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
48  llvm::Type *Ty = getTypes().GetFunctionTypeForVTable(GD);
49  return GetOrCreateLLVMFunction(Name, Ty, GD, /*ForVTable=*/true,
50                                 /*DontDefer=*/true, /*IsThunk=*/true);
51}
52
53static void setThunkVisibility(CodeGenModule &CGM, const CXXMethodDecl *MD,
54                               const ThunkInfo &Thunk, llvm::Function *Fn) {
55  CGM.setGlobalVisibility(Fn, MD);
56}
57
58static void setThunkProperties(CodeGenModule &CGM, const ThunkInfo &Thunk,
59                               llvm::Function *ThunkFn, bool ForVTable,
60                               GlobalDecl GD) {
61  CGM.setFunctionLinkage(GD, ThunkFn);
62  CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
63                                  !Thunk.Return.isEmpty());
64
65  // Set the right visibility.
66  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
67  setThunkVisibility(CGM, MD, Thunk, ThunkFn);
68
69  if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())
70    ThunkFn->setComdat(CGM.getModule().getOrInsertComdat(ThunkFn->getName()));
71}
72
73#ifndef NDEBUG
74static bool similar(const ABIArgInfo &infoL, CanQualType typeL,
75                    const ABIArgInfo &infoR, CanQualType typeR) {
76  return (infoL.getKind() == infoR.getKind() &&
77          (typeL == typeR ||
78           (isa<PointerType>(typeL) && isa<PointerType>(typeR)) ||
79           (isa<ReferenceType>(typeL) && isa<ReferenceType>(typeR))));
80}
81#endif
82
83static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
84                                      QualType ResultType, RValue RV,
85                                      const ThunkInfo &Thunk) {
86  // Emit the return adjustment.
87  bool NullCheckValue = !ResultType->isReferenceType();
88
89  llvm::BasicBlock *AdjustNull = nullptr;
90  llvm::BasicBlock *AdjustNotNull = nullptr;
91  llvm::BasicBlock *AdjustEnd = nullptr;
92
93  llvm::Value *ReturnValue = RV.getScalarVal();
94
95  if (NullCheckValue) {
96    AdjustNull = CGF.createBasicBlock("adjust.null");
97    AdjustNotNull = CGF.createBasicBlock("adjust.notnull");
98    AdjustEnd = CGF.createBasicBlock("adjust.end");
99
100    llvm::Value *IsNull = CGF.Builder.CreateIsNull(ReturnValue);
101    CGF.Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);
102    CGF.EmitBlock(AdjustNotNull);
103  }
104
105  auto ClassDecl = ResultType->getPointeeType()->getAsCXXRecordDecl();
106  auto ClassAlign = CGF.CGM.getClassPointerAlignment(ClassDecl);
107  ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(CGF,
108                                            Address(ReturnValue, ClassAlign),
109                                            Thunk.Return);
110
111  if (NullCheckValue) {
112    CGF.Builder.CreateBr(AdjustEnd);
113    CGF.EmitBlock(AdjustNull);
114    CGF.Builder.CreateBr(AdjustEnd);
115    CGF.EmitBlock(AdjustEnd);
116
117    llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
118    PHI->addIncoming(ReturnValue, AdjustNotNull);
119    PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
120                     AdjustNull);
121    ReturnValue = PHI;
122  }
123
124  return RValue::get(ReturnValue);
125}
126
127// This function does roughly the same thing as GenerateThunk, but in a
128// very different way, so that va_start and va_end work correctly.
129// FIXME: This function assumes "this" is the first non-sret LLVM argument of
130//        a function, and that there is an alloca built in the entry block
131//        for all accesses to "this".
132// FIXME: This function assumes there is only one "ret" statement per function.
133// FIXME: Cloning isn't correct in the presence of indirect goto!
134// FIXME: This implementation of thunks bloats codesize by duplicating the
135//        function definition.  There are alternatives:
136//        1. Add some sort of stub support to LLVM for cases where we can
137//           do a this adjustment, then a sibcall.
138//        2. We could transform the definition to take a va_list instead of an
139//           actual variable argument list, then have the thunks (including a
140//           no-op thunk for the regular definition) call va_start/va_end.
141//           There's a bit of per-call overhead for this solution, but it's
142//           better for codesize if the definition is long.
143llvm::Function *
144CodeGenFunction::GenerateVarArgsThunk(llvm::Function *Fn,
145                                      const CGFunctionInfo &FnInfo,
146                                      GlobalDecl GD, const ThunkInfo &Thunk) {
147  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
148  const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
149  QualType ResultType = FPT->getReturnType();
150
151  // Get the original function
152  assert(FnInfo.isVariadic());
153  llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);
154  llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
155  llvm::Function *BaseFn = cast<llvm::Function>(Callee);
156
157  // Clone to thunk.
