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 // Producing an alias to a base class ctor/dtor can degrade debug quality
38 // as the debugger cannot tell them apart.
39 if (getCodeGenOpts().OptimizationLevel == 0)
40 return true;
41
42 // If the destructor doesn't have a trivial body, we have to emit it
43 // separately.
44 if (!D->hasTrivialBody())
45 return true;
46
47 const CXXRecordDecl *Class = D->getParent();
48
49 // We are going to instrument this destructor, so give up even if it is
50 // currently empty.
51 if (Class->mayInsertExtraPadding())
52 return true;
53
54 // If we need to manipulate a VTT parameter, give up.
55 if (Class->getNumVBases()) {
56 // Extra Credit: passing extra parameters is perfectly safe
57 // in many calling conventions, so only bail out if the ctor's
58 // calling convention is nonstandard.
59 return true;
60 }
61
62 // If any field has a non-trivial destructor, we have to emit the
63 // destructor separately.
64 for (const auto *I : Class->fields())
65 if (I->getType().isDestructedType())
66 return true;
67
68 // Try to find a unique base class with a non-trivial destructor.
69 const CXXRecordDecl *UniqueBase = nullptr;
70 for (const auto &I : Class->bases()) {
71
72 // We're in the base destructor, so skip virtual bases.
73 if (I.isVirtual()) continue;
74
75 // Skip base classes with trivial destructors.
76 const auto *Base =
77 cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl());
78 if (Base->hasTrivialDestructor()) continue;
79
80 // If we've already found a base class with a non-trivial
81 // destructor, give up.
82 if (UniqueBase) return true;
83 UniqueBase = Base;
84 }
85
86 // If we didn't find any bases with a non-trivial destructor, then
87 // the base destructor is actually effectively trivial, which can
88 // happen if it was needlessly user-defined or if there are virtual
89 // bases with non-trivial destructors.
90 if (!UniqueBase)
91 return true;
92
93 // If the base is at a non-zero offset, give up.
94 const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
95 if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
96 return true;
97
98 // Give up if the calling conventions don't match. We could update the call,
99 // but it is probably not worth it.
100 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
101 if (BaseD->getType()->getAs<FunctionType>()->getCallConv() !=
102 D->getType()->getAs<FunctionType>()->getCallConv())
103 return true;
104
105 return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base),
106 GlobalDecl(BaseD, Dtor_Base),
107 false);
108 }
109
110 /// Try to emit a definition as a global alias for another definition.
111 /// If \p InEveryTU is true, we know that an equivalent alias can be produced
112 /// in every translation unit.
TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,GlobalDecl TargetDecl,bool InEveryTU)113 bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
114 GlobalDecl TargetDecl,
115 bool InEveryTU) {
116 if (!getCodeGenOpts().CXXCtorDtorAliases)
117 return true;
118
119 // The alias will use the linkage of the referent. If we can't
120 // support aliases with that linkage, fail.
121 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
122
123 // We can't use an alias if the linkage is not valid for one.
124 if (!llvm::GlobalAlias::isValidLinkage(Linkage))
125 return true;
126
127 // Don't create a weak alias for a dllexport'd symbol.
128 if (AliasDecl.getDecl()->hasAttr<DLLExportAttr>() &&
129 llvm::GlobalValue::isWeakForLinker(Linkage))
130 return true;
131
132 llvm::GlobalValue::LinkageTypes TargetLinkage =
133 getFunctionLinkage(TargetDecl);
134
135 // Check if we have it already.
136 StringRef MangledName = getMangledName(AliasDecl);
137 llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
138 if (Entry && !Entry->isDeclaration())
139 return false;
140 if (Replacements.count(MangledName))
141 return false;
142
143 // Derive the type for the alias.
144 llvm::PointerType *AliasType
145 = getTypes().GetFunctionType(AliasDecl)->getPointerTo();
146
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);
154
155 // Instead of creating as alias to a linkonce_odr, replace all of the uses
156 // of the aliasee.
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 Replacements[MangledName] = Aliasee;
166 return false;
167 }
168
169 if (!InEveryTU) {
170 // If we don't have a definition for the destructor yet, don't
171 // emit. We can't emit aliases to declarations; that's just not
172 // how aliases work.
173 if (Ref->isDeclaration())
174 return true;
175 }
176
177 // Don't create an alias to a linker weak symbol. This avoids producing
178 // different COMDATs in different TUs. Another option would be to
179 // output the alias both for weak_odr and linkonce_odr, but that
180 // requires explicit comdat support in the IL.
181 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
182 return true;
183
184 // Create the alias with no name.
185 auto *Alias = llvm::GlobalAlias::create(AliasType->getElementType(), 0,
186 Linkage, "", Aliasee, &getModule());
187
188 // Switch any previous uses to the alias.
189 if (Entry) {
190 assert(Entry->getType() == AliasType &&
191 "declaration exists with different type");
192 Alias->takeName(Entry);
193 Entry->replaceAllUsesWith(Alias);
194 Entry->eraseFromParent();
195 } else {
196 Alias->setName(MangledName);
197 }
198
199 // Finally, set up the alias with its proper name and attributes.
