CGCXX.cpp revision 1f6f961293da9c2b1c23da2411c1b439a9502ed0 
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 "CGCXXABI.h"
17#include "CodeGenFunction.h"
18#include "CodeGenModule.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/Mangle.h"
25#include "clang/AST/StmtCXX.h"
26#include "clang/Frontend/CodeGenOptions.h"
27#include "llvm/ADT/StringExtras.h"
28using namespace clang;
29using namespace CodeGen;
30
31/// Determines whether the given function has a trivial body that does
32/// not require any specific codegen.
33static bool HasTrivialBody(const FunctionDecl *FD) {
34  Stmt *S = FD->getBody();
35  if (!S)
36    return true;
37  if (isa<CompoundStmt>(S) && cast<CompoundStmt>(S)->body_empty())
38    return true;
39  return false;
40}
41
42/// Try to emit a base destructor as an alias to its primary
43/// base-class destructor.
44bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
45  if (!getCodeGenOpts().CXXCtorDtorAliases)
46    return true;
47
48  // If the destructor doesn't have a trivial body, we have to emit it
49  // separately.
50  if (!HasTrivialBody(D))
51    return true;
52
53  const CXXRecordDecl *Class = D->getParent();
54
55  // If we need to manipulate a VTT parameter, give up.
56  if (Class->getNumVBases()) {
57    // Extra Credit:  passing extra parameters is perfectly safe
58    // in many calling conventions, so only bail out if the ctor's
59    // calling convention is nonstandard.
60    return true;
61  }
62
63  // If any field has a non-trivial destructor, we have to emit the
64  // destructor separately.
65  for (CXXRecordDecl::field_iterator I = Class->field_begin(),
66         E = Class->field_end(); I != E; ++I)
67    if ((*I)->getType().isDestructedType())
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();
100  if (!BaseD->isImplicit() && !BaseD->hasBody())
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.getBaseClassOffsetInBits(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  llvm::StringRef MangledName = getMangledName(AliasDecl);
169  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
170  if (Entry) {
171    assert(Entry->isDeclaration() && "definition already exists for alias");
172    assert(Entry->getType() == AliasType &&
173           "declaration exists with different type");
174    Alias->takeName(Entry);
175    Entry->replaceAllUsesWith(Alias);
176    Entry->eraseFromParent();
177  } else {
178    Alias->setName(MangledName);
179  }
180
181  // Finally, set up the alias with its proper name and attributes.
182  SetCommonAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias);
183
184  return false;
185}
186
187void CodeGenModule::EmitCXXConstructors(const CXXConstructorDecl *D) {
188  // The constructor used for constructing this as a complete class;
189  // constucts the virtual bases, then calls the base constructor.
190  EmitGlobal(GlobalDecl(D, Ctor_Complete));
191
192  // The constructor used for constructing this as a base class;
193  // ignores virtual bases.
194  EmitGlobal(GlobalDecl(D, Ctor_Base));
195}
196
197void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *ctor,
198                                       CXXCtorType ctorType) {
199  // The complete constructor is equivalent to the base constructor
200  // for classes with no virtual bases.  Try to emit it as an alias.