158  llvm::ValueToValueMapTy VMap;
159  llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap);
160  Fn->replaceAllUsesWith(NewFn);
161  NewFn->takeName(Fn);
162  Fn->eraseFromParent();
163  Fn = NewFn;
164
165  // "Initialize" CGF (minimally).
166  CurFn = Fn;
167
168  // Get the "this" value
169  llvm::Function::arg_iterator AI = Fn->arg_begin();
170  if (CGM.ReturnTypeUsesSRet(FnInfo))
171    ++AI;
172
173  // Find the first store of "this", which will be to the alloca associated
174  // with "this".
175  Address ThisPtr(&*AI, CGM.getClassPointerAlignment(MD->getParent()));
176  llvm::BasicBlock *EntryBB = &Fn->front();
177  llvm::BasicBlock::iterator ThisStore =
178      std::find_if(EntryBB->begin(), EntryBB->end(), [&](llvm::Instruction &I) {
179        return isa<llvm::StoreInst>(I) &&
180               I.getOperand(0) == ThisPtr.getPointer();
181      });
182  assert(ThisStore != EntryBB->end() &&
183         "Store of this should be in entry block?");
184  // Adjust "this", if necessary.
185  Builder.SetInsertPoint(&*ThisStore);
186  llvm::Value *AdjustedThisPtr =
187      CGM.getCXXABI().performThisAdjustment(*this, ThisPtr, Thunk.This);
188  ThisStore->setOperand(0, AdjustedThisPtr);
189
190  if (!Thunk.Return.isEmpty()) {
191    // Fix up the returned value, if necessary.
192    for (llvm::BasicBlock &BB : *Fn) {
193      llvm::Instruction *T = BB.getTerminator();
194      if (isa<llvm::ReturnInst>(T)) {
195        RValue RV = RValue::get(T->getOperand(0));
196        T->eraseFromParent();
197        Builder.SetInsertPoint(&BB);
198        RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
199        Builder.CreateRet(RV.getScalarVal());
200        break;
201      }
202    }
203  }
204
205  return Fn;
206}
207
208void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
209                                 const CGFunctionInfo &FnInfo) {
210  assert(!CurGD.getDecl() && "CurGD was already set!");
211  CurGD = GD;
212  CurFuncIsThunk = true;
213
214  // Build FunctionArgs.
215  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
216  QualType ThisType = MD->getThisType(getContext());
217  const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
218  QualType ResultType = CGM.getCXXABI().HasThisReturn(GD)
219                            ? ThisType
220                            : CGM.getCXXABI().hasMostDerivedReturn(GD)
221                                  ? CGM.getContext().VoidPtrTy
222                                  : FPT->getReturnType();
223  FunctionArgList FunctionArgs;
224
225  // Create the implicit 'this' parameter declaration.
226  CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
227
228  // Add the rest of the parameters.
229  FunctionArgs.append(MD->param_begin(), MD->param_end());
230
231  if (isa<CXXDestructorDecl>(MD))
232    CGM.getCXXABI().addImplicitStructorParams(*this, ResultType, FunctionArgs);
233
234  // Start defining the function.
235  StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
236                MD->getLocation(), MD->getLocation());
237
238  // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
239  CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
240  CXXThisValue = CXXABIThisValue;
241  CurCodeDecl = MD;
242  CurFuncDecl = MD;
243}
244
245void CodeGenFunction::FinishThunk() {
246  // Clear these to restore the invariants expected by
247  // StartFunction/FinishFunction.
248  CurCodeDecl = nullptr;
249  CurFuncDecl = nullptr;
250
251  FinishFunction();
252}
253
254void CodeGenFunction::EmitCallAndReturnForThunk(llvm::Value *Callee,
255                                                const ThunkInfo *Thunk) {
256  assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
257         "Please use a new CGF for this thunk");
258  const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurGD.getDecl());
259
260  // Adjust the 'this' pointer if necessary
261  llvm::Value *AdjustedThisPtr =
262    Thunk ? CGM.getCXXABI().performThisAdjustment(
263                          *this, LoadCXXThisAddress(), Thunk->This)
264          : LoadCXXThis();
265
266  if (CurFnInfo->usesInAlloca()) {
267    // We don't handle return adjusting thunks, because they require us to call
268    // the copy constructor.  For now, fall through and pretend the return
269    // adjustment was empty so we don't crash.
