clang  6.0.0svn
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 
113  GlobalDecl(BaseD, Dtor_Base));
114 }
115 
116 /// Try to emit a definition as a global alias for another definition.
117 /// If \p InEveryTU is true, we know that an equivalent alias can be produced
118 /// in every translation unit.
120  GlobalDecl TargetDecl) {
121  if (!getCodeGenOpts().CXXCtorDtorAliases)
122  return true;
123 
124  // The alias will use the linkage of the referent. If we can't
125  // support aliases with that linkage, fail.
126  llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
127 
128  // We can't use an alias if the linkage is not valid for one.
129  if (!llvm::GlobalAlias::isValidLinkage(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::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
145  llvm::PointerType *AliasType = AliasValueType->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  addReplacement(MangledName, Aliasee);
166  return false;
167  }
168 
169  // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
170  // template instantiation or a dllexported class, avoid forming it on COFF.
171  // A COFF weak external alias cannot satisfy a normal undefined symbol
172  // reference from another TU. The other TU must also mark the referenced
173  // symbol as weak, which we cannot rely on.
174  if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
175  getTriple().isOSBinFormatCOFF()) {
176  return true;
177  }
178 
179  // If we don't have a definition for the destructor yet or the definition is
180  // avaialable_externally, don't emit an alias. We can't emit aliases to
181  // declarations; that's just not how aliases work.
182  if (Ref->isDeclarationForLinker())
183  return true;
184 
185  // Don't create an alias to a linker weak symbol. This avoids producing
186  // different COMDATs in different TUs. Another option would be to
187  // output the alias both for weak_odr and linkonce_odr, but that
188  // requires explicit comdat support in the IL.
189  if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
190  return true;
191 
192  // Create the alias with no name.
193  auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
194  Aliasee, &getModule());
195 
196  // Switch any previous uses to the alias.
197  if (Entry) {
198  assert(Entry->getType() == AliasType &&
199  "declaration exists with different type");
200  Alias->takeName(Entry);
201  Entry->replaceAllUsesWith(Alias);
202  Entry->eraseFromParent();
203  } else {
204  Alias->setName(MangledName);
205  }
206 
207  // Finally, set up the alias with its proper name and attributes.
208  setAliasAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias);
209 
210  return false;
211 }
212 
214  StructorType Type) {
215  const CGFunctionInfo &FnInfo =
217  auto *Fn = cast<llvm::Function>(
218  getAddrOfCXXStructor(MD, Type, &FnInfo, /*FnType=*/nullptr,
219  /*DontDefer=*/true, ForDefinition));
220 
221  GlobalDecl GD;
222  if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD)) {
223  GD = GlobalDecl(DD, toCXXDtorType(Type));
224  } else {
225  const auto *CD = cast<CXXConstructorDecl>(MD);
226  GD = GlobalDecl(CD, toCXXCtorType(Type));
227  }
228 
229  setFunctionLinkage(GD, Fn);
231 
232  CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
235  return Fn;
236 }
237 
239  const CXXMethodDecl *MD, StructorType Type, const CGFunctionInfo *FnInfo,
240  llvm::FunctionType *FnType, bool DontDefer,
241  ForDefinition_t IsForDefinition) {
242  GlobalDecl GD;
243  if (auto *CD = dyn_cast<CXXConstructorDecl>(MD)) {
244  GD = GlobalDecl(CD, toCXXCtorType(Type));
245  } else {
246  GD = GlobalDecl(cast<CXXDestructorDecl>(MD), toCXXDtorType(Type));
247  }
248 
249  if (!FnType) {
250  if (!FnInfo)
251  FnInfo = &getTypes().arrangeCXXStructorDeclaration(MD, Type);
252  FnType = getTypes().GetFunctionType(*FnInfo);
253  }
254 
255  return GetOrCreateLLVMFunction(
256  getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,
257  /*isThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);
258 }
259 
261  GlobalDecl GD,
262  llvm::Type *Ty,
263  const CXXRecordDecl *RD) {
264  assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
265  "No kext in Microsoft ABI");
266  GD = GD.getCanonicalDecl();
267  CodeGenModule &CGM = CGF.CGM;
268  llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
269  Ty = Ty->getPointerTo()->getPointerTo();
270  VTable = CGF.Builder.CreateBitCast(VTable, Ty);
271  assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
272  uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
273  const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);
276  VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +
277  AddressPoint.AddressPointIndex;
278  llvm::Value *VFuncPtr =
279  CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt");
280  llvm::Value *VFunc =
281  CGF.Builder.CreateAlignedLoad(VFuncPtr, CGF.PointerAlignInBytes);
282  CGCallee Callee(GD.getDecl(), VFunc);
283  return Callee;
284 }
285 
286 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
287 /// indirect call to virtual functions. It makes the call through indexing
288 /// into the vtable.
