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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 
     32 CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
     33     : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
     34 
     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   Out.flush();
     48 
     49   llvm::Type *Ty = getTypes().GetFunctionTypeForVTable(GD);
     50   return GetOrCreateLLVMFunction(Name, Ty, GD, /*ForVTable=*/true,
     51                                  /*DontDefer=*/true, /*IsThunk=*/true);
     52 }
     53 
     54 static void setThunkVisibility(CodeGenModule &CGM, const CXXMethodDecl *MD,
     55                                const ThunkInfo &Thunk, llvm::Function *Fn) {
     56   CGM.setGlobalVisibility(Fn, MD);
     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   ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(CGF, ReturnValue,
     92                                                             Thunk.Return);
     93 
     94   if (NullCheckValue) {
     95     CGF.Builder.CreateBr(AdjustEnd);
     96     CGF.EmitBlock(AdjustNull);
     97     CGF.Builder.CreateBr(AdjustEnd);
     98     CGF.EmitBlock(AdjustEnd);
     99 
    100     llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
    101     PHI->addIncoming(ReturnValue, AdjustNotNull);
    102     PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
    103                      AdjustNull);
    104     ReturnValue = PHI;
    105   }
    106 
    107   return RValue::get(ReturnValue);
    108 }
    109 
    110 // This function does roughly the same thing as GenerateThunk, but in a
    111 // very different way, so that va_start and va_end work correctly.
    112 // FIXME: This function assumes "this" is the first non-sret LLVM argument of
    113 //        a function, and that there is an alloca built in the entry block
    114 //        for all accesses to "this".
    115 // FIXME: This function assumes there is only one "ret" statement per function.
    116 // FIXME: Cloning isn't correct in the presence of indirect goto!
    117 // FIXME: This implementation of thunks bloats codesize by duplicating the
    118 //        function definition.  There are alternatives:
    119 //        1. Add some sort of stub support to LLVM for cases where we can
    120 //           do a this adjustment, then a sibcall.
    121 //        2. We could transform the definition to take a va_list instead of an
    122 //           actual variable argument list, then have the thunks (including a
    123 //           no-op thunk for the regular definition) call va_start/va_end.
    124 //           There's a bit of per-call overhead for this solution, but it's
    125 //           better for codesize if the definition is long.
    126 void CodeGenFunction::GenerateVarArgsThunk(
    127                                       llvm::Function *Fn,
    128                                       const CGFunctionInfo &FnInfo,
    129                                       GlobalDecl GD, const ThunkInfo &Thunk) {
    130   const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
    131   const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
    132   QualType ResultType = FPT->getReturnType();
    133 
    134   // Get the original function
    135   assert(FnInfo.isVariadic());
    136   llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);
    137   llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
    138   llvm::Function *BaseFn = cast<llvm::Function>(Callee);
    139 
    140   // Clone to thunk.
    141   llvm::ValueToValueMapTy VMap;
    142   llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap,
    143                                               /*ModuleLevelChanges=*/false);
    144   CGM.getModule().getFunctionList().push_back(NewFn);
    145   Fn->replaceAllUsesWith(NewFn);
    146   NewFn->takeName(Fn);
    147   Fn->eraseFromParent();
    148   Fn = NewFn;
    149 
    150   // "Initialize" CGF (minimally).
    151   CurFn = Fn;
    152 
    153   // Get the "this" value
    154   llvm::Function::arg_iterator AI = Fn->arg_begin();
    155   if (CGM.ReturnTypeUsesSRet(FnInfo))
    156     ++AI;
    157 
    158   // Find the first store of "this", which will be to the alloca associated
    159   // with "this".
    160   llvm::Value *ThisPtr = &*AI;
    161   llvm::BasicBlock *EntryBB = Fn->begin();
    162   llvm::Instruction *ThisStore =
    163       std::find_if(EntryBB->begin(), EntryBB->end(), [&](llvm::Instruction &I) {
    164     return isa<llvm::StoreInst>(I) && I.getOperand(0) == ThisPtr;
    165   });
    166   assert(ThisStore && "Store of this should be in entry block?");
    167   // Adjust "this", if necessary.
    168   Builder.SetInsertPoint(ThisStore);
    169   llvm::Value *AdjustedThisPtr =
    170       CGM.getCXXABI().performThisAdjustment(*this, ThisPtr, Thunk.This);
    171   ThisStore->setOperand(0, AdjustedThisPtr);
    172 
    173   if (!Thunk.Return.isEmpty()) {
    174     // Fix up the returned value, if necessary.
