Dealing with C++98/11 ABI incompatibilities

[Jason Merrill]

On 07/04/2012 09:41 AM, Richard Guenther wrote:
> Btw, why use a bitmask?  Isn't it enough to have a single number, viewed
> as an ABI suffix?

Well, I think the question is whether we want to create a mechanism 
which is only useful for libstdc++ versioning or one which is useful for 
ABI changes in other libraries as well.  A single number which applies 
to the entire mangled name would be fine for just libstdc++, but I think 
people would appreciate having a more general facility.

I was thinking of something like defining an ABI suffix for a name, so 
that list would look like list__2 or some such in the mangled name.  And 
then a wrapper class would be wrapper__2.  If the wrapper class also 
contains a user class with an ABI suffix of "Boost2", then the wrapper 
would look like wrapper__2__Boost2 or wrapper__Boost2__2, depending on 
the order of the members.  There would be no need to repeat a suffix 
from something that is itself mangled, such as a function argument type 
or a template argument, but we would need to propagate a suffix from the 
return type of a (non-template) function or the type of a variable as 
well as from member/base types in a class.

Jason