466 lines
17 KiB
C++
466 lines
17 KiB
C++
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//===-- CodeGenTBAA.cpp - TBAA information for LLVM CodeGen ---------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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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/Basic/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/Module.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::Module &M,
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const CodeGenOptions &CGO,
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const LangOptions &Features, MangleContext &MContext)
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: Context(Ctx), Module(M), CodeGenOpts(CGO),
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Features(Features), MContext(MContext), MDHelper(M.getContext()),
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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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if (Features.CPlusPlus)
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Root = MDHelper.createTBAARoot("Simple C++ TBAA");
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else
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Root = MDHelper.createTBAARoot("Simple C/C++ TBAA");
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}
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return Root;
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}
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llvm::MDNode *CodeGenTBAA::createScalarTypeNode(StringRef Name,
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llvm::MDNode *Parent,
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uint64_t Size) {
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if (CodeGenOpts.NewStructPathTBAA) {
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llvm::Metadata *Id = MDHelper.createString(Name);
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return MDHelper.createTBAATypeNode(Parent, Size, Id);
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}
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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 = createScalarTypeNode("omnipotent char", getRoot(), /* Size= */ 1);
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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 (auto *TD = QTy->getAsTagDecl())
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if (TD->hasAttr<MayAliasAttr>())
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return true;
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// Also look for may_alias as a declaration attribute on a typedef.
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// FIXME: We should follow GCC and model may_alias as a type attribute
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// rather than as a declaration attribute.
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while (auto *TT = QTy->getAs<TypedefType>()) {
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if (TT->getDecl()->hasAttr<MayAliasAttr>())
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return true;
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QTy = TT->desugar();
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}
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return false;
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}
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/// Check if the given type is a valid base type to be used in access tags.
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static bool isValidBaseType(QualType QTy) {
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if (QTy->isReferenceType())
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return false;
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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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// Incomplete types are not valid base access types.
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if (!RD)
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return false;
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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 *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) {
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uint64_t Size = Context.getTypeSizeInChars(Ty).getQuantity();
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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 getTypeInfo(Context.ShortTy);
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case BuiltinType::UInt:
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return getTypeInfo(Context.IntTy);
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case BuiltinType::ULong:
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return getTypeInfo(Context.LongTy);
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case BuiltinType::ULongLong:
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return getTypeInfo(Context.LongLongTy);
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case BuiltinType::UInt128:
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return getTypeInfo(Context.Int128Ty);
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case BuiltinType::UShortFract:
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return getTypeInfo(Context.ShortFractTy);
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case BuiltinType::UFract:
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return getTypeInfo(Context.FractTy);
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case BuiltinType::ULongFract:
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return getTypeInfo(Context.LongFractTy);
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case BuiltinType::SatUShortFract:
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return getTypeInfo(Context.SatShortFractTy);
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case BuiltinType::SatUFract:
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return getTypeInfo(Context.SatFractTy);
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case BuiltinType::SatULongFract:
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return getTypeInfo(Context.SatLongFractTy);
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case BuiltinType::UShortAccum:
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return getTypeInfo(Context.ShortAccumTy);
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case BuiltinType::UAccum:
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return getTypeInfo(Context.AccumTy);
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case BuiltinType::ULongAccum:
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return getTypeInfo(Context.LongAccumTy);
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case BuiltinType::SatUShortAccum:
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return getTypeInfo(Context.SatShortAccumTy);
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case BuiltinType::SatUAccum:
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return getTypeInfo(Context.SatAccumTy);
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case BuiltinType::SatULongAccum:
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return getTypeInfo(Context.SatLongAccumTy);
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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 createScalarTypeNode(BTy->getName(Features), getChar(), Size);
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}
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}
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// C++1z [basic.lval]p10: "If a program attempts to access the stored value of
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// an object through a glvalue of other than one of the following types the
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// behavior is undefined: [...] a char, unsigned char, or std::byte type."
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if (Ty->isStdByteType())
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return getChar();
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// Handle pointers and references.
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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() || Ty->isReferenceType())
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return createScalarTypeNode("any pointer", getChar(), Size);
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// Accesses to arrays are accesses to objects of their element types.
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if (CodeGenOpts.NewStructPathTBAA && Ty->isArrayType())
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return getTypeInfo(cast<ArrayType>(Ty)->getElementType());
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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 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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return createScalarTypeNode(OutName, getChar(), Size);
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}
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if (const auto *EIT = dyn_cast<ExtIntType>(Ty)) {
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SmallString<256> OutName;
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llvm::raw_svector_ostream Out(OutName);
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// Don't specify signed/unsigned since integer types can alias despite sign
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// differences.
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Out << "_ExtInt(" << EIT->getNumBits() << ')';
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return createScalarTypeNode(OutName, getChar(), Size);
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}
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// For now, handle any other kind of type conservatively.
