry && !Entry->isDeclaration())
132 if (Replacements.count(MangledName))
135 // Derive the type for the alias.
136 llvm::PointerType *AliasType
137 = getTypes().GetFunctionType(AliasDecl)->getPointerTo();
139 // Find the referrent. Some aliases might require a bitcast, in
140 // which case the caller is responsible for ensuring the soundness
141 // of these semantics.
142 llvm::GlobalValue *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
143 llvm::Constant *Aliasee = Ref;
144 if (Ref->getType() != AliasType)
145 Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
147 // Instead of creating as alias to a linkonce_odr, replace all of the uses
149 if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
150 (TargetLinkage != llvm::GlobalValue::AvailableExternallyLinkage ||
151 !TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
152 // FIXME: An extern template instanciation will create functions with
153 // linkage "AvailableExternally". In libc++, some classes also define
154 // members with attribute "AlwaysInline" and expect no reference to
155 // be generated. It is desirable to reenable this optimisation after
156 // corresponding LLVM changes.
157 Replacements[MangledName] = Aliasee;
162 /// If we don't have a definition for the destructor yet, don't
163 /// emit. We can't emit aliases to declarations; that's just not
164 /// how aliases work.
165 if (Ref->isDeclaration())
169 // Don't create an alias to a linker weak symbol. This avoids producing
170 // different COMDATs in different TUs. Another option would be to
171 // output the alias both for weak_odr and linkonce_odr, but that
172 // requires explicit comdat support in the IL.
173 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
176 // Create the alias with no name.
177 llvm::GlobalAlias *Alias =
178 new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule());
180 // Switch any previous uses to the alias.
182 assert(Entry->getType() == AliasType &&
183 "declaration exists with different type");
184 Alias->takeName(Entry);
185 Entry->replaceAllUsesWith(Alias);
186 Entry->eraseFromParent();
188 Alias->setName(MangledName);
191 // Finally, set up the alias with its proper name and attributes.
192 SetCommonAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias);
197 void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *ctor,
198 CXXCtorType ctorType) {
199 // The complete constructor is equivalent to the base constructor
200 // for classes with no virtual bases. Try to emit it as an alias.
201 if (getTarget().getCXXABI().hasConstructorVariants() &&
202 !ctor->getParent()->getNumVBases() &&
203 (ctorType == Ctor_Complete || ctorType == Ctor_Base)) {
205 !TryEmitDefinitionAsAlias(GlobalDecl(ctor, Ctor_Complete),
206 GlobalDecl(ctor, Ctor_Base), true);
207 if (ctorType == Ctor_Complete && ProducedAlias)
211 const CGFunctionInfo &fnInfo =
212 getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType);
215 cast<llvm::Function>(GetAddrOfCXXConstructor(ctor, ctorType, &fnInfo));
216 setFunctionLinkage(GlobalDecl(ctor, ctorType), fn);
218 CodeGenFunction(*this).GenerateCode(GlobalDecl(ctor, ctorType), fn, fnInfo);
220 SetFunctionDefinitionAttributes(ctor, fn);
221 SetLLVMFunctionAttributesForDefinition(ctor, fn);
225 CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *ctor,
226 CXXCtorType ctorType,
227 const CGFunctionInfo *fnInfo) {
228 GlobalDecl GD(ctor, ctorType);
230 StringRef name = getMangledName(GD);
231 if (llvm::GlobalValue *existing = GetGlobalValue(name))
235 fnInfo = &getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType);
237 llvm::FunctionType *fnType = getTypes().GetFunctionType(*fnInfo);
238 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD,
239 /*ForVTable=*/false));
242 void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *dtor,
243 CXXDtorType dtorType) {
244 // The complete destructor is equivalent to the base destructor for
245 // classes with no virtual bases, so try to emit it as an alias.
