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CheckExprLifetime.cpp
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CheckExprLifetime.cpp
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//===--- CheckExprLifetime.cpp --------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "CheckExprLifetime.h"
#include "clang/AST/Decl.h"
#include "clang/AST/Expr.h"
#include "clang/Basic/DiagnosticSema.h"
#include "clang/Sema/Initialization.h"
#include "clang/Sema/Sema.h"
#include "llvm/ADT/PointerIntPair.h"
namespace clang::sema {
namespace {
enum LifetimeKind {
/// The lifetime of a temporary bound to this entity ends at the end of the
/// full-expression, and that's (probably) fine.
LK_FullExpression,
/// The lifetime of a temporary bound to this entity is extended to the
/// lifeitme of the entity itself.
LK_Extended,
/// The lifetime of a temporary bound to this entity probably ends too soon,
/// because the entity is allocated in a new-expression.
LK_New,
/// The lifetime of a temporary bound to this entity ends too soon, because
/// the entity is a return object.
LK_Return,
/// The lifetime of a temporary bound to this entity ends too soon, because
/// the entity passed to a musttail function call.
LK_MustTail,
/// The lifetime of a temporary bound to this entity ends too soon, because
/// the entity is the result of a statement expression.
LK_StmtExprResult,
/// This is a mem-initializer: if it would extend a temporary (other than via
/// a default member initializer), the program is ill-formed.
LK_MemInitializer,
/// The lifetime of a temporary bound to this entity probably ends too soon,
/// because the entity is a pointer and we assign the address of a temporary
/// object to it.
LK_Assignment,
};
using LifetimeResult =
llvm::PointerIntPair<const InitializedEntity *, 3, LifetimeKind>;
} // namespace
/// Determine the declaration which an initialized entity ultimately refers to,
/// for the purpose of lifetime-extending a temporary bound to a reference in
/// the initialization of \p Entity.
static LifetimeResult
getEntityLifetime(const InitializedEntity *Entity,
const InitializedEntity *InitField = nullptr) {
// C++11 [class.temporary]p5:
switch (Entity->getKind()) {
case InitializedEntity::EK_Variable:
// The temporary [...] persists for the lifetime of the reference
return {Entity, LK_Extended};
case InitializedEntity::EK_Member:
// For subobjects, we look at the complete object.
if (Entity->getParent())
return getEntityLifetime(Entity->getParent(), Entity);
// except:
// C++17 [class.base.init]p8:
// A temporary expression bound to a reference member in a
// mem-initializer is ill-formed.
// C++17 [class.base.init]p11:
// A temporary expression bound to a reference member from a
// default member initializer is ill-formed.
//
// The context of p11 and its example suggest that it's only the use of a
// default member initializer from a constructor that makes the program
// ill-formed, not its mere existence, and that it can even be used by
// aggregate initialization.
return {Entity, Entity->isDefaultMemberInitializer() ? LK_Extended
: LK_MemInitializer};
case InitializedEntity::EK_Binding:
// Per [dcl.decomp]p3, the binding is treated as a variable of reference
// type.
return {Entity, LK_Extended};
case InitializedEntity::EK_Parameter:
case InitializedEntity::EK_Parameter_CF_Audited:
// -- A temporary bound to a reference parameter in a function call
// persists until the completion of the full-expression containing
// the call.
return {nullptr, LK_FullExpression};
case InitializedEntity::EK_TemplateParameter:
// FIXME: This will always be ill-formed; should we eagerly diagnose it
// here?
return {nullptr, LK_FullExpression};
case InitializedEntity::EK_Result:
// -- The lifetime of a temporary bound to the returned value in a
// function return statement is not extended; the temporary is
// destroyed at the end of the full-expression in the return statement.
return {nullptr, LK_Return};
case InitializedEntity::EK_StmtExprResult:
// FIXME: Should we lifetime-extend through the result of a statement
// expression?
return {nullptr, LK_StmtExprResult};
case InitializedEntity::EK_New:
// -- A temporary bound to a reference in a new-initializer persists
// until the completion of the full-expression containing the
// new-initializer.
return {nullptr, LK_New};
case InitializedEntity::EK_Temporary:
case InitializedEntity::EK_CompoundLiteralInit:
case InitializedEntity::EK_RelatedResult:
// We don't yet know the storage duration of the surrounding temporary.
