clang/lib/AST/ItaniumCXXABI.cpp

   1 //===------- ItaniumCXXABI.cpp - AST support for the Itanium C++ ABI ------===//
   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 provides C++ AST support targeting the Itanium C++ ABI, which is
  10 // documented at:
  11 //  http://www.codesourcery.com/public/cxx-abi/abi.html
  12 //  http://www.codesourcery.com/public/cxx-abi/abi-eh.html
  13 //
  14 // It also supports the closely-related ARM C++ ABI, documented at:
  15 // http://infocenter.arm.com/help/topic/com.arm.doc.ihi0041c/IHI0041C_cppabi.pdf
  16 //
  17 //===----------------------------------------------------------------------===//
  18
  19 #include "CXXABI.h"
  20 #include "clang/AST/ASTContext.h"
  21 #include "clang/AST/DeclCXX.h"
  22 #include "clang/AST/Mangle.h"
  23 #include "clang/AST/MangleNumberingContext.h"
  24 #include "clang/AST/RecordLayout.h"
  25 #include "clang/AST/Type.h"
  26 #include "clang/Basic/TargetInfo.h"
  27 #include "llvm/ADT/FoldingSet.h"
  28 #include "llvm/ADT/iterator.h"
  29 #include <optional>
  30
  31 using namespace clang;
  32
  33 namespace {
  34
  35 /// According to Itanium C++ ABI 5.1.2:
  36 /// the name of an anonymous union is considered to be
  37 /// the name of the first named data member found by a pre-order,
  38 /// depth-first, declaration-order walk of the data members of
  39 /// the anonymous union.
  40 /// If there is no such data member (i.e., if all of the data members
  41 /// in the union are unnamed), then there is no way for a program to
  42 /// refer to the anonymous union, and there is therefore no need to mangle its name.
  43 ///
  44 /// Returns the name of anonymous union VarDecl or nullptr if it is not found.
  45 static const IdentifierInfo *findAnonymousUnionVarDeclName(const VarDecl& VD) {
  46   const RecordType *RT = VD.getType()->getAs<RecordType>();
  47   assert(RT && "type of VarDecl is expected to be RecordType.");
  48   assert(RT->getDecl()->isUnion() && "RecordType is expected to be a union.");
  49   if (const FieldDecl *FD = RT->getDecl()->findFirstNamedDataMember()) {
  50     return FD->getIdentifier();
  51   }
  52
  53   return nullptr;
  54 }
  55
  56 /// The name of a decomposition declaration.
  57 struct DecompositionDeclName {
  58   using BindingArray = ArrayRef<const BindingDecl*>;
  59
  60   /// Representative example of a set of bindings with these names.
  61   BindingArray Bindings;
  62
  63   /// Iterators over the sequence of identifiers in the name.
  64   struct Iterator
  65       : llvm::iterator_adaptor_base<Iterator, BindingArray::const_iterator,
  66                                     std::random_access_iterator_tag,
  67                                     const IdentifierInfo *> {
  68     Iterator(BindingArray::const_iterator It) : iterator_adaptor_base(It) {}
  69     const IdentifierInfo *operator*() const {
  70       return (*this->I)->getIdentifier();
  71     }
  72   };
  73   Iterator begin() const { return Iterator(Bindings.begin()); }
  74   Iterator end() const { return Iterator(Bindings.end()); }
  75 };
  76 }
  77
  78 namespace llvm {
  79 template<typename T> bool isDenseMapKeyEmpty(T V) {
  80   return llvm::DenseMapInfo<T>::isEqual(
  81       V, llvm::DenseMapInfo<T>::getEmptyKey());
  82 }
  83 template<typename T> bool isDenseMapKeyTombstone(T V) {
  84   return llvm::DenseMapInfo<T>::isEqual(
  85       V, llvm::DenseMapInfo<T>::getTombstoneKey());
  86 }
  87
  88 template <typename T>
  89 std::optional<bool> areDenseMapKeysEqualSpecialValues(T LHS, T RHS) {
  90   bool LHSEmpty = isDenseMapKeyEmpty(LHS);
  91   bool RHSEmpty = isDenseMapKeyEmpty(RHS);
  92   if (LHSEmpty || RHSEmpty)
  93     return LHSEmpty && RHSEmpty;
  94
  95   bool LHSTombstone = isDenseMapKeyTombstone(LHS);
  96   bool RHSTombstone = isDenseMapKeyTombstone(RHS);
  97   if (LHSTombstone || RHSTombstone)
  98     return LHSTombstone && RHSTombstone;
  99
 100   return std::nullopt;
 101 }
 102
 103 template<>
 104 struct DenseMapInfo<DecompositionDeclName> {
 105   using ArrayInfo = llvm::DenseMapInfo<ArrayRef<const BindingDecl*>>;
 106   static DecompositionDeclName getEmptyKey() {
 107     return {ArrayInfo::getEmptyKey()};
 108   }
 109   static DecompositionDeclName getTombstoneKey() {
 110     return {ArrayInfo::getTombstoneKey()};
 111   }
 112   static unsigned getHashValue(DecompositionDeclName Key) {
 113     assert(!isEqual(Key, getEmptyKey()) && !isEqual(Key, getTombstoneKey()));
 114     return llvm::hash_combine_range(Key.begin(), Key.end());
 115   }
 116   static bool isEqual(DecompositionDeclName LHS, DecompositionDeclName RHS) {
 117     if (std::optional<bool> Result =
 118             areDenseMapKeysEqualSpecialValues(LHS.Bindings, RHS.Bindings))
 119       return *Result;
 120
 121     return LHS.Bindings.size() == RHS.Bindings.size() &&
 122            std::equal(LHS.begin(), LHS.end(), RHS.begin());
 123   }
 124 };
 125 }
 126
 127 namespace {
 128
 129 /// Keeps track of the mangled names of lambda expressions and block
 130 /// literals within a particular context.
