1//===--- CGVTables.cpp - Emit LLVM Code for C++ vtables -------------------===//
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 of virtual tables.
11//
12//===----------------------------------------------------------------------===//
13
14#include "CodeGenFunction.h"
15#include "CGCXXABI.h"
16#include "CodeGenModule.h"
17#include "clang/AST/CXXInheritance.h"
18#include "clang/AST/RecordLayout.h"
19#include "clang/CodeGen/CGFunctionInfo.h"
20#include "clang/Frontend/CodeGenOptions.h"
21#include "llvm/ADT/DenseSet.h"
22#include "llvm/ADT/SetVector.h"
23#include "llvm/Support/Compiler.h"
24#include "llvm/Support/Format.h"
25#include "llvm/Transforms/Utils/Cloning.h"
26#include <algorithm>
27#include <cstdio>
28
29using namespace clang;
30using namespace CodeGen;
31
32CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
33    : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
34
35llvm::Constant *CodeGenModule::GetAddrOfThunk(GlobalDecl GD,
36                                              const ThunkInfo &Thunk) {
37  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
38
39  // Compute the mangled name.
40  SmallString<256> Name;
41  llvm::raw_svector_ostream Out(Name);
42  if (const CXXDestructorDecl* DD = dyn_cast<CXXDestructorDecl>(MD))
43    getCXXABI().getMangleContext().mangleCXXDtorThunk(DD, GD.getDtorType(),
44                                                      Thunk.This, Out);
45  else
46    getCXXABI().getMangleContext().mangleThunk(MD, Thunk, Out);
47  Out.flush();
48
49  llvm::Type *Ty = getTypes().GetFunctionTypeForVTable(GD);
50  return GetOrCreateLLVMFunction(Name, Ty, GD, /*ForVTable=*/true,
51                                 /*DontDefer*/ true);
52}
53
54static void setThunkVisibility(CodeGenModule &CGM, const CXXMethodDecl *MD,
55                               const ThunkInfo &Thunk, llvm::Function *Fn) {
56  CGM.setGlobalVisibility(Fn, MD);
57}
58
59#ifndef NDEBUG
60static bool similar(const ABIArgInfo &infoL, CanQualType typeL,
61                    const ABIArgInfo &infoR, CanQualType typeR) {
62  return (infoL.getKind() == infoR.getKind() &&
63          (typeL == typeR ||
64           (isa<PointerType>(typeL) && isa<PointerType>(typeR)) ||
65           (isa<ReferenceType>(typeL) && isa<ReferenceType>(typeR))));
66}
67#endif
68
69static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
70                                      QualType ResultType, RValue RV,
71                                      const ThunkInfo &Thunk) {
72  // Emit the return adjustment.
73  bool NullCheckValue = !ResultType->isReferenceType();
74
75  llvm::BasicBlock *AdjustNull = nullptr;
76  llvm::BasicBlock *AdjustNotNull = nullptr;
77  llvm::BasicBlock *AdjustEnd = nullptr;
78
79  llvm::Value *ReturnValue = RV.getScalarVal();
80
81  if (NullCheckValue) {
82    AdjustNull = CGF.createBasicBlock("adjust.null");
83    AdjustNotNull = CGF.createBasicBlock("adjust.notnull");
84    AdjustEnd = CGF.createBasicBlock("adjust.end");
85
86    llvm::Value *IsNull = CGF.Builder.CreateIsNull(ReturnValue);
87    CGF.Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);
88    CGF.EmitBlock(AdjustNotNull);
89  }
90
91  ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(CGF, ReturnValue,
92                                                            Thunk.Return);
93
94  if (NullCheckValue) {
95    CGF.Builder.CreateBr(AdjustEnd);
96    CGF.EmitBlock(AdjustNull);
97    CGF.Builder.CreateBr(AdjustEnd);
98    CGF.EmitBlock(AdjustEnd);
99
100    llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
101    PHI->addIncoming(ReturnValue, AdjustNotNull);
102    PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
103                     AdjustNull);
104    ReturnValue = PHI;
105  }
106
107  return RValue::get(ReturnValue);
108}
109
110// This function does roughly the same thing as GenerateThunk, but in a
111// very different way, so that va_start and va_end work correctly.
