[fortran,patch] Don't write common more than once in a module file (PR 30285)

[FX Coudert]

>> This is quadratic in the numbers of commons in a module.  Please  
>> make written_common a balanced tree (such as our BBT_HEADER &  
>> associates, this would leave us with O(N log(N)) complexity) or a  
>> hashtable (leaving us with O(N) or something like that).
>

Here's the updated patch, using a balanced tree. A careful review is  
welcome, as it's the first time I deal with these bbt features.

Boostrapped and finishing regtesting on x86_64-linux. OK to commit if  
it passes?

FX


-------------- next part --------------
A non-text attachment was scrubbed...
Name: pr30285_2.diff
Type: application/octet-stream
Size: 3043 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/fortran/attachments/20071117/42be94a9/attachment.obj>