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/RecordLayout.h"
21 #include "clang/AST/Mangle.h"
22 #include "clang/Frontend/CodeGenOptions.h"
23 #include "llvm/LLVMContext.h"
24 #include "llvm/Metadata.h"
25 #include "llvm/Constants.h"
26 #include "llvm/Type.h"
27 using namespace clang;
28 using namespace CodeGen;
30 CodeGenTBAA::CodeGenTBAA(ASTContext &Ctx, llvm::LLVMContext& VMContext,
31 const CodeGenOptions &CGO,
32 const LangOptions &Features, MangleContext &MContext)
33 : Context(Ctx), CodeGenOpts(CGO), Features(Features), MContext(MContext),
34 MDHelper(VMContext), Root(0), Char(0) {
37 CodeGenTBAA::~CodeGenTBAA() {
40 llvm::MDNode *CodeGenTBAA::getRoot() {
41 // Define the root of the tree. This identifies the tree, so that
42 // if our LLVM IR is linked with LLVM IR from a different front-end
43 // (or a different version of this front-end), their TBAA trees will
44 // remain distinct, and the optimizer will treat them conservatively.
46 Root = MDHelper.createTBAARoot("Simple C/C++ TBAA");
51 llvm::MDNode *CodeGenTBAA::getChar() {
52 // Define the root of the tree for user-accessible memory. C and C++
53 // give special powers to char and certain similar types. However,
54 // these special powers only cover user-accessible memory, and doesn't
55 // include things like vtables.
57 Char = MDHelper.createTBAANode("omnipotent char", getRoot());
62 static bool TypeHasMayAlias(QualType QTy) {
63 // Tagged types have declarations, and therefore may have attributes.
64 if (const TagType *TTy = dyn_cast<TagType>(QTy))
65 return TTy->getDecl()->hasAttr<MayAliasAttr>();
67 // Typedef types have declarations, and therefore may have attributes.
68 if (const TypedefType *TTy = dyn_cast<TypedefType>(QTy)) {
69 if (TTy->getDecl()->hasAttr<MayAliasAttr>())
71 // Also, their underlying types may have relevant attributes.
72 return TypeHasMayAlias(TTy->desugar());
79 CodeGenTBAA::getTBAAInfo(QualType QTy) {
80 // At -O0 TBAA is not emitted for regular types.
81 if (CodeGenOpts.OptimizationLevel == 0 || CodeGenOpts.RelaxedAliasing)
84 // If the type has the may_alias attribute (even on a typedef), it is
85 // effectively in the general char alias class.
86 if (TypeHasMayAlias(QTy))
89 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
91 if (llvm::MDNode *N = MetadataCache[Ty])
94 // Handle builtin types.
95 if (const BuiltinType *BTy = dyn_cast<BuiltinType>(Ty)) {
96 switch (BTy->getKind()) {
97 // Character types are special and can alias anything.
98 // In C++, this technically only includes "char" and "unsigned char",
99 // and not "signed char". In C, it includes all three. For now,
100 // the risk of exploiting this detail in C++ seems likely to outweigh
102 case BuiltinType::Char_U:
103 case BuiltinType::Char_S:
104 case BuiltinType::UChar:
105 case BuiltinType::SChar:
108 // Unsigned types can alias their corresponding signed types.
109 case BuiltinType::UShort:
110 return getTBAAInfo(Context.ShortTy);
111 case BuiltinType::UInt:
112 return getTBAAInfo(Context.IntTy);
113 case BuiltinType::ULong:
114 return getTBAAInfo(Context.LongTy);
115 case BuiltinType::ULongLong:
116 return getTBAAInfo(Context.LongLongTy);
117 case BuiltinType::UInt128:
118 return getTBAAInfo(Context.Int128Ty);
120 // Treat all other builtin types as distinct types. This includes
121 // treating wchar_t, char16_t, and char32_t as distinct from their
122 // "underlying types".
124 return MetadataCache[Ty] =
125 MDHelper.createTBAANode(BTy->getName(Features), getChar());
130 // TODO: Implement C++'s type "similarity" and consider dis-"similar"
131 // pointers distinct.
132 if (Ty->isPointerType())
133 return MetadataCache[Ty] = MDHelper.createTBAANode("any pointer",
136 // Enum types are distinct types. In C++ they have "underlying types",
137 // however they aren't related for TBAA.
138 if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) {
139 // In C mode, two anonymous enums are compatible iff their members
140 // are the same -- see C99 6.2.7p1. For now, be conservative. We could
141 // theoretically implement this by combining information about all the
142 // members into a single identifying MDNode.
143 if (!Features.CPlusPlus &&
144 ETy->getDecl()->getTypedefNameForAnonDecl())
145 return MetadataCache[Ty] = getChar();
147 // In C++ mode, types have linkage, so we can rely on the ODR and
148 // on their mangled names, if they're external.
149 // TODO: Is there a way to get a program-wide unique name for a
150 // decl with local linkage or no linkage?
151 if (Features.CPlusPlus &&
152 ETy->getDecl()->getLinkage() != ExternalLinkage)
153 return MetadataCache[Ty] = getChar();
155 // TODO: This is using the RTTI name. Is there a better way to get
156 // a unique string for a type?
157 SmallString<256> OutName;
158 llvm::raw_svector_ostream Out(OutName);
159 MContext.mangleCXXRTTIName(QualType(ETy, 0), Out);
161 return MetadataCache[Ty] = MDHelper.createTBAANode(OutName, getChar());
164 // For now, handle any other kind of type conservatively.
165 return MetadataCache[Ty] = getChar();
168 llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() {
169 return MDHelper.createTBAANode("vtable pointer", getRoot());
173 CodeGenTBAA::CollectFields(uint64_t BaseOffset,
175 SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &
178 /* Things not handled yet include: C++ base classes, bitfields, */
180 if (const RecordType *TTy = QTy->getAs<RecordType>()) {
181 const RecordDecl *RD = TTy->getDecl()->getDefinition();
182 if (RD->hasFlexibleArrayMember())
185 // TODO: Handle C++ base classes.
186 if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD))
187 if (Decl->bases_begin() != Decl->bases_end())
190 const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
193 for (RecordDecl::field_iterator i = RD->field_begin(),
194 e = RD->field_end(); i != e; ++i, ++idx) {
195 uint64_t Offset = BaseOffset +
196 Layout.getFieldOffset(idx) / Context.getCharWidth();
197 QualType FieldQTy = i->getType();
198 if (!CollectFields(Offset, FieldQTy, Fields,
199 MayAlias || TypeHasMayAlias(FieldQTy)))
205 /* Otherwise, treat whatever it is as a field. */
206 uint64_t Offset = BaseOffset;
207 uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity();
208 llvm::MDNode *TBAAInfo = MayAlias ? getChar() : getTBAAInfo(QTy);
209 Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAAInfo));
214 CodeGenTBAA::getTBAAStructInfo(QualType QTy) {
215 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
217 if (llvm::MDNode *N = StructMetadataCache[Ty])
220 SmallVector<llvm::MDBuilder::TBAAStructField, 4> Fields;
221 if (CollectFields(0, QTy, Fields, TypeHasMayAlias(QTy)))
222 return MDHelper.createTBAAStructNode(Fields);
224 // For now, handle any other kind of type conservatively.
225 return StructMetadataCache[Ty] = NULL;