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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 
29 using namespace clang;
30 using namespace CodeGen;
31 
CodeGenVTables(CodeGenModule & CGM)32 CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
33     : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
34 
GetAddrOfThunk(GlobalDecl GD,const ThunkInfo & Thunk)35 llvm::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 
setThunkVisibility(CodeGenModule & CGM,const CXXMethodDecl * MD,const ThunkInfo & Thunk,llvm::Function * Fn)53 static void setThunkVisibility(CodeGenModule &CGM, const CXXMethodDecl *MD,
54                                const ThunkInfo &Thunk, llvm::Function *Fn) {
55   CGM.setGlobalVisibility(Fn, MD);
56 }
57 
setThunkProperties(CodeGenModule & CGM,const ThunkInfo & Thunk,llvm::Function * ThunkFn,bool ForVTable,GlobalDecl GD)58 static 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
similar(const ABIArgInfo & infoL,CanQualType typeL,const ABIArgInfo & infoR,CanQualType typeR)74 static 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 
PerformReturnAdjustment(CodeGenFunction & CGF,QualType ResultType,RValue RV,const ThunkInfo & Thunk)83 static 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.
143 llvm::Function *
GenerateVarArgsThunk(llvm::Function * Fn,const CGFunctionInfo & FnInfo,GlobalDecl GD,const ThunkInfo & Thunk)144 CodeGenFunction::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 
StartThunk(llvm::Function * Fn,GlobalDecl GD,const CGFunctionInfo & FnInfo)208 void 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 
FinishThunk()245 void 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 
EmitCallAndReturnForThunk(llvm::Value * Callee,const ThunkInfo * Thunk)254 void 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 
EmitMustTailThunk(const CXXMethodDecl * MD,llvm::Value * AdjustedThisPtr,llvm::Value * Callee)341 void 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 
generateThunk(llvm::Function * Fn,const CGFunctionInfo & FnInfo,GlobalDecl GD,const ThunkInfo & Thunk)396 void 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 
emitThunk(GlobalDecl GD,const ThunkInfo & Thunk,bool ForVTable)410 void 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 
maybeEmitThunkForVTable(GlobalDecl GD,const ThunkInfo & Thunk)485 void 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 
EmitThunks(GlobalDecl GD)504 void 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 
CreateVTableInitializer(const CXXRecordDecl * RD,const VTableComponent * Components,unsigned NumComponents,const VTableLayout::VTableThunkTy * VTableThunks,unsigned NumVTableThunks,llvm::Constant * RTTI)523 llvm::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 
659 llvm::GlobalVariable *
GenerateConstructionVTable(const CXXRecordDecl * RD,const BaseSubobject & Base,bool BaseIsVirtual,llvm::GlobalVariable::LinkageTypes Linkage,VTableAddressPointsMapTy & AddressPoints)660 CodeGenVTables::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 
shouldEmitAvailableExternallyVTable(const CodeGenModule & CGM,const CXXRecordDecl * RD)717 static 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.
726 llvm::GlobalVariable::LinkageTypes
getVTableLinkage(const CXXRecordDecl * RD)727 CodeGenModule::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.
EmitVTable(CXXRecordDecl * theClass)818 void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
819   VTables.GenerateClassData(theClass);
820 }
821 
822 void
GenerateClassData(const CXXRecordDecl * RD)823 CodeGenVTables::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.
isVTableExternal(const CXXRecordDecl * RD)843 bool 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?
shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule & CGM,const CXXRecordDecl * RD)877 static 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.
EmitDeferredVTables()890 void 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 
HasHiddenLTOVisibility(const CXXRecordDecl * RD)906 bool 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 
EmitVTableTypeMetadata(llvm::GlobalVariable * VTable,const VTableLayout & VTLayout)940 void 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