270    if (Thunk && !Thunk->Return.isEmpty()) {
271      CGM.ErrorUnsupported(
272          MD, "non-trivial argument copy for return-adjusting thunk");
273    }
274    EmitMustTailThunk(MD, AdjustedThisPtr, Callee);
275    return;
276  }
277
278  // Start building CallArgs.
279  CallArgList CallArgs;
280  QualType ThisType = MD->getThisType(getContext());
281  CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
282
283  if (isa<CXXDestructorDecl>(MD))
284    CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);
285
286  // Add the rest of the arguments.
287  for (const ParmVarDecl *PD : MD->parameters())
288    EmitDelegateCallArg(CallArgs, PD, PD->getLocStart());
289
290  const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
291
292#ifndef NDEBUG
293  const CGFunctionInfo &CallFnInfo = CGM.getTypes().arrangeCXXMethodCall(
294      CallArgs, FPT, RequiredArgs::forPrototypePlus(FPT, 1, MD));
295  assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
296         CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
297         CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
298  assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
299         similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
300                 CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
301  assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
302  for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
303    assert(similar(CallFnInfo.arg_begin()[i].info,
304                   CallFnInfo.arg_begin()[i].type,
305                   CurFnInfo->arg_begin()[i].info,
306                   CurFnInfo->arg_begin()[i].type));
307#endif
308
309  // Determine whether we have a return value slot to use.
310  QualType ResultType = CGM.getCXXABI().HasThisReturn(CurGD)
311                            ? ThisType
312                            : CGM.getCXXABI().hasMostDerivedReturn(CurGD)
313                                  ? CGM.getContext().VoidPtrTy
314                                  : FPT->getReturnType();
315  ReturnValueSlot Slot;
316  if (!ResultType->isVoidType() &&
317      CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect &&
318      !hasScalarEvaluationKind(CurFnInfo->getReturnType()))
319    Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified());
320
321  // Now emit our call.
322  llvm::Instruction *CallOrInvoke;
323  RValue RV = EmitCall(*CurFnInfo, Callee, Slot, CallArgs, MD, &CallOrInvoke);
324
325  // Consider return adjustment if we have ThunkInfo.
326  if (Thunk && !Thunk->Return.isEmpty())
327    RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
328  else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(CallOrInvoke))
329    Call->setTailCallKind(llvm::CallInst::TCK_Tail);
330
331  // Emit return.
332  if (!ResultType->isVoidType() && Slot.isNull())
333    CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
334
335  // Disable the final ARC autorelease.
336  AutoreleaseResult = false;
337
338  FinishThunk();
339}
340
341void CodeGenFunction::EmitMustTailThunk(const CXXMethodDecl *MD,
342                                        llvm::Value *AdjustedThisPtr,
343                                        llvm::Value *Callee) {
344  // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
345  // to translate AST arguments into LLVM IR arguments.  For thunks, we know
346  // that the caller prototype more or less matches the callee prototype with
347  // the exception of 'this'.
348  SmallVector<llvm::Value *, 8> Args;
349  for (llvm::Argument &A : CurFn->args())
350    Args.push_back(&A);
351
352  // Set the adjusted 'this' pointer.
353  const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
354  if (ThisAI.isDirect()) {
355    const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
356    int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
357    llvm::Type *ThisType = Args[ThisArgNo]->getType();
358    if (ThisType != AdjustedThisPtr->getType())
359      AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
360    Args[ThisArgNo] = AdjustedThisPtr;
361  } else {
362    assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
363    Address ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);
364    llvm::Type *ThisType = ThisAddr.getElementType();
365    if (ThisType != AdjustedThisPtr->getType())
366      AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
367    Builder.CreateStore(AdjustedThisPtr, ThisAddr);
368  }
369
370  // Emit the musttail call manually.  Even if the prologue pushed cleanups, we
371  // don't actually want to run them.
372  llvm::CallInst *Call = Builder.CreateCall(Callee, Args);
373  Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
374
375  // Apply the standard set of call attributes.
376  unsigned CallingConv;
377  CodeGen::AttributeListType AttributeList;
378  CGM.ConstructAttributeList(Callee->getName(), *CurFnInfo, MD, AttributeList,
379                             CallingConv, /*AttrOnCallSite=*/true);
380  llvm::AttributeSet Attrs =
381      llvm::AttributeSet::get(getLLVMContext(), AttributeList);
382  Call->setAttributes(Attrs);
383  Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
384
385  if (Call->getType()->isVoidTy())
386    Builder.CreateRetVoid();
387  else
388    Builder.CreateRet(Call);
389
390  // Finish the function to maintain CodeGenFunction invariants.