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return getChar();
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}
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llvm::MDNode *CodeGenTBAA::getTypeInfo(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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// We need this function to not fall back to returning the "omnipotent char"
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// type node for aggregate and union types. Otherwise, any dereference of an
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// aggregate will result into the may-alias access descriptor, meaning all
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// subsequent accesses to direct and indirect members of that aggregate will
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// be considered may-alias too.
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// TODO: Combine getTypeInfo() and getBaseTypeInfo() into a single function.
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if (isValidBaseType(QTy))
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return getBaseTypeInfo(QTy);
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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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// Note that the following helper call is allowed to add new nodes to the
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// cache, which invalidates all its previously obtained iterators. So we
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// first generate the node for the type and then add that node to the cache.
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llvm::MDNode *TypeNode = getTypeInfoHelper(Ty);
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return MetadataCache[Ty] = TypeNode;
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}
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TBAAAccessInfo CodeGenTBAA::getAccessInfo(QualType AccessType) {
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// Pointee values may have incomplete types, but they shall never be
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// dereferenced.
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if (AccessType->isIncompleteType())
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return TBAAAccessInfo::getIncompleteInfo();
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if (TypeHasMayAlias(AccessType))
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return TBAAAccessInfo::getMayAliasInfo();
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uint64_t Size = Context.getTypeSizeInChars(AccessType).getQuantity();
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return TBAAAccessInfo(getTypeInfo(AccessType), Size);
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}
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TBAAAccessInfo CodeGenTBAA::getVTablePtrAccessInfo(llvm::Type *VTablePtrType) {
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llvm::DataLayout DL(&Module);
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unsigned Size = DL.getPointerTypeSize(VTablePtrType);
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return TBAAAccessInfo(createScalarTypeNode("vtable pointer", getRoot(), Size),
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Size);
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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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if ((*i)->isZeroSize(Context) || (*i)->isUnnamedBitfield())
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continue;
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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 *TBAAType = MayAlias ? getChar() : getTypeInfo(QTy);
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llvm::MDNode *TBAATag = getAccessTagInfo(TBAAAccessInfo(TBAAType, Size));
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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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llvm::MDNode *CodeGenTBAA::getBaseTypeInfoHelper(const Type *Ty) {
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if (auto *TTy = dyn_cast<RecordType>(Ty)) {
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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<llvm::MDBuilder::TBAAStructField, 4> Fields;
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for (FieldDecl *Field : RD->fields()) {
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if (Field->isZeroSize(Context) || Field->isUnnamedBitfield())
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continue;
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QualType FieldQTy = Field->getType();
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llvm::MDNode *TypeNode = isValidBaseType(FieldQTy) ?
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getBaseTypeInfo(FieldQTy) : getTypeInfo(FieldQTy);
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if (!TypeNode)
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return BaseTypeMetadataCache[Ty] = nullptr;
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uint64_t BitOffset = Layout.getFieldOffset(Field->getFieldIndex());
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||
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|
uint64_t Offset = Context.toCharUnitsFromBits(BitOffset).getQuantity();
|
||
|
|
uint64_t Size = Context.getTypeSizeInChars(FieldQTy).getQuantity();
|
||
|
|
Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size,
|
||
|
|
TypeNode));
|
||
|
|
}
|
||
|
|
|
||
|
|
SmallString<256> OutName;
|
||
|
|
if (Features.CPlusPlus) {
|
||
|
|
// Don't use the mangler for C code.
|
||
|
|
llvm::raw_svector_ostream Out(OutName);
|
||
|
|
MContext.mangleTypeName(QualType(Ty, 0), Out);
|
||
|
|
} else {
|
||
|
|
OutName = RD->getName();
|
||
|
|
}
|
||
|
|
|
||
|
|
if (CodeGenOpts.NewStructPathTBAA) {
|
||
|
|
llvm::MDNode *Parent = getChar();
|
||
|
|
uint64_t Size = Context.getTypeSizeInChars(Ty).getQuantity();
|
||
|
|
llvm::Metadata *Id = MDHelper.createString(OutName);
|
||
|
|
return MDHelper.createTBAATypeNode(Parent, Size, Id, Fields);
|
||
|
|
}
|
||
|
|
|
||
|
|
// Create the struct type node with a vector of pairs (offset, type).
|
||
|
|
SmallVector<std::pair<llvm::MDNode*, uint64_t>, 4> OffsetsAndTypes;
|
||
|
|
for (const auto &Field : Fields)
|
||
|
|
OffsetsAndTypes.push_back(std::make_pair(Field.Type, Field.Offset));
|
||
|
|
return MDHelper.createTBAAStructTypeNode(OutName, OffsetsAndTypes);
|
||
|
|
}
|
||
|
|
|
||
|
|
return nullptr;
|
||
|
|
}
|
||
|
|
|
||
|
|
llvm::MDNode *CodeGenTBAA::getBaseTypeInfo(QualType QTy) {
|
||
|
|
if (!isValidBaseType(QTy))
|
||
|
|
return nullptr;
|
||
|
|
|
||
|
|
const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
|
||
|
|
if (llvm::MDNode *N = BaseTypeMetadataCache[Ty])
|
||
|
|
return N;
|
||
|
|
|
||
|
|
// Note that the following helper call is allowed to add new nodes to the
|
||
|
|
// cache, which invalidates all its previously obtained iterators. So we
|
||
|
|
// first generate the node for the type and then add that node to the cache.
