ItaniumCXXABI.cpp revision 360784 
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
30using namespace clang;
31
32namespace {
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.
44static 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.
56struct 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
77namespace llvm {
78template<typename T> bool isDenseMapKeyEmpty(T V) {
79  return llvm::DenseMapInfo<T>::isEqual(
80      V, llvm::DenseMapInfo<T>::getEmptyKey());
81}
82template<typename T> bool isDenseMapKeyTombstone(T V) {
83  return llvm::DenseMapInfo<T>::isEqual(
84      V, llvm::DenseMapInfo<T>::getTombstoneKey());
85}
86
87template<typename T>
88Optional<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
102template<>
103struct 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
126namespace {
127
128/// Keeps track of the mangled names of lambda expressions and block
129/// literals within a particular context.
130class 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
139public:
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
184class ItaniumCXXABI : public CXXABI {
185private:
186  std::unique_ptr<MangleContext> Mangler;
187protected:
188  ASTContext &Context;
189public:
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
258CXXABI *clang::CreateItaniumCXXABI(ASTContext &Ctx) {
259  return new ItaniumCXXABI(Ctx);
260}
261