391  // FIXME: Don't emit unreachable code.
392  EmitBlock(createBasicBlock());
393  FinishFunction();
394}
395
396void CodeGenFunction::generateThunk(llvm::Function *Fn,
397                                    const CGFunctionInfo &FnInfo,
398                                    GlobalDecl GD, const ThunkInfo &Thunk) {
399  StartThunk(Fn, GD, FnInfo);
400
401  // Get our callee.
402  llvm::Type *Ty =
403    CGM.getTypes().GetFunctionType(CGM.getTypes().arrangeGlobalDeclaration(GD));
404  llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
405
406  // Make the call and return the result.
407  EmitCallAndReturnForThunk(Callee, &Thunk);
408}
409
410void CodeGenVTables::emitThunk(GlobalDecl GD, const ThunkInfo &Thunk,
411                               bool ForVTable) {
412  const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeGlobalDeclaration(GD);
413
414  // FIXME: re-use FnInfo in this computation.
415  llvm::Constant *C = CGM.GetAddrOfThunk(GD, Thunk);
416  llvm::GlobalValue *Entry;
417
418  // Strip off a bitcast if we got one back.
419  if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(C)) {
420    assert(CE->getOpcode() == llvm::Instruction::BitCast);
421    Entry = cast<llvm::GlobalValue>(CE->getOperand(0));
422  } else {
423    Entry = cast<llvm::GlobalValue>(C);
424  }
425
426  // There's already a declaration with the same name, check if it has the same
427  // type or if we need to replace it.
428  if (Entry->getType()->getElementType() !=
429      CGM.getTypes().GetFunctionTypeForVTable(GD)) {
430    llvm::GlobalValue *OldThunkFn = Entry;
431
432    // If the types mismatch then we have to rewrite the definition.
433    assert(OldThunkFn->isDeclaration() &&
434           "Shouldn't replace non-declaration");
435
436    // Remove the name from the old thunk function and get a new thunk.
437    OldThunkFn->setName(StringRef());
438    Entry = cast<llvm::GlobalValue>(CGM.GetAddrOfThunk(GD, Thunk));
439
440    // If needed, replace the old thunk with a bitcast.
441    if (!OldThunkFn->use_empty()) {
442      llvm::Constant *NewPtrForOldDecl =
443        llvm::ConstantExpr::getBitCast(Entry, OldThunkFn->getType());
444      OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
445    }
446
447    // Remove the old thunk.
448    OldThunkFn->eraseFromParent();
449  }
450
451  llvm::Function *ThunkFn = cast<llvm::Function>(Entry);
452  bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
453  bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
454
455  if (!ThunkFn->isDeclaration()) {
456    if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
457      // There is already a thunk emitted for this function, do nothing.
458      return;
459    }
460
461    setThunkProperties(CGM, Thunk, ThunkFn, ForVTable, GD);
462    return;
463  }
464
465  CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
466
467  if (ThunkFn->isVarArg()) {
468    // Varargs thunks are special; we can't just generate a call because
469    // we can't copy the varargs.  Our implementation is rather
470    // expensive/sucky at the moment, so don't generate the thunk unless
471    // we have to.
472    // FIXME: Do something better here; GenerateVarArgsThunk is extremely ugly.
473    if (UseAvailableExternallyLinkage)
474      return;
475    ThunkFn =
476        CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, Thunk);
477  } else {
478    // Normal thunk body generation.
479    CodeGenFunction(CGM).generateThunk(ThunkFn, FnInfo, GD, Thunk);
480  }
481
482  setThunkProperties(CGM, Thunk, ThunkFn, ForVTable, GD);
483}
484
485void CodeGenVTables::maybeEmitThunkForVTable(GlobalDecl GD,
486                                             const ThunkInfo &Thunk) {
487  // If the ABI has key functions, only the TU with the key function should emit
488  // the thunk. However, we can allow inlining of thunks if we emit them with
489  // available_externally linkage together with vtables when optimizations are
490  // enabled.
491  if (CGM.getTarget().getCXXABI().hasKeyFunctions() &&
492      !CGM.getCodeGenOpts().OptimizationLevel)
493    return;
494
495  // We can't emit thunks for member functions with incomplete types.
496  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
497  if (!CGM.getTypes().isFuncTypeConvertible(
498           MD->getType()->castAs<FunctionType>()))
499    return;
500
501  emitThunk(GD, Thunk, /*ForVTable=*/true);
502}
503
504void CodeGenVTables::EmitThunks(GlobalDecl GD)
505{
506  const CXXMethodDecl *MD =
507    cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
508
509  // We don't need to generate thunks for the base destructor.
