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 
30 using namespace clang;
31 
32 namespace {
33 
34 /// According to Itanium C++ ABI 5.1.2:
35 /// the name of an anonymous union is considered to be
36 /// the name of the first named data member found by a pre-order,
37 /// depth-first, declaration-order walk of the data members of
38 /// the anonymous union.
39 /// If there is no such data member (i.e., if all of the data members
40 /// in the union are unnamed), then there is no way for a program to
41 /// refer to the anonymous union, and there is therefore no need to mangle its name.
42 ///
43 /// Returns the name of anonymous union VarDecl or nullptr if it is not found.
44 static const IdentifierInfo *findAnonymousUnionVarDeclName(const VarDecl& VD) {
45   const RecordType *RT = VD.getType()->getAs<RecordType>();
46   assert(RT && "type of VarDecl is expected to be RecordType.");
47   assert(RT->getDecl()->isUnion() && "RecordType is expected to be a union.");
48   if (const FieldDecl *FD = RT->getDecl()->findFirstNamedDataMember()) {
49     return FD->getIdentifier();
50   }
51 
52   return nullptr;
53 }
54 
55 /// The name of a decomposition declaration.
56 struct DecompositionDeclName {
57   using BindingArray = ArrayRef<const BindingDecl*>;
58 
59   /// Representative example of a set of bindings with these names.
60   BindingArray Bindings;
61 
62   /// Iterators over the sequence of identifiers in the name.
63   struct Iterator
64       : llvm::iterator_adaptor_base<Iterator, BindingArray::const_iterator,
65                                     std::random_access_iterator_tag,
66                                     const IdentifierInfo *> {
67     Iterator(BindingArray::const_iterator It) : iterator_adaptor_base(It) {}
68     const IdentifierInfo *operator*() const {
69       return (*this->I)->getIdentifier();
70     }
71   };
72   Iterator begin() const { return Iterator(Bindings.begin()); }
73   Iterator end() const { return Iterator(Bindings.end()); }
74 };
75 }
76 
77 namespace llvm {
78 template<typename T> bool isDenseMapKeyEmpty(T V) {
79   return llvm::DenseMapInfo<T>::isEqual(
80       V, llvm::DenseMapInfo<T>::getEmptyKey());
81 }
82 template<typename T> bool isDenseMapKeyTombstone(T V) {
83   return llvm::DenseMapInfo<T>::isEqual(
84       V, llvm::DenseMapInfo<T>::getTombstoneKey());
85 }
86 
87 template<typename T>
88 Optional<bool> areDenseMapKeysEqualSpecialValues(T LHS, T RHS) {
89   bool LHSEmpty = isDenseMapKeyEmpty(LHS);
90   bool RHSEmpty = isDenseMapKeyEmpty(RHS);
91   if (LHSEmpty || RHSEmpty)
92     return LHSEmpty && RHSEmpty;
93 
94   bool LHSTombstone = isDenseMapKeyTombstone(LHS);
95   bool RHSTombstone = isDenseMapKeyTombstone(RHS);
96   if (LHSTombstone || RHSTombstone)
97     return LHSTombstone && RHSTombstone;
98 
99   return None;
100 }
101 
102 template<>
103 struct DenseMapInfo<DecompositionDeclName> {
104   using ArrayInfo = llvm::DenseMapInfo<ArrayRef<const BindingDecl*>>;
105   static DecompositionDeclName getEmptyKey() {
106     return {ArrayInfo::getEmptyKey()};
107   }
108   static DecompositionDeclName getTombstoneKey() {
109     return {ArrayInfo::getTombstoneKey()};
110   }
111   static unsigned getHashValue(DecompositionDeclName Key) {
112     assert(!isEqual(Key, getEmptyKey()) && !isEqual(Key, getTombstoneKey()));
113     return llvm::hash_combine_range(Key.begin(), Key.end());
114   }
115   static bool isEqual(DecompositionDeclName LHS, DecompositionDeclName RHS) {
116     if (Optional<bool> Result = areDenseMapKeysEqualSpecialValues(
117             LHS.Bindings, RHS.Bindings))
118       return *Result;
119 
120     return LHS.Bindings.size() == RHS.Bindings.size() &&
121            std::equal(LHS.begin(), LHS.end(), RHS.begin());
122   }
123 };
124 }
125 
126 namespace {
127 
128 /// Keeps track of the mangled names of lambda expressions and block
129 /// literals within a particular context.
130 class ItaniumNumberingContext : public MangleNumberingContext {
131   ItaniumMangleContext *Mangler;
132   llvm::StringMap<unsigned> LambdaManglingNumbers;
133   unsigned BlockManglingNumber = 0;
134   llvm::DenseMap<const IdentifierInfo *, unsigned> VarManglingNumbers;
135   llvm::DenseMap<const IdentifierInfo *, unsigned> TagManglingNumbers;
136   llvm::DenseMap<DecompositionDeclName, unsigned>
137       DecompsitionDeclManglingNumbers;
138 
139 public:
140   ItaniumNumberingContext(ItaniumMangleContext *Mangler) : Mangler(Mangler) {}
141 
142   unsigned getManglingNumber(const CXXMethodDecl *CallOperator) override {
143     const CXXRecordDecl *Lambda = CallOperator->getParent();
144     assert(Lambda->isLambda());
145 
146     // Computation of the <lambda-sig> is non-trivial and subtle. Rather than
147     // duplicating it here, just mangle the <lambda-sig> directly.
