xref: /freebsd/contrib/llvm-project/clang/lib/CodeGen/CGVTables.cpp (revision e32fecd0c2c3ee37c47ee100f169e7eb0282a873)
1 //===--- CGVTables.cpp - Emit LLVM Code for C++ vtables -------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This contains code dealing with C++ code generation of virtual tables.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "CGCXXABI.h"
14 #include "CodeGenFunction.h"
15 #include "CodeGenModule.h"
16 #include "clang/AST/Attr.h"
17 #include "clang/AST/CXXInheritance.h"
18 #include "clang/AST/RecordLayout.h"
19 #include "clang/Basic/CodeGenOptions.h"
20 #include "clang/CodeGen/CGFunctionInfo.h"
21 #include "clang/CodeGen/ConstantInitBuilder.h"
22 #include "llvm/IR/IntrinsicInst.h"
23 #include "llvm/Support/Format.h"
24 #include "llvm/Transforms/Utils/Cloning.h"
25 #include <algorithm>
26 #include <cstdio>
27 
28 using namespace clang;
29 using namespace CodeGen;
30 
31 CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
32     : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
33 
34 llvm::Constant *CodeGenModule::GetAddrOfThunk(StringRef Name, llvm::Type *FnTy,
35                                               GlobalDecl GD) {
36   return GetOrCreateLLVMFunction(Name, FnTy, GD, /*ForVTable=*/true,
37                                  /*DontDefer=*/true, /*IsThunk=*/true);
38 }
39 
40 static void setThunkProperties(CodeGenModule &CGM, const ThunkInfo &Thunk,
41                                llvm::Function *ThunkFn, bool ForVTable,
42                                GlobalDecl GD) {
43   CGM.setFunctionLinkage(GD, ThunkFn);
44   CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
45                                   !Thunk.Return.isEmpty());
46 
47   // Set the right visibility.
48   CGM.setGVProperties(ThunkFn, GD);
49 
50   if (!CGM.getCXXABI().exportThunk()) {
51     ThunkFn->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
52     ThunkFn->setDSOLocal(true);
53   }
54 
55   if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())
56     ThunkFn->setComdat(CGM.getModule().getOrInsertComdat(ThunkFn->getName()));
57 }
58 
59 #ifndef NDEBUG
60 static 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 
69 static 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   auto ClassDecl = ResultType->getPointeeType()->getAsCXXRecordDecl();
92   auto ClassAlign = CGF.CGM.getClassPointerAlignment(ClassDecl);
93   ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(
94       CGF,
95       Address(ReturnValue, CGF.ConvertTypeForMem(ResultType->getPointeeType()),
96               ClassAlign),
97       Thunk.Return);
98 
99   if (NullCheckValue) {
100     CGF.Builder.CreateBr(AdjustEnd);
101     CGF.EmitBlock(AdjustNull);
102     CGF.Builder.CreateBr(AdjustEnd);
103     CGF.EmitBlock(AdjustEnd);
104 
105     llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
106     PHI->addIncoming(ReturnValue, AdjustNotNull);
107     PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
108                      AdjustNull);
109     ReturnValue = PHI;
110   }
111 
112   return RValue::get(ReturnValue);
113 }
114 
115 /// This function clones a function's DISubprogram node and enters it into
116 /// a value map with the intent that the map can be utilized by the cloner
117 /// to short-circuit Metadata node mapping.
118 /// Furthermore, the function resolves any DILocalVariable nodes referenced
119 /// by dbg.value intrinsics so they can be properly mapped during cloning.
120 static void resolveTopLevelMetadata(llvm::Function *Fn,
121                                     llvm::ValueToValueMapTy &VMap) {
122   // Clone the DISubprogram node and put it into the Value map.
123   auto *DIS = Fn->getSubprogram();
124   if (!DIS)
125     return;
126   auto *NewDIS = DIS->replaceWithDistinct(DIS->clone());
127   VMap.MD()[DIS].reset(NewDIS);
128 
129   // Find all llvm.dbg.declare intrinsics and resolve the DILocalVariable nodes
130   // they are referencing.
131   for (auto &BB : Fn->getBasicBlockList()) {
132     for (auto &I : BB) {
133       if (auto *DII = dyn_cast<llvm::DbgVariableIntrinsic>(&I)) {
134         auto *DILocal = DII->getVariable();
135         if (!DILocal->isResolved())
136           DILocal->resolve();
137       }
138     }
139   }
140 }
141 
142 // This function does roughly the same thing as GenerateThunk, but in a
143 // very different way, so that va_start and va_end work correctly.
144 // FIXME: This function assumes "this" is the first non-sret LLVM argument of
145 //        a function, and that there is an alloca built in the entry block
146 //        for all accesses to "this".
147 // FIXME: This function assumes there is only one "ret" statement per function.
148 // FIXME: Cloning isn't correct in the presence of indirect goto!
149 // FIXME: This implementation of thunks bloats codesize by duplicating the
150 //        function definition.  There are alternatives:
151 //        1. Add some sort of stub support to LLVM for cases where we can
152 //           do a this adjustment, then a sibcall.
153 //        2. We could transform the definition to take a va_list instead of an
154 //           actual variable argument list, then have the thunks (including a
155 //           no-op thunk for the regular definition) call va_start/va_end.
156 //           There's a bit of per-call overhead for this solution, but it's
157 //           better for codesize if the definition is long.
158 llvm::Function *
159 CodeGenFunction::GenerateVarArgsThunk(llvm::Function *Fn,
160                                       const CGFunctionInfo &FnInfo,
161                                       GlobalDecl GD, const ThunkInfo &Thunk) {
162   const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
163   const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
164   QualType ResultType = FPT->getReturnType();
165 
166   // Get the original function
167   assert(FnInfo.isVariadic());
168   llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);
169   llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
170   llvm::Function *BaseFn = cast<llvm::Function>(Callee);
171 
172   // Cloning can't work if we don't have a definition. The Microsoft ABI may
173   // require thunks when a definition is not available. Emit an error in these
174   // cases.
175   if (!MD->isDefined()) {
176     CGM.ErrorUnsupported(MD, "return-adjusting thunk with variadic arguments");
177     return Fn;
178   }
179   assert(!BaseFn->isDeclaration() && "cannot clone undefined variadic method");
180 
181   // Clone to thunk.
182   llvm::ValueToValueMapTy VMap;
183 
184   // We are cloning a function while some Metadata nodes are still unresolved.
185   // Ensure that the value mapper does not encounter any of them.
186   resolveTopLevelMetadata(BaseFn, VMap);
187   llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap);
188   Fn->replaceAllUsesWith(NewFn);
189   NewFn->takeName(Fn);
190   Fn->eraseFromParent();
191   Fn = NewFn;
192 
193   // "Initialize" CGF (minimally).
