clang  3.7.0
CodeGenTBAA.cpp
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1 //===--- CodeGenTypes.cpp - TBAA information for LLVM CodeGen -------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This is the code that manages TBAA information and defines the TBAA policy
11 // for the optimizer to use. Relevant standards text includes:
12 //
13 // C99 6.5p7
14 // C++ [basic.lval] (p10 in n3126, p15 in some earlier versions)
15 //
16 //===----------------------------------------------------------------------===//
17 
18 #include "CodeGenTBAA.h"
19 #include "clang/AST/ASTContext.h"
20 #include "clang/AST/Attr.h"
21 #include "clang/AST/Mangle.h"
22 #include "clang/AST/RecordLayout.h"
24 #include "llvm/ADT/SmallSet.h"
25 #include "llvm/IR/Constants.h"
26 #include "llvm/IR/LLVMContext.h"
27 #include "llvm/IR/Metadata.h"
28 #include "llvm/IR/Type.h"
29 using namespace clang;
30 using namespace CodeGen;
31 
32 CodeGenTBAA::CodeGenTBAA(ASTContext &Ctx, llvm::LLVMContext& VMContext,
33  const CodeGenOptions &CGO,
34  const LangOptions &Features, MangleContext &MContext)
35  : Context(Ctx), CodeGenOpts(CGO), Features(Features), MContext(MContext),
36  MDHelper(VMContext), Root(nullptr), Char(nullptr) {
37 }
38 
40 }
41 
42 llvm::MDNode *CodeGenTBAA::getRoot() {
43  // Define the root of the tree. This identifies the tree, so that
44  // if our LLVM IR is linked with LLVM IR from a different front-end
45  // (or a different version of this front-end), their TBAA trees will
46  // remain distinct, and the optimizer will treat them conservatively.
47  if (!Root)
48  Root = MDHelper.createTBAARoot("Simple C/C++ TBAA");
49 
50  return Root;
51 }
52 
53 // For both scalar TBAA and struct-path aware TBAA, the scalar type has the
54 // same format: name, parent node, and offset.
55 llvm::MDNode *CodeGenTBAA::createTBAAScalarType(StringRef Name,
56  llvm::MDNode *Parent) {
57  return MDHelper.createTBAAScalarTypeNode(Name, Parent);
58 }
59 
60 llvm::MDNode *CodeGenTBAA::getChar() {
61  // Define the root of the tree for user-accessible memory. C and C++
62  // give special powers to char and certain similar types. However,
63  // these special powers only cover user-accessible memory, and doesn't
64  // include things like vtables.
65  if (!Char)
66  Char = createTBAAScalarType("omnipotent char", getRoot());
67 
68  return Char;
69 }
70 
71 static bool TypeHasMayAlias(QualType QTy) {
72  // Tagged types have declarations, and therefore may have attributes.
73  if (const TagType *TTy = dyn_cast<TagType>(QTy))
74  return TTy->getDecl()->hasAttr<MayAliasAttr>();
75 
76  // Typedef types have declarations, and therefore may have attributes.
77  if (const TypedefType *TTy = dyn_cast<TypedefType>(QTy)) {
78  if (TTy->getDecl()->hasAttr<MayAliasAttr>())
79  return true;
80  // Also, their underlying types may have relevant attributes.
81  return TypeHasMayAlias(TTy->desugar());
82  }
83 
84  return false;
85 }
86 
87 llvm::MDNode *
89  // At -O0 or relaxed aliasing, TBAA is not emitted for regular types.
90  if (CodeGenOpts.OptimizationLevel == 0 || CodeGenOpts.RelaxedAliasing)
91  return nullptr;
92 
93  // If the type has the may_alias attribute (even on a typedef), it is
94  // effectively in the general char alias class.
95  if (TypeHasMayAlias(QTy))
96  return getChar();
97 
98  const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
99 
100  if (llvm::MDNode *N = MetadataCache[Ty])
101  return N;
102 
103  // Handle builtin types.
