1 //===--- CodeGenTypes.cpp - TBAA information for LLVM CodeGen -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This is the code that manages TBAA information and defines the TBAA policy
11 // for the optimizer to use. Relevant standards text includes:
14 // C++ [basic.lval] (p10 in n3126, p15 in some earlier versions)
16 //===----------------------------------------------------------------------===//
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"
23 #include "clang/Frontend/CodeGenOptions.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;
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(0), Char(0) {
39 CodeGenTBAA::~CodeGenTBAA() {
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.
48 Root = MDHelper.createTBAARoot("Simple C/C++ TBAA");
53 // For struct-path aware TBAA, the scalar type has the same format as
54 // the struct type: name, offset, pointer to another node in the type DAG.
55 // For scalar TBAA, the scalar type is the same as the scalar tag:
56 // name and a parent pointer.
57 llvm::MDNode *CodeGenTBAA::createTBAAScalarType(StringRef Name,
58 llvm::MDNode *Parent) {
59 if (CodeGenOpts.StructPathTBAA)
60 return MDHelper.createTBAAScalarTypeNode(Name, Parent);
62 return MDHelper.createTBAANode(Name, Parent);
65 llvm::MDNode *CodeGenTBAA::getChar() {
66 // Define the root of the tree for user-accessible memory. C and C++
67 // give special powers to char and certain similar types. However,
68 // these special powers only cover user-accessible memory, and doesn't
69 // include things like vtables.
71 Char = createTBAAScalarType("omnipotent char", getRoot());
76 static bool TypeHasMayAlias(QualType QTy) {
77 // Tagged types have declarations, and therefore may have attributes.
78 if (const TagType *TTy = dyn_cast<TagType>(QTy))
79 return TTy->getDecl()->hasAttr<MayAliasAttr>();
81 // Typedef types have declarations, and therefore may have attributes.
82 if (const TypedefType *TTy = dyn_cast<TypedefType>(QTy)) {
83 if (TTy->getDecl()->hasAttr<MayAliasAttr>())
85 // Also, their underlying types may have relevant attributes.
86 return TypeHasMayAlias(TTy->desugar());
93 CodeGenTBAA::getTBAAInfo(QualType QTy) {
94 // At -O0 TBAA is not emitted for regular types.
95 if (CodeGenOpts.OptimizationLevel == 0 || CodeGenOpts.RelaxedAliasing)
98 // If the type has the may_alias attribute (even on a typedef), it is
99 // effectively in the general char alias class.
100 if (TypeHasMayAlias(QTy))
103 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
105 if (llvm::MDNode *N = MetadataCache[Ty])
108 // Handle builtin types.
109 if (const BuiltinType *BTy = dyn_cast<BuiltinType>(Ty)) {
110 switch (BTy->getKind()) {
111 // Character types are special and can alias anything.
112 // In C++, this technically only includes "char" and "unsigned char",
113 // and not "signed char". In C, it includes all three. For now,
114 // the risk of exploiting this detail in C++ seems likely to outweigh
116 case BuiltinType::Char_U:
117 case BuiltinType::Char_S:
118 case BuiltinType::UChar:
119 case BuiltinType::SChar:
122 // Unsigned types can alias their corresponding signed types.
123 case BuiltinType::UShort:
124 return getTBAAInfo(Context.ShortTy);
125 case BuiltinType::UInt:
126 return getTBAAInfo(Context.IntTy);
127 case BuiltinType::ULong:
128 return getTBAAInfo(Context.LongTy);
129 case BuiltinType::ULongLong:
130 return getTBAAInfo(Context.LongLongTy);
131 case BuiltinType::UInt128:
132 return getTBAAInfo(Context.Int128Ty);
134 // Treat all other builtin types as distinct types. This includes
135 // treating wchar_t, char16_t, and char32_t as distinct from their
136 // "underlying types".
138 return MetadataCache[Ty] =
139 createTBAAScalarType(BTy->getName(Features), getChar());
144 // TODO: Implement C++'s type "similarity" and consider dis-"similar"
145 // pointers distinct.
146 if (Ty->isPointerType())
147 return MetadataCache[Ty] = createTBAAScalarType("any pointer",
150 // Enum types are distinct types. In C++ they have "underlying types",
151 // however they aren't related for TBAA.
152 if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) {
153 // In C mode, two anonymous enums are compatible iff their members
154 // are the same -- see C99 6.2.7p1. For now, be conservative. We could
155 // theoretically implement this by combining information about all the
156 // members into a single identifying MDNode.
157 if (!Features.CPlusPlus &&
158 ETy->getDecl()->getTypedefNameForAnonDecl())
159 return MetadataCache[Ty] = getChar();
161 // In C++ mode, types have linkage, so we can rely on the ODR and
162 // on their mangled names, if they're external.
163 // TODO: Is there a way to get a program-wide unique name for a
164 // decl with local linkage or no linkage?
165 if (Features.CPlusPlus &&
166 ETy->getDecl()->getLinkage() != ExternalLinkage)
167 return MetadataCache[Ty] = getChar();
169 // TODO: This is using the RTTI name. Is there a better way to get
170 // a unique string for a type?
171 SmallString<256> OutName;
172 llvm::raw_svector_ostream Out(OutName);
173 MContext.mangleCXXRTTIName(QualType(ETy, 0), Out);
175 return MetadataCache[Ty] = createTBAAScalarType(OutName, getChar());
178 // For now, handle any other kind of type conservatively.
