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/Basic/CodeGenOptions.h"
  26 using namespace clang;
  27 using namespace CodeGen;
  28
  29
  30 /// Try to emit a base destructor as an alias to its primary
  31 /// base-class destructor.
  32 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
  33   if (!getCodeGenOpts().CXXCtorDtorAliases)
  34     return true;
  35
  36   // Producing an alias to a base class ctor/dtor can degrade debug quality
  37   // as the debugger cannot tell them apart.
  38   if (getCodeGenOpts().OptimizationLevel == 0)
  39     return true;
  40
  41   // Disable this optimization for ARM64EC.  FIXME: This probably should work,
  42   // but getting the symbol table correct is complicated.
  43   if (getTarget().getTriple().isWindowsArm64EC())
  44     return true;
  45
  46   // If sanitizing memory to check for use-after-dtor, do not emit as
  47   //  an alias, unless this class owns no members.
  48   if (getCodeGenOpts().SanitizeMemoryUseAfterDtor &&
  49       !D->getParent()->field_empty())
  50     return true;
  51
  52   // If the destructor doesn't have a trivial body, we have to emit it
  53   // separately.
  54   if (!D->hasTrivialBody())
  55     return true;
  56
  57   const CXXRecordDecl *Class = D->getParent();
  58
  59   // We are going to instrument this destructor, so give up even if it is
  60   // currently empty.
  61   if (Class->mayInsertExtraPadding())
  62     return true;
  63
  64   // If we need to manipulate a VTT parameter, give up.
  65   if (Class->getNumVBases()) {
  66     // Extra Credit:  passing extra parameters is perfectly safe
  67     // in many calling conventions, so only bail out if the ctor's
  68     // calling convention is nonstandard.
  69     return true;
  70   }
  71
  72   // If any field has a non-trivial destructor, we have to emit the
  73   // destructor separately.
  74   for (const auto *I : Class->fields())
  75     if (I->getType().isDestructedType())
  76       return true;
  77
  78   // Try to find a unique base class with a non-trivial destructor.
  79   const CXXRecordDecl *UniqueBase = nullptr;
  80   for (const auto &I : Class->bases()) {
  81
  82     // We're in the base destructor, so skip virtual bases.
  83     if (I.isVirtual()) continue;
  84
  85     // Skip base classes with trivial destructors.
  86     const auto *Base =
  87         cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
  88     if (Base->hasTrivialDestructor()) continue;
  89
  90     // If we've already found a base class with a non-trivial
  91     // destructor, give up.
  92     if (UniqueBase) return true;
  93     UniqueBase = Base;
  94   }
  95
  96   // If we didn't find any bases with a non-trivial destructor, then
  97   // the base destructor is actually effectively trivial, which can
  98   // happen if it was needlessly user-defined or if there are virtual
  99   // bases with non-trivial destructors.
 100   if (!UniqueBase)
 101     return true;
 102
 103   // If the base is at a non-zero offset, give up.
 104   const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
 105   if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
 106     return true;
 107
 108   // Give up if the calling conventions don't match. We could update the call,
 109   // but it is probably not worth it.
 110   const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
 111   if (BaseD->getType()->castAs<FunctionType>()->getCallConv() !=
 112       D->getType()->castAs<FunctionType>()->getCallConv())
 113     return true;
 114
 115   GlobalDecl AliasDecl(D, Dtor_Base);
 116   GlobalDecl TargetDecl(BaseD, Dtor_Base);
 117
 118   // The alias will use the linkage of the referent.  If we can't
 119   // support aliases with that linkage, fail.
 120   llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
 121
 122   // We can't use an alias if the linkage is not valid for one.
 123   if (!llvm::GlobalAlias::isValidLinkage(Linkage))
 124     return true;
 125
 126   llvm::GlobalValue::LinkageTypes TargetLinkage =
 127       getFunctionLinkage(TargetDecl);
 128
 129   // Check if we have it already.
 130   StringRef MangledName = getMangledName(AliasDecl);
 131   llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
 132   if (Entry && !Entry->isDeclaration())
 133     return false;
 134   if (Replacements.count(MangledName))
 135     return false;
 136
 137   llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
 138
 139   // Find the referent.
 140   auto *Aliasee = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
 141
 142   // Instead of creating as alias to a linkonce_odr, replace all of the uses
 143   // of the aliasee.
 144   if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
 145       !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&
 146         TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
 147     // FIXME: An extern template instantiation will create functions with
 148     // linkage "AvailableExternally". In libc++, some classes also define
 149     // members with attribute "AlwaysInline" and expect no reference to
 150     // be generated. It is desirable to reenable this optimisation after
 151     // corresponding LLVM changes.
 152     addReplacement(MangledName, Aliasee);
 153     return false;
 154   }
 155
 156   // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
 157   // template instantiation or a dllexported class, avoid forming it on COFF.
 158   // A COFF weak external alias cannot satisfy a normal undefined symbol
 159   // reference from another TU. The other TU must also mark the referenced
 160   // symbol as weak, which we cannot rely on.
 161   if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
 162       getTriple().isOSBinFormatCOFF()) {
 163     return true;
 164   }
 165
 166   // If we don't have a definition for the destructor yet or the definition is
 167   // avaialable_externally, don't emit an alias.  We can't emit aliases to
 168   // declarations; that's just not how aliases work.
