322 lines
11 KiB
C++
322 lines
11 KiB
C++
//===--- CodeGenTypes.cpp - TBAA information for LLVM CodeGen -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This is the code that manages TBAA information and defines the TBAA policy
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// for the optimizer to use. Relevant standards text includes:
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//
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// C99 6.5p7
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// C++ [basic.lval] (p10 in n3126, p15 in some earlier versions)
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//
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//===----------------------------------------------------------------------===//
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#include "CodeGenTBAA.h"
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#include "clang/AST/ASTContext.h"
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#include "clang/AST/Attr.h"
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#include "clang/AST/Mangle.h"
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#include "clang/AST/RecordLayout.h"
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#include "clang/Frontend/CodeGenOptions.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/IR/Type.h"
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using namespace clang;
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using namespace CodeGen;
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CodeGenTBAA::CodeGenTBAA(ASTContext &Ctx, llvm::LLVMContext& VMContext,
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const CodeGenOptions &CGO,
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const LangOptions &Features, MangleContext &MContext)
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: Context(Ctx), CodeGenOpts(CGO), Features(Features), MContext(MContext),
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MDHelper(VMContext), Root(nullptr), Char(nullptr) {
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}
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CodeGenTBAA::~CodeGenTBAA() {
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}
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llvm::MDNode *CodeGenTBAA::getRoot() {
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// Define the root of the tree. This identifies the tree, so that
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// if our LLVM IR is linked with LLVM IR from a different front-end
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// (or a different version of this front-end), their TBAA trees will
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// remain distinct, and the optimizer will treat them conservatively.
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if (!Root)
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Root = MDHelper.createTBAARoot("Simple C/C++ TBAA");
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return Root;
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}
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// For both scalar TBAA and struct-path aware TBAA, the scalar type has the
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// same format: name, parent node, and offset.
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llvm::MDNode *CodeGenTBAA::createTBAAScalarType(StringRef Name,
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llvm::MDNode *Parent) {
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return MDHelper.createTBAAScalarTypeNode(Name, Parent);
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}
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llvm::MDNode *CodeGenTBAA::getChar() {
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// Define the root of the tree for user-accessible memory. C and C++
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// give special powers to char and certain similar types. However,
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// these special powers only cover user-accessible memory, and doesn't
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// include things like vtables.
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if (!Char)
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Char = createTBAAScalarType("omnipotent char", getRoot());
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return Char;
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}
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static bool TypeHasMayAlias(QualType QTy) {
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// Tagged types have declarations, and therefore may have attributes.
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if (const TagType *TTy = dyn_cast<TagType>(QTy))
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return TTy->getDecl()->hasAttr<MayAliasAttr>();
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// Typedef types have declarations, and therefore may have attributes.
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if (const TypedefType *TTy = dyn_cast<TypedefType>(QTy)) {
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if (TTy->getDecl()->hasAttr<MayAliasAttr>())
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return true;
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// Also, their underlying types may have relevant attributes.
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return TypeHasMayAlias(TTy->desugar());
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}
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return false;
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}
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llvm::MDNode *
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CodeGenTBAA::getTBAAInfo(QualType QTy) {
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// At -O0 or relaxed aliasing, TBAA is not emitted for regular types.
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if (CodeGenOpts.OptimizationLevel == 0 || CodeGenOpts.RelaxedAliasing)
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return nullptr;
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// If the type has the may_alias attribute (even on a typedef), it is
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// effectively in the general char alias class.
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if (TypeHasMayAlias(QTy))
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return getChar();
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const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
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if (llvm::MDNode *N = MetadataCache[Ty])
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return N;
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// Handle builtin types.
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if (const BuiltinType *BTy = dyn_cast<BuiltinType>(Ty)) {
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switch (BTy->getKind()) {
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// Character types are special and can alias anything.
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// In C++, this technically only includes "char" and "unsigned char",
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// and not "signed char". In C, it includes all three. For now,
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// the risk of exploiting this detail in C++ seems likely to outweigh
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// the benefit.
