AMDG Eric Niebler wrote:
Also added to the wiki are the result of a template profile run over miniphoenix.cpp. The results should interest Aleksey:
Total instantiations: 2983
Location count cum. ----------------------------------------------------------- C:\boost\org\trunk\boost/mpl/if.hpp(56) 59 59 C:\boost\org\trunk\boost/mpl/if.hpp(44) 48 107 <snip>
The top two templates instantiated in this program are mpl::if_ and mpl::if_c, respectively. The sad thing is that most of the instantiations of mpl::if_c are totally unnecessary. mpl::if_ happens to be implemented in terms of mpl::if_c so that any instantiation of mpl::if_ causes an additional instantiation of mpl::if_c.
If anything can be done to eliminate this unnecessary instantiation, it'll speed up most template metaprograms across the board.
Something like this should work: template<class Cond, class If, class Else, class Tester = boost::mpl::true_> struct if_ { typedef Else type; }; template<class Cond, class If, class Else> struct if_<Cond, If, Else, boost::mpl::bool_<Cond::value> > { typedef If type; }; but it may be less portable.
For my part, I always take care in Proto to use mpl::if_c instead of mpl::if_ for just this reason, but other libraries used by Proto don't take this measure.
eval_if is even worse in libraries that use it heavily. eval_if -> if_ -> if_c.
Isn't profiling interesting?
In Christ, Steven Watanabe