104  if (const BuiltinType *BTy = dyn_cast<BuiltinType>(Ty)) {
105  switch (BTy->getKind()) {
106  // Character types are special and can alias anything.
107  // In C++, this technically only includes "char" and "unsigned char",
108  // and not "signed char". In C, it includes all three. For now,
109  // the risk of exploiting this detail in C++ seems likely to outweigh
110  // the benefit.
111  case BuiltinType::Char_U:
112  case BuiltinType::Char_S:
113  case BuiltinType::UChar:
114  case BuiltinType::SChar:
115  return getChar();
116 
117  // Unsigned types can alias their corresponding signed types.
118  case BuiltinType::UShort:
119  return getTBAAInfo(Context.ShortTy);
120  case BuiltinType::UInt:
121  return getTBAAInfo(Context.IntTy);
122  case BuiltinType::ULong:
123  return getTBAAInfo(Context.LongTy);
124  case BuiltinType::ULongLong:
125  return getTBAAInfo(Context.LongLongTy);
126  case BuiltinType::UInt128:
127  return getTBAAInfo(Context.Int128Ty);
128 
129  // Treat all other builtin types as distinct types. This includes
130  // treating wchar_t, char16_t, and char32_t as distinct from their
131  // "underlying types".
132  default:
133  return MetadataCache[Ty] =
134  createTBAAScalarType(BTy->getName(Features), getChar());
135  }
136  }
137 
138  // Handle pointers.
139  // TODO: Implement C++'s type "similarity" and consider dis-"similar"
140  // pointers distinct.
141  if (Ty->isPointerType())
142  return MetadataCache[Ty] = createTBAAScalarType("any pointer",
143  getChar());
144 
145  // Enum types are distinct types. In C++ they have "underlying types",
146  // however they aren't related for TBAA.
147  if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) {
148  // In C++ mode, types have linkage, so we can rely on the ODR and
149  // on their mangled names, if they're external.
150  // TODO: Is there a way to get a program-wide unique name for a
151  // decl with local linkage or no linkage?
152  if (!Features.CPlusPlus || !ETy->getDecl()->isExternallyVisible())
153  return MetadataCache[Ty] = getChar();
154 
155  SmallString<256> OutName;
156  llvm::raw_svector_ostream Out(OutName);
157  MContext.mangleTypeName(QualType(ETy, 0), Out);
158  Out.flush();
159  return MetadataCache[Ty] = createTBAAScalarType(OutName, getChar());
160  }
161 
162  // For now, handle any other kind of type conservatively.
163  return MetadataCache[Ty] = getChar();
164 }
165 
167  return createTBAAScalarType("vtable pointer", getRoot());
168 }
169 
170 bool
171 CodeGenTBAA::CollectFields(uint64_t BaseOffset,
172  QualType QTy,
174  Fields,
175  bool MayAlias) {
176  /* Things not handled yet include: C++ base classes, bitfields, */
177 
178  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
179  const RecordDecl *RD = TTy->getDecl()->getDefinition();
180  if (RD->hasFlexibleArrayMember())
181  return false;
182 
183  // TODO: Handle C++ base classes.
184  if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD))
185  if (Decl->bases_begin() != Decl->bases_end())
186  return false;
187 
188  const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
189 
190  unsigned idx = 0;
192  e = RD->field_end(); i != e; ++i, ++idx) {
193  uint64_t Offset = BaseOffset +
194  Layout.getFieldOffset(idx) / Context.getCharWidth();
195  QualType FieldQTy = i->getType();
196  if (!CollectFields(Offset, FieldQTy, Fields,
197  MayAlias || TypeHasMayAlias(FieldQTy)))
198  return false;
199  }
200  return true;
201  }
202 
203  /* Otherwise, treat whatever it is as a field. */
204  uint64_t Offset = BaseOffset;
205  uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity();
206  llvm::MDNode *TBAAInfo = MayAlias ? getChar() : getTBAAInfo(QTy);
207  llvm::MDNode *TBAATag = getTBAAScalarTagInfo(TBAAInfo);
208  Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag));
209  return true;
210 }
211 
212 llvm::MDNode *
214  const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
215 
216  if (llvm::MDNode *N = StructMetadataCache[Ty])
217  return N;
218 
220  if (CollectFields(0, QTy, Fields, TypeHasMayAlias(QTy)))
221  return MDHelper.createTBAAStructNode(Fields);
222 
223  // For now, handle any other kind of type conservatively.