 131 class ItaniumNumberingContext : public MangleNumberingContext {
 132   ItaniumMangleContext *Mangler;
 133   llvm::StringMap<unsigned> LambdaManglingNumbers;
 134   unsigned BlockManglingNumber = 0;
 135   llvm::DenseMap<const IdentifierInfo *, unsigned> VarManglingNumbers;
 136   llvm::DenseMap<const IdentifierInfo *, unsigned> TagManglingNumbers;
 137   llvm::DenseMap<DecompositionDeclName, unsigned>
 138       DecompsitionDeclManglingNumbers;
 139
 140 public:
 141   ItaniumNumberingContext(ItaniumMangleContext *Mangler) : Mangler(Mangler) {}
 142
 143   unsigned getManglingNumber(const CXXMethodDecl *CallOperator) override {
 144     const CXXRecordDecl *Lambda = CallOperator->getParent();
 145     assert(Lambda->isLambda());
 146
 147     // Computation of the <lambda-sig> is non-trivial and subtle. Rather than
 148     // duplicating it here, just mangle the <lambda-sig> directly.
 149     llvm::SmallString<128> LambdaSig;
 150     llvm::raw_svector_ostream Out(LambdaSig);
 151     Mangler->mangleLambdaSig(Lambda, Out);
 152
 153     return ++LambdaManglingNumbers[LambdaSig];
 154   }
 155
 156   unsigned getManglingNumber(const BlockDecl *BD) override {
 157     return ++BlockManglingNumber;
 158   }
 159
 160   unsigned getStaticLocalNumber(const VarDecl *VD) override {
 161     return 0;
 162   }
 163
 164   /// Variable decls are numbered by identifier.
 165   unsigned getManglingNumber(const VarDecl *VD, unsigned) override {
 166     if (auto *DD = dyn_cast<DecompositionDecl>(VD)) {
 167       DecompositionDeclName Name{DD->bindings()};
 168       return ++DecompsitionDeclManglingNumbers[Name];
 169     }
 170
 171     const IdentifierInfo *Identifier = VD->getIdentifier();
 172     if (!Identifier) {
 173       // VarDecl without an identifier represents an anonymous union
 174       // declaration.
 175       Identifier = findAnonymousUnionVarDeclName(*VD);
 176     }
 177     return ++VarManglingNumbers[Identifier];
 178   }
 179
 180   unsigned getManglingNumber(const TagDecl *TD, unsigned) override {
 181     return ++TagManglingNumbers[TD->getIdentifier()];
 182   }
 183 };
 184
 185 // A version of this for SYCL that makes sure that 'device' mangling context
 186 // matches the lambda mangling number, so that __builtin_sycl_unique_stable_name
 187 // can be consistently generated between a MS and Itanium host by just referring
 188 // to the device mangling number.
