clang  7.0.0svn
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/Module.h"
29 #include "llvm/IR/Type.h"
30 using namespace clang;
31 using namespace CodeGen;
32 
33 CodeGenTBAA::CodeGenTBAA(ASTContext &Ctx, llvm::Module &M,
34  const CodeGenOptions &CGO,
35  const LangOptions &Features, MangleContext &MContext)
36  : Context(Ctx), Module(M), CodeGenOpts(CGO),
37  Features(Features), MContext(MContext), MDHelper(M.getContext()),
38  Root(nullptr), Char(nullptr)
39 {}
40 
42 }
43 
44 llvm::MDNode *CodeGenTBAA::getRoot() {
45  // Define the root of the tree. This identifies the tree, so that
46  // if our LLVM IR is linked with LLVM IR from a different front-end
47  // (or a different version of this front-end), their TBAA trees will
48  // remain distinct, and the optimizer will treat them conservatively.
49  if (!Root) {
50  if (Features.CPlusPlus)
51  Root = MDHelper.createTBAARoot("Simple C++ TBAA");
52  else
53  Root = MDHelper.createTBAARoot("Simple C/C++ TBAA");
54  }
55 
56  return Root;
57 }
58 
59 llvm::MDNode *CodeGenTBAA::createScalarTypeNode(StringRef Name,
60  llvm::MDNode *Parent,
61  uint64_t Size) {
62  if (CodeGenOpts.NewStructPathTBAA) {
63  llvm::Metadata *Id = MDHelper.createString(Name);
64  return MDHelper.createTBAATypeNode(Parent, Size, Id);
65  }
66  return MDHelper.createTBAAScalarTypeNode(Name, Parent);
67 }
68 
69 llvm::MDNode *CodeGenTBAA::getChar() {
70  // Define the root of the tree for user-accessible memory. C and C++
71  // give special powers to char and certain similar types. However,
72  // these special powers only cover user-accessible memory, and doesn't
73  // include things like vtables.
74  if (!Char)
75  Char = createScalarTypeNode("omnipotent char", getRoot(), /* Size= */ 1);
76 
77  return Char;
78 }
79 
80 static bool TypeHasMayAlias(QualType QTy) {
81  // Tagged types have declarations, and therefore may have attributes.
82  if (const TagType *TTy = dyn_cast<TagType>(QTy))
83  return TTy->getDecl()->hasAttr<MayAliasAttr>();
84 
85  // Typedef types have declarations, and therefore may have attributes.
86  if (const TypedefType *TTy = dyn_cast<TypedefType>(QTy)) {
87  if (TTy->getDecl()->hasAttr<MayAliasAttr>())
88  return true;
89  // Also, their underlying types may have relevant attributes.
90  return TypeHasMayAlias(TTy->desugar());
91  }
92 
93  return false;
94 }
95 
96 /// Check if the given type is a valid base type to be used in access tags.
97 static bool isValidBaseType(QualType QTy) {
98  if (QTy->isReferenceType())
99  return false;
100  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
101  const RecordDecl *RD = TTy->getDecl()->getDefinition();
102  // Incomplete types are not valid base access types.
103  if (!RD)
104  return false;
105  if (RD->hasFlexibleArrayMember())
106  return false;
107  // RD can be struct, union, class, interface or enum.
108  // For now, we only handle struct and class.
109  if (RD->isStruct() || RD->isClass())
110  return true;
111  }
112  return false;
113 }
114 
115 llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) {
116  uint64_t Size = Context.getTypeSizeInChars(Ty).getQuantity();
117 
118  // Handle builtin types.
119  if (const BuiltinType *BTy = dyn_cast<BuiltinType>(Ty)) {
120  switch (BTy->getKind()) {
121  // Character types are special and can alias anything.
122  // In C++, this technically only includes "char" and "unsigned char",
123  // and not "signed char". In C, it includes all three. For now,
124  // the risk of exploiting this detail in C++ seems likely to outweigh
125  // the benefit.
126  case BuiltinType::Char_U:
127  case BuiltinType::Char_S:
128  case BuiltinType::UChar:
129  case BuiltinType::SChar:
130  return getChar();
131 
132  // Unsigned types can alias their corresponding signed types.
