CGCXX.cpp revision 8b2423361648c39a7d8a3c5e8129e12006deac32 
1//===--- CGDecl.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 "CodeGenFunction.h"
17#include "CodeGenModule.h"
18#include "Mangle.h"
19#include "clang/AST/ASTContext.h"
20#include "clang/AST/RecordLayout.h"
21#include "clang/AST/Decl.h"
22#include "clang/AST/DeclCXX.h"
23#include "clang/AST/DeclObjC.h"
24#include "clang/AST/StmtCXX.h"
25#include "clang/CodeGen/CodeGenOptions.h"
26#include "llvm/ADT/StringExtras.h"
27using namespace clang;
28using namespace CodeGen;
29
30/// Determines whether the given function has a trivial body that does
31/// not require any specific codegen.
32static bool HasTrivialBody(const FunctionDecl *FD) {
33  Stmt *S = FD->getBody();
34  if (!S)
35    return true;
36  if (isa<CompoundStmt>(S) && cast<CompoundStmt>(S)->body_empty())
37    return true;
38  return false;
39}
40
41/// Try to emit a base destructor as an alias to its primary
42/// base-class destructor.
43bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
44  if (!getCodeGenOpts().CXXCtorDtorAliases)
45    return true;
46
47  // If the destructor doesn't have a trivial body, we have to emit it
48  // separately.
49  if (!HasTrivialBody(D))
50    return true;
51
52  const CXXRecordDecl *Class = D->getParent();
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 fields have a non-trivial destructor, we have to emit it
63  // separately.
64  for (CXXRecordDecl::field_iterator I = Class->field_begin(),
65         E = Class->field_end(); I != E; ++I)
66    if (const RecordType *RT = (*I)->getType()->getAs<RecordType>())
67      if (!cast<CXXRecordDecl>(RT->getDecl())->hasTrivialDestructor())
68        return true;
69
70  // Try to find a unique base class with a non-trivial destructor.
71  const CXXRecordDecl *UniqueBase = 0;
72  for (CXXRecordDecl::base_class_const_iterator I = Class->bases_begin(),
73         E = Class->bases_end(); I != E; ++I) {
74
75    // We're in the base destructor, so skip virtual bases.
76    if (I->isVirtual()) continue;
77
78    // Skip base classes with trivial destructors.
79    const CXXRecordDecl *Base
80      = cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
81    if (Base->hasTrivialDestructor()) continue;
82
83    // If we've already found a base class with a non-trivial
84    // destructor, give up.
85    if (UniqueBase) return true;
86    UniqueBase = Base;
87  }
88
89  // If we didn't find any bases with a non-trivial destructor, then
90  // the base destructor is actually effectively trivial, which can
91  // happen if it was needlessly user-defined or if there are virtual
92  // bases with non-trivial destructors.
93  if (!UniqueBase)
94    return true;
95
96  /// If we don't have a definition for the destructor yet, don't
97  /// emit.  We can't emit aliases to declarations; that's just not
98  /// how aliases work.
99  const CXXDestructorDecl *BaseD = UniqueBase->getDestructor(getContext());
100  if (!BaseD->isImplicit() && !BaseD->getBody())
101    return true;
102
103  // If the base is at a non-zero offset, give up.
104  const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
105  if (ClassLayout.getBaseClassOffset(UniqueBase) != 0)
106    return true;
107
108  return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base),
109                                  GlobalDecl(BaseD, Dtor_Base));
110}
111
112/// Try to emit a definition as a global alias for another definition.
113bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
114                                             GlobalDecl TargetDecl) {
115  if (!getCodeGenOpts().CXXCtorDtorAliases)
116    return true;
117
118  // The alias will use the linkage of the referrent.  If we can't
119  // support aliases with that linkage, fail.
120  llvm::GlobalValue::LinkageTypes Linkage
121    = getFunctionLinkage(cast<FunctionDecl>(AliasDecl.getDecl()));
122
123  switch (Linkage) {
124  // We can definitely emit aliases to definitions with external linkage.
125  case llvm::GlobalValue::ExternalLinkage:
126  case llvm::GlobalValue::ExternalWeakLinkage:
127    break;
128
129  // Same with local linkage.