510  if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
511    return;
512
513  const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
514      VTContext->getThunkInfo(GD);
515
516  if (!ThunkInfoVector)
517    return;
518
519  for (const ThunkInfo& Thunk : *ThunkInfoVector)
520    emitThunk(GD, Thunk, /*ForVTable=*/false);
521}
522
523llvm::Constant *CodeGenVTables::CreateVTableInitializer(
524    const CXXRecordDecl *RD, const VTableComponent *Components,
525    unsigned NumComponents, const VTableLayout::VTableThunkTy *VTableThunks,
526    unsigned NumVTableThunks, llvm::Constant *RTTI) {
527  SmallVector<llvm::Constant *, 64> Inits;
528
529  llvm::Type *Int8PtrTy = CGM.Int8PtrTy;
530
531  llvm::Type *PtrDiffTy =
532    CGM.getTypes().ConvertType(CGM.getContext().getPointerDiffType());
533
534  unsigned NextVTableThunkIndex = 0;
535
536  llvm::Constant *PureVirtualFn = nullptr, *DeletedVirtualFn = nullptr;
537
538  for (unsigned I = 0; I != NumComponents; ++I) {
539    VTableComponent Component = Components[I];
540
541    llvm::Constant *Init = nullptr;
542
543    switch (Component.getKind()) {
544    case VTableComponent::CK_VCallOffset:
545      Init = llvm::ConstantInt::get(PtrDiffTy,
546                                    Component.getVCallOffset().getQuantity());
547      Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
548      break;
549    case VTableComponent::CK_VBaseOffset:
550      Init = llvm::ConstantInt::get(PtrDiffTy,
551                                    Component.getVBaseOffset().getQuantity());
552      Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
553      break;
554    case VTableComponent::CK_OffsetToTop:
555      Init = llvm::ConstantInt::get(PtrDiffTy,
556                                    Component.getOffsetToTop().getQuantity());
557      Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
558      break;
559    case VTableComponent::CK_RTTI:
560      Init = llvm::ConstantExpr::getBitCast(RTTI, Int8PtrTy);
561      break;
562    case VTableComponent::CK_FunctionPointer:
563    case VTableComponent::CK_CompleteDtorPointer:
564    case VTableComponent::CK_DeletingDtorPointer: {
565      GlobalDecl GD;
566
567      // Get the right global decl.
568      switch (Component.getKind()) {
569      default:
570        llvm_unreachable("Unexpected vtable component kind");
571      case VTableComponent::CK_FunctionPointer:
572        GD = Component.getFunctionDecl();
573        break;
574      case VTableComponent::CK_CompleteDtorPointer:
575        GD = GlobalDecl(Component.getDestructorDecl(), Dtor_Complete);
576        break;
577      case VTableComponent::CK_DeletingDtorPointer:
578        GD = GlobalDecl(Component.getDestructorDecl(), Dtor_Deleting);
579        break;
580      }
581
582      if (CGM.getLangOpts().CUDA) {
583        // Emit NULL for methods we can't codegen on this
584        // side. Otherwise we'd end up with vtable with unresolved
585        // references.
586        const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
587        // OK on device side: functions w/ __device__ attribute
588        // OK on host side: anything except __device__-only functions.
589        bool CanEmitMethod = CGM.getLangOpts().CUDAIsDevice
590                                 ? MD->hasAttr<CUDADeviceAttr>()
591                                 : (MD->hasAttr<CUDAHostAttr>() ||
592                                    !MD->hasAttr<CUDADeviceAttr>());
593        if (!CanEmitMethod) {
594          Init = llvm::ConstantExpr::getNullValue(Int8PtrTy);
595          break;
596        }
597        // Method is acceptable, continue processing as usual.
598      }
599
600      if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
601        // We have a pure virtual member function.
602        if (!PureVirtualFn) {
603          llvm::FunctionType *Ty =
604            llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
605          StringRef PureCallName = CGM.getCXXABI().GetPureVirtualCallName();
606          PureVirtualFn = CGM.CreateRuntimeFunction(Ty, PureCallName);
607          if (auto *F = dyn_cast<llvm::Function>(PureVirtualFn))
608            F->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
609          PureVirtualFn = llvm::ConstantExpr::getBitCast(PureVirtualFn,
610                                                         CGM.Int8PtrTy);
611        }
612        Init = PureVirtualFn;
613      } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
614        if (!DeletedVirtualFn) {
615          llvm::FunctionType *Ty =
616            llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
617          StringRef DeletedCallName =
618            CGM.getCXXABI().GetDeletedVirtualCallName();
619          DeletedVirtualFn = CGM.CreateRuntimeFunction(Ty, DeletedCallName);
620          if (auto *F = dyn_cast<llvm::Function>(DeletedVirtualFn))
621            F->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
622          DeletedVirtualFn = llvm::ConstantExpr::getBitCast(DeletedVirtualFn,
623                                                         CGM.Int8PtrTy);
624        }
625        Init = DeletedVirtualFn;
626      } else {
627        // Check if we should use a thunk.