200 setAliasAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias);
201
202 return false;
203 }
204
codegenCXXStructor(const CXXMethodDecl * MD,StructorType Type)205 llvm::Function *CodeGenModule::codegenCXXStructor(const CXXMethodDecl *MD,
206 StructorType Type) {
207 const CGFunctionInfo &FnInfo =
208 getTypes().arrangeCXXStructorDeclaration(MD, Type);
209 auto *Fn = cast<llvm::Function>(
210 getAddrOfCXXStructor(MD, Type, &FnInfo, nullptr, true));
211
212 GlobalDecl GD;
213 if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD)) {
214 GD = GlobalDecl(DD, toCXXDtorType(Type));
215 } else {
216 const auto *CD = cast<CXXConstructorDecl>(MD);
217 GD = GlobalDecl(CD, toCXXCtorType(Type));
218 }
219
220 setFunctionLinkage(GD, Fn);
221 CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
222 setFunctionDefinitionAttributes(MD, Fn);
223 SetLLVMFunctionAttributesForDefinition(MD, Fn);
224 return Fn;
225 }
226
getAddrOfCXXStructor(const CXXMethodDecl * MD,StructorType Type,const CGFunctionInfo * FnInfo,llvm::FunctionType * FnType,bool DontDefer)227 llvm::GlobalValue *CodeGenModule::getAddrOfCXXStructor(
228 const CXXMethodDecl *MD, StructorType Type, const CGFunctionInfo *FnInfo,
229 llvm::FunctionType *FnType, bool DontDefer) {
230 GlobalDecl GD;
231 if (auto *CD = dyn_cast<CXXConstructorDecl>(MD)) {
232 GD = GlobalDecl(CD, toCXXCtorType(Type));
233 } else {
234 auto *DD = dyn_cast<CXXDestructorDecl>(MD);
235 GD = GlobalDecl(DD, toCXXDtorType(Type));
236 }
237
238 StringRef Name = getMangledName(GD);
239 if (llvm::GlobalValue *Existing = GetGlobalValue(Name))
240 return Existing;
241
242 if (!FnType) {
243 if (!FnInfo)
244 FnInfo = &getTypes().arrangeCXXStructorDeclaration(MD, Type);
245 FnType = getTypes().GetFunctionType(*FnInfo);
246 }
247
248 return cast<llvm::Function>(GetOrCreateLLVMFunction(Name, FnType, GD,
249 /*ForVTable=*/false,
250 DontDefer));
251 }
252
BuildAppleKextVirtualCall(CodeGenFunction & CGF,GlobalDecl GD,llvm::Type * Ty,const CXXRecordDecl * RD)253 static llvm::Value *BuildAppleKextVirtualCall(CodeGenFunction &CGF,
254 GlobalDecl GD,
255 llvm::Type *Ty,
256 const CXXRecordDecl *RD) {
257 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
258 "No kext in Microsoft ABI");
259 GD = GD.getCanonicalDecl();
260 CodeGenModule &CGM = CGF.CGM;
261 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
262 Ty = Ty->getPointerTo()->getPointerTo();
263 VTable = CGF.Builder.CreateBitCast(VTable, Ty);
264 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
265 uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
266 uint64_t AddressPoint =
267 CGM.getItaniumVTableContext().getVTableLayout(RD)
268 .getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
269 VTableIndex += AddressPoint;
270 llvm::Value *VFuncPtr =
271 CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt");
272 return CGF.Builder.CreateLoad(VFuncPtr);
273 }
274
275 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
276 /// indirect call to virtual functions. It makes the call through indexing
277 /// into the vtable.
278 llvm::Value *
BuildAppleKextVirtualCall(const CXXMethodDecl * MD,NestedNameSpecifier * Qual,llvm::Type * Ty)279 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
280 NestedNameSpecifier *Qual,
281 llvm::Type *Ty) {
282 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
283 "BuildAppleKextVirtualCall - bad Qual kind");
284
285 const Type *QTy = Qual->getAsType();
286 QualType T = QualType(QTy, 0);
287 const RecordType *RT = T->getAs<RecordType>();
288 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
289 const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
290
291 if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
292 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
293
294 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
295 }
296
297 /// BuildVirtualCall - This routine makes indirect vtable call for
298 /// call to virtual destructors. It returns 0 if it could not do it.
299 llvm::Value *
BuildAppleKextVirtualDestructorCall(const CXXDestructorDecl * DD,CXXDtorType Type,const CXXRecordDecl * RD)300 CodeGenFunction::BuildAppleKextVirtualDestructorCall(
301 const CXXDestructorDecl *DD,
302 CXXDtorType Type,
303 const CXXRecordDecl *RD) {
304 const auto *MD = cast<CXXMethodDecl>(DD);
305 // FIXME. Dtor_Base dtor is always direct!!
306 // It need be somehow inline expanded into the caller.
307 // -O does that. But need to support -O0 as well.
308 if (MD->isVirtual() && Type != Dtor_Base) {
309 // Compute the function type we're calling.
310 const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
311 DD, StructorType::Complete);
312 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
313 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);
314 }
315 return nullptr;
316 }
317