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case BuiltinType::Char_U:
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case BuiltinType::Char_S:
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case BuiltinType::UChar:
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case BuiltinType::SChar:
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return getChar();
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// Unsigned types can alias their corresponding signed types.
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case BuiltinType::UShort:
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return getTBAAInfo(Context.ShortTy);
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case BuiltinType::UInt:
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return getTBAAInfo(Context.IntTy);
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case BuiltinType::ULong:
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return getTBAAInfo(Context.LongTy);
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case BuiltinType::ULongLong:
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return getTBAAInfo(Context.LongLongTy);
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case BuiltinType::UInt128:
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return getTBAAInfo(Context.Int128Ty);
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// Treat all other builtin types as distinct types. This includes
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// treating wchar_t, char16_t, and char32_t as distinct from their
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// "underlying types".
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default:
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return MetadataCache[Ty] =
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createTBAAScalarType(BTy->getName(Features), getChar());
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}
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}
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// Handle pointers.
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// TODO: Implement C++'s type "similarity" and consider dis-"similar"
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// pointers distinct.
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if (Ty->isPointerType())
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return MetadataCache[Ty] = createTBAAScalarType("any pointer",
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getChar());
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// Enum types are distinct types. In C++ they have "underlying types",
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// however they aren't related for TBAA.
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if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) {
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// In C++ mode, types have linkage, so we can rely on the ODR and
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// on their mangled names, if they're external.
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// TODO: Is there a way to get a program-wide unique name for a
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// decl with local linkage or no linkage?
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if (!Features.CPlusPlus || !ETy->getDecl()->isExternallyVisible())
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return MetadataCache[Ty] = getChar();
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SmallString<256> OutName;
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llvm::raw_svector_ostream Out(OutName);
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MContext.mangleTypeName(QualType(ETy, 0), Out);
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Out.flush();
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return MetadataCache[Ty] = createTBAAScalarType(OutName, getChar());
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}
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// For now, handle any other kind of type conservatively.
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return MetadataCache[Ty] = getChar();
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}
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llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() {
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return createTBAAScalarType("vtable pointer", getRoot());
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}
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bool
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CodeGenTBAA::CollectFields(uint64_t BaseOffset,
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QualType QTy,
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SmallVectorImpl<llvm::MDBuilder::TBAAStructField> &
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Fields,
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bool MayAlias) {
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/* Things not handled yet include: C++ base classes, bitfields, */
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if (const RecordType *TTy = QTy->getAs<RecordType>()) {
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const RecordDecl *RD = TTy->getDecl()->getDefinition();
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if (RD->hasFlexibleArrayMember())
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return false;
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// TODO: Handle C++ base classes.
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if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD))
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if (Decl->bases_begin() != Decl->bases_end())
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return false;
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const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
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unsigned idx = 0;
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for (RecordDecl::field_iterator i = RD->field_begin(),
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e = RD->field_end(); i != e; ++i, ++idx) {
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uint64_t Offset = BaseOffset +
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Layout.getFieldOffset(idx) / Context.getCharWidth();
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QualType FieldQTy = i->getType();
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if (!CollectFields(Offset, FieldQTy, Fields,
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MayAlias || TypeHasMayAlias(FieldQTy)))
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return false;
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}
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return true;
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}
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/* Otherwise, treat whatever it is as a field. */
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uint64_t Offset = BaseOffset;
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uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity();
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llvm::MDNode *TBAAInfo = MayAlias ? getChar() : getTBAAInfo(QTy);
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llvm::MDNode *TBAATag = getTBAAScalarTagInfo(TBAAInfo);
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Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAATag));
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return true;
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}
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llvm::MDNode *
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CodeGenTBAA::getTBAAStructInfo(QualType QTy) {
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const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
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if (llvm::MDNode *N = StructMetadataCache[Ty])
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return N;
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SmallVector<llvm::MDBuilder::TBAAStructField, 4> Fields;
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if (CollectFields(0, QTy, Fields, TypeHasMayAlias(QTy)))
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return MDHelper.createTBAAStructNode(Fields);
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// For now, handle any other kind of type conservatively.