148     llvm::SmallString<128> LambdaSig;
149     llvm::raw_svector_ostream Out(LambdaSig);
150     Mangler->mangleLambdaSig(Lambda, Out);
151 
152     return ++LambdaManglingNumbers[LambdaSig];
153   }
154 
155   unsigned getManglingNumber(const BlockDecl *BD) override {
156     return ++BlockManglingNumber;
157   }
158 
159   unsigned getStaticLocalNumber(const VarDecl *VD) override {
160     return 0;
161   }
162 
163   /// Variable decls are numbered by identifier.
164   unsigned getManglingNumber(const VarDecl *VD, unsigned) override {
165     if (auto *DD = dyn_cast<DecompositionDecl>(VD)) {
166       DecompositionDeclName Name{DD->bindings()};
167       return ++DecompsitionDeclManglingNumbers[Name];
168     }
169 
170     const IdentifierInfo *Identifier = VD->getIdentifier();
171     if (!Identifier) {
172       // VarDecl without an identifier represents an anonymous union
173       // declaration.
174       Identifier = findAnonymousUnionVarDeclName(*VD);
175     }
176     return ++VarManglingNumbers[Identifier];
177   }
178 
179   unsigned getManglingNumber(const TagDecl *TD, unsigned) override {
180     return ++TagManglingNumbers[TD->getIdentifier()];
181   }
182 };
183 
184 class ItaniumCXXABI : public CXXABI {
185 private:
186   std::unique_ptr<MangleContext> Mangler;
187 protected:
188   ASTContext &Context;
189 public:
190   ItaniumCXXABI(ASTContext &Ctx)
191       : Mangler(Ctx.createMangleContext()), Context(Ctx) {}
192 
193   MemberPointerInfo
194   getMemberPointerInfo(const MemberPointerType *MPT) const override {
195     const TargetInfo &Target = Context.getTargetInfo();
196     TargetInfo::IntType PtrDiff = Target.getPtrDiffType(0);
197     MemberPointerInfo MPI;
198     MPI.Width = Target.getTypeWidth(PtrDiff);
199     MPI.Align = Target.getTypeAlign(PtrDiff);
200     MPI.HasPadding = false;
201     if (MPT->isMemberFunctionPointer())
202       MPI.Width *= 2;
203     return MPI;
204   }
205 
206   CallingConv getDefaultMethodCallConv(bool isVariadic) const override {
207     const llvm::Triple &T = Context.getTargetInfo().getTriple();
208     if (!isVariadic && T.isWindowsGNUEnvironment() &&
209         T.getArch() == llvm::Triple::x86)
210       return CC_X86ThisCall;
211     return Context.getTargetInfo().getDefaultCallingConv();
212   }
213 
214   // We cheat and just check that the class has a vtable pointer, and that it's
215   // only big enough to have a vtable pointer and nothing more (or less).
216   bool isNearlyEmpty(const CXXRecordDecl *RD) const override {
217 
218     // Check that the class has a vtable pointer.
219     if (!RD->isDynamicClass())
220       return false;
221 
222     const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
223     CharUnits PointerSize =
224       Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
225     return Layout.getNonVirtualSize() == PointerSize;
226   }
227 
228   const CXXConstructorDecl *
229   getCopyConstructorForExceptionObject(CXXRecordDecl *RD) override {
230     return nullptr;
231   }
232 
233   void addCopyConstructorForExceptionObject(CXXRecordDecl *RD,
234                                             CXXConstructorDecl *CD) override {}
235 
236   void addTypedefNameForUnnamedTagDecl(TagDecl *TD,
237                                        TypedefNameDecl *DD) override {}
238 
239   TypedefNameDecl *getTypedefNameForUnnamedTagDecl(const TagDecl *TD) override {
240     return nullptr;
241   }
242 
243   void addDeclaratorForUnnamedTagDecl(TagDecl *TD,
244                                       DeclaratorDecl *DD) override {}
245 
246   DeclaratorDecl *getDeclaratorForUnnamedTagDecl(const TagDecl *TD) override {
247     return nullptr;
248   }
249 
250   std::unique_ptr<MangleNumberingContext>
251   createMangleNumberingContext() const override {
252     return std::make_unique<ItaniumNumberingContext>(
253         cast<ItaniumMangleContext>(Mangler.get()));
254   }
255 };
256 }
257 
258 CXXABI *clang::CreateItaniumCXXABI(ASTContext &Ctx) {
259   return new ItaniumCXXABI(Ctx);
260 }
261