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/Mangle.h"
21 #include "llvm/LLVMContext.h"
22 #include "llvm/Metadata.h"
23 #include "llvm/Constants.h"
24 #include "llvm/Type.h"
25 using namespace clang;
26 using namespace CodeGen;
28 CodeGenTBAA::CodeGenTBAA(ASTContext &Ctx, llvm::LLVMContext& VMContext,
29 const LangOptions &Features, MangleContext &MContext)
30 : Context(Ctx), VMContext(VMContext), Features(Features), MContext(MContext),
31 MDHelper(VMContext), Root(0), Char(0) {
34 CodeGenTBAA::~CodeGenTBAA() {
37 llvm::MDNode *CodeGenTBAA::getRoot() {
38 // Define the root of the tree. This identifies the tree, so that
39 // if our LLVM IR is linked with LLVM IR from a different front-end
40 // (or a different version of this front-end), their TBAA trees will
41 // remain distinct, and the optimizer will treat them conservatively.
43 Root = MDHelper.createTBAARoot("Simple C/C++ TBAA");
48 llvm::MDNode *CodeGenTBAA::getChar() {
49 // Define the root of the tree for user-accessible memory. C and C++
50 // give special powers to char and certain similar types. However,
51 // these special powers only cover user-accessible memory, and doesn't
52 // include things like vtables.
54 Char = MDHelper.createTBAANode("omnipotent char", getRoot());
59 static bool TypeHasMayAlias(QualType QTy) {
60 // Tagged types have declarations, and therefore may have attributes.
61 if (const TagType *TTy = dyn_cast<TagType>(QTy))
62 return TTy->getDecl()->hasAttr<MayAliasAttr>();
64 // Typedef types have declarations, and therefore may have attributes.
65 if (const TypedefType *TTy = dyn_cast<TypedefType>(QTy)) {
66 if (TTy->getDecl()->hasAttr<MayAliasAttr>())
68 // Also, their underlying types may have relevant attributes.
69 return TypeHasMayAlias(TTy->desugar());
76 CodeGenTBAA::getTBAAInfo(QualType QTy) {
77 // If the type has the may_alias attribute (even on a typedef), it is
78 // effectively in the general char alias class.
79 if (TypeHasMayAlias(QTy))
82 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
84 if (llvm::MDNode *N = MetadataCache[Ty])
87 // Handle builtin types.
88 if (const BuiltinType *BTy = dyn_cast<BuiltinType>(Ty)) {
89 switch (BTy->getKind()) {
90 // Character types are special and can alias anything.
91 // In C++, this technically only includes "char" and "unsigned char",
92 // and not "signed char". In C, it includes all three. For now,
93 // the risk of exploiting this detail in C++ seems likely to outweigh
95 case BuiltinType::Char_U:
96 case BuiltinType::Char_S:
97 case BuiltinType::UChar:
98 case BuiltinType::SChar:
101 // Unsigned types can alias their corresponding signed types.
102 case BuiltinType::UShort:
103 return getTBAAInfo(Context.ShortTy);
104 case BuiltinType::UInt:
105 return getTBAAInfo(Context.IntTy);
106 case BuiltinType::ULong:
107 return getTBAAInfo(Context.LongTy);
108 case BuiltinType::ULongLong:
109 return getTBAAInfo(Context.LongLongTy);
110 case BuiltinType::UInt128:
111 return getTBAAInfo(Context.Int128Ty);
113 // Treat all other builtin types as distinct types. This includes
114 // treating wchar_t, char16_t, and char32_t as distinct from their
115 // "underlying types".
117 return MetadataCache[Ty] =
118 MDHelper.createTBAANode(BTy->getName(Features), getChar());
123 // TODO: Implement C++'s type "similarity" and consider dis-"similar"
124 // pointers distinct.
125 if (Ty->isPointerType())
126 return MetadataCache[Ty] = MDHelper.createTBAANode("any pointer",
129 // Enum types are distinct types. In C++ they have "underlying types",
130 // however they aren't related for TBAA.
131 if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) {
132 // In C mode, two anonymous enums are compatible iff their members
133 // are the same -- see C99 6.2.7p1. For now, be conservative. We could
134 // theoretically implement this by combining information about all the
135 // members into a single identifying MDNode.
136 if (!Features.CPlusPlus &&
137 ETy->getDecl()->getTypedefNameForAnonDecl())
138 return MetadataCache[Ty] = getChar();
140 // In C++ mode, types have linkage, so we can rely on the ODR and
141 // on their mangled names, if they're external.
142 // TODO: Is there a way to get a program-wide unique name for a
143 // decl with local linkage or no linkage?
144 if (Features.CPlusPlus &&
145 ETy->getDecl()->getLinkage() != ExternalLinkage)
146 return MetadataCache[Ty] = getChar();
148 // TODO: This is using the RTTI name. Is there a better way to get
149 // a unique string for a type?
150 SmallString<256> OutName;
151 llvm::raw_svector_ostream Out(OutName);
152 MContext.mangleCXXRTTIName(QualType(ETy, 0), Out);
154 return MetadataCache[Ty] = MDHelper.createTBAANode(OutName, getChar());
157 // For now, handle any other kind of type conservatively.
158 return MetadataCache[Ty] = getChar();
161 llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() {
162 return MDHelper.createTBAANode("vtable pointer", getRoot());