clang/lib/CodeGen/CGCXX.cpp

   1 //===--- CGCXX.cpp - Emit LLVM Code for declarations ----------------------===//
   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.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 // We might split this into multiple files if it gets too unwieldy
  14
  15 #include "CGCXXABI.h"
  16 #include "CodeGenFunction.h"
  17 #include "CodeGenModule.h"
  18 #include "clang/AST/ASTContext.h"
  19 #include "clang/AST/Attr.h"
  20 #include "clang/AST/Decl.h"
  21 #include "clang/AST/DeclCXX.h"
  22 #include "clang/AST/DeclObjC.h"
  23 #include "clang/AST/Mangle.h"
  24 #include "clang/AST/RecordLayout.h"
  25 #include "clang/AST/StmtCXX.h"
  26 #include "clang/Basic/CodeGenOptions.h"
  27 #include "llvm/ADT/StringExtras.h"
  28 using namespace clang;
  29 using namespace CodeGen;
  30
  31
  32 /// Try to emit a base destructor as an alias to its primary
  33 /// base-class destructor.
  34 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
  35   if (!getCodeGenOpts().CXXCtorDtorAliases)
  36     return true;
  37
  38   // Producing an alias to a base class ctor/dtor can degrade debug quality
  39   // as the debugger cannot tell them apart.
  40   if (getCodeGenOpts().OptimizationLevel == 0)
  41     return true;
  42
  43   // If sanitizing memory to check for use-after-dtor, do not emit as
  44   //  an alias, unless this class owns no members.
  45   if (getCodeGenOpts().SanitizeMemoryUseAfterDtor &&
  46       !D->getParent()->field_empty())
  47     return true;
  48
  49   // If the destructor doesn't have a trivial body, we have to emit it
  50   // separately.
  51   if (!D->hasTrivialBody())
  52     return true;
  53
  54   const CXXRecordDecl *Class = D->getParent();
  55
  56   // We are going to instrument this destructor, so give up even if it is
  57   // currently empty.
  58   if (Class->mayInsertExtraPadding())
  59     return true;
  60
  61   // If we need to manipulate a VTT parameter, give up.
  62   if (Class->getNumVBases()) {
  63     // Extra Credit:  passing extra parameters is perfectly safe
  64     // in many calling conventions, so only bail out if the ctor's
  65     // calling convention is nonstandard.
  66     return true;
  67   }
  68
  69   // If any field has a non-trivial destructor, we have to emit the
  70   // destructor separately.
  71   for (const auto *I : Class->fields())
  72     if (I->getType().isDestructedType())
  73       return true;
  74
  75   // Try to find a unique base class with a non-trivial destructor.
  76   const CXXRecordDecl *UniqueBase = nullptr;
  77   for (const auto &I : Class->bases()) {
  78
  79     // We're in the base destructor, so skip virtual bases.
  80     if (I.isVirtual()) continue;
  81
  82     // Skip base classes with trivial destructors.
  83     const auto *Base =
  84         cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
  85     if (Base->hasTrivialDestructor()) continue;
  86
  87     // If we've already found a base class with a non-trivial
  88     // destructor, give up.
  89     if (UniqueBase) return true;
  90     UniqueBase = Base;
  91   }
  92
  93   // If we didn't find any bases with a non-trivial destructor, then
  94   // the base destructor is actually effectively trivial, which can
  95   // happen if it was needlessly user-defined or if there are virtual
  96   // bases with non-trivial destructors.
  97   if (!UniqueBase)
  98     return true;
  99
 100   // If the base is at a non-zero offset, give up.
 101   const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
 102   if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
 103     return true;
 104
 105   // Give up if the calling conventions don't match. We could update the call,
 106   // but it is probably not worth it.
 107   const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
 108   if (BaseD->getType()->castAs<FunctionType>()->getCallConv() !=
 109       D->getType()->castAs<FunctionType>()->getCallConv())
 110     return true;
 111
 112   GlobalDecl AliasDecl(D, Dtor_Base);
 113   GlobalDecl TargetDecl(BaseD, Dtor_Base);
 114
 115   // The alias will use the linkage of the referent.  If we can't
 116   // support aliases with that linkage, fail.
 117   llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
 118
 119   // We can't use an alias if the linkage is not valid for one.
 120   if (!llvm::GlobalAlias::isValidLinkage(Linkage))
 121     return true;
 122
 123   llvm::GlobalValue::LinkageTypes TargetLinkage =
 124       getFunctionLinkage(TargetDecl);
 125
 126   // Check if we have it already.
 127   StringRef MangledName = getMangledName(AliasDecl);
 128   llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
 129   if (Entry && !Entry->isDeclaration())
 130     return false;
 131   if (Replacements.count(MangledName))
 132     return false;
 133
 134   // Derive the type for the alias.
 135   llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
 136   llvm::PointerType *AliasType = AliasValueType->getPointerTo();
 137
 138   // Find the referent.  Some aliases might require a bitcast, in
 139   // which case the caller is responsible for ensuring the soundness
 140   // of these semantics.
 141   auto *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
 142   llvm::Constant *Aliasee = Ref;
 143   if (Ref->getType() != AliasType)
 144     Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
 145
 146   // Instead of creating as alias to a linkonce_odr, replace all of the uses
 147   // of the aliasee.
 148   if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
 149       !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&
 150         TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
 151     // FIXME: An extern template instantiation will create functions with
 152     // linkage "AvailableExternally". In libc++, some classes also define
 153     // members with attribute "AlwaysInline" and expect no reference to
 154     // be generated. It is desirable to reenable this optimisation after
 155     // corresponding LLVM changes.