112// FIXME: This function assumes "this" is the first non-sret LLVM argument of
113//        a function, and that there is an alloca built in the entry block
114//        for all accesses to "this".
115// FIXME: This function assumes there is only one "ret" statement per function.
116// FIXME: Cloning isn't correct in the presence of indirect goto!
117// FIXME: This implementation of thunks bloats codesize by duplicating the
118//        function definition.  There are alternatives:
119//        1. Add some sort of stub support to LLVM for cases where we can
120//           do a this adjustment, then a sibcall.
121//        2. We could transform the definition to take a va_list instead of an
122//           actual variable argument list, then have the thunks (including a
123//           no-op thunk for the regular definition) call va_start/va_end.
124//           There's a bit of per-call overhead for this solution, but it's
125//           better for codesize if the definition is long.
126void CodeGenFunction::GenerateVarArgsThunk(
127                                      llvm::Function *Fn,
128                                      const CGFunctionInfo &FnInfo,
129                                      GlobalDecl GD, const ThunkInfo &Thunk) {
130  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
131  const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
132  QualType ResultType = FPT->getReturnType();
133
134  // Get the original function
135  assert(FnInfo.isVariadic());
136  llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);
137  llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
138  llvm::Function *BaseFn = cast<llvm::Function>(Callee);
139
140  // Clone to thunk.
141  llvm::ValueToValueMapTy VMap;
142  llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap,
143                                              /*ModuleLevelChanges=*/false);
144  CGM.getModule().getFunctionList().push_back(NewFn);
145  Fn->replaceAllUsesWith(NewFn);
146  NewFn->takeName(Fn);
147  Fn->eraseFromParent();
148  Fn = NewFn;
149
150  // "Initialize" CGF (minimally).
151  CurFn = Fn;
152
153  // Get the "this" value
154  llvm::Function::arg_iterator AI = Fn->arg_begin();
155  if (CGM.ReturnTypeUsesSRet(FnInfo))
156    ++AI;
157
158  // Find the first store of "this", which will be to the alloca associated
159  // with "this".
160  llvm::Value *ThisPtr = &*AI;
161  llvm::BasicBlock *EntryBB = Fn->begin();
162  llvm::Instruction *ThisStore = nullptr;
163  for (llvm::BasicBlock::iterator I = EntryBB->begin(), E = EntryBB->end();
164       I != E; I++) {
165    if (isa<llvm::StoreInst>(I) && I->getOperand(0) == ThisPtr) {
166      ThisStore = cast<llvm::StoreInst>(I);
167      break;
168    }
169  }
170  assert(ThisStore && "Store of this should be in entry block?");
171  // Adjust "this", if necessary.
172  Builder.SetInsertPoint(ThisStore);
173  llvm::Value *AdjustedThisPtr =
174      CGM.getCXXABI().performThisAdjustment(*this, ThisPtr, Thunk.This);
175  ThisStore->setOperand(0, AdjustedThisPtr);
176
177  if (!Thunk.Return.isEmpty()) {
178    // Fix up the returned value, if necessary.
179    for (llvm::Function::iterator I = Fn->begin(), E = Fn->end(); I != E; I++) {
180      llvm::Instruction *T = I->getTerminator();
181      if (isa<llvm::ReturnInst>(T)) {
182        RValue RV = RValue::get(T->getOperand(0));
183        T->eraseFromParent();
184        Builder.SetInsertPoint(&*I);
185        RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
186        Builder.CreateRet(RV.getScalarVal());
187        break;
188      }
189    }
190  }
191}
192
193void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
194                                 const CGFunctionInfo &FnInfo) {
195  assert(!CurGD.getDecl() && "CurGD was already set!");
196  CurGD = GD;
197
198  // Build FunctionArgs.
199  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
200  QualType ThisType = MD->getThisType(getContext());
201  const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
202  QualType ResultType =
203      CGM.getCXXABI().HasThisReturn(GD) ? ThisType : FPT->getReturnType();
204  FunctionArgList FunctionArgs;
205
206  // Create the implicit 'this' parameter declaration.
207  CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
208
209  // Add the rest of the parameters.
210  for (FunctionDecl::param_const_iterator I = MD->param_begin(),
211                                          E = MD->param_end();
212       I != E; ++I)
213    FunctionArgs.push_back(*I);
214
215  if (isa<CXXDestructorDecl>(MD))
216    CGM.getCXXABI().addImplicitStructorParams(*this, ResultType, FunctionArgs);
217
218  // Start defining the function.