194   CurFn = Fn;
195 
196   // Get the "this" value
197   llvm::Function::arg_iterator AI = Fn->arg_begin();
198   if (CGM.ReturnTypeUsesSRet(FnInfo))
199     ++AI;
200 
201   // Find the first store of "this", which will be to the alloca associated
202   // with "this".
203   Address ThisPtr =
204       Address(&*AI, ConvertTypeForMem(MD->getThisType()->getPointeeType()),
205               CGM.getClassPointerAlignment(MD->getParent()));
206   llvm::BasicBlock *EntryBB = &Fn->front();
207   llvm::BasicBlock::iterator ThisStore =
208       llvm::find_if(*EntryBB, [&](llvm::Instruction &I) {
209         return isa<llvm::StoreInst>(I) &&
210                I.getOperand(0) == ThisPtr.getPointer();
211       });
212   assert(ThisStore != EntryBB->end() &&
213          "Store of this should be in entry block?");
214   // Adjust "this", if necessary.
215   Builder.SetInsertPoint(&*ThisStore);
216   llvm::Value *AdjustedThisPtr =
217       CGM.getCXXABI().performThisAdjustment(*this, ThisPtr, Thunk.This);
218   AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr,
219                                           ThisStore->getOperand(0)->getType());
220   ThisStore->setOperand(0, AdjustedThisPtr);
221 
222   if (!Thunk.Return.isEmpty()) {
223     // Fix up the returned value, if necessary.
224     for (llvm::BasicBlock &BB : *Fn) {
225       llvm::Instruction *T = BB.getTerminator();
226       if (isa<llvm::ReturnInst>(T)) {
227         RValue RV = RValue::get(T->getOperand(0));
228         T->eraseFromParent();
229         Builder.SetInsertPoint(&BB);
230         RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
231         Builder.CreateRet(RV.getScalarVal());
232         break;
233       }
234     }
235   }
236 
237   return Fn;
238 }
239 
240 void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
241                                  const CGFunctionInfo &FnInfo,
242                                  bool IsUnprototyped) {
243   assert(!CurGD.getDecl() && "CurGD was already set!");
244   CurGD = GD;
245   CurFuncIsThunk = true;
246 
247   // Build FunctionArgs.
248   const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
249   QualType ThisType = MD->getThisType();
250   QualType ResultType;
251   if (IsUnprototyped)
252     ResultType = CGM.getContext().VoidTy;
253   else if (CGM.getCXXABI().HasThisReturn(GD))
254     ResultType = ThisType;
255   else if (CGM.getCXXABI().hasMostDerivedReturn(GD))
256     ResultType = CGM.getContext().VoidPtrTy;
257   else
258     ResultType = MD->getType()->castAs<FunctionProtoType>()->getReturnType();
259   FunctionArgList FunctionArgs;
260 
261   // Create the implicit 'this' parameter declaration.
262   CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
263 
264   // Add the rest of the parameters, if we have a prototype to work with.
265   if (!IsUnprototyped) {
266     FunctionArgs.append(MD->param_begin(), MD->param_end());
267 
268     if (isa<CXXDestructorDecl>(MD))
269       CGM.getCXXABI().addImplicitStructorParams(*this, ResultType,
270                                                 FunctionArgs);
271   }
272 
273   // Start defining the function.
274   auto NL = ApplyDebugLocation::CreateEmpty(*this);
275   StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
276                 MD->getLocation());
277   // Create a scope with an artificial location for the body of this function.
278   auto AL = ApplyDebugLocation::CreateArtificial(*this);
279 
280   // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
281   CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
282   CXXThisValue = CXXABIThisValue;
283   CurCodeDecl = MD;
284   CurFuncDecl = MD;
285 }
286 
287 void CodeGenFunction::FinishThunk() {
288   // Clear these to restore the invariants expected by
289   // StartFunction/FinishFunction.
290   CurCodeDecl = nullptr;
291   CurFuncDecl = nullptr;
292 
293   FinishFunction();
294 }
295 
296 void CodeGenFunction::EmitCallAndReturnForThunk(llvm::FunctionCallee Callee,
297                                                 const ThunkInfo *Thunk,
298                                                 bool IsUnprototyped) {
299   assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
300          "Please use a new CGF for this thunk");
301   const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurGD.getDecl());
302 
303   // Adjust the 'this' pointer if necessary
304   llvm::Value *AdjustedThisPtr =
305     Thunk ? CGM.getCXXABI().performThisAdjustment(
306                           *this, LoadCXXThisAddress(), Thunk->This)
307           : LoadCXXThis();
308 
309   // If perfect forwarding is required a variadic method, a method using
310   // inalloca, or an unprototyped thunk, use musttail. Emit an error if this
311   // thunk requires a return adjustment, since that is impossible with musttail.
312   if (CurFnInfo->usesInAlloca() || CurFnInfo->isVariadic() || IsUnprototyped) {
313     if (Thunk && !Thunk->Return.isEmpty()) {
314       if (IsUnprototyped)
315         CGM.ErrorUnsupported(
316             MD, "return-adjusting thunk with incomplete parameter type");
317       else if (CurFnInfo->isVariadic())
318         llvm_unreachable("shouldn't try to emit musttail return-adjusting "
319                          "thunks for variadic functions");
320       else
321         CGM.ErrorUnsupported(
322             MD, "non-trivial argument copy for return-adjusting thunk");
323     }
324     EmitMustTailThunk(CurGD, AdjustedThisPtr, Callee);
325     return;
326   }
327 
328   // Start building CallArgs.
329   CallArgList CallArgs;
330   QualType ThisType = MD->getThisType();
331   CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
332 
333   if (isa<CXXDestructorDecl>(MD))
334     CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);
335 
336 #ifndef NDEBUG
337   unsigned PrefixArgs = CallArgs.size() - 1;
338 #endif
339   // Add the rest of the arguments.
340   for (const ParmVarDecl *PD : MD->parameters())
341     EmitDelegateCallArg(CallArgs, PD, SourceLocation());
342 
343   const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
344 
345 #ifndef NDEBUG
346   const CGFunctionInfo &CallFnInfo = CGM.getTypes().arrangeCXXMethodCall(
347       CallArgs, FPT, RequiredArgs::forPrototypePlus(FPT, 1), PrefixArgs);
348   assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
349          CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
350          CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
351   assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
352          similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
353                  CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
354   assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
355   for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
356     assert(similar(CallFnInfo.arg_begin()[i].info,
357                    CallFnInfo.arg_begin()[i].type,
358                    CurFnInfo->arg_begin()[i].info,
359                    CurFnInfo->arg_begin()[i].type));
360 #endif
361 
362   // Determine whether we have a return value slot to use.