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return StructMetadataCache[Ty] = nullptr;
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}
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/// Check if the given type can be handled by path-aware TBAA.
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static bool isTBAAPathStruct(QualType QTy) {
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if (const RecordType *TTy = QTy->getAs<RecordType>()) {
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const RecordDecl *RD = TTy->getDecl()->getDefinition();
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if (RD->hasFlexibleArrayMember())
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return false;
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// RD can be struct, union, class, interface or enum.
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// For now, we only handle struct and class.
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if (RD->isStruct() || RD->isClass())
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return true;
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}
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return false;
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}
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llvm::MDNode *
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CodeGenTBAA::getTBAAStructTypeInfo(QualType QTy) {
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const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
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assert(isTBAAPathStruct(QTy));
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if (llvm::MDNode *N = StructTypeMetadataCache[Ty])
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return N;
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if (const RecordType *TTy = QTy->getAs<RecordType>()) {
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const RecordDecl *RD = TTy->getDecl()->getDefinition();
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const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
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SmallVector <std::pair<llvm::MDNode*, uint64_t>, 4> Fields;
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unsigned idx = 0;
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for (RecordDecl::field_iterator i = RD->field_begin(),
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e = RD->field_end(); i != e; ++i, ++idx) {
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QualType FieldQTy = i->getType();
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llvm::MDNode *FieldNode;
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if (isTBAAPathStruct(FieldQTy))
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FieldNode = getTBAAStructTypeInfo(FieldQTy);
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else
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FieldNode = getTBAAInfo(FieldQTy);
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if (!FieldNode)
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return StructTypeMetadataCache[Ty] = nullptr;
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Fields.push_back(std::make_pair(
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FieldNode, Layout.getFieldOffset(idx) / Context.getCharWidth()));
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}
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SmallString<256> OutName;
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if (Features.CPlusPlus) {
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// Don't use the mangler for C code.
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llvm::raw_svector_ostream Out(OutName);
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MContext.mangleTypeName(QualType(Ty, 0), Out);
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Out.flush();
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} else {
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OutName = RD->getName();
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}
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// Create the struct type node with a vector of pairs (offset, type).
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return StructTypeMetadataCache[Ty] =
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MDHelper.createTBAAStructTypeNode(OutName, Fields);
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}
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return StructMetadataCache[Ty] = nullptr;
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}
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/// Return a TBAA tag node for both scalar TBAA and struct-path aware TBAA.
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llvm::MDNode *
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CodeGenTBAA::getTBAAStructTagInfo(QualType BaseQTy, llvm::MDNode *AccessNode,
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uint64_t Offset) {
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if (!AccessNode)
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return nullptr;
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if (!CodeGenOpts.StructPathTBAA)
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return getTBAAScalarTagInfo(AccessNode);
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const Type *BTy = Context.getCanonicalType(BaseQTy).getTypePtr();
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TBAAPathTag PathTag = TBAAPathTag(BTy, AccessNode, Offset);
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if (llvm::MDNode *N = StructTagMetadataCache[PathTag])
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return N;
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llvm::MDNode *BNode = nullptr;
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if (isTBAAPathStruct(BaseQTy))
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BNode = getTBAAStructTypeInfo(BaseQTy);
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if (!BNode)
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return StructTagMetadataCache[PathTag] =
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MDHelper.createTBAAStructTagNode(AccessNode, AccessNode, 0);
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return StructTagMetadataCache[PathTag] =
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MDHelper.createTBAAStructTagNode(BNode, AccessNode, Offset);
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}
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llvm::MDNode *
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CodeGenTBAA::getTBAAScalarTagInfo(llvm::MDNode *AccessNode) {
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if (!AccessNode)
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return nullptr;
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if (llvm::MDNode *N = ScalarTagMetadataCache[AccessNode])
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return N;
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return ScalarTagMetadataCache[AccessNode] =
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MDHelper.createTBAAStructTagNode(AccessNode, AccessNode, 0);
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}
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