    175     for (llvm::Function::iterator I = Fn->begin(), E = Fn->end(); I != E; I++) {
    176       llvm::Instruction *T = I->getTerminator();
    177       if (isa<llvm::ReturnInst>(T)) {
    178         RValue RV = RValue::get(T->getOperand(0));
    179         T->eraseFromParent();
    180         Builder.SetInsertPoint(&*I);
    181         RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
    182         Builder.CreateRet(RV.getScalarVal());
    183         break;
    184       }
    185     }
    186   }
    187 }
    188 
    189 void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
    190                                  const CGFunctionInfo &FnInfo) {
    191   assert(!CurGD.getDecl() && "CurGD was already set!");
    192   CurGD = GD;
    193   CurFuncIsThunk = true;
    194 
    195   // Build FunctionArgs.
    196   const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
    197   QualType ThisType = MD->getThisType(getContext());
    198   const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
    199   QualType ResultType = CGM.getCXXABI().HasThisReturn(GD)
    200                             ? ThisType
    201                             : CGM.getCXXABI().hasMostDerivedReturn(GD)
    202                                   ? CGM.getContext().VoidPtrTy
    203                                   : FPT->getReturnType();
    204   FunctionArgList FunctionArgs;
    205 
    206   // Create the implicit 'this' parameter declaration.
    207   CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
    208 
    209   // Add the rest of the parameters.
    210   FunctionArgs.append(MD->param_begin(), MD->param_end());
    211 
    212   if (isa<CXXDestructorDecl>(MD))
    213     CGM.getCXXABI().addImplicitStructorParams(*this, ResultType, FunctionArgs);
    214 
    215   // Start defining the function.
    216   StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
    217                 MD->getLocation(), MD->getLocation());
    218 
    219   // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
    220   CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
    221   CXXThisValue = CXXABIThisValue;
    222 }
    223 
    224 void CodeGenFunction::EmitCallAndReturnForThunk(llvm::Value *Callee,
    225                                                 const ThunkInfo *Thunk) {
    226   assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
    227          "Please use a new CGF for this thunk");
    228   const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurGD.getDecl());
    229 
    230   // Adjust the 'this' pointer if necessary
    231   llvm::Value *AdjustedThisPtr = Thunk ? CGM.getCXXABI().performThisAdjustment(
    232                                              *this, LoadCXXThis(), Thunk->This)
    233                                        : LoadCXXThis();
    234 
    235   if (CurFnInfo->usesInAlloca()) {
    236     // We don't handle return adjusting thunks, because they require us to call
    237     // the copy constructor.  For now, fall through and pretend the return
    238     // adjustment was empty so we don't crash.
    239     if (Thunk && !Thunk->Return.isEmpty()) {
    240       CGM.ErrorUnsupported(
    241           MD, "non-trivial argument copy for return-adjusting thunk");
    242     }
    243     EmitMustTailThunk(MD, AdjustedThisPtr, Callee);
    244     return;
    245   }
    246 
    247   // Start building CallArgs.
    248   CallArgList CallArgs;
    249   QualType ThisType = MD->getThisType(getContext());
    250   CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
    251 
    252   if (isa<CXXDestructorDecl>(MD))
    253     CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);
    254 
    255   // Add the rest of the arguments.
    256   for (const ParmVarDecl *PD : MD->params())
    257     EmitDelegateCallArg(CallArgs, PD, PD->getLocStart());
    258 
    259   const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
    260 
    261 #ifndef NDEBUG
    262   const CGFunctionInfo &CallFnInfo =
    263     CGM.getTypes().arrangeCXXMethodCall(CallArgs, FPT,
    264                                        RequiredArgs::forPrototypePlus(FPT, 1));
    265   assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
    266          CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
    267          CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
    268   assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
    269          similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
    270                  CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
    271   assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
    272   for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
    273     assert(similar(CallFnInfo.arg_begin()[i].info,
    274                    CallFnInfo.arg_begin()[i].type,
    275                    CurFnInfo->arg_begin()[i].info,
    276                    CurFnInfo->arg_begin()[i].type));
    277 #endif
    278 
    279   // Determine whether we have a return value slot to use.