130  case llvm::GlobalValue::InternalLinkage:
131  case llvm::GlobalValue::PrivateLinkage:
132  case llvm::GlobalValue::LinkerPrivateLinkage:
133    break;
134
135  // We should try to support linkonce linkages.
136  case llvm::GlobalValue::LinkOnceAnyLinkage:
137  case llvm::GlobalValue::LinkOnceODRLinkage:
138    return true;
139
140  // Other linkages will probably never be supported.
141  default:
142    return true;
143  }
144
145  llvm::GlobalValue::LinkageTypes TargetLinkage
146    = getFunctionLinkage(cast<FunctionDecl>(TargetDecl.getDecl()));
147
148  if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
149    return true;
150
151  // Derive the type for the alias.
152  const llvm::PointerType *AliasType
153    = getTypes().GetFunctionType(AliasDecl)->getPointerTo();
154
155  // Find the referrent.  Some aliases might require a bitcast, in
156  // which case the caller is responsible for ensuring the soundness
157  // of these semantics.
158  llvm::GlobalValue *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
159  llvm::Constant *Aliasee = Ref;
160  if (Ref->getType() != AliasType)
161    Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
162
163  // Create the alias with no name.
164  llvm::GlobalAlias *Alias =
165    new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule());
166
167  // Switch any previous uses to the alias.
168  MangleBuffer MangledName;
169  getMangledName(MangledName, AliasDecl);
170  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
171  if (Entry) {
172    assert(Entry->isDeclaration() && "definition already exists for alias");
173    assert(Entry->getType() == AliasType &&
174           "declaration exists with different type");
175    Alias->takeName(Entry);
176    Entry->replaceAllUsesWith(Alias);
177    Entry->eraseFromParent();
178  } else {
179    Alias->setName(MangledName.getString());
180  }
181
182  // Finally, set up the alias with its proper name and attributes.
183  SetCommonAttributes(AliasDecl.getDecl(), Alias);
184
185  return false;
186}
187
188void CodeGenModule::EmitCXXConstructors(const CXXConstructorDecl *D) {
189  // The constructor used for constructing this as a complete class;
190  // constucts the virtual bases, then calls the base constructor.
191  EmitGlobal(GlobalDecl(D, Ctor_Complete));
192
193  // The constructor used for constructing this as a base class;
194  // ignores virtual bases.
195  EmitGlobal(GlobalDecl(D, Ctor_Base));
196}
197
198void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *D,
199                                       CXXCtorType Type) {
200  // The complete constructor is equivalent to the base constructor
201  // for classes with no virtual bases.  Try to emit it as an alias.
202  if (Type == Ctor_Complete &&
203      !D->getParent()->getNumVBases() &&
204      !TryEmitDefinitionAsAlias(GlobalDecl(D, Ctor_Complete),
205                                GlobalDecl(D, Ctor_Base)))
206    return;
207
208  llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXConstructor(D, Type));
209  setFunctionLinkage(D, Fn);
210
211  CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn);
212
213  SetFunctionDefinitionAttributes(D, Fn);
214  SetLLVMFunctionAttributesForDefinition(D, Fn);
215}
216
217llvm::GlobalValue *
218CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *D,
219                                       CXXCtorType Type) {
220  MangleBuffer Name;
221  getMangledCXXCtorName(Name, D, Type);
222  if (llvm::GlobalValue *V = GetGlobalValue(Name))
223    return V;
224
225  const FunctionProtoType *FPT = D->getType()->getAs<FunctionProtoType>();
226  const llvm::FunctionType *FTy =
227    getTypes().GetFunctionType(getTypes().getFunctionInfo(D, Type),
228                               FPT->isVariadic());
229  return cast<llvm::Function>(
230                      GetOrCreateLLVMFunction(Name, FTy, GlobalDecl(D, Type)));
231}
232
233void CodeGenModule::getMangledCXXCtorName(MangleBuffer &Name,
234                                          const CXXConstructorDecl *D,
235                                          CXXCtorType Type) {
236  getMangleContext().mangleCXXCtor(D, Type, Name.getBuffer());
237}
238
239void CodeGenModule::EmitCXXDestructors(const CXXDestructorDecl *D) {
240  // The destructor in a virtual table is always a 'deleting'
241  // destructor, which calls the complete destructor and then uses the
242  // appropriate operator delete.
