[cfe-dev] Fix for PR4701

[David Chisnall]

Hi Steve,

there's a test case attached to PR4701 (http://llvm.org/bugs/show_bug.cgi?id=4701 
).  I've just discovered that this still breaks assigning Class  
variables to struct objc_class* variables and vice versa.  I think I  
can fix this by adding another hack in  
Sema::CheckPointerTypesForAssignment(), but I'd still prefer a better  
approach if you can suggest one...

When I try to compile GNUstep, I discover a more subtle problem which  
my patch now fixes, which is that MetaClass is defined like this:

typedef struct objc_class *MetaClass;

This means that clang fails to notice that MetaClass and Class (which  
are both typedefs for the same underlying type) are compatible when  
using the builtin definition of Class, which breaks any assignment of  
a MetaClass value to a Class-typed variable and vice versa.

David

On 14 Aug 2009, at 22:08, steve naroff wrote:

> Hi David,
>
> If you can include a test case that demonstrate what this patch  
> fixes, I believe I can give you a better approach...
>
> Thanks,
>
> snaroff
>
> On Aug 14, 2009, at 4:56 PM, David Chisnall wrote:
>
>> Hi Everyone,
>>
>> This patch provides an actual fix (as opposed to my previous  
>> attempt, which just moved the bugs around) for PR4701, where code  
>> accessing fields declared on Objective-C pseudo-builtin types id  
>> and Class broke.
>>
>> With this patch applied, all test pass and programs that include  
>> the GNU runtime's <obj/objc-api.h> compile correctly.
>>
>> I am not totally convinced by the approach here.  If a redefinition  
>> of id or Class is encountered, this is stored any any attempt to  
>> access a field on one of these builtins is then implicitly cast to  
>> the real type.  This is quite ugly, but seems less ugly than doing  
>> it the other way around (adding special cases to all of the  
>> Objective-C stuff to let struct objc_object* act as a receiver, and  
>> so on).
>>
>> David
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>