    280   QualType ResultType = CGM.getCXXABI().HasThisReturn(CurGD)
    281                             ? ThisType
    282                             : CGM.getCXXABI().hasMostDerivedReturn(CurGD)
    283                                   ? CGM.getContext().VoidPtrTy
    284                                   : FPT->getReturnType();
    285   ReturnValueSlot Slot;
    286   if (!ResultType->isVoidType() &&
    287       CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect &&
    288       !hasScalarEvaluationKind(CurFnInfo->getReturnType()))
    289     Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified());
    290 
    291   // Now emit our call.
    292   llvm::Instruction *CallOrInvoke;
    293   RValue RV = EmitCall(*CurFnInfo, Callee, Slot, CallArgs, MD, &CallOrInvoke);
    294 
    295   // Consider return adjustment if we have ThunkInfo.
    296   if (Thunk && !Thunk->Return.isEmpty())
    297     RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
    298 
    299   // Emit return.
    300   if (!ResultType->isVoidType() && Slot.isNull())
    301     CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
    302 
    303   // Disable the final ARC autorelease.
    304   AutoreleaseResult = false;
    305 
    306   FinishFunction();
    307 }
    308 
    309 void CodeGenFunction::EmitMustTailThunk(const CXXMethodDecl *MD,
    310                                         llvm::Value *AdjustedThisPtr,
    311                                         llvm::Value *Callee) {
    312   // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
    313   // to translate AST arguments into LLVM IR arguments.  For thunks, we know
    314   // that the caller prototype more or less matches the callee prototype with
    315   // the exception of 'this'.
    316   SmallVector<llvm::Value *, 8> Args;
    317   for (llvm::Argument &A : CurFn->args())
    318     Args.push_back(&A);
    319 
    320   // Set the adjusted 'this' pointer.
    321   const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
    322   if (ThisAI.isDirect()) {
    323     const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
    324     int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
    325     llvm::Type *ThisType = Args[ThisArgNo]->getType();
    326     if (ThisType != AdjustedThisPtr->getType())
    327       AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
    328     Args[ThisArgNo] = AdjustedThisPtr;
    329   } else {
    330     assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
    331     llvm::Value *ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);
    332     llvm::Type *ThisType =
    333         cast<llvm::PointerType>(ThisAddr->getType())->getElementType();
    334     if (ThisType != AdjustedThisPtr->getType())
    335       AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
    336     Builder.CreateStore(AdjustedThisPtr, ThisAddr);
    337   }
    338 
    339   // Emit the musttail call manually.  Even if the prologue pushed cleanups, we
    340   // don't actually want to run them.
    341   llvm::CallInst *Call = Builder.CreateCall(Callee, Args);
    342   Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
    343 
    344   // Apply the standard set of call attributes.
    345   unsigned CallingConv;
    346   CodeGen::AttributeListType AttributeList;
    347   CGM.ConstructAttributeList(*CurFnInfo, MD, AttributeList, CallingConv,
    348                              /*AttrOnCallSite=*/true);
    349   llvm::AttributeSet Attrs =
    350       llvm::AttributeSet::get(getLLVMContext(), AttributeList);
    351   Call->setAttributes(Attrs);
    352   Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
    353 
    354   if (Call->getType()->isVoidTy())
    355     Builder.CreateRetVoid();
    356   else
    357     Builder.CreateRet(Call);
    358 
    359   // Finish the function to maintain CodeGenFunction invariants.
    360   // FIXME: Don't emit unreachable code.
    361   EmitBlock(createBasicBlock());
    362   FinishFunction();
    363 }
    364 
    365 void CodeGenFunction::GenerateThunk(llvm::Function *Fn,
    366                                     const CGFunctionInfo &FnInfo,
    367                                     GlobalDecl GD, const ThunkInfo &Thunk) {
    368   StartThunk(Fn, GD, FnInfo);
    369 
    370   // Get our callee.
    371   llvm::Type *Ty =
    372     CGM.getTypes().GetFunctionType(CGM.getTypes().arrangeGlobalDeclaration(GD));
    373   llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
    374 
    375   // Make the call and return the result.
    376   EmitCallAndReturnForThunk(Callee, &Thunk);
    377 
    378   // Set the right linkage.
    379   CGM.setFunctionLinkage(GD, Fn);
    380 
    381   if (CGM.supportsCOMDAT() && Fn->isWeakForLinker())
    382     Fn->setComdat(CGM.getModule().getOrInsertComdat(Fn->getName()));
    383 
    384   // Set the right visibility.