243  if (D->isVirtual())
244    EmitGlobal(GlobalDecl(D, Dtor_Deleting));
245
246  // The destructor used for destructing this as a most-derived class;
247  // call the base destructor and then destructs any virtual bases.
248  EmitGlobal(GlobalDecl(D, Dtor_Complete));
249
250  // The destructor used for destructing this as a base class; ignores
251  // virtual bases.
252  EmitGlobal(GlobalDecl(D, Dtor_Base));
253}
254
255void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *D,
256                                      CXXDtorType Type) {
257  // The complete destructor is equivalent to the base destructor for
258  // classes with no virtual bases, so try to emit it as an alias.
259  if (Type == Dtor_Complete &&
260      !D->getParent()->getNumVBases() &&
261      !TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Complete),
262                                GlobalDecl(D, Dtor_Base)))
263    return;
264
265  // The base destructor is equivalent to the base destructor of its
266  // base class if there is exactly one non-virtual base class with a
267  // non-trivial destructor, there are no fields with a non-trivial
268  // destructor, and the body of the destructor is trivial.
269  if (Type == Dtor_Base && !TryEmitBaseDestructorAsAlias(D))
270    return;
271
272  llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXDestructor(D, Type));
273  setFunctionLinkage(D, Fn);
274
275  CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn);
276
277  SetFunctionDefinitionAttributes(D, Fn);
278  SetLLVMFunctionAttributesForDefinition(D, Fn);
279}
280
281llvm::GlobalValue *
282CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *D,
283                                      CXXDtorType Type) {
284  MangleBuffer Name;
285  getMangledCXXDtorName(Name, D, Type);
286  if (llvm::GlobalValue *V = GetGlobalValue(Name))
287    return V;
288
289  const llvm::FunctionType *FTy =
290    getTypes().GetFunctionType(getTypes().getFunctionInfo(D, Type), false);
291
292  return cast<llvm::Function>(
293                      GetOrCreateLLVMFunction(Name, FTy, GlobalDecl(D, Type)));
294}
295
296void CodeGenModule::getMangledCXXDtorName(MangleBuffer &Name,
297                                          const CXXDestructorDecl *D,
298                                          CXXDtorType Type) {
299  getMangleContext().mangleCXXDtor(D, Type, Name.getBuffer());
300}
301
302static llvm::Value *BuildVirtualCall(CodeGenFunction &CGF, uint64_t VTableIndex,
303                                     llvm::Value *This, const llvm::Type *Ty) {
304  Ty = Ty->getPointerTo()->getPointerTo()->getPointerTo();
305
306  llvm::Value *VTable = CGF.Builder.CreateBitCast(This, Ty);
307  VTable = CGF.Builder.CreateLoad(VTable);
308
309  llvm::Value *VFuncPtr =
310    CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfn");
311  return CGF.Builder.CreateLoad(VFuncPtr);
312}
313
314llvm::Value *
315CodeGenFunction::BuildVirtualCall(const CXXMethodDecl *MD, llvm::Value *This,
316                                  const llvm::Type *Ty) {
317  MD = MD->getCanonicalDecl();
318  uint64_t VTableIndex = CGM.getVTables().getMethodVTableIndex(MD);
319
320  return ::BuildVirtualCall(*this, VTableIndex, This, Ty);
321}
322
323llvm::Value *
324CodeGenFunction::BuildVirtualCall(const CXXDestructorDecl *DD, CXXDtorType Type,
325                                  llvm::Value *&This, const llvm::Type *Ty) {
326  DD = cast<CXXDestructorDecl>(DD->getCanonicalDecl());
327  uint64_t VTableIndex =
328    CGM.getVTables().getMethodVTableIndex(GlobalDecl(DD, Type));
329
330  return ::BuildVirtualCall(*this, VTableIndex, This, Ty);
331}
332