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

[John McCall]

On Sep 16, 2014, at 5:06 PM, Ben Langmuir <blangmuir at apple.com> wrote:
>> On Sep 16, 2014, at 1:25 PM, John McCall <rjmccall at apple.com> wrote:
>> 
>> On Sep 16, 2014, at 12:54 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>>> 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; }
>> 
>> That works for me, or we could even give it its own bit in the definition data; it’s not like we aren’t tracking a number of other things there for similar purposes.
>> 
>> John.
> 
> John and I took a look and it turns out we killed the warning in question as part of removing -Warc-abi.  I’ve attached an updated patch that just eagerly sets these bits in addedMember so we will get the correct value inside AddImplicitlyDeclaredMembersToClass.

Looks great to me; thanks, Ben.

John.
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