133  case BuiltinType::UShort:
134  return getTypeInfo(Context.ShortTy);
135  case BuiltinType::UInt:
136  return getTypeInfo(Context.IntTy);
137  case BuiltinType::ULong:
138  return getTypeInfo(Context.LongTy);
139  case BuiltinType::ULongLong:
140  return getTypeInfo(Context.LongLongTy);
141  case BuiltinType::UInt128:
142  return getTypeInfo(Context.Int128Ty);
143 
144  // Treat all other builtin types as distinct types. This includes
145  // treating wchar_t, char16_t, and char32_t as distinct from their
146  // "underlying types".
147  default:
148  return createScalarTypeNode(BTy->getName(Features), getChar(), Size);
149  }
150  }
151 
152  // C++1z [basic.lval]p10: "If a program attempts to access the stored value of
153  // an object through a glvalue of other than one of the following types the
154  // behavior is undefined: [...] a char, unsigned char, or std::byte type."
155  if (Ty->isStdByteType())
156  return getChar();
157 
158  // Handle pointers and references.
159  // TODO: Implement C++'s type "similarity" and consider dis-"similar"
160  // pointers distinct.
161  if (Ty->isPointerType() || Ty->isReferenceType())
162  return createScalarTypeNode("any pointer", getChar(), Size);
163 
164  // Accesses to arrays are accesses to objects of their element types.
165  if (CodeGenOpts.NewStructPathTBAA && Ty->isArrayType())
166  return getTypeInfo(cast<ArrayType>(Ty)->getElementType());
167 
168  // Enum types are distinct types. In C++ they have "underlying types",
169  // however they aren't related for TBAA.
170  if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) {
171  // In C++ mode, types have linkage, so we can rely on the ODR and
172  // on their mangled names, if they're external.
173  // TODO: Is there a way to get a program-wide unique name for a
174  // decl with local linkage or no linkage?
175  if (!Features.CPlusPlus || !ETy->getDecl()->isExternallyVisible())
176  return getChar();
177 
178  SmallString<256> OutName;
179  llvm::raw_svector_ostream Out(OutName);
180  MContext.mangleTypeName(QualType(ETy, 0), Out);
181  return createScalarTypeNode(OutName, getChar(), Size);
182  }
183 
184  // For now, handle any other kind of type conservatively.
185  return getChar();
186 }
187 
188 llvm::MDNode *CodeGenTBAA::getTypeInfo(QualType QTy) {
189  // At -O0 or relaxed aliasing, TBAA is not emitted for regular types.
190  if (CodeGenOpts.OptimizationLevel == 0 || CodeGenOpts.RelaxedAliasing)
191  return nullptr;
192 
193  // If the type has the may_alias attribute (even on a typedef), it is
194  // effectively in the general char alias class.
195  if (TypeHasMayAlias(QTy))
196  return getChar();
197 
198  // We need this function to not fall back to returning the "omnipotent char"
199  // type node for aggregate and union types. Otherwise, any dereference of an
200  // aggregate will result into the may-alias access descriptor, meaning all
201  // subsequent accesses to direct and indirect members of that aggregate will
202  // be considered may-alias too.
203  // TODO: Combine getTypeInfo() and getBaseTypeInfo() into a single function.
204  if (isValidBaseType(QTy))
205  return getBaseTypeInfo(QTy);
206 
207  const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
208  if (llvm::MDNode *N = MetadataCache[Ty])
209  return N;
210 
211  // Note that the following helper call is allowed to add new nodes to the
212  // cache, which invalidates all its previously obtained iterators. So we
213  // first generate the node for the type and then add that node to the cache.
214  llvm::MDNode *TypeNode = getTypeInfoHelper(Ty);
215  return MetadataCache[Ty] = TypeNode;
216 }
217 
219  // Pointee values may have incomplete types, but they shall never be
220  // dereferenced.
221  if (AccessType->isIncompleteType())
223 
224  if (TypeHasMayAlias(AccessType))
226 
227  uint64_t Size = Context.getTypeSizeInChars(AccessType).getQuantity();
228  return TBAAAccessInfo(getTypeInfo(AccessType), Size);
229 }
230 
232  llvm::DataLayout DL(&Module);
233  unsigned Size = DL.getPointerTypeSize(VTablePtrType);
234  return TBAAAccessInfo(createScalarTypeNode("vtable pointer", getRoot(), Size),
235  Size);
236 }
237 
238 bool
239 CodeGenTBAA::CollectFields(uint64_t BaseOffset,
240  QualType QTy,
242  Fields,
243  bool MayAlias) {
244  /* Things not handled yet include: C++ base classes, bitfields, */
245 
246  if (const RecordType *TTy = QTy->getAs<RecordType>()) {
247  const RecordDecl *RD = TTy->getDecl()->getDefinition();
248  if (RD->hasFlexibleArrayMember())
249  return false;
250 
251  // TODO: Handle C++ base classes.