    385   const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
    386   setThunkVisibility(CGM, MD, Thunk, Fn);
    387 }
    388 
    389 void CodeGenVTables::emitThunk(GlobalDecl GD, const ThunkInfo &Thunk,
    390                                bool ForVTable) {
    391   const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeGlobalDeclaration(GD);
    392 
    393   // FIXME: re-use FnInfo in this computation.
    394   llvm::Constant *C = CGM.GetAddrOfThunk(GD, Thunk);
    395   llvm::GlobalValue *Entry;
    396 
    397   // Strip off a bitcast if we got one back.
    398   if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(C)) {
    399     assert(CE->getOpcode() == llvm::Instruction::BitCast);
    400     Entry = cast<llvm::GlobalValue>(CE->getOperand(0));
    401   } else {
    402     Entry = cast<llvm::GlobalValue>(C);
    403   }
    404 
    405   // There's already a declaration with the same name, check if it has the same
    406   // type or if we need to replace it.
    407   if (Entry->getType()->getElementType() !=
    408       CGM.getTypes().GetFunctionTypeForVTable(GD)) {
    409     llvm::GlobalValue *OldThunkFn = Entry;
    410 
    411     // If the types mismatch then we have to rewrite the definition.
    412     assert(OldThunkFn->isDeclaration() &&
    413            "Shouldn't replace non-declaration");
    414 
    415     // Remove the name from the old thunk function and get a new thunk.
    416     OldThunkFn->setName(StringRef());
    417     Entry = cast<llvm::GlobalValue>(CGM.GetAddrOfThunk(GD, Thunk));
    418 
    419     // If needed, replace the old thunk with a bitcast.
    420     if (!OldThunkFn->use_empty()) {
    421       llvm::Constant *NewPtrForOldDecl =
    422         llvm::ConstantExpr::getBitCast(Entry, OldThunkFn->getType());
    423       OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
    424     }
    425 
    426     // Remove the old thunk.
    427     OldThunkFn->eraseFromParent();
    428   }
    429 
    430   llvm::Function *ThunkFn = cast<llvm::Function>(Entry);
    431   bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
    432   bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
    433 
    434   if (!ThunkFn->isDeclaration()) {
    435     if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
    436       // There is already a thunk emitted for this function, do nothing.
    437       return;
    438     }
    439 
    440     // Change the linkage.
    441     CGM.setFunctionLinkage(GD, ThunkFn);
    442     return;
    443   }
    444 
    445   CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
    446 
    447   if (ThunkFn->isVarArg()) {
    448     // Varargs thunks are special; we can't just generate a call because
    449     // we can't copy the varargs.  Our implementation is rather
    450     // expensive/sucky at the moment, so don't generate the thunk unless
    451     // we have to.
    452     // FIXME: Do something better here; GenerateVarArgsThunk is extremely ugly.
    453     if (!UseAvailableExternallyLinkage) {
    454       CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, Thunk);
    455       CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
    456                                       !Thunk.Return.isEmpty());
    457     }
    458   } else {
    459     // Normal thunk body generation.
    460     CodeGenFunction(CGM).GenerateThunk(ThunkFn, FnInfo, GD, Thunk);
    461     CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
    462                                     !Thunk.Return.isEmpty());
    463   }
    464 }
    465 
    466 void CodeGenVTables::maybeEmitThunkForVTable(GlobalDecl GD,
    467                                              const ThunkInfo &Thunk) {
    468   // If the ABI has key functions, only the TU with the key function should emit
    469   // the thunk. However, we can allow inlining of thunks if we emit them with
    470   // available_externally linkage together with vtables when optimizations are
    471   // enabled.
    472   if (CGM.getTarget().getCXXABI().hasKeyFunctions() &&
    473       !CGM.getCodeGenOpts().OptimizationLevel)
    474     return;
    475 
    476   // We can't emit thunks for member functions with incomplete types.
    477   const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
    478   if (!CGM.getTypes().isFuncTypeConvertible(
    479            MD->getType()->castAs<FunctionType>()))
    480     return;
    481 
    482   emitThunk(GD, Thunk, /*ForVTable=*/true);
    483 }
    484 
    485 void CodeGenVTables::EmitThunks(GlobalDecl GD)
    486 {
    487   const CXXMethodDecl *MD =
    488     cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
    489 
    490   // We don't need to generate thunks for the base destructor.
