DR1672, DR1813, DR1881, DR2120: Implement recent fixes to "standard
layout" rules.
The new rules say that a standard-layout struct has its first non-static
data member and all base classes at offset 0, and consider a class to
not be standard-layout if that would result in multiple subobjects of a
single type having the same address.
We track "is C++11 standard-layout class" separately from "is
standard-layout class" so that the ABIs that need this information can
still use it.
Differential Revision: https://reviews.llvm.org/D45176
llvm-svn: 329332
diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 2d9e1c8..98bde8b 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -1071,7 +1071,10 @@
ToData.Polymorphic = FromData.Polymorphic;
ToData.Abstract = FromData.Abstract;
ToData.IsStandardLayout = FromData.IsStandardLayout;
- ToData.HasNoNonEmptyBases = FromData.HasNoNonEmptyBases;
+ ToData.IsCXX11StandardLayout = FromData.IsCXX11StandardLayout;
+ ToData.HasBasesWithFields = FromData.HasBasesWithFields;
+ ToData.HasBasesWithNonStaticDataMembers =
+ FromData.HasBasesWithNonStaticDataMembers;
ToData.HasPrivateFields = FromData.HasPrivateFields;
ToData.HasProtectedFields = FromData.HasProtectedFields;
ToData.HasPublicFields = FromData.HasPublicFields;
diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index 736b933..3cb1867 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -74,7 +74,8 @@
CXXRecordDecl::DefinitionData::DefinitionData(CXXRecordDecl *D)
: UserDeclaredConstructor(false), UserDeclaredSpecialMembers(0),
Aggregate(true), PlainOldData(true), Empty(true), Polymorphic(false),
- Abstract(false), IsStandardLayout(true), HasNoNonEmptyBases(true),
+ Abstract(false), IsStandardLayout(true), IsCXX11StandardLayout(true),
+ HasBasesWithFields(false), HasBasesWithNonStaticDataMembers(false),
HasPrivateFields(false), HasProtectedFields(false),
HasPublicFields(false), HasMutableFields(false), HasVariantMembers(false),
HasOnlyCMembers(true), HasInClassInitializer(false),
@@ -161,6 +162,25 @@
return R;
}
+/// Determine whether a class has a repeated base class. This is intended for
+/// use when determining if a class is standard-layout, so makes no attempt to
+/// handle virtual bases.
+static bool hasRepeatedBaseClass(const CXXRecordDecl *StartRD) {
+ llvm::SmallPtrSet<const CXXRecordDecl*, 8> SeenBaseTypes;
+ SmallVector<const CXXRecordDecl*, 8> WorkList = {StartRD};
+ while (!WorkList.empty()) {
+ const CXXRecordDecl *RD = WorkList.pop_back_val();
+ for (const CXXBaseSpecifier &BaseSpec : RD->bases()) {
+ if (const CXXRecordDecl *B = BaseSpec.getType()->getAsCXXRecordDecl()) {
+ if (!SeenBaseTypes.insert(B).second)
+ return true;
+ WorkList.push_back(B);
+ }
+ }
+ }
+ return false;
+}
+
void
CXXRecordDecl::setBases(CXXBaseSpecifier const * const *Bases,
unsigned NumBases) {
@@ -200,26 +220,37 @@
auto *BaseClassDecl =
cast<CXXRecordDecl>(BaseType->getAs<RecordType>()->getDecl());
- if (!BaseClassDecl->isEmpty()) {
- if (!data().Empty) {
- // C++0x [class]p7:
- // A standard-layout class is a class that:
- // [...]
- // -- either has no non-static data members in the most derived
- // class and at most one base class with non-static data members,
- // or has no base classes with non-static data members, and
- // If this is the second non-empty base, then neither of these two
- // clauses can be true.
+ // C++2a [class]p7:
+ // A standard-layout class is a class that:
+ // [...]
+ // -- has all non-static data members and bit-fields in the class and
+ // its base classes first declared in the same class
+ if (BaseClassDecl->data().HasBasesWithFields ||
+ !BaseClassDecl->field_empty()) {
+ if (data().HasBasesWithFields)
+ // Two bases have members or bit-fields: not standard-layout.
data().IsStandardLayout = false;
- }
+ data().HasBasesWithFields = true;
+ }
+ // C++11 [class]p7:
+ // A standard-layout class is a class that:
+ // -- [...] has [...] at most one base class with non-static data
+ // members
+ if (BaseClassDecl->data().HasBasesWithNonStaticDataMembers ||
+ BaseClassDecl->hasDirectFields()) {
+ if (data().HasBasesWithNonStaticDataMembers)
+ data().IsCXX11StandardLayout = false;
+ data().HasBasesWithNonStaticDataMembers = true;
+ }
+
+ if (!BaseClassDecl->isEmpty()) {
// C++14 [meta.unary.prop]p4:
// T is a class type [...] with [...] no base class B for which
// is_empty<B>::value is false.
data().Empty = false;
- data().HasNoNonEmptyBases = false;
}
-
+
// C++1z [dcl.init.agg]p1:
// An aggregate is a class with [...] no private or protected base classes
if (Base->getAccessSpecifier() != AS_public)
@@ -236,6 +267,8 @@
// -- has no non-standard-layout base classes
if (!BaseClassDecl->isStandardLayout())
data().IsStandardLayout = false;
+ if (!BaseClassDecl->isCXX11StandardLayout())
+ data().IsCXX11StandardLayout = false;
// Record if this base is the first non-literal field or base.
if (!hasNonLiteralTypeFieldsOrBases() && !BaseType->isLiteralType(C))
@@ -287,6 +320,7 @@
// A standard-layout class is a class that: [...]