|
||
|
|
llvm::MDNode *TypeNode = getBaseTypeInfoHelper(Ty);
|
||
|
|
return BaseTypeMetadataCache[Ty] = TypeNode;
|
||
|
|
}
|
||
|
|
|
||
|
|
llvm::MDNode *CodeGenTBAA::getAccessTagInfo(TBAAAccessInfo Info) {
|
||
|
|
assert(!Info.isIncomplete() && "Access to an object of an incomplete type!");
|
||
|
|
|
||
|
|
if (Info.isMayAlias())
|
||
|
|
Info = TBAAAccessInfo(getChar(), Info.Size);
|
||
|
|
|
||
|
|
if (!Info.AccessType)
|
||
|
|
return nullptr;
|
||
|
|
|
||
|
|
if (!CodeGenOpts.StructPathTBAA)
|
||
|
|
Info = TBAAAccessInfo(Info.AccessType, Info.Size);
|
||
|
|
|
||
|
|
llvm::MDNode *&N = AccessTagMetadataCache[Info];
|
||
|
|
if (N)
|
||
|
|
return N;
|
||
|
|
|
||
|
|
if (!Info.BaseType) {
|
||
|
|
Info.BaseType = Info.AccessType;
|
||
|
|
assert(!Info.Offset && "Nonzero offset for an access with no base type!");
|
||
|
|
}
|
||
|
|
if (CodeGenOpts.NewStructPathTBAA) {
|
||
|
|
return N = MDHelper.createTBAAAccessTag(Info.BaseType, Info.AccessType,
|
||
|
|
Info.Offset, Info.Size);
|
||
|
|
}
|
||
|
|
return N = MDHelper.createTBAAStructTagNode(Info.BaseType, Info.AccessType,
|
||
|
|
Info.Offset);
|
||
|
|
}
|
||
|
|
|
||
|
|
TBAAAccessInfo CodeGenTBAA::mergeTBAAInfoForCast(TBAAAccessInfo SourceInfo,
|
||
|
|
TBAAAccessInfo TargetInfo) {
|
||
|
|
if (SourceInfo.isMayAlias() || TargetInfo.isMayAlias())
|
||
|
|
return TBAAAccessInfo::getMayAliasInfo();
|
||
|
|
return TargetInfo;
|
||
|
|
}
|
||
|
|
|
||
|
|
TBAAAccessInfo
|
||
|
|
CodeGenTBAA::mergeTBAAInfoForConditionalOperator(TBAAAccessInfo InfoA,
|
||
|
|
TBAAAccessInfo InfoB) {
|
||
|
|
if (InfoA == InfoB)
|
||
|
|
return InfoA;
|
||
|
|
|
||
|
|
if (!InfoA || !InfoB)
|
||
|
|
return TBAAAccessInfo();
|
||
|
|
|
||
|
|
if (InfoA.isMayAlias() || InfoB.isMayAlias())
|
||
|
|
return TBAAAccessInfo::getMayAliasInfo();
|
||
|
|
|
||
|
|
// TODO: Implement the rest of the logic here. For example, two accesses
|
||
|
|
// with same final access types result in an access to an object of that final
|
||
|
|
// access type regardless of their base types.
|
||
|
|
return TBAAAccessInfo::getMayAliasInfo();
|
||
|
|
}
|
||
|
|
|
||
|
|
TBAAAccessInfo
|
||
|
|
CodeGenTBAA::mergeTBAAInfoForMemoryTransfer(TBAAAccessInfo DestInfo,
|
||
|
|
TBAAAccessInfo SrcInfo) {
|
||
|
|
if (DestInfo == SrcInfo)
|
||
|
|
return DestInfo;
|
||
|
|
|
||
|
|
if (!DestInfo || !SrcInfo)
|
||
|
|
return TBAAAccessInfo();
|
||
|
|
|
||
|
|
if (DestInfo.isMayAlias() || SrcInfo.isMayAlias())
|
||
|
|
return TBAAAccessInfo::getMayAliasInfo();
|
||
|
|
|
||
|
|
// TODO: Implement the rest of the logic here. For example, two accesses
|
||
|
|
// with same final access types result in an access to an object of that final
|
||
|
|
// access type regardless of their base types.
|
||
|
|
return TBAAAccessInfo::getMayAliasInfo();
|
||
|
|
}
|