// Assume it's got full-expression duration for now, it will patch up our
// storage duration if that's not correct.
return {nullptr, LK_FullExpression};
case InitializedEntity::EK_ArrayElement:
// For subobjects, we look at the complete object.
return getEntityLifetime(Entity->getParent(), InitField);
case InitializedEntity::EK_Base:
// For subobjects, we look at the complete object.
if (Entity->getParent())
return getEntityLifetime(Entity->getParent(), InitField);
return {InitField, LK_MemInitializer};
case InitializedEntity::EK_Delegating:
// We can reach this case for aggregate initialization in a constructor:
// struct A { int &&r; };
// struct B : A { B() : A{0} {} };
// In this case, use the outermost field decl as the context.
return {InitField, LK_MemInitializer};
case InitializedEntity::EK_BlockElement:
case InitializedEntity::EK_LambdaToBlockConversionBlockElement:
case InitializedEntity::EK_LambdaCapture:
case InitializedEntity::EK_VectorElement:
case InitializedEntity::EK_ComplexElement:
return {nullptr, LK_FullExpression};
case InitializedEntity::EK_Exception:
// FIXME: Can we diagnose lifetime problems with exceptions?
return {nullptr, LK_FullExpression};
case InitializedEntity::EK_ParenAggInitMember:
// -- A temporary object bound to a reference element of an aggregate of
// class type initialized from a parenthesized expression-list
// [dcl.init, 9.3] persists until the completion of the full-expression
// containing the expression-list.
return {nullptr, LK_FullExpression};
}
llvm_unreachable("unknown entity kind");
}
namespace {
enum ReferenceKind {
/// Lifetime would be extended by a reference binding to a temporary.
RK_ReferenceBinding,
/// Lifetime would be extended by a std::initializer_list object binding to
/// its backing array.
RK_StdInitializerList,
};
/// A temporary or local variable. This will be one of:
/// * A MaterializeTemporaryExpr.
/// * A DeclRefExpr whose declaration is a local.
/// * An AddrLabelExpr.
/// * A BlockExpr for a block with captures.
using Local = Expr *;
/// Expressions we stepped over when looking for the local state. Any steps
/// that would inhibit lifetime extension or take us out of subexpressions of
/// the initializer are included.
struct IndirectLocalPathEntry {
enum EntryKind {
DefaultInit,
AddressOf,
VarInit,
LValToRVal,
LifetimeBoundCall,
TemporaryCopy,
LambdaCaptureInit,
GslReferenceInit,
GslPointerInit,
GslPointerAssignment,
DefaultArg,
} Kind;
Expr *E;
union {
const Decl *D = nullptr;
const LambdaCapture *Capture;
};
IndirectLocalPathEntry() {}
IndirectLocalPathEntry(EntryKind K, Expr *E) : Kind(K), E(E) {}
IndirectLocalPathEntry(EntryKind K, Expr *E, const Decl *D)
: Kind(K), E(E), D(D) {}
IndirectLocalPathEntry(EntryKind K, Expr *E, const LambdaCapture *Capture)
: Kind(K), E(E), Capture(Capture) {}
};
using IndirectLocalPath = llvm::SmallVectorImpl<IndirectLocalPathEntry>;
struct RevertToOldSizeRAII {
IndirectLocalPath &Path;
unsigned OldSize = Path.size();
RevertToOldSizeRAII(IndirectLocalPath &Path) : Path(Path) {}
~RevertToOldSizeRAII() { Path.resize(OldSize); }
};
using LocalVisitor = llvm::function_ref<bool(IndirectLocalPath &Path, Local L,
ReferenceKind RK)>;
} // namespace
static bool isVarOnPath(IndirectLocalPath &Path, VarDecl *VD) {
for (auto E : Path)
if (E.Kind == IndirectLocalPathEntry::VarInit && E.D == VD)
return true;
return false;
}
static bool pathContainsInit(IndirectLocalPath &Path) {
return llvm::any_of(Path, [=](IndirectLocalPathEntry E) {
return E.Kind == IndirectLocalPathEntry::DefaultInit ||
E.Kind == IndirectLocalPathEntry::VarInit;
});
}
static void visitLocalsRetainedByInitializer(IndirectLocalPath &Path,
Expr *Init, LocalVisitor Visit,
bool RevisitSubinits);
static void visitLocalsRetainedByReferenceBinding(IndirectLocalPath &Path,
Expr *Init, ReferenceKind RK,
LocalVisitor Visit);
template <typename T> static bool isRecordWithAttr(QualType Type) {
if (auto *RD = Type->getAsCXXRecordDecl())
return RD->hasAttr<T>();
return false;
}
// Decl::isInStdNamespace will return false for iterators in some STL
// implementations due to them being defined in a namespace outside of the std
// namespace.
static bool isInStlNamespace(const Decl *D) {
const DeclContext *DC = D->getDeclContext();
if (!DC)
return false;
if (const auto *ND = dyn_cast<NamespaceDecl>(DC))
if (const IdentifierInfo *II = ND->getIdentifier()) {
StringRef Name = II->getName();
if (Name.size() >= 2 && Name.front() == '_' &&
(Name[1] == '_' || isUppercase(Name[1])))
return true;
}
return DC->isStdNamespace();
}
static bool isPointerLikeType(QualType Type) {
return isRecordWithAttr<PointerAttr>(Type) || Type->isPointerType() ||
Type->isNullPtrType();
}
// Returns true if the given Record decl is a form of `GSLOwner<Pointer>`
// type, e.g. std::vector<string_view>, std::optional<string_view>.