628        if (NextVTableThunkIndex < NumVTableThunks &&
629            VTableThunks[NextVTableThunkIndex].first == I) {
630          const ThunkInfo &Thunk = VTableThunks[NextVTableThunkIndex].second;
631
632          maybeEmitThunkForVTable(GD, Thunk);
633          Init = CGM.GetAddrOfThunk(GD, Thunk);
634
635          NextVTableThunkIndex++;
636        } else {
637          llvm::Type *Ty = CGM.getTypes().GetFunctionTypeForVTable(GD);
638
639          Init = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
640        }
641
642        Init = llvm::ConstantExpr::getBitCast(Init, Int8PtrTy);
643      }
644      break;
645    }
646
647    case VTableComponent::CK_UnusedFunctionPointer:
648      Init = llvm::ConstantExpr::getNullValue(Int8PtrTy);
649      break;
650    };
651
652    Inits.push_back(Init);
653  }
654
655  llvm::ArrayType *ArrayType = llvm::ArrayType::get(Int8PtrTy, NumComponents);
656  return llvm::ConstantArray::get(ArrayType, Inits);
657}
658
659llvm::GlobalVariable *
660CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
661                                      const BaseSubobject &Base,
662                                      bool BaseIsVirtual,
663                                   llvm::GlobalVariable::LinkageTypes Linkage,
664                                      VTableAddressPointsMapTy& AddressPoints) {
665  if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
666    DI->completeClassData(Base.getBase());
667
668  std::unique_ptr<VTableLayout> VTLayout(
669      getItaniumVTableContext().createConstructionVTableLayout(
670          Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
671
672  // Add the address points.
673  AddressPoints = VTLayout->getAddressPoints();
674
675  // Get the mangled construction vtable name.
676  SmallString<256> OutName;
677  llvm::raw_svector_ostream Out(OutName);
678  cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
679      .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
680                           Base.getBase(), Out);
681  StringRef Name = OutName.str();
682
683  llvm::ArrayType *ArrayType =
684    llvm::ArrayType::get(CGM.Int8PtrTy, VTLayout->getNumVTableComponents());
685
686  // Construction vtable symbols are not part of the Itanium ABI, so we cannot
687  // guarantee that they actually will be available externally. Instead, when
688  // emitting an available_externally VTT, we provide references to an internal
689  // linkage construction vtable. The ABI only requires complete-object vtables
690  // to be the same for all instances of a type, not construction vtables.
691  if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
692    Linkage = llvm::GlobalVariable::InternalLinkage;
693
694  // Create the variable that will hold the construction vtable.
695  llvm::GlobalVariable *VTable =
696    CGM.CreateOrReplaceCXXRuntimeVariable(Name, ArrayType, Linkage);
697  CGM.setGlobalVisibility(VTable, RD);
698
699  // V-tables are always unnamed_addr.
700  VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
701
702  llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
703      CGM.getContext().getTagDeclType(Base.getBase()));
704
705  // Create and set the initializer.
706  llvm::Constant *Init = CreateVTableInitializer(
707      Base.getBase(), VTLayout->vtable_component_begin(),
708      VTLayout->getNumVTableComponents(), VTLayout->vtable_thunk_begin(),
709      VTLayout->getNumVTableThunks(), RTTI);
710  VTable->setInitializer(Init);
711
712  CGM.EmitVTableTypeMetadata(VTable, *VTLayout.get());
713
714  return VTable;
715}
716
717static bool shouldEmitAvailableExternallyVTable(const CodeGenModule &CGM,
718                                                const CXXRecordDecl *RD) {
719  return CGM.getCodeGenOpts().OptimizationLevel > 0 &&
720         CGM.getCXXABI().canSpeculativelyEmitVTable(RD);
721}
722
723/// Compute the required linkage of the vtable for the given class.
724///
725/// Note that we only call this at the end of the translation unit.
726llvm::GlobalVariable::LinkageTypes
727CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
728  if (!RD->isExternallyVisible())
729    return llvm::GlobalVariable::InternalLinkage;
730
731  // We're at the end of the translation unit, so the current key
732  // function is fully correct.