224  return StructMetadataCache[Ty] = nullptr;
225 }
226 
227 /// Check if the given type can be handled by path-aware TBAA.
228 static bool isTBAAPathStruct(QualType QTy) {
229  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
230  const RecordDecl *RD = TTy->getDecl()->getDefinition();
231  if (RD->hasFlexibleArrayMember())
232  return false;
233  // RD can be struct, union, class, interface or enum.
234  // For now, we only handle struct and class.
235  if (RD->isStruct() || RD->isClass())
236  return true;
237  }
238  return false;
239 }
240 
241 llvm::MDNode *
243  const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
244  assert(isTBAAPathStruct(QTy));
245 
246  if (llvm::MDNode *N = StructTypeMetadataCache[Ty])
247  return N;
248 
249  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
250  const RecordDecl *RD = TTy->getDecl()->getDefinition();
251 
252  const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
254  unsigned idx = 0;
256  e = RD->field_end(); i != e; ++i, ++idx) {
257  QualType FieldQTy = i->getType();
258  llvm::MDNode *FieldNode;
259  if (isTBAAPathStruct(FieldQTy))
260  FieldNode = getTBAAStructTypeInfo(FieldQTy);
261  else
262  FieldNode = getTBAAInfo(FieldQTy);
263  if (!FieldNode)
264  return StructTypeMetadataCache[Ty] = nullptr;
265  Fields.push_back(std::make_pair(
266  FieldNode, Layout.getFieldOffset(idx) / Context.getCharWidth()));
267  }
268 
269  SmallString<256> OutName;
270  if (Features.CPlusPlus) {
271  // Don't use the mangler for C code.
272  llvm::raw_svector_ostream Out(OutName);
273  MContext.mangleTypeName(QualType(Ty, 0), Out);
274  Out.flush();
275  } else {
276  OutName = RD->getName();
277  }
278  // Create the struct type node with a vector of pairs (offset, type).
279  return StructTypeMetadataCache[Ty] =
280  MDHelper.createTBAAStructTypeNode(OutName, Fields);
281  }
282 
283  return StructMetadataCache[Ty] = nullptr;
284 }
285 
286 /// Return a TBAA tag node for both scalar TBAA and struct-path aware TBAA.
287 llvm::MDNode *
288 CodeGenTBAA::getTBAAStructTagInfo(QualType BaseQTy, llvm::MDNode *AccessNode,
289  uint64_t Offset) {
290  if (!AccessNode)
291  return nullptr;
292 
293  if (!CodeGenOpts.StructPathTBAA)
294  return getTBAAScalarTagInfo(AccessNode);
295 
296  const Type *BTy = Context.getCanonicalType(BaseQTy).getTypePtr();
297  TBAAPathTag PathTag = TBAAPathTag(BTy, AccessNode, Offset);
298  if (llvm::MDNode *N = StructTagMetadataCache[PathTag])
299  return N;
300 
301  llvm::MDNode *BNode = nullptr;
302  if (isTBAAPathStruct(BaseQTy))
303  BNode = getTBAAStructTypeInfo(BaseQTy);
304  if (!BNode)
305  return StructTagMetadataCache[PathTag] =
306  MDHelper.createTBAAStructTagNode(AccessNode, AccessNode, 0);
307 
308  return StructTagMetadataCache[PathTag] =
309  MDHelper.createTBAAStructTagNode(BNode, AccessNode, Offset);
310 }
311 
312 llvm::MDNode *
313 CodeGenTBAA::getTBAAScalarTagInfo(llvm::MDNode *AccessNode) {
314  if (!AccessNode)
315  return nullptr;
316  if (llvm::MDNode *N = ScalarTagMetadataCache[AccessNode])
317  return N;
318 
319  return ScalarTagMetadataCache[AccessNode] =
320  MDHelper.createTBAAStructTagNode(AccessNode, AccessNode, 0);
321 }
Defines the clang::ASTContext interface.
