[cfe-commits] r61746 - in /cfe/trunk: include/clang/AST/ include/clang/Basic/ include/clang/Parse/ lib/AST/ lib/Parse/ lib/Sema/ test/SemaCXX/

[Chris Lattner]

On Jan 5, 2009, at 8:10 PM, Douglas Gregor wrote:
>> Doing this comparison with types seems awkward, can you just do
>> something like:
>>
>> if (const RecordType *RT = ArgType->getAsRecordType())
>>  if (RT->getDecl() == this) ...
>>
>> instead?  likewise in hasConstCopyAssignment.
>
> That won't work, since there can be multiple RecordDecls for a given  
> record type.

Is there a similar mechanism that will work?

>>> +  if (getLangOptions().CPlusPlus) {
>>>   CheckExtraCXXDefaultArguments(D);
>>> +    if (!T->isPODType())
>>> +      cast<CXXRecordDecl>(Record)->setPOD(false);
>>
>> I see that you basically clear the 'ispod' bit whenever something is
>> parsed that prevents a class from being a POD.  Would it be better to
>> make it a predicate that walks the member list to determine podness?
>> The advantage of doing this is that it would put all the "podness"
>> checks together into one method instead of scattered throughout sema.
>> What do you think?
>
> Most declarations of a class type will need to perform the check for  
> a POD type, which is recursive (it's only a POD if all of its non- 
> static data members are PODs, and so on), so it might be expensive  
> to compute this property on the fly. Personally, I prefer the way  
> Sebastian's doing it: there will be quite a few other class  
> properties like this, too.

What if the query is lazy but cached?  Many types are defined in  
headers that are never used, I can't believe that we'd end up querying  
isPod for all of them...

>> Would it be possible to synthesize these lazily
>> like G++ does?
>
>
> Yes, but let's implement the semantics of these operations first, so  
> that we have known, working regression tests when we go and optimize  
> away these implicitly-declared special member functions.

Ok, that is fair enough.  Would it make sense to add a README file or  
something for notes on C++ optimization opportunities?

-Chris