static bool isContainerOfPointer(const RecordDecl *Container) {
if (const auto *CTSD =
dyn_cast_if_present<ClassTemplateSpecializationDecl>(Container)) {
if (!CTSD->hasAttr<OwnerAttr>()) // Container must be a GSL owner type.
return false;
const auto &TAs = CTSD->getTemplateArgs();
return TAs.size() > 0 && TAs[0].getKind() == TemplateArgument::Type &&
isPointerLikeType(TAs[0].getAsType());
}
return false;
}
static bool isContainerOfOwner(const RecordDecl *Container) {
const auto *CTSD =
dyn_cast_if_present<ClassTemplateSpecializationDecl>(Container);
if (!CTSD)
return false;
if (!CTSD->hasAttr<OwnerAttr>()) // Container must be a GSL owner type.
return false;
const auto &TAs = CTSD->getTemplateArgs();
return TAs.size() > 0 && TAs[0].getKind() == TemplateArgument::Type &&
isRecordWithAttr<OwnerAttr>(TAs[0].getAsType());
}
// Returns true if the given Record is `std::initializer_list<pointer>`.
static bool isStdInitializerListOfPointer(const RecordDecl *RD) {
if (const auto *CTSD =
dyn_cast_if_present<ClassTemplateSpecializationDecl>(RD)) {
const auto &TAs = CTSD->getTemplateArgs();
return isInStlNamespace(RD) && RD->getIdentifier() &&
RD->getName() == "initializer_list" && TAs.size() > 0 &&
TAs[0].getKind() == TemplateArgument::Type &&
isPointerLikeType(TAs[0].getAsType());
}
return false;
}
static bool shouldTrackImplicitObjectArg(const CXXMethodDecl *Callee) {
if (auto *Conv = dyn_cast_or_null<CXXConversionDecl>(Callee))
if (isRecordWithAttr<PointerAttr>(Conv->getConversionType()) &&
Callee->getParent()->hasAttr<OwnerAttr>())
return true;
if (!isInStlNamespace(Callee->getParent()))
return false;
if (!isRecordWithAttr<PointerAttr>(
Callee->getFunctionObjectParameterType()) &&
!isRecordWithAttr<OwnerAttr>(Callee->getFunctionObjectParameterType()))
return false;
if (isPointerLikeType(Callee->getReturnType())) {
if (!Callee->getIdentifier())
return false;
return llvm::StringSwitch<bool>(Callee->getName())
.Cases("begin", "rbegin", "cbegin", "crbegin", true)
.Cases("end", "rend", "cend", "crend", true)
.Cases("c_str", "data", "get", true)
// Map and set types.
.Cases("find", "equal_range", "lower_bound", "upper_bound", true)
.Default(false);
}
if (Callee->getReturnType()->isReferenceType()) {
if (!Callee->getIdentifier()) {
auto OO = Callee->getOverloadedOperator();
return OO == OverloadedOperatorKind::OO_Subscript ||
OO == OverloadedOperatorKind::OO_Star;
}
return llvm::StringSwitch<bool>(Callee->getName())
.Cases("front", "back", "at", "top", "value", true)
.Default(false);
}
return false;
}
static bool shouldTrackFirstArgument(const FunctionDecl *FD) {
if (!FD->getIdentifier() || FD->getNumParams() != 1)
return false;
const auto *RD = FD->getParamDecl(0)->getType()->getPointeeCXXRecordDecl();
if (!FD->isInStdNamespace() || !RD || !RD->isInStdNamespace())
return false;
if (!RD->hasAttr<PointerAttr>() && !RD->hasAttr<OwnerAttr>())
return false;
if (FD->getReturnType()->isPointerType() ||
isRecordWithAttr<PointerAttr>(FD->getReturnType())) {
return llvm::StringSwitch<bool>(FD->getName())
.Cases("begin", "rbegin", "cbegin", "crbegin", true)
.Cases("end", "rend", "cend", "crend", true)
.Case("data", true)
.Default(false);
}
if (FD->getReturnType()->isReferenceType()) {
return llvm::StringSwitch<bool>(FD->getName())
.Cases("get", "any_cast", true)
.Default(false);
}
return false;
}
// Returns true if the given constructor is a copy-like constructor, such as
// `Ctor(Owner<U>&&)` or `Ctor(const Owner<U>&)`.
static bool isCopyLikeConstructor(const CXXConstructorDecl *Ctor) {
if (!Ctor || Ctor->param_size() != 1)
return false;
const auto *ParamRefType =
Ctor->getParamDecl(0)->getType()->getAs<ReferenceType>();
if (!ParamRefType)
return false;
// Check if the first parameter type is "Owner<U>".
if (const auto *TST =
ParamRefType->getPointeeType()->getAs<TemplateSpecializationType>())
return TST->getTemplateName()
.getAsTemplateDecl()
->getTemplatedDecl()
->hasAttr<OwnerAttr>();
return false;
}
// Returns true if we should perform the GSL analysis on the first argument for
// the given constructor.
static bool
shouldTrackFirstArgumentForConstructor(const CXXConstructExpr *Ctor) {
const auto *LHSRecordDecl = Ctor->getConstructor()->getParent();
// Case 1, construct a GSL pointer, e.g. std::string_view
// Always inspect when LHS is a pointer.
if (LHSRecordDecl->hasAttr<PointerAttr>())
return true;
if (Ctor->getConstructor()->param_empty() ||
!isContainerOfPointer(LHSRecordDecl))
return false;
// Now, the LHS is an Owner<Pointer> type, e.g., std::vector<string_view>.
