1 //===--- CGCXX.cpp - Emit LLVM Code for declarations ----------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This contains code dealing with C++ code generation.
11 //
12 //===----------------------------------------------------------------------===//
13
14 // We might split this into multiple files if it gets too unwieldy
15
16 #include "CodeGenModule.h"
17 #include "CGCXXABI.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;
30
31 /// Try to emit a base destructor as an alias to its primary
32 /// base-class destructor.
TryEmitBaseDestructorAsAlias(const CXXDestructorDecl * D)33 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
34 if (!getCodeGenOpts().CXXCtorDtorAliases)
35 return true;
36
37 // If the destructor doesn't have a trivial body, we have to emit it
38 // separately.
39 if (!D->hasTrivialBody())
40 return true;
41
42 const CXXRecordDecl *Class = D->getParent();
43
44 // If we need to manipulate a VTT parameter, give up.
45 if (Class->getNumVBases()) {
46 // Extra Credit: passing extra parameters is perfectly safe
47 // in many calling conventions, so only bail out if the ctor's
48 // calling convention is nonstandard.
49 return true;
50 }
51
52 // If any field has a non-trivial destructor, we have to emit the
53 // destructor separately.
54 for (CXXRecordDecl::field_iterator I = Class->field_begin(),
55 E = Class->field_end(); I != E; ++I)
56 if (I->getType().isDestructedType())
57 return true;
58
59 // Try to find a unique base class with a non-trivial destructor.
60 const CXXRecordDecl *UniqueBase = 0;
61 for (CXXRecordDecl::base_class_const_iterator I = Class->bases_begin(),
62 E = Class->bases_end(); I != E; ++I) {
63
64 // We're in the base destructor, so skip virtual bases.
65 if (I->isVirtual()) continue;
66
67 // Skip base classes with trivial destructors.
68 const CXXRecordDecl *Base
69 = cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
70 if (Base->hasTrivialDestructor()) continue;
71
72 // If we've already found a base class with a non-trivial
73 // destructor, give up.
74 if (UniqueBase) return true;
75 UniqueBase = Base;
76 }
77
78 // If we didn't find any bases with a non-trivial destructor, then
79 // the base destructor is actually effectively trivial, which can
80 // happen if it was needlessly user-defined or if there are virtual
81 // bases with non-trivial destructors.
82 if (!UniqueBase)
83 return true;
84
85 /// If we don't have a definition for the destructor yet, don't
86 /// emit. We can't emit aliases to declarations; that's just not
87 /// how aliases work.
88 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
89 if (!BaseD->isImplicit() && !BaseD->hasBody())
90 return true;
91
92 // If the base is at a non-zero offset, give up.
93 const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
94 if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
95 return true;
96
97 return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base),
98 GlobalDecl(BaseD, Dtor_Base));
99 }
100
101 /// Try to emit a definition as a global alias for another definition.
TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,GlobalDecl TargetDecl)102 bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
103 GlobalDecl TargetDecl) {
104 if (!getCodeGenOpts().CXXCtorDtorAliases)
105 return true;
106
107 // The alias will use the linkage of the referrent. If we can't
108 // support aliases with that linkage, fail.
109 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
110
111 switch (Linkage) {
112 // We can definitely emit aliases to definitions with external linkage.
113 case llvm::GlobalValue::ExternalLinkage:
114 case llvm::GlobalValue::ExternalWeakLinkage:
115 break;
116
117 // Same with local linkage.
118 case llvm::GlobalValue::InternalLinkage:
119 case llvm::GlobalValue::PrivateLinkage:
120 case llvm::GlobalValue::LinkerPrivateLinkage:
121 break;
122
123 // We should try to support linkonce linkages.
124 case llvm::GlobalValue::LinkOnceAnyLinkage:
125 case llvm::GlobalValue::LinkOnceODRLinkage:
126 return true;
127
128 // Other linkages will probably never be supported.
129 default:
130 return true;
131 }
132
133 llvm::GlobalValue::LinkageTypes TargetLinkage
134 = getFunctionLinkage(TargetDecl);
135
136 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
137 return true;
138
139 // Derive the type for the alias.
140 llvm::PointerType *AliasType
141 = getTypes().GetFunctionType(AliasDecl)->getPointerTo();
142
143 // Find the referrent. Some aliases might require a bitcast, in
144 // which case the caller is responsible for ensuring the soundness
145 // of these semantics.
146 llvm::GlobalValue *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
147 llvm::Constant *Aliasee = Ref;
148 if (Ref->getType() != AliasType)
149 Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
150
151 // Create the alias with no name.
