1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
|
//===--- CodeGenTypes.cpp - TBAA information for LLVM CodeGen -------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This is the code that manages TBAA information and defines the TBAA policy
// for the optimizer to use. Relevant standards text includes:
//
// C99 6.5p7
// C++ [basic.lval] (p10 in n3126, p15 in some earlier versions)
//
//===----------------------------------------------------------------------===//
#include "CodeGenTBAA.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Mangle.h"
#include "llvm/LLVMContext.h"
#include "llvm/Metadata.h"
#include "llvm/Constants.h"
#include "llvm/Type.h"
using namespace clang;
using namespace CodeGen;
CodeGenTBAA::CodeGenTBAA(ASTContext &Ctx, llvm::LLVMContext& VMContext,
const LangOptions &Features, MangleContext &MContext)
: Context(Ctx), VMContext(VMContext), Features(Features), MContext(MContext),
Root(0), Char(0) {
}
CodeGenTBAA::~CodeGenTBAA() {
}
llvm::MDNode *CodeGenTBAA::getRoot() {
// Define the root of the tree. This identifies the tree, so that
// if our LLVM IR is linked with LLVM IR from a different front-end
// (or a different version of this front-end), their TBAA trees will
// remain distinct, and the optimizer will treat them conservatively.
if (!Root)
Root = getTBAAInfoForNamedType("Simple C/C++ TBAA", 0);
return Root;
}
llvm::MDNode *CodeGenTBAA::getChar() {
// Define the root of the tree for user-accessible memory. C and C++
// give special powers to char and certain similar types. However,
// these special powers only cover user-accessible memory, and doesn't
// include things like vtables.
if (!Char)
Char = getTBAAInfoForNamedType("omnipotent char", getRoot());
return Char;
}
/// getTBAAInfoForNamedType - Create a TBAA tree node with the given string
/// as its identifier, and the given Parent node as its tree parent.
llvm::MDNode *CodeGenTBAA::getTBAAInfoForNamedType(StringRef NameStr,
llvm::MDNode *Parent,
bool Readonly) {
// Currently there is only one flag defined - the readonly flag.
llvm::Value *Flags = 0;
if (Readonly)
Flags = llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext), true);
// Set up the mdnode operand list.
llvm::Value *Ops[] = {
llvm::MDString::get(VMContext, NameStr),
Parent,
Flags
};
// Create the mdnode.
unsigned Len = llvm::array_lengthof(Ops) - !Flags;
return llvm::MDNode::get(VMContext, llvm::makeArrayRef(Ops, Len));
}
static bool TypeHasMayAlias(QualType QTy) {
// Tagged types have declarations, and therefore may have attributes.
if (const TagType *TTy = dyn_cast<TagType>(QTy))
return TTy->getDecl()->hasAttr<MayAliasAttr>();
// Typedef types have declarations, and therefore may have attributes.
if (const TypedefType *TTy = dyn_cast<TypedefType>(QTy)) {
if (TTy->getDecl()->hasAttr<MayAliasAttr>())
return true;
// Also, their underlying types may have relevant attributes.
return TypeHasMayAlias(TTy->desugar());
}
return false;
}
llvm::MDNode *
CodeGenTBAA::getTBAAInfo(QualType QTy) {
// If the type has the may_alias attribute (even on a typedef), it is
// effectively in the general char alias class.
if (TypeHasMayAlias(QTy))
return getChar();
const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
if (llvm::MDNode *N = MetadataCache[Ty])
return N;
// Handle builtin types.
if (const BuiltinType *BTy = dyn_cast<BuiltinType>(Ty)) {
switch (BTy->getKind()) {
// Character types are special and can alias anything.
// In C++, this technically only includes "char" and "unsigned char",
// and not "signed char". In C, it includes all three. For now,
// the risk of exploiting this detail in C++ seems likely to outweigh
// the benefit.
case BuiltinType::Char_U:
case BuiltinType::Char_S:
case BuiltinType::UChar:
case BuiltinType::SChar:
return getChar();
// Unsigned types can alias their corresponding signed types.
case BuiltinType::UShort:
return getTBAAInfo(Context.ShortTy);
case BuiltinType::UInt:
return getTBAAInfo(Context.IntTy);
case BuiltinType::ULong:
return getTBAAInfo(Context.LongTy);
case BuiltinType::ULongLong:
return getTBAAInfo(Context.LongLongTy);
case BuiltinType::UInt128:
return getTBAAInfo(Context.Int128Ty);
// Treat all other builtin types as distinct types. This includes
// treating wchar_t, char16_t, and char32_t as distinct from their
// "underlying types".
default:
return MetadataCache[Ty] =
getTBAAInfoForNamedType(BTy->getName(Features), getChar());
}
}
// Handle pointers.
// TODO: Implement C++'s type "similarity" and consider dis-"similar"
// pointers distinct.
if (Ty->isPointerType())
return MetadataCache[Ty] = getTBAAInfoForNamedType("any pointer",
getChar());
// Enum types are distinct types. In C++ they have "underlying types",
// however they aren't related for TBAA.
if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) {
// In C mode, two anonymous enums are compatible iff their members
// are the same -- see C99 6.2.7p1. For now, be conservative. We could
// theoretically implement this by combining information about all the
// members into a single identifying MDNode.
if (!Features.CPlusPlus &&
ETy->getDecl()->getTypedefNameForAnonDecl())
return MetadataCache[Ty] = getChar();
// In C++ mode, types have linkage, so we can rely on the ODR and
// on their mangled names, if they're external.
// TODO: Is there a way to get a program-wide unique name for a
// decl with local linkage or no linkage?
if (Features.CPlusPlus &&
ETy->getDecl()->getLinkage() != ExternalLinkage)
return MetadataCache[Ty] = getChar();
// TODO: This is using the RTTI name. Is there a better way to get
// a unique string for a type?
SmallString<256> OutName;
llvm::raw_svector_ostream Out(OutName);
MContext.mangleCXXRTTIName(QualType(ETy, 0), Out);
Out.flush();
return MetadataCache[Ty] = getTBAAInfoForNamedType(OutName, getChar());
}
// For now, handle any other kind of type conservatively.
return MetadataCache[Ty] = getChar();
}
llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() {
return getTBAAInfoForNamedType("vtable pointer", getRoot());
}
|