363   QualType ResultType = CGM.getCXXABI().HasThisReturn(CurGD)
364                             ? ThisType
365                             : CGM.getCXXABI().hasMostDerivedReturn(CurGD)
366                                   ? CGM.getContext().VoidPtrTy
367                                   : FPT->getReturnType();
368   ReturnValueSlot Slot;
369   if (!ResultType->isVoidType() &&
370       (CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect ||
371        hasAggregateEvaluationKind(ResultType)))
372     Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified(),
373                            /*IsUnused=*/false, /*IsExternallyDestructed=*/true);
374 
375   // Now emit our call.
376   llvm::CallBase *CallOrInvoke;
377   RValue RV = EmitCall(*CurFnInfo, CGCallee::forDirect(Callee, CurGD), Slot,
378                        CallArgs, &CallOrInvoke);
379 
380   // Consider return adjustment if we have ThunkInfo.
381   if (Thunk && !Thunk->Return.isEmpty())
382     RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
383   else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(CallOrInvoke))
384     Call->setTailCallKind(llvm::CallInst::TCK_Tail);
385 
386   // Emit return.
387   if (!ResultType->isVoidType() && Slot.isNull())
388     CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
389 
390   // Disable the final ARC autorelease.
391   AutoreleaseResult = false;
392 
393   FinishThunk();
394 }
395 
396 void CodeGenFunction::EmitMustTailThunk(GlobalDecl GD,
397                                         llvm::Value *AdjustedThisPtr,
398                                         llvm::FunctionCallee Callee) {
399   // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
400   // to translate AST arguments into LLVM IR arguments.  For thunks, we know
401   // that the caller prototype more or less matches the callee prototype with
402   // the exception of 'this'.
403   SmallVector<llvm::Value *, 8> Args(llvm::make_pointer_range(CurFn->args()));
404 
405   // Set the adjusted 'this' pointer.
406   const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
407   if (ThisAI.isDirect()) {
408     const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
409     int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
410     llvm::Type *ThisType = Args[ThisArgNo]->getType();
411     if (ThisType != AdjustedThisPtr->getType())
412       AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
413     Args[ThisArgNo] = AdjustedThisPtr;
414   } else {
415     assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
416     Address ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);
417     llvm::Type *ThisType = ThisAddr.getElementType();
418     if (ThisType != AdjustedThisPtr->getType())
419       AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
420     Builder.CreateStore(AdjustedThisPtr, ThisAddr);
421   }
422 
423   // Emit the musttail call manually.  Even if the prologue pushed cleanups, we
424   // don't actually want to run them.
425   llvm::CallInst *Call = Builder.CreateCall(Callee, Args);
426   Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
427 
428   // Apply the standard set of call attributes.
429   unsigned CallingConv;
430   llvm::AttributeList Attrs;
431   CGM.ConstructAttributeList(Callee.getCallee()->getName(), *CurFnInfo, GD,
432                              Attrs, CallingConv, /*AttrOnCallSite=*/true,
433                              /*IsThunk=*/false);
434   Call->setAttributes(Attrs);
435   Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
436 
437   if (Call->getType()->isVoidTy())
438     Builder.CreateRetVoid();
439   else
440     Builder.CreateRet(Call);
441 
442   // Finish the function to maintain CodeGenFunction invariants.
443   // FIXME: Don't emit unreachable code.
444   EmitBlock(createBasicBlock());
445 
446   FinishThunk();
447 }
448 
449 void CodeGenFunction::generateThunk(llvm::Function *Fn,
450                                     const CGFunctionInfo &FnInfo, GlobalDecl GD,
451                                     const ThunkInfo &Thunk,
452                                     bool IsUnprototyped) {
453   StartThunk(Fn, GD, FnInfo, IsUnprototyped);
454   // Create a scope with an artificial location for the body of this function.
455   auto AL = ApplyDebugLocation::CreateArtificial(*this);
456 
457   // Get our callee. Use a placeholder type if this method is unprototyped so
458   // that CodeGenModule doesn't try to set attributes.
459   llvm::Type *Ty;
460   if (IsUnprototyped)
461     Ty = llvm::StructType::get(getLLVMContext());
462   else
463     Ty = CGM.getTypes().GetFunctionType(FnInfo);
464 
465   llvm::Constant *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
466 
467   // Fix up the function type for an unprototyped musttail call.
468   if (IsUnprototyped)
469     Callee = llvm::ConstantExpr::getBitCast(Callee, Fn->getType());
470 
471   // Make the call and return the result.
472   EmitCallAndReturnForThunk(llvm::FunctionCallee(Fn->getFunctionType(), Callee),
473                             &Thunk, IsUnprototyped);
474 }
475 
476 static bool shouldEmitVTableThunk(CodeGenModule &CGM, const CXXMethodDecl *MD,
477                                   bool IsUnprototyped, bool ForVTable) {
478   // Always emit thunks in the MS C++ ABI. We cannot rely on other TUs to
479   // provide thunks for us.
480   if (CGM.getTarget().getCXXABI().isMicrosoft())
481     return true;
482 
483   // In the Itanium C++ ABI, vtable thunks are provided by TUs that provide
484   // definitions of the main method. Therefore, emitting thunks with the vtable
485   // is purely an optimization. Emit the thunk if optimizations are enabled and
486   // all of the parameter types are complete.
487   if (ForVTable)
488     return CGM.getCodeGenOpts().OptimizationLevel && !IsUnprototyped;
489 
490   // Always emit thunks along with the method definition.
491   return true;
492 }
493 
494 llvm::Constant *CodeGenVTables::maybeEmitThunk(GlobalDecl GD,
495                                                const ThunkInfo &TI,
496                                                bool ForVTable) {
497   const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
498 
499   // First, get a declaration. Compute the mangled name. Don't worry about
500   // getting the function prototype right, since we may only need this
501   // declaration to fill in a vtable slot.
502   SmallString<256> Name;
503   MangleContext &MCtx = CGM.getCXXABI().getMangleContext();
504   llvm::raw_svector_ostream Out(Name);
505   if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))
506     MCtx.mangleCXXDtorThunk(DD, GD.getDtorType(), TI.This, Out);
507   else
508     MCtx.mangleThunk(MD, TI, Out);
509   llvm::Type *ThunkVTableTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
510   llvm::Constant *Thunk = CGM.GetAddrOfThunk(Name, ThunkVTableTy, GD);
511 
512   // If we don't need to emit a definition, return this declaration as is.
513   bool IsUnprototyped = !CGM.getTypes().isFuncTypeConvertible(
514       MD->getType()->castAs<FunctionType>());
515   if (!shouldEmitVTableThunk(CGM, MD, IsUnprototyped, ForVTable))
516     return Thunk;
517 
518   // Arrange a function prototype appropriate for a function definition. In some
519   // cases in the MS ABI, we may need to build an unprototyped musttail thunk.
