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

[Ben Langmuir]

> 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 <mailto:richard at metafoo.co.uk>> wrote:
>> On Tue, Sep 16, 2014 at 12:47 PM, John McCall <rjmccall at apple.com <mailto:rjmccall at apple.com>> wrote:
>> On Sep 16, 2014, at 12:11 PM, Richard Smith <richard at metafoo.co.uk <mailto:richard at metafoo.co.uk>> wrote:
>>> On Tue, Sep 16, 2014 at 11:45 AM, John McCall <rjmccall at apple.com <mailto:rjmccall at apple.com>> wrote:
>>> On Sep 15, 2014, at 9:47 AM, Ben Langmuir <blangmuir at apple.com <mailto: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.

Ben



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