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   // Disable this optimization for ARM64EC.  FIXME: This probably should work,
  44   // but getting the symbol table correct is complicated.
  45   if (getTarget().getTriple().isWindowsArm64EC())
  46     return true;
  47
  48   // If sanitizing memory to check for use-after-dtor, do not emit as
  49   //  an alias, unless this class owns no members.
  50   if (getCodeGenOpts().SanitizeMemoryUseAfterDtor &&
  51       !D->getParent()->field_empty())
  52     return true;
  53
  54   // If the destructor doesn't have a trivial body, we have to emit it
  55   // separately.
  56   if (!D->hasTrivialBody())
  57     return true;
  58
  59   const CXXRecordDecl *Class = D->getParent();
  60
  61   // We are going to instrument this destructor, so give up even if it is
  62   // currently empty.
  63   if (Class->mayInsertExtraPadding())
  64     return true;
  65
  66   // If we need to manipulate a VTT parameter, give up.
  67   if (Class->getNumVBases()) {
  68     // Extra Credit:  passing extra parameters is perfectly safe
  69     // in many calling conventions, so only bail out if the ctor's
  70     // calling convention is nonstandard.
  71     return true;
  72   }
  73
  74   // If any field has a non-trivial destructor, we have to emit the
  75   // destructor separately.
  76   for (const auto *I : Class->fields())
  77     if (I->getType().isDestructedType())
  78       return true;
  79
  80   // Try to find a unique base class with a non-trivial destructor.
  81   const CXXRecordDecl *UniqueBase = nullptr;
  82   for (const auto &I : Class->bases()) {
  83
  84     // We're in the base destructor, so skip virtual bases.
  85     if (I.isVirtual()) continue;
  86
  87     // Skip base classes with trivial destructors.
  88     const auto *Base =
  89         cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
  90     if (Base->hasTrivialDestructor()) continue;
  91
  92     // If we've already found a base class with a non-trivial
  93     // destructor, give up.
  94     if (UniqueBase) return true;
  95     UniqueBase = Base;
  96   }
  97
  98   // If we didn't find any bases with a non-trivial destructor, then
  99   // the base destructor is actually effectively trivial, which can
 100   // happen if it was needlessly user-defined or if there are virtual
 101   // bases with non-trivial destructors.
 102   if (!UniqueBase)
 103     return true;
 104
 105   // If the base is at a non-zero offset, give up.
 106   const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
 107   if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
 108     return true;
 109
 110   // Give up if the calling conventions don't match. We could update the call,
 111   // but it is probably not worth it.
 112   const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
 113   if (BaseD->getType()->castAs<FunctionType>()->getCallConv() !=
 114       D->getType()->castAs<FunctionType>()->getCallConv())
 115     return true;
 116
 117   GlobalDecl AliasDecl(D, Dtor_Base);
 118   GlobalDecl TargetDecl(BaseD, Dtor_Base);
 119
 120   // The alias will use the linkage of the referent.  If we can't
 121   // support aliases with that linkage, fail.
 122   llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
 123
 124   // We can't use an alias if the linkage is not valid for one.
 125   if (!llvm::GlobalAlias::isValidLinkage(Linkage))
 126     return true;
 127
 128   llvm::GlobalValue::LinkageTypes TargetLinkage =
 129       getFunctionLinkage(TargetDecl);
 130
 131   // Check if we have it already.
 132   StringRef MangledName = getMangledName(AliasDecl);
 133   llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
 134   if (Entry && !Entry->isDeclaration())
 135     return false;
 136   if (Replacements.count(MangledName))
 137     return false;
 138
 139   llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
 140
 141   // Find the referent.
 142   auto *Aliasee = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
 143
 144   // Instead of creating as alias to a linkonce_odr, replace all of the uses
 145   // of the aliasee.
 146   if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
 147       !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&
 148         TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
 149     // FIXME: An extern template instantiation will create functions with
 150     // linkage "AvailableExternally". In libc++, some classes also define
 151     // members with attribute "AlwaysInline" and expect no reference to
 152     // be generated. It is desirable to reenable this optimisation after
 153     // corresponding LLVM changes.
 154     addReplacement(MangledName, Aliasee);
 155     return false;
 156   }
 157
 158   // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
 159   // template instantiation or a dllexported class, avoid forming it on COFF.
 160   // A COFF weak external alias cannot satisfy a normal undefined symbol
 161   // reference from another TU. The other TU must also mark the referenced
 162   // symbol as weak, which we cannot rely on.
 163   if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
 164       getTriple().isOSBinFormatCOFF()) {
 165     return true;
 166   }
 167
 168   // If we don't have a definition for the destructor yet or the definition is
 169   // avaialable_externally, don't emit an alias.  We can't emit aliases to
 170   // declarations; that's just not how aliases work.
 171   if (Aliasee->isDeclarationForLinker())
 172     return true;
 173
 174   // Don't create an alias to a linker weak symbol. This avoids producing
 175   // different COMDATs in different TUs. Another option would be to
 176   // output the alias both for weak_odr and linkonce_odr, but that
 177   // requires explicit comdat support in the IL.