520   const CGFunctionInfo &FnInfo =
521       IsUnprototyped ? CGM.getTypes().arrangeUnprototypedMustTailThunk(MD)
522                      : CGM.getTypes().arrangeGlobalDeclaration(GD);
523   llvm::FunctionType *ThunkFnTy = CGM.getTypes().GetFunctionType(FnInfo);
524 
525   // If the type of the underlying GlobalValue is wrong, we'll have to replace
526   // it. It should be a declaration.
527   llvm::Function *ThunkFn = cast<llvm::Function>(Thunk->stripPointerCasts());
528   if (ThunkFn->getFunctionType() != ThunkFnTy) {
529     llvm::GlobalValue *OldThunkFn = ThunkFn;
530 
531     assert(OldThunkFn->isDeclaration() && "Shouldn't replace non-declaration");
532 
533     // Remove the name from the old thunk function and get a new thunk.
534     OldThunkFn->setName(StringRef());
535     ThunkFn = llvm::Function::Create(ThunkFnTy, llvm::Function::ExternalLinkage,
536                                      Name.str(), &CGM.getModule());
537     CGM.SetLLVMFunctionAttributes(MD, FnInfo, ThunkFn, /*IsThunk=*/false);
538 
539     // If needed, replace the old thunk with a bitcast.
540     if (!OldThunkFn->use_empty()) {
541       llvm::Constant *NewPtrForOldDecl =
542           llvm::ConstantExpr::getBitCast(ThunkFn, OldThunkFn->getType());
543       OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
544     }
545 
546     // Remove the old thunk.
547     OldThunkFn->eraseFromParent();
548   }
549 
550   bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
551   bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
552 
553   if (!ThunkFn->isDeclaration()) {
554     if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
555       // There is already a thunk emitted for this function, do nothing.
556       return ThunkFn;
557     }
558 
559     setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
560     return ThunkFn;
561   }
562 
563   // If this will be unprototyped, add the "thunk" attribute so that LLVM knows
564   // that the return type is meaningless. These thunks can be used to call
565   // functions with differing return types, and the caller is required to cast
566   // the prototype appropriately to extract the correct value.
567   if (IsUnprototyped)
568     ThunkFn->addFnAttr("thunk");
569 
570   CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
571 
572   // Thunks for variadic methods are special because in general variadic
573   // arguments cannot be perfectly forwarded. In the general case, clang
574   // implements such thunks by cloning the original function body. However, for
575   // thunks with no return adjustment on targets that support musttail, we can
576   // use musttail to perfectly forward the variadic arguments.
577   bool ShouldCloneVarArgs = false;
578   if (!IsUnprototyped && ThunkFn->isVarArg()) {
579     ShouldCloneVarArgs = true;
580     if (TI.Return.isEmpty()) {
581       switch (CGM.getTriple().getArch()) {
582       case llvm::Triple::x86_64:
583       case llvm::Triple::x86:
584       case llvm::Triple::aarch64:
585         ShouldCloneVarArgs = false;
586         break;
587       default:
588         break;
589       }
590     }
591   }
592 
593   if (ShouldCloneVarArgs) {
594     if (UseAvailableExternallyLinkage)
595       return ThunkFn;
596     ThunkFn =
597         CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, TI);
598   } else {
599     // Normal thunk body generation.
600     CodeGenFunction(CGM).generateThunk(ThunkFn, FnInfo, GD, TI, IsUnprototyped);
601   }
602 
603   setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
604   return ThunkFn;
605 }
606 
607 void CodeGenVTables::EmitThunks(GlobalDecl GD) {
608   const CXXMethodDecl *MD =
609     cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
610 
611   // We don't need to generate thunks for the base destructor.
612   if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
613     return;
614 
615   const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
616       VTContext->getThunkInfo(GD);
617 
618   if (!ThunkInfoVector)
619     return;
620 
621   for (const ThunkInfo& Thunk : *ThunkInfoVector)
622     maybeEmitThunk(GD, Thunk, /*ForVTable=*/false);
623 }
624 
625 void CodeGenVTables::addRelativeComponent(ConstantArrayBuilder &builder,
626                                           llvm::Constant *component,
627                                           unsigned vtableAddressPoint,
628                                           bool vtableHasLocalLinkage,
629                                           bool isCompleteDtor) const {
630   // No need to get the offset of a nullptr.
631   if (component->isNullValue())
632     return builder.add(llvm::ConstantInt::get(CGM.Int32Ty, 0));
633 
634   auto *globalVal =
635       cast<llvm::GlobalValue>(component->stripPointerCastsAndAliases());
636   llvm::Module &module = CGM.getModule();
637 
638   // We don't want to copy the linkage of the vtable exactly because we still
639   // want the stub/proxy to be emitted for properly calculating the offset.
640   // Examples where there would be no symbol emitted are available_externally
641   // and private linkages.
642   auto stubLinkage = vtableHasLocalLinkage ? llvm::GlobalValue::InternalLinkage
643                                            : llvm::GlobalValue::ExternalLinkage;
644 
645   llvm::Constant *target;
646   if (auto *func = dyn_cast<llvm::Function>(globalVal)) {
647     target = llvm::DSOLocalEquivalent::get(func);
648   } else {
649     llvm::SmallString<16> rttiProxyName(globalVal->getName());
650     rttiProxyName.append(".rtti_proxy");
651 
652     // The RTTI component may not always be emitted in the same linkage unit as
653     // the vtable. As a general case, we can make a dso_local proxy to the RTTI
654     // that points to the actual RTTI struct somewhere. This will result in a
655     // GOTPCREL relocation when taking the relative offset to the proxy.