219  StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
220                MD->getLocation(), SourceLocation());
221
222  // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
223  CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
224  CXXThisValue = CXXABIThisValue;
225}
226
227void CodeGenFunction::EmitCallAndReturnForThunk(GlobalDecl GD,
228                                                llvm::Value *Callee,
229                                                const ThunkInfo *Thunk) {
230  assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
231         "Please use a new CGF for this thunk");
232  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
233
234  // Adjust the 'this' pointer if necessary
235  llvm::Value *AdjustedThisPtr = Thunk ? CGM.getCXXABI().performThisAdjustment(
236                                             *this, LoadCXXThis(), Thunk->This)
237                                       : LoadCXXThis();
238
239  // Start building CallArgs.
240  CallArgList CallArgs;
241  QualType ThisType = MD->getThisType(getContext());
242  CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
243
244  if (isa<CXXDestructorDecl>(MD))
245    CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, GD, CallArgs);
246
247  // Add the rest of the arguments.
248  for (FunctionDecl::param_const_iterator I = MD->param_begin(),
249       E = MD->param_end(); I != E; ++I)
250    EmitDelegateCallArg(CallArgs, *I, (*I)->getLocStart());
251
252  const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
253
254#ifndef NDEBUG
255  const CGFunctionInfo &CallFnInfo =
256    CGM.getTypes().arrangeCXXMethodCall(CallArgs, FPT,
257                                       RequiredArgs::forPrototypePlus(FPT, 1));
258  assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
259         CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
260         CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
261  assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
262         similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
263                 CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
264  assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
265  for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
266    assert(similar(CallFnInfo.arg_begin()[i].info,
267                   CallFnInfo.arg_begin()[i].type,
268                   CurFnInfo->arg_begin()[i].info,
269                   CurFnInfo->arg_begin()[i].type));
270#endif
271
272  // Determine whether we have a return value slot to use.
273  QualType ResultType =
274      CGM.getCXXABI().HasThisReturn(GD) ? ThisType : FPT->getReturnType();
275  ReturnValueSlot Slot;
276  if (!ResultType->isVoidType() &&
277      CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect &&
278      !hasScalarEvaluationKind(CurFnInfo->getReturnType()))
279    Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified());
280
281  // Now emit our call.
282  RValue RV = EmitCall(*CurFnInfo, Callee, Slot, CallArgs, MD);
283
284  // Consider return adjustment if we have ThunkInfo.
285  if (Thunk && !Thunk->Return.isEmpty())
286    RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
287
288  // Emit return.
289  if (!ResultType->isVoidType() && Slot.isNull())
290    CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
291
292  // Disable the final ARC autorelease.
293  AutoreleaseResult = false;
294
295  FinishFunction();
296}
297
298void CodeGenFunction::GenerateThunk(llvm::Function *Fn,
299                                    const CGFunctionInfo &FnInfo,
300                                    GlobalDecl GD, const ThunkInfo &Thunk) {
301  StartThunk(Fn, GD, FnInfo);
302
303  // Get our callee.
304  llvm::Type *Ty =
305    CGM.getTypes().GetFunctionType(CGM.getTypes().arrangeGlobalDeclaration(GD));
306  llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
307
308  // Make the call and return the result.
309  EmitCallAndReturnForThunk(GD, Callee, &Thunk);
310
311  // Set the right linkage.
312  CGM.setFunctionLinkage(GD, Fn);
313
314  // Set the right visibility.
315  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
316  setThunkVisibility(CGM, MD, Thunk, Fn);
317}
318
319void CodeGenVTables::emitThunk(GlobalDecl GD, const ThunkInfo &Thunk,
320                               bool ForVTable) {
321  const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeGlobalDeclaration(GD);
322
323  // FIXME: re-use FnInfo in this computation.
324  llvm::Constant *C = CGM.GetAddrOfThunk(GD, Thunk);
325  llvm::GlobalValue *Entry;
326
327  // Strip off a bitcast if we got one back.