289 CGCallee
291  NestedNameSpecifier *Qual,
292  llvm::Type *Ty) {
293  assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
294  "BuildAppleKextVirtualCall - bad Qual kind");
295 
296  const Type *QTy = Qual->getAsType();
297  QualType T = QualType(QTy, 0);
298  const RecordType *RT = T->getAs<RecordType>();
299  assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
300  const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
301 
302  if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
303  return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
304 
305  return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
306 }
307 
308 /// BuildVirtualCall - This routine makes indirect vtable call for
309 /// call to virtual destructors. It returns 0 if it could not do it.
310 CGCallee
312  const CXXDestructorDecl *DD,
314  const CXXRecordDecl *RD) {
315  assert(DD->isVirtual() && Type != Dtor_Base);
316  // Compute the function type we're calling.
317  const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
319  llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
320  return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);
321 }
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:290
A (possibly-)qualified type.
Definition: Type.h:653
base_class_range bases()
Definition: DeclCXX.h:773
static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF, GlobalDecl GD, llvm::Type *Ty, const CXXRecordDecl *RD)
Definition: CGCXX.cpp:260
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:3058
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:788
bool isVirtual() const
Definition: DeclCXX.h:2009
void setAliasAttributes(const Decl *D, llvm::GlobalValue *GV)
Set attributes which must be preserved by an alias.
GlobalDecl getCanonicalDecl() const
Definition: GlobalDecl.h:56
The base class of the type hierarchy.
Definition: Type.h:1353
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
void setFunctionDefinitionAttributes(const FunctionDecl *D, llvm::Function *F)
Set attributes for a global definition.
const T * getAs() const
Member-template getAs<specific type>&#39;.
Definition: Type.h:6307
void setFunctionDLLStorageClass(GlobalDecl GD, llvm::Function *F)
Set the DLL storage class on F.
bool field_empty() const
Definition: Decl.h:3618
const CGFunctionInfo & arrangeCXXStructorDeclaration(const CXXMethodDecl *MD, StructorType Type)
Definition: CGCall.cpp:288
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:25
bool mayInsertExtraPadding(bool EmitRemark=false) const
Whether we are allowed to insert extra padding between fields.
Definition: Decl.cpp:3984
TargetCXXABI getCXXABI() const
Get the C++ ABI currently in use.
Definition: TargetInfo.h:859
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:2587
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:311
field_range fields() const
Definition: Decl.h:3609
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:238
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:213
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:1458
uint64_t getMethodVTableIndex(GlobalDecl GD)
Locate a virtual function in the vtable.
bool hasAttr() const
Definition: DeclBase.h:535
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
const FunctionProtoType * T
Represents a C++ destructor within a class.
Definition: DeclCXX.h:2620
Base object dtor.
Definition: ABI.h:37
llvm::GlobalVariable::LinkageTypes getFunctionLinkage(GlobalDecl GD)
const TargetInfo & getTarget() const
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:3988
bool TryEmitDefinitionAsAlias(GlobalDecl Alias, GlobalDecl Target)
Try to emit a definition as a global alias for another definition.
Definition: CGCXX.cpp:119
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:1964
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:66
Complete object dtor.
Definition: ABI.h:36
ItaniumVTableContext & getItaniumVTableContext()
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.
virtual llvm::GlobalVariable * getAddrOfVTable(const CXXRecordDecl *RD, CharUnits VPtrOffset)=0
Get the address of the vtable for the given record decl which should be used for the vptr at the give...
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:2085
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:3978
StringRef getMangledName(GlobalDecl GD)
Defines the C++ Decl subclasses, other than those for templates (found in DeclTemplate.h) and friends (in DeclFriend.h).
const VTableLayout & getVTableLayout(const CXXRecordDecl *RD)
Represents a C++ struct/union/class.
Definition: DeclCXX.h:299
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:638
size_t getVTableOffset(size_t i) const
llvm::FunctionType * GetFunctionType(const CGFunctionInfo &Info)
GetFunctionType - Get the LLVM function type for.
Definition: CGCall.cpp:1524
const llvm::Triple & getTriple() const