656     llvm::GlobalVariable *proxy = module.getNamedGlobal(rttiProxyName);
657     if (!proxy) {
658       proxy = new llvm::GlobalVariable(module, globalVal->getType(),
659                                        /*isConstant=*/true, stubLinkage,
660                                        globalVal, rttiProxyName);
661       proxy->setDSOLocal(true);
662       proxy->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
663       if (!proxy->hasLocalLinkage()) {
664         proxy->setVisibility(llvm::GlobalValue::HiddenVisibility);
665         proxy->setComdat(module.getOrInsertComdat(rttiProxyName));
666       }
667     }
668     target = proxy;
669   }
670 
671   builder.addRelativeOffsetToPosition(CGM.Int32Ty, target,
672                                       /*position=*/vtableAddressPoint);
673 }
674 
675 bool CodeGenVTables::useRelativeLayout() const {
676   return CGM.getTarget().getCXXABI().isItaniumFamily() &&
677          CGM.getItaniumVTableContext().isRelativeLayout();
678 }
679 
680 llvm::Type *CodeGenVTables::getVTableComponentType() const {
681   if (useRelativeLayout())
682     return CGM.Int32Ty;
683   return CGM.Int8PtrTy;
684 }
685 
686 static void AddPointerLayoutOffset(const CodeGenModule &CGM,
687                                    ConstantArrayBuilder &builder,
688                                    CharUnits offset) {
689   builder.add(llvm::ConstantExpr::getIntToPtr(
690       llvm::ConstantInt::get(CGM.PtrDiffTy, offset.getQuantity()),
691       CGM.Int8PtrTy));
692 }
693 
694 static void AddRelativeLayoutOffset(const CodeGenModule &CGM,
695                                     ConstantArrayBuilder &builder,
696                                     CharUnits offset) {
697   builder.add(llvm::ConstantInt::get(CGM.Int32Ty, offset.getQuantity()));
698 }
699 
700 void CodeGenVTables::addVTableComponent(ConstantArrayBuilder &builder,
701                                         const VTableLayout &layout,
702                                         unsigned componentIndex,
703                                         llvm::Constant *rtti,
704                                         unsigned &nextVTableThunkIndex,
705                                         unsigned vtableAddressPoint,
706                                         bool vtableHasLocalLinkage) {
707   auto &component = layout.vtable_components()[componentIndex];
708 
709   auto addOffsetConstant =
710       useRelativeLayout() ? AddRelativeLayoutOffset : AddPointerLayoutOffset;
711 
712   switch (component.getKind()) {
713   case VTableComponent::CK_VCallOffset:
714     return addOffsetConstant(CGM, builder, component.getVCallOffset());
715 
716   case VTableComponent::CK_VBaseOffset:
717     return addOffsetConstant(CGM, builder, component.getVBaseOffset());
718 
719   case VTableComponent::CK_OffsetToTop:
720     return addOffsetConstant(CGM, builder, component.getOffsetToTop());
721 
722   case VTableComponent::CK_RTTI:
723     if (useRelativeLayout())
724       return addRelativeComponent(builder, rtti, vtableAddressPoint,
725                                   vtableHasLocalLinkage,
726                                   /*isCompleteDtor=*/false);
727     else
728       return builder.add(llvm::ConstantExpr::getBitCast(rtti, CGM.Int8PtrTy));
729 
730   case VTableComponent::CK_FunctionPointer:
731   case VTableComponent::CK_CompleteDtorPointer:
732   case VTableComponent::CK_DeletingDtorPointer: {
733     GlobalDecl GD = component.getGlobalDecl();
734 
735     if (CGM.getLangOpts().CUDA) {
736       // Emit NULL for methods we can't codegen on this
737       // side. Otherwise we'd end up with vtable with unresolved
738       // references.
739       const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
740       // OK on device side: functions w/ __device__ attribute
741       // OK on host side: anything except __device__-only functions.
742       bool CanEmitMethod =
743           CGM.getLangOpts().CUDAIsDevice
744               ? MD->hasAttr<CUDADeviceAttr>()
745               : (MD->hasAttr<CUDAHostAttr>() || !MD->hasAttr<CUDADeviceAttr>());
746       if (!CanEmitMethod)
747         return builder.add(llvm::ConstantExpr::getNullValue(CGM.Int8PtrTy));
748       // Method is acceptable, continue processing as usual.
749     }
750 
751     auto getSpecialVirtualFn = [&](StringRef name) -> llvm::Constant * {
752       // FIXME(PR43094): When merging comdat groups, lld can select a local
753       // symbol as the signature symbol even though it cannot be accessed
754       // outside that symbol's TU. The relative vtables ABI would make
755       // __cxa_pure_virtual and __cxa_deleted_virtual local symbols, and
756       // depending on link order, the comdat groups could resolve to the one
757       // with the local symbol. As a temporary solution, fill these components
758       // with zero. We shouldn't be calling these in the first place anyway.
759       if (useRelativeLayout())
760         return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
761 
762       // For NVPTX devices in OpenMP emit special functon as null pointers,
763       // otherwise linking ends up with unresolved references.
764       if (CGM.getLangOpts().OpenMP && CGM.getLangOpts().OpenMPIsDevice &&
765           CGM.getTriple().isNVPTX())
766         return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
767       llvm::FunctionType *fnTy =
768           llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
769       llvm::Constant *fn = cast<llvm::Constant>(
770           CGM.CreateRuntimeFunction(fnTy, name).getCallee());
771       if (auto f = dyn_cast<llvm::Function>(fn))
772         f->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
773       return llvm::ConstantExpr::getBitCast(fn, CGM.Int8PtrTy);
774     };
775 
776     llvm::Constant *fnPtr;
777 
778     // Pure virtual member functions.
779     if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
780       if (!PureVirtualFn)
781         PureVirtualFn =
782             getSpecialVirtualFn(CGM.getCXXABI().GetPureVirtualCallName());
783       fnPtr = PureVirtualFn;
784 
785     // Deleted virtual member functions.
786     } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
787       if (!DeletedVirtualFn)
788         DeletedVirtualFn =
789             getSpecialVirtualFn(CGM.getCXXABI().GetDeletedVirtualCallName());
790       fnPtr = DeletedVirtualFn;
791 
792     // Thunks.
793     } else if (nextVTableThunkIndex < layout.vtable_thunks().size() &&
794                layout.vtable_thunks()[nextVTableThunkIndex].first ==
795                    componentIndex) {
796       auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;
797 
798       nextVTableThunkIndex++;
799       fnPtr = maybeEmitThunk(GD, thunkInfo, /*ForVTable=*/true);
800 
801     // Otherwise we can use the method definition directly.