733  const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
734  if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
735    // If this class has a key function, use that to determine the
736    // linkage of the vtable.
737    const FunctionDecl *def = nullptr;
738    if (keyFunction->hasBody(def))
739      keyFunction = cast<CXXMethodDecl>(def);
740
741    switch (keyFunction->getTemplateSpecializationKind()) {
742      case TSK_Undeclared:
743      case TSK_ExplicitSpecialization:
744        assert((def || CodeGenOpts.OptimizationLevel > 0) &&
745               "Shouldn't query vtable linkage without key function or "
746               "optimizations");
747        if (!def && CodeGenOpts.OptimizationLevel > 0)
748          return llvm::GlobalVariable::AvailableExternallyLinkage;
749
750        if (keyFunction->isInlined())
751          return !Context.getLangOpts().AppleKext ?
752                   llvm::GlobalVariable::LinkOnceODRLinkage :
753                   llvm::Function::InternalLinkage;
754
755        return llvm::GlobalVariable::ExternalLinkage;
756
757      case TSK_ImplicitInstantiation:
758        return !Context.getLangOpts().AppleKext ?
759                 llvm::GlobalVariable::LinkOnceODRLinkage :
760                 llvm::Function::InternalLinkage;
761
762      case TSK_ExplicitInstantiationDefinition:
763        return !Context.getLangOpts().AppleKext ?
764                 llvm::GlobalVariable::WeakODRLinkage :
765                 llvm::Function::InternalLinkage;
766
767      case TSK_ExplicitInstantiationDeclaration:
768        llvm_unreachable("Should not have been asked to emit this");
769    }
770  }
771
772  // -fapple-kext mode does not support weak linkage, so we must use
773  // internal linkage.
774  if (Context.getLangOpts().AppleKext)
775    return llvm::Function::InternalLinkage;
776
777  llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
778      llvm::GlobalValue::LinkOnceODRLinkage;
779  llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
780      llvm::GlobalValue::WeakODRLinkage;
781  if (RD->hasAttr<DLLExportAttr>()) {
782    // Cannot discard exported vtables.
783    DiscardableODRLinkage = NonDiscardableODRLinkage;
784  } else if (RD->hasAttr<DLLImportAttr>()) {
785    // Imported vtables are available externally.
786    DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
787    NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
788  }
789
790  switch (RD->getTemplateSpecializationKind()) {
791    case TSK_Undeclared:
792    case TSK_ExplicitSpecialization:
793    case TSK_ImplicitInstantiation:
794      return DiscardableODRLinkage;
795
796    case TSK_ExplicitInstantiationDeclaration:
797      // Explicit instantiations in MSVC do not provide vtables, so we must emit
798      // our own.
799      if (getTarget().getCXXABI().isMicrosoft())
800        return DiscardableODRLinkage;
801      return shouldEmitAvailableExternallyVTable(*this, RD)
802                 ? llvm::GlobalVariable::AvailableExternallyLinkage
803                 : llvm::GlobalVariable::ExternalLinkage;
804
805    case TSK_ExplicitInstantiationDefinition:
806      return NonDiscardableODRLinkage;
807  }
808
809  llvm_unreachable("Invalid TemplateSpecializationKind!");
810}
811
812/// This is a callback from Sema to tell us that that a particular vtable is
813/// required to be emitted in this translation unit.
814///
815/// This is only called for vtables that _must_ be emitted (mainly due to key
816/// functions).  For weak vtables, CodeGen tracks when they are needed and
817/// emits them as-needed.
818void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
819  VTables.GenerateClassData(theClass);
820}
821
822void
823CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
824  if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
825    DI->completeClassData(RD);
826
827  if (RD->getNumVBases())
828    CGM.getCXXABI().emitVirtualInheritanceTables(RD);
829
830  CGM.getCXXABI().emitVTableDefinitions(*this, RD);
831}
832
833/// At this point in the translation unit, does it appear that can we
834/// rely on the vtable being defined elsewhere in the program?
835///
836/// The response is really only definitive when called at the end of
837/// the translation unit.
838///
839/// The only semantic restriction here is that the object file should
840/// not contain a vtable definition when that vtable is defined
841/// strongly elsewhere.  Otherwise, we'd just like to avoid emitting
842/// vtables when unnecessary.
843bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
844  assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
845
846  // We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't
847  // emit them even if there is an explicit template instantiation.
