clang  7.0.0svn
CGCXX.cpp
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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"
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.
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  GlobalDecl AliasDecl(D, Dtor_Base);
113  GlobalDecl TargetDecl(BaseD, Dtor_Base);
114 
115  // The alias will use the linkage of the referent. If we can't
116  // support aliases with that linkage, fail.
117  llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
118 
119  // We can't use an alias if the linkage is not valid for one.
120  if (!llvm::GlobalAlias::isValidLinkage(Linkage))
121  return true;
122 
123  llvm::GlobalValue::LinkageTypes TargetLinkage =
124  getFunctionLinkage(TargetDecl);
125 
126  // Check if we have it already.
127  StringRef MangledName = getMangledName(AliasDecl);
128  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
129  if (Entry && !Entry->isDeclaration())
130  return false;
131  if (Replacements.count(MangledName))
132  return false;
133 
134  // Derive the type for the alias.
135  llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
136  llvm::PointerType *AliasType = AliasValueType->getPointerTo();
137 
138  // Find the referent. Some aliases might require a bitcast, in
139  // which case the caller is responsible for ensuring the soundness
140  // of these semantics.
141  auto *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
142  llvm::Constant *Aliasee = Ref;
143  if (Ref->getType() != AliasType)
144  Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
145 
146  // Instead of creating as alias to a linkonce_odr, replace all of the uses
147  // of the aliasee.
148  if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
149  !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&
150  TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
151  // FIXME: An extern template instantiation will create functions with
152  // linkage "AvailableExternally". In libc++, some classes also define
153  // members with attribute "AlwaysInline" and expect no reference to
154  // be generated. It is desirable to reenable this optimisation after
155  // corresponding LLVM changes.
156  addReplacement(MangledName, Aliasee);
157  return false;
158  }
159 
160  // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
161  // template instantiation or a dllexported class, avoid forming it on COFF.
162  // A COFF weak external alias cannot satisfy a normal undefined symbol
163  // reference from another TU. The other TU must also mark the referenced
164  // symbol as weak, which we cannot rely on.
165  if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
166  getTriple().isOSBinFormatCOFF()) {
167  return true;
168  }
169 
170  // If we don't have a definition for the destructor yet or the definition is
171  // avaialable_externally, don't emit an alias. We can't emit aliases to
172  // declarations; that's just not how aliases work.
173  if (Ref->isDeclarationForLinker())
174  return true;
175 
176  // Don't create an alias to a linker weak symbol. This avoids producing
177  // different COMDATs in different TUs. Another option would be to
178  // output the alias both for weak_odr and linkonce_odr, but that
179  // requires explicit comdat support in the IL.
180  if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
181  return true;
182 
183  // Create the alias with no name.
184  auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
185  Aliasee, &getModule());
186 
187  // Destructors are always unnamed_addr.
188  Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
189 
190  // Switch any previous uses to the alias.
191  if (Entry) {
192  assert(Entry->getType() == AliasType &&
193  "declaration exists with different type");
194  Alias->takeName(Entry);
195  Entry->replaceAllUsesWith(Alias);
196  Entry->eraseFromParent();
197  } else {
198  Alias->setName(MangledName);
199  }
200 
201  // Finally, set up the alias with its proper name and attributes.
202  SetCommonAttributes(AliasDecl, Alias);
203 
204  return false;
205 }
206 
208  StructorType Type) {
209  const CGFunctionInfo &FnInfo =
211  auto *Fn = cast<llvm::Function>(
212  getAddrOfCXXStructor(MD, Type, &FnInfo, /*FnType=*/nullptr,
213  /*DontDefer=*/true, ForDefinition));
214 
215  GlobalDecl GD;
216  if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD)) {
217  GD = GlobalDecl(DD, toCXXDtorType(Type));
218  } else {
219  const auto *CD = cast<CXXConstructorDecl>(MD);
220  GD = GlobalDecl(CD, toCXXCtorType(Type));
221  }
222 
223  setFunctionLinkage(GD, Fn);
224 
225  CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
226  setNonAliasAttributes(GD, Fn);
228  return Fn;
229 }
230 
232  const CXXMethodDecl *MD, StructorType Type, const CGFunctionInfo *FnInfo,
233  llvm::FunctionType *FnType, bool DontDefer,
234  ForDefinition_t IsForDefinition) {
235  GlobalDecl GD;
236  if (auto *CD = dyn_cast<CXXConstructorDecl>(MD)) {
237  GD = GlobalDecl(CD, toCXXCtorType(Type));
238  } else {
239  // Always alias equivalent complete destructors to base destructors in the
240  // MS ABI.