// -- has [...] no virtual base classes
data().IsStandardLayout = false;
+ data().IsCXX11StandardLayout = false;
// C++11 [dcl.constexpr]p4:
// In the definition of a constexpr constructor [...]
@@ -401,6 +435,16 @@
addedClassSubobject(BaseClassDecl);
}
+
+ // C++2a [class]p7:
+ // A class S is a standard-layout class if it:
+ // -- has at most one base class subobject of any given type
+ //
+ // Note that we only need to check this for classes with more than one base
+ // class. If there's only one base class, and it's standard layout, then
+ // we know there are no repeated base classes.
+ if (data().IsStandardLayout && NumBases > 1 && hasRepeatedBaseClass(this))
+ data().IsStandardLayout = false;
if (VBases.empty()) {
data().IsParsingBaseSpecifiers = false;
@@ -501,6 +545,81 @@
data().Abstract = true;
}
+bool CXXRecordDecl::hasSubobjectAtOffsetZeroOfEmptyBaseType(
+ ASTContext &Ctx, const CXXRecordDecl *XFirst) {
+ if (!getNumBases())
+ return false;
+
+ llvm::SmallPtrSet<const CXXRecordDecl*, 8> Bases;
+ llvm::SmallPtrSet<const CXXRecordDecl*, 8> M;
+ SmallVector<const CXXRecordDecl*, 8> WorkList;
+
+ // Visit a type that we have determined is an element of M(S).
+ auto Visit = [&](const CXXRecordDecl *RD) -> bool {
+ RD = RD->getCanonicalDecl();
+
+ // C++2a [class]p8:
+ // A class S is a standard-layout class if it [...] has no element of the
+ // set M(S) of types as a base class.
+ //
+ // If we find a subobject of an empty type, it might also be a base class,
+ // so we'll need to walk the base classes to check.
+ if (!RD->data().HasBasesWithFields) {
+ // Walk the bases the first time, stopping if we find the type. Build a
+ // set of them so we don't need to walk them again.
+ if (Bases.empty()) {
+ bool RDIsBase = !forallBases([&](const CXXRecordDecl *Base) -> bool {
+ Base = Base->getCanonicalDecl();
+ if (RD == Base)
+ return false;
+ Bases.insert(Base);
+ return true;
+ });
+ if (RDIsBase)
+ return true;
+ } else {
+ if (Bases.count(RD))
+ return true;
+ }
+ }
+
+ if (M.insert(RD).second)
+ WorkList.push_back(RD);
+ return false;
+ };
+
+ if (Visit(XFirst))
+ return true;
+
+ while (!WorkList.empty()) {
+ const CXXRecordDecl *X = WorkList.pop_back_val();
+
+ // FIXME: We don't check the bases of X. That matches the standard, but
+ // that sure looks like a wording bug.
+
+ // -- If X is a non-union class type with a non-static data member
+ // [recurse to] the first non-static data member of X
+ // -- If X is a union type, [recurse to union members]
+ for (auto *FD : X->fields()) {
+ // FIXME: Should we really care about the type of the first non-static
+ // data member of a non-union if there are preceding unnamed bit-fields?
+ if (FD->isUnnamedBitfield())
+ continue;
+
+ // -- If X is n array type, [visit the element type]
+ QualType T = Ctx.getBaseElementType(FD->getType());
+ if (auto *RD = T->getAsCXXRecordDecl())
+ if (Visit(RD))
+ return true;
+
+ if (!X->isUnion())
+ break;
+ }
+ }
+
+ return false;
+}
+
void CXXRecordDecl::addedMember(Decl *D) {
if (!D->isImplicit() &&
!isa<FieldDecl>(D) &&
@@ -555,6 +674,7 @@
// A standard-layout class is a class that: [...]
// -- has no virtual functions
data().IsStandardLayout = false;
+ data().IsCXX11StandardLayout = false;
}
}
@@ -732,8 +852,18 @@
return;
}
+ ASTContext &Context = getASTContext();
+
// Handle non-static data members.
if (const auto *Field = dyn_cast<FieldDecl>(D)) {
+ // C++2a [class]p7:
+ // A standard-layout class is a class that:
+ // [...]