    491   if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
    492     return;
    493 
    494   const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
    495       VTContext->getThunkInfo(GD);
    496 
    497   if (!ThunkInfoVector)
    498     return;
    499 
    500   for (unsigned I = 0, E = ThunkInfoVector->size(); I != E; ++I)
    501     emitThunk(GD, (*ThunkInfoVector)[I], /*ForVTable=*/false);
    502 }
    503 
    504 llvm::Constant *CodeGenVTables::CreateVTableInitializer(
    505     const CXXRecordDecl *RD, const VTableComponent *Components,
    506     unsigned NumComponents, const VTableLayout::VTableThunkTy *VTableThunks,
    507     unsigned NumVTableThunks, llvm::Constant *RTTI) {
    508   SmallVector<llvm::Constant *, 64> Inits;
    509 
    510   llvm::Type *Int8PtrTy = CGM.Int8PtrTy;
    511 
    512   llvm::Type *PtrDiffTy =
    513     CGM.getTypes().ConvertType(CGM.getContext().getPointerDiffType());
    514 
    515   unsigned NextVTableThunkIndex = 0;
    516 
    517   llvm::Constant *PureVirtualFn = nullptr, *DeletedVirtualFn = nullptr;
    518 
    519   for (unsigned I = 0; I != NumComponents; ++I) {
    520     VTableComponent Component = Components[I];
    521 
    522     llvm::Constant *Init = nullptr;
    523 
    524     switch (Component.getKind()) {
    525     case VTableComponent::CK_VCallOffset:
    526       Init = llvm::ConstantInt::get(PtrDiffTy,
    527                                     Component.getVCallOffset().getQuantity());
    528       Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
    529       break;
    530     case VTableComponent::CK_VBaseOffset:
    531       Init = llvm::ConstantInt::get(PtrDiffTy,
    532                                     Component.getVBaseOffset().getQuantity());
    533       Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
    534       break;
    535     case VTableComponent::CK_OffsetToTop:
    536       Init = llvm::ConstantInt::get(PtrDiffTy,
    537                                     Component.getOffsetToTop().getQuantity());
    538       Init = llvm::ConstantExpr::getIntToPtr(Init, Int8PtrTy);
    539       break;
    540     case VTableComponent::CK_RTTI:
    541       Init = llvm::ConstantExpr::getBitCast(RTTI, Int8PtrTy);
    542       break;
    543     case VTableComponent::CK_FunctionPointer:
    544     case VTableComponent::CK_CompleteDtorPointer:
    545     case VTableComponent::CK_DeletingDtorPointer: {
    546       GlobalDecl GD;
    547 
    548       // Get the right global decl.
    549       switch (Component.getKind()) {
    550       default:
    551         llvm_unreachable("Unexpected vtable component kind");
    552       case VTableComponent::CK_FunctionPointer:
    553         GD = Component.getFunctionDecl();
    554         break;
    555       case VTableComponent::CK_CompleteDtorPointer:
    556         GD = GlobalDecl(Component.getDestructorDecl(), Dtor_Complete);
    557         break;
    558       case VTableComponent::CK_DeletingDtorPointer:
    559         GD = GlobalDecl(Component.getDestructorDecl(), Dtor_Deleting);
    560         break;
    561       }
    562 
    563       if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
    564         // We have a pure virtual member function.
    565         if (!PureVirtualFn) {
    566           llvm::FunctionType *Ty =
    567             llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
    568           StringRef PureCallName = CGM.getCXXABI().GetPureVirtualCallName();
    569           PureVirtualFn = CGM.CreateRuntimeFunction(Ty, PureCallName);
    570           PureVirtualFn = llvm::ConstantExpr::getBitCast(PureVirtualFn,
    571                                                          CGM.Int8PtrTy);
    572         }
    573         Init = PureVirtualFn;
    574       } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
    575         if (!DeletedVirtualFn) {
    576           llvm::FunctionType *Ty =
    577             llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
    578           StringRef DeletedCallName =
    579             CGM.getCXXABI().GetDeletedVirtualCallName();
    580           DeletedVirtualFn = CGM.CreateRuntimeFunction(Ty, DeletedCallName);
    581           DeletedVirtualFn = llvm::ConstantExpr::getBitCast(DeletedVirtualFn,
    582                                                          CGM.Int8PtrTy);
    583         }
    584         Init = DeletedVirtualFn;
    585       } else {
    586         // Check if we should use a thunk.
