Implement the likely resolution of core issue 253.

C++11 requires const objects to have a user-provided constructor, even for
classes without any fields. DR 253 relaxes this to say "If the implicit default
constructor initializes all subobjects, no initializer should be required."

clang is currently the only compiler that implements this C++11 rule, and e.g.
libstdc++ relies on something like DR 253 to compile in newer versions.  This
change  makes it possible to build code that says `const vector<int> v;' again
when using libstdc++5.2 and _GLIBCXX_DEBUG
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60284).

Fixes PR23381.

http://reviews.llvm.org/D16552

llvm-svn: 261297

2 files changed, 38 insertions, 28 deletions

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 039ea20eedf..1ea44fe6006 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -2024,6 +2024,7 @@ bool ASTNodeImporter::ImportDefinition(RecordDecl *From, RecordDecl *To,
     ToData.HasInClassInitializer = FromData.HasInClassInitializer;
     ToData.HasUninitializedReferenceMember
       = FromData.HasUninitializedReferenceMember;
+    ToData.HasUninitializedFields = FromData.HasUninitializedFields;
     ToData.NeedOverloadResolutionForMoveConstructor
       = FromData.NeedOverloadResolutionForMoveConstructor;
     ToData.NeedOverloadResolutionForMoveAssignment
diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index 4f24fdc28f7..c8edd5a1b4f 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -46,34 +46,31 @@ void LazyASTUnresolvedSet::getFromExternalSource(ASTContext &C) const {
 }
 
 CXXRecordDecl::DefinitionData::DefinitionData(CXXRecordDecl *D)
-  : UserDeclaredConstructor(false), UserDeclaredSpecialMembers(0),
-    Aggregate(true), PlainOldData(true), Empty(true), Polymorphic(false),
-    Abstract(false), IsStandardLayout(true), HasNoNonEmptyBases(true),
-    HasPrivateFields(false), HasProtectedFields(false), HasPublicFields(false),
-    HasMutableFields(false), HasVariantMembers(false), HasOnlyCMembers(true),
-    HasInClassInitializer(false), HasUninitializedReferenceMember(false),
-    NeedOverloadResolutionForMoveConstructor(false),
-    NeedOverloadResolutionForMoveAssignment(false),
-    NeedOverloadResolutionForDestructor(false),
-    DefaultedMoveConstructorIsDeleted(false),
-    DefaultedMoveAssignmentIsDeleted(false),
-    DefaultedDestructorIsDeleted(false),
-    HasTrivialSpecialMembers(SMF_All),
-    DeclaredNonTrivialSpecialMembers(0),
-    HasIrrelevantDestructor(true),
-    HasConstexprNonCopyMoveConstructor(false),
-    DefaultedDefaultConstructorIsConstexpr(true),
-    HasConstexprDefaultConstructor(false),
-    HasNonLiteralTypeFieldsOrBases(false), ComputedVisibleConversions(false),
-    UserProvidedDefaultConstructor(false), DeclaredSpecialMembers(0),
-    ImplicitCopyConstructorHasConstParam(true),
-    ImplicitCopyAssignmentHasConstParam(true),
-    HasDeclaredCopyConstructorWithConstParam(false),
-    HasDeclaredCopyAssignmentWithConstParam(false),
-    IsLambda(false), IsParsingBaseSpecifiers(false), NumBases(0), NumVBases(0),
-    Bases(), VBases(),
-    Definition(D), FirstFriend() {
-}
+    : UserDeclaredConstructor(false), UserDeclaredSpecialMembers(0),
+      Aggregate(true), PlainOldData(true), Empty(true), Polymorphic(false),
+      Abstract(false), IsStandardLayout(true), HasNoNonEmptyBases(true),
+      HasPrivateFields(false), HasProtectedFields(false),
+      HasPublicFields(false), HasMutableFields(false), HasVariantMembers(false),
+      HasOnlyCMembers(true), HasInClassInitializer(false),
+      HasUninitializedReferenceMember(false), HasUninitializedFields(false),
+      NeedOverloadResolutionForMoveConstructor(false),
+      NeedOverloadResolutionForMoveAssignment(false),
+      NeedOverloadResolutionForDestructor(false),
+      DefaultedMoveConstructorIsDeleted(false),
+      DefaultedMoveAssignmentIsDeleted(false),
+      DefaultedDestructorIsDeleted(false), HasTrivialSpecialMembers(SMF_All),
+      DeclaredNonTrivialSpecialMembers(0), HasIrrelevantDestructor(true),
+      HasConstexprNonCopyMoveConstructor(false),
+      DefaultedDefaultConstructorIsConstexpr(true),
+      HasConstexprDefaultConstructor(false),
+      HasNonLiteralTypeFieldsOrBases(false), ComputedVisibleConversions(false),
+      UserProvidedDefaultConstructor(false), DeclaredSpecialMembers(0),
+      ImplicitCopyConstructorHasConstParam(true),
+      ImplicitCopyAssignmentHasConstParam(true),
+      HasDeclaredCopyConstructorWithConstParam(false),
+      HasDeclaredCopyAssignmentWithConstParam(false), IsLambda(false),
+      IsParsingBaseSpecifiers(false), NumBases(0), NumVBases(0), Bases(),
+      VBases(), Definition(D), FirstFriend() {}
 
 CXXBaseSpecifier *CXXRecordDecl::DefinitionData::getBasesSlowCase() const {
   return Bases.get(Definition->getASTContext().getExternalSource());
@@ -332,6 +329,9 @@ CXXRecordDecl::setBases(CXXBaseSpecifier const * const *Bases,
     if (BaseClassDecl->hasUninitializedReferenceMember())
       data().HasUninitializedReferenceMember = true;
 
+    if (!BaseClassDecl->allowConstDefaultInit())
+      data().HasUninitializedFields = true;
+
     addedClassSubobject(BaseClassDecl);
   }
   
@@ -702,6 +702,15 @@ void CXXRecordDecl::addedMember(Decl *D) {
       data().IsStandardLayout = false;
     }
 
+    if (!Field->hasInClassInitializer() && !Field->isMutable()) {
+      if (CXXRecordDecl *FieldType = Field->getType()->getAsCXXRecordDecl()) {
+        if (!FieldType->allowConstDefaultInit())
+          data().HasUninitializedFields = true;
+      } else {
+        data().HasUninitializedFields = true;
+      }
+    }
+
     // Record if this field is the first non-literal or volatile field or base.
     if (!T->isLiteralType(Context) || T.isVolatileQualified())
       data().HasNonLiteralTypeFieldsOrBases = true;