[Bug c++/62056] Long compile times with large tuples

["piotrdz at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62056

--- Comment #5 from Piotr Dziwinski <piotrdz at gmail dot com> ---
(In reply to Jonathan Wakely from comment #4)
> tr1::tuple doesn't support perfect-forwarding or move semantics
> 
> tr1::tuple doesn't support uses-allocator construction
> 
> tr1::tuple doesn't support 'final' classes
> 
> tr1::tuple doesn't have correct exception specifications
> 
> tr1::tuple doesn't prevent implicit conversions that would use explicit
> constructors
> 
> tr1::tuple doesn't support tuple concatenation
> 
> If you can add all those features to the <tr1/tuple> implementation so that
> it meets the C++11 requirements and it still compiles faster then I'd be
> interested in your analysis of the remaining differences. Otherwise I'm
> going to assume the difference is because the <tuple> header contains more
> than twice as many lines of code and several additional features.

Ok, I understand it now. I was speaking from only somewhat experienced user
perspective and I did not realise the deeper implications of standard
compliance.

Just for the record, I did some testing and found two important factors here
are:
 - dependency to <array> (to enable it in tuple concatenation) - (change in
compile time 0.357s -> 0.231s),
 - allocator constructors - (change 0.231s -> 0.185s).

So in the end please ignore my interruption with `std::tr1::tuple`. It seems
the recursive version of `std::tuple` is not going to be optimized easily and
the new flat implementation is the way to go here.