    587         if (NextVTableThunkIndex < NumVTableThunks &&
    588             VTableThunks[NextVTableThunkIndex].first == I) {
    589           const ThunkInfo &Thunk = VTableThunks[NextVTableThunkIndex].second;
    590 
    591           maybeEmitThunkForVTable(GD, Thunk);
    592           Init = CGM.GetAddrOfThunk(GD, Thunk);
    593 
    594           NextVTableThunkIndex++;
    595         } else {
    596           llvm::Type *Ty = CGM.getTypes().GetFunctionTypeForVTable(GD);
    597 
    598           Init = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
    599         }
    600 
    601         Init = llvm::ConstantExpr::getBitCast(Init, Int8PtrTy);
    602       }
    603       break;
    604     }
    605 
    606     case VTableComponent::CK_UnusedFunctionPointer:
    607       Init = llvm::ConstantExpr::getNullValue(Int8PtrTy);
    608       break;
    609     };
    610 
    611     Inits.push_back(Init);
    612   }
    613 
    614   llvm::ArrayType *ArrayType = llvm::ArrayType::get(Int8PtrTy, NumComponents);
    615   return llvm::ConstantArray::get(ArrayType, Inits);
    616 }
    617 
    618 llvm::GlobalVariable *
    619 CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
    620                                       const BaseSubobject &Base,
    621                                       bool BaseIsVirtual,
    622                                    llvm::GlobalVariable::LinkageTypes Linkage,
    623                                       VTableAddressPointsMapTy& AddressPoints) {
    624   if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
    625     DI->completeClassData(Base.getBase());
    626 
    627   std::unique_ptr<VTableLayout> VTLayout(
    628       getItaniumVTableContext().createConstructionVTableLayout(
    629           Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
    630 
    631   // Add the address points.
    632   AddressPoints = VTLayout->getAddressPoints();
    633 
    634   // Get the mangled construction vtable name.
    635   SmallString<256> OutName;
    636   llvm::raw_svector_ostream Out(OutName);
    637   cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
    638       .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
    639                            Base.getBase(), Out);
    640   Out.flush();
    641   StringRef Name = OutName.str();
    642 
    643   llvm::ArrayType *ArrayType =
    644     llvm::ArrayType::get(CGM.Int8PtrTy, VTLayout->getNumVTableComponents());
    645 
    646   // Construction vtable symbols are not part of the Itanium ABI, so we cannot
    647   // guarantee that they actually will be available externally. Instead, when
    648   // emitting an available_externally VTT, we provide references to an internal
    649   // linkage construction vtable. The ABI only requires complete-object vtables
    650   // to be the same for all instances of a type, not construction vtables.
    651   if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
    652     Linkage = llvm::GlobalVariable::InternalLinkage;
    653 
    654   // Create the variable that will hold the construction vtable.
    655   llvm::GlobalVariable *VTable =
    656     CGM.CreateOrReplaceCXXRuntimeVariable(Name, ArrayType, Linkage);
    657   CGM.setGlobalVisibility(VTable, RD);
    658 
    659   // V-tables are always unnamed_addr.
    660   VTable->setUnnamedAddr(true);
    661 
    662   llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
    663       CGM.getContext().getTagDeclType(Base.getBase()));
    664 
    665   // Create and set the initializer.
    666   llvm::Constant *Init = CreateVTableInitializer(
    667       Base.getBase(), VTLayout->vtable_component_begin(),
    668       VTLayout->getNumVTableComponents(), VTLayout->vtable_thunk_begin(),
    669       VTLayout->getNumVTableThunks(), RTTI);
    670   VTable->setInitializer(Init);
    671 
    672   CGM.EmitVTableBitSetEntries(VTable, *VTLayout.get());
    673 
    674   return VTable;
    675 }
    676 
    677 /// Compute the required linkage of the v-table for the given class.
    678 ///
    679 /// Note that we only call this at the end of the translation unit.
    680 llvm::GlobalVariable::LinkageTypes
    681 CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
    682   if (!RD->isExternallyVisible())
    683     return llvm::GlobalVariable::InternalLinkage;
    684 
    685   // We're at the end of the translation unit, so the current key
    686   // function is fully correct.
    687   const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
    688   if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
    689     // If this class has a key function, use that to determine the
    690     // linkage of the vtable.
    691     const FunctionDecl *def = nullptr;
    692     if (keyFunction->hasBody(def))
    693       keyFunction = cast<CXXMethodDecl>(def);
    694 
    695     switch (keyFunction->getTemplateSpecializationKind()) {
    696       case TSK_Undeclared:
    697       case TSK_ExplicitSpecialization:
    698         assert(def && "Should not have been asked to emit this");
    699         if (keyFunction->isInlined())
    700           return !Context.getLangOpts().AppleKext ?