201  if (ctorType == Ctor_Complete &&
202      !ctor->getParent()->getNumVBases() &&
203      !TryEmitDefinitionAsAlias(GlobalDecl(ctor, Ctor_Complete),
204                                GlobalDecl(ctor, Ctor_Base)))
205    return;
206
207  const CGFunctionInfo &fnInfo = getTypes().getFunctionInfo(ctor, ctorType);
208
209  llvm::Function *fn =
210    cast<llvm::Function>(GetAddrOfCXXConstructor(ctor, ctorType, &fnInfo));
211  setFunctionLinkage(ctor, fn);
212
213  CodeGenFunction(*this).GenerateCode(GlobalDecl(ctor, ctorType), fn, fnInfo);
214
215  SetFunctionDefinitionAttributes(ctor, fn);
216  SetLLVMFunctionAttributesForDefinition(ctor, fn);
217}
218
219llvm::GlobalValue *
220CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *ctor,
221                                       CXXCtorType ctorType,
222                                       const CGFunctionInfo *fnInfo) {
223  GlobalDecl GD(ctor, ctorType);
224
225  llvm::StringRef name = getMangledName(GD);
226  if (llvm::GlobalValue *existing = GetGlobalValue(name))
227    return existing;
228
229  if (!fnInfo) fnInfo = &getTypes().getFunctionInfo(ctor, ctorType);
230
231  const FunctionProtoType *proto = ctor->getType()->castAs<FunctionProtoType>();
232  const llvm::FunctionType *fnType =
233    getTypes().GetFunctionType(*fnInfo, proto->isVariadic());
234  return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD,
235                                                      /*ForVTable=*/false));
236}
237
238void CodeGenModule::EmitCXXDestructors(const CXXDestructorDecl *D) {
239  // The destructor in a virtual table is always a 'deleting'
240  // destructor, which calls the complete destructor and then uses the
241  // appropriate operator delete.
242  if (D->isVirtual())
243    EmitGlobal(GlobalDecl(D, Dtor_Deleting));
244
245  // The destructor used for destructing this as a most-derived class;
246  // call the base destructor and then destructs any virtual bases.
247  EmitGlobal(GlobalDecl(D, Dtor_Complete));
248
249  // The destructor used for destructing this as a base class; ignores
250  // virtual bases.
251  EmitGlobal(GlobalDecl(D, Dtor_Base));
252}
253
254void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *dtor,
255                                      CXXDtorType dtorType) {
256  // The complete destructor is equivalent to the base destructor for
257  // classes with no virtual bases, so try to emit it as an alias.
258  if (dtorType == Dtor_Complete &&
259      !dtor->getParent()->getNumVBases() &&
260      !TryEmitDefinitionAsAlias(GlobalDecl(dtor, Dtor_Complete),
261                                GlobalDecl(dtor, Dtor_Base)))
262    return;
263
264  // The base destructor is equivalent to the base destructor of its
265  // base class if there is exactly one non-virtual base class with a
266  // non-trivial destructor, there are no fields with a non-trivial
267  // destructor, and the body of the destructor is trivial.
268  if (dtorType == Dtor_Base && !TryEmitBaseDestructorAsAlias(dtor))
269    return;
270
271  const CGFunctionInfo &fnInfo = getTypes().getFunctionInfo(dtor, dtorType);
272
273  llvm::Function *fn =
274    cast<llvm::Function>(GetAddrOfCXXDestructor(dtor, dtorType, &fnInfo));
275  setFunctionLinkage(dtor, fn);
276
277  CodeGenFunction(*this).GenerateCode(GlobalDecl(dtor, dtorType), fn, fnInfo);
278
279  SetFunctionDefinitionAttributes(dtor, fn);
280  SetLLVMFunctionAttributesForDefinition(dtor, fn);
281}
282
283llvm::GlobalValue *
284CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *dtor,
285                                      CXXDtorType dtorType,
286                                      const CGFunctionInfo *fnInfo) {
287  GlobalDecl GD(dtor, dtorType);
288
289  llvm::StringRef name = getMangledName(GD);
290  if (llvm::GlobalValue *existing = GetGlobalValue(name))
291    return existing;
292
293  if (!fnInfo) fnInfo = &getTypes().getFunctionInfo(dtor, dtorType);
294
295  const llvm::FunctionType *fnType =
296    getTypes().GetFunctionType(*fnInfo, false);
297
298  return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD,
299                                                      /*ForVTable=*/false));
300}
301
302static llvm::Value *BuildVirtualCall(CodeGenFunction &CGF, uint64_t VTableIndex,
303                                     llvm::Value *This, const llvm::Type *Ty) {
304  Ty = Ty->getPointerTo()->getPointerTo();
305
306  llvm::Value *VTable = CGF.GetVTablePtr(This, Ty);
307  llvm::Value *VFuncPtr =
308    CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfn");
309  return CGF.Builder.CreateLoad(VFuncPtr);
310}
311
312llvm::Value *
313CodeGenFunction::BuildVirtualCall(const CXXMethodDecl *MD, llvm::Value *This,
314                                  const llvm::Type *Ty) {
315  MD = MD->getCanonicalDecl();
316  uint64_t VTableIndex = CGM.getVTables().getMethodVTableIndex(MD);
317
318  return ::BuildVirtualCall(*this, VTableIndex, This, Ty);
319}
320
321/// BuildVirtualCall - This routine is to support gcc's kext ABI making
322/// indirect call to virtual functions. It makes the call through indexing
323/// into the vtable.