 178   if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
 179     return true;
 180
 181   // Create the alias with no name.
 182   auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
 183                                           Aliasee, &getModule());
 184
 185   // Destructors are always unnamed_addr.
 186   Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
 187
 188   // Switch any previous uses to the alias.
 189   if (Entry) {
 190     assert(Entry->getValueType() == AliasValueType &&
 191            Entry->getAddressSpace() == Alias->getAddressSpace() &&
 192            "declaration exists with different type");
 193     Alias->takeName(Entry);
 194     Entry->replaceAllUsesWith(Alias);
 195     Entry->eraseFromParent();
 196   } else {
 197     Alias->setName(MangledName);
 198   }
 199
 200   // Finally, set up the alias with its proper name and attributes.
 201   SetCommonAttributes(AliasDecl, Alias);
 202
 203   return false;
 204 }
 205
 206 llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) {
 207   const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD);
 208   auto *Fn = cast<llvm::Function>(
 209       getAddrOfCXXStructor(GD, &FnInfo, /*FnType=*/nullptr,
 210                            /*DontDefer=*/true, ForDefinition));
 211
 212   setFunctionLinkage(GD, Fn);
 213
 214   CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
 215   setNonAliasAttributes(GD, Fn);
 216   SetLLVMFunctionAttributesForDefinition(cast<CXXMethodDecl>(GD.getDecl()), Fn);
 217   return Fn;
 218 }
 219
 220 llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor(
 221     GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType,
 222     bool DontDefer, ForDefinition_t IsForDefinition) {
 223   auto *MD = cast<CXXMethodDecl>(GD.getDecl());
 224
 225   if (isa<CXXDestructorDecl>(MD)) {
 226     // Always alias equivalent complete destructors to base destructors in the
 227     // MS ABI.
 228     if (getTarget().getCXXABI().isMicrosoft() &&
 229         GD.getDtorType() == Dtor_Complete &&
 230         MD->getParent()->getNumVBases() == 0)
 231       GD = GD.getWithDtorType(Dtor_Base);
 232   }
 233
 234   if (!FnType) {
 235     if (!FnInfo)
 236       FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD);
 237     FnType = getTypes().GetFunctionType(*FnInfo);
 238   }
 239
 240   llvm::Constant *Ptr = GetOrCreateLLVMFunction(
 241       getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,
 242       /*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);
 243   return {FnType, Ptr};
 244 }
 245
 246 static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,
 247                                           GlobalDecl GD,
 248                                           llvm::Type *Ty,
 249                                           const CXXRecordDecl *RD) {
 250   assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
 251          "No kext in Microsoft ABI");
 252   CodeGenModule &CGM = CGF.CGM;
 253   llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
 254   Ty = llvm::PointerType::getUnqual(CGM.getLLVMContext());
 255   assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
 256   uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
 257   const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);
 258   VTableLayout::AddressPointLocation AddressPoint =
 259       VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
 260   VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +
 261                  AddressPoint.AddressPointIndex;
 262   llvm::Value *VFuncPtr =
 263     CGF.Builder.CreateConstInBoundsGEP1_64(Ty, VTable, VTableIndex, "vfnkxt");
 264   llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad(
 265       Ty, VFuncPtr, llvm::Align(CGF.PointerAlignInBytes));
 266
 267   CGPointerAuthInfo PointerAuth;
 268   if (auto &Schema =
 269           CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers) {
 270     GlobalDecl OrigMD =
 271         CGM.getItaniumVTableContext().findOriginalMethod(GD.getCanonicalDecl());
 272     PointerAuth = CGF.EmitPointerAuthInfo(Schema, VFuncPtr, OrigMD, QualType());
 273   }
 274
 275   CGCallee Callee(GD, VFunc, PointerAuth);
 276   return Callee;
 277 }
 278
 279 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
 280 /// indirect call to virtual functions. It makes the call through indexing
 281 /// into the vtable.
 282 CGCallee
 283 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
 284                                            NestedNameSpecifier *Qual,
 285                                            llvm::Type *Ty) {
 286   assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
 287          "BuildAppleKextVirtualCall - bad Qual kind");
 288
 289   const Type *QTy = Qual->getAsType();
 290   QualType T = QualType(QTy, 0);
 291   const RecordType *RT = T->getAs<RecordType>();
 292   assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
 293   const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
 294
 295   if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
 296     return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
 297
 298   return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
 299 }
 300
 301 /// BuildVirtualCall - This routine makes indirect vtable call for
 302 /// call to virtual destructors. It returns 0 if it could not do it.
 303 CGCallee
 304 CodeGenFunction::BuildAppleKextVirtualDestructorCall(
 305                                             const CXXDestructorDecl *DD,
 306                                             CXXDtorType Type,
 307                                             const CXXRecordDecl *RD) {
 308   assert(DD->isVirtual() && Type != Dtor_Base);
 309   // Compute the function type we're calling.
 310   const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
 311       GlobalDecl(DD, Dtor_Complete));
 312   llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
 313   return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);
 314 }