+ // -- has all non-static data members and bit-fields in the class and
+ // its base classes first declared in the same class
+ if (data().HasBasesWithFields)
+ data().IsStandardLayout = false;
+
// C++ [class.bit]p2:
// A declaration for a bit-field that omits the identifier declares an
// unnamed bit-field. Unnamed bit-fields are not members and cannot be
@@ -741,6 +871,13 @@
if (Field->isUnnamedBitfield())
return;
+ // C++11 [class]p7:
+ // A standard-layout class is a class that:
+ // -- either has no non-static data members in the most derived class
+ // [...] or has no base classes with non-static data members
+ if (data().HasBasesWithNonStaticDataMembers)
+ data().IsCXX11StandardLayout = false;
+
// C++ [dcl.init.aggr]p1:
// An aggregate is an array or a class (clause 9) with [...] no
// private or protected non-static data members (clause 11).
@@ -751,6 +888,11 @@
data().PlainOldData = false;
}
+ // Track whether this is the first field. We use this when checking
+ // whether the class is standard-layout below.
+ bool IsFirstField = !data().HasPrivateFields &&
+ !data().HasProtectedFields && !data().HasPublicFields;
+
// C++0x [class]p7:
// A standard-layout class is a class that:
// [...]
@@ -762,8 +904,10 @@
case AS_none: llvm_unreachable("Invalid access specifier");
};
if ((data().HasPrivateFields + data().HasProtectedFields +
- data().HasPublicFields) > 1)
+ data().HasPublicFields) > 1) {
data().IsStandardLayout = false;
+ data().IsCXX11StandardLayout = false;
+ }
// Keep track of the presence of mutable fields.
if (Field->isMutable()) {
@@ -784,7 +928,6 @@
//
// Automatic Reference Counting: the presence of a member of Objective-C pointer type
// that does not explicitly have no lifetime makes the class a non-POD.
- ASTContext &Context = getASTContext();
QualType T = Context.getBaseElementType(Field->getType());
if (T->isObjCRetainableType() || T.isObjCGCStrong()) {
if (T.hasNonTrivialObjCLifetime()) {
@@ -824,6 +967,7 @@
// A standard-layout class is a class that:
// -- has no non-static data members of type [...] reference,
data().IsStandardLayout = false;
+ data().IsCXX11StandardLayout = false;
// C++1z [class.copy.ctor]p10:
// A defaulted copy constructor for a class X is defined as deleted if X has:
@@ -980,31 +1124,32 @@
// class (or array of such types) [...]
if (!FieldRec->isStandardLayout())
data().IsStandardLayout = false;
+ if (!FieldRec->isCXX11StandardLayout())
+ data().IsCXX11StandardLayout = false;
- // C++0x [class]p7:
+ // C++2a [class]p7:
// A standard-layout class is a class that:
// [...]
+ // -- has no element of the set M(S) of types as a base class.
+ if (data().IsStandardLayout && (isUnion() || IsFirstField) &&
+ hasSubobjectAtOffsetZeroOfEmptyBaseType(Context, FieldRec))
+ data().IsStandardLayout = false;
+
+ // C++11 [class]p7:
+ // A standard-layout class is a class that:
// -- has no base classes of the same type as the first non-static
- // data member.
- // We don't want to expend bits in the state of the record decl
- // tracking whether this is the first non-static data member so we
- // cheat a bit and use some of the existing state: the empty bit.
- // Virtual bases and virtual methods make a class non-empty, but they
- // also make it non-standard-layout so we needn't check here.
- // A non-empty base class may leave the class standard-layout, but not
- // if we have arrived here, and have at least one non-static data
- // member. If IsStandardLayout remains true, then the first non-static
- // data member must come through here with Empty still true, and Empty
- // will subsequently be set to false below.
- if (data().IsStandardLayout && data().Empty) {
+ // data member
+ if (data().IsCXX11StandardLayout && IsFirstField) {
+ // FIXME: We should check all base classes here, not just direct
+ // base classes.
for (const auto &BI : bases()) {
if (Context.hasSameUnqualifiedType(BI.getType(), T)) {
- data().IsStandardLayout = false;
+ data().IsCXX11StandardLayout = false;
break;
}
}
}
-
+
// Keep track of the presence of mutable fields.
if (FieldRec->hasMutableFields()) {
data().HasMutableFields = true;
@@ -1067,17 +1212,6 @@
data().DefaultedMoveAssignmentIsDeleted = true;
}
- // C++0x [class]p7:
- // A standard-layout class is a class that:
- // [...]
- // -- either has no non-static data members in the most derived
- // class and at most one base class with non-static data members,
- // or has no base classes with non-static data members, and
- // At this point we know that we have a non-static data member, so the last
- // clause holds.
- if (!data().HasNoNonEmptyBases)
- data().IsStandardLayout = false;
-
// C++14 [meta.unary.prop]p4:
// T is a class type [...] with [...] no non-static data members other
// than bit-fields of length 0...
diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index e95bc91..390c8e0 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -2134,7 +2134,7 @@
// mode; fortunately, that is true because we want to assign
// consistently semantics to the type-traits intrinsics (or at
// least as many of them as possible).
- return RD->isTrivial() && RD->isStandardLayout();
+ return RD->isTrivial() && RD->isCXX11StandardLayout();
}
llvm_unreachable("bad tail-padding use kind");