802     } else {
803       llvm::Type *fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
804       fnPtr = CGM.GetAddrOfFunction(GD, fnTy, /*ForVTable=*/true);
805     }
806 
807     if (useRelativeLayout()) {
808       return addRelativeComponent(
809           builder, fnPtr, vtableAddressPoint, vtableHasLocalLinkage,
810           component.getKind() == VTableComponent::CK_CompleteDtorPointer);
811     } else
812       return builder.add(llvm::ConstantExpr::getBitCast(fnPtr, CGM.Int8PtrTy));
813   }
814 
815   case VTableComponent::CK_UnusedFunctionPointer:
816     if (useRelativeLayout())
817       return builder.add(llvm::ConstantExpr::getNullValue(CGM.Int32Ty));
818     else
819       return builder.addNullPointer(CGM.Int8PtrTy);
820   }
821 
822   llvm_unreachable("Unexpected vtable component kind");
823 }
824 
825 llvm::Type *CodeGenVTables::getVTableType(const VTableLayout &layout) {
826   SmallVector<llvm::Type *, 4> tys;
827   llvm::Type *componentType = getVTableComponentType();
828   for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i)
829     tys.push_back(llvm::ArrayType::get(componentType, layout.getVTableSize(i)));
830 
831   return llvm::StructType::get(CGM.getLLVMContext(), tys);
832 }
833 
834 void CodeGenVTables::createVTableInitializer(ConstantStructBuilder &builder,
835                                              const VTableLayout &layout,
836                                              llvm::Constant *rtti,
837                                              bool vtableHasLocalLinkage) {
838   llvm::Type *componentType = getVTableComponentType();
839 
840   const auto &addressPoints = layout.getAddressPointIndices();
841   unsigned nextVTableThunkIndex = 0;
842   for (unsigned vtableIndex = 0, endIndex = layout.getNumVTables();
843        vtableIndex != endIndex; ++vtableIndex) {
844     auto vtableElem = builder.beginArray(componentType);
845 
846     size_t vtableStart = layout.getVTableOffset(vtableIndex);
847     size_t vtableEnd = vtableStart + layout.getVTableSize(vtableIndex);
848     for (size_t componentIndex = vtableStart; componentIndex < vtableEnd;
849          ++componentIndex) {
850       addVTableComponent(vtableElem, layout, componentIndex, rtti,
851                          nextVTableThunkIndex, addressPoints[vtableIndex],
852                          vtableHasLocalLinkage);
853     }
854     vtableElem.finishAndAddTo(builder);
855   }
856 }
857 
858 llvm::GlobalVariable *CodeGenVTables::GenerateConstructionVTable(
859     const CXXRecordDecl *RD, const BaseSubobject &Base, bool BaseIsVirtual,
860     llvm::GlobalVariable::LinkageTypes Linkage,
861     VTableAddressPointsMapTy &AddressPoints) {
862   if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
863     DI->completeClassData(Base.getBase());
864 
865   std::unique_ptr<VTableLayout> VTLayout(
866       getItaniumVTableContext().createConstructionVTableLayout(
867           Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
868 
869   // Add the address points.
870   AddressPoints = VTLayout->getAddressPoints();
871 
872   // Get the mangled construction vtable name.
873   SmallString<256> OutName;
874   llvm::raw_svector_ostream Out(OutName);
875   cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
876       .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
877                            Base.getBase(), Out);
878   SmallString<256> Name(OutName);
879 
880   bool UsingRelativeLayout = getItaniumVTableContext().isRelativeLayout();
881   bool VTableAliasExists =
882       UsingRelativeLayout && CGM.getModule().getNamedAlias(Name);
883   if (VTableAliasExists) {
884     // We previously made the vtable hidden and changed its name.
885     Name.append(".local");
886   }
887 
888   llvm::Type *VTType = getVTableType(*VTLayout);
889 
890   // Construction vtable symbols are not part of the Itanium ABI, so we cannot
891   // guarantee that they actually will be available externally. Instead, when
892   // emitting an available_externally VTT, we provide references to an internal
893   // linkage construction vtable. The ABI only requires complete-object vtables
894   // to be the same for all instances of a type, not construction vtables.
895   if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
896     Linkage = llvm::GlobalVariable::InternalLinkage;
897 
898   unsigned Align = CGM.getDataLayout().getABITypeAlignment(VTType);
899 
900   // Create the variable that will hold the construction vtable.
901   llvm::GlobalVariable *VTable =
902       CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage, Align);
903 
904   // V-tables are always unnamed_addr.
905   VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
906 
907   llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
908       CGM.getContext().getTagDeclType(Base.getBase()));
909 
910   // Create and set the initializer.
911   ConstantInitBuilder builder(CGM);
912   auto components = builder.beginStruct();
913   createVTableInitializer(components, *VTLayout, RTTI,
914                           VTable->hasLocalLinkage());
915   components.finishAndSetAsInitializer(VTable);
916 
917   // Set properties only after the initializer has been set to ensure that the
918   // GV is treated as definition and not declaration.
919   assert(!VTable->isDeclaration() && "Shouldn't set properties on declaration");
920   CGM.setGVProperties(VTable, RD);
921 
922   CGM.EmitVTableTypeMetadata(RD, VTable, *VTLayout.get());
923 
924   if (UsingRelativeLayout && !VTable->isDSOLocal())
925     GenerateRelativeVTableAlias(VTable, OutName);
926 
927   return VTable;
928 }
929 
930 // If the VTable is not dso_local, then we will not be able to indicate that
931 // the VTable does not need a relocation and move into rodata. A frequent
932 // time this can occur is for classes that should be made public from a DSO
933 // (like in libc++). For cases like these, we can make the vtable hidden or
934 // private and create a public alias with the same visibility and linkage as
935 // the original vtable type.
936 void CodeGenVTables::GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
937                                                  llvm::StringRef AliasNameRef) {
938   assert(getItaniumVTableContext().isRelativeLayout() &&
939          "Can only use this if the relative vtable ABI is used");
940   assert(!VTable->isDSOLocal() && "This should be called only if the vtable is "
941                                   "not guaranteed to be dso_local");
942 
943   // If the vtable is available_externally, we shouldn't (or need to) generate
944   // an alias for it in the first place since the vtable won't actually by
945   // emitted in this compilation unit.
946   if (VTable->hasAvailableExternallyLinkage())
947     return;
948 
949   // Create a new string in the event the alias is already the name of the
950   // vtable. Using the reference directly could lead to use of an inititialized
951   // value in the module's StringMap.
952   llvm::SmallString<256> AliasName(AliasNameRef);
953   VTable->setName(AliasName + ".local");
954 
955   auto Linkage = VTable->getLinkage();
956   assert(llvm::GlobalAlias::isValidLinkage(Linkage) &&
957          "Invalid vtable alias linkage");
958 
959   llvm::GlobalAlias *VTableAlias = CGM.getModule().getNamedAlias(AliasName);
960   if (!VTableAlias) {
961     VTableAlias = llvm::GlobalAlias::create(VTable->getValueType(),
962                                             VTable->getAddressSpace(), Linkage,
963                                             AliasName, &CGM.getModule());
964   } else {
965     assert(VTableAlias->getValueType() == VTable->getValueType());
966     assert(VTableAlias->getLinkage() == Linkage);
967   }
968   VTableAlias->setVisibility(VTable->getVisibility());
969   VTableAlias->setUnnamedAddr(VTable->getUnnamedAddr());
970 
971   // Both of these imply dso_local for the vtable.
972   if (!VTable->hasComdat()) {
973     // If this is in a comdat, then we shouldn't make the linkage private due to
974     // an issue in lld where private symbols can be used as the key symbol when
975     // choosing the prevelant group. This leads to "relocation refers to a
976     // symbol in a discarded section".
977     VTable->setLinkage(llvm::GlobalValue::PrivateLinkage);
978   } else {
979     // We should at least make this hidden since we don't want to expose it.