//
// At a high level, we cannot precisely determine what the nested pointer
// owns. However, by analyzing the RHS owner type, we can use heuristics to
// infer ownership information. These heuristics are designed to be
// conservative, minimizing false positives while still providing meaningful
// diagnostics.
//
// While this inference isn't perfect, it helps catch common use-after-free
// patterns.
auto RHSArgType = Ctor->getArg(0)->getType();
const auto *RHSRD = RHSArgType->getAsRecordDecl();
// LHS is constructed from an intializer_list.
//
// std::initializer_list is a proxy object that provides access to the backing
// array. We perform analysis on it to determine if there are any dangling
// temporaries in the backing array.
// E.g. std::vector<string_view> abc = {string()};
if (isStdInitializerListOfPointer(RHSRD))
return true;
// RHS must be an owner.
if (!isRecordWithAttr<OwnerAttr>(RHSArgType))
return false;
// Bail out if the RHS is Owner<Pointer>.
//
// We cannot reliably determine what the LHS nested pointer owns -- it could
// be the entire RHS or the nested pointer in RHS. To avoid false positives,
// we skip this case, such as:
// std::stack<std::string_view> s(std::deque<std::string_view>{});
//
// TODO: this also has a false negative, it doesn't catch the case like:
// std::optional<span<int*>> os = std::vector<int*>{}
if (isContainerOfPointer(RHSRD))
return false;
// Assume that the nested Pointer is constructed from the nested Owner.
// E.g. std::optional<string_view> sv = std::optional<string>(s);
if (isContainerOfOwner(RHSRD))
return true;
// Now, the LHS is an Owner<Pointer> and the RHS is an Owner<X>, where X is
// neither an `Owner` nor a `Pointer`.
//
// Use the constructor's signature as a hint. If it is a copy-like constructor
// `Owner1<Pointer>(Owner2<X>&&)`, we assume that the nested pointer is
// constructed from X. In such cases, we do not diagnose, as `X` is not an
// owner, e.g.
// std::optional<string_view> sv = std::optional<Foo>();
if (const auto *PrimaryCtorTemplate =
Ctor->getConstructor()->getPrimaryTemplate();
PrimaryCtorTemplate &&
isCopyLikeConstructor(dyn_cast_if_present<CXXConstructorDecl>(
PrimaryCtorTemplate->getTemplatedDecl()))) {
return false;
}
// Assume that the nested pointer is constructed from the whole RHS.
// E.g. optional<string_view> s = std::string();
return true;
}
// Return true if this is an "normal" assignment operator.
// We assuments that a normal assingment operator always returns *this, that is,
// an lvalue reference that is the same type as the implicit object parameter
// (or the LHS for a non-member operator$=).
static bool isNormalAssignmentOperator(const FunctionDecl *FD) {
OverloadedOperatorKind OO = FD->getDeclName().getCXXOverloadedOperator();
if (OO == OO_Equal || isCompoundAssignmentOperator(OO)) {
QualType RetT = FD->getReturnType();
if (RetT->isLValueReferenceType()) {
ASTContext &Ctx = FD->getASTContext();
QualType LHST;
auto *MD = dyn_cast<CXXMethodDecl>(FD);
if (MD && MD->isCXXInstanceMember())
LHST = Ctx.getLValueReferenceType(MD->getFunctionObjectParameterType());
else
LHST = MD->getParamDecl(0)->getType();
if (Ctx.hasSameType(RetT, LHST))
return true;
}
}
return false;
}
static bool implicitObjectParamIsLifetimeBound(const FunctionDecl *FD) {
const TypeSourceInfo *TSI = FD->getTypeSourceInfo();
if (!TSI)
return false;
// Don't declare this variable in the second operand of the for-statement;
// GCC miscompiles that by ending its lifetime before evaluating the
// third operand. See gcc.gnu.org/PR86769.