328  if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(C)) {
329    assert(CE->getOpcode() == llvm::Instruction::BitCast);
330    Entry = cast<llvm::GlobalValue>(CE->getOperand(0));
331  } else {
332    Entry = cast<llvm::GlobalValue>(C);
333  }
334
335  // There's already a declaration with the same name, check if it has the same
336  // type or if we need to replace it.
337  if (Entry->getType()->getElementType() !=
338      CGM.getTypes().GetFunctionTypeForVTable(GD)) {
339    llvm::GlobalValue *OldThunkFn = Entry;
340
341    // If the types mismatch then we have to rewrite the definition.
342    assert(OldThunkFn->isDeclaration() &&
343           "Shouldn't replace non-declaration");
344
345    // Remove the name from the old thunk function and get a new thunk.
346    OldThunkFn->setName(StringRef());
347    Entry = cast<llvm::GlobalValue>(CGM.GetAddrOfThunk(GD, Thunk));
348
349    // If needed, replace the old thunk with a bitcast.
350    if (!OldThunkFn->use_empty()) {
351      llvm::Constant *NewPtrForOldDecl =
352        llvm::ConstantExpr::getBitCast(Entry, OldThunkFn->getType());
353      OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
354    }
355
356    // Remove the old thunk.
357    OldThunkFn->eraseFromParent();
358  }
359
360  llvm::Function *ThunkFn = cast<llvm::Function>(Entry);
361  bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
362  bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
363
364  if (!ThunkFn->isDeclaration()) {
365    if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
366      // There is already a thunk emitted for this function, do nothing.
367      return;
368    }
369
370    // Change the linkage.
371    CGM.setFunctionLinkage(GD, ThunkFn);
372    return;
373  }
374
375  CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
376
377  if (ThunkFn->isVarArg()) {
378    // Varargs thunks are special; we can't just generate a call because
379    // we can't copy the varargs.  Our implementation is rather
380    // expensive/sucky at the moment, so don't generate the thunk unless
381    // we have to.
382    // FIXME: Do something better here; GenerateVarArgsThunk is extremely ugly.
383    if (!UseAvailableExternallyLinkage) {
384      CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, Thunk);
385      CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
386                                      !Thunk.Return.isEmpty());
387    }
388  } else {
389    // Normal thunk body generation.
390    CodeGenFunction(CGM).GenerateThunk(ThunkFn, FnInfo, GD, Thunk);
391    CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
392                                    !Thunk.Return.isEmpty());
393  }
394}
395
396void CodeGenVTables::maybeEmitThunkForVTable(GlobalDecl GD,
397                                             const ThunkInfo &Thunk) {
398  // If the ABI has key functions, only the TU with the key function should emit
399  // the thunk. However, we can allow inlining of thunks if we emit them with
400  // available_externally linkage together with vtables when optimizations are
401  // enabled.
402  if (CGM.getTarget().getCXXABI().hasKeyFunctions() &&
403      !CGM.getCodeGenOpts().OptimizationLevel)
404    return;
405
406  // We can't emit thunks for member functions with incomplete types.
407  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
408  if (!CGM.getTypes().isFuncTypeConvertible(
409           MD->getType()->castAs<FunctionType>()))
410    return;
411
412  emitThunk(GD, Thunk, /*ForVTable=*/true);
413}
414
415void CodeGenVTables::EmitThunks(GlobalDecl GD)
416{
417  const CXXMethodDecl *MD =
418    cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
419
420  // We don't need to generate thunks for the base destructor.
