[cfe-dev] Smart pointer usage in the Parser/Actions

[Douglas Gregor]

On Dec 19, 2008, at 2:26 PM, Fariborz Jahanian wrote:

>
> On Dec 19, 2008, at 1:21 PM, Douglas Gregor wrote:
>
>> On Dec 19, 2008, at 3:39 PM, steve naroff wrote:
>>> On Dec 19, 2008, at 3:09 PM, Fariborz Jahanian wrote:
>>> A variation on the FIXME is to have a subclass of ParmVarDecl  
>>> (e.g. ObjCParmVarDecl) that contains the original type (to support  
>>> method encoding). This is still wasteful, however the waste is  
>>> isolated to ObjC. Note that C++ is already wasting space (with the  
>>> DefaultArg slot). Conceptually, I like the idea of having ObjC and  
>>> C++ subclasses of ParmVarDecl.
>>
>> I'm not a fan of having separate ObjC/C++ subclasses for Decls  
>> unless there are differences in the data we need to store in the  
>> AST. In this case, the difference isn't whether we're in Objective- 
>> C or not; it's whether or not the original type is different from  
>> the converted type. So, why not have ParmVarWithOriginalTypeDecl be  
>> a subclass of ParmVarDecl, and create ParmVarWithOriginalTypeDecls  
>> whenever we've actually performed some kind of promotion of the  
>> declaration's type? That will capture all of the information in the  
>> source code while not special-casing Objective-C or introducing an  
>> extra slot into ParmVarDecls that aren't promoted.
>>
>> I've been meaning to do the same thing with FieldDecl, by creating  
>> a subclass BitFieldDecl that's has the extra Stmt* containing the  
>> bitfield size. The FieldDecl class's interface won't change... but  
>> it will perform a dyn_cast<BitFieldDecl> in FieldDecl::getBitWidth 
>> (), so that clients of FieldDecl's won't ever have to know about  
>> BitFieldDecl.
>
> Does't c++ mangles the decayed type or the original type (like  
> Objc)? If the latter, then the same issue exists for c++ as well.

C++ mangles the decayed type, since we need to mangle the signature of  
the function (C++ [defns.signature]; the C++0x version of this  
paragraph is far clearer about this requirement than the C++03 version).

Besides, the type used for mangling may still be different from the  
decayed type of the function parameter. For example, given:

   void f(const int x) { }

The type of the function is void(int), but the type of the ParmVarDecl  
is "const int" (so x can't be modified in the body).

	- Doug