AttributedTypeLoc ATL;
for (TypeLoc TL = TSI->getTypeLoc();
(ATL = TL.getAsAdjusted<AttributedTypeLoc>());
TL = ATL.getModifiedLoc()) {
if (ATL.getAttrAs<LifetimeBoundAttr>())
return true;
}
return isNormalAssignmentOperator(FD);
}
// Visit lifetimebound or gsl-pointer arguments.
static void visitFunctionCallArguments(IndirectLocalPath &Path, Expr *Call,
LocalVisitor Visit) {
const FunctionDecl *Callee;
ArrayRef<Expr *> Args;
if (auto *CE = dyn_cast<CallExpr>(Call)) {
Callee = CE->getDirectCallee();
Args = llvm::ArrayRef(CE->getArgs(), CE->getNumArgs());
} else {
auto *CCE = cast<CXXConstructExpr>(Call);
Callee = CCE->getConstructor();
Args = llvm::ArrayRef(CCE->getArgs(), CCE->getNumArgs());
}
if (!Callee)
return;
bool EnableGSLAnalysis = !Callee->getASTContext().getDiagnostics().isIgnored(
diag::warn_dangling_lifetime_pointer, SourceLocation());
Expr *ObjectArg = nullptr;
if (isa<CXXOperatorCallExpr>(Call) && Callee->isCXXInstanceMember()) {
ObjectArg = Args[0];
Args = Args.slice(1);
} else if (auto *MCE = dyn_cast<CXXMemberCallExpr>(Call)) {
ObjectArg = MCE->getImplicitObjectArgument();
}
auto VisitLifetimeBoundArg = [&](const Decl *D, Expr *Arg) {
Path.push_back({IndirectLocalPathEntry::LifetimeBoundCall, Arg, D});
if (Arg->isGLValue())
visitLocalsRetainedByReferenceBinding(Path, Arg, RK_ReferenceBinding,
Visit);
else
visitLocalsRetainedByInitializer(Path, Arg, Visit, true);
Path.pop_back();
};
auto VisitGSLPointerArg = [&](const FunctionDecl *Callee, Expr *Arg) {
// We are not interested in the temporary base objects of gsl Pointers:
// Temp().ptr; // Here ptr might not dangle.
if (isa<MemberExpr>(Arg->IgnoreImpCasts()))
return;
auto ReturnType = Callee->getReturnType();
// Once we initialized a value with a non gsl-owner reference, it can no
// longer dangle.
if (ReturnType->isReferenceType() &&
!isRecordWithAttr<OwnerAttr>(ReturnType->getPointeeType())) {
for (const IndirectLocalPathEntry &PE : llvm::reverse(Path)) {
if (PE.Kind == IndirectLocalPathEntry::GslReferenceInit ||
PE.Kind == IndirectLocalPathEntry::LifetimeBoundCall)
continue;
if (PE.Kind == IndirectLocalPathEntry::GslPointerInit ||
PE.Kind == IndirectLocalPathEntry::GslPointerAssignment)
return;
break;
}
}
Path.push_back({ReturnType->isReferenceType()
? IndirectLocalPathEntry::GslReferenceInit
: IndirectLocalPathEntry::GslPointerInit,
Arg, Callee});
if (Arg->isGLValue())
visitLocalsRetainedByReferenceBinding(Path, Arg, RK_ReferenceBinding,
Visit);
else
visitLocalsRetainedByInitializer(Path, Arg, Visit, true);
Path.pop_back();
};
bool CheckCoroCall = false;
if (const auto *RD = Callee->getReturnType()->getAsRecordDecl()) {
CheckCoroCall = RD->hasAttr<CoroLifetimeBoundAttr>() &&
RD->hasAttr<CoroReturnTypeAttr>() &&
!Callee->hasAttr<CoroDisableLifetimeBoundAttr>();
}
if (ObjectArg) {
bool CheckCoroObjArg = CheckCoroCall;
// Coroutine lambda objects with empty capture list are not lifetimebound.
if (auto *LE = dyn_cast<LambdaExpr>(ObjectArg->IgnoreImplicit());
LE && LE->captures().empty())
CheckCoroObjArg = false;
// Allow `get_return_object()` as the object param (__promise) is not
// lifetimebound.
if (Sema::CanBeGetReturnObject(Callee))
CheckCoroObjArg = false;
if (implicitObjectParamIsLifetimeBound(Callee) || CheckCoroObjArg)
VisitLifetimeBoundArg(Callee, ObjectArg);
else if (EnableGSLAnalysis) {
if (auto *CME = dyn_cast<CXXMethodDecl>(Callee);
CME && shouldTrackImplicitObjectArg(CME))
VisitGSLPointerArg(Callee, ObjectArg);
}
}
for (unsigned I = 0,
N = std::min<unsigned>(Callee->getNumParams(), Args.size());
I != N; ++I) {
Expr *Arg = Args[I];
RevertToOldSizeRAII RAII(Path);
if (auto *DAE = dyn_cast<CXXDefaultArgExpr>(Arg)) {
Path.push_back(
{IndirectLocalPathEntry::DefaultArg, DAE, DAE->getParam()});
Arg = DAE->getExpr();
}
if (CheckCoroCall || Callee->getParamDecl(I)->hasAttr<LifetimeBoundAttr>())
VisitLifetimeBoundArg(Callee->getParamDecl(I), Arg);
else if (EnableGSLAnalysis && I == 0) {
// Perform GSL analysis for the first argument
if (shouldTrackFirstArgument(Callee)) {
VisitGSLPointerArg(Callee, Arg);
} else if (auto *Ctor = dyn_cast<CXXConstructExpr>(Call);
Ctor && shouldTrackFirstArgumentForConstructor(Ctor)) {
VisitGSLPointerArg(Ctor->getConstructor(), Arg);
}
}
}
}
/// Visit the locals that would be reachable through a reference bound to the
/// glvalue expression \c Init.
static void visitLocalsRetainedByReferenceBinding(IndirectLocalPath &Path,
Expr *Init, ReferenceKind RK,
LocalVisitor Visit) {
RevertToOldSizeRAII RAII(Path);
// Walk past any constructs which we can lifetime-extend across.
