[tree-ssa] Garbage collector x bb annotations

[Daniel Berlin]

>> They used to be obstack allocated, so consider yourself lucky :P.
>>
>> You could add a "fields_only" flag and modify gengtype to not mark the
>> actual bb, only it's fields.
>
> This won't work, since bb structures refer to each other.
>
So?

If a bb is marked fields_only, and we recursively call the marker 
routine on the next bb, it's still not going to try to mark that bb.

> -- 
> - Geoffrey Keating <geoffk@geoffk.org>