252  if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD))
253  if (Decl->bases_begin() != Decl->bases_end())
254  return false;
255 
256  const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
257 
258  unsigned idx = 0;
260  e = RD->field_end(); i != e; ++i, ++idx) {
261  uint64_t Offset = BaseOffset +
262  Layout.getFieldOffset(idx) / Context.getCharWidth();
263  QualType FieldQTy = i->getType();
264  if (!CollectFields(Offset, FieldQTy, Fields,
265  MayAlias || TypeHasMayAlias(FieldQTy)))
266  return false;
267  }
268  return true;
269  }
270 
271  /* Otherwise, treat whatever it is as a field. */
272  uint64_t Offset = BaseOffset;
273  uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity();
274  llvm::MDNode *TBAAType = MayAlias ? getChar() : getTypeInfo(QTy);
275  llvm::MDNode *TBAATag = getAccessTagInfo(TBAAAccessInfo(TBAAType, Size));
276  Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag));
277  return true;
278 }
279 
280 llvm::MDNode *
282  const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
283 
284  if (llvm::MDNode *N = StructMetadataCache[Ty])
285  return N;
286 
288  if (CollectFields(0, QTy, Fields, TypeHasMayAlias(QTy)))
289  return MDHelper.createTBAAStructNode(Fields);
290 
291  // For now, handle any other kind of type conservatively.
292  return StructMetadataCache[Ty] = nullptr;
293 }
294 
295 llvm::MDNode *CodeGenTBAA::getBaseTypeInfoHelper(const Type *Ty) {
296  if (auto *TTy = dyn_cast<RecordType>(Ty)) {
297  const RecordDecl *RD = TTy->getDecl()->getDefinition();
298  const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
300  for (FieldDecl *Field : RD->fields()) {
301  QualType FieldQTy = Field->getType();
302  llvm::MDNode *TypeNode = isValidBaseType(FieldQTy) ?
303  getBaseTypeInfo(FieldQTy) : getTypeInfo(FieldQTy);
304  if (!TypeNode)
305  return BaseTypeMetadataCache[Ty] = nullptr;
306 
307  uint64_t BitOffset = Layout.getFieldOffset(Field->getFieldIndex());
308  uint64_t Offset = Context.toCharUnitsFromBits(BitOffset).getQuantity();
309  uint64_t Size = Context.getTypeSizeInChars(FieldQTy).getQuantity();
310  Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size,
311  TypeNode));
312  }
313 
314  SmallString<256> OutName;
315  if (Features.CPlusPlus) {
316  // Don't use the mangler for C code.
317  llvm::raw_svector_ostream Out(OutName);
318  MContext.mangleTypeName(QualType(Ty, 0), Out);
319  } else {
320  OutName = RD->getName();
321  }
322 
323  if (CodeGenOpts.NewStructPathTBAA) {
324  llvm::MDNode *Parent = getChar();
325  uint64_t Size = Context.getTypeSizeInChars(Ty).getQuantity();
326  llvm::Metadata *Id = MDHelper.createString(OutName);
327  return MDHelper.createTBAATypeNode(Parent, Size, Id, Fields);
328  }
329 
330  // Create the struct type node with a vector of pairs (offset, type).
332  for (const auto &Field : Fields)
333  OffsetsAndTypes.push_back(std::make_pair(Field.Type, Field.Offset));
334  return MDHelper.createTBAAStructTypeNode(OutName, OffsetsAndTypes);
335  }
336 
337  return nullptr;
338 }
339 
341  if (!isValidBaseType(QTy))
342  return nullptr;
343 
344  const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
345  if (llvm::MDNode *N = BaseTypeMetadataCache[Ty])
346  return N;
347 
348  // Note that the following helper call is allowed to add new nodes to the
349  // cache, which invalidates all its previously obtained iterators. So we
350  // first generate the node for the type and then add that node to the cache.