Expr *Old;
do {
Old = Init;
if (auto *FE = dyn_cast<FullExpr>(Init))
Init = FE->getSubExpr();
if (InitListExpr *ILE = dyn_cast<InitListExpr>(Init)) {
// If this is just redundant braces around an initializer, step over it.
if (ILE->isTransparent())
Init = ILE->getInit(0);
}
// Step over any subobject adjustments; we may have a materialized
// temporary inside them.
Init = const_cast<Expr *>(Init->skipRValueSubobjectAdjustments());
// Per current approach for DR1376, look through casts to reference type
// when performing lifetime extension.
if (CastExpr *CE = dyn_cast<CastExpr>(Init))
if (CE->getSubExpr()->isGLValue())
Init = CE->getSubExpr();
// Per the current approach for DR1299, look through array element access
// on array glvalues when performing lifetime extension.
if (auto *ASE = dyn_cast<ArraySubscriptExpr>(Init)) {
Init = ASE->getBase();
auto *ICE = dyn_cast<ImplicitCastExpr>(Init);
if (ICE && ICE->getCastKind() == CK_ArrayToPointerDecay)
Init = ICE->getSubExpr();
else
// We can't lifetime extend through this but we might still find some
// retained temporaries.
return visitLocalsRetainedByInitializer(Path, Init, Visit, true);
}
// Step into CXXDefaultInitExprs so we can diagnose cases where a
// constructor inherits one as an implicit mem-initializer.
if (auto *DIE = dyn_cast<CXXDefaultInitExpr>(Init)) {
Path.push_back(
{IndirectLocalPathEntry::DefaultInit, DIE, DIE->getField()});
Init = DIE->getExpr();
}
} while (Init != Old);
if (auto *MTE = dyn_cast<MaterializeTemporaryExpr>(Init)) {
if (Visit(Path, Local(MTE), RK))
visitLocalsRetainedByInitializer(Path, MTE->getSubExpr(), Visit, true);
}
if (auto *M = dyn_cast<MemberExpr>(Init)) {
// Lifetime of a non-reference type field is same as base object.
if (auto *F = dyn_cast<FieldDecl>(M->getMemberDecl());
F && !F->getType()->isReferenceType())
visitLocalsRetainedByInitializer(Path, M->getBase(), Visit, true);
}
if (isa<CallExpr>(Init))
return visitFunctionCallArguments(Path, Init, Visit);
switch (Init->getStmtClass()) {
case Stmt::DeclRefExprClass: {
// If we find the name of a local non-reference parameter, we could have a
// lifetime problem.
auto *DRE = cast<DeclRefExpr>(Init);
auto *VD = dyn_cast<VarDecl>(DRE->getDecl());
if (VD && VD->hasLocalStorage() &&
!DRE->refersToEnclosingVariableOrCapture()) {
if (!VD->getType()->isReferenceType()) {
Visit(Path, Local(DRE), RK);
} else if (isa<ParmVarDecl>(DRE->getDecl())) {
// The lifetime of a reference parameter is unknown; assume it's OK
// for now.
break;
} else if (VD->getInit() && !isVarOnPath(Path, VD)) {
Path.push_back({IndirectLocalPathEntry::VarInit, DRE, VD});
visitLocalsRetainedByReferenceBinding(Path, VD->getInit(),
RK_ReferenceBinding, Visit);
}
}
break;
}
case Stmt::UnaryOperatorClass: {
// The only unary operator that make sense to handle here
// is Deref. All others don't resolve to a "name." This includes
// handling all sorts of rvalues passed to a unary operator.
const UnaryOperator *U = cast<UnaryOperator>(Init);
if (U->getOpcode() == UO_Deref)
visitLocalsRetainedByInitializer(Path, U->getSubExpr(), Visit, true);
break;
}
case Stmt::ArraySectionExprClass: {
visitLocalsRetainedByInitializer(
Path, cast<ArraySectionExpr>(Init)->getBase(), Visit, true);
break;
}
case Stmt::ConditionalOperatorClass:
case Stmt::BinaryConditionalOperatorClass: {
auto *C = cast<AbstractConditionalOperator>(Init);
if (!C->getTrueExpr()->getType()->isVoidType())
visitLocalsRetainedByReferenceBinding(Path, C->getTrueExpr(), RK, Visit);
if (!C->getFalseExpr()->getType()->isVoidType())
visitLocalsRetainedByReferenceBinding(Path, C->getFalseExpr(), RK, Visit);
break;
}
case Stmt::CompoundLiteralExprClass: {
if (auto *CLE = dyn_cast<CompoundLiteralExpr>(Init)) {
if (!CLE->isFileScope())
Visit(Path, Local(CLE), RK);
}
break;
}
// FIXME: Visit the left-hand side of an -> or ->*.
