[PATCH] Fix an assertion failure trying to emit a trivial destructor in ObjC++

[Richard Smith]

On Tue, Sep 16, 2014 at 12:47 PM, John McCall <rjmccall at apple.com> wrote:

> On Sep 16, 2014, at 12:11 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>
> On Tue, Sep 16, 2014 at 11:45 AM, John McCall <rjmccall at apple.com> wrote:
>
>> On Sep 15, 2014, at 9:47 AM, Ben Langmuir <blangmuir at apple.com> wrote:
>> > Hi John,
>> >
>> > This patch fixes the assertion failure I talked to you about in
>> Objective C++ codegen.  It turned out to have nothing to do with templates.
>> >
>> >    Fix an assertion failure trying to emit a trivial destructor in
>> ObjC++
>> >
>> >    If a base class declares a destructor, we will add the implicit
>> >    destructor for the subclass in
>> >    ActOnFields -> AddImplicitlyDeclaredMembersToClass
>> >
>> >    But in Objective C++, we did not compute whether we have a trivial
>> >    destructor until after that in
>> >    CXXRecordDecl::completeDefinition()
>> >
>> >    This was leading to a mismatch between the class, which thought it
>> had
>> >    no trivial destructor, and the CXXDestructorDecl, which considered
>> >    itself trivial.
>>
>> I feel like hasTrivialDestructor should return the right value here.  I
>> understand (and am saddened by) the hack about not setting PlainOldData
>> until completeDefinition, but maybe we can set/clear the rest of the bits
>> eagerly?
>
>
> Why do we have to delay setting the PlainOldData flag?
>
>
> There is a diagnostic which wants to warn about structs that are only POD
> in non-ARC modes.
>

Thanks, I suspected something along those lines. Perhaps we could track
both properties and still perform the calculation eagerly:

-  bool isPOD() const { return data().PlainOldData; }
+  bool isPOD() const { return data().PlainOldData &&
!data().HasARCObjectMember; }
+  bool wouldHaveBeenPODIfItWerentForYouMeddlingKids() const { return
data().PlainOldData; }
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