    701                    llvm::GlobalVariable::LinkOnceODRLinkage :
    702                    llvm::Function::InternalLinkage;
    703 
    704         return llvm::GlobalVariable::ExternalLinkage;
    705 
    706       case TSK_ImplicitInstantiation:
    707         return !Context.getLangOpts().AppleKext ?
    708                  llvm::GlobalVariable::LinkOnceODRLinkage :
    709                  llvm::Function::InternalLinkage;
    710 
    711       case TSK_ExplicitInstantiationDefinition:
    712         return !Context.getLangOpts().AppleKext ?
    713                  llvm::GlobalVariable::WeakODRLinkage :
    714                  llvm::Function::InternalLinkage;
    715 
    716       case TSK_ExplicitInstantiationDeclaration:
    717         llvm_unreachable("Should not have been asked to emit this");
    718     }
    719   }
    720 
    721   // -fapple-kext mode does not support weak linkage, so we must use
    722   // internal linkage.
    723   if (Context.getLangOpts().AppleKext)
    724     return llvm::Function::InternalLinkage;
    725 
    726   llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
    727       llvm::GlobalValue::LinkOnceODRLinkage;
    728   llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
    729       llvm::GlobalValue::WeakODRLinkage;
    730   if (RD->hasAttr<DLLExportAttr>()) {
    731     // Cannot discard exported vtables.
    732     DiscardableODRLinkage = NonDiscardableODRLinkage;
    733   } else if (RD->hasAttr<DLLImportAttr>()) {
    734     // Imported vtables are available externally.
    735     DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
    736     NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
    737   }
    738 
    739   switch (RD->getTemplateSpecializationKind()) {
    740   case TSK_Undeclared:
    741   case TSK_ExplicitSpecialization:
    742   case TSK_ImplicitInstantiation:
    743     return DiscardableODRLinkage;
    744 
    745   case TSK_ExplicitInstantiationDeclaration:
    746     return llvm::GlobalVariable::ExternalLinkage;
    747 
    748   case TSK_ExplicitInstantiationDefinition:
    749     return NonDiscardableODRLinkage;
    750   }
    751 
    752   llvm_unreachable("Invalid TemplateSpecializationKind!");
    753 }
    754 
    755 /// This is a callback from Sema to tell us that that a particular v-table is
    756 /// required to be emitted in this translation unit.
    757 ///
    758 /// This is only called for vtables that _must_ be emitted (mainly due to key
    759 /// functions).  For weak vtables, CodeGen tracks when they are needed and
    760 /// emits them as-needed.
    761 void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
    762   VTables.GenerateClassData(theClass);
    763 }
    764 
    765 void
    766 CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
    767   if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
    768     DI->completeClassData(RD);
    769 
    770   if (RD->getNumVBases())
    771     CGM.getCXXABI().emitVirtualInheritanceTables(RD);
    772 
    773   CGM.getCXXABI().emitVTableDefinitions(*this, RD);
    774 }
    775 
    776 /// At this point in the translation unit, does it appear that can we
    777 /// rely on the vtable being defined elsewhere in the program?
    778 ///
    779 /// The response is really only definitive when called at the end of
    780 /// the translation unit.
    781 ///
    782 /// The only semantic restriction here is that the object file should
    783 /// not contain a v-table definition when that v-table is defined
    784 /// strongly elsewhere.  Otherwise, we'd just like to avoid emitting
    785 /// v-tables when unnecessary.
    786 bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
    787   assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
    788 
    789   // If we have an explicit instantiation declaration (and not a
    790   // definition), the v-table is defined elsewhere.
    791   TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
    792   if (TSK == TSK_ExplicitInstantiationDeclaration)
    793     return true;
    794 
    795   // Otherwise, if the class is an instantiated template, the
    796   // v-table must be defined here.
    797   if (TSK == TSK_ImplicitInstantiation ||
    798       TSK == TSK_ExplicitInstantiationDefinition)
    799     return false;
    800 
    801   // Otherwise, if the class doesn't have a key function (possibly
    802   // anymore), the v-table must be defined here.
    803   const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
    804   if (!keyFunction)
    805     return false;
    806 
    807   // Otherwise, if we don't have a definition of the key function, the
    808   // v-table must be defined somewhere else.
    809   return !keyFunction->hasBody();
    810 }
    811 
    812 /// Given that we're currently at the end of the translation unit, and
    813 /// we've emitted a reference to the v-table for this class, should
    814 /// we define that v-table?