324llvm::Value *
325CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
326                                  NestedNameSpecifier *Qual,
327                                  const llvm::Type *Ty) {
328  llvm::Value *VTable = 0;
329  assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
330         "BuildAppleKextVirtualCall - bad Qual kind");
331
332  const Type *QTy = Qual->getAsType();
333  QualType T = QualType(QTy, 0);
334  const RecordType *RT = T->getAs<RecordType>();
335  assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
336  const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
337
338  if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))
339    return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
340
341  VTable = CGM.getVTables().GetAddrOfVTable(RD);
342  Ty = Ty->getPointerTo()->getPointerTo();
343  VTable = Builder.CreateBitCast(VTable, Ty);
344  assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
345  MD = MD->getCanonicalDecl();
346  uint64_t VTableIndex = CGM.getVTables().getMethodVTableIndex(MD);
347  uint64_t AddressPoint =
348    CGM.getVTables().getAddressPoint(BaseSubobject(RD, 0), RD);
349  VTableIndex += AddressPoint;
350  llvm::Value *VFuncPtr =
351    Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt");
352  return Builder.CreateLoad(VFuncPtr);
353}
354
355/// BuildVirtualCall - This routine makes indirect vtable call for
356/// call to virtual destructors. It returns 0 if it could not do it.
357llvm::Value *
358CodeGenFunction::BuildAppleKextVirtualDestructorCall(
359                                            const CXXDestructorDecl *DD,
360                                            CXXDtorType Type,
361                                            const CXXRecordDecl *RD) {
362  llvm::Value * Callee = 0;
363  const CXXMethodDecl *MD = cast<CXXMethodDecl>(DD);
364  // FIXME. Dtor_Base dtor is always direct!!
365  // It need be somehow inline expanded into the caller.
366  // -O does that. But need to support -O0 as well.
367  if (MD->isVirtual() && Type != Dtor_Base) {
368    // Compute the function type we're calling.
369    const CGFunctionInfo *FInfo =
370    &CGM.getTypes().getFunctionInfo(cast<CXXDestructorDecl>(MD),
371                                    Dtor_Complete);
372    const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
373    const llvm::Type *Ty
374      = CGM.getTypes().GetFunctionType(*FInfo, FPT->isVariadic());
375
376    llvm::Value *VTable = CGM.getVTables().GetAddrOfVTable(RD);
377    Ty = Ty->getPointerTo()->getPointerTo();
378    VTable = Builder.CreateBitCast(VTable, Ty);
379    DD = cast<CXXDestructorDecl>(DD->getCanonicalDecl());
380    uint64_t VTableIndex =
381      CGM.getVTables().getMethodVTableIndex(GlobalDecl(DD, Type));
382    uint64_t AddressPoint =
383      CGM.getVTables().getAddressPoint(BaseSubobject(RD, 0), RD);
384    VTableIndex += AddressPoint;
385    llvm::Value *VFuncPtr =
386      Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt");
387    Callee = Builder.CreateLoad(VFuncPtr);
388  }
389  return Callee;
390}
391
392llvm::Value *
393CodeGenFunction::BuildVirtualCall(const CXXDestructorDecl *DD, CXXDtorType Type,
394                                  llvm::Value *This, const llvm::Type *Ty) {
395  DD = cast<CXXDestructorDecl>(DD->getCanonicalDecl());
396  uint64_t VTableIndex =
397    CGM.getVTables().getMethodVTableIndex(GlobalDecl(DD, Type));
398
399  return ::BuildVirtualCall(*this, VTableIndex, This, Ty);
400}
401
402