179 return MetadataCache[Ty] = getChar();
182 llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() {
183 return createTBAAScalarType("vtable pointer", getRoot());
187 CodeGenTBAA::CollectFields(uint64_t BaseOffset,
189 SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &
192 /* Things not handled yet include: C++ base classes, bitfields, */
194 if (const RecordType *TTy = QTy->getAs<RecordType>()) {
195 const RecordDecl *RD = TTy->getDecl()->getDefinition();
196 if (RD->hasFlexibleArrayMember())
199 // TODO: Handle C++ base classes.
200 if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD))
201 if (Decl->bases_begin() != Decl->bases_end())
204 const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
207 const FieldDecl *LastFD = 0;
208 bool IsMsStruct = RD->isMsStruct(Context);
209 for (RecordDecl::field_iterator i = RD->field_begin(),
210 e = RD->field_end(); i != e; ++i, ++idx) {
212 // Zero-length bitfields following non-bitfield members are ignored.
213 if (Context.ZeroBitfieldFollowsNonBitfield(*i, LastFD)) {
219 uint64_t Offset = BaseOffset +
220 Layout.getFieldOffset(idx) / Context.getCharWidth();
221 QualType FieldQTy = i->getType();
222 if (!CollectFields(Offset, FieldQTy, Fields,
223 MayAlias || TypeHasMayAlias(FieldQTy)))
229 /* Otherwise, treat whatever it is as a field. */
230 uint64_t Offset = BaseOffset;
231 uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity();
232 llvm::MDNode *TBAAInfo = MayAlias ? getChar() : getTBAAInfo(QTy);
233 llvm::MDNode *TBAATag = CodeGenOpts.StructPathTBAA ?
234 getTBAAScalarTagInfo(TBAAInfo) : TBAAInfo;
235 Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag));
240 CodeGenTBAA::getTBAAStructInfo(QualType QTy) {
241 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
243 if (llvm::MDNode *N = StructMetadataCache[Ty])
246 SmallVector<llvm::MDBuilder::TBAAStructField, 4> Fields;
247 if (CollectFields(0, QTy, Fields, TypeHasMayAlias(QTy)))
248 return MDHelper.createTBAAStructNode(Fields);
250 // For now, handle any other kind of type conservatively.
251 return StructMetadataCache[Ty] = NULL;
254 /// Check if the given type can be handled by path-aware TBAA.
255 static bool isTBAAPathStruct(QualType QTy) {
256 if (const RecordType *TTy = QTy->getAs<RecordType>()) {
257 const RecordDecl *RD = TTy->getDecl()->getDefinition();
258 if (RD->hasFlexibleArrayMember())
260 // RD can be struct, union, class, interface or enum.
261 // For now, we only handle struct and class.
262 if (RD->isStruct() || RD->isClass())
269 CodeGenTBAA::getTBAAStructTypeInfo(QualType QTy) {
270 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
271 assert(isTBAAPathStruct(QTy));
273 if (llvm::MDNode *N = StructTypeMetadataCache[Ty])
276 if (const RecordType *TTy = QTy->getAs<RecordType>()) {
277 const RecordDecl *RD = TTy->getDecl()->getDefinition();
279 const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
280 SmallVector <std::pair<llvm::MDNode*, uint64_t>, 4> Fields;
282 const FieldDecl *LastFD = 0;
283 bool IsMsStruct = RD->isMsStruct(Context);
284 for (RecordDecl::field_iterator i = RD->field_begin(),
285 e = RD->field_end(); i != e; ++i, ++idx) {
287 // Zero-length bitfields following non-bitfield members are ignored.
288 if (Context.ZeroBitfieldFollowsNonBitfield(*i, LastFD)) {
295 QualType FieldQTy = i->getType();
296 llvm::MDNode *FieldNode;
297 if (isTBAAPathStruct(FieldQTy))
298 FieldNode = getTBAAStructTypeInfo(FieldQTy);
300 FieldNode = getTBAAInfo(FieldQTy);
302 return StructTypeMetadataCache[Ty] = NULL;
303 Fields.push_back(std::make_pair(
304 FieldNode, Layout.getFieldOffset(idx) / Context.getCharWidth()));
307 // TODO: This is using the RTTI name. Is there a better way to get
308 // a unique string for a type?
309 SmallString<256> OutName;
310 llvm::raw_svector_ostream Out(OutName);
311 MContext.mangleCXXRTTIName(QualType(Ty, 0), Out);
313 // Create the struct type node with a vector of pairs (offset, type).
314 return StructTypeMetadataCache[Ty] =
315 MDHelper.createTBAAStructTypeNode(OutName, Fields);
318 return StructMetadataCache[Ty] = NULL;
322 CodeGenTBAA::getTBAAStructTagInfo(QualType BaseQTy, llvm::MDNode *AccessNode,
324 if (!CodeGenOpts.StructPathTBAA)
327 const Type *BTy = Context.getCanonicalType(BaseQTy).getTypePtr();
328 TBAAPathTag PathTag = TBAAPathTag(BTy, AccessNode, Offset);
329 if (llvm::MDNode *N = StructTagMetadataCache[PathTag])
332 llvm::MDNode *BNode = 0;
333 if (isTBAAPathStruct(BaseQTy))
334 BNode = getTBAAStructTypeInfo(BaseQTy);
336 return StructTagMetadataCache[PathTag] =
337 MDHelper.createTBAAStructTagNode(AccessNode, AccessNode, 0);
339 return StructTagMetadataCache[PathTag] =
340 MDHelper.createTBAAStructTagNode(BNode, AccessNode, Offset);
344 CodeGenTBAA::getTBAAScalarTagInfo(llvm::MDNode *AccessNode) {
345 if (llvm::MDNode *N = ScalarTagMetadataCache[AccessNode])
348 return ScalarTagMetadataCache[AccessNode] =
349 MDHelper.createTBAAStructTagNode(AccessNode, AccessNode, 0);