    815 static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
    816                                                    const CXXRecordDecl *RD) {
    817   return !CGM.getVTables().isVTableExternal(RD);
    818 }
    819 
    820 /// Given that at some point we emitted a reference to one or more
    821 /// v-tables, and that we are now at the end of the translation unit,
    822 /// decide whether we should emit them.
    823 void CodeGenModule::EmitDeferredVTables() {
    824 #ifndef NDEBUG
    825   // Remember the size of DeferredVTables, because we're going to assume
    826   // that this entire operation doesn't modify it.
    827   size_t savedSize = DeferredVTables.size();
    828 #endif
    829 
    830   typedef std::vector<const CXXRecordDecl *>::const_iterator const_iterator;
    831   for (const_iterator i = DeferredVTables.begin(),
    832                       e = DeferredVTables.end(); i != e; ++i) {
    833     const CXXRecordDecl *RD = *i;
    834     if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
    835       VTables.GenerateClassData(RD);
    836   }
    837 
    838   assert(savedSize == DeferredVTables.size() &&
    839          "deferred extra v-tables during v-table emission?");
    840   DeferredVTables.clear();
    841 }
    842 
    843 void CodeGenModule::EmitVTableBitSetEntries(llvm::GlobalVariable *VTable,
    844                                             const VTableLayout &VTLayout) {
    845   if (!LangOpts.Sanitize.has(SanitizerKind::CFIVCall) &&
    846       !LangOpts.Sanitize.has(SanitizerKind::CFINVCall) &&
    847       !LangOpts.Sanitize.has(SanitizerKind::CFIDerivedCast) &&
    848       !LangOpts.Sanitize.has(SanitizerKind::CFIUnrelatedCast))
    849     return;
    850 
    851   llvm::Metadata *VTableMD = llvm::ConstantAsMetadata::get(VTable);
    852 
    853   std::vector<llvm::MDTuple *> BitsetEntries;
    854   // Create a bit set entry for each address point.
    855   for (auto &&AP : VTLayout.getAddressPoints()) {
    856     // FIXME: Add blacklisting scheme.
    857     if (AP.first.getBase()->isInStdNamespace())
    858       continue;
    859 
    860     std::string OutName;
    861     llvm::raw_string_ostream Out(OutName);
    862     getCXXABI().getMangleContext().mangleCXXVTableBitSet(AP.first.getBase(),
    863                                                          Out);
    864 
    865     CharUnits PointerWidth =
    866         Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
    867     uint64_t AddrPointOffset = AP.second * PointerWidth.getQuantity();
    868 
    869     llvm::Metadata *BitsetOps[] = {
    870         llvm::MDString::get(getLLVMContext(), Out.str()),
    871         VTableMD,
    872         llvm::ConstantAsMetadata::get(
    873             llvm::ConstantInt::get(Int64Ty, AddrPointOffset))};
    874     llvm::MDTuple *BitsetEntry =
    875         llvm::MDTuple::get(getLLVMContext(), BitsetOps);
    876     BitsetEntries.push_back(BitsetEntry);
    877   }
    878 
    879   // Sort the bit set entries for determinism.
    880   std::sort(BitsetEntries.begin(), BitsetEntries.end(), [](llvm::MDTuple *T1,
    881                                                            llvm::MDTuple *T2) {
    882     if (T1 == T2)
    883       return false;
    884 
    885     StringRef S1 = cast<llvm::MDString>(T1->getOperand(0))->getString();
    886     StringRef S2 = cast<llvm::MDString>(T2->getOperand(0))->getString();
    887     if (S1 < S2)
    888       return true;
    889     if (S1 != S2)
    890       return false;
    891 
    892     uint64_t Offset1 = cast<llvm::ConstantInt>(
    893                            cast<llvm::ConstantAsMetadata>(T1->getOperand(2))
    894                                ->getValue())->getZExtValue();
    895     uint64_t Offset2 = cast<llvm::ConstantInt>(
    896                            cast<llvm::ConstantAsMetadata>(T2->getOperand(2))
    897                                ->getValue())->getZExtValue();
    898     assert(Offset1 != Offset2);
    899     return Offset1 < Offset2;
    900   });
    901 
    902   llvm::NamedMDNode *BitsetsMD =
    903       getModule().getOrInsertNamedMetadata("llvm.bitsets");
    904   for (auto BitsetEntry : BitsetEntries)
    905     BitsetsMD->addOperand(BitsetEntry);
    906 }
    907