980     VTable->setVisibility(llvm::GlobalValue::HiddenVisibility);
981   }
982 
983   VTableAlias->setAliasee(VTable);
984 }
985 
986 static bool shouldEmitAvailableExternallyVTable(const CodeGenModule &CGM,
987                                                 const CXXRecordDecl *RD) {
988   return CGM.getCodeGenOpts().OptimizationLevel > 0 &&
989          CGM.getCXXABI().canSpeculativelyEmitVTable(RD);
990 }
991 
992 /// Compute the required linkage of the vtable for the given class.
993 ///
994 /// Note that we only call this at the end of the translation unit.
995 llvm::GlobalVariable::LinkageTypes
996 CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
997   if (!RD->isExternallyVisible())
998     return llvm::GlobalVariable::InternalLinkage;
999 
1000   // We're at the end of the translation unit, so the current key
1001   // function is fully correct.
1002   const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
1003   if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
1004     // If this class has a key function, use that to determine the
1005     // linkage of the vtable.
1006     const FunctionDecl *def = nullptr;
1007     if (keyFunction->hasBody(def))
1008       keyFunction = cast<CXXMethodDecl>(def);
1009 
1010     switch (keyFunction->getTemplateSpecializationKind()) {
1011       case TSK_Undeclared:
1012       case TSK_ExplicitSpecialization:
1013         assert((def || CodeGenOpts.OptimizationLevel > 0 ||
1014                 CodeGenOpts.getDebugInfo() != codegenoptions::NoDebugInfo) &&
1015                "Shouldn't query vtable linkage without key function, "
1016                "optimizations, or debug info");
1017         if (!def && CodeGenOpts.OptimizationLevel > 0)
1018           return llvm::GlobalVariable::AvailableExternallyLinkage;
1019 
1020         if (keyFunction->isInlined())
1021           return !Context.getLangOpts().AppleKext ?
1022                    llvm::GlobalVariable::LinkOnceODRLinkage :
1023                    llvm::Function::InternalLinkage;
1024 
1025         return llvm::GlobalVariable::ExternalLinkage;
1026 
1027       case TSK_ImplicitInstantiation:
1028         return !Context.getLangOpts().AppleKext ?
1029                  llvm::GlobalVariable::LinkOnceODRLinkage :
1030                  llvm::Function::InternalLinkage;
1031 
1032       case TSK_ExplicitInstantiationDefinition:
1033         return !Context.getLangOpts().AppleKext ?
1034                  llvm::GlobalVariable::WeakODRLinkage :
1035                  llvm::Function::InternalLinkage;
1036 
1037       case TSK_ExplicitInstantiationDeclaration:
1038         llvm_unreachable("Should not have been asked to emit this");
1039     }
1040   }
1041 
1042   // -fapple-kext mode does not support weak linkage, so we must use
1043   // internal linkage.
1044   if (Context.getLangOpts().AppleKext)
1045     return llvm::Function::InternalLinkage;
1046 
1047   llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
1048       llvm::GlobalValue::LinkOnceODRLinkage;
1049   llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
1050       llvm::GlobalValue::WeakODRLinkage;
1051   if (RD->hasAttr<DLLExportAttr>()) {
1052     // Cannot discard exported vtables.
1053     DiscardableODRLinkage = NonDiscardableODRLinkage;
1054   } else if (RD->hasAttr<DLLImportAttr>()) {
1055     // Imported vtables are available externally.
1056     DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
1057     NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
1058   }
1059 
1060   switch (RD->getTemplateSpecializationKind()) {
1061     case TSK_Undeclared:
1062     case TSK_ExplicitSpecialization:
1063     case TSK_ImplicitInstantiation:
1064       return DiscardableODRLinkage;
1065 
1066     case TSK_ExplicitInstantiationDeclaration:
1067       // Explicit instantiations in MSVC do not provide vtables, so we must emit
1068       // our own.
1069       if (getTarget().getCXXABI().isMicrosoft())
1070         return DiscardableODRLinkage;
1071       return shouldEmitAvailableExternallyVTable(*this, RD)
1072                  ? llvm::GlobalVariable::AvailableExternallyLinkage
1073                  : llvm::GlobalVariable::ExternalLinkage;
1074 
1075     case TSK_ExplicitInstantiationDefinition:
1076       return NonDiscardableODRLinkage;
1077   }
1078 
1079   llvm_unreachable("Invalid TemplateSpecializationKind!");
1080 }
1081 
1082 /// This is a callback from Sema to tell us that a particular vtable is
1083 /// required to be emitted in this translation unit.
1084 ///
1085 /// This is only called for vtables that _must_ be emitted (mainly due to key
1086 /// functions).  For weak vtables, CodeGen tracks when they are needed and
1087 /// emits them as-needed.
1088 void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
1089   VTables.GenerateClassData(theClass);
1090 }
1091 
1092 void
1093 CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
1094   if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
1095     DI->completeClassData(RD);
1096 
1097   if (RD->getNumVBases())
1098     CGM.getCXXABI().emitVirtualInheritanceTables(RD);
1099 
1100   CGM.getCXXABI().emitVTableDefinitions(*this, RD);
1101 }
1102 
1103 /// At this point in the translation unit, does it appear that can we
1104 /// rely on the vtable being defined elsewhere in the program?
1105 ///
1106 /// The response is really only definitive when called at the end of
1107 /// the translation unit.
1108 ///
1109 /// The only semantic restriction here is that the object file should
1110 /// not contain a vtable definition when that vtable is defined
1111 /// strongly elsewhere.  Otherwise, we'd just like to avoid emitting
1112 /// vtables when unnecessary.
1113 bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
1114   assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
1115 
1116   // We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't
1117   // emit them even if there is an explicit template instantiation.
1118   if (CGM.getTarget().getCXXABI().isMicrosoft())
1119     return false;
1120 
1121   // If we have an explicit instantiation declaration (and not a
1122   // definition), the vtable is defined elsewhere.
1123   TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
1124   if (TSK == TSK_ExplicitInstantiationDeclaration)
1125     return true;
1126 
1127   // Otherwise, if the class is an instantiated template, the
1128   // vtable must be defined here.
1129   if (TSK == TSK_ImplicitInstantiation ||
1130       TSK == TSK_ExplicitInstantiationDefinition)
1131     return false;
1132 
1133   // Otherwise, if the class doesn't have a key function (possibly
1134   // anymore), the vtable must be defined here.
1135   const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
1136   if (!keyFunction)
1137     return false;
1138 
1139   // Otherwise, if we don't have a definition of the key function, the
1140   // vtable must be defined somewhere else.
1141   return !keyFunction->hasBody();
1142 }
1143 
1144 /// Given that we're currently at the end of the translation unit, and
1145 /// we've emitted a reference to the vtable for this class, should
1146 /// we define that vtable?
1147 static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
1148                                                    const CXXRecordDecl *RD) {
1149   // If vtable is internal then it has to be done.
1150   if (!CGM.getVTables().isVTableExternal(RD))
1151     return true;
1152 
1153   // If it's external then maybe we will need it as available_externally.