152 llvm::GlobalAlias *Alias =
153 new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule());
154
155 // Switch any previous uses to the alias.
156 StringRef MangledName = getMangledName(AliasDecl);
157 llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
158 if (Entry) {
159 assert(Entry->isDeclaration() && "definition already exists for alias");
160 assert(Entry->getType() == AliasType &&
161 "declaration exists with different type");
162 Alias->takeName(Entry);
163 Entry->replaceAllUsesWith(Alias);
164 Entry->eraseFromParent();
165 } else {
166 Alias->setName(MangledName);
167 }
168
169 // Finally, set up the alias with its proper name and attributes.
170 SetCommonAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias);
171
172 return false;
173 }
174
EmitCXXConstructor(const CXXConstructorDecl * ctor,CXXCtorType ctorType)175 void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *ctor,
176 CXXCtorType ctorType) {
177 // The complete constructor is equivalent to the base constructor
178 // for classes with no virtual bases. Try to emit it as an alias.
179 if (getTarget().getCXXABI().hasConstructorVariants() &&
180 ctorType == Ctor_Complete &&
181 !ctor->getParent()->getNumVBases() &&
182 !TryEmitDefinitionAsAlias(GlobalDecl(ctor, Ctor_Complete),
183 GlobalDecl(ctor, Ctor_Base)))
184 return;
185
186 const CGFunctionInfo &fnInfo =
187 getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType);
188
189 llvm::Function *fn =
190 cast<llvm::Function>(GetAddrOfCXXConstructor(ctor, ctorType, &fnInfo));
191 setFunctionLinkage(GlobalDecl(ctor, ctorType), fn);
192
193 CodeGenFunction(*this).GenerateCode(GlobalDecl(ctor, ctorType), fn, fnInfo);
194
195 SetFunctionDefinitionAttributes(ctor, fn);
196 SetLLVMFunctionAttributesForDefinition(ctor, fn);
197 }
198
199 llvm::GlobalValue *
GetAddrOfCXXConstructor(const CXXConstructorDecl * ctor,CXXCtorType ctorType,const CGFunctionInfo * fnInfo)200 CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *ctor,
201 CXXCtorType ctorType,
202 const CGFunctionInfo *fnInfo) {
203 GlobalDecl GD(ctor, ctorType);
204
205 StringRef name = getMangledName(GD);
206 if (llvm::GlobalValue *existing = GetGlobalValue(name))
207 return existing;
208
209 if (!fnInfo)
210 fnInfo = &getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType);
211
212 llvm::FunctionType *fnType = getTypes().GetFunctionType(*fnInfo);
213 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD,
214 /*ForVTable=*/false));
215 }
216
EmitCXXDestructor(const CXXDestructorDecl * dtor,CXXDtorType dtorType)217 void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *dtor,
218 CXXDtorType dtorType) {
219 // The complete destructor is equivalent to the base destructor for
220 // classes with no virtual bases, so try to emit it as an alias.
221 if (dtorType == Dtor_Complete &&
222 !dtor->getParent()->getNumVBases() &&
223 !TryEmitDefinitionAsAlias(GlobalDecl(dtor, Dtor_Complete),
224 GlobalDecl(dtor, Dtor_Base)))
225 return;
226
227 // The base destructor is equivalent to the base destructor of its
228 // base class if there is exactly one non-virtual base class with a
229 // non-trivial destructor, there are no fields with a non-trivial
230 // destructor, and the body of the destructor is trivial.
231 if (dtorType == Dtor_Base && !TryEmitBaseDestructorAsAlias(dtor))
232 return;
233
234 const CGFunctionInfo &fnInfo =
235 getTypes().arrangeCXXDestructor(dtor, dtorType);
236
237 llvm::Function *fn =
238 cast<llvm::Function>(GetAddrOfCXXDestructor(dtor, dtorType, &fnInfo));
239 setFunctionLinkage(GlobalDecl(dtor, dtorType), fn);
240
241 CodeGenFunction(*this).GenerateCode(GlobalDecl(dtor, dtorType), fn, fnInfo);
242
243 SetFunctionDefinitionAttributes(dtor, fn);
244 SetLLVMFunctionAttributesForDefinition(dtor, fn);
245 }
246
247 llvm::GlobalValue *
GetAddrOfCXXDestructor(const CXXDestructorDecl * dtor,CXXDtorType dtorType,const CGFunctionInfo * fnInfo,llvm::FunctionType * fnType)248 CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *dtor,
249 CXXDtorType dtorType,
250 const CGFunctionInfo *fnInfo,
251 llvm::FunctionType *fnType) {
252 // If the class has no virtual bases, then the complete and base destructors
253 // are equivalent, for all C++ ABIs supported by clang. We can save on code
254 // size by calling the base dtor directly, especially if we'd have to emit a
255 // thunk otherwise.