421  if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
422    return;
423
424  const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
425      VTContext->getThunkInfo(GD);
426
427  if (!ThunkInfoVector)
428    return;
429
430  for (unsigned I = 0, E = ThunkInfoVector->size(); I != E; ++I)
431    emitThunk(GD, (*ThunkInfoVector)[I], /*ForVTable=*/false);
432}
433
434llvm::Constant *CodeGenVTables::CreateVTableInitializer(
435    const CXXRecordDecl *RD, const VTableComponent *Components,
436    unsigned NumComponents, const VTableLayout::VTableThunkTy *VTableThunks,
437    unsigned NumVTableThunks, llvm::Constant *RTTI) {
438  SmallVector<llvm::Constant *, 64> Inits;
439
440  llvm::Type *Int8PtrTy = CGM.Int8PtrTy;
441
442  llvm::Type *PtrDiffTy =
443    CGM.getTypes().ConvertType(CGM.getContext().getPointerDiffType());
444
445  unsigned NextVTableThunkIndex = 0;
446
447  llvm::Constant *PureVirtualFn = nullptr, *DeletedVirtualFn = nullptr;
448
449  for (unsigned I = 0; I != NumComponents; ++I) {
450    VTableComponent Component = Components[I];
451
452    llvm::Constant *Init = nullptr;
453
454    switch (Component.getKind()) {
455    case VTableComponent::CK_VCallOffset:
456      Init = llvm::ConstantInt::get(PtrDiffTy,
457                                    Component.getVCallOffset().getQuantity());
458      Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
459      break;
460    case VTableComponent::CK_VBaseOffset:
461      Init = llvm::ConstantInt::get(PtrDiffTy,
462                                    Component.getVBaseOffset().getQuantity());
463      Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
464      break;
465    case VTableComponent::CK_OffsetToTop:
466      Init = llvm::ConstantInt::get(PtrDiffTy,
467                                    Component.getOffsetToTop().getQuantity());
468      Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
469      break;
470    case VTableComponent::CK_RTTI:
471      Init = llvm::ConstantExpr::getBitCast(RTTI, Int8PtrTy);
472      break;
473    case VTableComponent::CK_FunctionPointer:
474    case VTableComponent::CK_CompleteDtorPointer:
475    case VTableComponent::CK_DeletingDtorPointer: {
476      GlobalDecl GD;
477
478      // Get the right global decl.
479      switch (Component.getKind()) {
480      default:
481        llvm_unreachable("Unexpected vtable component kind");
482      case VTableComponent::CK_FunctionPointer:
483        GD = Component.getFunctionDecl();
484        break;
485      case VTableComponent::CK_CompleteDtorPointer:
486        GD = GlobalDecl(Component.getDestructorDecl(), Dtor_Complete);
487        break;
488      case VTableComponent::CK_DeletingDtorPointer:
489        GD = GlobalDecl(Component.getDestructorDecl(), Dtor_Deleting);
490        break;
491      }
492
493      if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
494        // We have a pure virtual member function.
495        if (!PureVirtualFn) {
496          llvm::FunctionType *Ty =
497            llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
498          StringRef PureCallName = CGM.getCXXABI().GetPureVirtualCallName();
499          PureVirtualFn = CGM.CreateRuntimeFunction(Ty, PureCallName);
500          PureVirtualFn = llvm::ConstantExpr::getBitCast(PureVirtualFn,
501                                                         CGM.Int8PtrTy);
502        }
503        Init = PureVirtualFn;
504      } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
505        if (!DeletedVirtualFn) {
506          llvm::FunctionType *Ty =
507            llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
508          StringRef DeletedCallName =
509            CGM.getCXXABI().GetDeletedVirtualCallName();
510          DeletedVirtualFn = CGM.CreateRuntimeFunction(Ty, DeletedCallName);
511          DeletedVirtualFn = llvm::ConstantExpr::getBitCast(DeletedVirtualFn,
512                                                         CGM.Int8PtrTy);
513        }
514        Init = DeletedVirtualFn;
515      } else {
516        // Check if we should use a thunk.
517        if (NextVTableThunkIndex < NumVTableThunks &&
518            VTableThunks[NextVTableThunkIndex].first == I) {
519          const ThunkInfo &Thunk = VTableThunks[NextVTableThunkIndex].second;
520
521          maybeEmitThunkForVTable(GD, Thunk);
522          Init = CGM.GetAddrOfThunk(GD, Thunk);
523
524          NextVTableThunkIndex++;
525        } else {
526          llvm::Type *Ty = CGM.getTypes().GetFunctionTypeForVTable(GD);
527
528          Init = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
529        }
530
531        Init = llvm::ConstantExpr::getBitCast(Init, Int8PtrTy);
532      }
533      break;
534    }
535
536    case VTableComponent::CK_UnusedFunctionPointer:
537      Init = llvm::ConstantExpr::getNullValue(Int8PtrTy);
538      break;
539    };
540
541    Inits.push_back(Init);
542  }
543
544  llvm::ArrayType *ArrayType = llvm::ArrayType::get(Int8PtrTy, NumComponents);
545  return llvm::ConstantArray::get(ArrayType, Inits);
546}
547
548llvm::GlobalVariable *
549CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
550                                      const BaseSubobject &Base,
551                                      bool BaseIsVirtual,
552                                   llvm::GlobalVariable::LinkageTypes Linkage,
553                                      VTableAddressPointsMapTy& AddressPoints) {
554  if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
555    DI->completeClassData(Base.getBase());
556
557  std::unique_ptr<VTableLayout> VTLayout(
558      getItaniumVTableContext().createConstructionVTableLayout(
559          Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
560
561  // Add the address points.
