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 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);
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.
66 Char = createTBAAScalarType("omnipotent char", getRoot());
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>();
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>())
80 // Also, their underlying types may have relevant attributes.
81 return TypeHasMayAlias(TTy->desugar());
88 CodeGenTBAA::getTBAAInfo(QualType QTy) {
89 // At -O0 or relaxed aliasing, TBAA is not emitted for regular types.
90 if (CodeGenOpts.OptimizationLevel == 0 || CodeGenOpts.RelaxedAliasing)
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))
98 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
100 if (llvm::MDNode *N = MetadataCache[Ty])
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
111 case BuiltinType::Char_U:
112 case BuiltinType::Char_S:
113 case BuiltinType::UChar:
114 case BuiltinType::SChar:
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);
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".
133 return MetadataCache[Ty] =
134 createTBAAScalarType(BTy->getName(Features), getChar());
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",
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();
155 SmallString<256> OutName;
156 llvm::raw_svector_ostream Out(OutName);
157 MContext.mangleTypeName(QualType(ETy, 0), Out);
159 return MetadataCache[Ty] = createTBAAScalarType(OutName, getChar());
162 // For now, handle any other kind of type conservatively.
163 return MetadataCache[Ty] = getChar();
166 llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() {
167 return createTBAAScalarType("vtable pointer", getRoot());
171 CodeGenTBAA::CollectFields(uint64_t BaseOffset,
173 SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &
176 /* Things not handled yet include: C++ base classes, bitfields, */
178 if (const RecordType *TTy = QTy->getAs<RecordType>()) {
179 const RecordDecl *RD = TTy->getDecl()->getDefinition();
180 if (RD->hasFlexibleArrayMember())
183 // TODO: Handle C++ base classes.
184 if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD))
185 if (Decl->bases_begin() != Decl->bases_end())
188 const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
191 for (RecordDecl::field_iterator i = RD->field_begin(),
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)))
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));
213 CodeGenTBAA::getTBAAStructInfo(QualType QTy) {
214 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
216 if (llvm::MDNode *N = StructMetadataCache[Ty])
219 SmallVector<llvm::MDBuilder::TBAAStructField, 4> Fields;
220 if (CollectFields(0, QTy, Fields, TypeHasMayAlias(QTy)))
221 return MDHelper.createTBAAStructNode(Fields);
223 // For now, handle any other kind of type conservatively.
224 return StructMetadataCache[Ty] = NULL;
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())
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())
242 CodeGenTBAA::getTBAAStructTypeInfo(QualType QTy) {
243 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
244 assert(isTBAAPathStruct(QTy));
246 if (llvm::MDNode *N = StructTypeMetadataCache[Ty])
249 if (const RecordType *TTy = QTy->getAs<RecordType>()) {
250 const RecordDecl *RD = TTy->getDecl()->getDefinition();
252 const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
253 SmallVector <std::pair<llvm::MDNode*, uint64_t>, 4> Fields;
255 for (RecordDecl::field_iterator i = RD->field_begin(),
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);
262 FieldNode = getTBAAInfo(FieldQTy);
264 return StructTypeMetadataCache[Ty] = NULL;
265 Fields.push_back(std::make_pair(
266 FieldNode, Layout.getFieldOffset(idx) / Context.getCharWidth()));
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);
276 OutName = RD->getName();
278 // Create the struct type node with a vector of pairs (offset, type).
279 return StructTypeMetadataCache[Ty] =
280 MDHelper.createTBAAStructTypeNode(OutName, Fields);
283 return StructMetadataCache[Ty] = NULL;
286 /// Return a TBAA tag node for both scalar TBAA and struct-path aware TBAA.
288 CodeGenTBAA::getTBAAStructTagInfo(QualType BaseQTy, llvm::MDNode *AccessNode,
293 if (!CodeGenOpts.StructPathTBAA)
294 return getTBAAScalarTagInfo(AccessNode);
296 const Type *BTy = Context.getCanonicalType(BaseQTy).getTypePtr();
297 TBAAPathTag PathTag = TBAAPathTag(BTy, AccessNode, Offset);
298 if (llvm::MDNode *N = StructTagMetadataCache[PathTag])
301 llvm::MDNode *BNode = 0;
302 if (isTBAAPathStruct(BaseQTy))
303 BNode = getTBAAStructTypeInfo(BaseQTy);
305 return StructTagMetadataCache[PathTag] =
306 MDHelper.createTBAAStructTagNode(AccessNode, AccessNode, 0);
308 return StructTagMetadataCache[PathTag] =
309 MDHelper.createTBAAStructTagNode(BNode, AccessNode, Offset);
313 CodeGenTBAA::getTBAAScalarTagInfo(llvm::MDNode *AccessNode) {
316 if (llvm::MDNode *N = ScalarTagMetadataCache[AccessNode])
319 return ScalarTagMetadataCache[AccessNode] =
320 MDHelper.createTBAAStructTagNode(AccessNode, AccessNode, 0);