246 if (!dtor->getParent()->getNumVBases() &&
247 (dtorType == Dtor_Complete || dtorType == Dtor_Base)) {
249 !TryEmitDefinitionAsAlias(GlobalDecl(dtor, Dtor_Complete),
250 GlobalDecl(dtor, Dtor_Base), true);
252 if (dtorType == Dtor_Complete)
254 if (dtor->isVirtual())
255 getVTables().EmitThunks(GlobalDecl(dtor, Dtor_Complete));
259 // The base destructor is equivalent to the base destructor of its
260 // base class if there is exactly one non-virtual base class with a
261 // non-trivial destructor, there are no fields with a non-trivial
262 // destructor, and the body of the destructor is trivial.
263 if (dtorType == Dtor_Base && !TryEmitBaseDestructorAsAlias(dtor))
266 const CGFunctionInfo &fnInfo =
267 getTypes().arrangeCXXDestructor(dtor, dtorType);
270 cast<llvm::Function>(GetAddrOfCXXDestructor(dtor, dtorType, &fnInfo));
271 setFunctionLinkage(GlobalDecl(dtor, dtorType), fn);
273 CodeGenFunction(*this).GenerateCode(GlobalDecl(dtor, dtorType), fn, fnInfo);
275 SetFunctionDefinitionAttributes(dtor, fn);
276 SetLLVMFunctionAttributesForDefinition(dtor, fn);
280 CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *dtor,
281 CXXDtorType dtorType,
282 const CGFunctionInfo *fnInfo,
283 llvm::FunctionType *fnType) {
284 GlobalDecl GD(dtor, dtorType);
286 StringRef name = getMangledName(GD);
287 if (llvm::GlobalValue *existing = GetGlobalValue(name))
291 if (!fnInfo) fnInfo = &getTypes().arrangeCXXDestructor(dtor, dtorType);
292 fnType = getTypes().GetFunctionType(*fnInfo);
294 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD,
295 /*ForVTable=*/false));
298 static llvm::Value *BuildAppleKextVirtualCall(CodeGenFunction &CGF,
301 const CXXRecordDecl *RD) {
302 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
303 "No kext in Microsoft ABI");
304 GD = GD.getCanonicalDecl();
305 CodeGenModule &CGM = CGF.CGM;
306 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
307 Ty = Ty->getPointerTo()->getPointerTo();
308 VTable = CGF.Builder.CreateBitCast(VTable, Ty);
309 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
310 uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
311 uint64_t AddressPoint =
312 CGM.getItaniumVTableContext().getVTableLayout(RD)
313 .getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
314 VTableIndex += AddressPoint;
315 llvm::Value *VFuncPtr =
316 CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt");
317 return CGF.Builder.CreateLoad(VFuncPtr);
320 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
321 /// indirect call to virtual functions. It makes the call through indexing
324 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
325 NestedNameSpecifier *Qual,
327 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
328 "BuildAppleKextVirtualCall - bad Qual kind");
330 const Type *QTy = Qual->getAsType();
331 QualType T = QualType(QTy, 0);
332 const RecordType *RT = T->getAs<RecordType>();
333 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
334 const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
336 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))
337 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
339 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
342 /// BuildVirtualCall - This routine makes indirect vtable call for
343 /// call to virtual destructors. It returns 0 if it could not do it.
345 CodeGenFunction::BuildAppleKextVirtualDestructorCall(
346 const CXXDestructorDecl *DD,
348 const CXXRecordDecl *RD) {
349 const CXXMethodDecl *MD = cast<CXXMethodDecl>(DD);
350 // FIXME. Dtor_Base dtor is always direct!!
351 // It need be somehow inline expanded into the caller.
352 // -O does that. But need to support -O0 as well.
353 if (MD->isVirtual() && Type != Dtor_Base) {
354 // Compute the function type we're calling.
355 const CGFunctionInfo &FInfo =
356 CGM.getTypes().arrangeCXXDestructor(DD, Dtor_Complete);
357 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
358 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);