1154   return shouldEmitAvailableExternallyVTable(CGM, RD);
1155 }
1156 
1157 /// Given that at some point we emitted a reference to one or more
1158 /// vtables, and that we are now at the end of the translation unit,
1159 /// decide whether we should emit them.
1160 void CodeGenModule::EmitDeferredVTables() {
1161 #ifndef NDEBUG
1162   // Remember the size of DeferredVTables, because we're going to assume
1163   // that this entire operation doesn't modify it.
1164   size_t savedSize = DeferredVTables.size();
1165 #endif
1166 
1167   for (const CXXRecordDecl *RD : DeferredVTables)
1168     if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
1169       VTables.GenerateClassData(RD);
1170     else if (shouldOpportunisticallyEmitVTables())
1171       OpportunisticVTables.push_back(RD);
1172 
1173   assert(savedSize == DeferredVTables.size() &&
1174          "deferred extra vtables during vtable emission?");
1175   DeferredVTables.clear();
1176 }
1177 
1178 bool CodeGenModule::AlwaysHasLTOVisibilityPublic(const CXXRecordDecl *RD) {
1179   if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>())
1180     return true;
1181 
1182   if (!getCodeGenOpts().LTOVisibilityPublicStd)
1183     return false;
1184 
1185   const DeclContext *DC = RD;
1186   while (true) {
1187     auto *D = cast<Decl>(DC);
1188     DC = DC->getParent();
1189     if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {
1190       if (auto *ND = dyn_cast<NamespaceDecl>(D))
1191         if (const IdentifierInfo *II = ND->getIdentifier())
1192           if (II->isStr("std") || II->isStr("stdext"))
1193             return true;
1194       break;
1195     }
1196   }
1197 
1198   return false;
1199 }
1200 
1201 bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
1202   LinkageInfo LV = RD->getLinkageAndVisibility();
1203   if (!isExternallyVisible(LV.getLinkage()))
1204     return true;
1205 
1206   if (getTriple().isOSBinFormatCOFF()) {
1207     if (RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())
1208       return false;
1209   } else {
1210     if (LV.getVisibility() != HiddenVisibility)
1211       return false;
1212   }
1213 
1214   return !AlwaysHasLTOVisibilityPublic(RD);
1215 }
1216 
1217 llvm::GlobalObject::VCallVisibility CodeGenModule::GetVCallVisibilityLevel(
1218     const CXXRecordDecl *RD, llvm::DenseSet<const CXXRecordDecl *> &Visited) {
1219   // If we have already visited this RD (which means this is a recursive call
1220   // since the initial call should have an empty Visited set), return the max
1221   // visibility. The recursive calls below compute the min between the result
1222   // of the recursive call and the current TypeVis, so returning the max here
1223   // ensures that it will have no effect on the current TypeVis.
1224   if (!Visited.insert(RD).second)
1225     return llvm::GlobalObject::VCallVisibilityTranslationUnit;
1226 
1227   LinkageInfo LV = RD->getLinkageAndVisibility();
1228   llvm::GlobalObject::VCallVisibility TypeVis;
1229   if (!isExternallyVisible(LV.getLinkage()))
1230     TypeVis = llvm::GlobalObject::VCallVisibilityTranslationUnit;
1231   else if (HasHiddenLTOVisibility(RD))
1232     TypeVis = llvm::GlobalObject::VCallVisibilityLinkageUnit;
1233   else
1234     TypeVis = llvm::GlobalObject::VCallVisibilityPublic;
1235 
1236   for (auto B : RD->bases())
1237     if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1238       TypeVis = std::min(
1239           TypeVis,
1240           GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));
1241 
1242   for (auto B : RD->vbases())
1243     if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1244       TypeVis = std::min(
1245           TypeVis,
1246           GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));
1247 
1248   return TypeVis;
1249 }
1250 
1251 void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
1252                                            llvm::GlobalVariable *VTable,
1253                                            const VTableLayout &VTLayout) {
1254   if (!getCodeGenOpts().LTOUnit)
1255     return;
1256 
1257   CharUnits PointerWidth =
1258       Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
1259 
1260   typedef std::pair<const CXXRecordDecl *, unsigned> AddressPoint;
1261   std::vector<AddressPoint> AddressPoints;
1262   for (auto &&AP : VTLayout.getAddressPoints())
1263     AddressPoints.push_back(std::make_pair(
1264         AP.first.getBase(), VTLayout.getVTableOffset(AP.second.VTableIndex) +
1265                                 AP.second.AddressPointIndex));
1266 
1267   // Sort the address points for determinism.
1268   llvm::sort(AddressPoints, [this](const AddressPoint &AP1,
1269                                    const AddressPoint &AP2) {
1270     if (&AP1 == &AP2)
1271       return false;
1272 
1273     std::string S1;
1274     llvm::raw_string_ostream O1(S1);
1275     getCXXABI().getMangleContext().mangleTypeName(
1276         QualType(AP1.first->getTypeForDecl(), 0), O1);
1277     O1.flush();
1278 
1279     std::string S2;
1280     llvm::raw_string_ostream O2(S2);
1281     getCXXABI().getMangleContext().mangleTypeName(
1282         QualType(AP2.first->getTypeForDecl(), 0), O2);
1283     O2.flush();
1284 
1285     if (S1 < S2)
1286       return true;
1287     if (S1 != S2)
1288       return false;
1289 
1290     return AP1.second < AP2.second;
1291   });
1292 
1293   ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();
1294   for (auto AP : AddressPoints) {
1295     // Create type metadata for the address point.
1296     AddVTableTypeMetadata(VTable, PointerWidth * AP.second, AP.first);
1297 
1298     // The class associated with each address point could also potentially be
1299     // used for indirect calls via a member function pointer, so we need to
1300     // annotate the address of each function pointer with the appropriate member
1301     // function pointer type.
1302     for (unsigned I = 0; I != Comps.size(); ++I) {
1303       if (Comps[I].getKind() != VTableComponent::CK_FunctionPointer)
1304         continue;
1305       llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(
1306           Context.getMemberPointerType(
1307               Comps[I].getFunctionDecl()->getType(),
1308               Context.getRecordType(AP.first).getTypePtr()));
1309       VTable->addTypeMetadata((PointerWidth * I).getQuantity(), MD);
1310     }
1311   }
1312 
1313   if (getCodeGenOpts().VirtualFunctionElimination ||
1314       getCodeGenOpts().WholeProgramVTables) {
1315     llvm::DenseSet<const CXXRecordDecl *> Visited;
1316     llvm::GlobalObject::VCallVisibility TypeVis =
1317         GetVCallVisibilityLevel(RD, Visited);
1318     if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)
1319       VTable->setVCallVisibilityMetadata(TypeVis);
1320   }
1321 }
1322