351  llvm::MDNode *TypeNode = getBaseTypeInfoHelper(Ty);
352  return BaseTypeMetadataCache[Ty] = TypeNode;
353 }
354 
356  assert(!Info.isIncomplete() && "Access to an object of an incomplete type!");
357 
358  if (Info.isMayAlias())
359  Info = TBAAAccessInfo(getChar(), Info.Size);
360 
361  if (!Info.AccessType)
362  return nullptr;
363 
364  if (!CodeGenOpts.StructPathTBAA)
365  Info = TBAAAccessInfo(Info.AccessType, Info.Size);
366 
367  llvm::MDNode *&N = AccessTagMetadataCache[Info];
368  if (N)
369  return N;
370 
371  if (!Info.BaseType) {
372  Info.BaseType = Info.AccessType;
373  assert(!Info.Offset && "Nonzero offset for an access with no base type!");
374  }
375  if (CodeGenOpts.NewStructPathTBAA) {
376  return N = MDHelper.createTBAAAccessTag(Info.BaseType, Info.AccessType,
377  Info.Offset, Info.Size);
378  }
379  return N = MDHelper.createTBAAStructTagNode(Info.BaseType, Info.AccessType,
380  Info.Offset);
381 }
382 
385  if (SourceInfo.isMayAlias() || TargetInfo.isMayAlias())
387  return TargetInfo;
388 }
389 
392  TBAAAccessInfo InfoB) {
393  if (InfoA == InfoB)
394  return InfoA;
395 
396  if (!InfoA || !InfoB)
397  return TBAAAccessInfo();
398 
399  if (InfoA.isMayAlias() || InfoB.isMayAlias())
401 
402  // TODO: Implement the rest of the logic here. For example, two accesses
403  // with same final access types result in an access to an object of that final
404  // access type regardless of their base types.
406 }
407 
410  TBAAAccessInfo SrcInfo) {
411  if (DestInfo == SrcInfo)
412  return DestInfo;
413 
414  if (!DestInfo || !SrcInfo)
415  return TBAAAccessInfo();
416 
417  if (DestInfo.isMayAlias() || SrcInfo.isMayAlias())
419 
420  // TODO: Implement the rest of the logic here. For example, two accesses
421  // with same final access types result in an access to an object of that final
422  // access type regardless of their base types.
424 }
Defines the clang::ASTContext interface.
bool isStruct() const
Definition: Decl.h:3222
CanQualType LongLongTy
Definition: ASTContext.h:1006
A (possibly-)qualified type.
Definition: Type.h:654
bool isArrayType() const
Definition: Type.h:6097
const ASTRecordLayout & getASTRecordLayout(const RecordDecl *D) const
Get or compute information about the layout of the specified record (struct/union/class) D...
Decl - This represents one declaration (or definition), e.g.
Definition: DeclBase.h:86
llvm::MDNode * AccessType
AccessType - The final access type.
Definition: CodeGenTBAA.h:106
The base class of the type hierarchy.
Definition: Type.h:1420
CanQualType LongTy
Definition: ASTContext.h:1006
TBAAAccessInfo getAccessInfo(QualType AccessType)
getAccessInfo - Get TBAA information that describes an access to an object of the given type...
CodeGenTBAA(ASTContext &Ctx, llvm::Module &M, const CodeGenOptions &CGO, const LangOptions &Features, MangleContext &MContext)
Definition: CodeGenTBAA.cpp:33
const T * getAs() const
Member-template getAs<specific type>&#39;.
Definition: Type.h:6455
bool isClass() const
Definition: Decl.h:3224
Represents a struct/union/class.
Definition: Decl.h:3548
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:150
bool isStdByteType() const
Definition: Type.cpp:2408
RecordDecl * getDefinition() const
Returns the RecordDecl that actually defines this struct/union/class.
Definition: Decl.h:3754
field_range fields() const
Definition: Decl.h:3764
Represents a member of a struct/union/class.
Definition: Decl.h:2521
bool isReferenceType() const
Definition: Type.h:6060
Keeps track of the various options that can be enabled, which controls the dialect of C or C++ that i...
Definition: LangOptions.h:50
Describes a module or submodule.
Definition: Module.h:65
static bool isValidBaseType(QualType QTy)
Check if the given type is a valid base type to be used in access tags.
Definition: CodeGenTBAA.cpp:97
uint32_t Offset
Definition: CacheTokens.cpp:43
TBAAAccessInfo getVTablePtrAccessInfo(llvm::Type *VTablePtrType)
getVTablePtrAccessInfo - Get the TBAA information that describes an access to a virtual table pointer...
field_iterator field_begin() const
Definition: Decl.cpp:4027
static TBAAAccessInfo getIncompleteInfo()
Definition: CodeGenTBAA.h:72
const T * getTypePtr() const
Retrieve the underlying type pointer, which refers to a canonical type.
Definition: CanonicalType.h:84
NodeId Parent
Definition: ASTDiff.cpp:192
QuantityType getQuantity() const
getQuantity - Get the raw integer representation of this quantity.