241  if (getTarget().getCXXABI().isMicrosoft() &&
242  Type == StructorType::Complete && MD->getParent()->getNumVBases() == 0)
243  Type = StructorType::Base;
244  GD = GlobalDecl(cast<CXXDestructorDecl>(MD), toCXXDtorType(Type));
245  }
246 
247  if (!FnType) {
248  if (!FnInfo)
249  FnInfo = &getTypes().arrangeCXXStructorDeclaration(MD, Type);
250  FnType = getTypes().GetFunctionType(*FnInfo);
251  }
252 
253  return GetOrCreateLLVMFunction(
254  getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,
255  /*isThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);
256 }
257 
259  GlobalDecl GD,
260  llvm::Type *Ty,
261  const CXXRecordDecl *RD) {
262  assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
263  "No kext in Microsoft ABI");
264  CodeGenModule &CGM = CGF.CGM;
265  llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
266  Ty = Ty->getPointerTo()->getPointerTo();
267  VTable = CGF.Builder.CreateBitCast(VTable, Ty);
268  assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
269  uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
270  const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);
273  VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +
274  AddressPoint.AddressPointIndex;
275  llvm::Value *VFuncPtr =
276  CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt");
277  llvm::Value *VFunc =
278  CGF.Builder.CreateAlignedLoad(VFuncPtr, CGF.PointerAlignInBytes);
279  CGCallee Callee(GD.getDecl()->getCanonicalDecl(), VFunc);
280  return Callee;
281 }
282 
283 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
284 /// indirect call to virtual functions. It makes the call through indexing
285 /// into the vtable.
286 CGCallee
288  NestedNameSpecifier *Qual,
289  llvm::Type *Ty) {
290  assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
291  "BuildAppleKextVirtualCall - bad Qual kind");
292 
293  const Type *QTy = Qual->getAsType();
294  QualType T = QualType(QTy, 0);
295  const RecordType *RT = T->getAs<RecordType>();
296  assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
297  const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
298 
299  if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
300  return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
301 
302  return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
303 }
304 
305 /// BuildVirtualCall - This routine makes indirect vtable call for
306 /// call to virtual destructors. It returns 0 if it could not do it.
307 CGCallee
309  const CXXDestructorDecl *DD,
311  const CXXRecordDecl *RD) {
312  assert(DD->isVirtual() && Type != Dtor_Base);
313  // Compute the function type we're calling.
314  const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
316  llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
317  return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);
318 }
Defines the clang::ASTContext interface.
CGCallee BuildAppleKextVirtualCall(const CXXMethodDecl *MD, NestedNameSpecifier *Qual, llvm::Type *Ty)
BuildAppleKextVirtualCall - This routine is to support gcc&#39;s kext ABI making indirect call to virtual...
Definition: CGCXX.cpp:287
A (possibly-)qualified type.
Definition: Type.h:655
base_class_range bases()
Definition: DeclCXX.h:823
static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF, GlobalDecl GD, llvm::Type *Ty, const CXXRecordDecl *RD)
Definition: CGCXX.cpp:258
const CodeGenOptions & getCodeGenOpts() const
const ASTRecordLayout & getASTRecordLayout(const RecordDecl *D) const
Get or compute information about the layout of the specified record (struct/union/class) D...
FunctionType - C99 6.7.5.3 - Function Declarators.
Definition: Type.h:3205
CharUnits getBaseClassOffset(const CXXRecordDecl *Base) const
getBaseClassOffset - Get the offset, in chars, for the given base class.
Definition: RecordLayout.h:223
unsigned getNumVBases() const
Retrieves the number of virtual base classes of this class.
Definition: DeclCXX.h:838
bool isVirtual() const
Definition: DeclCXX.h:2088
The base class of the type hierarchy.
Definition: Type.h:1428
void setFunctionLinkage(GlobalDecl GD, llvm::Function *F)
void GenerateCode(GlobalDecl GD, llvm::Function *Fn, const CGFunctionInfo &FnInfo)
AddressPointLocation getAddressPoint(BaseSubobject Base) const
bool isZero() const
isZero - Test whether the quantity equals zero.
Definition: CharUnits.h:116
bool TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D)
Try to emit a base destructor as an alias to its primary base-class destructor.
Definition: CGCXX.cpp:34
const T * getAs() const
Member-template getAs<specific type>&#39;.
Definition: Type.h:6519
bool field_empty() const
Definition: Decl.h:3783
const CGFunctionInfo & arrangeCXXStructorDeclaration(const CXXMethodDecl *MD, StructorType Type)
Definition: CGCall.cpp:300
SpecifierKind getKind() const
Determine what kind of nested name specifier is stored.
Linkage
Describes the different kinds of linkage (C++ [basic.link], C99 6.2.2) that an entity may have...
Definition: Linkage.h:24
bool mayInsertExtraPadding(bool EmitRemark=false) const
Whether we are allowed to insert extra padding between fields.
Definition: Decl.cpp:4079
TargetCXXABI getCXXABI() const
Get the C++ ABI currently in use.
Definition: TargetInfo.h:1010
CodeGenFunction - This class organizes the per-function state that is used while generating LLVM code...
bool hasTrivialBody() const
Returns whether the function has a trivial body that does not require any specific codegen...