default:
break;
}
}
/// Visit the locals that would be reachable through an object initialized by
/// the prvalue expression \c Init.
static void visitLocalsRetainedByInitializer(IndirectLocalPath &Path,
Expr *Init, LocalVisitor Visit,
bool RevisitSubinits) {
RevertToOldSizeRAII RAII(Path);
Expr *Old;
do {
Old = Init;
// Step into CXXDefaultInitExprs so we can diagnose cases where a
// constructor inherits one as an implicit mem-initializer.
if (auto *DIE = dyn_cast<CXXDefaultInitExpr>(Init)) {
Path.push_back(
{IndirectLocalPathEntry::DefaultInit, DIE, DIE->getField()});
Init = DIE->getExpr();
}
if (auto *FE = dyn_cast<FullExpr>(Init))
Init = FE->getSubExpr();
// Dig out the expression which constructs the extended temporary.
Init = const_cast<Expr *>(Init->skipRValueSubobjectAdjustments());
if (CXXBindTemporaryExpr *BTE = dyn_cast<CXXBindTemporaryExpr>(Init))
Init = BTE->getSubExpr();
Init = Init->IgnoreParens();
// Step over value-preserving rvalue casts.
if (auto *CE = dyn_cast<CastExpr>(Init)) {
switch (CE->getCastKind()) {
case CK_LValueToRValue:
// If we can match the lvalue to a const object, we can look at its
// initializer.
Path.push_back({IndirectLocalPathEntry::LValToRVal, CE});
return visitLocalsRetainedByReferenceBinding(
Path, Init, RK_ReferenceBinding,
[&](IndirectLocalPath &Path, Local L, ReferenceKind RK) -> bool {
if (auto *DRE = dyn_cast<DeclRefExpr>(L)) {
auto *VD = dyn_cast<VarDecl>(DRE->getDecl());
if (VD && VD->getType().isConstQualified() && VD->getInit() &&
!isVarOnPath(Path, VD)) {
Path.push_back({IndirectLocalPathEntry::VarInit, DRE, VD});
visitLocalsRetainedByInitializer(Path, VD->getInit(), Visit,
true);
}
} else if (auto *MTE = dyn_cast<MaterializeTemporaryExpr>(L)) {
if (MTE->getType().isConstQualified())
visitLocalsRetainedByInitializer(Path, MTE->getSubExpr(),
Visit, true);
}
return false;
});
// We assume that objects can be retained by pointers cast to integers,
// but not if the integer is cast to floating-point type or to _Complex.
// We assume that casts to 'bool' do not preserve enough information to
// retain a local object.
case CK_NoOp:
case CK_BitCast:
case CK_BaseToDerived:
case CK_DerivedToBase:
case CK_UncheckedDerivedToBase:
case CK_Dynamic:
case CK_ToUnion:
case CK_UserDefinedConversion:
case CK_ConstructorConversion:
case CK_IntegralToPointer:
case CK_PointerToIntegral:
case CK_VectorSplat:
case CK_IntegralCast:
case CK_CPointerToObjCPointerCast:
case CK_BlockPointerToObjCPointerCast:
case CK_AnyPointerToBlockPointerCast:
case CK_AddressSpaceConversion:
break;
case CK_ArrayToPointerDecay:
// Model array-to-pointer decay as taking the address of the array
// lvalue.
Path.push_back({IndirectLocalPathEntry::AddressOf, CE});
return visitLocalsRetainedByReferenceBinding(
Path, CE->getSubExpr(), RK_ReferenceBinding, Visit);
default:
return;
}
Init = CE->getSubExpr();
}
} while (Old != Init);
// C++17 [dcl.init.list]p6:
// initializing an initializer_list object from the array extends the
// lifetime of the array exactly like binding a reference to a temporary.
if (auto *ILE = dyn_cast<CXXStdInitializerListExpr>(Init))
return visitLocalsRetainedByReferenceBinding(Path, ILE->getSubExpr(),
RK_StdInitializerList, Visit);
if (InitListExpr *ILE = dyn_cast<InitListExpr>(Init)) {
// We already visited the elements of this initializer list while
// performing the initialization. Don't visit them again unless we've
// changed the lifetime of the initialized entity.
