Re: [Patch] libstdc++/23425

[Paolo Carlini <pcarlini at suse dot de>]

Paolo Carlini wrote:

>>Yes, _M_erase_at_end would be useful under assign, pop_back, erase, 
>>and resize.  A good _M_erase_at_end will do more than simply run the 
>>iterator through.  It will do the "segmented iterator" optimization 
>>as  promoted by Dietmar for so many years.  That is, it will consist 
>>of nested loops where the inner loop runs through a node (or partial 
>>node) at a time with pointers.
>>    
>>
>FYI, I'm working on this. It looks like, we are already using the
>optimization for deque::clear() and we are not for
>deque::erase(iterator, iterator). It seems to me that we should just
>take out the code in clear() which implements the double loop pattern
>and call it from both. Which in fact would be _M_erase_at_end or
>_M_erase_at_begin ;) ...
>  
>
... and of course, going to loops over plain pointers, instead of
deque::iterators means that _Destroy will be optimized very, very well
by the compiler, similarly to what happens for vector! (especially so if
we overload it for random access iterators)

:-)

Paolo.