562  AddressPoints = VTLayout->getAddressPoints();
563
564  // Get the mangled construction vtable name.
565  SmallString<256> OutName;
566  llvm::raw_svector_ostream Out(OutName);
567  cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
568      .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
569                           Base.getBase(), Out);
570  Out.flush();
571  StringRef Name = OutName.str();
572
573  llvm::ArrayType *ArrayType =
574    llvm::ArrayType::get(CGM.Int8PtrTy, VTLayout->getNumVTableComponents());
575
576  // Construction vtable symbols are not part of the Itanium ABI, so we cannot
577  // guarantee that they actually will be available externally. Instead, when
578  // emitting an available_externally VTT, we provide references to an internal
579  // linkage construction vtable. The ABI only requires complete-object vtables
580  // to be the same for all instances of a type, not construction vtables.
581  if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
582    Linkage = llvm::GlobalVariable::InternalLinkage;
583
584  // Create the variable that will hold the construction vtable.
585  llvm::GlobalVariable *VTable =
586    CGM.CreateOrReplaceCXXRuntimeVariable(Name, ArrayType, Linkage);
587  CGM.setGlobalVisibility(VTable, RD);
588
589  // V-tables are always unnamed_addr.
590  VTable->setUnnamedAddr(true);
591
592  llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
593      CGM.getContext().getTagDeclType(Base.getBase()));
594
595  // Create and set the initializer.
596  llvm::Constant *Init = CreateVTableInitializer(
597      Base.getBase(), VTLayout->vtable_component_begin(),
598      VTLayout->getNumVTableComponents(), VTLayout->vtable_thunk_begin(),
599      VTLayout->getNumVTableThunks(), RTTI);
600  VTable->setInitializer(Init);
601
602  return VTable;
603}
604
605/// Compute the required linkage of the v-table for the given class.
606///
607/// Note that we only call this at the end of the translation unit.
608llvm::GlobalVariable::LinkageTypes
609CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
610  if (!RD->isExternallyVisible())
611    return llvm::GlobalVariable::InternalLinkage;
612
613  // We're at the end of the translation unit, so the current key
614  // function is fully correct.
615  if (const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD)) {
616    // If this class has a key function, use that to determine the
617    // linkage of the vtable.
618    const FunctionDecl *def = nullptr;
619    if (keyFunction->hasBody(def))
620      keyFunction = cast<CXXMethodDecl>(def);
621
622    switch (keyFunction->getTemplateSpecializationKind()) {
623      case TSK_Undeclared:
624      case TSK_ExplicitSpecialization:
625        assert(def && "Should not have been asked to emit this");
626        if (keyFunction->isInlined())
627          return !Context.getLangOpts().AppleKext ?
628                   llvm::GlobalVariable::LinkOnceODRLinkage :
629                   llvm::Function::InternalLinkage;
630
631        return llvm::GlobalVariable::ExternalLinkage;
632
633      case TSK_ImplicitInstantiation:
634        return !Context.getLangOpts().AppleKext ?
635                 llvm::GlobalVariable::LinkOnceODRLinkage :
636                 llvm::Function::InternalLinkage;
637
638      case TSK_ExplicitInstantiationDefinition:
639        return !Context.getLangOpts().AppleKext ?
640                 llvm::GlobalVariable::WeakODRLinkage :
641                 llvm::Function::InternalLinkage;
642
643      case TSK_ExplicitInstantiationDeclaration:
644        llvm_unreachable("Should not have been asked to emit this");
645    }
646  }
647
648  // -fapple-kext mode does not support weak linkage, so we must use
649  // internal linkage.