CanQualType LongLongTy
Definition: ASTContext.h:825
StringRef getName() const
Definition: Decl.h:168
QuantityType getQuantity() const
getQuantity - Get the raw integer representation of this quantity.
Definition: CharUnits.h:163
bool hasFlexibleArrayMember() const
Definition: Decl.h:3279
CanQualType LongTy
Definition: ASTContext.h:825
field_iterator field_begin() const
Definition: Decl.cpp:3629
CodeGenTBAA(ASTContext &Ctx, llvm::LLVMContext &VMContext, const CodeGenOptions &CGO, const LangOptions &Features, MangleContext &MContext)
Definition: CodeGenTBAA.cpp:32
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:89
bool isClass() const
Definition: Decl.h:2905
llvm::MDNode * getTBAAInfoForVTablePtr()
Keeps track of the various options that can be enabled, which controls the dialect of C or C++ that i...
Definition: LangOptions.h:48
uint32_t Offset
Definition: CacheTokens.cpp:43
const ASTRecordLayout & getASTRecordLayout(const RecordDecl *D) const
Get or compute information about the layout of the specified record (struct/union/class) D...
llvm::MDNode * getTBAAStructTypeInfo(QualType QType)
Get the MDNode in the type DAG for given struct type QType.
uint64_t getFieldOffset(unsigned FieldNo) const
Definition: RecordLayout.h:181
CharUnits getTypeSizeInChars(QualType T) const
Return the size of the specified (complete) type T, in characters.
field_iterator field_end() const
Definition: Decl.h:3352
static bool isTBAAPathStruct(QualType QTy)
Check if the given type can be handled by path-aware TBAA.
ASTContext * Context
llvm::MDNode * getTBAAScalarTagInfo(llvm::MDNode *AccessNode)
Get the scalar tag MDNode for a given scalar type.
bool isStruct() const
Definition: Decl.h:2903
static bool TypeHasMayAlias(QualType QTy)
Definition: CodeGenTBAA.cpp:71
CanQualType ShortTy
Definition: ASTContext.h:825
RecordDecl * getDefinition() const
Definition: Decl.h:3339
CanQualType Int128Ty
Definition: ASTContext.h:825
llvm::MDNode * getTBAAStructInfo(QualType QTy)
llvm::MDNode * getTBAAStructTagInfo(QualType BaseQType, llvm::MDNode *AccessNode, uint64_t Offset)
Return a TBAA tag node for both scalar TBAA and struct-path aware TBAA.
virtual void mangleTypeName(QualType T, raw_ostream &)=0
llvm::MDNode * getTBAAInfo(QualType QTy)
Definition: CodeGenTBAA.cpp:88
CanQualType getCanonicalType(QualType T) const
Return the canonical (structural) type corresponding to the specified potentially non-canonical type ...
Definition: ASTContext.h:1855
const T * getAs() const
Definition: Type.h:5555
uint64_t getCharWidth() const
Return the size of the character type, in bits.
Definition: ASTContext.h:1705
Represents a C++ struct/union/class.
Definition: DeclCXX.h:285
const T * getTypePtr() const
Retrieve the underlying type pointer, which refers to a canonical type.
Definition: CanonicalType.h:70
CanQualType IntTy
Definition: ASTContext.h:825