 189 class ItaniumSYCLNumberingContext : public ItaniumNumberingContext {
 190   llvm::DenseMap<const CXXMethodDecl *, unsigned> ManglingNumbers;
 191   using ManglingItr = decltype(ManglingNumbers)::iterator;
 192
 193 public:
 194   ItaniumSYCLNumberingContext(ItaniumMangleContext *Mangler)
 195       : ItaniumNumberingContext(Mangler) {}
 196
 197   unsigned getManglingNumber(const CXXMethodDecl *CallOperator) override {
 198     unsigned Number = ItaniumNumberingContext::getManglingNumber(CallOperator);
 199     std::pair<ManglingItr, bool> emplace_result =
 200         ManglingNumbers.try_emplace(CallOperator, Number);
 201     (void)emplace_result;
 202     assert(emplace_result.second && "Lambda number set multiple times?");
 203     return Number;
 204   }
 205
 206   using ItaniumNumberingContext::getManglingNumber;
 207
 208   unsigned getDeviceManglingNumber(const CXXMethodDecl *CallOperator) override {
 209     ManglingItr Itr = ManglingNumbers.find(CallOperator);
 210     assert(Itr != ManglingNumbers.end() && "Lambda not yet mangled?");
 211
 212     return Itr->second;
 213   }
 214 };
 215
 216 class ItaniumCXXABI : public CXXABI {
 217 private:
 218   std::unique_ptr<MangleContext> Mangler;
 219 protected:
 220   ASTContext &Context;
 221 public:
 222   ItaniumCXXABI(ASTContext &Ctx)
 223       : Mangler(Ctx.createMangleContext()), Context(Ctx) {}
 224
 225   MemberPointerInfo
 226   getMemberPointerInfo(const MemberPointerType *MPT) const override {
 227     const TargetInfo &Target = Context.getTargetInfo();
 228     TargetInfo::IntType PtrDiff = Target.getPtrDiffType(LangAS::Default);
 229     MemberPointerInfo MPI;
 230     MPI.Width = Target.getTypeWidth(PtrDiff);
 231     MPI.Align = Target.getTypeAlign(PtrDiff);
 232     MPI.HasPadding = false;
 233     if (MPT->isMemberFunctionPointer())
 234       MPI.Width *= 2;
 235     return MPI;
 236   }
 237
 238   CallingConv getDefaultMethodCallConv(bool isVariadic) const override {
 239     const llvm::Triple &T = Context.getTargetInfo().getTriple();
 240     if (!isVariadic && T.isWindowsGNUEnvironment() &&
 241         T.getArch() == llvm::Triple::x86)
 242       return CC_X86ThisCall;
 243     return Context.getTargetInfo().getDefaultCallingConv();
 244   }
 245
 246   // We cheat and just check that the class has a vtable pointer, and that it's
 247   // only big enough to have a vtable pointer and nothing more (or less).
 248   bool isNearlyEmpty(const CXXRecordDecl *RD) const override {
 249
 250     // Check that the class has a vtable pointer.
 251     if (!RD->isDynamicClass())
 252       return false;
 253
 254     const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
 255     CharUnits PointerSize = Context.toCharUnitsFromBits(
 256         Context.getTargetInfo().getPointerWidth(LangAS::Default));
 257     return Layout.getNonVirtualSize() == PointerSize;
 258   }
 259
 260   const CXXConstructorDecl *
 261   getCopyConstructorForExceptionObject(CXXRecordDecl *RD) override {
 262     return nullptr;
 263   }
 264
 265   void addCopyConstructorForExceptionObject(CXXRecordDecl *RD,
 266                                             CXXConstructorDecl *CD) override {}
 267
 268   void addTypedefNameForUnnamedTagDecl(TagDecl *TD,
 269                                        TypedefNameDecl *DD) override {}
 270
 271   TypedefNameDecl *getTypedefNameForUnnamedTagDecl(const TagDecl *TD) override {
 272     return nullptr;
 273   }
 274
 275   void addDeclaratorForUnnamedTagDecl(TagDecl *TD,
 276                                       DeclaratorDecl *DD) override {}
 277
 278   DeclaratorDecl *getDeclaratorForUnnamedTagDecl(const TagDecl *TD) override {
 279     return nullptr;
 280   }
 281
 282   std::unique_ptr<MangleNumberingContext>
 283   createMangleNumberingContext() const override {
 284     if (Context.getLangOpts().isSYCL())
 285       return std::make_unique<ItaniumSYCLNumberingContext>(
 286           cast<ItaniumMangleContext>(Mangler.get()));
 287     return std::make_unique<ItaniumNumberingContext>(
 288         cast<ItaniumMangleContext>(Mangler.get()));
 289   }
 290 };
 291 }
 292
 293 CXXABI *clang::CreateItaniumCXXABI(ASTContext &Ctx) {
 294   return new ItaniumCXXABI(Ctx);
 295 }
 296
 297 std::unique_ptr<MangleNumberingContext>
 298 clang::createItaniumNumberingContext(MangleContext *Mangler) {
 299   return std::make_unique<ItaniumNumberingContext>(
 300       cast<ItaniumMangleContext>(Mangler));
 301 }