650  if (Context.getLangOpts().AppleKext)
651    return llvm::Function::InternalLinkage;
652
653  llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
654      llvm::GlobalValue::LinkOnceODRLinkage;
655  llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
656      llvm::GlobalValue::WeakODRLinkage;
657  if (RD->hasAttr<DLLExportAttr>()) {
658    // Cannot discard exported vtables.
659    DiscardableODRLinkage = NonDiscardableODRLinkage;
660  } else if (RD->hasAttr<DLLImportAttr>()) {
661    // Imported vtables are available externally.
662    DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
663    NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
664  }
665
666  switch (RD->getTemplateSpecializationKind()) {
667  case TSK_Undeclared:
668  case TSK_ExplicitSpecialization:
669  case TSK_ImplicitInstantiation:
670    return DiscardableODRLinkage;
671
672  case TSK_ExplicitInstantiationDeclaration:
673    llvm_unreachable("Should not have been asked to emit this");
674
675  case TSK_ExplicitInstantiationDefinition:
676    return NonDiscardableODRLinkage;
677  }
678
679  llvm_unreachable("Invalid TemplateSpecializationKind!");
680}
681
682/// This is a callback from Sema to tell us that it believes that a
683/// particular v-table is required to be emitted in this translation
684/// unit.
685///
686/// The reason we don't simply trust this callback is because Sema
687/// will happily report that something is used even when it's used
688/// only in code that we don't actually have to emit.
689///
690/// \param isRequired - if true, the v-table is mandatory, e.g.
691///   because the translation unit defines the key function
692void CodeGenModule::EmitVTable(CXXRecordDecl *theClass, bool isRequired) {
693  if (!isRequired) return;
694
695  VTables.GenerateClassData(theClass);
696}
697
698void
699CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
700  if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
701    DI->completeClassData(RD);
702
703  if (RD->getNumVBases())
704    CGM.getCXXABI().emitVirtualInheritanceTables(RD);
705
706  CGM.getCXXABI().emitVTableDefinitions(*this, RD);
707}
708
709/// At this point in the translation unit, does it appear that can we
710/// rely on the vtable being defined elsewhere in the program?
711///
712/// The response is really only definitive when called at the end of
713/// the translation unit.
714///
715/// The only semantic restriction here is that the object file should
716/// not contain a v-table definition when that v-table is defined
717/// strongly elsewhere.  Otherwise, we'd just like to avoid emitting
718/// v-tables when unnecessary.
719bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
720  assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
721
722  // If we have an explicit instantiation declaration (and not a
723  // definition), the v-table is defined elsewhere.
724  TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
725  if (TSK == TSK_ExplicitInstantiationDeclaration)
726    return true;
727
728  // Otherwise, if the class is an instantiated template, the
729  // v-table must be defined here.
730  if (TSK == TSK_ImplicitInstantiation ||
731      TSK == TSK_ExplicitInstantiationDefinition)
732    return false;
733
734  // Otherwise, if the class doesn't have a key function (possibly
735  // anymore), the v-table must be defined here.
736  const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
737  if (!keyFunction)
738    return false;
739
740  // Otherwise, if we don't have a definition of the key function, the
741  // v-table must be defined somewhere else.
742  return !keyFunction->hasBody();
743}
744
745/// Given that we're currently at the end of the translation unit, and
746/// we've emitted a reference to the v-table for this class, should
747/// we define that v-table?
748static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
749                                                   const CXXRecordDecl *RD) {
750  return !CGM.getVTables().isVTableExternal(RD);
751}
752
753/// Given that at some point we emitted a reference to one or more
754/// v-tables, and that we are now at the end of the translation unit,
755/// decide whether we should emit them.
756void CodeGenModule::EmitDeferredVTables() {
757#ifndef NDEBUG
758  // Remember the size of DeferredVTables, because we're going to assume
759  // that this entire operation doesn't modify it.
760  size_t savedSize = DeferredVTables.size();
761#endif
762
763  typedef std::vector<const CXXRecordDecl *>::const_iterator const_iterator;
764  for (const_iterator i = DeferredVTables.begin(),
765                      e = DeferredVTables.end(); i != e; ++i) {
766    const CXXRecordDecl *RD = *i;
767    if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
768      VTables.GenerateClassData(RD);
769  }
770
771  assert(savedSize == DeferredVTables.size() &&
772         "deferred extra v-tables during v-table emission?");
773  DeferredVTables.clear();
774}
775