256 // FIXME: We should do this for Itanium, after verifying that nothing breaks.
257 if (dtorType == Dtor_Complete && dtor->getParent()->getNumVBases() == 0 &&
258 getCXXABI().useThunkForDtorVariant(dtor, Dtor_Complete))
259 dtorType = Dtor_Base;
260
261 GlobalDecl GD(dtor, dtorType);
262
263 StringRef name = getMangledName(GD);
264 if (llvm::GlobalValue *existing = GetGlobalValue(name))
265 return existing;
266
267 if (!fnType) {
268 if (!fnInfo) fnInfo = &getTypes().arrangeCXXDestructor(dtor, dtorType);
269 fnType = getTypes().GetFunctionType(*fnInfo);
270 }
271 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD,
272 /*ForVTable=*/false));
273 }
274
275 llvm::Value *
BuildVirtualCall(GlobalDecl GD,llvm::Value * This,llvm::Type * Ty)276 CodeGenFunction::BuildVirtualCall(GlobalDecl GD, llvm::Value *This,
277 llvm::Type *Ty) {
278 GD = GD.getCanonicalDecl();
279 uint64_t VTableIndex = CGM.getVTableContext().getMethodVTableIndex(GD);
280
281 Ty = Ty->getPointerTo()->getPointerTo();
282 llvm::Value *VTable = GetVTablePtr(This, Ty);
283 llvm::Value *VFuncPtr =
284 Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfn");
285 return Builder.CreateLoad(VFuncPtr);
286 }
287
BuildAppleKextVirtualCall(CodeGenFunction & CGF,GlobalDecl GD,llvm::Type * Ty,const CXXRecordDecl * RD)288 static llvm::Value *BuildAppleKextVirtualCall(CodeGenFunction &CGF,
289 GlobalDecl GD,
290 llvm::Type *Ty,
291 const CXXRecordDecl *RD) {
292 GD = GD.getCanonicalDecl();
293 CodeGenModule &CGM = CGF.CGM;
294 llvm::Value *VTable = CGM.getVTables().GetAddrOfVTable(RD);
295 Ty = Ty->getPointerTo()->getPointerTo();
296 VTable = CGF.Builder.CreateBitCast(VTable, Ty);
297 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
298 uint64_t VTableIndex = CGM.getVTableContext().getMethodVTableIndex(GD);
299 uint64_t AddressPoint =
300 CGM.getVTableContext().getVTableLayout(RD)
301 .getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
302 VTableIndex += AddressPoint;
303 llvm::Value *VFuncPtr =
304 CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt");
305 return CGF.Builder.CreateLoad(VFuncPtr);
306 }
307
308 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
309 /// indirect call to virtual functions. It makes the call through indexing
310 /// into the vtable.
311 llvm::Value *
BuildAppleKextVirtualCall(const CXXMethodDecl * MD,NestedNameSpecifier * Qual,llvm::Type * Ty)312 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
313 NestedNameSpecifier *Qual,
314 llvm::Type *Ty) {
315 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
316 "BuildAppleKextVirtualCall - bad Qual kind");
317
318 const Type *QTy = Qual->getAsType();
319 QualType T = QualType(QTy, 0);
320 const RecordType *RT = T->getAs<RecordType>();
321 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
322 const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
323
324 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))
325 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
326
327 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
328 }
329
330 /// BuildVirtualCall - This routine makes indirect vtable call for
331 /// call to virtual destructors. It returns 0 if it could not do it.
332 llvm::Value *
BuildAppleKextVirtualDestructorCall(const CXXDestructorDecl * DD,CXXDtorType Type,const CXXRecordDecl * RD)333 CodeGenFunction::BuildAppleKextVirtualDestructorCall(
334 const CXXDestructorDecl *DD,
335 CXXDtorType Type,
336 const CXXRecordDecl *RD) {
337 const CXXMethodDecl *MD = cast<CXXMethodDecl>(DD);
338 // FIXME. Dtor_Base dtor is always direct!!
339 // It need be somehow inline expanded into the caller.
340 // -O does that. But need to support -O0 as well.
341 if (MD->isVirtual() && Type != Dtor_Base) {
342 // Compute the function type we're calling.
343 const CGFunctionInfo &FInfo =
344 CGM.getTypes().arrangeCXXDestructor(DD, Dtor_Complete);
345 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
346 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);
347 }
348 return 0;
349 }
350