diff options
author | Richard Smith <richard-llvm@metafoo.co.uk> | 2018-07-17 00:11:41 +0000 |
---|---|---|
committer | Richard Smith <richard-llvm@metafoo.co.uk> | 2018-07-17 00:11:41 +0000 |
commit | bd8c87930bc3817282e4c040c16a90a66ca7f267 (patch) | |
tree | 29a3c5673d9fcd678f97f311c03732c30fd973cf /lib/Sema | |
parent | 3ad62f50a0a775140c6c35308ade2f2caea67ed1 (diff) |
Restructure checking for, and warning on, lifetime extension.
This change implements C++ DR1696, which makes initialization of a
reference member of a class from a temporary object ill-formed. The
standard wording here is imprecise, but we interpret it as meaning that
any time a mem-initializer would result in lifetime extension, the
program is ill-formed.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@337226 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Sema')
-rw-r--r-- | lib/Sema/SemaDeclCXX.cpp | 7 | ||||
-rw-r--r-- | lib/Sema/SemaExprCXX.cpp | 7 | ||||
-rw-r--r-- | lib/Sema/SemaInit.cpp | 370 |
3 files changed, 272 insertions, 112 deletions
diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp index 63d01c9d85..eda6e16195 100644 --- a/lib/Sema/SemaDeclCXX.cpp +++ b/lib/Sema/SemaDeclCXX.cpp @@ -3621,7 +3621,8 @@ void Sema::ActOnFinishCXXInClassMemberInitializer(Decl *D, ExprResult Init = InitExpr; if (!FD->getType()->isDependentType() && !InitExpr->isTypeDependent()) { - InitializedEntity Entity = InitializedEntity::InitializeMember(FD); + InitializedEntity Entity = + InitializedEntity::InitializeMemberFromDefaultMemberInitializer(FD); InitializationKind Kind = FD->getInClassInitStyle() == ICIS_ListInit ? InitializationKind::CreateDirectList(InitExpr->getLocStart(), @@ -4646,6 +4647,10 @@ static bool CollectFieldInitializer(Sema &SemaRef, BaseAndFieldInfo &Info, SemaRef.BuildCXXDefaultInitExpr(Info.Ctor->getLocation(), Field); if (DIE.isInvalid()) return true; + + auto Entity = InitializedEntity::InitializeMember(Field, nullptr, true); + SemaRef.checkInitializerLifetime(Entity, DIE.get()); + CXXCtorInitializer *Init; if (Indirect) Init = new (SemaRef.Context) diff --git a/lib/Sema/SemaExprCXX.cpp b/lib/Sema/SemaExprCXX.cpp index fbf572e398..a7ad8e322d 100644 --- a/lib/Sema/SemaExprCXX.cpp +++ b/lib/Sema/SemaExprCXX.cpp @@ -1864,13 +1864,6 @@ Sema::BuildCXXNew(SourceRange Range, bool UseGlobal, if (CheckAllocatedType(AllocType, TypeRange.getBegin(), TypeRange)) return ExprError(); - if (initStyle == CXXNewExpr::ListInit && - isStdInitializerList(AllocType, nullptr)) { - Diag(AllocTypeInfo->getTypeLoc().getBeginLoc(), - diag::warn_dangling_std_initializer_list) - << /*at end of FE*/0 << Inits[0]->getSourceRange(); - } - // In ARC, infer 'retaining' for the allocated if (getLangOpts().ObjCAutoRefCount && AllocType.getObjCLifetime() == Qualifiers::OCL_None && diff --git a/lib/Sema/SemaInit.cpp b/lib/Sema/SemaInit.cpp index 320d93a99a..f94eabd671 100644 --- a/lib/Sema/SemaInit.cpp +++ b/lib/Sema/SemaInit.cpp @@ -572,6 +572,7 @@ void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field, hadError = true; return; } + SemaRef.checkInitializerLifetime(MemberEntity, DIE.get()); if (Init < NumInits) ILE->setInit(Init, DIE.get()); else { @@ -6197,17 +6198,43 @@ InitializedEntityOutlivesFullExpression(const InitializedEntity &Entity) { llvm_unreachable("unknown entity kind"); } +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, + + /// 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, +}; +using LifetimeResult = + llvm::PointerIntPair<const InitializedEntity *, 3, LifetimeKind>; +} + /// 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 const InitializedEntity *getEntityForTemporaryLifetimeExtension( +static LifetimeResult getEntityForTemporaryLifetimeExtension( const InitializedEntity *Entity, - const InitializedEntity *FallbackDecl = nullptr) { + 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; + return {Entity, LK_Extended}; case InitializedEntity::EK_Member: // For subobjects, we look at the complete object. @@ -6216,29 +6243,43 @@ static const InitializedEntity *getEntityForTemporaryLifetimeExtension( Entity); // except: - // -- A temporary bound to a reference member in a constructor's - // ctor-initializer persists until the constructor exits. - return Entity; + // 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; + 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_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_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; + return {nullptr, LK_New}; case InitializedEntity::EK_Temporary: case InitializedEntity::EK_CompoundLiteralInit: @@ -6246,25 +6287,26 @@ static const InitializedEntity *getEntityForTemporaryLifetimeExtension( // 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; + return {nullptr, LK_FullExpression}; case InitializedEntity::EK_ArrayElement: // For subobjects, we look at the complete object. return getEntityForTemporaryLifetimeExtension(Entity->getParent(), - FallbackDecl); + InitField); case InitializedEntity::EK_Base: // For subobjects, we look at the complete object. if (Entity->getParent()) return getEntityForTemporaryLifetimeExtension(Entity->getParent(), - Entity); - LLVM_FALLTHROUGH; + 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 innermost field decl as the context. - return FallbackDecl; + // In this case, use the outermost field decl as the context. + return {InitField, LK_MemInitializer}; case InitializedEntity::EK_BlockElement: case InitializedEntity::EK_LambdaToBlockConversionBlockElement: @@ -6272,30 +6314,54 @@ static const InitializedEntity *getEntityForTemporaryLifetimeExtension( case InitializedEntity::EK_Exception: case InitializedEntity::EK_VectorElement: case InitializedEntity::EK_ComplexElement: - return nullptr; + return {nullptr, LK_FullExpression}; } llvm_unreachable("unknown entity kind"); } -static void performLifetimeExtension(Expr *Init, - const InitializedEntity *ExtendingEntity); +namespace { +enum ExtensionKind { + /// Lifetime would be extended by a reference binding to a temporary. + EK_ReferenceBinding, + /// Lifetime would be extended by a std::initializer_list object binding to + /// its backing array. + EK_StdInitializerList, +}; +using IndirectTemporaryPathEntry = + llvm::PointerUnion<CXXDefaultInitExpr *, ValueDecl *>; +using IndirectTemporaryPath = llvm::SmallVectorImpl<IndirectTemporaryPathEntry>; + +struct RevertToOldSizeRAII { + IndirectTemporaryPath &Path; + unsigned OldSize = Path.size(); + RevertToOldSizeRAII(IndirectTemporaryPath &Path) : Path(Path) {} + ~RevertToOldSizeRAII() { Path.resize(OldSize); } +}; +} + +template <typename TemporaryVisitor> +static void visitTemporariesExtendedByInitializer(IndirectTemporaryPath &Path, + Expr *Init, + TemporaryVisitor Visit); + +/// Visit the temporaries whose lifetimes would be extended by binding a +/// reference to the glvalue expression \c Init. +template <typename TemporaryVisitor> +static void +visitTemporariesExtendedByReferenceBinding(IndirectTemporaryPath &Path, + Expr *Init, ExtensionKind EK, + TemporaryVisitor Visit) { + RevertToOldSizeRAII RAII(Path); -/// Update a glvalue expression that is used as the initializer of a reference -/// to note that its lifetime is extended. -/// \return \c true if any temporary had its lifetime extended. -static bool -performReferenceExtension(Expr *Init, - const InitializedEntity *ExtendingEntity) { // Walk past any constructs which we can lifetime-extend across. Expr *Old; do { Old = Init; if (InitListExpr *ILE = dyn_cast<InitListExpr>(Init)) { - if (ILE->getNumInits() == 1 && ILE->isGLValue()) { - // This is just redundant braces around an initializer. Step over it. + // 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 @@ -6312,40 +6378,65 @@ performReferenceExtension(Expr *Init, // when performing lifetime extension. if (auto *ASE = dyn_cast<ArraySubscriptExpr>(Init)) Init = ASE->getBase(); + + // 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(DIE); + Init = DIE->getExpr(); + + if (auto *EWC = dyn_cast<ExprWithCleanups>(Init)) + Init = EWC->getSubExpr(); + } } while (Init != Old); - if (MaterializeTemporaryExpr *ME = dyn_cast<MaterializeTemporaryExpr>(Init)) { - // Update the storage duration of the materialized temporary. - // FIXME: Rebuild the expression instead of mutating it. - ME->setExtendingDecl(ExtendingEntity->getDecl(), - ExtendingEntity->allocateManglingNumber()); - performLifetimeExtension(ME->GetTemporaryExpr(), ExtendingEntity); - return true; + if (auto *MTE = dyn_cast<MaterializeTemporaryExpr>(Init)) { + if (Visit(Path, MTE, EK)) + visitTemporariesExtendedByInitializer(Path, MTE->GetTemporaryExpr(), + Visit); } - - return false; } -/// Update a prvalue expression that is going to be materialized as a -/// lifetime-extended temporary. -static void performLifetimeExtension(Expr *Init, - const InitializedEntity *ExtendingEntity) { +/// Visit the temporaries whose lifetimes would be extended by +/// lifetime-extending the object initialized by the prvalue expression \c +/// Init. +template <typename TemporaryVisitor> +static void visitTemporariesExtendedByInitializer(IndirectTemporaryPath &Path, + Expr *Init, + TemporaryVisitor Visit) { + RevertToOldSizeRAII RAII(Path); + + // 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(DIE); + Init = DIE->getExpr(); + + if (auto *EWC = dyn_cast<ExprWithCleanups>(Init)) + Init = EWC->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(); - if (CXXStdInitializerListExpr *ILE = - dyn_cast<CXXStdInitializerListExpr>(Init)) { - performReferenceExtension(ILE->getSubExpr(), ExtendingEntity); - return; - } + // 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 visitTemporariesExtendedByReferenceBinding( + Path, ILE->getSubExpr(), EK_StdInitializerList, Visit); if (InitListExpr *ILE = dyn_cast<InitListExpr>(Init)) { + if (ILE->isTransparent()) + return visitTemporariesExtendedByInitializer(Path, ILE->getInit(0), + Visit); + if (ILE->getType()->isArrayType()) { for (unsigned I = 0, N = ILE->getNumInits(); I != N; ++I) - performLifetimeExtension(ILE->getInit(I), ExtendingEntity); + visitTemporariesExtendedByInitializer(Path, ILE->getInit(I), Visit); return; } @@ -6357,7 +6448,8 @@ static void performLifetimeExtension(Expr *Init, // bound to temporaries, those temporaries are also lifetime-extended. if (RD->isUnion() && ILE->getInitializedFieldInUnion() && ILE->getInitializedFieldInUnion()->getType()->isReferenceType()) - performReferenceExtension(ILE->getInit(0), ExtendingEntity); + visitTemporariesExtendedByReferenceBinding(Path, ILE->getInit(0), + EK_ReferenceBinding, Visit); else { unsigned Index = 0; for (const auto *I : RD->fields()) { @@ -6367,13 +6459,13 @@ static void performLifetimeExtension(Expr *Init, continue; Expr *SubInit = ILE->getInit(Index); if (I->getType()->isReferenceType()) - performReferenceExtension(SubInit, ExtendingEntity); - else if (isa<InitListExpr>(SubInit) || - isa<CXXStdInitializerListExpr>(SubInit)) - // This may be either aggregate-initialization of a member or - // initialization of a std::initializer_list object. Either way, + visitTemporariesExtendedByReferenceBinding( + Path, SubInit, EK_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. - performLifetimeExtension(SubInit, ExtendingEntity); + visitTemporariesExtendedByInitializer(Path, SubInit, Visit); ++Index; } } @@ -6381,37 +6473,123 @@ static void performLifetimeExtension(Expr *Init, } } -static void warnOnLifetimeExtension(Sema &S, const InitializedEntity &Entity, - const Expr *Init, bool IsInitializerList, - const ValueDecl *ExtendingDecl) { - // Warn if a field lifetime-extends a temporary. - if (isa<FieldDecl>(ExtendingDecl)) { - if (IsInitializerList) { - S.Diag(Init->getExprLoc(), diag::warn_dangling_std_initializer_list) - << /*at end of constructor*/true; - return; +/// Determine whether this is an indirect path to a temporary that we are +/// supposed to lifetime-extend along (but don't). +static bool shouldLifetimeExtendThroughPath(const IndirectTemporaryPath &Path) { + for (auto Elem : Path) { + if (!Elem.is<CXXDefaultInitExpr*>()) + return false; + } + return true; +} + +void Sema::checkInitializerLifetime(const InitializedEntity &Entity, + Expr *Init) { + LifetimeResult LR = getEntityForTemporaryLifetimeExtension(&Entity); + LifetimeKind LK = LR.getInt(); + const InitializedEntity *ExtendingEntity = LR.getPointer(); + + // If this entity doesn't have an interesting lifetime, don't bother looking + // for temporaries within its initializer. + if (LK == LK_FullExpression) + return; + + auto TemporaryVisitor = [&](IndirectTemporaryPath &Path, + MaterializeTemporaryExpr *MTE, + ExtensionKind EK) -> bool { + switch (LK) { + case LK_FullExpression: + llvm_unreachable("already handled this"); + + case LK_Extended: + // Lifetime-extend the temporary. + if (Path.empty()) { + // Update the storage duration of the materialized temporary. + // FIXME: Rebuild the expression instead of mutating it. + MTE->setExtendingDecl(ExtendingEntity->getDecl(), + ExtendingEntity->allocateManglingNumber()); + // Also visit the temporaries lifetime-extended by this initializer. + return true; + } + + if (shouldLifetimeExtendThroughPath(Path)) { + // We're supposed to lifetime-extend the temporary along this path (per + // the resolution of DR1815), but we don't support that yet. + // + // FIXME: Properly handle this situation. Perhaps the easiest approach + // would be to clone the initializer expression on each use that would + // lifetime extend its temporaries. + Diag(MTE->getExprLoc(), + EK == EK_ReferenceBinding + ? diag::warn_default_member_init_temporary_not_extended + : diag::warn_default_member_init_init_list_not_extended); + } else { + llvm_unreachable("unexpected indirect temporary path"); + } + break; + + case LK_MemInitializer: + // Under C++ DR1696, if a mem-initializer (or a default member + // initializer used by the absence of one) would lifetime-extend a + // temporary, the program is ill-formed. + if (auto *ExtendingDecl = ExtendingEntity->getDecl()) { + bool IsSubobjectMember = ExtendingEntity != &Entity; + Diag(MTE->getExprLoc(), diag::err_bind_ref_member_to_temporary) + << ExtendingDecl << Init->getSourceRange() << IsSubobjectMember + << EK; + // Don't bother adding a note pointing to the field if we're inside its + // default member initializer; our primary diagnostic points to the + // same place in that case. + if (Path.empty() || !Path.back().is<CXXDefaultInitExpr*>()) { + Diag(ExtendingDecl->getLocation(), + diag::note_lifetime_extending_member_declared_here) + << EK << IsSubobjectMember; + } + } else { + // We have a mem-initializer but no particular field within it; this + // is either a base class or a delegating initializer directly + // initializing the base-class from something that doesn't live long + // enough. Either way, that can't happen. + // FIXME: Move CheckForDanglingReferenceOrPointer checks here. + llvm_unreachable( + "temporary initializer for base class / delegating ctor"); + } + break; + + case LK_New: + if (EK == EK_ReferenceBinding) { + Diag(MTE->getExprLoc(), diag::warn_new_dangling_reference); + } else { + Diag(MTE->getExprLoc(), diag::warn_new_dangling_initializer_list) + << (ExtendingEntity != &Entity); + } + break; + + case LK_Return: + // FIXME: Move -Wreturn-stack-address checks here. + return false; } - bool IsSubobjectMember = false; - for (const InitializedEntity *Ent = Entity.getParent(); Ent; - Ent = Ent->getParent()) { - if (Ent->getKind() != InitializedEntity::EK_Base) { - IsSubobjectMember = true; - break; + // FIXME: Model these as CodeSynthesisContexts to fix the note emission + // order. + for (auto Elem : llvm::reverse(Path)) { + if (auto *DIE = Elem.dyn_cast<CXXDefaultInitExpr*>()) { + Diag(DIE->getExprLoc(), diag::note_in_default_member_initalizer_here) + << DIE->getField(); } } - S.Diag(Init->getExprLoc(), - diag::warn_bind_ref_member_to_temporary) - << ExtendingDecl << Init->getSourceRange() - << IsSubobjectMember << IsInitializerList; - if (IsSubobjectMember) - S.Diag(ExtendingDecl->getLocation(), - diag::note_ref_subobject_of_member_declared_here); - else - S.Diag(ExtendingDecl->getLocation(), - diag::note_ref_or_ptr_member_declared_here) - << /*is pointer*/false; - } + + // We didn't lifetime-extend, so don't go any further; we don't need more + // warnings or errors on inner temporaries within this one's initializer. + return false; + }; + + llvm::SmallVector<IndirectTemporaryPathEntry, 8> Path; + if (Init->isGLValue()) + visitTemporariesExtendedByReferenceBinding(Path, Init, EK_ReferenceBinding, + TemporaryVisitor); + else + visitTemporariesExtendedByInitializer(Path, Init, TemporaryVisitor); } static void DiagnoseNarrowingInInitList(Sema &S, @@ -6838,14 +7016,9 @@ InitializationSequence::Perform(Sema &S, } // Even though we didn't materialize a temporary, the binding may still - // extend the lifetime of a temporary. This happens if we bind a reference - // to the result of a cast to reference type. - if (const InitializedEntity *ExtendingEntity = - getEntityForTemporaryLifetimeExtension(&Entity)) - if (performReferenceExtension(CurInit.get(), ExtendingEntity)) - warnOnLifetimeExtension(S, Entity, CurInit.get(), - /*IsInitializerList=*/false, - ExtendingEntity->getDecl()); + // extend the lifetime of a temporary. This happens if we bind a + // reference to the result of a cast to reference type. + S.checkInitializerLifetime(Entity, CurInit.get()); CheckForNullPointerDereference(S, CurInit.get()); break; @@ -6861,23 +7034,17 @@ InitializationSequence::Perform(Sema &S, // Materialize the temporary into memory. MaterializeTemporaryExpr *MTE = S.CreateMaterializeTemporaryExpr( Step->Type, CurInit.get(), Entity.getType()->isLValueReferenceType()); + CurInit = MTE; // Maybe lifetime-extend the temporary's subobjects to match the // entity's lifetime. - if (const InitializedEntity *ExtendingEntity = - getEntityForTemporaryLifetimeExtension(&Entity)) - if (performReferenceExtension(MTE, ExtendingEntity)) - warnOnLifetimeExtension(S, Entity, CurInit.get(), - /*IsInitializerList=*/false, - ExtendingEntity->getDecl()); + S.checkInitializerLifetime(Entity, CurInit.get()); // If we're extending this temporary to automatic storage duration -- we // need to register its cleanup during the full-expression's cleanups. if (MTE->getStorageDuration() == SD_Automatic && MTE->getType().isDestructedType()) S.Cleanup.setExprNeedsCleanups(true); - - CurInit = MTE; break; } @@ -7320,18 +7487,13 @@ InitializationSequence::Perform(Sema &S, CurInit.get()->getType(), CurInit.get(), /*BoundToLvalueReference=*/false); - // Maybe lifetime-extend the array temporary's subobjects to match the - // entity's lifetime. - if (const InitializedEntity *ExtendingEntity = - getEntityForTemporaryLifetimeExtension(&Entity)) - if (performReferenceExtension(MTE, ExtendingEntity)) - warnOnLifetimeExtension(S, Entity, CurInit.get(), - /*IsInitializerList=*/true, - ExtendingEntity->getDecl()); - // Wrap it in a construction of a std::initializer_list<T>. CurInit = new (S.Context) CXXStdInitializerListExpr(Step->Type, MTE); + // Maybe lifetime-extend the array temporary's subobjects to match the + // entity's lifetime. + S.checkInitializerLifetime(Entity, CurInit.get()); + // Bind the result, in case the library has given initializer_list a // non-trivial destructor. if (shouldBindAsTemporary(Entity)) |