 169   if (Aliasee->isDeclarationForLinker())
 170     return true;
 171
 172   // Don't create an alias to a linker weak symbol. This avoids producing
 173   // different COMDATs in different TUs. Another option would be to
 174   // output the alias both for weak_odr and linkonce_odr, but that
 175   // requires explicit comdat support in the IL.
 176   if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
 177     return true;
 178
 179   // Create the alias with no name.
 180   auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
 181                                           Aliasee, &getModule());
 182
 183   // Destructors are always unnamed_addr.
 184   Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
 185
 186   // Switch any previous uses to the alias.
 187   if (Entry) {
 188     assert(Entry->getValueType() == AliasValueType &&
 189            Entry->getAddressSpace() == Alias->getAddressSpace() &&
 190            "declaration exists with different type");
 191     Alias->takeName(Entry);
 192     Entry->replaceAllUsesWith(Alias);
 193     Entry->eraseFromParent();
 194   } else {
 195     Alias->setName(MangledName);
 196   }
 197
 198   // Finally, set up the alias with its proper name and attributes.
 199   SetCommonAttributes(AliasDecl, Alias);
 200
 201   return false;
 202 }
 203
 204 llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) {
 205   const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD);
 206   auto *Fn = cast<llvm::Function>(
 207       getAddrOfCXXStructor(GD, &FnInfo, /*FnType=*/nullptr,
 208                            /*DontDefer=*/true, ForDefinition));
 209
 210   setFunctionLinkage(GD, Fn);
 211
 212   CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
 213   setNonAliasAttributes(GD, Fn);
 214   SetLLVMFunctionAttributesForDefinition(cast<CXXMethodDecl>(GD.getDecl()), Fn);
 215   return Fn;
 216 }
 217
 218 llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor(
 219     GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType,
 220     bool DontDefer, ForDefinition_t IsForDefinition) {
 221   auto *MD = cast<CXXMethodDecl>(GD.getDecl());
 222
 223   if (isa<CXXDestructorDecl>(MD)) {
 224     // Always alias equivalent complete destructors to base destructors in the
 225     // MS ABI.
 226     if (getTarget().getCXXABI().isMicrosoft() &&
 227         GD.getDtorType() == Dtor_Complete &&
 228         MD->getParent()->getNumVBases() == 0)
 229       GD = GD.getWithDtorType(Dtor_Base);
 230   }
 231
 232   if (!FnType) {
 233     if (!FnInfo)
 234       FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD);
 235     FnType = getTypes().GetFunctionType(*FnInfo);
 236   }
 237
 238   llvm::Constant *Ptr = GetOrCreateLLVMFunction(
 239       getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,
 240       /*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);
 241   return {FnType, Ptr};
 242 }
 243
 244 static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,
 245                                           GlobalDecl GD,
 246                                           llvm::Type *Ty,
 247                                           const CXXRecordDecl *RD) {
 248   assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
 249          "No kext in Microsoft ABI");
 250   CodeGenModule &CGM = CGF.CGM;
 251   llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
 252   Ty = llvm::PointerType::getUnqual(CGM.getLLVMContext());
 253   assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
 254   uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
 255   const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);
 256   VTableLayout::AddressPointLocation AddressPoint =
 257       VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
 258   VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +
 259                  AddressPoint.AddressPointIndex;
 260   llvm::Value *VFuncPtr =
 261     CGF.Builder.CreateConstInBoundsGEP1_64(Ty, VTable, VTableIndex, "vfnkxt");
 262   llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad(
 263       Ty, VFuncPtr, llvm::Align(CGF.PointerAlignInBytes));
 264
 265   CGPointerAuthInfo PointerAuth;
 266   if (auto &Schema =
 267           CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers) {
 268     GlobalDecl OrigMD =
 269         CGM.getItaniumVTableContext().findOriginalMethod(GD.getCanonicalDecl());
 270     PointerAuth = CGF.EmitPointerAuthInfo(Schema, VFuncPtr, OrigMD, QualType());
 271   }
 272
 273   CGCallee Callee(GD, VFunc, PointerAuth);
 274   return Callee;
 275 }
 276
 277 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
 278 /// indirect call to virtual functions. It makes the call through indexing
 279 /// into the vtable.
 280 CGCallee
 281 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
 282                                            NestedNameSpecifier *Qual,
 283                                            llvm::Type *Ty) {
 284   assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
 285          "BuildAppleKextVirtualCall - bad Qual kind");
 286
 287   const Type *QTy = Qual->getAsType();
 288   QualType T = QualType(QTy, 0);
 289   const RecordType *RT = T->getAs<RecordType>();
 290   assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
 291   const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
 292
 293   if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
 294     return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
 295
 296   return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
 297 }
 298
 299 /// BuildVirtualCall - This routine makes indirect vtable call for
 300 /// call to virtual destructors. It returns 0 if it could not do it.
 301 CGCallee
 302 CodeGenFunction::BuildAppleKextVirtualDestructorCall(
 303                                             const CXXDestructorDecl *DD,
 304                                             CXXDtorType Type,
 305                                             const CXXRecordDecl *RD) {
 306   assert(DD->isVirtual() && Type != Dtor_Base);
 307   // Compute the function type we're calling.
 308   const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
 309       GlobalDecl(DD, Dtor_Complete));
 310   llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
 311   return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);
 312 }