[cfe-dev] Adding memory spaces to types

[Chris Lattner]

On Nov 11, 2007, at 12:32 AM, Neil Booth wrote:

> Chris Lattner wrote:-
>
>> Yep, I think this is a very reasonable way to go.  QualType itself is
>> just an optimization for representing types.  Instead of having
>> Type*'s everywhere, and having a "ConstType" type and "RestrictType"
>> type (that wrapped some other type), the information is encoded into
>> QualType.
>>
>> However,  this optimization for CVR qualifiers doesn't impact other
>> "qualifiers".  It would be very reasonable to have an
>> AddressSpaceQualifiedType class, which takes an address space ID  
>> and a
>> QualType.   This combines the space/time efficiency niceties of
>> QualType with the generality of having explicit classes for all of
>> these.
>
> Having qualifiers in multiple places will make "qualifier calculus"  
> like
>
> o is A unqualified?
> o does A have all the qualifiers of B?
>>
> etc., awkward, no?

Nope, it is very simple.  CVR qualifiers *only* exist on QualType.   
This means that for something like:

"const volatile randomqual int"

The node for "randomqual" would contain *just* a "Type*" (not a  
qualtype) to int.

The reference to "const volatile randomqual int" would be a qualtype  
whose Type* points to the above node, but has the "CV" bits set.  This  
means you can have exact type equality checks in constant time with  
qualtype comparison still.

> o what is the unqualified form of A?
>

This does require an extra check, but that should be hidden in  
QualType itself.

-Chris