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
32 /// Try to emit a base destructor as an alias to its primary
33 /// base-class destructor.
TryEmitBaseDestructorAsAlias(const CXXDestructorDecl * D)34 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
35 if (!getCodeGenOpts().CXXCtorDtorAliases)
36 return true;
37
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)
41 return true;
42
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())
47 return true;
48
49 // If the destructor doesn't have a trivial body, we have to emit it
50 // separately.
51 if (!D->hasTrivialBody())
52 return true;
53
54 const CXXRecordDecl *Class = D->getParent();
55
56 // We are going to instrument this destructor, so give up even if it is
57 // currently empty.
58 if (Class->mayInsertExtraPadding())
59 return true;
60
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.
66 return true;
67 }
68
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())
73 return true;
74
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()) {
78
79 // We're in the base destructor, so skip virtual bases.
80 if (I.isVirtual()) continue;
81
82 // Skip base classes with trivial destructors.
83 const auto *Base =
84 cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl());
85 if (Base->hasTrivialDestructor()) continue;
86
87 // If we've already found a base class with a non-trivial
88 // destructor, give up.
89 if (UniqueBase) return true;
90 UniqueBase = Base;
91 }
92
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.
97 if (!UniqueBase)
98 return true;
99
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())
103 return true;
104
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())
110 return true;
111
112 return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base),
113 GlobalDecl(BaseD, Dtor_Base),
114 false);
115 }
116
117 /// Try to emit a definition as a global alias for another definition.
118 /// If \p InEveryTU is true, we know that an equivalent alias can be produced
119 /// in every translation unit.
TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,GlobalDecl TargetDecl,bool InEveryTU)120 bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
121 GlobalDecl TargetDecl,
122 bool InEveryTU) {
123 if (!getCodeGenOpts().CXXCtorDtorAliases)
124 return true;
125
126 // The alias will use the linkage of the referent. If we can't
127 // support aliases with that linkage, fail.
128 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
129
130 // We can't use an alias if the linkage is not valid for one.
131 if (!llvm::GlobalAlias::isValidLinkage(Linkage))
132 return true;
133
134 llvm::GlobalValue::LinkageTypes TargetLinkage =
135 getFunctionLinkage(TargetDecl);
136
137 // Check if we have it already.
138 StringRef MangledName = getMangledName(AliasDecl);
139 llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
140 if (Entry && !Entry->isDeclaration())
141 return false;
142 if (Replacements.count(MangledName))
143 return false;
144
145 // Derive the type for the alias.
146 llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
147 llvm::PointerType *AliasType = AliasValueType->getPointerTo();
148
149 // Find the referent. Some aliases might require a bitcast, in
150 // which case the caller is responsible for ensuring the soundness
151 // of these semantics.
152 auto *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
153 llvm::Constant *Aliasee = Ref;
154 if (Ref->getType() != AliasType)
155 Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
156
157 // Instead of creating as alias to a linkonce_odr, replace all of the uses
158 // of the aliasee.
159 if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
160 (TargetLinkage != llvm::GlobalValue::AvailableExternallyLinkage ||
161 !TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
162 // FIXME: An extern template instantiation will create functions with
163 // linkage "AvailableExternally". In libc++, some classes also define
164 // members with attribute "AlwaysInline" and expect no reference to
165 // be generated. It is desirable to reenable this optimisation after
166 // corresponding LLVM changes.
167 Replacements[MangledName] = Aliasee;
168 return false;
169 }
170
171 // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
172 // template instantiation or a dllexported class, avoid forming it on COFF.
173 // A COFF weak external alias cannot satisfy a normal undefined symbol
174 // reference from another TU. The other TU must also mark the referenced
175 // symbol as weak, which we cannot rely on.
176 if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
177 getTriple().isOSBinFormatCOFF()) {
178 return true;
179 }
180
181 if (!InEveryTU) {
182 // If we don't have a definition for the destructor yet, don't
183 // emit. We can't emit aliases to declarations; that's just not
184 // how aliases work.
185 if (Ref->isDeclaration())
186 return true;
187 }
188
189 // Don't create an alias to a linker weak symbol. This avoids producing
190 // different COMDATs in different TUs. Another option would be to
191 // output the alias both for weak_odr and linkonce_odr, but that
192 // requires explicit comdat support in the IL.
193 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
194 return true;
195
196 // Create the alias with no name.
197 auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
198 Aliasee, &getModule());
199
200 // Switch any previous uses to the alias.
201 if (Entry) {
202 assert(Entry->getType() == AliasType &&
203 "declaration exists with different type");
204 Alias->takeName(Entry);
205 Entry->replaceAllUsesWith(Alias);
206 Entry->eraseFromParent();
207 } else {
208 Alias->setName(MangledName);
209 }
210
211 // Finally, set up the alias with its proper name and attributes.