848  if (CGM.getTarget().getCXXABI().isMicrosoft())
849    return false;
850
851  // If we have an explicit instantiation declaration (and not a
852  // definition), the vtable is defined elsewhere.
853  TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
854  if (TSK == TSK_ExplicitInstantiationDeclaration)
855    return true;
856
857  // Otherwise, if the class is an instantiated template, the
858  // vtable must be defined here.
859  if (TSK == TSK_ImplicitInstantiation ||
860      TSK == TSK_ExplicitInstantiationDefinition)
861    return false;
862
863  // Otherwise, if the class doesn't have a key function (possibly
864  // anymore), the vtable must be defined here.
865  const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
866  if (!keyFunction)
867    return false;
868
869  // Otherwise, if we don't have a definition of the key function, the
870  // vtable must be defined somewhere else.
871  return !keyFunction->hasBody();
872}
873
874/// Given that we're currently at the end of the translation unit, and
875/// we've emitted a reference to the vtable for this class, should
876/// we define that vtable?
877static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
878                                                   const CXXRecordDecl *RD) {
879  // If vtable is internal then it has to be done.
880  if (!CGM.getVTables().isVTableExternal(RD))
881    return true;
882
883  // If it's external then maybe we will need it as available_externally.
884  return shouldEmitAvailableExternallyVTable(CGM, RD);
885}
886
887/// Given that at some point we emitted a reference to one or more
888/// vtables, and that we are now at the end of the translation unit,
889/// decide whether we should emit them.
890void CodeGenModule::EmitDeferredVTables() {
891#ifndef NDEBUG
892  // Remember the size of DeferredVTables, because we're going to assume
893  // that this entire operation doesn't modify it.
894  size_t savedSize = DeferredVTables.size();
895#endif
896
897  for (const CXXRecordDecl *RD : DeferredVTables)
898    if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
899      VTables.GenerateClassData(RD);
900
901  assert(savedSize == DeferredVTables.size() &&
902         "deferred extra vtables during vtable emission?");
903  DeferredVTables.clear();
904}
905
906bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
907  LinkageInfo LV = RD->getLinkageAndVisibility();
908  if (!isExternallyVisible(LV.getLinkage()))
909    return true;
910
911  if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>())
912    return false;
913
914  if (getTriple().isOSBinFormatCOFF()) {
915    if (RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())
916      return false;
917  } else {
918    if (LV.getVisibility() != HiddenVisibility)
919      return false;
920  }
921
922  if (getCodeGenOpts().LTOVisibilityPublicStd) {
923    const DeclContext *DC = RD;
924    while (1) {
925      auto *D = cast<Decl>(DC);
926      DC = DC->getParent();
927      if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {
928        if (auto *ND = dyn_cast<NamespaceDecl>(D))
929          if (const IdentifierInfo *II = ND->getIdentifier())
930            if (II->isStr("std") || II->isStr("stdext"))
931              return false;
932        break;
933      }
934    }
935  }
936
937  return true;
938}
939
940void CodeGenModule::EmitVTableTypeMetadata(llvm::GlobalVariable *VTable,
941                                           const VTableLayout &VTLayout) {
942  if (!getCodeGenOpts().PrepareForLTO)
943    return;
944
945  CharUnits PointerWidth =
946      Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
947
948  typedef std::pair<const CXXRecordDecl *, unsigned> BSEntry;
949  std::vector<BSEntry> BitsetEntries;
950  // Create a bit set entry for each address point.
951  for (auto &&AP : VTLayout.getAddressPoints())
952    BitsetEntries.push_back(std::make_pair(AP.first.getBase(), AP.second));
953
954  // Sort the bit set entries for determinism.
955  std::sort(BitsetEntries.begin(), BitsetEntries.end(),
956            [this](const BSEntry &E1, const BSEntry &E2) {
957    if (&E1 == &E2)
958      return false;
959
960    std::string S1;
961    llvm::raw_string_ostream O1(S1);
962    getCXXABI().getMangleContext().mangleTypeName(
963        QualType(E1.first->getTypeForDecl(), 0), O1);
964    O1.flush();
965
966    std::string S2;
967    llvm::raw_string_ostream O2(S2);
968    getCXXABI().getMangleContext().mangleTypeName(
969        QualType(E2.first->getTypeForDecl(), 0), O2);
970    O2.flush();
971
972    if (S1 < S2)
973      return true;
974    if (S1 != S2)
975      return false;
976
977    return E1.second < E2.second;
978  });
979
980  for (auto BitsetEntry : BitsetEntries)
981    AddVTableTypeMetadata(VTable, PointerWidth * BitsetEntry.second,
982                          BitsetEntry.first);
983}
984