Definition: Decl.cpp:2637
CGCallee BuildAppleKextVirtualDestructorCall(const CXXDestructorDecl *DD, CXXDtorType Type, const CXXRecordDecl *RD)
BuildVirtualCall - This routine makes indirect vtable call for call to virtual destructors.
Definition: CGCXX.cpp:308
field_range fields() const
Definition: Decl.h:3775
llvm::Constant * getAddrOfCXXStructor(const CXXMethodDecl *MD, StructorType Type, const CGFunctionInfo *FnInfo=nullptr, llvm::FunctionType *FnType=nullptr, bool DontDefer=false, ForDefinition_t IsForDefinition=NotForDefinition)
Return the address of the constructor/destructor of the given type.
Definition: CGCXX.cpp:231
const Type * getAsType() const
Retrieve the type stored in this nested name specifier.
static CharUnits Zero()
Zero - Construct a CharUnits quantity of zero.
Definition: CharUnits.h:53
llvm::Function * codegenCXXStructor(const CXXMethodDecl *MD, StructorType Type)
Definition: CGCXX.cpp:207
CharUnits - This is an opaque type for sizes expressed in character units.
Definition: CharUnits.h:38
CXXDestructorDecl * getDestructor() const
Returns the destructor decl for this class.
Definition: DeclCXX.cpp:1663
virtual Decl * getCanonicalDecl()
Retrieves the "canonical" declaration of the given declaration.
Definition: DeclBase.h:875
bool hasAttr() const
Definition: DeclBase.h:536
ASTRecordLayout - This class contains layout information for one RecordDecl, which is a struct/union/...
Definition: RecordLayout.h:39
CXXDtorType
C++ destructor types.
Definition: ABI.h:34
Represents a C++ destructor within a class.
Definition: DeclCXX.h:2698
Base object dtor.
Definition: ABI.h:37
llvm::GlobalVariable::LinkageTypes getFunctionLinkage(GlobalDecl GD)
const TargetInfo & getTarget() const
void SetCommonAttributes(GlobalDecl GD, llvm::GlobalValue *GV)
Set attributes which are common to any form of a global definition (alias, Objective-C method...
GlobalDecl - represents a global declaration.
Definition: GlobalDecl.h:35
The l-value was considered opaque, so the alignment was determined from a type.
RecordDecl * getDecl() const
Definition: Type.h:4139
Address CreateBitCast(Address Addr, llvm::Type *Ty, const llvm::Twine &Name="")
Definition: CGBuilder.h:142
const Decl * getDecl() const
Definition: GlobalDecl.h:64
Represents a static or instance method of a struct/union/class.
Definition: DeclCXX.h:2043
Represents a C++ nested name specifier, such as "\::std::vector<int>::".
void SetLLVMFunctionAttributesForDefinition(const Decl *D, llvm::Function *F)
Set the LLVM function attributes which only apply to a function definition.
All available information about a concrete callee.
Definition: CGCall.h:67
Complete object dtor.
Definition: ABI.h:36
void addReplacement(StringRef Name, llvm::Constant *C)
llvm::Constant * GetAddrOfGlobal(GlobalDecl GD, ForDefinition_t IsForDefinition=NotForDefinition)
CGFunctionInfo - Class to encapsulate the information about a function definition.
This class organizes the cross-function state that is used while generating LLVM code.
llvm::GlobalValue * GetGlobalValue(StringRef Ref)
Dataflow Directional Tag Classes.
CXXDtorType toCXXDtorType(StructorType T)
Definition: CodeGenTypes.h:92
llvm::LoadInst * CreateAlignedLoad(llvm::Value *Addr, CharUnits Align, const llvm::Twine &Name="")
Definition: CGBuilder.h:91
std::unique_ptr< DiagnosticConsumer > create(StringRef OutputFile, DiagnosticOptions *Diags, bool MergeChildRecords=false)
Returns a DiagnosticConsumer that serializes diagnostics to a bitcode file.
const CXXRecordDecl * getParent() const
Returns the parent of this method declaration, which is the class in which this method is defined...
Definition: DeclCXX.h:2163
llvm::Module & getModule() const
A helper class that allows the use of isa/cast/dyncast to detect TagType objects of structs/unions/cl...
Definition: Type.h:4129
StringRef getMangledName(GlobalDecl GD)
Defines the C++ Decl subclasses, other than those for templates (found in DeclTemplate.h) and friends (in DeclFriend.h).
Represents a C++ struct/union/class.
Definition: DeclCXX.h:300
bool isMicrosoft() const
Is this ABI an MSVC-compatible ABI?
Definition: TargetCXXABI.h:154
CGCXXABI & getCXXABI() const
CXXCtorType toCXXCtorType(StructorType T)
Definition: CodeGenTypes.h:65
QualType getType() const
Definition: Decl.h:647
size_t getVTableOffset(size_t i) const
llvm::FunctionType * GetFunctionType(const CGFunctionInfo &Info)
GetFunctionType - Get the LLVM function type for.
Definition: CGCall.cpp:1544
const llvm::Triple & getTriple() const