 156     addReplacement(MangledName, Aliasee);
 157     return false;
 158   }
 159
 160   // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
 161   // template instantiation or a dllexported class, avoid forming it on COFF.
 162   // A COFF weak external alias cannot satisfy a normal undefined symbol
 163   // reference from another TU. The other TU must also mark the referenced
 164   // symbol as weak, which we cannot rely on.
 165   if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
 166       getTriple().isOSBinFormatCOFF()) {
 167     return true;
 168   }
 169
 170   // If we don't have a definition for the destructor yet or the definition is
 171   // avaialable_externally, don't emit an alias.  We can't emit aliases to
 172   // declarations; that's just not how aliases work.
 173   if (Ref->isDeclarationForLinker())
 174     return true;
 175
 176   // Don't create an alias to a linker weak symbol. This avoids producing
 177   // different COMDATs in different TUs. Another option would be to
 178   // output the alias both for weak_odr and linkonce_odr, but that
 179   // requires explicit comdat support in the IL.
 180   if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
 181     return true;
 182
 183   // Create the alias with no name.
 184   auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
 185                                           Aliasee, &getModule());
 186
 187   // Destructors are always unnamed_addr.
 188   Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
 189
 190   // Switch any previous uses to the alias.
 191   if (Entry) {
 192     assert(Entry->getType() == AliasType &&
 193            "declaration exists with different type");
 194     Alias->takeName(Entry);
 195     Entry->replaceAllUsesWith(Alias);
 196     Entry->eraseFromParent();
 197   } else {
 198     Alias->setName(MangledName);
 199   }
 200
 201   // Finally, set up the alias with its proper name and attributes.
 202   SetCommonAttributes(AliasDecl, Alias);
 203
 204   return false;
 205 }
 206
 207 llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) {
 208   const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD);
 209   auto *Fn = cast<llvm::Function>(
 210       getAddrOfCXXStructor(GD, &FnInfo, /*FnType=*/nullptr,
 211                            /*DontDefer=*/true, ForDefinition));
 212
 213   setFunctionLinkage(GD, Fn);
 214
 215   CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
 216   setNonAliasAttributes(GD, Fn);
 217   SetLLVMFunctionAttributesForDefinition(cast<CXXMethodDecl>(GD.getDecl()), Fn);
 218   return Fn;
 219 }
 220
 221 llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor(
 222     GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType,
 223     bool DontDefer, ForDefinition_t IsForDefinition) {
 224   auto *MD = cast<CXXMethodDecl>(GD.getDecl());
 225
 226   if (isa<CXXDestructorDecl>(MD)) {
 227     // Always alias equivalent complete destructors to base destructors in the
 228     // MS ABI.
 229     if (getTarget().getCXXABI().isMicrosoft() &&
 230         GD.getDtorType() == Dtor_Complete &&
 231         MD->getParent()->getNumVBases() == 0)
 232       GD = GD.getWithDtorType(Dtor_Base);
 233   }
 234
 235   if (!FnType) {
 236     if (!FnInfo)
 237       FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD);
 238     FnType = getTypes().GetFunctionType(*FnInfo);
 239   }
 240
 241   llvm::Constant *Ptr = GetOrCreateLLVMFunction(
 242       getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,
 243       /*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);
 244   return {FnType, Ptr};
 245 }
 246
 247 static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,
 248                                           GlobalDecl GD,
 249                                           llvm::Type *Ty,
 250                                           const CXXRecordDecl *RD) {
 251   assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
 252          "No kext in Microsoft ABI");
 253   CodeGenModule &CGM = CGF.CGM;
 254   llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
 255   Ty = Ty->getPointerTo();
 256   VTable = CGF.Builder.CreateBitCast(VTable, Ty->getPointerTo());
 257   assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
 258   uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
 259   const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);
 260   VTableLayout::AddressPointLocation AddressPoint =
 261       VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
 262   VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +
 263                  AddressPoint.AddressPointIndex;
 264   llvm::Value *VFuncPtr =
 265     CGF.Builder.CreateConstInBoundsGEP1_64(Ty, VTable, VTableIndex, "vfnkxt");
 266   llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad(
 267       Ty, VFuncPtr, llvm::Align(CGF.PointerAlignInBytes));
 268   CGCallee Callee(GD, VFunc);
 269   return Callee;
 270 }
 271
 272 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
 273 /// indirect call to virtual functions. It makes the call through indexing
 274 /// into the vtable.
 275 CGCallee
 276 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
 277                                            NestedNameSpecifier *Qual,
 278                                            llvm::Type *Ty) {
 279   assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
 280          "BuildAppleKextVirtualCall - bad Qual kind");
 281
 282   const Type *QTy = Qual->getAsType();
 283   QualType T = QualType(QTy, 0);
 284   const RecordType *RT = T->getAs<RecordType>();
 285   assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
 286   const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
 287
 288   if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
 289     return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
 290
 291   return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
 292 }
 293
 294 /// BuildVirtualCall - This routine makes indirect vtable call for
 295 /// call to virtual destructors. It returns 0 if it could not do it.
 296 CGCallee
 297 CodeGenFunction::BuildAppleKextVirtualDestructorCall(
 298                                             const CXXDestructorDecl *DD,
 299                                             CXXDtorType Type,
 300                                             const CXXRecordDecl *RD) {
 301   assert(DD->isVirtual() && Type != Dtor_Base);
 302   // Compute the function type we're calling.
 303   const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
 304       GlobalDecl(DD, Dtor_Complete));
 305   llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
 306   return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);
 307 }