Definition: CharUnits.h:179
ASTRecordLayout - This class contains layout information for one RecordDecl, which is a struct/union/...
Definition: RecordLayout.h:39
Exposes information about the current target.
Definition: TargetInfo.h:54
int Id
Definition: ASTDiff.cpp:191
TBAAAccessInfo mergeTBAAInfoForMemoryTransfer(TBAAAccessInfo DestInfo, TBAAAccessInfo SrcInfo)
mergeTBAAInfoForMemoryTransfer - Get merged TBAA information for the purpose of memory transfer calls...
static bool TypeHasMayAlias(QualType QTy)
Definition: CodeGenTBAA.cpp:80
field_iterator field_end() const
Definition: Decl.h:3767
CanQualType ShortTy
Definition: ASTContext.h:1006
llvm::MDNode * getBaseTypeInfo(QualType QTy)
getBaseTypeInfo - Get metadata that describes the given base access type.
TBAAAccessInfo mergeTBAAInfoForCast(TBAAAccessInfo SourceInfo, TBAAAccessInfo TargetInfo)
mergeTBAAInfoForCast - Get merged TBAA information for the purpose of type casts. ...
The l-value was considered opaque, so the alignment was determined from a type.
uint64_t getFieldOffset(unsigned FieldNo) const
getFieldOffset - Get the offset of the given field index, in bits.
Definition: RecordLayout.h:181
TBAAAccessInfo mergeTBAAInfoForConditionalOperator(TBAAAccessInfo InfoA, TBAAAccessInfo InfoB)
mergeTBAAInfoForConditionalOperator - Get merged TBAA information for the purpose of conditional oper...
A helper class that allows the use of isa/cast/dyncast to detect TagType objects of enums...
Definition: Type.h:4097
CanQualType Int128Ty
Definition: ASTContext.h:1006
llvm::MDNode * BaseType
BaseType - The base/leading access type.
Definition: CodeGenTBAA.h:102
MangleContext - Context for tracking state which persists across multiple calls to the C++ name mangl...
Definition: Mangle.h:43
uint64_t Size
Size - The size of access, in bytes.
Definition: CodeGenTBAA.h:113
llvm::MDNode * getTBAAStructInfo(QualType QTy)
getTBAAStructInfo - Get the TBAAStruct MDNode to be used for a memcpy of the given type...
bool hasFlexibleArrayMember() const
Definition: Decl.h:3639
virtual void mangleTypeName(QualType T, raw_ostream &)=0
Generates a unique string for an externally visible type for use with TBAA or type uniquing...
llvm::MDNode * getTypeInfo(QualType QTy)
getTypeInfo - Get metadata used to describe accesses to objects of the given type.
Dataflow Directional Tag Classes.
specific_decl_iterator - Iterates over a subrange of declarations stored in a DeclContext, providing only those that are of type SpecificDecl (or a class derived from it).
Definition: DeclBase.h:1606
A helper class that allows the use of isa/cast/dyncast to detect TagType objects of structs/unions/cl...
Definition: Type.h:4071
uint64_t getCharWidth() const
Return the size of the character type, in bits.
Definition: ASTContext.h:2041
CodeGenOptions - Track various options which control how the code is optimized and passed to the back...
bool isIncompleteType(NamedDecl **Def=nullptr) const
Types are partitioned into 3 broad categories (C99 6.2.5p1): object types, function types...
Definition: Type.cpp:1993
CanQualType getCanonicalType(QualType T) const
Return the canonical (structural) type corresponding to the specified potentially non-canonical type ...
Definition: ASTContext.h:2204
CharUnits toCharUnitsFromBits(int64_t BitSize) const
Convert a size in bits to a size in characters.
Represents a C++ struct/union/class.
Definition: DeclCXX.h:300
This class is used for builtin types like &#39;int&#39;.
Definition: Type.h:2234
llvm::MDNode * getAccessTagInfo(TBAAAccessInfo Info)
getAccessTagInfo - Get TBAA tag for a given memory access.
StringRef getName() const
Get the name of identifier for this declaration as a StringRef.
Definition: Decl.h:275
CanQualType IntTy
Definition: ASTContext.h:1006
bool isPointerType() const
Definition: Type.h:6048
CharUnits getTypeSizeInChars(QualType T) const
Return the size of the specified (complete) type T, in characters.
uint64_t Offset
Offset - The byte offset of the final access within the base one.
Definition: CodeGenTBAA.h:110
static TBAAAccessInfo getMayAliasInfo()
Definition: CodeGenTBAA.h:64