if (!RevisitSubinits)
return;
if (ILE->isTransparent())
return visitLocalsRetainedByInitializer(Path, ILE->getInit(0), Visit,
RevisitSubinits);
if (ILE->getType()->isArrayType()) {
for (unsigned I = 0, N = ILE->getNumInits(); I != N; ++I)
visitLocalsRetainedByInitializer(Path, ILE->getInit(I), Visit,
RevisitSubinits);
return;
}
if (CXXRecordDecl *RD = ILE->getType()->getAsCXXRecordDecl()) {
assert(RD->isAggregate() && "aggregate init on non-aggregate");
// If we lifetime-extend a braced initializer which is initializing an
// aggregate, and that aggregate contains reference members which are
// bound to temporaries, those temporaries are also lifetime-extended.
if (RD->isUnion() && ILE->getInitializedFieldInUnion() &&
ILE->getInitializedFieldInUnion()->getType()->isReferenceType())
visitLocalsRetainedByReferenceBinding(Path, ILE->getInit(0),
RK_ReferenceBinding, Visit);
else {
unsigned Index = 0;
for (; Index < RD->getNumBases() && Index < ILE->getNumInits(); ++Index)
visitLocalsRetainedByInitializer(Path, ILE->getInit(Index), Visit,
RevisitSubinits);
for (const auto *I : RD->fields()) {
if (Index >= ILE->getNumInits())
break;
if (I->isUnnamedBitField())
continue;
Expr *SubInit = ILE->getInit(Index);
if (I->getType()->isReferenceType())
visitLocalsRetainedByReferenceBinding(Path, SubInit,
RK_ReferenceBinding, Visit);
else
// This might be either aggregate-initialization of a member or
// initialization of a std::initializer_list object. Regardless,
// we should recursively lifetime-extend that initializer.
visitLocalsRetainedByInitializer(Path, SubInit, Visit,
RevisitSubinits);
++Index;
}
}
}
return;
}
// The lifetime of an init-capture is that of the closure object constructed
// by a lambda-expression.
if (auto *LE = dyn_cast<LambdaExpr>(Init)) {
LambdaExpr::capture_iterator CapI = LE->capture_begin();
for (Expr *E : LE->capture_inits()) {
assert(CapI != LE->capture_end());
const LambdaCapture &Cap = *CapI++;
if (!E)
continue;
if (Cap.capturesVariable())
Path.push_back({IndirectLocalPathEntry::LambdaCaptureInit, E, &Cap});
if (E->isGLValue())
visitLocalsRetainedByReferenceBinding(Path, E, RK_ReferenceBinding,
Visit);
else
visitLocalsRetainedByInitializer(Path, E, Visit, true);
if (Cap.capturesVariable())
Path.pop_back();
}
}
// Assume that a copy or move from a temporary references the same objects
// that the temporary does.
if (auto *CCE = dyn_cast<CXXConstructExpr>(Init)) {
if (CCE->getConstructor()->isCopyOrMoveConstructor()) {
if (auto *MTE = dyn_cast<MaterializeTemporaryExpr>(CCE->getArg(0))) {
Expr *Arg = MTE->getSubExpr();
Path.push_back({IndirectLocalPathEntry::TemporaryCopy, Arg,
CCE->getConstructor()});
visitLocalsRetainedByInitializer(Path, Arg, Visit, true);
Path.pop_back();
}
}
}
if (isa<CallExpr>(Init) || isa<CXXConstructExpr>(Init))
return visitFunctionCallArguments(Path, Init, Visit);
switch (Init->getStmtClass()) {
case Stmt::UnaryOperatorClass: {
auto *UO = cast<UnaryOperator>(Init);
// If the initializer is the address of a local, we could have a lifetime
// problem.
if (UO->getOpcode() == UO_AddrOf) {
// If this is &rvalue, then it's ill-formed and we have already diagnosed
// it. Don't produce a redundant warning about the lifetime of the
// temporary.
if (isa<MaterializeTemporaryExpr>(UO->getSubExpr()))
return;
Path.push_back({IndirectLocalPathEntry::AddressOf, UO});
visitLocalsRetainedByReferenceBinding(Path, UO->getSubExpr(),
RK_ReferenceBinding, Visit);
}
break;
}
case Stmt::BinaryOperatorClass: {
// Handle pointer arithmetic.
auto *BO = cast<BinaryOperator>(Init);
BinaryOperatorKind BOK = BO->getOpcode();
if (!BO->getType()->isPointerType() || (BOK != BO_Add && BOK != BO_Sub))
break;
if (BO->getLHS()->getType()->isPointerType())
visitLocalsRetainedByInitializer(Path, BO->getLHS(), Visit, true);
else if (BO->getRHS()->getType()->isPointerType())
visitLocalsRetainedByInitializer(Path, BO->getRHS(), Visit, true);
break;
}
case Stmt::ConditionalOperatorClass:
case Stmt::BinaryConditionalOperatorClass: {
auto *C = cast<AbstractConditionalOperator>(Init);
// In C++, we can have a throw-expression operand, which has 'void' type
// and isn't interesting from a lifetime perspective.
if (!C->getTrueExpr()->getType()->isVoidType())
visitLocalsRetainedByInitializer(Path, C->getTrueExpr(), Visit, true);
if (!C->getFalseExpr()->getType()->isVoidType())