212 setAliasAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias);
213
214 return false;
215 }
216
codegenCXXStructor(const CXXMethodDecl * MD,StructorType Type)217 llvm::Function *CodeGenModule::codegenCXXStructor(const CXXMethodDecl *MD,
218 StructorType Type) {
219 const CGFunctionInfo &FnInfo =
220 getTypes().arrangeCXXStructorDeclaration(MD, Type);
221 auto *Fn = cast<llvm::Function>(
222 getAddrOfCXXStructor(MD, Type, &FnInfo, /*FnType=*/nullptr,
223 /*DontDefer=*/true, /*IsForDefinition=*/true));
224
225 GlobalDecl GD;
226 if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD)) {
227 GD = GlobalDecl(DD, toCXXDtorType(Type));
228 } else {
229 const auto *CD = cast<CXXConstructorDecl>(MD);
230 GD = GlobalDecl(CD, toCXXCtorType(Type));
231 }
232
233 setFunctionLinkage(GD, Fn);
234 setFunctionDLLStorageClass(GD, Fn);
235
236 CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
237 setFunctionDefinitionAttributes(MD, Fn);
238 SetLLVMFunctionAttributesForDefinition(MD, Fn);
239 return Fn;
240 }
241
getAddrOfCXXStructor(const CXXMethodDecl * MD,StructorType Type,const CGFunctionInfo * FnInfo,llvm::FunctionType * FnType,bool DontDefer,bool IsForDefinition)242 llvm::Constant *CodeGenModule::getAddrOfCXXStructor(
243 const CXXMethodDecl *MD, StructorType Type, const CGFunctionInfo *FnInfo,
244 llvm::FunctionType *FnType, bool DontDefer, bool IsForDefinition) {
245 GlobalDecl GD;
246 if (auto *CD = dyn_cast<CXXConstructorDecl>(MD)) {
247 GD = GlobalDecl(CD, toCXXCtorType(Type));
248 } else {
249 GD = GlobalDecl(cast<CXXDestructorDecl>(MD), toCXXDtorType(Type));
250 }
251
252 if (!FnType) {
253 if (!FnInfo)
254 FnInfo = &getTypes().arrangeCXXStructorDeclaration(MD, Type);
255 FnType = getTypes().GetFunctionType(*FnInfo);
256 }
257
258 return GetOrCreateLLVMFunction(
259 getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,
260 /*isThunk=*/false, /*ExtraAttrs=*/llvm::AttributeSet(), IsForDefinition);
261 }
262
BuildAppleKextVirtualCall(CodeGenFunction & CGF,GlobalDecl GD,llvm::Type * Ty,const CXXRecordDecl * RD)263 static llvm::Value *BuildAppleKextVirtualCall(CodeGenFunction &CGF,
264 GlobalDecl GD,
265 llvm::Type *Ty,
266 const CXXRecordDecl *RD) {
267 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
268 "No kext in Microsoft ABI");
269 GD = GD.getCanonicalDecl();
270 CodeGenModule &CGM = CGF.CGM;
271 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
272 Ty = Ty->getPointerTo()->getPointerTo();
273 VTable = CGF.Builder.CreateBitCast(VTable, Ty);
274 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
275 uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
276 uint64_t AddressPoint =
277 CGM.getItaniumVTableContext().getVTableLayout(RD)
278 .getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
279 VTableIndex += AddressPoint;
280 llvm::Value *VFuncPtr =
281 CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt");
282 return CGF.Builder.CreateAlignedLoad(VFuncPtr, CGF.PointerAlignInBytes);
283 }
284
285 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
286 /// indirect call to virtual functions. It makes the call through indexing
287 /// into the vtable.
288 llvm::Value *
BuildAppleKextVirtualCall(const CXXMethodDecl * MD,NestedNameSpecifier * Qual,llvm::Type * Ty)289 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
290 NestedNameSpecifier *Qual,
291 llvm::Type *Ty) {
292 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
293 "BuildAppleKextVirtualCall - bad Qual kind");
294
295 const Type *QTy = Qual->getAsType();
296 QualType T = QualType(QTy, 0);
297 const RecordType *RT = T->getAs<RecordType>();
298 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
299 const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
300
301 if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
302 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
303
304 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
305 }
306
307 /// BuildVirtualCall - This routine makes indirect vtable call for
308 /// call to virtual destructors. It returns 0 if it could not do it.
309 llvm::Value *
BuildAppleKextVirtualDestructorCall(const CXXDestructorDecl * DD,CXXDtorType Type,const CXXRecordDecl * RD)310 CodeGenFunction::BuildAppleKextVirtualDestructorCall(
311 const CXXDestructorDecl *DD,
312 CXXDtorType Type,
313 const CXXRecordDecl *RD) {
314 const auto *MD = cast<CXXMethodDecl>(DD);
315 // FIXME. Dtor_Base dtor is always direct!!
316 // It need be somehow inline expanded into the caller.
317 // -O does that. But need to support -O0 as well.
318 if (MD->isVirtual() && Type != Dtor_Base) {
319 // Compute the function type we're calling.
320 const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
321 DD, StructorType::Complete);
322 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
323 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);
324 }
325 return nullptr;
326 }
327