On 26 May 2011 00:15, Phil Endecott <spam_from_boost_dev@chezphil.org>wrote:
Phil Bouchard <philippe@fornux.com> wrote:
On 5/25/2011 3:27 PM, Nevin Liber wrote:
You have yet to explain why your make_auto is so much slower than new directly. It just isn't that expensive to copy one pointer and zero out another. I can't imagine what else your code can possibly be doing. I can't imagine how that can be more, let alone significantly more expensive than a heap allocation. Enlighten me.
Well if you have a direct assignment coming from operator new then the pointer can be transferred directly into a register. If you have temporary r-values to copy it into then the transfer will be done from one memory location to another, but it won't be a fast as a register-to-register transfer.
That effect should be immeasurably small, or eliminated entirely by the compiler.
I think you had better post your benchmark code. There must surely be something else going on here.
I believe he has already (modulo if he incorporated the minor change I mentioned): https://svn.boost.org/svn/boost/sandbox/block_ptr/libs/smart_ptr/example/ben... I agree though, it isn't clear that your code is representative of "real" code. You should try not using templates - which take function pointers - to do the work and inline the code into the tests *. It would be interesting to see the assembly produced by your compiler (I'm not sure you've said which one you're using) in a fully optimised release build of the tests too, just to see what's going on under the hood. -- Darren * If using the templates to do the tests impact performance, that's still useful information, I think.